control and optimization of flocculation processes in the laboratory and in plant

8/13/2019 Control and Optimization of Flocculation Processes in the Laboratory and in Plant

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Progr Colloid Polym Sci (1994) 95:161--167 SteinkopffVerlag 1994

A . BarteltD. HornW. GeigerG. Kern

o n t r o l a n d o p t im i z a t io n o f f l o c c u l a t io np r o c e s s e s i n t h e l a b o r a to r y a n d i n p l a n t

Dr. A. Bartelt (~ ) Dr. D. HornPolymer Research DivisionPolymer and Solid-State Physics, ZKMD. I. W. Geiger D. I. G. KernWaste Water Treatment PlantDUR/WKBASF AG67056 Ludwigshafen,FRG

Abst ract Flocculation processesare of great importance fornumerous industrial processes, suchas paper manufacture, mining, andthe treatment of industrial andmunicipal waste waters. Polymericflocculants having molecularweights up to 1 1 7 g/mol aregenerally used for this purpose.The flocculation mechanism(bridging, charge-mosaic) is deter-mined by the chain length, thecharge density and the molecularweight of the polymeric flocculant.There is a closely defined optimumfor the dosing rates of flocculants,from both an ecological and aneconomic point of view. Thespecific choice of flocculantstherefore requires a reliablemeasuring method with which tests

of effectiveness can be carried out,ideally under service conditions.This paper describes a fiber-opticflocculation sensor (FOFS) formeasuring the flocculation state inflowing systems, which has proveduseful in practice for bothlaboratory flocculation tests and asa measuring component of controlsystems for dosing equipment. Thefocus of this contribution is the useof the FOFS for assessing theeffectiveness of polymericflocculants in relation to wastewater treatment.Key words Flocculation --polymeric flocculants -- fiber-opticflocculation sensor -- waste watertreatment

ntroductionFlocculation processes with following solid/liquid sepa-ration are the basis of numerous industrial processes.Significant sectors, such as the paper industry, textilefinishing, the detergent industry and the ecologically im-portant sector of water treatment and protection, owetheir technological progress in large measure to the use oforganic flocculants. These are polymeric, water-solublematerials of different charge density having molecularweights up to 1 1 7 g/mol [1]. The most importantproduct group for the waste water sector is that of ca-tionically and anionically modified polyacrylamides.Flocculation processes involve a complex interactionof individual, elementary processes (Fig. 1) determinedby aspects of colloid and surface chemistry:

produc t i on of a homogeneous mixture of thepolymeric flocculation aid and the substrate to be floc-culated;-- adsorption of the polymer onto the particle surfacewhich thus becomes destabilized after a particulardegree of polymer coating;-- rearrangement of the adsorbed polymer on the particlesurface to achieve an equilibrium conformation;--collision of destabilized particles (before or afterrearrangement) which initiates aggregation or floc-culation;-- floc growth;

-- breakup of flocs by shear stress.The nature of the polymers determines their mode ofaction, which is explained by structural differences in


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162 A BarteltContro l and op t imiza t ion o f f loccu la t ion p rocesses in the labora to ry and in p lan t

A d s o r p t i o n a n d F lo c c u l a t i o n K i n e t i c s

N1~ '~2 N1~ ' )k12N1N d s o r p t i o n ~ l k12N1N2

rearrangement

~ f k 11N 12 f l oc c u l a t i o n ~ .~f k12N2~_

~-_bridgingmodel p tch ch rge model152JOQO.035e)

Fig 1 Interactio n of adsorption and flocculation kinetics

t he adsorbed layers [3 - -5 ] . The f loccu la t ion me chan i sm ofb r idg ing is enha nced by h igh m olecu lar weigh t s and a lowaff in i ty be tween the f loccu la t ion a id and the su r face .Destabi l izat ion and f locculat ion is achieved when avo luminous fa r - reach ing po lym er conformat ion is p resen tand the su r face i s abou t ha l f -coa ted . Po lye lec t ro ly tes wi tha h igh c harge den s i ty t end to g ive a f i a t su r face adsorp tion ;the resu l t ing mosa ic s t ruc tu re a t a par t i cu la r degree o fpo lym er coa t ing is therefo re charac te r i zed by reg ions hav-ing posi t ive and nega t ive charges pa tch charge model ) . Acorre la t ion be twe en f loccu la t ion e f fec t and su r face charg ec a n o n l y b e d e r i v e d f o r t h e c h a r g e - mo s a i c me c h a n i sm.D i f f e r e n t ia t i o n o f t h e t w o f l o c c u la t i o n me c h a n i s ms i so f t en poss ib le by observ ing the shear s t ab i l i ty . Po lymerbr idges a re re l a t ive ly shear -s t ab le , t he des t ruc t ion o ff loes by increased shear s t res s genera l ly be ing i r revers i -b l e . F l o e s f o r me d b y t h e c h a r g e - mo s a i c me c h a n i s m, o nthe o ther hand , a re subs tan t i a l ly mo re com pact and shear -l ab i l e ; however , des t royed f loes re tu rn revers ib ly to theoriginal s tate after the s t ress is s topped [6 , 7] .

