Biomass characteristics of two types of submerged membrane bioreactors for nitrogen removal from was

Biomass characteristics of two types of submerged membrane bioreactors for nitrogen removal from wastewater

Zhihua Liang,Atreyee Das,Daniel Beerman,Zhiqiang Hu *

Department of Civil and Environmental Engineering,University of Missouri,E2509Lafferre Hall,Columbia,MO 65211,USA

a r t i c l e i n f o

Article history:

Received 27December 2009Received in revised form 3March 2010

Accepted 8March 2010

Available online 17March 2010Keywords:

Membrane bioreactor Alternating anoxic/aerobic Nitrifying bacterial activity Microbial community structure qPCR

a b s t r a c t

Biomass characteristics and microbial community diversity between a submerged membrane bioreactor with mixed liquor recirculation (MLE/MBR)and a membrane biore-actor with the addition of integrated ?xed bio?lm medium (IFMBR)were compared for organic carbon and nitrogen removal from wastewater.The two bench-scale MBRs were continuously operated in parallel at a hydraulic retention time (HRT)of 24h and solids retention time (SRT)of 20d.Both MBRs demonstrated good COD removal ef?ciencies (>97.7%)at incremental in?ow organic loading rates.The total nitrogen removal ef?cien-cies were 67%for MLE/MBR and 41%for IFMBR.The recirculation of mixed liquor from aerobic zone to anoxic zone in the MLE/MBR resulted in higher microbial activities of heterotrophic (46.96mg O 2/gVSS h)and autotrophic bacteria (30.37mg O 2/gVSS h)in the MLE/MBR compared to those from IFMBR.Terminal Restriction Fragment Length Poly-morphism analysis indicated that the higher nitrifying activities were correlated with more diversity of nitrifying bacterial populations in the MLE/MBR.Membrane fouling due to bacterial growth was evident in both the reactors.Even though the trans-membrane pressure and ?ux pro?les of MLE/MBR and IFMBR were different,the patterns of total membrane resistance changes had no considerable difference under the same operating conditions.The results suggest that metabolic selection via alternating anoxic/aerobic processes has the potential of having higher bacterial activities and improved nutrient removal in MBR systems.

1.Introduction

Membrane bioreactor (MBR)technology is increasingly applied in wastewater treatment plants (WWTPs)as wastewater ef?uent discharge permits become progressively stringent and the demand for clean water keeps rising.The advantages of using MBR technology for wastewater treatment include:(1)capability of dealing with high volumetric organic loading rates and therefore small reactor volume because of increased biomass concentration in the bioreactor (Ben Aim and Semmens,2003;Chu et al.,2008;Huang et al.,2001);(2)

improved ef?uent water quality for water reuse since bacteria and suspended solids larger than the membrane pore size are retained by membrane (Krauth and Staab,1993;Pollice et al.,2008;Rosenberger et al.,2002);and (3)complete and stable nitri?cation owing to the retention of slow-growing nitrifying bacteria at a prolonged solids retention time (SRT)(Davies et al.,1998;Li et al.,2006;Yoon et al.,2004).

Traditionally MBRs have poor nitrogen removal because of the intensive aeration presented in the system (Kimura et al.,2008;Patel et al.,2005).Recent research efforts have been directed towards improved nitrogen removal by using modi?ed

*Corresponding author .Tel.:t1(573)8840497;fax:t1(573)8824784.E-mail address:huzh@https://www.360docs.net/doc/bf11632926.html, (Z.

Hu).

A v a i l a b l e a t w w w.s c i e n c e d i r e c t.c o m

j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /w a t r e s

w a t e r r e s e a r c h 44(2010)3313e 3320

reactor con?gurations such as baf?ed membrane bioreactors (Kimura et al.,2008)and modi?ed Ludzack e Ettinger(MLE)type MBR(MLE/MBR)systems(Abegglen et al.,2008;Song et al.,2003). Through anoxic/aerobic sequencing or simultaneous nitri?ca-tion/denitri?cation,more than77%of total N in wastewater can be removed(Abegglen et al.,2008;Kimura et al.,2008).

