mbr for food-processing.pdf

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Combined biological and membrane treatment of food-processing wastewater to achieve dry-ditch criteria:

Pilot and full-scale performance

George Nakhla a, * , Andrew Lugowski b , Javnika Patel b , Victor Rivest c

a Department of Chemical and Biochemical Engineering, University of Western Ontario, London, ON, Canada N6A 5B9b Conestoga-Rovers & Associates, 651 Colby Street, Waterloo, ON, Canada N2V 1C2

c Sun-Brite Canning, P.O. Box 70, Ruthven, ON, Canada N0P 2G0

Received 6 December 2004; received in revised form 10 March 2005; accepted 10 March 2005

Available online 31 May 2005

Abstract

This study tested the applicability of a submerged vacuum ultraltration membrane technology in combination with the biolog-ical treatment system to achieve dry-ditch criteria stipulated as follows: BOD 5, TSS, NH 3-N, and total phosphorous (TP) concen-tration not exceeding 10, 10, 1, and 0.5 mg/L respectively for the treatment of high strength food-processing wastewater. During thestudy, the biological system, operated at average hydraulic retention time of 56 days, achieved 9596.5% BOD removal and9699% COD removal. The external membrane system ensured the achievability of the BOD and TSS criteria, with BOD andTSS concentrations in the permeate of 12 and 18 mg/L respectively. Nitrate, and nitrite concentrations increased during mem-brane ltration, while ammonia concentrations decreased. The most salient nding of this study is that, contrary to common belief,for industrial wastewaters, the lterability of the mixed liquor is inuenced by the soluble organics, and may be low, thus necessi-tating operation of bioreactors at low mixed liquor solids. This study demonstrated that bioreactors operated at low SRTs and incombination with ultraltration can still achieve superior effluent quality that may meet reuse criteria at reasonable cost.

2005 Elsevier Ltd. All rights reserved.

Keywords: Suspended solids; Biological treatment; Ultraltration membrane; Food-processing

1. Introduction

Membrane technology has been used for the treat-ment of municipal and industrial wastewaters from tan-neries ( Krauth, 1996 ), textiles ( Rozzi et al., 2000 ),

chemical ( Livingston et al., 1998 ; Greene et al., 2000 ),and food-processing ( Mavrov and Be lieres, 2000 ; Cupe-rus, 1998 ; Mavrov et al., 1997 ) facilities. Membranetechnology has been applied successfully to the food-processing industry as membrane bioreactors ( Cantoret al., 2000 ) and physical separators ( Kuemmel et al.,

2000 ; Fakhru l-Razi and Noor, 1999 ). By far, most of the MBRs applied for municipal and industrial waste-water treatment utilize external membranes in contrastto the submerged vacuum membranes, which are em-ployed in this study. The vacuum submerged mem-

branes, used in this study were provided by ZenonEnvironmental (Oakville, Ontario, Canada), have anominal pore opening of 0.036 l m, molecular cutoff point of 300 kilodaltons, and operate at low vacuumpressures (less than 0.3 atm). The main advantages of these membranes include lower energy consumption,better effluent quality, better retention of microbes andviruses, and less fouling due to continuous cleaning of the membranes by air. Due to operation at high solidsretention times (SRTs) and consequently high mixed

0960-8524/$ - see front matter 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.biortech.2005.03.034

* Corresponding author. Tel.: +1 519 661 2111/85470; fax: +1 519850 2921.

E-mail address: [email protected] (G. Nakhla).

Bioresource Technology 97 (2006) 114
mailto:[email protected]:[email protected]


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liquor suspended solids (MLSS) concentrations, mem-brane bioreactors have been reported to enhance bio-degradation of non-readily biodegradable compoundsincluding high molecular weight compounds ( Reemtsmaet al., 2002 ; Schro der, 2002 ). However, even when usedfor solids separation only, biological activity on mem-

branes cannot be ruled out due to the formation of abiolm on the membrane surface. Despite the very brief contact time in the membrane unit, the very high bio-solids concentrations will inevitably inuence effluentquality. While MBRs have recently elicited signicantinterest, biological activity during membrane separationand its impact on effluent quality has not receivedattention.

While the operation of membrane bioreactors at highSRTs and consequently high MLSS concentrations hasbeen thoroughly reported in the literature, the perfor-mance of membranes at low SRTs has not been thor-oughly investigated. Chaize and Huyard (1990) ran apilot plant MBR with external ultraltration mem-branes on municipal wastewaters at hydraulic retentiontimes (HRT) of 28 h, long SRT of 50100 days, andhigh biomass concentrations of 810 g/L, and achievedvirtually complete removal of organics and nitrica-tion. Similarly Muller et al. (1995) have operated anMBR system with external ultraltration on domesticwastewater at biomass concentrations of 4050 g/Land reported greater than 90% removal of carbon andcomplete nitrication. On the other hand, Ng andHermanowicz (2003) have operated an MBR systememploying submerged pressure membranes on synthetic

wastewater with average COD of 400 mg/L at HRTs of 36 h and SRT of 0.255 days, and average mixed liquorsuspended solids concentration of 3462300 mg/L andreported complete removal of carbon and nitricationat an SRT of 5 days. Cicek et al. (2001) have shown thatthe lterability of wastewater by membranes is inu-

enced not only by suspended solids but also by solubleproducts. Thus, the performance of membranes inindustrial wastes applications may differ markedlyfrom municipal wastewater treatment. Furthermore,the achievability of strict surface discharge criteria withultraltration membrane bioreactors has not solicitedmuch attention since this feat is readily accomplishedby nanoltration and reverse osmosis systems, despitethe high energy requirements. The primary objective of this study was to test the applicability of a submergedvacuum ultraltration membrane in combination withbiological treatment in the food-processing industry toachieve stringent dry-ditch criteria. A detailed pilotstudy was undertaken at a food-processing facility toinvestigate the achievability of effluent discharge criteriaof 5-day biochemical oxygen demand (BOD 5), total sus-pended solids (TSS), ammonia nitrogen (NH 3-N), andtotal phosphorous (TP) concentration not exceeding10, 10, 1, and 0.5 mg/L respectively from the treatmentof wastewaters generated primarily during the off-seasonfrom canning of various products, predominantly beans.Preliminary data from full-scale operations is also in-cluded. This study demonstrated that biological activityoccurred in membrane ltration systems even at rela-tively low inuent biomass concentrations.

