V

PUBLIC TJTILITItrS BOARD OF SINGAPORtrCorporate Training Departrnenr

1 r*-;

Reverse Osmosis Guide

Design & trngineering

a

Thble of Csntent

C H A O T E O l

Reverse Osmos is Fsndamenta ls

Presure Drivff Membrane Preeses

How Ooes A rrlembrane Work?

Different Membrane Processes

l r rembEne Modu le Conf -gura t -ons

Hoilow Fine Fiber (HFF) Membranes

Sp i ra l Wound Membranes

Pla te & Frame

C e r a m i c

C H A P T E R 2

RO Opera t ing Pammeters

Osmot ic Pressure

Water Transport

Salt Transport

Salt Passage

Sall Rejection

Permeate Recovery (Gonversion)

Conce ntration-Factor

Goncent ra t ion Po lar iza t ion (8 Fac tor )

5

6

I

C H A P T E R 3

Factors Affectang Performance

Feed Waler Sa l in i ty

Feed Pressure

Feed YVater Temperature

Permeate Recovery Ratio

C H A P T E R 4 .

RO Sys(em Oes ign

System Components

Concent ra te Rerarcu la t ion

Concent ra te S tag ing

Flow Oistribution'

Permeate Stagang

RO Sys tem Oes ign cu ide l ines

Average Flux Rate

Salt Passage lncrease per Year

Flow Limitations

G H A P T E R 5

RO Pre-Treatment

1

7

1

3

1 5

l f

1 6

l 7

f 8

I

9

9

' to

7 1

1 1

1 2

1 2

1 3

20

20

2 2

23

24

26

2A

2A

z9

29

3 0

Fre-Trcatment Considerations 3O

Satuiat ion Limi ts in the Concen(rate 33

Thhle of Gemtent ( con t i nued )

C H A P T E R 6

Membrane Star t -up , Shutdom and

Flush ing Gu ide l ines

Preservative Ftushing

RO Sys tem Star l -up

RO Sys tem Shutdown

P l a t e & F r a m e

C e r a m i c

C H A P T E R 8

Genera l S torage Procedure fo r

MembEnes

Short-term Storuge

Long- te rm Storage

Pr io r to Ins ta l la t ion

C H A P T E R 9

l m p l e m e n t i n g a R O P r o i e c t

A P P E N D I X A

References

A P P E N O I X B

Lange l ie r Satura t ion Index

3 5

3 8

35

3 6

I

46

46

46

4 7

C H A P T E R 7

R O M e m b r a n e F o u l a n ( s &

Fou lan ts

Fou lan t Remova l

Membane Glean ing

Data Mon i to r ing

T h e i r R e m o v a l 3 7

3 t

3 7

4 1

4?

42

4 3

43

44

52-

Clean ing Sys tem $pec i f i ca t ions

Vo lume Requ i rements

Mater ia ls / Components

Cleanang Procedqre

R O D E S I G N & E N G I H E E R I N G

Reverse SsmcsEsFundarmenta!s

Pressure D rtuen fuIembrane Processes

Reverse Osmosis (R-O), Nano Frltrauon (NF), Ulta Elrrarion (UF) and rucro-Frl trauon ( ivIF) are the commonly used pressure dnven membrane processes in theorder oF increasing pore opemng MF rnembranes are prunari l1, used to rernovepart culate n-Latter and bacteru'r frorn rvatcr and proce ss l iquids L. l l tra Frlranonmcntl lrenes are usecl to remo\re partrculate, col. loiclel ntatter and [ractene, +]]rroBen,vlruses frour rvater and process l iclurds

-f 'hcy are also used to concentratc r-aluable

so lu tes s r tch as in r r ,he l ' concenLra t ion , c lec t to -dcpos i t ion p2r i l t recc) \ 'e11 , . coo lan tconce ntrat iori :rncl a varre t] ' <i[ appl icatrons Nano Frltrauon nre nrbranes arc oftcrrca l led as l r tosc [ lO: r I td a re used as so f ten ing rnernbranes or to re r ] rovc d1 'es andorgaruc com;rouuds f lorn water and l iqurd eff luents RO as u,c knorv rs rrsed tcrtemorre i lorganic salts, conrmonly termed as roLal dissolved salts or sunply TDSfrorn brackish and sea water and ftom wastewater. Table 1.0 gn'en belorv gives acomparison oI these membrane processes with the conventional hlt tauon

FIow Does A Menbrane Work?A membrane can be consideted as z. very thrn Frlm oI a barricr rvith small pores. A

4

fhble 1. Con(aminan( Fi t t ra(aon

l zc rf Fil er C@taru-mt R@oval ['rwe psi lr,latsiels Filbrod

lomstioul (CB 1 r m o 1 0 0 . 0 0 0 - T A to > l 000 Ftbs. SaM. Ht ir . Pol lm Red EimdCdl

Rou, Y€9

Itidodltosti@ O{F) l 0 0 m o r 2 0 0 - 1 0 0 0 0 0 4 to >100 (ave 10J Fibo, Baasia, Hgnerds. Sroole Dast,Frnulsitred OiIs. Collo&l SilicarPstr-orlabs, Wus, H6vt' Mdrli, L€b/-

Jttoi_filtosdm ruF) 0 0 2 p m o r 1 0 - m 0 A to 250 CilloidBl SiUca,tPonicles, Dre, Cubo,

Polmss, Fmd Stu&, &otien, Gdatin

' l@[10abon fNF) - 0 0 0 l p m o r 5 - l 0 A to 1000 SuEAr, Srnftdc Drrc,lr{eel lm- Ssls

(xqt drloride sJts| Akdrds

lew*mcis (RO) 0 0 0 0 5 1 m o r 1 - 5 4 to 1000 Gilori& Sslts rrd Ar@ic Rldii

1 rm lmiom)- ]0.000 A {mestrm)

R O D L 5 I G N 8 F N G I N L L R I N G

nre tnbrar tc can have s l rapc c r i . r c1 'L rdnca l f iber o I r ] r r rne tc r as s rn , rU as 45 m-rc rons

or 1 0 nun or rn a rub t r la r fo r tn t t c rn bc 1 rnch A rnernbrane car r a lso be Ln fo rmof a f la t sheet l - rkc a paper l t can be r ladc o I d rF [e ren t n ra te na ls such as ce l lu lc lsc2cet2 te , a tomat rc Po l1 ,21- t - t16" , o l , lo r t dcnr . 'an1 'e s , po l l ' r . rny l a lco Io l der iyahr - .e , po l l 'ac11, [snr r r t ] . , po l l rspr ip l to r t . , po lyg i [ . . r r . . t1pho1e anc ] o ther . -s Se l I suppor t rngmembranes o i one tna ter ra l a re caUed as l ' ITunc t r rc rnd those \ \ j l th a sLrppor t a rccai led syrnrnetl lc or composrte meimbranes

For a membrane process to rvork, f i rst, membrane rnatenal should be such that i tpreferennally attracts the solvent, that is rvater and rejects contaminants that aresa l ts in case oF RO N4embrane mater ia ls such as ce l lu lose ace ta tc , a romauc

polyamrde have a pre[erenn-rl athacLion for lr ,atcr and prefere naal rejecnon forcharged ronic substances

Second, the membrane should lrave proper rnor?holog)/ to ger desired separadonand producuvrq,. N' loqrholopl ' can be vern sunply stated to rnclude pore siz€s aodpore sze distf ibunon If the pore srze rs smail , solute separadon rwll be very goodbut membrane producti ! ' rry that is penneate f low drrough the membranes wtl l berrery lo\\r arld to get a- desired penne ate f lorv u'ould requre large rncmb rane ̂ telLI-atger potes wLll ) ' ield [rrgh proclgcttvtq, but lorve r salt separatror.r

E , r 'en a f te r havrng a su tab le rna tc ru l and nrorp [ ro logy , one need to p ressunze t ] rcfecd watc r appropnate ly

- fh is i s rJ rc rh i rd reL lu r r€nr r : n t F [ i cher p rcssLr res produce

tnorc pcr rneatc b r r t Lncrcasc c l l xncc : r , f f r t r rL r r t

Once dre membrane process ls operar rn€ l the separaoor r per fon leoce dependsprunanly on three factors - attracuve and repi-r lsive forces and sterjc factors Asolute having attractron to\vards t lre memL;rane and snral l enougfi ( to pass t lrroughthe membrane) l .ras lrrgher probabrhty of appeanng rn the permeare sLream,Hydrophil ic (water lormg) and polar compounds, for example metl-ranol and urea,can Pass easrly through the RO membtanes With dre rcpulsive forces Lhe result is

opposite for non pol-ar and hydrophobic (warer rejecrlg) compounds, Mernbranesurface cl"rarge plays an important role rn the separation. Steric Factors meaosthose related to the size of the solute molecule Even a hghly hydrophrliccompound n' i l l not pass through the membrane i [- t ts size is much larger dran the

pore operung o[ the rnernbraue Herc pore geometry, geomefty o[ the soiutcrno lecu le and r ts one nu t ion can a iso p lay a par t ,

Based on the pore operung o[ fhe membranes, steric or attract ive/repulsive forccs

or both pl^y ^ role rn the membrane processes In RO and NF al l forces aretmportant u'hi le ur UF and I\ , lF stenc forces are predorninanr for separadonalthough al l forces are responsible for fouhng ir al l membranes

R O D E S I G N & E N G I H E E R I N G

D fiere n I i\{etn b tztne P ro ce.rse t' f herc

a re th ree mau- l q ,pes o Imembtane s ] /s tem conunon l l ,used Ln rnd t rs tu i , .

Reverse osmosi-s and Nano f i l t rat ion arc uied ertensrvclr [or r, ,ater punFcauon,desal inatron and dtsi l fccdon. RO aod NF rnernbranes are usecl ro rernovedrssolr-cd norgatuc and orgaruc unpuntles In RO and NF, r,ater and srnal lera icoho ls and po la r compounds pass th tough thc rnembrane in to the permcate s idebut al l ioruc rmpunaes, Large molecules, col loids, emulsif ied orls, [ats, proteins,bactcria arc coocentrated on the concentrate side.

Prcsent day Ro rnembranes are made o f po lyamrde layer on a po lysu lphonesuDpor t N l ' mernbranes are a lso made o f cornpos i re po l \ :a rn ide and o&erpolyrneric tnatenals, Although these are avarlable Ln vanous configurations, thesrngie rnost popul-ar configrrat ion used al l over is spual

In the rvater irdustty RO Frnds applicatrons ur treaffnent o[ bracl<rsh water, seawater and vaste water rncludrng city sewage, Lzrge sized plants are operaturg forseveral yeats Proper design o€ a pre-treatrnent system rs ' , . i tal for successfuloPerauon o f an1 ' RC) sys tem Of ten i t rs found no t g iver r the a t tenuon dra t i trequrrcs.

-f lus results rn operatlng uoubles once the systetn rs corrunissroned

\X/ : rs teu ,a tc t ap l i cauons need to be rnon i to red c lose ly becar - rsc u r r r ros t cascs r t i srtot posstblc to csorrtate thc exact r-rarlrre of the eff lr .rent t !) l ]c treated n l tOs)'stern

- l 'he pre treatrnent miglrt need to bc rnodrfted bascd on dre operatlng

e.\penencc wrth dre cff lucnt received rn dre plant, Process c[rcrmsq' ls vcrylf i rPortant and good undersundng o[i t can make a drfferencc betrveen sLrccess or

' l a i l t r r c o f a R O s y s ( e m

U]tra filtration ts ,'videly used [or: oil, water and emulsron separatrons; parntrecovery; and thc separadon of [ats, oi ls or greases n thc food urdustry Ultrafiltratron membranes remove parricularcs, collods, emulsified oils and largernolcculcs frorn liqurd streams. In ultra Frltrauon, \rrater, a[ ioruc substances,smallcr alcohols pass through the mernbrane into the petrneate srde but largemolecules, col loids, emulsrf led orls, fats, protems, bacteria are concentrated on thetoncent ra te s tde-

Ultra Frl t tauotr nrembranes are made oI a varie $, of polymenc lnatef lals and areavar.lable rn hollou' hber, spual, tubular and plate & frame confrgurations Whiletubular ot plate & frame conEgurauon is best toi high sohds loadrng, therr lowmembrane atea to volume rat ios make them too expensive €or u,atcr apphcations.

SpLra[s have a lugh mernbt^rTearea to volume ratios but tlreir narrou, florv channel

cao get pl%ged unless a t lucker channel (or feed -bnne spacer ) is used, Hollorv

6bers are good for pure *ater appl icatrons and thel ' provide srrarghr f low paths

e

R O O € S I G N & E N G I H E E R I N G

a{rd have l lgir rnenrbr:rne area to r.c., [u.rtre Lauc,s Spuai systcnls ate \:er]J easy to

bui ld and have been used even ur \ \ 'astc-\r,atcr applrcalrons r"t th hlgh cl ' .ances c. ' [

[ouirng

In ttrc * 'ater rni]ust5y r-rI tra f i l l r2tuor] L.d. rpplr.auon) ut bactcrta ar-rd pl,rogen

remova l Ln the phannaceubca l u rdus t r t ' , p roducnon o I po tab le and mnera l rva ter

and Lreatment o[ \L,astewater contalrung e urulsrf ied coolants, [ t rs also Lncreasr.ngly

used as a pre treaunent for RO systems because l t pro\ndes an ercel lent quai i ty oI

RO feed water. Wtule ultra filtraaon docs remorre colloidal and paruculate

rrnpuntres from u'ater, RO membranes can st l l l get fouled u' i th dissolved and

brologrcal substances as observed dunng extensive studres catr ied out at the Water

Fac tory 21 Ln L ISA \ , 'nbrhg o f a UF RO combLnaoon is case depcndent and user

shou l r j eva lu : i ie a l i op f ions be fo te gourg fo r r t

Ai l drese systems requlre carehrl system design Nlost cnncal patameter is the

cross f low over the membrane u,hich has to [re high enough to keep the

tnembrane clean Either batch or feed & bleed or condnuous systems are used It

is essential to carry out a pi lot study for a rrcrv apphcation to establ ish separatron

petfonrrance ; f lux \rersLls pressute, tetnperaRrrc, f lou, and conceotratron

rclauonsl lps and the cleaning protocol

Micro f i l t rat ion rs epplred to tr lauttaln dcgrcasrng pr,. . .r , soluoons for metal

l tarr icf e recctvery / retnoval or to concentlatc other parl icu[atc materials frotn

l rc lu rds or s lu r r rcs N ' l [ ' rncnrbranes rc rn( ) r ' t parL lc .uh tcs , co l lo ic ls and

nucrobiokigcal irrrpurrtres ftour l iquid streatns Irt N1ft, \r ' i r tet, aU torrc and orgaruc

sr-rbsLenccs pass drror,rglr the rnembrane urto t ]re permeate side but coUoids,

parl iculates; bactena are concenLrated or ' t the coocenLrate sicle

MI r mernbranes are a lso rnade o f a var ie ty o Ipo lymenc mater ta ls , comrnon bcng

po lysu lphone, : rnd a te ave i lqb lg rn ho l lou ' f ibe t , spua l and p la tc & f rame

conFtgutations

In dre water rndLrstrl, N{tr finds applicauons rn paruculate and bacter-ia removal tn

the pharnraceudcal, electronics and semiconductot Lndustry and producuon oF

potable and rnineral water. I t is also mcreasmgly used as a pre-t-reatment [ot RO

systems l ike Ultra f i l ratron membranes.

M em brcne A'''Io d u /e eo nfgu rdttz nr

The ru'o rnajor mernbrane module configuraubns used for reverse osmosis

applicanons are hollorv fiber and spiral wound. Two other configuradons, rubular

and plate and frame, lrave found good acceptance tn the food aod daty rndustry

and rn some specl"l appircatuons, but modules oItfus confrgurau.on have been Lcss

frequently used rn reverse osmosis applicauons

R O O E S I G N A E N G I N E E R T N G

- I -uh t r la r rnembranes l - rave bcen around [o r a long nr r i c

- l -he de- :Lgn rs sunp le and

easy to unders ta r rd - i ' ubu la r

membrane s c : rn to [e ra te suspcndec i s .Lds Lnc l t rd rnqf iber - . to a la rgc c \ rcn t

A l l n rbu la r mern t r l : rncs s r r f f c r [ ' r c t rn severa l d_Lsadr .an fages

' ' I 'he,v requrrc a lot of space.

' Change oImcrnbranes ft ' ray be qurte chff icult and f ime conisuprlr-rI. T'he tubular sJrsterns rvith large tD (1 mch) use a lot oIenergl,' I-arge internal volume makes f lushing and CIP costly ln rerms of usage of

chemicals and rr.ater' I t is cosdy and drff icult for the manufacruret to clrange rhc rubrrr lar desrgn

l l le advantages clI drc rubular systcms somebrrles oun'ergh t-he cl-rsadvantages, andd-re tubulrr rnembr:rrrc desrgn has a place in the market, aldrough q,., ,r . r ,r ,r l

Ilo/low Fine Fiber @fry A.4embranes

ThLrs conltlgutatron uses membrane rn the form of hollou,'f ibers rvluch [rar.c becnextruded frrtn.r cclluloslc or non cellulosic material T[rc fibcr rs :rs),rrlrnetnc mstructure and ts as lurc as a human harr, about 42 rrrcron (0 001(r urch) I l_] and 85rrucron (0 0033) urch) O lJ. lv{i l l ioos o[ rhese Frbers are formed urto a brrgclle andfo ldecl rn hal f to a length o[ approxrnrate ly 120 cm (4 f t ) A pcr fcr rated p last icntbe, scrv lng as a feed \ \ 'a tcr dts t f lbutor is rnser ted in the center . . r r rc l cxrcnds t ] refull le ngtir ott thc [tr-rlrdlc

-fhe bundle rs u,rappcd and borl 'r eods arc cpoxy sealed

to fomr a shect'Uke Pcrrneate tube end and a termirral end rvhich prevcnts rhe fccdsLream from bypassrrg to the bnne outlet

The hollou, f iber nrembrane bundle, 10 cm to 20 cm (4 to B rnchcs) rn drarnetcr, iscorrtarned in a cyllndlcal housing or shell approxirnately 137 cm (54 Lnchcs) longand 15 30 cm (6 12 mches) in diameter The assembly is cailcd a permeator1-he pressunzed fced watet entets the penneator feed end through thc centerdistributor nrbe, passes through dre rube rvall, and flows radially around thc fibcrbunclle toward the outer permeato( pressure shell Water permeates tlrrough theoutside rvall of rhe Frbcrs tnto the ho[ow core or f iber bore, throug[-r t l ie bore todre tube sheet or product end o[ the fiber bundle, and e xirs throlrftr rhe prodtrctconnecuon on dre feed end oI the permeator.