The effect of bioreactor con?gurations and operating conditions on the performance and biomass characteristics of MBR systems is a subject to be studied.MLE type MBR systems coupled with ozonation to reduce sludge reproduction present slightly better nutrient removal(70%total N removal ef?-ciency)performance than without sludge ozonation,possibly due to additional carbon source provided by ozonation for denitri?cation(Song et al.,2003).In a pilot-scale MBR system, consistently excellent ef?uent quality was observed in the test range of F/M ratio between0.34and1.41gCOD/gVSS d while the membrane fouling rates appeared to be positively corre-lated with the F/M ratio and the concentration of soluble microbial products(Trussell et al.,2006).In another study, a moving bed membrane bioreactor(MBMBR)exhibited better total nitrogen removal ef?ciencies(>70%)than those of a conventional MBR at the same operating conditions although membrane fouling became signi?cant in the MBMBR due to the formation of a thick and dense cake layer on the membrane (Yang et al.,2009).

A recent study of nitri?cation rates in conventional and membrane-assisted enhanced biological phosphorus removal(EBPR)processes also demonstrated that the speci?c nitri?cation activities from the conventional EBPR process can be15e75%greater than those from regular membrane process under identical operating conditions(Monti and Hall, 2008).These results indicate that MBR based operations could alter the nitri?cation kinetics of conventional biolog-ical nutrient removal processes.For instance,the speci?c oxygen uptake rate(SOUR)of the biomass from the submerged micro?ltration MBR was4.3mg O2gà1MLSS hà1, higher than that of nano?ltration MBR(2.9O2gà1MLSS hà1) at the same solids retention time(80d)although microbial diversity analysis using denaturing gradient gel electropho-resis(DGGE)indicated no signi?cant difference between the MBRs(Choi et al.,2007).More information on the sludge characteristics and microbial community structure of the modi?ed MBR systems is needed to better understand the reactor performance and associated bacterial activity/pop-ulation and membrane fouling for optimal MBR design and operation.

A major hypothesis of this study was that metabolic selection via alternating anoxic/aerobic processes(Grady et al.,1999)in the MBR systems resulted in improved nutrient removal,higher bacterial activities and less biofouling.The objective of the study was to compare two modi?ed MBR systems(integrated?xed-?lm MBR and MLE/ MBR)using the same type of membrane module with respect to their system performance(e.g.,nitrogen removal),biomass characteristics,microbial activity and nitrifying bacterial community structure at a de?ned solids retention time(SRT). In addition,the membrane?ux and the total membrane resistance of the two types of MBRs at a constant hydraulic retention time(HRT)were compared to assess the extent of biofouling in the two systems.2.Materials and methods

2.1.Reactor operation

Two lab-scale submerged membrane bioreactors having the same type of membrane module with identical reactor volume (7.2L)were constructed(Fig.1).The membrane modules used for both MBRs were ZeeWeed hollow?ber membrane from Zenon Environmental Systems Inc.The membrane hollow ?ber had a nominal pore size of0.1m m and a total membrane surface area of0.047m2per module.One MBR was divided into anoxic,aerobic and settling chambers by glass baf?es to introduce alternating anoxic/aerobic conditions(hereafter referred to as MLE/MBR).The effective volumes of the anoxic, aerobic chambers and the clari?er were1.8,3.6and1.8L, respectively.The other MBR called integrated?xed-?lm MBR (IFMBR)was divided into two chambers:reaction chamber (5.1L)and settling chamber(2.1L).A bio?lm support plastic medium(AqWise Biomass Carrier,Siemens Water,WI)was added to the IFMBR to occupy50%volume of the reaction chamber.The dimension of biomass carrier was10?10mm, diameter?height.The density of the carriers was0.98g/cm3 and the effective speci?c surface area was600m2/m3.