FACULTATIVE LAGOON SYSTEM

BLOWER/PUMP HOUSE

Concentrate

PUMPHOUSE

PRIMARYCLARIFIER

SPRAYIRRIGATION

FIELD

SCREEN

Influent

AERATION

TANKANOXIC

TANK

Waste Activated Sludge Final Effluent (DirectDischarge)

BLOWER/PUMP HOUSE

PUMPHOUSE

PRIMARYCLARIFIER

SPRAYIRRIGATION

FIELD

SCREEN

FINALCLARIFIER

Waste Activated Sludge

Internal Recirculation

UF UNIT

Permeate

Future AdditionsNOTE:

Fig. 1. Process ow diagram of treatment system including pilot-scale membrane.

2 G. Nakhla et al. / Bioresource Technology 97 (2006) 114


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2. Methods

2.1. Description of existing treatment system

The ultimate wastewater treatment system to beimplemented at the site includes primary clarication

to remove suspended solids, anoxic/oxic biological treat-ment for removal of organics followed by secondaryclarication for solid/liquid separation prior to dis-charge to a dry-ditch. The system has been built inphases and the existing facilities include primary clari-cation, a 480,365 US gal aeration tank and a secondaryclarier. Agitation and oxygen in the aeration tank areprovided by a diffused aeration system consisting of 284 medium-bubble diffusers and two 100-hp blowers.Dissolved oxygen (DO) concentrations in the aerationtank varied from 2 to 4 mg/L. Due to the lack of sludgerecirculation systems, daily disposal of the entire inu-ent wastewater quality was exercised. Settled sludgewas hauled directly from the aeration tank to the localwastewater treatment plant. The total volume of settledsludge hauled was equal to the daily wastewater ow.Mixing in the aeration tank was stopped for 8 h, duringwhich time the supernatant was pumped out of the aer-ation tank and trucked to the local wastewater treat-ment plant. Due to the lack of full-scale solid/liquidseparation process, the biological system was operatedas a fed sequencing batch reactor as opposed to an acti-vated sludge, i.e. the SRT was not equal to the hydraulicretention time (HRT) of approximately 56 days, basedon an average wastewater ow rate of 60,00075,000 US

gpd, due to allocation of 120,091 US gal of the aerationtank capacity for storage of wastewater in case of emergency.

The pilot-scale membrane system used in this studywas provided by Zenon Environmental Inc. of Oakville,Ontario and utilized a 180 US gal aerated tank toaccommodate the 500 ft 2 ZeeWeed hollow ber,vacuum ltration membrane. The membrane tank wascontinuously aerated to reduce fouling and cleaningrequirements, and as a result the DO concentration inthe permeate typically ranged from 2 to 3 mg/L. Dueto visible quantities of ne colloidal material in theraw wastewater, the selected membrane opening was0.04 l m to remove colloidal material, bacteria, andviruses, thus rendering the effluent amenable for recycleback to the production facility to be used for cleaningand other operations. The membrane ltration systemwas operated at four distinct permeate ows: 2.0, 2.5,3.5, and 3.8 US gpm corresponding to uxes of 5.8,7.2, 10, and 11 gpd/ft 2 . However, due to the close owsof 3.5 and 3.8 US gpm, the data has been combined.Thus the system operation is divided into three operat-ing periods: OP-1 at 2.0 US gpm which lasted for 25days, OP-2 at 2.5 US gpm which lasted for 9 days,and OP-3 at permeate ows was 3.53.8 US gpm, which T

a b l e 1

W a s t e w a t e r c h a r a c t e r i z a t i o n

B O D ( m g / L )

C O D ( m g / L )

T K N

( m g / L )

N H

3

( m g / L )

N O

3

( m g / L )

N O

2

( m g / L )

P O 4 - P

( m g / L )

P O 4

( m g / L )

T S S

( m g / L )

V S S

( m g / L )

T o t a l

S o l u b l e

T o t a l

S o l u b l e

R a n g e ( m i n m a x )

2 3 4 2 2 5 6

2 8 8 1 4 0 0

5 9 1 7 4 5 0

2 7 0 3 5 4 0

1 0 4 8 1

4 6 0

0 . 2 9 . 0

0 . 1 6 . 5

0 . 0 0 2 0 . 2 1 2

0 . 5 5 5

. 0

1 . 4 1 7 0 . 0

1 8 8 2 3 7 4

1 2 6 2 2 4 2

M e a n S D ( n )

1 4 4 8 4 7 5

( 2 2 )

9 2 0

3 2 6

( 2 2 )

3 1 2 0 1 6 1 9

( 3 8 )

1 9 6 5 9 9 6

( 2 3 )

1 2 5 4 2 9 1

( 2 )

3 . 0 2 . 0

( 3 9 )

1 . 5 2 . 0

( 3 8 )

0 . 0 2 6 0

. 0 4 4

( 3 8 )

2 0 . 6

1 3

. 0

( 3 6 )

6 8 . 5

3 7

. 0

( 3 3 )

4 8 8 4 2 9

( 2 4 )

4 4 7 4 0 9

( 2 4 )

( n ) : R e p r e s e n t s t h e n u m b e r o f d a t a p o i n t s .