In a hollow ftber rnodule, the permeate water f low per unit area of meribrane islow, and thereFore, the concentrauon polarizatron is oot high at the membranesurface- The net result is that hollorv Ftber uruts operate m a non-h,rrbulent orlarninar flov,' regrme The HFF membrane must operate abo'e a mirumum reiectflow ro mimmrze concenftation polaruauon and maintarn even florv drstnbuuonthrough dre fiber bundle, TypicaUy, a sLngle hollow fiber pennearor can be

R O D E S I G H A E N G I N E E R I N G

opcra tcd r r up ro 50 pcrc r : r r t r ( :co \ . co /and t lee( the rnuuurum re iec t f lo rv requucd- fhe

l - ro l lo rv hber u ru t aL lo r t ' s a la rgc rnembranc 2rc : r pe I uu t ! ,o lunre , - r f permeato t

r i ' h ich rcsu l ts rn co{npec t s \ s te l l s Ho l lo* , hbcr penrne tc rs a re ava i lab ie [o r

brack ish and sea\ \ ,a te r aoo l i canor rs

Nlembrane mated?ls are cel lu lose acetxte b lends and aranud (a propnetar)J

polyarrude fype rnaterlal rn an arusotroprc [orm) Bccairse oI r 'ery close packed

fibers and tornrous feed flou' ursrde t] ie module, l.rollot' f iber modules reclurre feed

water oI better qualiq' (o,,ver concentratlon oI suspended sohds) than the spLralwound module conEgurauon

Wound A4embranes

In a sprral wound contrguranon ru,o t]at shcets of metnbranc are separated wrdr a

permcatc col lector clrannel material to fcrt-. ' r t leaf This assernbl i , is sealed on

three srdes wlth t l-re fourt]r side left opcn for perrneate to exrt, A teed/bnne

spacer nu terL2 l sheet i s addcd to d re lea fassetnb ly A nurnbcr o I these assembbes

or leaves are u.or,.rnd arouncl a central pl-asnc pcffneatc tube Thls rube is

perforated to coi lect d.re penneate frorn thc mtrluple ieaI assemLrl ies. l l he rypical

rndus tna l sp i ra l rvound rnembrane e lement i s appr , rx -u la te ly 100 or 150 cm (40 or

60 rnches) long and 10 or 2 [ ) c t r r ( ' [ o r B) rnches r r t d t : r rn : te r

' fhe feec l , /bnne f low ' th rc i r - rg l r thc ' t : l cmcnt ts e s t ra iq l r t ava l p ; r t l r f ronr the feed e-nc i

to d re oppos i te bnne enc l . runn ing para l l c l to thc n rcmbrane s t r r f l ce The feed

channe l spaccr induces t r - r rL r rL le r rcc and reduces concent ra t lon po lanzauon-

lvlanufacrurers specrf i ' bnle f lorv reqLUrenrerl ts to control concenLrauon

po lanzanon by l r rn iung recovcr f ' (o r convers ton) per c le rnent go l0 ' 20 percer r t

Refer to Fg i 0 belor.r',

Thcrefore, recovery (or converston) is a Functiorr oI dre fced-bruc path lengdr In

ordet to operate at acceptable recovenes, spLral systems ate usually staged wrth

three to six membranc clements connected rn scries in a pressure tube. T[re bnne

strcam flrom the first element becomes dre fecd to t]re following elemerrt, and so

on for each element widun the pressure rube-

The brure stream frorn tlre last elernent exits the ptessurc tubc to rvaste The

permeate ftom each eLenrent enters [he penneate col-lector rube and exrts the

vessel as a conunon peffneate stream A surgle pressure vessel r'".td-r four to six

membrane elements connected in senes can be'opetated at up to SO-percent

recovery under norrnal design conditions Tl.re bnne seal on d.re element feed end

seal canier prelrents the feed/bnne strealn from bypassurg the followlng element.

Spira/

R O D E S I G H & E N G I N E E R I H G

Pe r fo ra led Cent ra l Tube

F e e d C h a r r r r e lS p a c e r

M e rrrhra ne

Permeate Co l lec t io r rMa ler ia l

Membrane

feed C l ra r r r re l S t lacer

0uter Wrap

Fig . 1 .0 . Cross sec t ion o Ia spra l rnernbrane

Spual wound elemcnts arc l ]rost conrLlonly rnanufacnued wrt l ' r n"t shccttnetnbrane o[ either a ccl lulose dtacetate and rrr-acerate ({-A) blend or a t ]r in Frhrco lnpos i te A t lun f i lm coml ros t te mcrn l : rane consrs ts < l Ia d iu - r acnr .c L rycr o f onc

Pollrmer cast on a thicker suPportrng Layer o[ a dif ferent polyme r -[ 'he

corn;rosrtemen-rbranes usuall l , exlrrbit l rrghcr relecuon at lou'er opcrattng pressures tharr thecel lulosc acetate blends The gornpositc membrane materials may be polyamdc,po lysr - r l [one , po lyurea , o r -odrer po lymers

Plate dy Frame

These werc largely pioneered by DDS and acrually domrnated tle darry market urE,urope for 15 years. Lack of devcloprnent and an nflcxible pnce structure moreor less kil lcd the deslgn berrveen 1989 and i995 There are several ncw plate and-frarne s1'51sms available fn- E,urope The be st knorvn rs the ROCHE,N4 desgn FIarsl-reet systems o[[er a very robust and compact desrgn, but for a pnce. Ir, lodern flarslreet systems are bu-tlt to tolerate very hrgh pressure, rn excess of 100 bar There isa small market [ot this extrelrle pressure range rn treatment of landfl l leachate andfor dcsalinauon o[sca watcr onboard shros.

I

R O O E S I G N A E N G I N E E R I H G

Ceranttc

-f l ' re1, 2Es very, vert expcnsnic

' f l reoredcaU]' , ceraffuc s];stems can be vcry effecuve

for N{F I r r rea l iq ' the marke t Ls ver t , luu ted to specLa l app l i canons

Ta6le 2 belou' provrdes a companson amongst drfferent rnembrane modules.

Table 2: Compar ison Amongst Di f ferent Me mbrane Modules

Sp i t a l

I {o l low

Fine

Fibet

Ho l l ow

F ibe rCeramic Tubu la r

Plate &

Frame

Pack ing Dens i t y ,

m2 /m3Hrgh Verv high Fhgtr [-ow Lorv fvtedium

Foul ing Tcndency N{cdrum \req, lugh Nledrun Nfedrurn Lor' Low

Cleanabi l i ty Cood Lou [.ou Good Good Good

Cross f l o * ' r equ i r emen t N,Iedrurl Low lvle ch unV"ryhlgh

\/eryHgh

I{rgh

Pre- f i l t ra t ion

rcqut fe rne n tI ( ) . : 5 l l 1 5 0 1 r ) c r e e n Sc ree n < 100 p t

P l r n t i n v e s t r n c n l Lr:r r. N(edrurn t tg l rVc11,

lwh Hgh Ir{edrum

T r e a t m e n t c o s t l-oq Lou' Nledr unrlrer)

t El.Hrgh N{edrum

R O D E S I G N 6 . E N G I N E E R I N G

RS Operatins Faranreters

O.rmotic Pres.rure

The osnrotrc pressure, n, o( a soiuuoo can be determrned experimentaLlt ' bi 'measufutg r-he concentraoon of dissolved salts in soludon,

n - l 1 9 ( T | : Z J t * f f n t t ( 1 )

t ' here n - osrnor rc p ressure ( rn psr ) , - l -

rs the te rnpera turc (Ln 'C) , and l (N, I ) rs the

sum o f Ino la l cor rcent rauon o f a i l cons t r t r ren ts L r a so lu t ron Ar r rpproKr rx iEon

lor n rne l 'bc mac lc by essurn ing dra t 1000 pprn o f fo ra l DLsso l r .ed So l ids GDS)equa ls ; rbor r t I 1 psr (0 16 t :a r ) o f c ismot tc [ ] ressure

IYt ater 'I'ran:port

Tl-re tatc oI rvater passage t l i rough a mernbrane rs de{l- ied irr Ecluanon 2

Q . . = ( A P A ^ ) * K _ * S / d (2)

u'here Q-. is the rate o[ water f low drrough dre membrane, I P is the hydraulic

pressute drfferenual across d-re membrane, An is the osmotic pressure drfferenttalacross the metnbrane, Kw is the membrane penneabr.hry coefficient for rvater, S isthe mcmbrane a(ea, and d ts the mcmbranc th ickncss, Because d is vcry smai l and

Q", /S equals u,ater f lux f l . ) , Equauon2 can be sunpl i f ied to:

J -=A- ( l \DP)

NDP rs thc net dnvrrg pressure or net drirnng force for the uansport of rvateracross the mcmbrane surface. Thc A is tefrperanue dependent and represents auruque coostarrt for each mcrnbrane material type [t rs referred to as the "A"

v'altre, solvent trensport coefficrent, or watei transport parameter The A value

(for a specific temperature) is easily obtarned expcdrnentaUy by measuring j" and

9 \

(3)

R O D E S I G N 8 E N G I H E E R I N G

NDP t l rc r ' rpp ivurg thenr io thc Equauor r 3 Oncc drc A v r lue fo r a spccr i rc

nrembran( ls kno\ ' . 'n, l ]ermeate fLtrx rna1, be predrctcd for a varteqi oI net drivurg

pressures fhe A va luc may har .e un t ts o Igp tn7 ' [ t2 * ps i o r t r l , ' ' s t kPa

(- L --r-,) ft1t I t'flil-rut7

The rate r,rI salt f lou' through the n.re n'rbrane ts defined by E.qLLaaon '1

Q, = (C- - C.) *' K. * S/d (4)

ivhere Q, is t [-re f low rate o[ salt through the membrane, K ts the membrane

permeabihry coeff icient fbr salt , C- is t ]rc salt concenLratloo at the membtane

surface, Cn is t l -re salt concentranon in the pcrmeate, S is the membraoc area, and d

is dre rnembrane t lr ickncss, Because d is very small and Q, / S equals salt f lux (JJ

ihrough i lre me inbr:rnc , this E.quation can by sirnpl- i f ied tc.,

1, = B*(C* C) (s)

Where (C- - C,.) rs the drivLng force for dre nr- lss transfer of salts The B is

temperature depenclar-rt and represents a r-rni<1ue constant Fot each membrane rype-Thc B rs oftcrr relerred to as the "B" r 'alr-re, t ]re solut 'e tr l l r lsPort Parameter, or the

,^a l t t ranspor t coe f f i c ien t Becat rse the concent ra t ion a t the tncm[ r rane su t [ace

( ( . , . , ) can t lo t bc o l r tau lec l ex [ ]cnr r rc r l ta l l t " t , . , , t l re tnore ch f f i c . r r [ t to ca lcu la tc thc B

value t[ ' rarr thc A r.alue A n e strtr late oI dre B valtre r-nay be obtarned

cxpentlett taUl, l t1' usl l tg the avcrage rtI drc leed concenLral ion and brule

conccnf f : l t lon rn o lace o f thc co0ccnt l2 r t lo r l a t the rne tnbrane sur f i t ce In o ther

rvords

C - = ( C , + C b ) 1 2

Where bodr the feed concentratron (C) and dre brine conce(lt fauon (Co) can be

easi ly measr.rted

The rvater transport Eguatron (Eguanon 2) and the salt LransPort Equanon

(E,quatron 5) shorv that fot a givert tnembrafte at a grven temPerafure:

a)

b)

Rate o[ u,ater f lot, t]rrough a membrane ls proporuonal to applied

pfessurc

Rate of sa[ t f lou,rs proport roual to dre concenLrauon d i f ferendal across

the mernbrane and is i rdependent oIappl ied Pressure

Permeate salinify, Co. depends on the reladve rates of water and salt transport

througl i reverse osmosis nrembrane.

R O O € S I G N & € N G I N E E R I N G

Ln - ( l . i (1. (6 )

The fac t t .ha t , . r 'a tc r and sa l t have dr fFerent nuss c rans fc r ra tes th r ( )ugh a grven

tnc tnbrane c rea tes the phenornena o I sa l t re jecaon No rncrnbranc is i t lea l rn d re

sense tha t L t abso lu te [1 r re fec ts sa l ts ; ra ther the dr f fe ren t L ranspor t ra tcs c rca te a r l

apparent re lccuon The Eguat lons 2 , J and 5 exp [ar r r rmp( ) r ran t desrgn

cons idera t ro r rs in RO s l ' s tems For example , an tnerc . rse ur opcr ; i t -u lg p ressurc , ,v r l J

tncrease u,ater f loq, g'rthout clranging salt f lor ' , ' , thus resultrng ur lo,ver peffneate]

sahnity.

C 1, T\J Ll/[ l-aSSt/9€

Sal t passage is dehned as the ra t io oFconccnt rauon o f sa l t on the pcrn ie : te s r t l r , I

the rnembrane relauve to t}re average feed concenftanon Nlathcmaucaliy, r t is

expressed rn E,qr-rat lon 7

9.,osP = 100 * (cPi c'.J

whcrc ozbSP is thc salt passage (rn %), eo is thc salt conceotraoon rn the pcrmeate,and C.,, is dre rrean salt concentratron ur feed stream T[us concentraticln may beestrmated as follou's.

c , , r = ( c f t c h ) / 2

\MrcreC , - [ i ecd (onccn t r ; l l l c )n

C,, = Brine conccr)trauofl

Applyrng the iundamental Equauon s of water f low and salt f lou, i l lustratcs solncof the basic pnncip les of RO membranes For example, sa l t passage is en Lf lverscfuncnon of pressure; d'rat is, the salt passage rncreases as applied pressuredecreases Thlrs is because reduced pressure decreases permeate flo',r ' rate, andhence, dilution oI salt (the salt f lows at a constant rate through the membrane asits rate o[ f lorv is rndependent of pressure)

.\ alt Ketectnn

Salt rejccuon is the opposite of salt passage, and is deFrred by EqLrauon

o/oSR = 100 - %SP (B)

\X4rere %SR is the sait rejectron (^"h), and %SP is tJre salt passage as deFrned rr

Equauon 7

(.j .)

1 1 o

R O D E S I G N & E N G I N E E R I N G

P erzzeate Re co uer1, (-,0 n ue, sto n)

o/oR = too. (e, . ieJ

Ln t l ie desgn :rnd operatron oI

\ ( a l e r t ( ) p r o 6 l u r l ( p e i l n c d t c I r \

t-o)

whete 7oR is recovery rate (nYo), Qo rs the product water f lou,rate, ahd Qrrs the

feed water f lorv ratc fhe recovery ratc affects salt passagc and product f lou' As

thc recovery rafe increases, the salt concentradon on the feed bnne side o[ dre

membrane increases, rvhich causes an incrcase in salt f lor ' . ' rate across the

mcmbrane as indicated b) ' Eqr-raoon 5 Also, a hrgher salt conccntrarion m the

feed-bnne so ludon increases drc osmot ic p ressure , reducrng the NDP and

consequerrdy reducrng the ptoduct ' ,r 'ater f lorr. , rate accordmg to Fiqrrat iol 2.

eoncentration Factor

Concentrat ion factor is unportant Ln calculaoons rnr.olvu)g saturation levels of

sparmglv so lub le sa l ts i r r a RC) sys tem ConcenuaLron lac to l rs ca lcu l r tcd f rom

per lneate fecovery t rs ing Equat ron l0

(_F = 100 / ( 100 u /oR) ( r0 )

As thc peffneate rccoverl Lncre:rses concenftadon [actor also urcreases but the

tncrease ts stceper at hlgh tecoveries as shown bclow-

Reiect concentration (Cj is obtarned by mutnplyurg feed concentrauon (C) andconcenttation factor [t is assurned that the Deffneate concent(atron is zero in thiscalculation

Permcate reco\rer! rs arrother mrportznt pararneter

RO s i ' s tems Rccot .en , o r consers ron ra tc o [ f leed

deFrned bi, Equatton 9

R O D E S I G N A € N G I N E E R I N G

C o n c c n t r r t l o ^ F c c r o . { C F )

Fig. 2.0: Concentration Fairor variauon u4fh Penneare 'Recoverv

eancentration P o lan<ation (B eta Jactor)l he 'a lue o f d re Concenuador ) Po la r lza f ion l jac to r oF | 2 , fo r example ,

corresponds to . l

89/o peffneate reco\/ery fcir a 40" lorrg rnernbrarre clement.

As rvater f lows t lrrough the membrane and saits are rejected by the rnembrane, aborindary layer is formed flear the

'membrane surface rn wlich thc salt

concentration exceeds the salt concentradon rn the bulk soluuon. This incteasc ofsalt concentradon is called concentration polarizatron. The effect ofconcentration polarization is to reduce acnlal product lvater flow rate and saltreicction versus theotetical esdmates Thc cffects of concentradon polanzzfrona.reas follows:

Greater osmodc pressure at the_mernbrane surflace than tn the bulk feedsoluuon, A n, and reduced Ner Dnvrng Pressure differenual across thcm e m b r a n e ( A P A n )

Reduced rvater tlorv across membrane (Q.)

Increased salt f lorv across mernbrane (QJ

1 3 r

R O D E S I G N & E H G I H E € R I N G

+ lncrtase,i piol,, ibiiq, t:I c:,:cecding soiubri_rq, <_ri sparrrgil, soluble salts atthe nremltrane surface, and dre drstrnct possibrJrty o[ preciprratron caus1ngnrembranc scai-r-rg

The Conccntrauon Polanzation Factor (CPF) or Beta carr be deFured ,rs a ratio oIsalt concentration ar the membrane surface (C") to bulk concentrauon (C,,).

CPF = C. /Co ( 1 1 )

An increase in permeate flux wrll inctease the delivery ratc of ions to themernbrane surface and increase C,. An increase of feed florv increascs turbulenceand reduces dre-ifuckness o[ the hgh concentradon layer near t]re membranesurface fherefore, the Beta is clitecdy propordonal to permeate florv (Q),

"nairrversely proporuonal ro arrerage feed flow (Qr",J

CPF = Ko * cxp(Qo/ Q""J (2)

Where I! is a propordonality constant dependrng on sysrem geomcul,

Usng the adthmeuc average of feed and concentrate florv as averagc f..d flort,dre CPF can be expressed as a funcLion o[ dre penxcate rcc()vcrl] ratc a o[membrane element (R)

( .PF - Kn ' exp(2R-/ (2 RJ) ( l l )

R O D E S I G H A E N G I N E E R I H G

Factors Affecti n g Pes-forsma FEee

Feed Water Sa/iniry

Some RO systems exoerience flucruatroo of fced l-r,reter ccmpcsidon d goperation. T[us may be due to seasonal Flucruadon <-,f fced warer salirury supphes,.or due to intermittent operadon of a nunrber oI water sources of drffetent saliruryAs long as different feed rvater compositions rvill not require a change in rhesystem recovery ratio, changing feed warer cornposidon wrll affect only drereguired feed pressute and permeate watcr sahrity

-f[-re chart below shows dre change in reqtrued feed pressure and projected

pertneate salrrury as a funcdon oI Feed salluq' fr;r a 51'519111 operartng at an averagcflux rate of 15 gfd and recovery tatc o[ B5'l 'b Calculations ,.r,ere made for r ',vr>membrane types: Lorv Pressr.rre type (b,SPA) and Standard Pressurc q,pc (CPA2)The ESPA membrane l 'ras spccific f lux o[ 024 gfd/psi nct, wluch is rwicc as l i lghas specific f lux oI CPA2- membranc

lt can be seen that for both membranes fleed pressure and permeate salinityincrease with feed salnity il a sirni-lar wa)r. The rate of increase in permeate salrruryis hrgher than the rate of increase ln feed pressure. If the drfferent feed water alsocontains concentrations of sparingly soluble salts higher than in dle design feedwater, then the recovery ratio may hal'e to bc rcduced to avoid t['re possibrlity ofprecipitation o[ scale from thc concentrate sLrcam

1 5 *

R O D E S I G N & E N G I N E E R I N G

EFFECT OF FEED SAL IT . I ITY ON SYSTEM PE RFORIV IA I . iCE

F L U X 1 5 G F D C P A 2 A N D E S P A M E M B R A N E s

EO

0 10m 70g] 30m 40m 50m

F E E D S A L I N I T Y , P P M T D S

FLg,i {) Etfcct of fccd s:rhnrlr,_grt lceci pressrrre andpq]Icalc s4lt!]_!1]

I-.etr/ Pr-e.rsurt

RC) s1'51srx5 cqLLipped s'idr sPrral wound metnbrane elements are de-srg-necl tooperate at a constant f lur rate ( i -e , to produce a constant pcrmcatc f lor r , , ) . ( l , "er

operaturg drne, dre feed pressure is adjusted to compensate for f luctuauon o[ fecdwater temperature, satrniS, and permeate flux decline due to foulurg or compactron

of the membrane For the purpose of specr[,mg the lugh pressure pump, lt ts

usually assumed drat spcciFrc flux o[ the membrane rvi-[ decLne by about 70oh rn

drree years. T[re purnp has to be desrgned to provrde feed pressure correspondingto the rrutral mernbrane performancc and to compensate fot expected flux decline

I[ thc RO systern is equrpped rvtth centrtfugal purnp, then the conventlonal

approach is to use an oversrzed purnp and regr-rlate leed pressure b1, f l l .o,6n*

(parually close dre leed r.alve). Today an incteasing number of RO system use

elecrric motors rvith vanable speed dnves, t ' lrrch,enable adjustment o[ f lorv and

feed pressure oI dre pump over a wrde range with very l itr le loss rn efficiency. Ther.artable speed ddve reduces unproducdve ptessure losses which were ccrtrrrnon ln

dre past Some. RLI s'/stems use positlt 'e drsplaccment Pumps (prstcn or plurrger

pumps) as a Lugh pressure process pump. The positive drsplacements pumps

enable reguiation of feed pressure at constant pump outpug rvith Iirt le changc of

100

Go oz. l-<Eur o_o _ -

t u FE =--) -= J

a;<g1 ul

r l u ro - Fo *u r =u r dL E

UIo-

R O D E S I G H & E N G I N E E R I N G

punrp e l f ic lcnc\ Posrove i1-rspLaccrnenr purnps aredi , ie io .apaci t1 L l rutauorr o l rh, rs purnp q 'pe,r ru[ntenancc, norsy opcra0oo and st rong ! , - lbraUor ls

l ess co rmnon u r RO svs temsh g i r i r c q u c n c \ o t r e q u L r e c i

Feed I.Yt ater Teruperatare

Change rn feed r ' , 'ater temperarure resulrs ur the change ur t l -rc rate o[ drffusron

through the metnbrar-re The change Ln the permeate Flux ratc r.vi th temperanrre isdescnbed by the followr-ng equatron.