For those f loccu la t ion p rocesses whic h a re in i t ia t ed byp o l y me r s , t h e d e p l e t i o n f l o c c u l a t i o n me c h a n i s m i s a l s ob e i n g d i s c u s s e d i n a d d i t io n t o t h e m e c h a n i s ms b a s e d o np o l y me r a d s o r p t i o n . I n t h e d e p l e t i o n me c h a n i s m, t h eo s mo t i c p r e s s u r e c a u s e s t h e d i s p l a c e me n t o f p o l y me rmo l e c u l e s f r o m b e t w e e n n e i g h b o r i n g p a r ti c le s a s s o o n a st h e s e a r e c l o s e r t h a n a p a r t i c u l a r m i n i mu m d i s t a n c e[8 - -10] . Theore t i ca l ly , t h i s mechan i sm i s qu i t e feas ib le ,a l though i t has as ye t no t been exp er ime n ta l ly ver i f i ed , inpar t i cu la r fo r rea l sys tems .Bes ides the po lye lec t ro ly te s t ruc tu re , t he dos ing andm ix ing cond i t ions p lay a dec i s ive ro le in the f loccu la t ion

resu l t [2, 16 ]. Bo th eco log ica l and econo mic fac to rs a rei mp o r t a n t i n d r i v i n g t h e t a r g e t e d d e v e l o p me n t o f f l o c -cu lan t s , t he i r spec i f i c se l ec t ion and the i r op t imal dos ing .T h i s r e q u i r e s e f f e c t i v e me a s u r e m e n t me t h o d s w h i c ha l low assessment o f the p reva i l ing f loccu la t ion s t a t eunde r def ined cond i t ions wh ich a re c lose to those in p rac-t i ce . Th i s pape r descr ibes a f iber -op t i c f loccu la t ion sensorFOFS) fo r measur ing the f loccu la t ion s t a t e in f lowingsys tems , w hich has p rove d i ts va lue bo th fo r bas ic s tud iesi n t h e l a b o r a to r y a n d a s t h e m e a s u r i n g c o mp o n e n t o f c o n -t ro l sys tems fo r ac tua l dos ing equ ipm ent [6, 11 - -13 , 16].The focus o f th i s con t r ibu t ion i s the use o f the FOF S fo rassess ing the e f fec t ivene ss o f po lym er ic f loccu lan t s in thet rea tmen t o f indus t r i a l and munic ipa l was te water .

F i b e r - o p t i c f l o c c u l a t i o n s en s o r F O F S )T h e me a s u r i n g d e v i c e i s ma d e u p o f t h r e e i n t e g r a t e duni ts :- - a n a r r a n g e m e n t f o r m i x i n g in t h e f l o c c u l a ti o n a id a n da reg ion fo r f loc fo rmat ion ,- - a f iber -op t i c sensor f i t t ed in an enveloped-f low ce l l ,- - d e t e c t o r e l e c tr o n i c s c o n n e c t e d to a c o m p u t e r f o r c o m-b ined da ta ana lys i s and con t ro l o f dos ing .

T h e p r i n c i p l e o f t h e e x p e r i me n t a l a r r a n g e me n t o f t h eFO FS is s h o w n s c h e ma t i c a l ly in F i g . 2 . T h e m e d i u m t obe f loccu la ted i s tu rbu len t ly mixed wi th the so lu t ion o fthe f loccu la t ion a id in a mix ing cha m ber , w h ich ach ievesr a p i d h o mo g e n e o u s d i s tr i b u ti o n o f b o t h t h e c o m p o n e n t s .F l o c c u l a ti o n t a k e s p l a c e s l o w l y u n d e r d e f i n e d s h e a r c o n -d i t ions in a reg ion o f l aminar f low. The l eng th o f thelamina r - f low tube can be match ed to the app l i cab le p rac-t ical condi t ions .A f t e r p a s s i n g t h r o u g h t h e l a mi n a r - f l o w r e g i o n , t h ef loccu la ted mater i a l f lows th rough the f iber -op t i ca lme asur ing ce l l F ig . 3 ) . The t ransmi t t ed ligh t o f a l aserb e a m p a s s i n g t h r o u g h t h e s a mp l e is d e t e c t e d I R l a s e r

w ste w ter ~~ flocculant

laminar flowube

Fig 2 Princ ip le o f the f loccu la t ion sensor


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Progr Colloid Polym Sci 1994) 95:16 1--16 7 163 Steinkopff Verlag 1994