G. Nakhla et al. / Bioresource Technology 97 (2006) 114 3


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lasted for 42 days, following complete start-up and com-missioning of the full-scale biological system and pilot-scale membrane unit. The maximum capacity of thepilot unit was 5 US gpm corresponding to 7205 USgpd or 7.5% of the total wastewater ow. A process owdiagram of the system including the pilot-scale mem-

brane system is shown in Fig. 1 .The membranes were cleaned in accordance with theprocedures specied by Zenon Environmental (Burling-ton, Ontario). Two types of cleanings were performed:maintenance clean and a recovery clean. A maintenanceclean is a preventative cleaning, that is performed on aregular basis, and basically involves 10 cycles each com-prised of stopping the permeate while continuing to aer-ate for 510 min, backpulsing (BP) with a 1000 mg/Lsodium hypochlorite solution at 12 gallons/ft 2 /days for30 s, and relaxing for 4.5 min. A recovery clean is per-formed when the suction required to permeate throughthe membrane reaches 79 psi, and involves alternatesoaking in concentrated solutions of sodium hypochlo-rite (1000 mg/L) to remove organic debris, and 2 g/Lof citric acid to remove inorganics. Two recovery cleanswere performed on day 13 and day 53, while weeklymaintenance cleans were initiated on day 42.

The full-scale membrane system designed for a per-meate ow of 82.3 US gpm (120,000 US gpd) consistedof forty-eight (48) 500-ft 2 membrane cassettes for a total

area of 24,000 ft 2 , submerged in a 12 0(L) 7.8 0(W) 8.67 0 (side water depth) aerated epoxy coated carbonsteel tank. At full operating capacity, with a permeateto concentrate ow ratio of 1:1, the HRT in the mem-brane tank was about 36 min only. The full-scale systemwas commissioned and fully operational by day 687

from the start of the pilot plant.

2.2. Wastewater characteristics

Wastewater generation and quality from the food-processing facilities varies considerably throughout theyear. Peak wastewater ows at approximately 480,365US gal are generated during the tomato canning seasonextending from August to October while much lowerwastewater ows at approximately 60,00075,000 USgal result from the processing of other vegetable prod-ucts during the rest of the year. The organic matter con-centrations during tomato canning are higher thanduring the rest of the year. The results presented herepertain to the treatment of wastewater from processingof vegetable products exclusive of tomato canningwastewater.

Table 1 presents the variations in primary effluent(inuent to biological system) quality. BOD total mostlyranged from 234 to 2256 mg/L while COD varied morewidely between 591 and 7450 mg/L. Phosphorus ranged

Table 2Pilotplant operational conditions

Permeate ow(US gpm)

Operation(days)

Aeration tankHRT (h)

Average F/M ratio inaeration tank

MBRHRT (h)

Average F/M ratio in MBR

BOD COD BODs CODs BOD CODg BOD/gMLVSS/day

g COD/gMLVSS/day

g BODs/gVSS/day

g CODs/gVSS/day

g BOD/gVSS/day

g COD/gVSS/day

2.0 25 215 0.10 0.29 0.74 1.26 1.28 6.31 13.72.5 9 185 0.10 0.25 0.59 0.55 1.06 7.20 14.53.53.8 42 187 0.31 0.35 0.42 0.65 NA 7.15 NA

NA: Not available.

Table 3Overall pilot plant system performance

Permeate ow Aeration tank Membrane

BOD T % removal BOD S % removal COD T % removal COD S % removal BOD % removal COD % removal

Operating period 1Range (minmax) 4172 4995 1389 9498 4899 4469Mean SD ( n) 59 11 (7) 84 18 (6) 68 24 (10) 96 2 (5) 75 27 (4) 56 13 (3)



(n): Represents the number of data points.



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from 0.5 to 55 mg/L depending on the production pro-cess with an average of 20 mg/L, which was satisfactoryfor maintaining biological activity. As presented inTable 1 , highly uctuating chemical characteristics of wastewater required a combined biological and mem-brane treatment system to operate over a wide range

of suspended solids concentrations, as well as to achievestringent effluent quality objectives.

2.3. Sampling and monitoring program

The pilot system was commissioned on April 26, 2002and the study lasted for 3 months. Daily grab samples of the primary clarier effluent (inuent to biological treat-ment), aeration tank mixed liquor (inuent to mem-brane system), and ZeeWeed permeate were collected

and analyzed for COD (total and soluble), NH 4-N, ni-trate nitrogen NO 3 -N , nitrite nitrogen NO 2 -N andphosphate phosphorus PO 34 -P concentrations. Grabsamples of the aforementioned three waste streams werecollected twice a week, and sent off-site for analysis of the 5-day BOD (total and soluble), total suspended sol-

ids (TSS), and volatile suspended solids (VSS) concen-trations. Weekly grab samples from the membranetank were collected and analyzed off-site for TSS andVSS. For the full-scale system, the same streams wereanalyzed and for the same parameters as the pilot unit,albeit at a lower frequency. Off-site analysis was doneonce a week and parameters determined on-site, i.e.COD, NH 4-N, NO 3 -N, NO 2 -N, and PO

34 -P were ana-

lyzed twice a week. For the membrane pilot plant, thepermeate ow, the reject ow, vacuum before and after

0.1

1

10

100

1000

10000

0 20 40 60 80 100 120

Time (days)

L o g

B O D ( m g

/ L )

Influent Aeration Tank Aeration Tank - SolublePermeate

MAC = 10 mg/L

Above MAC Aeration Tank: 15/15Permeate: 5/17

1

10

100

1000

10000

0 8 10 12 14Time (days)

L o g

B O D ( m g

/ L )


MAC = 10 mg/L

Above MAC Aeration Tank Soluble: 2/4Permeate: 0/4

2 4 6

(a)

(b)

Fig. 2. Temporal variation of inuent, aeration tank and permeate BOD: (a) pilot data; (b) full scale data.