The MBRs were operated in parallel at a target SRT of20d and a HRT of1d.The bioreactors were inoculated with 2000mL seed activated sludge from a local municipal waste-water treatment plant(Columbia,MO).The synthetic waste-water mainly containing nonfat dry milk powder with

a chemical oxygen demand(COD)concentration of500mg/L,

51.7mg/L TN,30mg/L NH4te N and6mg/L total P was used as the in?uent feed.From day0to day65,the in?uent COD was maintained at about300mg/L to evaluate the treatment of low strength wastewater.The composite feed also contained the following micronutrients/L:44mg MgSO4,14mg CaCl2?2H2O, 2mg FeCl2?4H2O, 3.4mg MnSO4$H2O, 1.2mg(NH4)6Mo7O24$ 4H2O,0.8mg CuSO4,and1.8mg Zn(NO3)2$6H2O.To support microbial growth and control membrane fouling,coarse bubble aeration was provided in the reactors through the membrane module’s built-in ori?ce connected by tubing to an air pump at a constant?ow-rate of8L/min.The permeate was extracted continuously by imposing on the membrane a negative pressure(indicated from trans-membrane pres-sure,TMP)via a?xed speed suction peristaltic pump.

In?uent and permeate water quality parameters such as NH4te N,NO3àe N,NO2àe N,COD,biomass properties including mixed liquor suspended solids(MLSS)and sludge volume index(SVI)were measured in duplicate following the Stan-dard Methods(APHA,1998).

2.2.Microbial activities

Autotrophic and heterotrophic activities of microorganisms in the reactors inferred from speci?c oxygen uptake rates(SOUR) due to ammonia oxidation and acetate oxidation,respectively, were measured separately using a batch extant respirometric assay(Hu et al.,2002).Aliquots(60mL)of the sludge collected from MLE/MBR or IFMBR were aerated with pure oxygen before being transferred to the respirometric bottles,and then tightly capped with no headspace.At a predetermined time,an

w a t e r r e s e a r c h44(2010)3313e3320 3314

aliquot of substrate (10mg N/L NH 4te N or 20mg/L COD in acetate)was added using a 10m L glass syringe.A decrease in the dissolved oxygen (DO)level in the respirometric vessel was measured by a DO probe (YSI Model 5300A,Yellow Springs,OH)and continuously monitored at 4Hz by an interfaced personal computer.The oxygen uptake rate was calculated based on a linear regression analysis because a zero-order reaction was observed for a long period of time.

2.3.Nitrifying bacterial community analysis

Terminal Restriction Fragment Length Polymorphism (T-RFLP)was used to analyze nitrifying bacterial community in the MBRs based on the known 16S rRNA genes of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria as described in a previous study (Siripong and Rittmann,2007).DNA was extracted from 5mL of mixed liquor in each bioreactor using Ultraclean Soil DNA Isolation Kit (Carlsbad,CA).All primers were synthesized by Integrated DNA Technologies (Coralville,IA).A ?uorescent dye,6-FAM,was incorporated into the DNA fragment in ?uorescence-labeled primers.Considering the

low concentration of DNA from the nitri?ers,we ampli?ed DNA from the 16S rRNA genes of ammonia-oxidizing bacteria (AOB)and nitrite-oxidizing bacteria (NOB)by a nested PCR,using the universal primers 11f and 1492r to produce an initial increase in template concentration.This was followed by the speci?c ampli?cation of the nitri?er genes (Siripong and Rittmann,2007).

The universal ampli?cation of the 16S rRNA gene was conducted using a PCR DNA thermocycler (Eppendorf,West-bury,NY).This was followed by puri?cation of the PCR amplicons using the Wizard SV Gel and PCR Clean-Up System (Madison,WI).The thermal pro?le used for the universal ampli?cation was:5min at 95 C;35cycles of 30s at 95 C,30s at 55 C,and 45s at 72 C;and a ?nal elongation for 10min at 72 C.The thermal pro?le used for the nitri?er-speci?c ampli?cation was:5min at 95 C;35cycles of 90s at 95 C,30s at 60 C,and 90s at 72 C;and a ?nal elongation for 10min at 72 C.The PCR products were puri?ed again and digested with MspI restriction endonuclease (Promega,Madison,WI)at 37 C for 3h as described before (Siripong and Rittmann,2007).The digested PCR products were run through an ABI 3730

Pump

Fig.1e Schematic diagram of the experimental set up:(A)MBR and (B)IFMBR.

w a t e r r e s e a r c h 44(2010)3313e 3320

3315

DNA Analyzer (Applied Biosystems,Foster City,CA)in DNA Core Facility at the University of Missouri.An internal lane standard that ranges from 20to 600bases (Genescan 600LIZ)was added to each sample for precise sizing of each fragment by adjusting for lane to lane loading variation.