F-value [V]

water ~

fiber optic measuring cell

~ water

um

substrate flow

4 . 0 -

sign l u t )~ i 0 3.5-3.0-2.5-

before floccul tlon u0 2.0-

ufter floecul tion tim 0.5-0

Fig . 3 Laser-optic flocculati on moni toring technique

beam 835 nm; diameter in the suspension 1 ram). The in-tensity fluctuations o f the transmitted laser light resultingfrom particle density variations very sensitively mirrorthe decrease in particle number caused by flocculationand the corresponding increase in particle size. The elec-trical signals of the detector are converted by an in-tegrated electronic component into the flocculation valueF in volts) by means of a root-mean-square analysis [14],this value serving as the assessment criterion for the ef-fectiveness of flocculation.It is of decisive importance for the optical measure-ment and for the use of the sensor that contamination ofthe measuring cell is avoided. This is achieved by meansof an enveloping stream of deionized water which sur-rounds the substrate stream and so prevents the contact ofthe latter with the wall of the measuring cell Fig. 3). Fu r-thermore, the optical path length can be adjusted for anoptimal signal-to-noise ratio by varying the ratio of thesample stream to the enveloping stream, thus enabling themeasurement of typical samples of practice, such assewage sludge, paper pulp, coal suspensions, etc., intheir original concentration without prior dilution.The measurement and evaluation of flocculation stateis typically carried out over 10 min by means of pro-grammed dosing, in which the flocculation value F isrecorded during a stepwise increase in flocculant dosing.Figure 4 shows an example of a flocculation curve. Theamount of flocculant required for optimal flocculation isthat whe re F reaches an asymptotic limit bridging mech-anism) or a maximum patch charge mechanism ).The degree of flocculation F derived from intensityfluctuations correlates with the floc size, which can be

: I I

I IO. 5 0.10 0.15 0.20 0 25 0 30polymeric concentration mg/I]

Fig. 4 Flocculation curve: dependence on the degree of floccula-tion F on flocculant dosing

F-value [V] model system: glass spheres/glycol10-

8-

6-

4-

2 o

amplification 2amplification 3

< 250 iiiiiiiii iil50-400i : . : . : . : .

i i i i i i iiiiiiiiii i i i i i i. : . : - : , :r . . .- . - . - . . .. - - - ,. . . . . ,- . - . . , ,: : : : : : : : . . . . , .; : : . : : : :

. . . , . . . -: i : : : i

. . . . . ,

400-500

, , , . . , .. . . . . .: : : : : : : : :i [ i l i ] :. . . . . ,

ii iiiiitll: : : : iE~: : : : : : : : :. : . : . : . : a . d: : : : : : : : 1 : I

: , : - : - : -1-1. : . : . : . :. : . : . : . :i i i i i ; i i

500-630spheres diameter [I-tm]

Fig. 5 Dependence of the degree of flocculation F on floc size forthe model system of glass spheres/glycol

shown both theoretically [15] and experimentally [13].Figure 5 shows the results of model experiments withglass spheres of differing size with glycol as the con-tinuous phase. A linear relationship betw een the degree o fflocculation F and the sphere size is obtained, regardlessof the amplification of the detector.

Screening method for assessing the effectivenessof flocculation aids for waste water treatmentIn waste water treatment, flocculation coagulation) of thesolid particles present in the water or sludge is induced


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164 A BarteltContro l and op t imiza t ion o f f loccu lat ion p rocesses in the labora to ry and in p lan tby po lymer ic f loccu lan t s . Vo luminous , s t ab le f locs a ref o r me d , w h i c h s p e e d s u p t h e p r o c e s s o f s e d i me n t a t i o na n d m a k e s d e w a t e r i n g o f t h e s l u d g e p o ss ib l e . D e p e n d i n gon the na tu re o f the water o r s ludge , i t i s nece ssary to 8Js e le c t p o l y me r i c f l o c c u l a n t s w h i c h h a v e o p t ima l p r o p e r -t i es wi th respec t t o e f fec t iveness and econo mics . The 7qf iber -op t i c f loccu la t ion sensor has the par t i cu la r advan- 6 -t a g e , w h e n c o mp a r e d w i t h c o n v e n t i o n a l l a b o r a to r y t e st ssuch as sed ime n ta t ion exper im en t s j a r t es t ), t ha t t he 5 -mo n i t o r i n g o f t h e f l o c c u la t i o n p r o c e s s a n d t h e r e f o r e t h eassessmen t o f the f loccu lan t i s poss ib le wi th in a few 4-minu tes . 3 -