TCF - 6 t - t zs )

Where - fC l - ' i s

tempera t i fe cor iecnon fac to r , K rs : i coos tar i t charac ie r is t i c io r a

gn'en membtanc matct ia[, and -f

is feed water temperatr,rre in degrces Celsius Inthis eqtratron, a remperature o[25"C rs used as a teFerence pomt, u' i t ]r TC[j = 1.' Ihe

change rn f lux rate w' i th temperarurc fcrr polyanlde mcrnbranes is sl-rown in

the follorvrng graph

FLUX CHANGE WITH IEMPERATURE

t ( l

u J 1 6F -4 . t trrx 1 2--l

- t oLL

U O B2osF{ o qJL J o zu

0 0

s 2 0 2 5 3 0 1 5

FEED WATER TEMPERAIURE C

Fig. 4.0 E,[[ect of feed temperature on permeate flux

The rate o[ change is about 3o/o per degree. Srnce RC) svstems are desrgned toopetate at constant output, feed pressure ts adjusted to cornpensate For water f ltrxchanges rvhen temperature changes The salt diffusion through tl.re membranechanges wtdr temperatute appfo teil ' 21 the same rate es t 'ater f lux Beca'lse

Permeate flux. rs marntarned constant, peffneate salrLify changes accordtngly to dretemDetature fluctuauons-

1 7 *

R O D E S I G N A E N G I N E € R I H G

IEI'/ P E RA TU RE E F F E C T ON n4Elyl B RA NE P ERF O R ldA N C E

1 5 2 0 1 5 l 0

FEEDTEruPERATURE C

I i c 5 0 l : l { c c t o I f c e t ] t e r n p e r J r u r c n n f c e d t , r c s s t r r t . r r r t l D r ' r r r r , ' a t e s r l u u r v

Ef fec t o [ feed u 'a te r te tnper : r fu te on RO s) ,s tenr feed pressure and pemleatesahniry t , *.r .r .r ,"6 rborre The calculatrons oI operatutg paral l ' Ieters were

condr-rcted [or an RO system operafurg at 859/o recover]r rate, using frvo membrane

g'pes; h-Lgh salt reject ion CPA2 and lugh permeate f lux ESPA Ttre gerreral trend

of perfonnance change is sirni lar for both membrarrc types However, as

cxpected, dre drfference oI feed pressure benveen two rnembranes tncreases with

decrease of temperaftrre T1-re permeate salrruty changes rn opposlte way The

absolute value and dif ference between f ivo membranes increases wrdr feed water

temPer2 ture

Penneate Recouery Ratto

Recovery ra r io a l fec ts sys tem pcr fo rmance, i .e penneate sa l in i ty and feed

pressure, by deterrnimng the average feed saluug, The average feed saliruty rs

calculated ftom feed saluurv uslng the averagc coocenuanon factor For

calculauon oF the avera.ge conceotrat lon factor (ACF), a logant]unic dependcncl '

on recovery rano [R) rs asslrrned.

150

aFs

L

EzJ

LN

utF

d

!1!(L

o7

;IL

UJ

la6utd

OuJuJtr

\ c t A PRES UREFEED :RECO\

A LINITY: K I h A

1500 PPtr tJDlil

{ T D 5

E S P PRES f JRE /*

7

E S A SALII rYCPA S , L IN ITY

R O O E S I G N & E N G I H E E R T N G

, \ C F = L r ( l / ( l R ) ) , ' R

\X/herc "ln" reprcsents tlrc narural log

Average Concentration Factor, ACF

ll-C)

6 0

s 0

4 0

3 0

2 0

1 n

oo4D 50 60 70

Recovery, To

BO 90 100

Fig. 6.0 Average Conccntrat ion [ jactor yariauon widr Penneate Recover]

Bccause recoverl ' rate strol lgly aff lects process econofiucs, drere rs a tendency todesign operation of RO systelns at the highe st pracrical value.

i5t

{ 9 i

a -

R O O E S I G N & E N G I N E E R I N G

Slstem Components

Permahpr t

d podregJ r e !€E:sd

RO System Design

A fyprcal RC) systeftrs consist oI the fol lo,,vrng basrc components

' Feed \vater supply urut' Pretreatment system' Hrglr pressure purnprng Lrrut' N'fembrane eletnent assembly unit' Instrurnenlat ictn and control systerr l' Pcrrneate tfe2rtJr lcnt;rrrd storage unit' C- leanmg r rmt

' l -he uenrLr ra r rc , rsscrnb ly un i t (RO b lock) cons ls rs o I a s tand suppor ru tg thc

pressure vessc ls , ln te rconneccurg p lp rng , and [ecd , penrez te and concent ra te

m;rrufolds fr ' lenrbrarre elcments are rnstai led tn dre pressurc vesscls fhc pressurevesse l has-permeate por ts on each end, loca ted in cenrer o f thcend p la te , and feedand concent ra te por ts , Ioca ted on the oppos i te ends o f the vesseI Each pressurcvessel mav contain from one to seven membtanc elernents coonected rn series

B r i r e s d I nl g conned o r

Fie 7 0: Pressue Vessei * l th l - r r ree Membrale E, iemcnrs

R O D E S I G N & E N G I N E E R I N G

A s s h o r v n a L r c - r r , e , t h c p e r r t t e : r t c t u l r c , r f t h e f r r s r a n d t h c l a s t e i e r n e n t r s c o n n e c t e d

t o t h c e n c i p l a i c s o f r i r c P r c s t u r c v e s s c [ l ) e n n c a t e t u b e s 9 [ e [ e r - n e l t s u t L h e

p r e s s u r c v c s s e l a r e c o n t t c c t e d t o c a c h o t h e r u s r n g r n t e r - c o n n e c t o r s C ) n o n e s r c l c o feach tncrnbrane e le tne t i t * rc re rs a bnne sea l , rvh- rch c loses rhe passagc be f rvecn

outs lde ru r - t o I the e le rner r t end urs idc r t 'aL i . o I the pressurc vcsse l ' f lus

sea l

p tc l i co ts fced u 'a te r f ro rn h l pessLng tLe tncmbrane rnodu le , and f t t rces r t ro f lo t ,

d r rough dre fced channe l -s o f the c lement As fced u ,a te r f lon 's th rough each

subsec luent mcrnbtane e [ement , par t o I thc [ced vo lume is removed as pcr rneateThe salt concentrat lon of the remaimng feed water increases along the pressurevcssel Pcrmeate rubes conduct the perncate- from al l connected elements The

collected penneate has the lorvest salniry at thc fecd end o[ the prcsswe vessci,

and rncreases gradua[y ur dre direcnon o[ the ct jncentrate f lou,

A sys tern is d i r . rded ur to g roups oF p tessure vessc ls , ca l led concent ra te s tages In

cach stage pressure r.essels arc connected Ln p:rral lel u,rdr respect to the drrecdon

oI thc fced /concent ra te f lo rv . The nunrber o f p ressure . 'esse ls rn each subsequent

stage decreases m the drrccrion of the feed f lorv, usua[y rn t lre rat io of 2:1, as

shos,n belorv rn Fig B 0

' l ' hus , one can r . i sua l i ze tha t the t lo rv o f tccd . ,va tc r th rough the pressure vesse ls o f

?r systern resen-rbles a pyramicl stnrcnrtc: a tugh volume of feed rr 'ater f lo\L's ut at

d re base o I pyrarmd, : rnc ] a rc l ; r t rve 11 's1r . t " i l t -o lu r lc o f co lcent ta te lear .cs a t t [e top

J 'he c lecreasrng numbe ' r o f para l le l p ressure vesse ls f ro rn s tage to s tzge

co lnPct lsa t -cs fo r the dccrers ing t -o lunre o f teec l f lou , , n ,h ich ts con[ tnuous l l ' l>erng

parua l l y c ( )nver tcd to pennc-a te ' I ' he

per t r iea te o f a I p ressLr re vesse ls in cach s tage,

is conrbinecl together furto ;r corrnron [)crnreate urarufold

.-I 'hc ob;ecur.e of the taper confrguraLion oI pressure vessels is to marntai lr a sirni lar

feed/concenftate f lorv rate per vessel t luough the length of the systen] and tcr

rnaintain feed/concentrate flou' wldiln the [rlrts spectfied for a grven type of

nrcmbtane element Very trgh flov,' through a pressure vcssel wrll result in r hrgh

prcssure drop and possible stt 'ucfutal darnage of the element Very low f lorv u' i l l

not provtde sufFrcient turbulence, and may result in excessive salt concenLral ion at

the tneu-rbrane surfacc

For a grven RO urut, the number o[ concencrate stages wdl depend on rhe

petmeate recovery tat io and the number of membrane elements per pressure

vesscl, In order to avoid excessive concenLration polartzadoo at thc membrane

surface, the recovery rate per indrvidual membrane elemeflt should not exceed

18"h It is common engmeenng practice to desrgn buacklsh RO systems so that the

arrerage recovery rate per 40 rnch long membrane clement u'r l l be a6out9o/o.

t

R O D E S I G N & E N G I N E E R I N G

I ' 1 1 1 l i 0 l ; l . r r . [ ) r : r q r r r r ( ] t r r i l ' o s t r g c I i L ) s f , s r c ( n

Accordrngl l ' , the nutnber of cc)nccnLrate stages [or an RO urut havrng 6 elerlents

per pressurc vessel rvould be two lor recoverl, rates ovet 600/o, and drree forIecov€ry rates over 7596 Wrdr pressure vessels contair l ing seven elernents, a furostage conflrgr-rrat ion rvould be suffrcient [r :r recovery rates up to B5%

e o n. ce n tr'ate Re - ctrca /ati o n

The srmplest membranc c ler-ncnt assembly consists of one pressure vessel ,contatrung one rnembrane element, Such a configuration, used in a '" 'ery srnallsystems, can operarc at a Li-rnited penneate recovery ratio, usualiy about 75o/o lnorder to increase dre overall systern recover!, raUo ind strl l marntarn an accepLebleconcentrate florr', a part of dre concentrate stream is rehrrned to the suction oI t]rellgh presstrre prmp

The concentratc recyciing configuration, shown belou', is used mainly in a veq,smaU RO umts An ad\rant j rge of such a desrgn rs the compacts ize of t l re RO uni t

Perrn=:tp

R O D E S I G N & E N G I N E E R I N G

- fhc d, rsadvantagc oI c( )ncenuate recucuiaaon dcsrgn Ls rc latcd to th€ need for a

laiger fee,i ptirrrlr t, harrdic lrrgircr ieeci f jo,,r. Accorcirngil,, rhe porver consumpuonrs relahlell ' l lglrer than tl 'rar rcqu-red rn a multrstage conEguradon Due tcrblendrng o[ the feed wrdr d'rc concerrtrate strearr\ the average feed salrniq, rsincrcased. There[ore, bodr ric feed pressure and the pcffneatc saliruft are lu,qhcras r,. 'eU-

F i g 9 0 : F l o . u D i a g r a m o f a s h g l e s t a g e R O s y s t e m w i t h c o n c e n t u a t i o n r e c i r c u l a r i o n

Concentr ate S tagng

A comrnerci-al RO utut usualiy consisrs of single pymp and a muldsage array ofpressure vessels. A simphflred block diagtam of a fwo stage RO urut is shorvn rnhere

t,f

I

?3

R O D E S I G N & E N G I N E E R I N G

20.1 psi14.{ bar

1 1 2 p m25.4 nB.,]T

150 pm14,0 rf8/tr

Frg l i ) 0 [ ] low L) ragr r r r r o I a nvo : i tagr I iC) sysrem

ftrc conccrtt tate [ i()n] the l trst st lrge []ecc)rnes r lre feecl to d1e seconcl stage, this isu'hat is l ] tcant b1, thc tenn "conccrl trate staging " -fhe

f lorvs and pressrrres i l r thenlr,r l trstagc utut ate conuoUed ,,vi th t l-rc [-eed and concentrate rralves f he [cedvalve, after the tugh pressure pLrmp, controls feed f lorv to the urut TheconcentJate vak'e, at the outlet of RO block, controls thc feed Dressure

Flow Dtstnbution

In some cases i t ts necessar)r to equi l i$12te permeate f low becwee11 sages te-decrease Peffneatc florv ftom the fust stage and increase perl-reate flow from thcl-ast stage

- l-hs can be accomplished rn one o[ rwo design confrguradons, onc

soludon is to nstal l a valve on thc perrneate l ine from t]re Frrst stage, as show.n

R O D E S I G H & E N G I N E E R I H G

200 gpm4 5 d m3,4-r

5 o p ;3 d b - ) r

n F n < t

1 6 3 b a r

150 gpm34 m?,,hr

dS gpm

11 1 trr3.,hr

-:,$

50gpn11 3 m3,hr

l j r g I I 0 : F l o t ' l ) r a g r a n r o i - ; r t t , o s r a g c I i ( ) s v s r e n r { r l h l r c r r r r c r l e t h r o t r L n g

1 \ u i r r ^ r 1

B-v throtthn{ this valve, pcrrneate lracl< pressLrre \\rrl l ncrcase, rcducrn!] nct dn\.urg

Pressurc and reducing Penneate flux from tlre fust stagc 'I 'hc

i l i fferenual penneareflux rs produced from drc sccond stage by operatrng'the RO unit at a bugher fcedptessLr re.

fhe odrer solution is to mstall a boostet pump on dre concentrate l lne berwecnthe fust and the second stagc, as dragrammed below. The booster pump rvil ltncrease feed pressute to the second stage rcsulting rn hlgher pen:neate flow- Theadvantage oI the peffneate thrordrng desrgo is sunphciq, oI t ie RC) urut and lorvcapital cost. However, dlis deslgn results rr additronal power losses due topetmeate throtdrng and hrgher power consulnption. The interstage punip desrgnrequres modificanon o[ the interstage marufold and a{.t addruonal purnprng urutThe utvestment cost is hrgher than rn tlre fust desrgn, but the po\\,er consumptronis lower,

21O p=i14 5 bar

25o

R O D E S I G N & E N G I N E E R I N G

'10 1 gpm7?9 mAtu

150 gp rn34 0 m3hr

136 ps1 2 8 b r

F ig l 2 i l F l o . t ' [ ) t a r r yan r o f a nvo s tage R ( ) s \ s t c r l r \ q r l ) r n t c r s r i l ] c pL r f t r p

n , t "l- ( l'//? ( t.t t(" \ / t 191 / /.q

l iot sornc applicauons, the srngLe pass RO sysrern rnaf sq1 be capable

producrng penrreatc q'2ter of a requi-red sallfriry Such condiLions rnayencountercd ln | \vo types of RO apphcaUons.

o fbe

A TSearvater RO systems, whrch operate on a very hlgh salrruty feed water,hlgh recovery ratio and/or at hlgh feed water remperafure

' Brackish RO applicatrons which req ' irg very low saltnity pemreate suchsuPPly o[ makeup water for pressufe bor lers or produdoon oF r inse water[or microelectronics app [ca tl.ons -

To achieve an addiuonal reducdon in penneate sal,rrury, the per-mearc waterproduced ur t1re fust pass is desalted agarn iri a second RO sysrem ThrsconEguratron is called a rwo pass desrgn, or "permeate stagmg " Dependrng onquality requrrements, aU ot part of the first pass p€tmeate volume is desalted agaurin the second pass system The system configurauon is knorvn as a corrrplete orparual two pass system dependrng on whether all of the permeate is fed to dresccond pass or not .