2.3.1.Quantitative PCR assays

To determine the fraction of AOB in biomass from the two MBRs,two independent quantitative real-time PCR (qPCR)assays were developed by quantifying the amount of AOB 16S rRNA and genes encoding the active site subunit of the enzyme ammonia monooxygenase (AmoA).

To determine the amount of AOB 16S rRNA genes,two forward primers CTO 189A/B and CTO189C,one reverse primer RT1r and the TaqMan probe TMP1(Table 1)were used as described previously by Hermansson and Lindgren (2001).The total volume of the PCR Mix was 12.5m L TaqMan Universal PCR Master Mix (Applied Biosystems,New Jersey,USA)containing 20m mol of a 2:1ratio of primers CTO 189fA/B (0.25m L)and CTO 189fC (0.125m L)and 20m mol of the reverse primer RT1r (0.375m L),3.125pmol of TaqMan probe TMP1and 5m L of the DNA sample.The PCR program for AOB 16S rRNA quanti?cation included 2min at 50 C,10min at 95 C,40cycles of 30s at 95 C and 60s at 60 C.For comparison purposes,the amount of total bacterial 16S rDNA was deter-mined by using primers 1055f and 1392r (Table 1).The TaqMan probe 16S Taq1115was modi?ed from the 1114f primer.The PCR Mix had a total volume of 25m L consisting of TaqMan Universal PCR Master Mix,20m mol primers,10m mol TaqMan probe and 5m L of the DNA sample.The PCR program for total bacterial quanti?cation was 2min at 50 C,10min at 95 C,45cycles of 30s at 95 C,60s at 50 C,and 45s at 72 C.

The bacterial amoA gene was also quanti?ed with SYBR òGreen PCR Master Mix (Applied Biosystems,Warrington,WA,UK)as a ?uorescent dye,using primers amoA -1F and amoA -2R.Each reaction was performed in a 25m l volume containing 10ng sample DNA,0.2mg mL à1BSA,20m mol of each primer and 12.5m l of SYBR òGreen PCR Master Mix.PCR cycling conditions were as follows:15min at 95 C,45cycles of 1min at 95 C,1min at 54 C,1min at 72 C,followed by ?nal extension reaction for 10min at 72 C and a dissociation step at 95 C for 15s.PCR product speci?city was con?rmed on 2%agarose gels showing speci?c product bands at the expected size of ca.500bp.

All qPCR assays were performed using three replicates per sample,and all PCR runs included control reactions without

template.The gene copy numbers were calculated by comparison of threshold cycles obtained in each PCR run with those of known standard DNA concentrations.Real-time PCR assays for bacterial 16S rRNA and AOB 16S rRNA gene were performed on a 7500Real-Time PCR System (Applied Bio-systems,CA)equipped with a ?uorescence detector and 7500SDS system software version 1.4(Applied Biosystems,CA).The threshold cycle (CT)of each PCR reaction was determined automatically by detecting the cycle at which the ?uorescence exceeded the calculated threshold.

Results and discussion

3.1.

Reactor performance

The in?uent and ef?uent COD concentrations in the two types of MBRs during the study period were presented in Fig.2.COD removal ef?ciency was not affected by increasing in?uent organic loading rate from day 65onwards.At the average in?uent COD concentration of 516?80mg/L,the ef?uent COD concentrations were 9.3?9.3mg/L for the MLE/MBR and 12?14mg/L for the IFMBR systems,respectively,with an average COD removal rate of 98.2and 97.7%,respectively.There was no signi?cant difference of ef?uent COD concen-tration between the MLE/MBR and IFMBR system (ANOVA,a ?0.05,P ?0.43).