2 -1-0~0

Fl o c c u l a ti o n o f e x c e s s s l u d g eExcess s ludge occurs in the t rea tmen t o f indus t r i a l e f -f luen t s in concen t ra t ions o f 10- -15 g /1 . F igu re 6 showsf loccu la t ion cu rves fo r excess s ludge , i n w hich an ion ica l -l y mo d i f i e d p o l y a c r y l a mi d e s f r o m t h e Se d i p u r r e g i s te r e dt r a d e m a r k o f B A S F ) p r o du c ts w e r e u se d A - - D ) w h i c ha r e d i f f e r e n t c o n c e r n i n g th e i r mo l e c u l a r w e i g h t a n d t h e i rc h a r g e d e n s i t y . A s s e s s me n t c r i t e r i a a r e t h e a mo u n t o ff loccu lan t neede d fo r op t imal f loccu la t ion and a l so , as ame a s u r e o f t h e f l o c s i z e , t h e d e r i v e d f l o c c u l a t i o np a r a m e t e r F . T h e d i f f e r in g e f f e c t iv e n e s s o f t h e p r o d u c t si s c l ear f rom a com par i son o f the resu l ts F ig . 6 ) .The f loccu la t ion cu rv e o f f loccu lan t A i s a lmos t idea l:a f t e r a shor t i n i ti a t ion o r respon se t ime, d ur ing wh ich theam ount o f po ly m er i s st il l t oo low fo r su f f i c i en tdes t ab i l i za t ion o f the par t i c l es , t here i s a s ign i f i can t in -c r e a s e i n t h e d e g r e e o f f l o c c u l a t i o n a t h i g h e r p o l y me rconcen t ra t ions . The f loccu la t ion cu rve i s l i near over aw i d e r a n g e a n d f i n a l ly a p p r o a c h e s a n a s y m p t o t e at e v e nh i g h e r p o l y m e r c o n c e n t r a t io n s . T h e f l o c c u la t io n c u r v e s

F-value V]10-9-87-6-5-4-3-2-1-0

A

1 2 3 4 5 6 7 8 9 10polymericconcentration ing/I]

F i g 6 F loccu la t ion curves fo r excess sludge with Sed ipur p ro-duc ts A, B, C, D ), which a re d if fe ren t concern ing molecu la rweigh t and charge dens i ty

E x c e s s S l u d g eF-value [V]

c h a r g e d e n s i t y = c o n s t . A1[M w: A1 > A 2 > A 3 1 S A2

I I I1 2 3 4 5 6 7 8 9 10

polymeric concentration ing/ I ]Fig . 7 Floccu lation curves for excess sludge with Sedipur pro-ducts A1 , A2 , A3); va r ia t ion o f molecu la r we igh t o f the f loc -culants

E x c e s s S l u d g eF-value [V]8

7-6-5-4-3-2-1-0

Mw = const .I c h a r g e d e n s i t y : A 4 < A 5 < A 6 1 A 4

A5

I I I i I i 1 2 3 4 5 6 7 8 9 1 0polymeric concentrat ion ing/ I ]

F i g 8 Flocculatio n curves for excess s ludge with Sedipur pro-d u c t s; v a r i at io n o f c h arg e d e ns i ty : A 4 :2 . 0 me q /g , A 5 :4 . 2 me q /g ,A 6 : 8 . 4 m e q / g

o f t h e p o l y m e r s B C a n d D a r e f a t t e r , w h i c h i mp l ie s ah i g h e r u s a g e o f f l o c c u la n t a n d a p o o r e r f l o c c u la t io n e f f e c -t iveness .Sys temat i c t es t s wi th se l ec t ed an ion ic p roduct s haves h o w n h i g h mo l e c u l a r w e i g h t f l o c c u l a n t s w i t h l o w t ome d i u m c h a r g e d e n s it ie s - - 2 t o - - 4 me q / g ) to b e o p ti ma lfo r f loccu la t ing excess s ludge Figs . 7 , 8 ) . In these f loc-