R O O E S I G H 8 E N G I N E E R I N G

- i - hc [ L r s t pass pe rmea tc r s a , . en ' c l can r r , a te r l r con tau rs r . e r1 ' l o r ' , ' concenL rauons

of suspended parncles and drssolvcd sal ts , thcre[c>rc, i r c- loes not requrc an1,srgruf icant pre[ reetment Thc second pass s) ,srenr cen operare at a re iaovcl l 'hghal'crage Permeate flux alld lugh recovcrl" ratc

-l 'hc conulron desgh pararneters For

r l ie second pass RO urut arc a\ .erage f lux rarc c , i 20 gtd and recoi .cr l rare of85% 90o,/o It a r\L'o pass s}'stern, thepcnneatc From the fust pass flou.s tl 'rrouglr astorage tank or is fed duecdy to the suction o[ dre second pass hrgh pressurepump Thcte are number o I possible configura uo n <-r f t]re rtvo pass RO uruts OneconFguration, which is a paru-al rwo pass slrstem, shown here, spIts the permeatefrom the first pass into nvo sLreams

F ig l 3 0 F [ou ,D rag ra rn o f a nvo pass RO s ) , s rem.v r t h b l end

One stteam is ptocessed by dre second pass unit, and is then combrned wrth theunprocessed Part o[ the permeate from dre fust pass. Provided that the partralsccond Pass system can produce the required pcrmeate quahty, tfr is configrlrationre sults io smaller caplt-al and operating costs, as wcll as lugher combrned peffneaterecovery rate (uulizauon o[ dre feed water), con'rpared to a complete flvo passsystcm

It is a cotnmon procedute tn a hr/o pass systcms to rcturo concentt-ate from thesecond pass unit to dre suction of the lugh pressure pump o[ the fr-rst pass urut,The d-rssolved salts coocentrahon u.r dre conceotrate From dre secdnd pass isusually lorver the concentraLion of dre feed to the first pass unit, Therefore,blendrng feed water wt_th dre second pass concentrate reduces shghdy the salniryof the [eed, and increases.the overall uri l izadon of the feed watcr

2 7 \

R O D E S I G N E E N G I N E E R I N G

i r , r { , , \ / I /f l( i . \) ' . t i i .4/ Uetl.qn I r/11ft/1111€.t

Follo,-r,rng r;rble i 0 pror-rdes gudelnes for desgrurrg RO st'srem-s -fhe

se arc

pror . rded as an examplc on[1 'and mal t -ary t . , rdr tnctnbrat te tnarru lacrurcr . prc

t reetment pLc,r ' rded and the rype oI nrenrbranc

Table 3.0, RiJ Svstem Desrsn GudelLna

R:w Water source Brackish Brack-rsh Sea Sea Wasre

Wel l Surface WeH Surface Teruary

Feed rva ter Pararne ters

Recommended N{ax tmum:

S D I @ 1 5 - L t . t e s 2 4 1 . 1 +

Turbidity as NTU 0 2 0 4 0 3 0 4 0 - {

T O C p p m a s C I 5 3 I l 0

I3OD ppm as ()2 B l l B 8 2 6

COD ppm as 02 1 1 1 8 i l l l J 6

System Average Flux (rr Lt\lFt) 1 0 6 2 0 4 n 1 4 4 5 n

Lr ' :d l i - lernent Fl r r r (ur LNGl) 4 5 9 1 0 6 1 0 8 l 4 2 5 5

7o Flu-r Dechne (rer year) 1 I 1 I 1 5

o o S a l t l - r . s a g c I r r . r e a s e ( p e r 1 ' " 3 1 y t 0 l 0 1 0 l 0 l f )

R e r : ( m d r v i d , u l c l e m e n t ) 1 2 0 1 2 0 1 2 0 r 2 0 I 2 0

f i ced nr ] , /h (n rarnrum per r .csse l )

1 " d r a r l c t c l 6 r 6 ) ( ) l ( 0

B " t h r m e t e r 1 7 0 1 7 0 1 7 0 1 1 0 l 7 { l

Reject m3,/h (nururnmr pe r vcssel)

' 1 " t i - temetcr 0 1 0 7 0 7 r ) 7 0 l

8" d iameter 2 1 2 1 2 1 2 i 2 l

Pressu re D rop (pe r vesse l , r n ba r ) 212 238 238 238 212 212

Pressure Drop (per e lement, rn bar) 0 68

Feed water Tempe rahrre (- C)

0 6 8 0 6 8 0 6 8 0 6 8 0 6 8

5 t o 4 5 5 t o 4 5 5 t o 4 5 5 t o 4 - 5 5 t o ' 1 5

A N,tluerage f lux rale

Fol.lowng table 4-0 pro\rldes guideltnes for average membrane flux ratcs and

percent decrease rn flux evefl, 'year for drfferent quahry oI fecd tr 'ater as

chz.ractenzed by the SDI of feed rvater. These are pro\,'1ded as an example only;

actuaI values m^y varti unt]r membrane tnanufactuter, pre-fteatment provided, feed

rvater qr.rality. type of mernbrane and deslgn philosophy

R O D E S I G N 8 E N G I N E E R I N G

T _ ' _I W a t e r l \ D e

S u r f a c e . . ' a t e r

\ \ t e U r r a c e r

R( l oe rn re r t e

\ \ : : t c rv l te r

\ I as te rva tc r

\ r " j 1 [ t ] r r i r : r e , . r nJ r l pec rcd o . decrease rn f lux oer

I tnli, gld i ' o F i u x D e c l i n e / y e a r

3 l l I j . 9 9

20 i0

l f the fced

flux rate to

rvater ls foul ing rt rs

reduce the chances

advrsable to desrgn drcof fouLng and obtah a

RO systcrn at loq'er average

stable performance.

Salt Paisage Increase 71er-year'Follorvrng table 5 0 proi 'rdes grudelmes for salt passage rncrease over trrnc Theseare pror.rded as an cxample on11,; actual valucs n1a\t vary wrth the rypc ottnembrane usec i

' l ' l te [)rcsctl t day cottr l tosttc t t tcrnbr:rncs :rrc qLrrtc sui lr le

- l- [rey rctatf l t [-rc

n lc t l rb rane sa l t re iec t ion fo r : r lo t rgcr t i rnc . \ n rcmbranc l - t f c o f about 5 ) ,ears u r . ru'el l ope rated planr is not uncomr-non

Flow ftnzitations

Follorvrng table 6 0 prorrdes feed and concentrate florv lirnitauons formembranes, Tlre actual values may vary u,rth the typc o[ membrane and feedrvater qualiq', The maxunum Limit for feed water is to lulrt the membrane

Prcssurc drop atrd mrnirnurn lirnit for concentrate flow is to marntain requrredcross florv 6r'er the'membrane surface

l 'ab le 5.0

Celltr losrc rr-rernbrane

Cornpos i tc N{cmbrar re

Increasc over dmc

Menrbrane T;pe %o SP Increa 'se/ye. t r

Tablc Passa Increase

Membrane Feed Floq ' Concentrate Floq,

Diameter (in) Max (m3lh) Min (m3lh)

R O D E S I G N & E N G I N E E R I N G

RO Fre-treatment

P re - tre a tm e n t C' o n st d e ra tt o ns

-Ihe feed watet, dependrng on i ts sourcc, may contafl1 various concentradons of

suspended so [ds and d isso lved mat te r Sr rspended so l ids may cons is t o I rnorgarucparrrcles, -col loids and biological, debris strch as rnicroorganisms- and algaeI l i sso l t ' cc l mat te r tn2y consrs ts oF t rgh ly so lub le sa l ts , s r - rch as c l r londes , andspanng l l , soh , t r le sa l ts , such r rs carbonate s , s r r l fa re s , .and s i l ca Dunng dre RO

Process , t l te vo lume o f feed u 'a te t decreases , and the concent rauon o f suspenc ledp: r r t rc lcs a r rc l c lsso l r ,c r l rons i r rc rcases Suspendec l per t i c Ics r ru t ' sc t t le on thet t r t r t t l ) t l t t c : t r r f l c c . t [ r t r s I r l o t . k t r r g t c c t l c h a n n e l s r r r c l t r r c r r : r s u l g f t - t . , , r , , r r l o s s c s(prcssr r rc dLop) ac . ross the svs tc ln

Spanng ly so l r . rb lc sa l ts tn : ry p rccrp i ta te f ro rn the cooccnt ra te sLrcarn , c rea te sca lc onthe membrane surface, and restr l t i r t lorver watcr pernreabrirty thrbr-rgir rhe RC)tnembranes (f lux decltne) Thrs process o[ formanon of a deposrted Leyer on a

t letnbtane surface rs cal led tnembrane fouLng and results in performance dechncof the RO systern

- lhe objecuve o[ dre feed u'ater preLrealment process is to

irnprove the quahty o[ t l re feed u'atel to the levcl t , l lch u'ould result ur rel lableoperahon o f the RO tnernbranes

-fhe qualiry of thc feed u'ater rs deEned rrr t€n-ns of concentraBon_oI suspcnded

parncles and sahrranon lev.els of the sparLngly soluble salts fhe cotr i l .rronindicators o[ suspended parucles used in the RO Lndustq, are turbLdrt l . and SLlt

Densrty Index (SDI). The rnaxrnrrrn lrrnits rviLh convcnuonal pre treatment are.

turbidiry of 1 NTLJ and SDI of 5

S i l t Dens i ry Index rs an emprr ica l res t deve lopec l fo r mernbrane sysre f i rs r ( - )tneasure dre ra te o [ fouhng o f a L ] 45 mcron h l te r pad b1 ' rhe suspended and

col-lordal parucles ur a feed u'atcr Tlus test rnvolves Lhe trme reqLurecl to Lilter a

spec i f ied vo lume o f fcec l a t a cons tan t 10 ps i a t t rme zero and then a f te r 5 r ru lu tes ,

10 nuoutes and l5 l l i l nu tes o f con t rnuous f i i t ra t ron Tvorca l R( - ) e le rnent

R O O E S I G N 8 E N G I N E E R I N G

\L ' : r t12 t l t l c ) l t : t : r t t t l l .L t t tu rn S l i l o i + .0 a t 15 mrnures fo r t l - i c fced \ r ' : t te r I i t - t t c SDI' .es t r : ; h . r r l t rc l to oa ly 5 o i 1C n i i ; - iu tc .ead i lg . , j r . r , , p luggurg o i i i r c i r j re r pac i , r i rcLrser can c \Pcc t a h rgh le t " 'e l o [ fouLng fo r the RC) Deepr u 'e [1s q ,p r rca lh 'havc :

SDI 's r - ' [ ] o r less and t r : rb id rdcs lcss rhan one u . i th l i r r l c o r no prer rcauneorSur face s ( )u rces t , ,p lca l . l \ requ i rc p rc t rea t1nent For remor -a l p I co l l r , , rda l : r .dsuspe nded soLds ro : rc l rLcvc acccptab le SDI and ru rbrdrq , r ,a lues

Con8-nuous oPerauon o f an RO sys tem wrdr leed u ,a te r u .huch has tu rbrc i r ry* o rSDI values near thc Lunrts o[ t ]rese values n'ray result rn sgnif icant rnernbranefoul ing For iong-term, re[able operafion oI the RO urut, the rveragc values ofrurbrdrt l ' ancl SDI n the fecd rvater should not exceed 0 5 NTU and ? 5 SDI uruts,resPectrvclJ/ for conventional pre-ueatment. When usrng micro f i l t rauon or ultrahltr 'at ion nrcrlbranes dre feed rvater l i rnitrng conditrons can be srncrcr

fhe rndrc ; r to rs o i sa fura t ron leve ls o [ spamgly so lub le sa l ts rn the concenr rarestreanr are t l le l-angelier Saruradon Index (I-SI) and dre saturadon rauos

-t-hc L.Sl

p rov idcs a t t tndrcauor r o [ the ca ic iu r r carbonate sa turadon Negauvc va lucs c , fLSI urdrcate thai the lvatcr is aggrcssivc and that i t rvi l l have a tendency to dissoh,ecalcium carbonare Posit ivc values of t-SI indicate the possrbrhty of calcrumcarbonate precrprtzuon. Refer to appcndr-x A for LSI calculaf lc,ns

l-he LSI ' ,r ' : rs t . ,ngutaUl' cle veloped b,y Langel-rer for potable u'ater of a lo.. , .sal inir]F -or lugh sa l in rq , \ \ ;a re r encountered rn RO apphc: rnons , thc t -S I i s ; rn epproxunarcind ica tor , ,n [1 ' Thc St i [ f L )a t ' i s index (SDSI ) a t te r r )p rs ro ( ) \ , c rc . ) r r r ( ' r l r cshor tco tn t r tgs c . , i thc l . ; rngc l re r Indcx rv i th res [ )ecr to [ r rg l - r to ta l d rssoh,cc l so l rc i : ;\ tTa tc ts : t r t c j t l t c l tn l tac t o f "c< t rn rnon ion" e i - fec ts on the c l r i r . r r rg fo rc .c For sca lcfonnaoon L- rJ tc thc I -S [ , t [ re Sof [ -Dav is index l ras i t s besrs u ) thc cor rccp t o fsa tura t ton lcve ' . i

- fhe so lubrh t ) 'p rodLrc t used to p rec [c t t l i c p l { o Isanr ranr i r ' , (pHJ-

For a water rs crnprncai ly ' mochfied rn the SufF-Davis inde x. Strf [ Da".rs indices wil . lpredict that rvatel ts less scale formng than the I-SI calculated for the sarnc rvaterchetnisul ' anci conditrons The devrauon bervee(t dre indiccs increases u, i t l r iorucstrength Interpretauon o[ the urdex is by the sarne scale as for the LangelierSaruradon index

The saturattc) l t tauo rs the rat io of the product oI the actual conccnuatr()n oI the

- lons rn Lhe concentratc strcam to the dreoretical solubrhrl , o[ the salt at a-grvencondit ions oI tempcrature and toruc sffength These raUos are apphcable marnlyto sPanng ly so lub le su l [a tes o Ica lc ium, bar ium and sLron t rum Sr l - tca cou]d be a lsoa potennal sc:r le fonmng constiruent. Other potentral scale form-mg salts, such ascalciutn f luoncie or phosphate wtr iclr may be present Ln RO [eed, seldoln representa orob lem,

3 {

R O D E S I G N A E N G I N E E R I N G

f ) . pc , , , Ju rg o i t r i r - r a \ ! : \ ! / i c r L1 u : r L f , i he p rChca i r n t l l t [ J r ( J ( t \ : i l l I ' l \ cC rn : , tS t ] : o i : r i j

, , r \ n l n ( , , I d i c t ' u L l o l i L n g L l c l t m ( n f s l c l . , '

I

I

a

I

a

I

a

a

Rcmor .a l o f Large par t rc ies L rs r lg 2 coarse s t raure I

\ \ 'ater cl-rsLnfecuon rt rd:r cl l lo rule

Clanftcatron unlh or u' tdlr-rrrt f loccuiatrort

Clantrcanon arrd hardness reducnon usrng Lnrc Lre2tlnerl t

N'{edra Frltrauon

Reducdon o[ alkalrrury by pH adiustrnent

Addruon of scale rnhLrbitor

Reducdon o [ l ree ch lonne usu lg sod lum brsu l f i t c o t acn t 'a ted carbon

filters

Vv-ater stenLzatron usng Li\r radrauon

F jnal removal oI suspended parucles using carurdge f i l tcrs

I

I

The rmtral remo.",al o[ large parucles ftom the feeci q'ater rs accot-npl isl ied usrng

mcsh strainers or travel ing screens- Mesh strarners are used ur t 'el l r t 'ater supply

systems to srop and rernove sand pardcles which may be purrrped frotn dre well

Travehng screens are used marnly for sutfacc watet sources, tvhtch ryprcal ly l-rave

la rge conccnt ra l ions o I b io logrca l debr is

I t t \ ( ( , n u r r ( ) n p r t c t l . ( . r o d r s r r t f e c r s r r r f a c c l c c d u : t t , t , r , , ' , , 1 . ' , l ' ) . , ) t l l t ( , 1 L t , r l , r g t c e l

, rc t i ! ' i t ) Bro log ica l acn \111 ' tn a rvc l l rva tc r Ls usua l ly vc ty l t - ru ' : rn t l t r t r l l ' t ; r . l r r f l ' o f

c l rscs . r ' , ,eL l wx ter does no t rcqLurc ch lo r tna t lon l r t so t r rc r . : rsc :s , c l t l c , t l r la t to t t rs r - l5ed

to oxrdrze i ro r r and mlngan€se m the r ' , ' eL l rv ; r tc r L re to re f l i t ra t to r t \ \ ' c l l n 'a te r

conta i rung hy ,c l rogen su lEdc shou ld no t be ch lonnatcd or exPosed to a r r [n

presence of an oxrdant, t- l-re sr-r l [de ton can oxlcl lze t() cletr ie r l tal str l fur rvFuch

eyeltpaLly ma1' plug meftrbrane eletnents

Setthng oI sutface rvater in a detention tank results ut soure ted'. ,cuon oI

suspended part j .cles Addrnon of f locculants, slrch as Lron or alumrnutr-r salts,

results rn formatron oI correspondtng hydtoxtdes; these lrydroxides neutral ize

surfacc cl.rargcs oI col loidal patt icles, agglegate, arrd adsorb to f loaring pardcles

be[ore setr lurg at t [-re lowcr part oI the clari f ier To increase thc size and suength

oI t [-rc f lock, a long chatn orgaruc Polymer cao be added to the \L'atet to bLnd f lock

part icles togetl-rer Use o[ l i rne results in increase of pH, forrnanon o[ calcrum

cerbonatc and rnagnestum hydtoxrde patf, lcles Ltrne clanfica| lon results rn

reductlon oI hardness and alkalrrr i ty, and the clanficaUon oF treated urafer

V, 'el l water usua[y contai-os low concenftadons oi , .r .p.nd.d parf lcles, due to the

Frluatron eflect oItlie aqui[er. The pre.treatment of $'eU u'2tet is usually lunrted to

screeolng o[ sand, addrUon of scale inhibitor to the feed q'ater, and cartndS:e

frltratron

R O O E S I G N & E N G I H E E R I N G

5ut tace \ ' \ ' a tc r ma\ r con tern \ . 'anous concent ra t lons o I sL lspende d par t tc les , $ luchzrc e l t i l c r o i Lnorgaruc or b ro iogrca i ong ln 5ur tacc ' . . va te r usuaUl rcqur resdrs rn fecuon to conr to l b ro logrca l ac t r f i r \ , and remo\ .a l o ( suspended parnc les brymedra hlrrauon T[.re eff iciency of f i ]ranon process can bc urcrcased br aclchngFr iua l ron a ids . suc [ r as f loccu lan ts and organ ie po l1 ,n ]cs5 5ornc sur tacr r ra te r r r r . rVconta-Ln lugh concent raoons o I d - rsso lved org2mcs

-1 -hosc can be remor .ed b1

Passlng Feed rvater tLrrough an acovatcd carbon fr l ter Depcndtrg on composruonof the l l rater, acidif icauon and addincin scale rnhibrtor may be requrred Thc f lo.r,dragram of pretrealment system for surface \r/ater ts shorvn belou.

Cartndge f i l ters, almost univcrsal ly used in ai l RO s)/srems pnor to t le hrgh

Tressure Pump, serve as the Frnal batr ier to water born parr icles The nominalraung conl lTlonly used rn RO applications rs rn the range of 5 l0 trucrons Somesystems use cartndges with tnicron ratr lgs as low as i mjcron There seems ro beIi tde bene f i t from lower micron ratcd Frl te rs as such Frl ters requrrc a hrgl.rrepLecen-reIrt rate with relanvcly small i rnprovemenr in r l-rr ' hnal {ecd .,r ,arer qual iq'

When etther mrcro fr l trauon or ultra f i l t rauon nrcmbranes are rrsed for prcfreatment then cartr- idge Frl ters are not neccssary These rnernbrane FLltrauolp roccsses reduce feed water ru rb id r ry to less than 01 NTLI enc l SDI ro l cssrhan ? 0

.\'rrturrt/ion I-tnits in the eoncentrate

[ ]oLlou'urg t:r l t le 7 0 ptovrdes safuradon hrruts fcrr spanr.rgl l , solLrl-r[e salts r,n t lrc(-clncenttate -fhese

values are with an assurnptron that a goocl antrsc;r l :rnt, , t , i l l beusecl. In nrost cascs the respecuve antrscalant closage calcr-r lauon progranresi l f i lates mzxlmull l recovery at rvhich dre systenl carl operate and therecomrnended dosage. I t rs adr-tsal-r le to [o[or,v the anuscalant manufacfurer 'sreconrrrrendations. The actual values m^y v^ry with the anoscalent r lanufacturer

Table 7,0: Saruration Limits

Salt Sanrrauon 7o

CaSO4 230

SrSO4 800

BaSO4 6000

sio2 100

3 3

R O D E S I G N & E N G I H E € R I N G

Deprii. i i lrg up(r11 wli-ther a,-, a,ti iscalari i is usctj anri lt 's ryPe, i jrnits oi saruratron

rrdrccs are used ul thc r-rrdusrr.r ' Witlrout :r.t i :niscalant ooe tries to be safer to

maintam negati. 'c- .., 'aluc ro thc conccntratc. ln dre Past SHiVtP rvas uscd

commonly unUl hrgl-r efficient orgaruc antrsqalant came tn thc markct Somc o[

these organic anuscalants allorv nruch h4;her values than thc trad-rUonal SHMP

Condition Value

LSI and SDSI without antiscalant < 0 2

I-^SI & SDSI wrFh SHN{P (sodruqn hexarnetaphosphate) < + 0-5

tSI & SDSI_with organic andscalant < + 2.5

lt is advisable to run the computet Pro,echons with actual feed u'ater comPositlon

and operadng pa-rameters to ensure the chosen antiscalant wril indeed perflorm rts -

dury of prevendng scaling on membrane surface It is a good pracUce to 6rst

evaluare the prospecdve andscalants in laboratory studies to confirtTr compatlbdlry

wi*r the feed.*rater and trrembranes

a .