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backwash, ZeeWeed tank temperature, and pH were re-corded several times a day. Due to the high concentra-tions of colloidal matter in the wastewater, the systemwas based on a permeate to concentrate ratio of 1:1.

2.4. Testing methodology

COD (total and soluble), NH 4-N, NO 3 -N, NO 2 -Nand PO 34 -P concentrations were measured on-site usinga Hach DR 2500 system. Standards with known con-centrations of the various analytes were run with allanalysis, and tests were repeated when the accuracy of standards determinations was below 95%. The chemicalanalyses for BOD (total and soluble), TSS, and VSSconcentrations were carried out off-site at certied labo-ratories in accordance with the Standard MethodsSM5210 B, SM2540 B, and SM2540 E respectively(APHA, 1985 ). It must be asserted that all BOD resultsreported here are 5-day BOD. Samples were transportedto the off-site laboratory in ice-packed coolers, andstored at the lab in a cold room for a maximum periodof 1 day prior to analysis. Standard deviations listed inthe various tables were calculated using all the pertinentanalytical data using the statistical formulae in Micro-soft Excel, and reect the variability of the water qual-ity, not the accuracy of the analytical tests.

3. Results and discussion

3.1. Organics removal

A summary of the operational conditions for thethree operational period OP-1 to OP-3 during the pilot

plant testing is presented in Table 2 . It is apparent that,despite the long HRT in the aeration tank, it operated atloadings similar to conventional activated sludge sys-tems with average food-to-microorganisms (F/M) ratiosranging from 0.1 to 0.3 g BOD/g VSS-d. For the mem-brane tank, the HRT was based on the total inuent

ow rate from the aeration system and not based onthe permeate ow. Due to the low HRT in the mem-brane tank, and despite the excellent removal of BODin the aeration tank, the soluble organic loadings werestill high in the 0.551.26 g BOD/g VSS-d range, typicalof high rate systems. It should be noted that ammonianitrogen in the raw wastewater ( Table 1 ) was extremelylow relative to organic matter with the BOD:NH 3-Nratio, based on average observed concentrations of 483:1, thus indicating a severe nitrogen deciency. Thisdeciency was corrected by addition of 751 kg of dryurea (40% nitrogen) over the course of the study to boththe inuent as well as the aeration tank. This translatesto an average nitrogen concentration based on a ow of 75,000 US gpd and 76 days of net operation of 10 mg/L,thus reducing the BOD:NH 3-N ratio to a more typical144:1.

A summary of the removals of total and soluble BODand COD in the full-scale aeration tank and across thepilot-scale membrane during the pilot plant study is de-picted in Table 3 . BOD and COD removals by the mem-brane system were based on inuent soluble BOD andCOD. Total BOD removal efficiency in the biologicalsystem ranged from 41% to 90% averaging at 65% whiletotal COD removal efficiencies were generally similar

varying from 13% to 94% with an average of 62%. Re-moval of soluble organics in the biological treatmentsystem on the other hand was much higher, averaging

1

10

100

1000

10000

0 10 20 30 40 50 60 70 80 90 100

Time (days)

L o g

C O D ( m

g / L )


Fig. 3. Temporal variation of inuent, aeration tank and permeate COD.



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at 88% and 94% based on BOD and COD respectively.Approximately 2/3 of the organics were in soluble formand the organics were moderately biodegradable as re-ected by a BOD 5-to-COD ratio of around 0.4:1. Thedifference between total and soluble organics removalin the aeration tank is attributed to the slower biodegra-

dation kinetics of particulate organics relative to the sol-uble organics, and the absence of full-scale solidliquidseparation, i.e. secondary clarication, which wouldhave increased particulates removal. It must be empha-sized that the organic removal efficiencies are remark-able considering that the biological system was run atlow SRT and consequently low MLSS of mostlyapproximately 10001500 mg/L despite the long HRT.

The diurnal variation of BOD, COD respectively, inthe inuent, aeration tank, and permeate together withthe anticipated discharge criteria is illustrated in Figs.2 and 3 . BOD results from the full-scale operation arealso included in Fig. 2 . As shown in Fig. 2 , 100% and50% of the aeration tank effluent samples taken for sol-uble BOD analysis during the pilot study and full-scalestudy, respectively, exceeded the effluent BOD criteriaof 10 mg/L. During the pilot study, the nal effluentBOD criteria was exceeded in ve out of 17 samples,four of them during the early commissioning andstart-up phase, i.e. the system readily met the criterionfor 94% of the time producing BOD of 12 mg/L, asshown in Table 4 . Thus, in any of the three operatingconditions listed in Table 4 , the membrane would easilymeet the 10 mg/L criterion, as conrmed by the perme-ate BOD data of Table 4 as well as the results of the full-

scale operation.As depicted in Fig. 3 , despite the highly uctuating

inuent COD, and the aeration tank soluble COD vary-ing from 30 to 200 mg/L, the permeate COD was stableat 3050 mg/L. It is noteworthy that the typical effluentsoluble COD from municipal wastewater treatmentplants, is 3050 mg/L, which constitutes the inert solubleCOD component of municipal waste ( IAWQ, 1995 ).Thus, the achievability of a similar effluent COD con-centration in the context of high strength wastes isremarkable.