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Prog r Colloid Polym Sci 1994) 95:161 --167 165 Steinkopff Verlag 1994

c u l a t io n p ro c e s s e s c a l c i u m i o n s s e rv e a s l i n k s b e t w e e n t h ean ion ic po lymers and the nega t ive par t i c le su rfaces .B e c a u s e t h e b r i d g i n g m e c h a n i s m i s r e s p o n s i b l e fo r t h ed e s t a b i l i z a t i o n , m e a s u r i n g m e t h o d s b a s e d o n a c h a rg ec h a ra c t e r iz a t i o n o f t h e s y s t e m s fo r a s s e s s i n g f l o c c u l a t io n(e .g . e lec t rok ine t ic methods) a re no t appropr ia te .F l o c c u l a t i o n o f d i g e s t e d s l u d g e f ro m a m u n i c i p a lwa s t e wa t e r t r e a t m e n t p l a n tF o r m o re h i g h l y c o n c e n t r a t e d g ra d e s o f s l u d g e , t o o , t h ee f f e c t i v e n e s s o f f l o c c u l a n t s c a n b e a s s e s s e d w i t h o u t d i f -f i c u l ty b y m e a n s o f t h e f i b e r -o p t i c f l o c c u l a ti o n s e n s o r .F i g u re 9 s h o ws t h i s fo r t h e e x a m p l e o f a d i g e s t e d s l u d g e(3 0 g / l ) f ro m t h e wa s t e wa t e r t r e a t m e n t p l a n t o fOb e re r l e n b a c h , wh i c h w a s f l o c c u l a t e d w i t h c a t i o n ic a l l ym o d i f i e d p o l y a c ry l a m i d e s (K1 , K2 ) .F o r t h e e x a m i n a t io n o f h ig h l y c o n c e n t r a t e d s y s t e m s(30 to 60 g / l ) , such as th ickener s ludge , a mod i f ica t ion tot h e m i x i n g c h a m b e r i s r e q u i r e d . T h e u s u a l m i x i n gc h a m b e r o p e ra t e s a s a s t a t i c m i x e r , i . e . , t h e m i x i n ge n e rg y i s d e r i v e d o n l y f ro m t h e v o l u m e f l o w s o f th e t wocom ponen ts . Fo r concen t ra t ions > 30 g / l , th i s a r range-m e n t c a n n o l o n g e r e n s u re t u rb u l e n t m i x i n g . T h e u s e o fa m i x i ng c h a m b e r t o wh i c h a d d i t io n a l m i x i n g e n e rg y c a nb e p ro v i d e d (U l t r a T u r r a x , b l a d e s t i r r e r ) i s t h e r e fo re r e -qu i red .

F - v a l u e [ V ]

c (s l u d g e ) = 3 0 g / I7-6 -5 -4 -3210 0

K 2

Use of the f iber -opt ic f loccu la t ion sen soras on- l ine contro l dev ice in the Sedipur dos ing fac i l i tyo f t h e B A S F wa s t e wa t e r tre a t m e n t p l a n tT h e i n d i v i d u a l s t e p s o f m e c h a n i c al a n d b i o l o g i c a l wa s t ewa t e r t r e a t m e n t i n t h e B AS F p l a n t (L u d wi g s h a fe n , F R G)[17 , 18 ] a re shown in F ig . 10 . Af te r neu t ra l i za t ion o f the

i i0 1 2 0 . 4 0 1 6 0 18 1 1 0 1 1 2 1 1 4 1 . 6 1 . 8 2 , 0p o l y m e r i c c o n c e n t r a t io n [ m g l g ]

Fig . 9 Flocculation of municipal sewage sludge with Sedipur pro -ducts K1, K2)

BASF Waste W ater Trea tment P lant

t

Yp r im a r y s l u d g e

n e u t r a l i z a t i o nm e c h a n i c a l re a t m e n t41c l a r i f i e r

- - > . ] a c t i v a t e d s I u d g e b a s i ns t a t i o n 4S e d i p u rFOFS

8 -0 -0 2 s e c o n d a r y c l a r i f i e r20

s t a t io n 5S e d i p u rt h i c k e n e r

c o n d i ti o n i n g , S e d i p u rc h a m b e r i l te r p r e s si n c i n e r a t i o n