R O O E S I G N & E N G I H E € R t N G

Mernbraffie Start-urp, Shu*downand Flushing GexidelEmes

P re s e rua tt ue I' iu s lt z ng-fo

preserue cletnents fror-n brologrcal grou'dr and tt.r help rnauitarn pcrfcrrmance o\rertirne, cornposite qpe membtanes are storcrcl rrt I 29/o sodrrun brsr-rlEtc and 5 10or'opropy lene g lyco l so lunon I t rs d rc re fo re advrscd to 0ush mernbrar res l ]n ( ) r ro use t ( - rcl lninatc rcsidual presen/atl \res m the prodr-rct stre: lrn

( . )nce the e le tnc t ' t t s l - ravc l rac l the preser la f rvcs t - lushcr l i ro r r r thcnr , rhc t , r r ,o r r ld ncec l t< thetc presc:n'xt. lvrrs rc-r.r[)pLiccl fcrr long tcnrr : , I i )r , \g(

Once e le rnents have bcen loac led : rnd vessc ls sea lcc l . r r i s rcc< i rn rner rded to f lus l r thcs) 'stenr to draul \r . i th feed rvatef at desrgrr opcratulg pressurc Frrr a nrirumurn o[.1hours If d're elernents are to be used ur sy'sterns requlnl lg ult-rapu-rc watcr, alrurlmurn flusl-rrng urne of 24 lrotr.rs is recornrnended to reduce the TOC-concentratron to [ .relou' 50 ppb (assumrng zero TOC ur drc fecd rvate r)

For pouble apphcauons, drscard the product ' ,varcr for ar leasr 24 hours pnor rodrtnkng or usr.ng in food appl- icauons Irgcsrion o[ dre prcscn'arive ma]r causcrr i taoon to dre gastrourtesonal tract, col ic, drar.rhea, or othcr suni lar symptoms

RO Syltent ,S tart-ap

It rs Lmportant to be sure drat dre elements arc loaded and shinlned correcdy tcrremove any excess slack that nuly cause discorinects A [ow pressure fhrsh to pugeatr from the metnbranes is alwal,s recommended before a lugh pressure starrup Th.iscan be accomphshed drrough dre usc of a soft start rleclrari lsrn, or a vad-ebleftequency ddr.e, Failute to do drG ian resuli rn a u,atcr sirock u,ar-e (rvater hamrner)drat can cause physical damage to the Ro rnembranes The permeatc ',,alrres shoLrldahvays be open to draur dururg tlus flush to pre'ent darnagc to drc membrancs

3 5 s

R O D E S I G N & E N G I N E E R I N G

After the lr fras bcen pr-ugtc irorr drc svstenr tire fecd pressurc shou]d be urcrc-asedgracluall l, up t,-., dre '.r 'or[.:rr-rg p[(,qsure oI drc l{(-) urut

RO .t;,-rir nt .l htftltiu'u

B rack: :h I I{/a s le lV a Ie r J- y rlent :

Upon shutdown for brackrsh systetns, a ilush wrth the feed u,atcr at low recovcrl.'(bnne valve u'rde open) rs usually suff icient to'remove the hgh coocentrauon oIsaltsfrom the membranes The penneate vah'es should be open to draLn dunng thrs flushto Pre\rent damage to dre membranes

S eatualer 51ilent s

LJpon shutdou'n tbt seel l iater s);sterns, a f luslr \ \r t th RO penneate rs recornlnended torctno\:e the irgh concencralron oi saits frorn Lire rnembranes- Tirc penneate valuesshould be open to drarn dLrnng tlus flush to prevent damage to dre membranes I{RO permeate is temporarily unaveil"$le, th<: rnembranes sh<-ruld be flushed rrndr ROfeccl at lott, recovery (undr bnrre ta.lve u,ide open) The membranes should tlren befh-rshed rindr RC) perrr-reate rs soon rrs rt rs available

'f[-re searvater RO systenr shou]d

not [ ]e le [ t tur-f lushed "r ' id-r

a l iglr corrcentraf ior) brurc oo t lre rnernbrane surface

'l-lre clttannq,oIt.'atcr trscd ur Lroth nonl,rl R(-) J'y.s16711 .Start trp anc{ RO -\^yslern J-hutdoan

flr-rsl tng shotr l t l be ccltral t() ()r qlcatcr t i r :rrr t l r :r t .r , tr ich is re tainccl in thc sl sterrr [ ;or

s t ; rn .h tc l 8 - inch X 40 urch c lcnrer r ts essr r rnc tcn ga l lons (37 85 D pcr e lement Forstetrr lard 4-urch X 40-rnch e le ments assurne tJrrcc gai lons ( i 1 35 D pcr clenrcnt

R O D E S I G N A E N G I N E E R I N G

RG Mermbl ane FouHar"nfrs mdTheEr Removal -

I:oa/ant.r

L)uring nonnal operauon over a penod of t ime, RO rnernbranc clernents aresub iec t to fouLurg b1 'suspcnded or spanng ly so lub lc mater ia ls r l -La t r la1 , bc p resentin the feed u'ater Cotnmon examples o[ such loulants are calcrrrrn carl ]or)atesca le , ca lc ium su l fa tc sca le , meta l o> i ides sca le , s ihca coat ln t l , anc l , rg . r l r ( ( i r

b iokrgrca l deposr ts

I -he na turc rnd rap ichry o f tou lng depends on the condruon , , , t r l r t - . t . . .1 * , . , t " ,[ - 'o l rhng is p rogrcss t r e , and. t f no t con t ro l led ear l l ' , r ' , ' r l l i rnpar r r l r t l ( t ) rncr r r l r r r r ' r celeme nt perfcrnnencc Ln a rclat ively short t lne,

N ' lon i tonng o 'e ra l l p lanr per fo r - rnance on a regu la r basrs rs a r r csscntLa l s rep inrecogruzlng t 'hen tnctnbrane elements are beconrrng fouled Pcrfcrrmance rsaffected progressr'ely and rn varylf lg degrecs, dcpendrng on thc narurc of rhefoulants. Table 8 provides a sufiunary of the cxpected cffects rhar conunorrfoulants have on performance and table 9 provides drf l ferent clean.urg soILruonsand drer r compos i t rons ,

Fou/ant Rernoua/Fo.rlant rernor.al is contro[ed by cleanurg and f iushrng or bv changrlg rhcoperaung condruons As a general gurde, foul-ant removal rs requrred lvhen any o[t l-re foUot'ng conditrons occur:

1 Penneate florv has dropped to 10-i5 percenr belorv rareclf-lorv at normal pressure

? -fernilerature,ccrtected feed rvater pressure has rncreascd 10

15 percent to marntain rated product water f lorv,

37t

R O T ] E S I G N & E H G I N E E R I N G

D - . . . , , 1 , . , . . . , . - , . - - - . , , ^ t , h , L - ^ , - 4 . , - - ^ ^ . - - )

p 2 s s e q e h a s i n c r e a s e d 1 0 - 1 5 p e r c c r r t

l ( ^ ^ - - ^ - . - ^ l -r - ,

P L r L C r r r ) J d t t

Apphed pressure l .Las rncrcased. about 10 i 5 perce n t

-i l ,e drlferentral pressure across an R() stage hes rncreased

oooceably (LnsLrumentat ton tnaY not be avar le[ [s to motutot

thus rndrcator)

The fol]owing paragraphs provrde a discussron of dre colrurron foulants and theu

t"t-t9r,al

Calnum Carbonate Sca/e

Calciurn carbonate may be deposLted frorn almost anl, f lsscl rvater iF there ts a

farlure in the inhibitor addrt-ron system or rn r-hc acrd Lnjectron or pH control

sysrenl that results ur a hgh feed rvater pl-{ An e:rt ly detecoon of the resultrng

calcium carbonate scalurg rs ab,solutely essentr-al to ptevent the damage that

crystals can cause on the acLive membranc layers Calcium carbonate scale that-has bcen detectcd early can be temoved by lo' .venng dre fecd u'ater pH to between

I 0 and 5 0 fo r one or two hours Longer res tdent accumula t ions o f ca lc ium

carbonate sca le can be re tnoved by re -c rcu la t rng a c i t r t c ac td so luuon o [2 percent

s t re ng th a r rd a pH o [no lcss than.1 0 th rough the RC) t t tenrbranc c lements

l l r rs r - r re tha t the 1 tH r l a r r l ' c lcan ing so lu t t , . rn docs r t< . r t t : r l i l r c l rw ' 4 0 Odrenvrse ,

darr-ragc to t lrc RO lncrnbranc elenre nts lna)/ t lccur, par hctr iar l l , at elevate d

te lnpera turcs - fhe

l r laK l rnum pF l shou lc l be less t l - ra r r 10 0 Use anunoruum

hydroxrde to ra isc thc pH, and su l f i r r rc o r hyd loch lonc ac td to los 'e r r t

Ca/rzum .f afale Scak

S<-rlutron 2 rs the be st knou,n medrod For remo., 'rng calctut-n sulfate scale frot l the

l{O men.rbrane

A,'Ieta/ Oxtdes .f ca/e

Ptecrpitated hydroxrdes (e g , Fernc hydroxrde) can usuaU;' [6 1s11eved by ustlg

thc techruques descr tbe d abor .e fo r ca [c ium ca tbonate sca le

Silica Coalrng

A srl-rca coatrng not associatcd u'ith elt l-rer metal l lydroxrdes or orgaruc uratter rvtl l

usually tespond only to ve[' specralized clcamng methods Consult [or

insrucdons relzted to a specrfic problem

3 8

R O O E S I G N 8 E N G I N E E R I N G

()ryantc Dtpoittt

Orgaruc deposr ts i c g . r 'mcrobro loq ica l s l rmes and rno lds) a rc bes t rc rnor .ed b1 '

us lng So lunon I fo r r rh ib r t : rdchuona l g rorv th , rc c rcu la tc and soak thc

membranes r .v t th a apProved broc ide so luc ion 1 ' [us reqLr r rcs cx tcndcd e \posure to

be e f fecuve; a b toc tc l , : , so lunon is besr e rnp lo l ,ed , , r ,her t an RO b lo t t i ( ] r r r rLn Ls ro

be le f t n a s tandb l , c . rnd toon For rnore than th ree days ( . -onsu l t [ r - r r sc lecDon o f a

b ioc ide compat rb le to r r rc rnbr i rncs

C/eaning Solzttons

The fo[owrrg chemrcal solunons ate recomrnended For cleaning rhc RO

membrane e lements The appropnate so ludo 'n to use can be de termned by

chemical analysis of dre [oulrng marcnal A detarled exarruoahon of the results oF

the anal;,si5 rvt l l pror-rclc addltronal clr-rcs as to the best method oI clcarung

Keepurg rccords oI t l ic rncdrods used and results obtaured rvrl l provrde data use ful

tn devc loprng the nrc thods and so lu t io r rs tha t rvork bes t under the feed rva ter

cond idons a t hand

Solunon 1 is recorrunended fot u'rorgaruc foulmg, Soludon 2 is specrfrcaLly

recommended fo r ca lc i r r tn su l fa te and orgamcs So lunon J i s recomrncnded fo r

hugh orgaruc fouLng All soltr[rons are to be used at the hrghcst avai lable

temperature up to 104! l- ' (40i l C) (30[] (- tor I-FCI) for rrp to 60 rrunu.tes <.,f

c lean ing Thc quar - r t r r , res g r \ rc r ) a re per 100 L l S ga l ions (379 l i te rs ) o f ' . va te r .

Preparc thc so luuons by prop<, ruor lu rg th< : e rno t rn t o f chcmrcaIs t ( ) t l i e a l roLrn t o l

c lcan tng wate t to bc L rser l I l sc c l i lo r r r re f rce pemreate to mL\ t ] re so l l r t to r rs NL i . r

thorough lv .

3 9 \

R O D E S I G N & E N G I R E E R I N G

I aD le a t t ( ( J t \ I cm l l t : r ne f - l c rnen t Founo t ) v rnD to t l l s

G e n e r a l S \ n l p t o m s

- { m a r k e d d e c r e a s e m s q l t r e l e c t r o n a n d a

, r r o d e r a t e r n r r e a s e r n l [ r b e u ' e e n [ e e d a r r d

c o r r a e n t r a t c r \ l s o , e s L g h r d e c r c a s e l n s v s t e m

p rod ucoor t

A rap id decrease rn sa l t re jecuon ar rd a rap id

rncrease Ln J P be tu .een feed and concer l t ra te

A lso , a raprd decrease tn sys tem produc f ,on

A sLght decrease t r r sa l t re ;ec t ion and a

gradu l rncrease in i l P ben"een feed and

c o n c e n t r a t e A l s O , a g r a d u a l d e c r e a s e o v e r

s e v e r a l r v e e k s i l s t ' s t e m P r o d u c n o o

A s ig ruEcant decrease tn sa l t re jecnon and a

shght to n rodera te tncre : rse u t -J P be twee n

[ e e d a n d c o n c e n t r a r e r \ l s o , a s l t g h t d e c r e a s e

ur s \ /s tenr p rodr rc t ion

[ ) o s s r l t l t c l e c r c a s c r n s a l t r t y r : c t r o r r a r t d a

g r r r J r r r l L n . r c i l s c r n J I ' l r c t l c e n f c c d a n d

c o r r a e n t c r f c , \ l s o , r g r l d r r a l d c c r c a s e u r s y s -

r e r n p r o d u c d o n

P o s s r b l e d e c r e a s e m s a I t r e l e c t r o n a n d a

marked acrease in U P ben"een feed and

concent ra te , { l so , a marked decrease tn sys-

tem p rooucuon

All ptoblems (equrrc

instructions rei2ted tothe cause oI the fouLng to bc couected. Consult for

a speci f ic problem

F o u l a n t

I Ca l c i um P rec rp r t a tes

( ca rbona res : nc l

pho spha re : .

ge neraUl ' fomd at

the concentr3te er ld

o f t he sys t cm)

2 Hydrated C)rudes

( i ron, ruckel . coppcr,

etc )

I \'tuied Collords

(rron, orgarucs, rnd

si l rcates)

4 Ca lc rurn Su l te tc

(genera l l v f t rmd a t

t h e c o n c c n ( r a t c e n d

o f t h e s l , s t c n r )

5 ( ) r g a n r r L ) e P . s t t s

6 Bacter ia l Foulng

R e s p o n s e

Chemrc rL I c l esn

r l re sfsterrr r r r t i r

S o l u o o n I

Chemrcal ly c lean

the system r t l th

So luoon I

ChemrcaUr, c lean

tJre s1'stenr * ' r th

So luuo r r 2

Chetnrca l l y c lean

the svs fe(n \u th

S o l u u o r r 2

Chern rca l J l , c l ea r r

i l le SVStern \ t l ut

So luhon 2 Fo r

heavl , fo, ' l ing,

use Soluoon 3

Chemical ly c lean

the system u'rth

either o f the

soludons,

dependrng on

poss ib l e com-

pounded foulrng

R O D E S I G N A E N G I H E E R I N G

Table 9 Sr-rnuna4' of Recornrncndcd Clearririg Soiuuons

Membr,tne (./ee.ning

Over tr,tne, tnembrane systerns can trecome foulecl rvid-r an1, o[ a number offoulants such as colloids, orgaoic marter, meralhc scales, and brologrcalconstifuents These materials can build up on tlrc rncrnbrane surface and ur thefeed brurc channel. If teft uncortected, dre accumulation oI these foulants cancause a se\rere loss oI petflormance in the systcrn: prcssure requrements rnctcascto maintain flou,, pressure drops Lncrcasc, and salt reiectlon can suffer- If thesystetn is not cleaned and the system contlnues to build up foulants, thc elementsmay "telescope," or shear intetna[y, causrng the rntegnry of the membrane surfaceto be cornprormsed and rendenng dre mcrnbrane irreversibly damaged.

This secnorr udi cover serreral pourts reLeted to cleanLng The fust part rvrl lconcern itself with data collccdon and syrnptoms o[ membrane fouLng. Thesecond part rvil l define the cornponents of a cleamng systern afid proradegu"rdehnes for buLldLng and operaong a cleamlg slud Frnall1,, direcrions andgudeLnes for perfonnrng a cleamng rvrli be g1r'efi; the reader rs encouraged todoublc click on topics relareci to specihc proccdures [or cleaorng , speclflcmembrane elements-

S o l u t i o r r I ng red ien t Quanuc l pe r J80

h te r s

p H A d ; u s r m e n t

C i t n c . \ c i d

RO Pemeate (Ch lor ine Free)

kg

l B0 h te r s

. \ d j u s r ' t o t , f J . l { r ' r r r h

r n l r n o r u u m l r l c l r o u J c

(1..iHrOF0

2 Sodrurn Topoiyphosphare

Tetrasodium EDTA ( \ 'erse ne

220 or equal)

RO Permeare (ChJonne Free)

t - 7 k g

i l B k g

180 l i t c r s

-\d jusr to pt{ l0 0 rurh

sulfunc acid (H2SO+)

l Sodiunr Tnpolyphospharr

Sodrunr Dodecl , l [61123..