Details of the performance of the membrane systemduring the pilot study are presented in Table 4 . Themembrane was operated at three different ow rates of 2.0, 2.5, and 3.53.8 US gpm. It should be noted thatthe BOD and COD removals calculated for the mem-brane were based on the soluble fractions of the inuentBOD and COD to the system. At a ow rate of 2.5 USgpm corresponding to a ux of 7.2 gpd/ft 2 , the averageBOD and COD removals achieved were 96% and 63%respectively. Effluent BOD and COD concentrations inthe permeate at 22.5 US gpm were mostly in the 1.3 1.8 mg/L while effluent CODs were in the range of 23 35 mg/L. At 3.53.8 US gpm or 10 gpd/ft 2 , averagepermeate BOD and COD concentrations increased T

a b l e 4

S u m m a r y o f m e m b r a n e o p e r a t i o n a l a n d p e r f o r m a n c e d a t a

B O D a n d C O D ( t o t a l a n d s o l u b l e )

P e r m e a t e

( U S g p m )

I n u e n t

A e r a t i o n t a n k

P e r m e a t e

B O D

T

( m g / L )

C O D

T

( m g / L )

B O D

S

( m g / L )

C O D

S

( m g / L )

B O D

T

( m g / L )

C O D

T

( m g / L )

B O D

S

( m g / L )

C O D

S

( m g / L )

B O D

( m g / L )

C O D

( m g / L )

B O D %

r e m o v a l

C O D %

r e m o v a l

T S S

( m g / L )

O p e r a t i n g p e r i o d

1

R a n g e ( m i n m a x ) 2 . 0 2 . 0

1 4 2 8 2 2

5 6

3 1 9 0 6

5 4 0

1 0 8 3 1

3 5 4

2 4 1 0 3 2

1 0

5 4 2 6 9 9

7 2 0 8 0 0

7 2 1

9 6

6 2 9

0

1 . 3 1 . 8

2 3 3

5

9 8 9

9

4 4 6

9

1 1

M e a n S D ( n )

2 . 0 0 . 0

( 9 )

1 7 7 0 4 3 2

( 3 )

4 9 0 3 1 6 7 6

( 3 )

1 2 1 0 1 3 6

( 3 )

2 9 0 0 4 2 9

( 3 )

6 1 4 7 9

( 3 )

7 6 0 4 0

( 3 )

1 3 4 8 8

( 2 )

8 0 1 5

( 3 )

1 . 5 0 . 3

( 3 )

2 8 6

( 3 )

9 9 0 . 6

( 2 )

5 6 1 8

( 2 )

1 0 . 1

( 2 )


2

R a n g e ( m i n m a x ) 2 . 5 2 . 5

1 1 9 1 1 3

4 7

2 9 2 0 3

6 1 0

8 6 0 9 3 9

2 1 1 0 2 7

5 0

4 3 7 7 0 5

1 0 3 0 1

3 0 0

2 4 6

5

7 0 9

9

1 . 0 2 . 1

2 2 3

6

9 6 9

7

4 9 7

8

3 1 4

M e a n S D ( n )

2 . 5 0 . 0

( 8 )

1 2 6 9 1 1 0

( 2 )

3 2 8 7 3 4 7

( 3 )

9 0 0 5 6

( 2 )

2 3 5 0 3 4 9

( 3 )

5 7 1 1 9 0

( 2 )

1 1 6 5 1 9 1

( 2 )

4 5 2 9

( 2 )

8 5 2 1

( 2 )

1 . 6 0 . 8

( 2 )

3 0 7

( 3 )

9 6 0 . 7

( 2 )

6 3 2 1

( 2 )

9 8

( 2 )


3

R a n g e ( m i n m a x ) 3 . 5 4 . 0

2 3 4 2 1 7 8

5 9 1 4 3 7 0

2 8 8 1 4 0 0

2 7 0 3 4 7 0

1 5 6 6 9 8

2 1 1 2 1 5 1

2 0 1

7 0

3 2 1

9 6

0 . 1 2 . 2

1 3 7

7

9 4 1

0 0

4 6 7

5

0 . 5 2 0

M e a n S D ( n )

3 . 8 0 . 1

( 3 0 )

1 5 2 3 5 5 2

( 1 1 )

2 1 9 9 1 1 5 3

( 1 6 )

9 9 0 3 3 1

( 1 1 )

1 5 6 8 1 1 0 6

( 1 2 )

4 0 4 1 9 5

( 8 )

9 7 4 5 7 4

( 1 5 )

8 6 4 7

( 1 1 )

8 8 4 7

( 1 2 )

1 . 3 0 . 7

( 7 )

3 7 2 1

( 8 )

9 8 2 . 1

( 7 )

6 4 1 1

( 5 )

3 . 7 5 . 4

( 1 2 )




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sharply to 5.5 and 68.5 mg/L. At the low ows, themembrane ltration affected removal of approximately43 mg BOD/L and approximately 50 mg COD/L. Sincethe soluble BOD and COD concentrations in the inu-ent were based on ltration through 0.45 l m while themembrane opening is 0.04 l m, it is possible that physical

separation of particles in the 0.040.45 l m range was theprimary removal mechanism. Alternatively, enhancedbiodegradation of slowly biodegradable waste constitu-ents that escaped biological treatment in the aerationtank may have contributed to the organics removal.Oxygen uptake rates in the membrane tank averaged0.64 0.07 mg/Lmin, and it is thus estimated that theaverage COD removed by biodegradation in the mem-brane tank at an average HRT of 5090 min is 3257mg/L. However, in the absence of the fraction of BOD

and COD in the aeration tank effluent that is lterablethrough 0.04 l m lter, the predominance of physicalseparation vis-a `-vis enhanced biodegradation cannotbe precisely delineated. While the short hydraulic con-tact time in the membrane tank of 5090 min may notbe conducive to the biodegradation of slowly biodegrad-

able organics escaping a 56-day HRT biological treat-ment system, the relatively much higher biomassconcentrations and different microbial groups ( Cicek etal., 2001 ) may have induced biodegradation.