~ 1 ~ w a s t e w a t e rB A S F , c o m m u n i li e s

a c t i v a t e d l u d g e 4 - 5 g / I

e x c e s s s l u d g e 1 0 - 1 5 g / I

t h i c k e n e d s l u d g e 5 0 6 0 g / I

Fig. 10 Flow diagram of the BASF waste water treatment plant

wa s t e wa t e r , m e c h a n i c a l t r e a t m e n t i s c a r r i e d o u t i n ascreen ing p lan t and in c la r if i e r . T h is i s fo l low ed byb io log ica l t rea tmen t in the ac t iva ted s ludge bas ins us ingb a c t e r i a l s l u d g e . T h e b a c t e r i a d e g ra d e d i s s o l v e d o rg a n i cs u b s t a n c e s w i t h t h e a id o f o x y g e n f ro m t h e a e r a ti o n , f o r -m i n g wa t e r , c a rb o n d i o x i d e , a n d a n e w b i o m a s s , t h e e x -c e s s s l u d g e m e n t i o n e d e a r l i e r ( 7 0 p ro t e in ) . T h es e d i m e n t a t io n o f t h e a c t i v a t e d s l u d g e i n t h e s e c o n d a ryc l a r i fi e r ( 4 - -5 g / l) a n d t h e c o n c e n t r a t i o n o f t h e e x c e s ss ludge in the th ickeners (10 --15 g / l ) i s a ided by an ion icSed ipur p roduc ts . A f te r add i t ion o f cond i t ion ing agen ts(ash and carbon) , the th ickened s ludge (50 --60 g / l ) i sf l o c c u l a t e d w i t h a c a t i o n i c S e d i p u r p ro d u c t . Af t e rdewater ing , the f i l t e r cake i s f ina l ly inc inera ted , the ashbeing la rge ly reused in the min ing indus t ry .T h e f l o c c u l a n t u s a g e o f t h e w a s t e wa t e r t r e a tm e n tp lan t i s abou t 8 tons per mon th . At p resen t , f loccu la t iond o s i n g o c c u r s o n t h e b a s i s o f e m p i r i c a l d a t a . W i t h t h e a i mo f a c h i e vi n g m o re e f f e c t i v e a n d m o re e c o n o m i c a l d o s i n gwhich wi l l , in par t i cu la r , a l so a l low the f loccu lan t u sageto match v ar ia t ions in the na tu re o f the s ludge , i t is p lann-ed to in s ta l l the f iber-op t ic f loccu la t ion senso r as the con-t ro l un i t in the Sed ipur dos ing fac i l i ty .The FOFS i s a t p resen t in s ta l l ed in the d i s t r ibu to r 4 o ft h e wa s t e w a t e r t r e a t m e n t p l a n t a n d i s f e d w i t h a r e p re s e n -t a t iv e b l e e d s t r e a m wh i c h i s ta k e n f ro m t h e u n f l o c c u l a te dm a i n s t r e a m o f a n a e ra t i o n b a s i n v i a a b y p a s s . T h e o p -t i m a l a m o u n t o f f l o c c u l a n t is d e t e rm i n e d fo r t h i s b l e e ds t ream every 15 min . In the long te rm, i t i s p lanned toc o n n e c t t h e f l o c c u l a t i o n s e n s o r t o t h e p ro c e s s c o n t ro ls y s t e m o f t h e wa s t e wa t e r t r e a t m e n t p l a n t. Af t e r a p ro p o r -t i o na l t r a n s m i s si o n c o n t ro l f a c t o r h a s b e e n d e t e rm i n e d fo rthe p rocess and p lan t , i t wi l l be poss ib le to con t ro l the


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166 A. BarteltControl and optimization of flocculation processes in the laboratory and in plant

O r i g i n a l R e c o r d o f t h e F O F S i n th e W a s t eW a t e r T r e a t m e n t P l a n t14.0~ .Ol* Zyk ] t. tt. - Nr. IBB14P. UhP Cp [~,9/ ] ] JF 1~.] F LV]1 15.22. 58 O.O00 252 0.182 15.23. 58 0.15- 456 0.983 15.24. 58 0.311 145 2.413 B 3 . 3 415.25.53 0 . 4 6 65 15.26. 58 0.622 15 3.866 15.27.58 0 . 777 I0 4 . 272 7 4~4 01~.~1 Z y k I u s - N r . t B 9~ r , k l h P C p [ m 9 / i ] ~ F [ ~ ] F [ V J1 15 . 44 . 5& 0 . 000 23~ 0 . 192 15 . 45 . 5& 0 , 155 48 i 1 . 133 15 . 46 . 56 0 . 311 129 2 . 5 84 15.47,56 0 . 46& 40 3.635 15,48. 5 0.622 11 4.056 15.49.56 0 7 7 7 12 4.5727414.03.91 2 y k l u s - N r , 1 /0t , l r . U h r C ~ [ m 9 / 1 3 ( I F I X ] F I V ]I 16.06. 54 0.000 250 0 . 182 I .07.5 4 0.155 452 0.973 I .08.5 4 0.311 142 2 . 3 44 16.09.54 0.466 38 3.265 1&. 10 . 30 0 . 622 19 3 . 9 16 16.11,30 0 7 7 7 14 4.482 751 4 . O ~ } . q ~ 2 v l : l u ~ N r 1 ( ;1NP Uhr C~ tmg/ ~ ] dE [~ ]1 l&. 23 . 25 O O O O 3442 1 6 . 2 7 . 2 ~ 0 . 155 4503 16,30.2B 0,311 1084 16 . 31 . 28 0 . 4 , ~ 6 40