Sul lonate (Sorhm l -aury l

S ulpha te)

[ ] . ( l Perr leate (ChlorLne Free)

r T k g

0 9 7 k g

l B l , | [ r r c r s

Ad ;us t t o pF I l 0 0

sul func acid (H2SOr)

4 1 \

R O O E S I G N & E H G I N E E R I N G

L)aia i\'lrintlonnp

Goqd r lo ruronng o i d rc pcr fonwrnce o I a svs tern can aLer t d re user to possrb le

[ i - ruhr rg be [orc the s r tua t ron b ,ccorne s se . 'e rc - [ l re

p racuce o I en te r tng opcra t ronaI

t la t r s rVer r r l UJnes a u ,cck t r t t r . r r r lo rn raLz : r t1 ( )11 p foq l : l tn c ln p rov tde thc mear rs to

Lr l . k p r r fo rnr rnc . o \ e l LL l t le

S ' i 'mptoms o f fou lng wou ld u rc ludc onc ( ) r aU o f the [o l lou 'mg condtdons

. Nomral ized \r,ater f lou'has dccrcased bv 10 150r'o fron.r start-up (rcfcrence)

condrtrons

Del ta P , o r p ress t r re d rop over : l s tage or thc s l ' s tem, has urc reascd by 10-

| 5o,i

Sa l t reyecdoo t ras c lecrcascd ( i c pcr rneate I - t )S [ ras tncreased) sgru f icaody

Note that l t ls unportal lr t .r usc rronnaLzed data Nonnalized data corrccts for

temperarure ef l fects ot l s\/steln perfonnance For instancc, i [ the tcmPcraturc

drops , r t i s c rpec ted- to requuc nrorc Fr ressure to ac . luevc the sa lne f lo rv LoSs o [

f lon 'due so le ly to a redr rc f lon ur tc rnpcra t r r re c loes n( ) t t ' r ]e2n the sys te tn rs fou lcd

, i / / / / / .1 ! , \ - ) ' . t [ ( / i , ' - \ l i ' t ' . t / 1 l r / /1 t ) / / t

[ 'hc fbUc,wng dngrarlr grvcs thc basrc perts oI arr [{L) c. lcarung s[<rd Clcamng

solutron is purnped lrcrm a storagc tank throrrqh a caruidge f i l tcr to thc RO arral '

So lu t ion rs then recyc led back tc i t l l c t : rnk l -he vo lu rne o [ so l r r t ion shou ld bc

adequare to f i l l the volurnc oI rhe vcssels, i l ters and pipurg The dirgiarn belorv

shou,s no lnstnrmentadon, hou,ever, t t rnay bc adviseable to add a low lcvel

su' i tch to thc taok to ptevent dre pump frorn mnmng dty Addruonally, a

telnperature controi ler and heate r/coci ler unit may be added to nrai lr tain solutron

at the optrn1um temPerahrte tenge

R O D E S I G N & E N G I H E E R I N G

r , / |l/ olume rcquu-emett/.r

To f igurc drc volurne of solutron

widr s r -x c le rncn ts pcr resse I andvo l r rme o [ thc t -cssc ls a r rd adr l r r

r.olurnc

l j t g I 4 0 F l o . . p 1 2 g 1 2 p o f a c l e a n n g s l , s t e n r

requred fo r a 51 ,5g6111 cons ls t [ rg o I s rx B" r resse ls40 teet o[ 4 urch prpe (3 82 " lL)), furr.rre dre

to thc r .o lunre o [ the l ) rp rng ro o l r raur the to ra l

lVate rza /s (,'o m pottr: r't t.r

N'latenals [cr-r the skid shoulcl bc the follorwrng:

-farrk Fibe rglass reinforced plasrtc (FRP) or po[y'propylene orrubberl,rned

Piprng: PVC schedule B0 or N)'l<.,,r reinforced flex hose

Valves Stau.rlcss Steel pre ferred

Pump. Starnless Stcel or Non metalLic composire pol;,esters

Pump should be a centrifugrl q?. able to attarn the florvs and pressures [sted rntable lof the next section, Carrridge Frlters should be 5 tnicron rarrng srr.rng woundmodules. Valves should bc rnstalied appropnately to control f low Tank shouldhave a removablc cover AII components should be able to rvithstand extremes in

0ncentrate

R O O E S I G N & E N G I N E E R I N G

; , , 1 1 , t . . i l p e . a a u i c J u p i , , , l l ] [ i + : , ( , , . i i i , ] e [ c i l c r l : , { / u L L a ! , ' : i i ' i i c l r c s s l r L r u l t i b c

p ro tec ted 211d r " cU g r c l t r r l r l ed

' 1 n llttr,,Lleutttttg i ' t 'oL'€t

Ger.reraLly, iow pH solu&ons arc used to clcan rnetaLhc scales rvlule aikal-[re

solut ioos are used to clean biologLcal and orgamc foul-urg RelauvelV lrrgh f lorv

(gor.,erncd by the srze oI the elemenr) rvi th lorv pressure ts tcconxnended (Do not,

h1*",,.r, exceed marimum florv L-nlts lor the elcments) lror 8-Lnch dr,ameter

vessels the cleaning f lorv shoulcl be about 9 m3/h Per vesscl '

A gencral procedure f lor clearung thc R(J membranc eletnents ts as fol lows'

i F tush t l re Pressure rubcs by purnp i r rg c lcan , ch lo r rne f ree

product ivater froi i i thc clcanmg rank (or eq'. l1.. 'alent source)

through the pressure tutres to draut [or scvetal trr lnutes

Lr Mor a fresh l tatch o[ t ]re sclectcd cleanrlg solut ion m the

cleaning tat 'r l<.-usrng clean prclduct rratcr

n t Cr rcu la t t the c lcarung so l r r t ion t l i r , rug l r thc p ressure f r - rbe s to r

a p p r o x i n r a t e l ] ' t " - t t l r o u r o r t h e d e s i r c c l p c r i < - r d o I t ] t r t e ' a t a

f l6 t ' r ; t te o [ - ]5 r , ! ) - l { ) gpr r l (8 9 n rJ i t r ) Pcr l l r css t r rc tube fo r

B ( ) anr l 8 5 - r r l c l r l ] rcssLr ic n r l rcs ( ) l { ) to I [ ) gPt l l

(2 - ? 3 rn37 'h ) l r - , r I [ ) r r r< - t r p rcssr r rc t t r l )L is

iv After compleuotr ' .) f cleaning, draur and l l trsh t l te cleamng

tank; fhcn f i l l the cleaning tank rvith clean product rvater fot

nnsmS

v Rinse the Pressure tubes by pumPtng ciean, chlorine-frce

p t o d u c t w a t e r f r o n r t l r e c l e a n i n g t a n k ( o r e q u r v a l e n t s o u t c e )

t_hrough the pressr-rre rubes to draLn for sevcral minutes

v i A f te r the l (o sys tern rs r rnsed, oPera te r t ,w i th the produc t dump

valves open unnl t l re product *^1s1 f lorvs clean and is free oI any'

foam or residues o[ cleanrng agents (ust-Lal ly 15 to 30 mLnutes)

Specr[c rnstrucdons for cleamng specrf ic metnbtane elemenfs should be obArned

from the tnembrane manufacfurer or plant sLrPplicr

{ utgRO

R Q D E S I G N 8 E H G I N € E R I H G

It rs worthu'hile cmphaslzrng the follo',r.Lng poLnrs

' Use o[ ch lonnc c l r o thcr suong oxidants on polyam.rde rnembranes cancause ureversiblc darnage to the mernbrane

' uflarm warcr, i.c J5t'c 40o c, grr.bs sgruflcantly better clcanurg thanlorver tcmperaturc soluDor-rs

' If the pH oI an actd solutron roctease s dunng recirculation, add rnore acidto retuio the pH back to the target value. W'l-rat is occurdng is that acid isberng consumed as it dissolr'es rnorgaruc scale

' Do not use suJfuric acid for low pH soludons as tlus creates a risk o[creating sulfate scalc.

' Permeate water is prcferred for mixrng solutrons_' f jse of frltered t2p warer for fugh pH soludons can result in carbonate

fouling rf the water is hard.' Flush the rnembranes with peffneate r,vater Followrng cleamng to remove \-/

the cleamng soluti<-rns. Under severe fouLng condiuons, it may be necessary to soak ovcrrught

R O D E S I G N & E H G I N E E R I N G

General Stonage Proeede"Etre for

fuIembranes

S hort-Term S torage

Shor t - tenn s to rage rs to r penods whcre ar i RO p lan t must re r rmr r i ou t o I operadon

[or more t lran f ive davs, but ferver than drLrq. ' da],s, , . ' , ' r lh the RO clements tn place.

Pteparc cach RO t ra in as f< r l lo . t ' s

I l j l ush thc lL ( l scc t ion v t th {ccc l \ r ' i r t c r . s ,h i le s r r r rL r l t : rncous ly

v.: otrf lg anv gas ftorn the s\;stcnl

2 \ \ /her r the pressurc rubes ar -c f i l l cd , c lose the appropnete

- \ ia lges to p re l "en t a i r f to rn cn tc ru lg the sys tem

3 Reflush as described above at 5-day urten'als

I-"0rug Term S tarage

Long-tenn storage is for penods where an RO plant rnust relnaln out o[ operanonfor rnore dran thirq, days w-ttl.r dre RC)- elernents ir-r place. Prepare each RO trainas [ol.lorvs.

1 Clean thc RO membrane e lements ur o lace,

2 t ' lush the RO sectroo rvith an approved biocide prcparedfrom Dermeate

3 Whcn the RO secoon is flr]led rvidr thrs solutjon (rnake surc

that it s cotnpletely frl led), closc the valves to retarn the

soluuon ur thc RO seccion

a : '

R O O E S T G N & E N G I N E E R T N G

Pnor -fo

Repeat Stcps 2 and J rv i th f rcsh soluuon csen. rhrrn,davs i fdrc temperarurc is bclorv 80J t- (2711 C), or evcry ftfrcen daysiI tJre remperarure ts ab<it'c 80il F (271] C)

\Xihen the RC) si51611 rs ready ro bc rcrurned to sen,icc, f lusl-rthe 51'51srn lor approxLmately one hour usurg lorv-pressurcfeed water wrth rhe product,dump valve open ro dran; thenflush it at Lugh pressurc for 5 to 10 mrnutcs rvith the productdump valve open to dtain. Before returmng the RO sysremto scrvice, check fot any residual biocide ur the product.

Insta/lation

\Mren RC) elements are stored pnor to rnstal latroa or in transit ro the plaot si te,thev should bc pr<-itected fronr direct sunllght and stored rn a cool, dry place rvirhan arnlr ient temperatuse range of 20oC to 35"C. New clements are rn heat sealedbags widr storage solut ion

l /

4 7 a

R O O E S I G N & E N G I N E E R I N G

lmplernentins a RG Froject

Hou' do tve bcgrl l Here arc a ie!r, ops [or eit .her pianmng or rmplementurg a ]tC)

s ),s teir I

Stt RO f l t lqm p{L0/14dnl:t t?qlr lrcmen/t. I ;rsL, decrde rIc RO stistcnr capecirv

r l ]a t l s permeate t lon , ra te Remenrbcr , cap i ta l cos t o [ a I IO sys tern rs

du 'ecdv propotuona l to thc 1 rc rmeate f lou ' ra te , say m3/h I f l ;o t r requr re a

cer t r r in pcnreate c luanuty pe f da1, (m3/c i ) then decrc lc n t r r r tbc r o f

o l re ra t rng l - rours pcr da1 'enc l c : r l c r r l ; r te pcnr re i r te f lo rv ra tc - l t i s ac l r ' i sab le

to opcra te the RC) ,s \ . : j t cn) io r longcr hours tc r rcduce c rpr ta l cos ts

' l ' [ re n dec i i le tJ rc : pcrnrca tc : r l r re i rq , l { rgh c l r rah ty w ' :1 tc r hes r ts pncc lJe

reaLstrc Fl igh quaLq' , . ' . , i l i c lcrnancl rrse of lugh salt rc,cctuig metnbrlnes

t l ' ra t a re cxpe ns ivc and o ; :c r a te a t l ' ugher p ressures

Decrde how you are go lng to d isposc o f f the concent ra te s t reanr What

are dre appl icable drsposal standards from the rcgulatrng authonty

Set inPutt. Fust, dre desrgn ra\r/ u,ater sotrrce and analysis II therc is oue

soutce, the job is easier [[ thete are mulnple sources or a combination oI

sur face and ground u,ater dren u 'ork out a wotst but real isdc b lend of

these source s and decrde desigrr u,ater analys is Coosider seasonalvariatrons A cornplete design analysrs report rncluclc Ca, N{g. Na, I( Fe,

alkalrrury, Cl- SO4, NO3, Srhca, pH, Conductrrnty, Turbidrry, TDS, ltee

chlonne and COD as minLmum For wasteurater applicatrons urclude

NH4, orl & grease, I)O4 and hearry metals present rn the water

ln a u,ater analys is repor t not ooly the concentrat ions of r 'a f lous lonstnlportant but drer ir lteracdons too For exarnple, Ca, alkalrnity, TDS,temper-ature aod pl-l valr.res rr't l l . decrde the tendencl' [ot Ca(.O3

precrpitauoo m the s1'56s111 Sirmlarly, Ca, SO4, TDS (roruc srength) and

temperarure rvLll decide CaSO4 scaling tendency. Ignonag one or more

R O O E S I G H & E N G I N E € R I H G

p a r ? m e t e r s s o u i d l c a d t o u r r p r e d t c t a b l e p c r [ o m r a n c e , , I t h c l { ( ) s \ s t c r l I t

goes , . r ' r t - t rou t sa) rng d ta t u ru ts o f measurernents o i e ach paranrc rc r :1 rc, l " . r l l r t e p ' ) r t e d m t l t c a n a l v s r \ r e p o t r s

{ccurac l 'o I RO Fced u ,a te r tempera fure rS u ] rpor tanr Lac t r degreercnrper : r fu re change can c [ range the penneatc f lu r ( le rneate t ]ow &r - rded

b_f n rembrane area) b ] ' "b r r r . . , t

25 to 3 0 per ccn t In an r_ rpcra t rne R( )

sl,stem leed pressure has to be , reduced to conrpensatc [or lughertemperature

-f fus could detcdorate pen-neate qLnliry

' l 'here could be

seasooal vanatlons r.n the RO feed watcr temperature, ur rvl lch case dreRO systern has to be destgned for maximum and rninirnurn temperatures

At maxrmum tempetature permeate qruhS'rrnl] bc worst and at rnif ixnum-

temperarurc RO feed pressure rvr] l be hrghest

Eua/uate RO Ertem sizrtng- RO s1'51snr slztng involves finaiizurg menrbraleq,pe , qurntiT, and arrar ' ; reco'. 'e.y' anC other parameters Tl-. ts is pre serrt[ydonc usrng RO prolecnon software provided b1, the membranemanufacrurer lns is t upon a copy o I the s rz rng ca lcu ladons or p ro jecoon,as rt rs comrnonly cal led, from the '" 'endot. \ ier i f l that al] the Lrpurcond l t ions are cor rccdy uscd- Here are some t rps

, { t ' c ' rapc l - )esuzn [ - lu - r . Thrs rs t l re tou l DCrqrcarc l lo r ' , c l rv rc le . l bvthc tou l n rernbrane area z rnd is cxpressed as l i t c rs f re r squarcrnckrs per hc ' ,u r G-NlH) o r LJS ga i lons pcr sc lL r i rc fce t l rc r da1,

Gf. i) t- jsurg l4ghet f lux re dr-rccs nrernbranc quroLlt l ancl hencc t lrc

caprtal cost, br-rt chanccs of f ouhng arc high N,lernbranc

manufacturers prorndc only a guldel inc fot desrgrr f lux In most

cascs r t i s sa fe no t to exceed desrgn f lux o f 10 , 14 and 1B g fd va l r res

For wastc \ ' , 'ater, surface and gtouad rvater feeds But the designcrhas to make a judgnent of the actual RO Feed u. 'ater q.n[ry before

finzltztng Feed water SDI r 'a[ues, numbcr of pre fteai lnent steps,

raw water q,rahty variations coLild be used as guide

Nlembrane selecuon. Check the membrane make and model

selected by the \rendor Srudy mernbrane technic^l d^t^ sheet that

shows membrane ratrng, rnembrane arca, feed rvater tirnitrng

cond.rt ions and opcrating parameters l .or Fugli foulng vaters

(wastcrvatct, surface water) rt rs advisablc to use lorv ioulng

[rydrophrhc rnernbranes oI neutral chargc. I I convendonal pre

trearmsnl rs provided d-ren i t is adrnsable to use membranes o[

standard area sucl 'r as 365 ft2 Lnstead of 400 or 440 [t2 because

chances of restoratron by cleamng are l lgher i f they are Fouledu' idr suspeoded sol ids

Recovery. Recovery ts dre rat io oI permcate f log' to feed f low and

is often reported as percentage An B0%o recorrery means peffneate

flou' ts B0% of dre fced floiv Hrgh recovery is desuable but it lras

4 9 s

f I O O E S I G N E E N G I N E E R I N G

l r : r i l c i \ . : : i cac l ' c r - ) ' lnc ieases , i I c ccnccn i r :aon i ; l co i l cea t ia te

suean l ( : r l sc , caUe d re ,cc t o r b rLne) Lncreascs and ths rncrease is

r l 1 r 1 l , , l u q l t r c ( , , \ p i l c s F l g l r c r r c l c L l . ( r n . r r l u : 1 E o n s c a u s e i e e d

prcssute ar td J rc rmeate sa l r ru r l , to inc rcasc I t cou ld a lso lnc rease

potenuals [ , ,r scalroq and foulrg Designs ,. , . ' rdr recovenes o[ 80ozo

or fugher rcqur res carc [ r - r l se lcc t lo r ] , t f sVs ter l components and

de srgl

t c a l i r r g I r c , r . n u , r l s 1 l r e p r r r l e r u ( l n p n n t ' ' r r t u L I l r c p o r t s c a i m g

potenr ia ls io r CaCC)1, CaSO- i , BaSO4, S ISO-1 and s r l i ca I t rs a

good ldea to check t lcse values rn companson to maxrmum

allou,able Lm-rts Desrgn o[ the pre ueatunent to RO system rs

based bn thesc va lues

Las t l l ' , l ook lo r \ r 'a rn rngs u) t t rc p ro fec t ioo pru ] tou t These wam o I

possrb le p rob le rns Ln dre s izLng tha t cou ld resu l t m opera t rona l p rob le rns

N[embranc rnanufac t r , r re rs l rave drer r u ,a ] ,o I cons iden-ng and no t

considen-lrg dif ferent saferv factors rn t ie computer pro,ectrons A desrgo

ru15[rt shorv reqrurement oF a rclai lr 'ely lrrghcr prcssure or a highe_r

penneatc t1r-ral i ty [rrrr r t rmght be a sa[er opoon to go [or rI these

requr re l l - ren ts a rc a rcs r - r l t , ' r f inc reased bu l t ' i n sa [e t1 ' anc l a n rore accuta te

ca lc r . r l ; roon o f t l i e t1 r rah t l ' px ranre te rs I t rs ad ' ; - rsaL- t l c t , . r consu l t mcrnbrane

cxpcr ts rv l ro cu . r t p r r i t ' i r l t c ( ) r rca t ac l r rce

4 l .yLtUU, l ,19Ig4U4yrt l l l lLt, / ] . I) tc Lre:rtnrcnt t i ) rr I i ( ) s\ ' : ;rcnr rs v'r tal to

r , [ r t a i , n c o n s i s t e n t ; r n d t r o u [ r l c F r c c ( ) l ) c r ^ u o n o I t h c p l a n t 1 - h e p r e -

f tcaUncr ' l t s l ' s tenr t r .c : r ts r : l$ i \ \ ,a te r to rnake r t s r r i taLr lc fo r t reaunent rn RO