3.2. Suspended solids removal

The temporal variation of the inuent, aeration tankeffluent, and permeate total suspended solids concentra-tions both during the pilot study and full-scale operation

0.1

1

10

100

1000

10000

0 20 40 60 80 100 120Time (days)

L o g

T S S ( m g

/ L )

Influent Aeration TankPermeate

MAC = 10 mg/L


0.01

0.1

1

10

100

1000

10000

0 2 4 6 10 12 14

Time (days)

L o g

T S S ( m g

/ L )


MAC = 10 mg/L


8

(a)

(b)

Fig. 4. Temporal variation of inuent, aeration tank and permeate TSS: (a) pilot data; (b) full scale data.



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is depicted in Fig. 4 . The effluent TSS criterion of 10 mg/L was met in 85% of the samples during the pilot and100% of the samples during full-scale operation ( Fig.4). Only three exceedances occurred, two being slightlyhigher than 10, i.e. 11 and 14 mg/L. Additionally, twoout of the three exceedances of the TSS criteria occurred

during the early commissioning and start-up phase of the pilot study. This data clearly demonstrates theachievability of the effluent TSS criterion of 10 mg/L.While the mixed liquor suspended solids concentrationin the aeration tank varied mildly, from 1000 to 2000mg/L, the nal effluent TSS concentrations were mostlyin the 12 mg/L during stable operation of the mem-brane system. It is note-worthy however that the perfor-mance of the membrane with respect to TSS removal atmuch higher inuent TSS, i.e. 40006000 mg/L has notbeen tested in this study.

Sludge yields in the aeration tank during the entireoperating period of the pilot plant study were derivedfrom charts of cumulative sludge produced (as VSS) ver-sus cumulative COD/BOD removals. The calculatedyields were 0.09 g VSS/g COD ( R2 = 0.89), 0.15 g VSS/g SCOD ( R2 = 0.89), 0.215 g VSS/g BOD ( R2 = 0.84),and 0.363 g VSS/g SBOD ( R2 = 0.88). Thus, it is appar-ent that the system biological sludge yield is relativelylow compared with the 0.5 g VSS/g BOD observed inmunicipal wastewater treatment. This low yield is attrib-uted to the relatively low F/M ratio that the systemoperated at. It must be asserted that the volatile fractionof the aeration tank MLSS during the pilot study was0.85, i.e. MLVSS was 85% of the MLSS. This atypically

high ratio is attributed to two factors: the low concen-tration of inuent inorganic suspended solids, as de-picted in Table 1 , and the low operational sludge age.The high volatile fraction of mixed liquor suspended sol-ids, combined with the low sludge yield indicates thatparticulate organics were biodegraded in the system.

3.3. Nutrient removal

The performance of the combined biological andpilot-scale membrane system with respect to nitrogenand phosphorous removal is presented in Table 5 whilethe diurnal variations of the two aforementioned para-meters are depicted graphically in Figs. 5 and 6 . Theadequacy of soluble phosphorous and deciency of sol-uble nitrogen is noteworthy. No chemicals to removephosphorous were added during the pilot study. Nitro-gen deciency was corrected by addition of urea as ela-borated upon earlier. As shown in Fig. 5 , during thepilot study the system exceeded the 1 mg/L NH 4-N cri-teria in 13 of 28 samples. Two out of 13 samples that ex-ceeded the NH 4-N criterion occurred during the earlycommissioning and start-up phase. In the aerationtank effluent, 50% of the samples exceeded the effluentNH 4-N criterion. Considering that the biological system T

a b l e 5

S u m m a r y o f m e m b r a n e o p e r a t i o n a l a n d p e r f o r m a n c e d a t a n i t r o g e n a n d p h o s p h o r u s

P e r m e a t e

( U S g p m )

I n u e n t

A e r a t i o n t a n k

P e r m e a t e

N H

3 - N

( m g / L )

N O

3 - N

+ N O

2 - N

( m g / L )

P O 4 - P

( m g / L )

N H

3 - N

( m g / L )

N O

3 - N

+ N O

2 - N

( m g / L )

P O 4 - P

( m g / L )

N H

3 - N

( m g / L )

N O

3 - N

+ N O

2 - N

( m g / L )

P O 4 - P

( m g / L )


1

R a n g e ( m i n m a x ) 2 . 0 2 . 0

2 . 2 8

. 1

0 . 3 0 . 5

2 2 . 1 5

5 . 0

0 . 4 3 . 7

2 . 9 1 9

. 4

6 . 4 5 3

. 9

0 . 1 3 . 4

2 . 3 3 2

. 5

7 . 4 5 1

. 9

M e a n S D ( n )

2 . 0 0 . 0 ( 9 )

4 . 5 2 . 6 ( 4 )

0 . 4 0 . 1 ( 4 )

4 1 . 1

1 5

. 2 ( 4 )

1 . 9 1 . 7 ( 4 )

1 4 . 4

7 . 7 ( 4 )

3 2 . 5

2 0

. 6 ( 4 ) 1 . 1 1 . 6 ( 4 )

1 7 . 9

1 3

. 5 ( 4 )

3 3 . 9

1 9

. 3 ( 4 )


2

R a n g e ( m i n m a x ) 2 . 5 2 . 5

2 . 8 4

. 7

0 . 1 6 . 5

6 . 6 2 1

. 0

2 . 7 4 1

. 6

1 . 0 1 3

. 0

5 . 8 2 1

. 6

2 . 3 4 7

. 1

1 . 3 2 2

. 6

4 . 2 1 9

. 6

M e a n S D ( n )

2 . 5 0 . 0 ( 8 )

3 . 5 1 . 0 ( 3 )

2 . 3 3 . 6 ( 3 )

1 5 . 7

8 . 0 ( 3 )

2 1 . 0

1 9

. 5 ( 3 ) 6 . 4 6 . 1 ( 3 )

1 1 . 4

8 . 9 ( 3 )

2 3 . 3

2 2

. 5 ( 3 ) 1 0

. 5 1 1

. 0 ( 3 )

1 0 . 2

8 . 3 ( 3 )