The modi?ed MBRs demonstrated excellent NH 4te N removals (removal ef?ciency >96%).The average ef?uent NH 4te N concentrations of the MLE/MBR and IFMBR were 0.88and 1.36mg/L,respectively.There was no signi?cant difference

Fig.2e In?uent and ef?uent COD concentrations in the MLE/MBR and IFMBR systems during the period of study.

w a t e r r e s e a r c h 44(2010)3313e 3320

3316

of ef?uent NH4te N concentration between the two MBRs (ANOVA,a?0.05,P?0.33).In contrast,the ef?uent total N concentration of the IFMBR(average value?30.7mg/L N)was signi?cantly higher than that of the MLE/MBR(17.0mg/L N) (ANOVA,a?0.05,P<0.001)(Fig.3).Due to high?ow coarse bubble aeration necessary to provide the scouring force for membrane fouling control,no signi?cant bio?lm was formed on the surface of plastic media in the aerated reaction chamber. Therefore,limited nitrogen removal(41%total nitrogen removal compared to in?uent concentration)through simul-taneous nitri?cation and denitri?cation was achieved.In contrast,the total nitrogen removal ef?ciency reached67%for the MLE/MBR reactor,demonstrating the ef?ciency of mixed liquor recirculation and anoxic/aerobic sequencing in nitrogen removal.The result of total nitrogen removal ef?ciency in the MLE/MBR was consistent with that previously reported (68.7e70.4%)using the same type of MBR system(Song et al.,2003).

3.2.Microbial activity

The heterotrophic microbial growth rates inferred from SOUR measurements were46.96?7.59and30.77?6.58mg O2/gVSS h for MLE/MBR and IFMBR,respectively.The autotrophic SOURs of biomass in MLE/MBR and IFMBR were30.37?6.09mg O2/gVSS h and22.55?5.86mg O2/gVSS h,respectively.These values of heterotrophic and autotrophic activities were in the same range as previous studies at same SRT(Pollice et al.,2008). The heterotrophic and autotrophic SOUR rates of biomass in the MLE/MBR were statistically higher than those of biomass in the IFMBR(ANOVA,a?0.05,P<0.05).The higher heterotrophic and autotrophic activities of the MLE/MBR system were attrib-uted to the harsh alternating anoxic/aerobic conditions,which selected for populations with inherently faster growth rates (Dytczak et al.,2008).

3.3.Nitrifying bacterial community structure

T-RFLP analysis indicated the difference of nitrifying bacterial community structure in the two MBRs.In the MLE/MBR, Nitrosomonas was the dominant genus of ammonia-oxidizing bacteria while Nitrospira and Nitrobacter species were domi-nant among nitrite-oxidizing bacterial populations(Fig.4).In contrast,there was no substantial AOB population detected in the IFMBR and Nitrospira was the only NOB detected.Therefore,it appeared that the higher nitrifying activities might be correlated with more diversity of nitrifying bacterial populations in the MLE/MBR.

qPCR assays were applied to determine the concentration of total bacteria and AOB in the MBRs.Assuming the average 16S rDNA copies per genome in bacterial cells were3.6copies based on the average16S rDNA copies found in cultured bacteria(Harms et al.,2003),one copy16S rDNA per cell based on copies16S rDNA found in AOB Nitrosomonas and Nitro-sospira(Aakra et al.,1999;Montuelle et al.,1996)and one

copy Fig4e Nitrosomonas(161,271bp)was the dominant genus of ammonia-oxidizing bacteria with a small peak representing Nitrosospira(102bp)in the MLE/MBR(top panel);both Nitrobacter and Nitrospira were present in the MLE/MBR(middle panels).No considerable AOB population was detected in the IFMBR and Nitrospira(261,272bp)with a relatively lower number was the only NOB in the IFMBR (bottom panel).