Fig. 11 Extract of an originalwater treatment plant

0 . 2 , 4 . . E;

i -0 - 2 . 4 . . 8O . 2 . 4 . 6 . O

F {V] u . . 4 . 6 ~ . 10~O .7:21 . 2 22 . 5 53.58t ~9

record of the FOFS in the waste

d o s i n g i n t h e m a i n s t r e a m w i t h t h e a id o f t h e o p t i m a l f l o c -c u l a n t a m o u n t i n t h e b y p a s s .C h a n g e s t o t h e l a b o r a to r y v e r s i o n o f th e F O F S r e la t ee s se n t i a l l y t o d a t a p r o c e s s i n g . I n s t e a d o f t h e c o m p u t e r u s -e d i n th e l a b o r a t o r y , t h e c o n t r o l p r o g r a m w i l l b e i n s t a l le do n a p r o g r a m m a b l e i n t e r f a c e ( M u l ti D a t a ) , e n a b l i n g c o n -n e c t i o n t o t h e p r o c e s s c o n t r o l sy s t e m o f t h e w a s t e w a t e rt r e a t m e n t p l a n t. A p r i n t e r c o u p l e d t o t h e i n t e r f a c e l o g s t h er e su l t s c o n t i n u o u s l y . F i g u r e 1 1 sh o w s a n e x t r a c t o f a no r i g i n a l r e c o r d .T h e t i m e o f d a y , t h e a c t u a l f l o c c u l a t i o n a id c o n c e n t r a -t i o n , t h e c h a n g e i n th e f l o c c u l a t i o n v a l u e i n c o m p a r i so nw i t h t h e p r e v i o u s c o n c e n t r a t i o n s t e p ( d F ) , a n d t h e a b -so l u t e f l o c c u l a t i o n v a l u e ( F ) a r e g i v e n ; t h e b a r c h a r t c o r -r e s p o n d s t o t h e f l o c c u l a ti o n c u r v e s h o w n b e f o r e . T h e o p -t i m a l f l o c c u l a n t c o n c e n t r a t i o n i s d e f i n e d a s t h a t a t w h i c hi n c r e a si n g o f t h e S e d i p u r c o n c e n t r a ti o n t w i c e n o l o n g e ri n c r ea s e s t h e f l o c c u l a ti o n v a l u e b y m o r e t h a n 2 0 % . O nt h e b a s is o f t h i s S e d i p u r c o n c e n t r a t i o n , w h i c h i s t r a n sm i t -

t e d t o t h e p r o c e s s c o n t r o l sy s t e m , t h e o p t i m a l d o s i n g f o rt h e m a i n s t r e a m i s d e t e r m i n e d , t a k i n g t h e v a r y i n g c o n d i -t i o n s ( f l o w r a t e s , c o n c e n t r a t i o n s , d i m e n s i o n s , e t c . ) i n t oa c c o u n t . I O V A s l o n g - t e r m e x p e r i m e n t s , t h e o p t i m a l f l o c c u l a n t c o n -c e n t r a t i o n s t o g e t h e r w i t h t h e c o r r e sp o n d i n g F - v a l u e sw e r e r e c o r d e d o v e r s e v e r a l m o n t h s . E v a l u a t i o n o f t h e s er e su l t s h a s m a d e i t c l e a r t h a t t h e a c t iv a t e d s l u d g e f l o c c u l a -t i o n is b e i n g c a r r i e d o u t w i t h c o n s i d e r a b l e o v e r - o r u n d e r -. 10q d o s i n g o f f l o c c u la n t o v e r e x t e n s i v e p e r i o d s o f t im e .C o n t r o l l e d d o s i n g m a t c h e d t o t h e s l u d g e p r o p e r t ie s w o u l dsa v e f l o c c u l a n t a n d g i v e i m p r o v e d f l o c c u l a t i o n s .

T h e F O F S i n d i s tr i b u to r 4 o f t h e w a s t e w a t e r t r e a tm e n tp l a n t i s s t il l in t h e t e s t p h a se , a l t h o u g h c o n n e c t i o n t o t h e. 10~ p r o c e s s c o n t r o l sy s t e m i s a p p r o a c h i n g .

onclusionsT h e f i b e r - o p t i c f l o c c u l a t i o n s e n so r h a s p r o v e d i t s u t i l i t ya s a r o b u s t m e a su r i n g d e v i c e w i t h sh o r t r e sp o n se t i m e sa n d h i g h r e so l u t i o n , b o t h i n r e se a r c h i n v e s t i g a t i o n s a n d i nf i e ld t e s t s .