3

R a n g e ( m i n m a x ) 3 . 5 4 . 0

0 . 2 9

. 0

0 . 2 4 . 4

3 . 5 4 1

. 3

0 . 1 5 . 4

0 . 3 7 3

. 7

0 . 2 2 6

. 9

0 . 1 3 . 4

0 . 3 9 7

. 3

0 . 2 2 1

. 8

M e a n S D ( n )

3 . 8 0 . 1 ( 3 0 ) 2 . 9 2 . 6 ( 1 7 ) 0 . 9 1 . 4 ( 1 6 )

2 2 . 5

1 1

. 1 ( 1 3 ) 1 . 3 1 . 6 ( 1 1 )

2 2 . 5

1 8

. 6 ( 1 6 )

1 1 . 7

8 . 2 ( 1 6 ) 1 . 0 1 . 0 ( 1 3 )

2 7 . 6

2 3

. 3 ( 1 6 )

7 . 4 6 . 0 ( 1 6 )




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operated at very low SRTs and low biological solidsconcentrations that are not conducive to nitrication,the inadequacy of the nitrication is not surprising. Fur-thermore, since the waste is nitrogen decient, morecontrolled addition of urea may alone be sufficient tomeet the criteria. Thus, based on the pilot study results,

for the three owrates 2.5, 2.0, 3.53.8 US gpm based on3-, 4-, 14-sample averages, respectively, the membranewill not meet the 1 mg/L NH 4-N criterion, as shownin Table 5 . However, the results of the full-scale systemindicate that the combined biological and membranesystem met the criterion in all ve samples ( Fig. 5 ).

As anticipated, phosphorus removal without chemi-cal addition was not adequate for meeting TP criterionof less than 0.5 mg/L. The effluent TP criterion wasexceeded in 86% of the samples. A chemical additionsystem is needed for phosphorus removal during the

full-scale operation. For all three operating permeateow rates during the pilot study, shown in Table 5 ,the membrane did not meet the 0.5 mg/L TP criterion.

3.4. Membrane system performance

The performance of the pilot-scale membrane ltra-tion system with respect to nitrogen and phosphorusremovals is presented in Table 5 . Orthophosphate con-centrations decreased during membrane ltration atthe three operational conditions. At uxes of 7.2 and1011 gpd/ft 2 , based on average conditions, 1.2and 3.4 mg/L of PO 34 -P were removed. Interestingly,nitrates and nitrites concentrations in the permeateincreased, while ammonia concentrations decreased.The relationship between ammonia and nitrates concen-trations in thepermeate, andthe inuent to themembrane

0.01

0.1

1

10

100

0 20 40 60 80 100 120Time (days)

L o g

N H

3 - N

( m g

/ L )


MAC = 1 mg/L


0.01

0.1

1

10

0 2 4 6 8 10 12 14 16Time (days)

L o g

N H

3 - N

( m

g / L )


MAC = 1 mg/L


(a)

(b)

Fig. 5. Temporal variation of inuent, aeration tank and permeate NH 3-N: (a) pilot data; (b) full scale data.



11/14

system both during the pilot study as well as during thefull-scale operation is depicted in Figs. 7 and 8 . It is evi-dent that strong statistical correlations, as reected byR2 values of 0.81 and 0.94 respectively were observed.Changes to these two soluble species are not anticipatedto occur during physical separation since ultraltersretain only particles with molecular weights of 1000 1,000,000 ( Scott, 1997 ) and the Zenon lter had a mole-cular cut-off point of 300 kilodaltons. The data of Fig. 7indicates that in the range of 0.110 mg/L inuentammonia concentration, ammonia decreased by about

24% during membrane ltration. The results of thefull-scale operation were also similar with permeateammonia concentrations of less than 0.1 mg/L at inu-ent concentrations of up to 2 mg/L. The concentrationof nitrates and nitrites in the permeate, during the pilot

study, increased by about 15% ( Fig. 8 ). The relativelygood agreement between the full-scale data and the pilotstudy correlation conrms the trend of substantial in-crease in nitrates and nitrites during membrane ltra-tion. Thus, nitrication was achieved in the membranetank, despite the very short HRT of 0.40.75 h. This isconsistent with the ndings of Muller et al. (1995) whoobserved up to 86% conversion of inuent nitrogen indomestic wastewater to nitrates in an MBR operatingat MLSS concentrations of 1040 g/L. It is interestingto note that nitrication in the membrane tank occurred

rapidly, after 20 days following start-up of the pilot sys-tem. While the change in ammonia concentration of only 24% may not be signicant considering theobserved concentrations of about 1 mg/L, the changein nitrates ( Fig. 8 ) and nitrites ( Table 5 ) is signicant.

0.01

0.1

1

10

100

0 10 20 30 40 50 60 70 80 90 100Time (days)

P O

4


Above MACInfluent: 35/36

Aeration Tank: 36/38Permeate: 24/28

MAC = 0.5 mg/L 3 - - P

( m g

/ L )

Fig. 6. Temporal variation of inuent, aeration tank and permeate PO 34 -P.

y = 0.7646xR 2 = 0.8107

0

1

2

3

4

5

6

7

8

9

10

0 8 10 12

Aeration Tank NH 3 (mg/L)

M e m

b r a n e

N H

3 - N

( m g

/ L )

Pilot DataFull Scale Data

2 4 6

Fig. 7. Relationship between permeate NH 3-N and aeration tank NH 3-N.



12/14

The increase in nitrates plus nitrites across the mem-brane varied from 20% to 40%. The implications of this for denitrifying membrane bioreactors may be seri-ous as it clearly manifests the potential for secondarynitrication.