Fig.3e Ef?uent total nitrogen concentrations from the

MLE/MBR and IFMBR systems during the period of study.

w a t e r r e s e a r c h44(2010)3313e33203317

AOB amoA gene per cell(Harms et al.,2003),the total bacterial concentrations were2.1?0.2?1012cells/L for the IFMBR and 1.74?0.07?1012(aerobic chamber)to2.7?0.3?1012cells/L (in?uent/anoxic chamber)for the MLE/MBR.These values are in the same order of magnitude as those obtained from acti-vated sludge samples from municipal WWTPs(Harms et al., 2003).The concentrations of AOB as determined using the independent AOB16S rDNA and amoA assays were similar at the order of magnitude around108cells/L for both bioreactors. The percentages of AOB populations within the total bacteria ranged from0.01to0.03%in the anoxic and aerobic chamber, respectively for the MLE/MBR and,up to0.005%for the IFMBR. These results are in the lower end of the reported values for the activated sludge samples obtained from the bioreactors treating industrial wastewater(0.01e9.1%)(Kuo et al.,2006)or sediments receiving wastewater ef?uent(0.1e1.1%)(Urakawa et al.,2006).We further calculated the average ammonia oxidation rate using the measured ammonia concentrations and AOB population,assuming that ammonia is removed by both assimilation into cells for cell growth and by autotrophic ammonia oxidation by AOB(Harms et al.,2003).For MLE/MBR, the mean ammonia-oxidizing activity based on the AOB16S rDNA gene copies was169fmol/h/cell and365fmol/h/cell based on amoA gene copies.These values are about4to9-fold higher than the highest reported value(43fmol/h/cell)for the activated sludge samples obtained from a municipal waste-water treatment plant(Daims et al.,2001).These results indicated that other microorganisms that could be involved in ammonia oxidation(e.g.,ammonia-oxidizing archaea)might not be detected by the AOB16S rDNA or amoA gene based qPCR assays.Further research is needed to determine other microorganisms involved in ammonia removal in the MBRs.

3.4.Membrane?ux and total membrane resistance

Membrane fouling inferred from the change of membrane?ux was evident in both the reactors.The change of trans-membrane pressure(TMP)after membrane cleaning exhibi-ted similar trend in the MLE/MBR and IFMBR:an initial rapid increase followed by a slow increase of TMP with time (Fig.5A).The TMP rise in the MLE/MBR was faster than that in IFMBR during the initial rapid increase phase.The time required to end the stage of a fast increase of TMP for MLE/ MBR(9h)was much shorter than that for IFMBR(97h).At the end of this phase,the TMP of IFMBR was1.5times higher than that of MBR.The increase of TMP during membrane operation

is commonly attributed to the cake layer formation on the membrane surface(Chang et al.,2002).The TMP pro?les and ?ux values are also correlated with different biomass char-acteristics in membrane fouling(Le-Clech et al.,2006).Both the reactors were designed to have identical suction force at the?xed speed of peristaltic pumps for permeate collection and identical shearing force on the membrane for fouling control and sludge aeration.Hence,other factors such as the difference in biomass characteristics(e.g.hydrophobicity, surface charge,and extracellular polymeric substances or EPS) of the MLE/MBR and IFMBR might count for the large TMP difference and corresponding?ux difference(Le-Clech et al., 2006).

Interestingly,the sludge of IFMBR had a better settling property(Fig.6)than that of the MLE/MBR with a correspond-ing sludge volume index(SVI)value of75mL/g(IFMBR)and 113mL/g(MLE/MBR),indicating that the sludge in both the reactors had good settling properties.Microscopic observa-tions con?rmed that little?lamentous bacteria were detected in both the reactors(data not shown).The better sludge settling property of IFMBR could be attributed to the presence of porous support media,which support attached growth and provide a settling base to increase the?oc size.Further studies are needed to assess the relationship between sludge settling property,EPS concentration,cake layer formation and TMP change at different operating periods.