S y s t e m a t i c i n v e s t i g a t i o n s w i t h m o d e l su sp e n s i o n s a n dw i t h r e a l sy s t e m s l e a d t o c l a r i f i c a t i o n o f f l o c c u l a t i o nm e c h a n i s m s . K n o w l e d g e o f t h e a p p l i c ab l e f l o c c u l a ti o nm e c h a n i s m s i s a f u n d a m e n t a l r e q u i re m e n t f o r u n d e r s t a n -d i n g a n d o p t i m i z i n g f l o c c u l a t i o n p r o c e s se s . T h e f i b e r - o p -t i c f l o c c u l a t i o n s e n so r i s , f u r t h e r m o r e , u se f u l a s a s c r e e n -i n g m e t h o d w h i c h i s c l o s e t o p r ac t i ce f o r d e v e l o p i n g a n df o r a s se s s i n g t h e e f f e c t i v e n e s s o f f l o c c u l a n t s .

U se o f t h e f lo c c u l a t i o n s e n so r a s a n o n - l i n e c o n t r o ld e v i c e i n r e a l d o s i n g f a c i li t ie s is p o s s i b l e , w h i c h c o u l d i nt h e f u t u r e b e o f p a r t i c u l a r l y g r e a t v a l u e f o r w a t e r t r e a t -m e n t i n i n d u s t r i a l a n d m u n i c i p a l w a s t e w a t e r t r e a t m e n tp l a n ts . W i t h r e g a r d t o t h e e c o n o m i c s a n d e f f e c t i v e n es s o fp r o c e s s o p e r a t i o n , t h e a d v a n t a g e s o f o p t i m i z e d f l o c c u l a n td o s i n g h a v e a l r e a d y b e e n s h o w n i n a c t iv a t e d s l u d g e t r e a t-m e n t , a n d w i l l c e rt a in l y b e c o m e e v e n c l e a r e r w i t h h i g h l yc o n c e n t r a t e d ty p e s o f s l u d g e ( e x c e s s , t h i c k e n e r , d i g e s t e ds l u d g e ) .Acknow ledgemen t We thank M rs. H. Debus for her diligence incarrying out the measurements and for her assistance in the im-plementation of all these projects.

References1.Eisenlauer J, Horn D (1985) DVGW-Schriftenreihe Wasser Nr. 42:59--722.Gregory J, G uibai L (1991) Chem EngComm 108:3; Gregory J (1988) Col-loids and Surfaces 31:2313.Gregory J (1989) Critical Review s inEnvironmental Control 19:185

4.Dickinson E, Eriksson L (1991) Ad-vances in Colloid and Interface Science34:15.Gill RIS, Herrington TM (1987) Col-loids and Surfaces 28:416. Ditter W, E isenlauer J, Horn D (1982)In Tadros (ed) The Effect of Polymers

on Disp ersion Properties. AcademicPress, London, pp 323--3427. Leif Eriksson, B arbro Aim, 5th Interna-t ional Gothe nburg Symposium onChemical Treatment of Water andWa stewater, Nice, Sept. 28--30, 1992.Model system studies of formation and


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Progr Col lo id Po lym Sc i (1994) 95 :161--167 Ste inkopff Verlag 1994 167

propert ie s o f f locs ob ta ined with ca -t ion ic po lye lec tro ly tes .8. Sperry PR et a l. (198 l) J Coil lnterf Sci82 :629 .Dick inson E (1989) J Coi l In te rf Sc i132:27410.Dobias B (ed) (1993) Coagulation andfloccu la tion -- Theory and A ppl ica tion .Surfactant science series vol 47. MarcelDekker , Inc , New York , Base l , HongK o n g

l l .E isen laue r J , H orn D (1983) Z Wasse rAbwasse r Forsch 16 :912 . E isen lauer J, H orn D, Linhar t F , H emelR (1987) N ord ic Pu lp & Paper R esearchJourna l 2 :13213 .Eisen lauer J , Horn D (1987) Col lo idsand Surfaces 25:11114 .Gregory J , Ne lson DW (1984) In :Gregory J (ed) Solid-Liquid Separation.Soc ie ty o f Chemica l Indus try /El l is H or-w o o d , L o n d o n , p p 1 7 2 - -1 8 2

15. Gr ego ry J (1985) J Colloid In terface Sci105:35716.Eisenlauer J , Horn D (1985) Colloidsand Surfaces 14:12117 . Enge lha rd t H, Neuwir th M , W eisbrod tW (1985) Korrespondenz Abwasse r3 2 :9 4 018 .Wilm s HE, W olf G, A hrens K (1992)Abwasse r techn ik Heft 5 :60

control and optimization of flocculation processes in the laboratory and in plant

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