3.5. Membrane cleaning

The temporal variation of vacuum prior to BP andaeration tank MLSS concentrations is illustrated inFig. 9 . It should be noted that due to employment of a

1:1 permeate to retentate ratio, the ambient solids con-centrations in the membrane tank were essentially twicethe aeration tank or inuent MLSS. It is conspicuous

from Fig. 9 that generally BP started to increase, asthe concentration of MLSS increased. However at-tempts to directly correlate BP vacuum with MLSS con-centrations, as depicted in Fig. 10 clearly indicate thatthe correlation is not very strong. This implies that thelterability of the mixed liquor is not solely related toMLSS, i.e. soluble products affect lterability. This isconsistent with the observations of Cicek et al. (2003) ,who provided evidence that the soluble fraction of mixed liquor, i.e. smaller size solutes, proteins, and sug-ars have a great impact on ltration performance in

MBRs. For this particular waste, the BP vacuum of 8to 9 psi, prescribed by the supplier as a trigger for recov-ery cleans, would be achieved at MLSS concentrations

y = 1.1983x

R 2 = 0.9377

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70 80

Aeration Tank NO 3 (mg/L)

M e m

b r a n e

N O

3 ( m g

/ L )

Pilot DataFull Scale Data

-

-

Fig. 8. Relationship between permeate NO 3 and aeration tank NO 3 .

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0 20 40 60 80 100 120

Time (days)

B e

f o r e

B P V a c u u m

( " H g

)

0

500

1000

1500

2000

2500

3000

3500

M L S S ( m g

/ L )

Group 1 - 3.5 US gpmGroup 2 - 2.5 US gpmGroup 3 - 2.0 US gpmGroup 4 - 3.8 US gpmMLSS

Fig. 9. Temporal variance of before BP vacuum and MLSS.



13/14

of about 3000 mg/L, which translates to 6000 mg/L inthe membrane tank. This is much lower than the typicalconcentration of 12,000 mg/L. Since one of the funda-mental premises for using membranes, is the ability of the MBR process to operate at high MLSS concen-trations, the lterability of this particular waste mayconstrain this kinetic advantage of MBRs over conven-tional activated sludge systems. Under such circumstan-ces, contrary to common practice, it is only possible tooperate the bioreactor at relatively low MLSS concen-

trations in the 20003000 mg/L range. Thus the achiev-ability of stringent soluble organics and nutrientscriteria at low biomass concentrations is critical, andtherefore the evidence provided in this study to theaforementioned effect is highly pertinent.

4. Summary and conclusions

Based on the results of this pilot study, the followingconclusions can be drawn:

The membrane ultraltration system has achievedcomplete removal of suspended solids and colloidalmatter, thus facilitating compliance with the dry-ditch discharge criteria.

Approximately 9099% of the soluble BOD as well as4050% of the soluble COD were removed by themembrane.

Membrane ux was relatively low with satisfactoryperformance achieved at 5.87.2 US gpd/ft 2 .

Orthophosphates removal across the membrane wasminimal varying between 0.5 and 2.6 mg/L, thusnecessitating chemical addition to meet the phospho-rus criteria.

Ammonia decreased, while nitrates, and nitritesincreased across the membrane, indicating that bio-logically mediated nitrication occurred in the mem-brane tank despite the short hydraulic retention timeof 5090 min.

For this particular wastewater, the lterability of thebiological sludges was fairly low and did not correlatewell with biomass concentrations. Accordingly, oper-ation of the bioreactor at low MLSS concentrationsin the range of 20004000 mg/L, may be required to

sustain satisfactory membrane performance withoutsignicantly increasing cleaning frequency.

Contrary to common applications of membraneswherein high biomass concentrations are employed,in this case the combination of biological treatmentat low biomass concentrations in conjunction withmembrane separation yielded excellent performancemeeting stringent criteria.

Acknowledgements

The analytical assistance provided by the LeamingtonWater Pollution Control Plant and Ontario Clean WaterAgency (OCWA) is greatly appreciated.

References

APHA, 1985. Standard Methods for the Examination of Water andWastewater, sixteenth ed. American Public Health Association,Washington, DC.

Cantor, J., Sutton, P.M., Steinheber, R., Novachis, L., 2000. IndustrialBiotreatment: Plant capacity expansion and upgrading through

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0 500 1000 1500 2000 2500 3000 3500

MLSS (mg/L)

B e

f o r e

B P V a c u u m

( " H g

)

Group 1 - 3.5 US gpmGroup 2 - 2.5 US gpmGroup 3 - 2.0 US gpmGroup 4 - 3.8 US gpm

Fig. 10. Relationship between before BP vacuum and MLSS.



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Krauth, K., 1996. Sustainable sewage treatment plantsapplication of nanoltration and ultraltration to a pressurized bioreactor. WaterSci. Technol. 34 (34), 389394.

Kuemmel, R., Robert, J., Loewen, A., 2000. Improvement of wastewater treatment, water recycling, and efficiency in the dairyindustry by combined membrane processes. Paper presented atWEFTEC Conference, Anaheim, California.

Livingston, A.G., Arcangeli, J., Boam, A.T., Zhang, S., Marangon,M., Freitas dos Santos, L.M., 1998. Extractive membrane bio-reactors for detoxication of chemical industry wastes: processdevelopment. J. Membrane Sci. 151 (1), 2944.

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Reemtsma, T., Zywicki, B., Stueber, M., Kloepfer, A., Jekel, M., 2002.Removal of sulfur-organic polar micropollutants in a membranebioreactor treating industrial wastewater. Environ. Sci. Technol.36, 11021106.

Rozzi, A., Malpei, F., Bianchi, R., Mattioli, D., 2000. Pilot-scalemembrane bioreactor and reverse osmosis studies for direct reuse of secondary textile effluents. Water Sci. Technol. 41 (1011), 189195.

Schroder, H., 2002. Mass spectrometric monitoring of the degradationand elimination efficiency for hardly eliminable and hardlybiodegradable polar compounds by membrane bioreactors. WaterSci. Technol. 46 (3), 5764.

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