Fig.5e The change of trans-membrane pressure(A),?ux (B)and total membrane resistance(C)of the same type of membrane module in the MLE/MBR and IFMBR after membrane cleaning.

w a t e r r e s e a r c h44(2010)3313e3320 3318

The?ux pro?les of the MLE/MBR and IFMBR showed the same trend of?ux decrease with time(Fig.5B).During the stage of cake layer formation(corresponding to a rapid TMP increase),the?uxes of the MLE/MBR and IFMBR were in the same range.Thereafter,the?ux of the MLE/MBR was about1.5 times lower than that of IFMBR(Fig.5B.Data of the total membrane resistance,de?ned as the ratio of TMP to?ux,was presented in Fig.5C).There was no statistically signi?cant difference of the total membrane resistance between the two types of modi?ed MBRs(ANOVA,a?0.05,P?0.57).As the total resistance consists of intrinsic membrane resistance, reversible cake resistance and irreversible fouling resistance (Chang et al.,2002),at the beginning of membrane operation the intrinsic membrane resistance were around1.0Et13mà1 for both the MBRs.The total membrane resistance increased thereafter,likely due to cake formation and biofouling.The patterns of changes in total membrane resistance suggested that under the similar operating conditions with the same type of membrane materials the fouling resistance variations were not considerably different between the MLE/MBR and IFMBR,although different stage of cake layer formation exis-ted due to the different biomass characteristics.

4.Conclusions

A parallel study of the two types of MBRs with respect to their COD and nitrogen removal,biomass characteristics,microbial activity,nitrifying bacterial community structure and membrane fouling at the constant SRT yielded the following conclusions:

Both the MLE/MBR and IFMBR systems showed excellent organic and ammonia removal ef?ciencies.The total N removal rates were67and41%for the MLE/MBR and IFMBR, respectively.

Compared to IFMBR,the heterotrophic and autotrophic microbial activities were higher in the MLE/MBR,which was attributed to the alternating anoxic/aerobic processes. T-RFLP analysis indicated that the higher nitrifying activi-ties were correlated with more diversity of nitrifying bacterial populations in the MLE/MBR.

Membrane fouling due to bacterial growth was evident for both the membrane reactors.Despite the considerably

different TMP and membrane?ux pro?les of the MLE/MBR and IFMBR,the patterns of the changes of total membrane resistance were not substantially different between the MLE/MBR and IFMBR.

The results indicate that metabolic selection via alternating anoxic/aerobic processes has the potential of having higher bacterial activities and improved nutrient removal in MBR systems.

r e f e r e n c e s

Aakra,A.,Utaker,J.B.,Nes,I.F.,1999.RFLP of rRNA genes and sequencing of the16S e23S rDNA intergenic spacer region of

ammonia-oxidizing bacteria:a phylogenetic approach.

International Journal of Systematic Bacteriology49(1),123e130. Abegglen,C.,Ospelt,M.,Siegrist,H.,2008.Biological nutrient removal in a small-scale MBR treating household wastewater.

Water Research42(1e2),338e346.

APHA,1998.Standard Methods for the Examination of Water and Wastewater.American Public Health Association,

Washington,DC.

Ben Aim,R.M.,Semmens,M.J.,2003.Membrane bioreactors for wastewater treatment and reuse:a success story.Water

Science and Technology47,1e5.

Chang,I.-S.,Le Clech,P.,Jefferson,B.,Judd,S.,2002.Membrane fouling in membrane bioreactors for wastewater treatment.

Journal of Environmental Engineering(New York,N.Y.)128

(11),1018e1029.

Choi,J.-H.,Lee,S.H.,Fukushi,K.,Yamamoto,K.,2007.

Comparison of sludge characteristics and PCR e DGGE based microbial diversity of nano?ltration and micro?ltration

membrane bioreactors.Chemosphere67(8),1543e1550. Chu,H.-Q.,Cao,D.-W.,Jin,W.,Dong,B.-Z.,2008.Characteristics of bio-diatomite dynamic membrane process for municipal wastewater treatment.Journal of Membrane Science325(1), 271e276.

Daims,H.,Purkhold,U.,Bjerrum,L.,Arnold,E.,Wilderer,P.A., Wagner,M.,2001.Nitri?cation in sequencing bio?lm batch reactors:lessons from molecular approaches.Water Science and Technology43,9e18.

Davies,W.J.,Le,M.S.,Heath,C.R.,1998.Intensi?ed activated sludge process with submerged membrane micro?ltration.