S]'Stern Its desrgrr rs gLudecl b1, rnenrlrrane fced w]rter lul l i t rng condlt lons

and scahng crl ten:i See table l0 belou, fcrr fccd water l i rninng cond]trons

for corrunonly used composlte rnetnbranes E.r 'aluate t lrat t l -re pre

Lreatr-nent s) 'stenl has Lreen designed to aclueve thc leed rvater l trutrng

condtt ions as specrf ied by the rrrcmbrane ruanufacrurer

The scalure potcotrals of spamrgly soluble salts arc calculated uslr lg

sa furadon urdexes anc l percent sa tura t lon r .a iues For e rarnp le , [o r

btackrsh \r,ater, Langeher saRrratron tndcx (LSI) rs <-alculeted for CaCO3

In absence o [ any anusca lan t dosurg , t i re re ;ec t LSI shou ld be negah, , .e

rvluch rs achie't 'ed dosrng actd m'the feed rvater But t l rrs cou]d reduce the

recovery l . rence SodrLr rn F lcxa N{e ta Phosphate rs dosed dra t ex tcnds the

rc,ect LSI hmrt to +0 5 For e', .en hugher rccovertes. ()rgarul antlscalants

can bc used to ex tend the LSI ImrL t to +2 5 Ln thc re jec t s t ream These

organ.ic andscalants are gffectrve a{airst CaSO.l and sihca scales toc,r Per

cent saturanon for CaSO,l ca6 be extended to +230a,/o and sihca

concentrat ion to up to 215 mg/l Ln the reject strealn

5 0

R O D E S I G N 8 E N G I N E E R I N G

I - h e r e a r e s c ' c r a l s u p p h e r s o f o r g a r u c a n t L s c a l a n f s a n d d r c u s c r l s a d r . r s c dto check re fc rences and sen ' rce suppor t be fore accepung a parocu_ lart 'nakc I t i s unpor ran t to car rJJ o r - r t a techruca l e r -a [uaL ig l c r f d rc p r ( )specn lcanhsca lan ts to ensure they are compaub le r t r ih the t {O tced u ,a tc r anc lrvit l r thc rncrnbranes t iat *"r- l l be used Consult for er,alr- ' raDon proccclrrreProduc ts u luch pass the cva lua t ron cn ter ia .shou ld bc chgrb le [o rs t r b m r t r u r g t r n J e r ' d u n n g p r o c u r e m c n t . \ s k f o r a p r , ) l ( . c t r o n p n n r u u tfrom rlre aotrscalant mar,ufacrurer fcrr dosagc recommendatrons for s].stenrundcr consrc le raUoo,

fab le 10: RO Feed Water Ltmrnng Conchuons

L i m r t r n g P a n m e ( c r V a l u c

P H I - l 0Temperarrrre ( 45 degrees Celsrus

Turbidrq < 1 O N T U

Sr l t dens iq ' u rdex < . 4 0

Ori & grease Nrl

Free clrlonne < 0 l m g , / l , c o n u n u o u s

lrr. lr ln < 0 l r n g , / l , t o t a l

(.onrhc/ ]>i/ol Planl t tu&et [ t rs:r good pract]ce rc.r concluct pi lot pla.nt tnal: ;to r la rgc s ) ' s te r l rs to l carn thc fced water r ran . . r t rons , pcr [on t rance , iI r t c t t r l r i : r t les , r :o i lpa t tb r l iq ,o f t ,anous c [ rcmrca ls , opera t ic ) r t : t l cor r t ro ls anc ic t ' i cc t i vc r tcss o l r le n rbr l r tc t l can tng opera t r ( ) r rs

- [ - l r i s rn [ , r rn re t to r r sho t r ld

bc t rsc r . l t c ) sca lc -up rhc fu l - l -sca le p l -au t ( . r - rnsu l t f r , r n rorc anc i spccr f rcin fc lnnat ion

Pro t , tde Sa. tz f i ta / , \ l cmbrane, I r r l r rge RO p l r r r rs L rexrurg \ \ ' : r s {c \ r ,a Ic ls , r t t s xgood pracuce to instal l a lead-end and a mil-end sacnficial membtaneelement with necessarl, insLrurnents Tlrcsc sacnficial rncmbranes lvarn

drc oprerators oI possible foul l ig and scal ing problerls before they

seriously afFect thc plant perfonn rnce

Eua/uctte OPeratnn and ll4aintcnance requireruents. Operadon and lnarntcnanceof an1, sys tc rn i s rmpor tanr and the mernbrane sys tems are -no t d i f fe ren t .

Eva lua te opcrauona l requr rernents rv i rh rcspec t to numbcr o I ours o fopetatro{1, operatrng rrunpowef a,. 'arJabrhry', chorce oI manual versus

2Utomat ic operauoD e tc

l lvalu-ate aU niai,ntenance options that nuglrt be requued in t l .rc continuous

operaBon o f the p lan t These s l rou ld rnc lude prevent ive schedu ledmalr l tenance rcqrt irsrDsnts and break clow.n rnamtenance requfernentS.

L-rst and provide al l the tools and r-eck.les and trainurg to the marntenance

personne l d ra t goes a long \ \ 'ay u l r roub le - f tee opera t ion o f the RO p lan t

s l \

R O D € S I G N & E T I G I N E E R I N G

(

I i rs a good idea to have a sngle element long RO systcm TIts system

can lre used for drffererrt purposes Fust, r[ t l-re mcrnbranes get fouled' ,v i thor , r t anv c lue to drc causcs, r t . is possib le to c lean one membrane

modulc rn this svstetn, try out drffereot ciearung chemlcal formulatrons

arrd clcaning procedures arrd finaLrze Lhe most effectrr'e cleamng protocol

that can be applied rn'the marn plant. Second, tt can be used to carry out

compaubilrry and-dosage perfectron studies for various andscabots before

they are actually used in the main plant Thlrd, it can be used to srudy

differcnt mcrribraoes to compare petformance with membranes that are

used rn the plant.

, e

R O O E S I G H A E N G I N E € R I H G

€L s*saasnr€ Ev fr*FsFdE-E EA#r rG ' FE

T l rI\f /C l'r'/ / t'€,1

i rec l - r rucal Senrcc Bul le t rns by F{ i , ,dranautrcs, :10 1 occansrde, cA 9105+USA

2 S Chilekar, Prcssure Dnve n Mernbrane Processes for Total \X/atcrTreahnenr, Everytlmg About Warcr (l\[a1,-f une 2002) 21-31

I S chrlekar, A Ncw Approacl.r To L)esignrng Seco.dar-r. -freated (-iry

Seu'age Reclamarion Plants fjor lndustr-ral Process t_lse, E.r.eryt1rrngAbout Wate r (l\{a1, f urie 2003) 22 30

\ j

5 3 *

R O D E S I G N & E N G I N E E R I N G

Appen#Ex ffi

Lttn,ge her 5' atnrzt iirt n I n dex CJ'I)

The Langelier Sarurauon rnder (LSf proudes an rndrcator of the degtee of saturao.on

of \r,ater u,ith respect to calcrum c-arbonate. [t c-an be shou'n t]Lat tSI approximates the

basc t0 logan*rm of rhc caicite saturatron level- the Langelier sahrratron level

approaches the concept_ of sarruation usurg pH as a nra-ir varjable The LSI can be

rnterpreted as the pH clr'ange requued b.-g"tg watet to equrJrbnum

Water rr,nth a l-angeher saruralion index o[ 10 is one pH urut above satufa0on

Reducrng the pH by' I uqrr n'rll bnng the u,ater rnto equhbnum. Thrs occurs because

the portron oI total alkairruty present as CC-),2 decreases as d're pH decreases, accorcirng

to che equilibnurns de scribrng the drssocnootr oI carboruc acid

H,CO3 a" HCO: I H*

HCO3 12CO. ' -+ H"

l i l .Sl s ncgxfl \-c No lrotcrrni i to sc;r lc, thc t ' ; 'atct r ' ,r l l dtssoh'c (-a(-Ll,

. I t ISI rs posit t"c: Sc:r lc cart forn'r and C.a(-O, PrccrPltat lc)n r l lz\ i ()ccu-t

' lf LSI rs closcr, ro zero: Borderl-rne scale potenoal \X/ater quahtl or changes ul

temperature, or et'aPoratron could cl-range dre rndex

The ISI s an equrl1bnum index and deals onlv wrth dre thernodynanuc drivlng force

for calcrun carbonate sc.ele fonnanon and growth. It pror.rdes no rndicauon o[ ho"t'

rnuch scale or calcrurn carbonate u-rll actr-rally preciprtate to bnng water to equilibnum

it sirrrply indicates the driung force for scalc formation and gou'dr in terms of pH as a

lr-Llster r.eriq$[s. [n order to ca]cuiate the LSI, it is necessan: to know the alkalLruty

(mg/l as CaCOr), the calcrurn Lr,erdr-ress fngll Crt. as CaC-O,), dre foral dissolved sohds

(rng/l TDS), the acnrd pl{, end d1e temPerature oI tlie rvater fQ

R O D E S I G N & E N G I N E E R I H G

i-SI s defrned as,

L S I = p f { - p H .

\\'-hcre,

' pH rs t-he rneasured rvater pH and

' PH" rs die pH at which the soluoorr of sarne composidon."vr,ll be saturated h

' calcium carbonate and Ls defined as

p H " = ( 9 . 3 + A + B ) - ( C + D )

\Vhere,

' ,'\ - (I-og,u [TDSJ 1) I 10

' B - 1l i2 x l.og,u f(-- + 213) + 3.t 5_5

' ( - - I - . ,g , , , [C. t ' : rs CaCO,l 01

- [,) - l.e1',n [allvrlrmty as C,a(-O,1

-3

5 5 5

R O M O N I T O R I N G & T R O U A L E S H O O T I N G

Membrane Element toading

Guide!ines

Eieruenl -L,narl/ry ( 'rririeiines

Ttre follorvr4g provides general urfonnatron fot urstalhng tnernbrane eicments

provrde opnrnally reliable perfcrnnance

FlushiilsI I t i re systcnl Ls nc\\ ' . l l is str i)ngl] ' recolnlnct lr le cl to f lush thc s) 'stenr 6rst [refbte:

loadrng elcnrcnts Tl 'r is al lot 's any clcbns, solvents, or ctr, lclnne to be cleare.l s,r t .ha(

drey do not cotrre ur contact.'vitl-r the metlbranes

Vesse/ Prcparultott

Clean the rnside of the vessels before loadrng, This u.rll temove any dust and debns

that could collect on the membrane surFace. Hosrng down the rnsides oI dre vessels

usually will not be sufEcient to clean the vessels Use o[ a sponge ball wrapped tn a

towel and soaked rn t 50o/o solution of glycedn and water s ttlghly recommended,

The sponge ball can be pLrlled tluough the vessel widr a piece oI rope. Altemanvely,

rhe sponge ball can be pushed duough the lengdr of the nrbe wrth a piece o[2illch

P\rC prpe with a PVC flange attached to the end, Be sure to avoid scrapmg the ptpe

along the vessel sutface.

J r]ra{e

II elements c:rrutot be loac]ed upon dekvery, store eler.-.ents out of dlrect sudlght. Do

not allow the eiements to fteeze

R O A { O N I T O R I N G 8 T R O U B L E S H O O T I N G

f t

I tt0rzcnnts

. \\'hen lcradmg elernent_s into a sysrern. do NO-f use orJ. grease, or petroleum

1ell1'based cornpourds to lubncate o no-qs and bnne seals

. [,]se stLcone based gel (sdicone grease ] ,,r a Llr-rnr-re o[ 50910 glicenn m $.aterto lubucate [] unss and brure seals

J D/mn//n3

Due to inconsist-enctes ur vessel lengt[ it rs lughly reconrrnended to shirn elements to

take Lrp ftee space ro the vessel 'ftus

helps to prevent elements from mormg u'hen

the slstenr is sirut dou'n ard restarted The appearance oFlsrks betu'een elements s

also mrrumrzed n,hcn dre eletnents are shi-rnmed

To shim, stmply place P\rC "wa-shers" oIr,ar]nng *r ickrress (1 /8" to 3,/8") over the

feed side tnboard adapter. Add as many shims as oecessarl, until dre end plate fits

sntrgly aga]nst the shrrms [[ necessary a shirn ma1' lte removed rF the end _cap rs

drfficrrlt to reinstall A gap of 1,/4 tnch beftr.een dre end plate end the shrms ir.rll not

catrse prolr lerns in pertbnnance

V'e s.rr: / 5' h int nttng P ro ce r/urc()

-l o reduce the trsk oI h-evurq discomccts beru'eerr eletncnts n'rt lrtr a pressLrre vessel

it rs advuable to slum the vessel propcrl1, Shurirnrng rs thc prrocess oI placurg pieces

of rnaterjil (shuns) bctween t\\'o parts to take up ft'ee space and hclp -to

preveat

tnolretnenl For membrane systeftrs, plasuc or P\rC washers ate used as shims This

TSB out-lrnes rhe procedue to shim a vessel

Note: Before begnmrrg dre shrm procedure, ensure that the spacer nrbe (called also

the thnrst nng) is in place on the reject or downstream end oI the r.'essel.

Remove dre end plate on the feed end o[ the pressure 'r'essel.

Push elements fimrly rnto the l'essel, and ensure that there ts no free

space between elements,

Place an rnboard corurector on dre lead clemenc

R O | r I O N T T O R I N G A T R O U B L E S H O O T I N G

4 obtain q,asher like pieces o[ plasUc (or other approved materials)

l/8" to Il4" tn tluckness wrth an inner diameter larger than the

outer drameter o[ the adapter. These are the shims-

5 Place the sfums b-v trnl and ertor method over the adaptet and then

replace the endplate Stims should be added unol the endplate ""dl

not 6t enurely ur place Then remove a shim so that the total

thickness oIthe shims rs ,ust enough to allorv the endplate to 6.t-

Repeat this procedure for all vessels.

R O M O N I T O R I H G & T R O U A L E S H O O T I N G

Mernbrane Start-up, $hutdownand Flushinq Guidelines

P rc se iv,t tiue F /us /t r,'gTo presen'e elernents from biologrcal gtowt]r and to help rnaintaur perforrrance

over t irne, composite q,pe membraoes 2re storecl tn 1 2o.io soc{ium bisulf i te and 5-

10% propylcne glycoI solutron. I t is thereforc aclr. tsed to f lush mernbranes prior

to use to elfurr irate resrdua] prcsen., luve s rn the ptocluct strcanr

C) t rce dre e lenren ts [ rzn 'e l rad the prcser r ' : r t rves f l r rshcd f ro rn thcnr , t ] re r u 'ou ld nced

to h:rve Presen':rt i r .cs re appl iccl fclr lonrl tenrr sf( i tegc

C)ncc e lements ha i 'e been loadec l and vesse ls sca lec l , i t i s recorn tnended to f lush

tl- le system to drarr u'rdr feed water at de srgn operxtrng prL-ssurc for a rntmmutn oI

4 hours. [ f the elements are tO be used m s) 'stenrs reqLLir-rng ultrapure water, a

minirnum flushrng tirne o[ 24 houts is recornmended to reducc the TOC

concentrat ion to below 50 ppb (assutning zero TL)C rn the feed $'ater)

For potab[e appl icauons, dtscard the ptoduct \ ' , .ater for at least 24 lrours pf lor to

dflnkrng or usrflg tn food applicauons lngesuon of the preservatr\.e trlay cause

rrntauon to the gastrointesnnal ract, colic, dtatrhea, or other sirni-lar symptoms,

RO ,!'stem Start-up

[t is trnportant to be sure that the elements are loaded and shimmed correcdl' t6

remove any excess slack drat may cause disconnects. A [ou' pressure flush to

purge atr ftom the tnenrbranes is alw'ays recommended befote a lugh ptessute

startup. This cari be accomplished drrough the use of a so[t start meclranisrn, or a

vaoable frequency' &ive. Failure to do thG can re-sult in a rr.'atet shock warie (water:

hamrnet) that can cause pfr1,5i6al d-amage to dre RO membranes The permeate

:

R O M O R I T O R I N G & T R O U B L E S H O O T I N G

salses sl-rouLd alu'a1'5 be open to ili:rrn dLr-nng tlrrs flush

membranes

to pteveot demage t<-, t i re

After ttre ur has been purged frt-ltn the s\rsletn the feed

Lncreased gtadually up to the n.orkna Pressure of t .hc R(] uut

pressure shouid be

n ' \ ' t ' z l r / , , t1 ' l tt(U .) J'tt(/// J ilt

Bra,.brhf LI; asrt l l , 'attr 51tte,r,

Upon slrutdorvn for brackistr systerr ls, a f lush q't th the feed [ 'ater at lon'tecoverl '

( tn_n. .r . ,r l rr . urde open) is usuallv suff icrent to remo\re the hrgh cooceota[on oI

,"1t, fro,rr the naembtanes The pemreete valves should be ooen to drain dunng

tlus flustr to Pre\'ent darr-rage to the tlembranes

Seautater Systems

upon shutdorr",n for sexw2ter systems, a f lus[r r. , .r th Ro Penneate is recomrnended

to rernove t l-re tugh concerrtratton o[ salts f tom the metnbranes The permeate

valves- should be open to dr-ain dunng tlus ftr'rsl-L to Prevent damage to. -q't"

rnerntrr:rnes It RC) penneate ts tempotadly r-rrrar, 'ai leble, the tnenrl lranes should be

flushecl rvrrh Ro Feed at lou, rccor-eq' (u'rtir brine 1'alr''e rvide open) Thc

me n'rbranes slrouLcl the r l Lre f luslred \t '1th l1O Perrneate T s soor] :rs t t is avaiL'rble

The seag,ater Ro sl,sterr l slrclult i t tr l t be lc[( un f luslred r\ath a luglr cotrcerlLr:rf lo1)

I r1111c ( ) ( l the urcnr [ l r lnc sur t i cc

f lre quantr0,of rvater used i l both normal RO |1,sten stat-ap ancl RC) J-] ' t t t , '

Shutdiu,n flushurg should be eqr-rai ro or greater than tha.t ri'hicl-r i-s tetained rr-r the

sysrem fto. rald-"rd 8-r-nctr X +0-ur.h elernents assutne ten gal lons{37.85 L) per

element For standard 4-lnch X 40 rnch elements assu-rne three gal lons (1 135 1)

per e lement .

Permeate Va/ue Operation

At no tiin-rc dur-rng operadon of a membrane element system should the petmeate

valve(s) be closed TLus ncludes Pre-start up ftushing, pte-shutdown Flushing'

cleamng(s) and standatd operation

Closrng t]re permeate valve dunng aoy pbase oF operatroo causes a Pressure

drfterenual actoss the tarl end o[ the system and ri.'ilI l-tkely tesult in rrteparable

damage to the glue l-ine,. of the terl element(s) This damage q,ill cause inmedrate

tncrease tn sait passaee oI the svstenl

R O M O N I T O R I N G A T R O U B L E S H O O T I H G

Perrneate ralr-e(s) rlun' be closed durLng shutdou,o afte r t]re s\,stem hasbeen f lusheci and,ror n 'herr input oI the teed u 'ater rs s topped [n r ruany cases fh isLS necess:rrr t() preveot an aerobrc e nrkonme nt Ln the pressLIre r.es-sels_ Thepermexte ralse as u'ell as the concenlrate) should be fl l ly re opened prior to reLntroductng [e ed rt 'ater

C- o n ca n rt'a te [,,' ttlt,,e Op eru tio n

Duflng start uP of any' system, tl- ie concentrate vali,e should be tn the fuIiy ooenposiuon llus valve shoutd be moved towards the closed posiuon ,ft.r strrt ,rp rrorder to obtaLn the desued system recovery.

NE,\iER S-fART A SYSTE,N,{ WITH THtr CL]N''EN]TF.ATL-] \, 'AI,\'E CLCSE,DAND THEN OPENING IT UNTII- THE, SYSTtrI \ , I RE(,O\TERY tSACHItr , \ /EL)

System tecovery should be set to the desrgn value as recornrneoded rn theoPera0trg procedures

Presencc of Frze e h/onne

At no ture should rhere be a Ftee C-hlome rcsi. lrral rn the fced q,ater oIgteatet t tran (J05PPA'I Even veq, lou' levels pf clr lor i l t- rJr rhc Iced strealru ' r l l resu l t tn tn -eparab le ox ida t ion damagc o I thc menrbr : r r rc l ] l case contac t

)rour sYstenr pror- ider for various medrods of renrovurg l j ree (. lr lonltc prror to t lret n e n r b r a n e s v s t e m .

f-lre ox-rdative effects of Free Chlonne are strongll, cttalyzed. rn the

Ptesence oItransit ion metals such as iron and manganese. [ [ transinon metalsare Present. lt ls tecotffnended that there be NO Free Clrlonne ur dre feed n'ater.

Lubncalion of O nngs and Bnne J'ea/,r

At no trme should peftoleum based lubricants be used w-lren lubncatrnginter-connector o-dngs, end adapter o-rings or the membrane element brineseal Acceptable lubncants rnclude sil icon-based gels or hqurds andf or gl1'ce nn

R O M O N T T O R I N G & T R O U S L E S H O O T I H G

RO SY$TEM MONITCIRING

I mportan t P aram e ters _for Monitonng

The srx important parameters th-at need tegular morutoring are given below.

7 Norwalzsed Permeate F/ow. Tttts is the permeate flow that is normalized to

rernove effects of feed water salinifir, acnral tecot'ery, temPerature, applled

Feed pressure and pressure drop rn the system The oormalized permeate

flow value calculated based on the actr-ral plant perfonnance has to be

cornPared to the same after commGsiomng the plant to Frnd out

vana[ons L)rop Ln tlrc values urdrcate scalrng or fouling or abnorm-al

compaction problems in the s1's1sm.

2 Normaluect Sa/f Rtlection. Thrs rs ttre average.salt reiecUon rn dre RO system-

that is normalized to remove eFfects of feed water sali-trity, actual tecovery,

remperamfe, applied feed pressure and pressure &op in the systern.

Normal-rsed salt reiecdon calculated based on the acrual plant petformance

has to be compared to the same after comrrrissiomng the plant to find out

variatrons. Drop ur the values rndicate membtane darnage ot scaling or

fouhng ptoblems ro the system-

3 Normalised Presnre Drop: -fbts is the average pressufe gtop (or delta-P, as tt

is commonly called) in the Ro sysrem that is normaltzed to remove ettects

of feed u,ater fiow, actual recovery and temPefatuJe, Normalised pressute

&op calculated based on the acrual plant performance has to be compared

to the same after comrnissiomng the plant to frrd out variations' [nctease

in the values indicates pluggmg of membraoe feed spacer u'ith susPended

solids or mrcroorganisms

4 Silt Den:tgt tnd.ex (SDI): SDI is an important Patameter to check the feed

u,ater qua[ty enteftfrg the RO s]rstem [t r.nchcates Prcsence of colioidal

R O A I O N I T O R I N G & T R O U B L E S H O O T I N G

parocles in dre feed q'ater and drerefore a possrbrLit l o[ foulng of themembrranes A i5-n'unute SDi vaiue rs commonil , used Lr the rndustr l ,

l r ' lost mernbrane manufactuers prescnbe a lrrmt oI ma:omum SDI Ln theRO feed v, 'ater bet*,een 3 and 5 \X/hen erther r ' rcro Eltratron or ultra&ltradon pre-treaffnent rs used, er.en lon'er SDI r.alued can be easi l1,o b u r n e d P l e a s c r c l e r t r . \ p p c r r d r r i f o r . r t l e r r i l e d p r t , c e d u r c [ o rmeasunng SDI

il4ic,tortanismt.. Presence and [e'e[ oI bacrenrl contar''[rarlon of the feedwatet is irnportant as r[ goes unchecked, the bactenl *dl evenrrrally gtou,tn the RO membranes and q,ill cause foulng and associated problems.Theteforc tn RO plants treahng \\ 'aste $'aters, ir rs necessary to reguJarlymorutor the bactenal contarninatron to check the feed watet q"rfirye ntenng the RO sistern

-I1rc_i. are rleasutc,j as

-lBC (total bactcnal coult)

or TPC (total plate count). The values rndicate a possrbrJrq'eI f6r ' l ing ofthe membranes- Another sLmple measllrement is done usLng drp-shdes atplant si tes, Although not as accurate as the TBC method, but the d-rp-shde

method provides an easlr way to monitor the contamination and dta.v a

proEle that helps rn tror-rbleshooting. Akhough drere is no absolute value

or tange-drat is expected but a regular checkurg u. ' i l l warn of a possrbleincrease n the cont2minauon [er'e[ that rnight lead to the membranefouhng larer

Pnrure Vere / Prof/ing Thls involves measurement of penneateconductivi t) ' from each pressrrrc r.essel q. ' [-rrch is the cornbined averageconductir. t t l from al i membrancs rn the pressure vcssel

-f lus data

indicates integnty oI dre pressLue vessel internals such as venous

coonectors, o-r ings and nrenrbranes- Penleate conducnviues from same

stage vessels wtll be ur dre salne range although they nught not be exacdl,same. [o case o[ an o-rtng leakage in a vessel the conductir,rty willincrease suddeniy. Carryrng out proEling of all vessels rvill identify d-revessel. ReguJar profilrng helps morutor the health oI the membtanes and

the internals so that i l case of a problem early actron can be caken

5 1

R O M O N I T O R I N G & T R O U B L E S H O O T I N G

RCI $Y$TEM

TR.OUBLE$HOOTI NG

t r | , ' n I 1 .I t'ou0/eshoo// tlt l'tr) urcn/ l

A suciden or gradual change rn the perforurauce o[ a t{O plant, r"hich G not

expected to occtLr, re.1'-, i r":s t l t" t t l -re charlge rs strrdiec-l and cortect ive atrd

pfeverlt l \ .e steps are taken RO pl.rnt troubleshootl lrg rcqulres a s)/steuratlc srucl l '

oI the Plat l t perFrnnancc, a'rtr l1' l1t^ of ciat:r ;r l ld ct)rtcLtivc ;1Ltl( ] l ls to rcstore t i le

plant pertonlrar)cc. [ l (-) Plent Pcr[bnnat]cc clranges c-arr be grotrPed ul thtec

categones

1 Dmp tn Perzneate F/our. Pcnneate flou, cao reduce dtre to lrlcfe2Lsc rn fced

*"L, , t1t. i ty, teducdo' r ' Feed water temPerafute, mimbraue tompacti 'on

and aiso because o[ mernbrans [6rr l ing and scal ing.

2 Dnp in sa/t l\ejectton- Ivlembrane salt reiecuon catt teduce due to tnct se

rn feed watet saliniry & feed wztet temPerature; tnembtanc

also because of membrane Foulng, scaLng and o-ring leakage

3 Increase in Pressure Drop: The pfessure drop can increase due to increase tn

feed water flsq,, leduced recovery; teduced feed watet temperature and

fouling of membrane feed sPacers by fouhng and scaling'

[n most sinlaf ions mote tharr one Petfoffnance change can occur srmultaneously'

For example, drop rn permeate [ iow and tn salt reiect ion can occur sLmultaneously

This can L" ". "

i"s,-r l i of one cause of muluple causes- Ttoubleslrootrng rn such

and other cases requ.ires three steps as belou'.

R O f r I O N I T O R I N G A T R O U B L E S H O O T T N G

I / L ' C ,t t'0a n/(sn00rz//g J r€pt

Tbe uoubleshooung acuvlues can be gtouped io tluee steps

1 [dent6, the Caur. Ttre lrst step ls to rdefinlr. the cause o[ drc problern-flu-s

requrres that the plant perfonnance dirta rs snrdred based on rlre logsheets A treod rn the behavior o[ the performance parameters can be.found ouL fmportant aspects ate v,'hether the prolrlem occurred suddeoll,or gtadually Acrual measuremeots oI the plant perfonnance, SDI, r.esselproELrng is also requued, In case of permeate qualiq,- problems, r[ thevessel proELng d-ata shows one or more vessels wrth abnormally [r4;hpenneate cooductrEues, and deen rhe cause of hlgh conductrr'rry rsidenufred by vessel probing

Ptobrng involves rnserting a small plastrc tubrng tnstde the permeate rubeso[ the dembraaes aod measururg the pernleate cooducttrnry cirange ftornthe fust to the last tnembrane rn the vessel. Refer to Appendl-x B for adetaried procedure for probrng oI vessels

Dependrng upon whether pertneate is clrarvn ftom the Feed or the rejectstde of the vessel a pro6ie of the perfireate conduccir.iq' G obteined tr anonnal vessel u'ith no appatent problems In case bf o-nng leak a suddenlrlcrease ln the Permeate conductr\, '1ty at that p()rnt ts obserr.ed In case oItnenrbrane darlage dre condr-rcrtrnti 'wil l rcfiraur lrrgl-r ovcr a longer lengthof thc t 'essel instead oIa surg le po[ ] t , Bcrc2use the urcasurcd values of the

Pcmreate conducuvlty are that of a ble nd of sevetal mcmbranes in a vessel(except the fust rcadrng), one has to consider the rndn'rduai penrreateconductivities and penneate flows while rrakrng conclusions &om theprobing observatrons

Study of normalised performance of the plant plal's ao irrrportant role rflidennfyurg problems. Normaltsauon calculations are mosdy rn-burlt rn thelarge systems and provide fot gtaphing the results that make it easier todraq, conclusions

ln some tare cases, if the problem cause can not be identrfied then anlembtane autopsy is performed Ln whrch one membrane elenrent is cutopen aod the foulant present ts analysed. Observadons oI the membtanefeed spacer, membrane shect and the nature o[ deposits ^re also

tmDortant

Take Cornctiue fuIeailrer Once the problenr cause rs idennfied then the next

step ts to take correcdve steps to restore the plant perforrnance These

tneaslrres rnav rnclude correctiflg the pre tfeatment replacrng o-nngs.

R O M O H T T O R I N G & T R O U A L E S H O O T I H G

impro.,-emeot., obtamed and operate the plaot at that peiform^nce level

' luke l)rcyenltue t\Tcuturer. \ \ 'hr lc correcuvc lneasufes are (or restonng the

plant petformance, the Prerreotrve measures ate necessary to Pfevent

recuffence of tl're same problem in t]re futute These measures might

involve smal-l to *od.."|" investmeots hence they are to be taken wrth

extreme care and with the tnvolvemeot oI the system supplier and odrer

paf ues r-nvolqed. Tlrese rr lelsufes rmght Lnvolve maiot chaoges r.n the pre

treatrneot equrpment, RO system and ro sotrre cases changlng the feed

\r,ater sources. A record of dre cofrecEve actions and thel-r outcome plavs

a very important rolc in correct 2ppl icatrons oI the preveotl l 'e measufes.

R O M O H I T O R I N G & T R O U B L E S I { O O T I T I G

&ppemdFN &

Ikferences

1 Techrucal Sen.rce Bulleuls by Hl'dranauncs. 40 1 (Jceanside, CA 92054USA

2 S Chdekar, Pressure Dnven lvlembrane Processes for Total WaterTreatment, Everl.thrng About Water Q{ay June 2002) ?1 3I

i

3 S Chrlekar. A Nerv Approach -fo

Desgmng Secondarl 'T'reated CtwSewage Reclanration Plants For Industrral Process 356, p1'6rything

About Water (.trJay'june 2043) 22-30

a

R O M O N I T O R I N G A T R O U A L E S H O O T I N G

Appeffidix ffi

1 ) t , \ t ( / , I \ , , , ' ^ , t - , | . . t . ^ . t C D l lI ' / ' n ( t ' , l l / t i ' l r l t ' , \ I ( , t . t / t l l l / . 1 . \ 1 / i I t ( l / s l n ' I t 70 i - \ ' ( J , ' 1

-fhe SDt s a popular method for deterrrumlg feed n'ater c1u:liry rn RO apPhcaaoos

It rs based oo the urne required to hlter a r.oltrme of leed w'ater tlrrougi-r a l) 45 pm

absolute fi l ter paper at a feed ptessLLre of 30 psg

- f oc / F n t r i hn ' t pn l I p t I I n

i ( J i . , i l i , L f t / t t t ' L u . " ' ' l

t Assemble the test equrPtl lcnt per frgtue 14

2 f.<tcate a sernple tri) oo thc feed u,etet plping and rnstall the test

equrPmeot

3 Adlirst the pressur-e tegularor ro -10 PSI \vrth a Elter pad mstalled

Llse a fresl'r 6-lter for L[re actrral test

For be-st restr l ts.

. [Jsc clu]l ftr,cczer5^ q.heo posltl()tlu-Ig thc f:rlter to Pfct-eot PLructul-urg

thc 6ltcr

. Ensure drat t f ie o-rurg rs clcarr : t lc l Ur go,td c() ldttrort, ancl is

propcrl l , posiuoned

. Avoid touclring dre [ltet u'Lth furgers

r lrlush the appata-tus to tetuo\.e anl' contalilnants that rnay be held

utthn tt

Test Pr'ocedure

1 Take the temperatufe oF the feed water The temPefatute should not

\rary rnore tlLan * 1 "C betu'een the stert and end o[dre tesc

2 Bleed any entrarned au rn the Eltet lrolder Dependng on dre rnodel

o[ the filter [rolder, either open the bleed valve, ot loosen the Elter

holder whrle crackrng the ball val.'e Ttren close the bleed valve or

6ltet holdet.

3 Place a 500 ml gtaduated cyllnder under the 6lter to mezsure the

amount of q'atet that passes througl"r the Elter-

o 5 6

R O M O N I T O R I N G E T R O U A L E S H O O f I N G

4 Open dre ba-[ r.alve [illl;-, and oreasure t]re ume requred to collecr100 ml aad 500 ml' from the ume the ball valve rs opeoed, Recordthese trmes, leavrng the valve open and letung the flow cooolue

5 Aftet 5 mi-outes, repeat the Brne measurement requrred to coliect 100ml and 500 ml samples Repeat agarn afier 10 and 15 mroutes o[elapsed nnre

6 If the ume requued to obtatn a 100 ml sample is greater tlLan about60 seconds, plugrrlg unll be about 9004, aod it is not necessaqr 1econfrnue the test.

7 Measwe the n'ater temperatufe agarrr to enstrre that it drd not vary bt

more thao 1 oC from the iruual temperahre,

a AFter completrng the test and disconnecung the apparahrs, t le 6lterpaper inay be saved tn a plasuc bag for Furure reference

e a/cu/attonsP,u ( l t , / r t r " '

J

S D I - = 1 0 0 *T, T , r J '

n'hcre SDI - Silt Density Indexl',,, -, 'l b pluggrng at 30 psg feed pressure-[, - -fotal

test f lmc m rrrff iutes (usually 15 nilntrtcs. bLLt nral,trc lcss r[ i5']u

pluggrr€ occlus m less dran 15 rninutcs)t, =- irutial time in seconds required to obtain sampletr I urne requrted to obLrrn sample after 15 minutes (or less)

NOTES* Tune to collect 500 ml should be apptorimately 5 urnes gteater dran the dn-re to

collect 100 ml. tf 500 rnl collection time is much greater drao 5{ SDI should becalculated using 100 ml collecdon dmes.

q

R O M O N I T O R I H G & T R O U B L E S H O O T I N G

Bal l Va lveor 1s t S tage

Regu la to r

PressureRegulator

30 ps i

Pressure Gauge

Figure 14 Appatatus for SDI Test

Bleed

nng

58

R O M O N I T O R I H G & T R O U B L E S H O O T I N G

AppeetdEx C

P roredtrre /ot' Ptvssurc f.,'eise/ Prubinp

lt-rs appendu prorndes genetal instructloos [or probrrrg a pressure sessel conLainngrevetse osmosls-membtane elements- Probrng a pressure vessel allorvs you todetermrne t'here there ts a problem rn a partrcular vessel. The problem may be eidrera pborly petfonnrng tnembrane element, an O-nng leak at an inter-conoector or endadaptet. or possibll' even a cracked adapter- Ptotrrng coosists oI rnserung semr-ogrdtuburg rnto the pefineate ctramel o[ the ptessure vessel and measunqg the tr.aterq""liq' at drfferent areas along the length oI the presswe vessel

, t - "

, ( ' , f r ,I esl L:qatpme//r Jer up

-1 Comect a 1 l/4" du'eaded

-fee to drc pemreate port Tliread ur a 1 I /4" by

1/4" tlrreaded reducer bushrng rnto the strarght opposite end o[ thc T'ee

Drau,pernreate from drc side end o[the Tee Ttread n t 1/1" nipplc ancl

1 ,/4" bal l vah'e Fine l ly, du-ead n a 1 /1" Patkcr Fast & Tite male c()nne ctor

llenrove the rnetal collrr and O ung frotn the Fast & Tite Etttlg

z C)btrur 2 plcce of l /4" outsrde diameter natutal colored pol l 'e6it t '1. ' ," o,

nylon trrbu-rg 1he ruburg should be several feet looger dran d-re lcngdr of dre

- r'essel Usurg a perrnaneot nrarkeq m'rk the total lengdr of rubrng necded to

place the end of the tubing at the pont where the farthest element corurects

to the adapter. Therq mark the t rbufg in 20" increments ftom this pornr

\.,

R O M O N I T O R I N G A T R O U B L E S H O O T I N G

Feed+".

Figure 15 Apparatus for Probing of vessels

Test Proccdurc

1

)

Close thc lrall t'elvc ou the pr,rbing Eto.ng:; Surrt t]re. Il-( ) svstenr

AFtcr rhc s\ '-stclrt has t ' rut for 15 tninutes, t t lseft thc ttrbmg tnkr thc [r:rst &.l- i te

frt trng.r ' l rr lc: openir lg u[] thc bal l r-alvc P'-r-sh t lrc t i .rbing tu rrrtdl dre

"totrr l lcrrqt lr" trutr l t t .s rcached

3 After 1 rutnute, melrsure the conductir-r$'o[ t]re n'ater cotrutlg out 'rF t]re

tubrng Recheck several tillcs to rnake sute tl-Lc value is t-onstant- Record

the conducdvi$' arld note dre locatlon-

4 Pull the tubrng out 20" usrng ]rour black nrarks as a gurde' walt 1 tnore

rninrrte, and repeat the measutement procedute. You may sltghtly close the

ball r,alve to Lrold the tubrng r-n place. This is espeoally requred if there is a

0-.-g leak urside the vessel. \X&en the end of the t"btog comes out of the

-\resselr close the ball valve, and continue to the next vessel

5 Ctrart the value o[ the peuneate conducdr.ity over the lerylh o[ the vessel. A

steadl. trend should be obsen'ed as a functioo of posiu-on'

Interpreting Ptobing Data

E,valuabtoo o[ the d;rta c:.n be done by rer.iewrng the conduchr'.rty values aloog the

length oI t]re pemteate cl-ulnel [or rndrrrdLral pressure vessels, and by comparittg t]re

l1

R O M O N I T O R I H G & T R O U S L E S H O O T I N . G

trcrnds oIparallel sessels aganst one anodrer. Srnce rndrvrdlrl situanons and s-r'stetns

are umque, tt ls best to consult for analysrrg data

In manl' cases, a sudden iocrease Lo the pemreate conductrr.rty at a ju.nctron betn,eenelemenls tndicates an O-ring problem or a gap between elemenLs and infer-

conoectors Replace taultY O nngs ard eflsure that elements are properly shirnmed

to elirnilate one possibLe soLucc, o[ a problenr I[ the problem shou,ld persrstloLlowrlg these cdrrechve actrons, coosult for speoic tnForrnaflon ontroubleshooflng a paracuJzr sys tem