Water Science and Technology38(4e5),421e428.

Dytczak,M.A.,Londry,K.L.,Oleszkiewicz,J.A.,2008.Nitrifying genera in activated sludge may in?uence nitri?cation rates.

Water Environment Research80,388e396.

Ferris,M.,Muyzer,G.,Ward,D.,1996.Denaturing gradient gel electrophoresis pro?les of16S rRNA-de?ned populations

inhabiting a hot spring microbial mat community.Applied and Environmental Microbiology62(2),340e346.

Grady,C.P.L.,Daigger,G.T.,Lim,H.C.,1999.Biological Wastewater Treatment.Marcel Dekker,New York.

Harms,G.,Layton,A.C.,Dionisi,H.M.,Gregory,I.R.,Garrett,V.M., Hawkins,S.A.,Robinson,K.G.,Sayler,G.S.,2003.Real-time PCR quanti?cation of nitrifying bacteria in a municipal wastewater treatment plant.Environmental Science&Technology37(2), 343e351.

Hermansson,A.,Lindgren,P.E.,2001.Quanti?cation of ammonia-oxidizing bacteria in arable soil by real-time PCR.Applied and Environmental Microbiology67(2),972e976.

Hu,Z.,Chandran,K.,Grasso,D.,Smets,B.F.,2002.Effect of nickel and cadmium speciation on nitri?cation inhibition.

Environmental Science&Technology36(14),3074e3078. Huang,X.,Gui,P.,Qian,Y.,2001.Effect of sludge retention time on microbial behavior in a submerged membrane bioreactor.

Process Biochemistry36(10),1001e1006.

Fig.6e Sludge settling curves from the MLE/MBR and

IFMBR systems.

w a t e r r e s e a r c h44(2010)3313e33203319

Kimura,K.,Nishisako,R.,Miyoshi,T.,Shimada,R.,Watanabe,Y., 2008.Baf?ed membrane bioreactor(BMBR)for ef?cient

nutrient removal from municipal wastewater.Water Research 42(3),625e632.

Krauth,K.,Staab,K.F.,1993.Pressurized bioreactor with membrane?ltration for wastewater treatment.Water

Research27(3),405e411.

Kuo,D.H.W.,Robinson,K.G.,Layton,A.C.,Meyers,A.J.,Sayler,G.

S.,2006.Real-time PCR quanti?cation of ammonia-oxidizing bacteria(AOB):solids retention time(SRT)impacts during

activated sludge treatment of industrial wastewater.

Environmental Engineering Science23(3),507e520.

Le-Clech,P.,Chen,V.,Fane,T.A.G.,2006.Fouling in membrane bioreactors used in wastewater treatment.Journal of

Membrane Science284(1e2),17e53.

Li,H.,Yang,M.,Zhang,Y.,Yu,T.,Kamagata,Y.,2006.Nitri?cation performance and microbial community dynamics in

a submerged membrane bioreactor with complete sludge

retention.Journal of Biotechnology123(1),60e70.

Monti,A.,Hall,E.R.,https://www.360docs.net/doc/bf11632926.html,parison of nitri?cation rates in conventional and membrane-assisted biological nutrient

removal processes.Water Environment Research80,

497e506.

Montuelle,B.,Volat,B.,Torio-Fernandez,M.M.,Navarro,E.,1996.

Changes in Nitrobacter serotypes biodiversity in a river:

impact of a wastewater treatment plant discharge.Water

Research30(5),1057e1064.

Patel,J.,Nakhla,G.,Margaritis,A.,2005.Optimization of biological nutrient removal in a membrane bioreactor system.Journal of Environmental Engineering(New York,N.Y.)131(7),

1021e1029.

Pollice,A.,Laera,G.,Saturno,D.,Giordano,C.,2008.Effects of sludge retention time on the performance of a membrane

bioreactor treating municipal sewage.Journal of Membrane Science317(1e2),65e70.Rosenberger,S.,Kruger,U.,Witzig,R.,Manz,W.,Szewzyk,U., Kraume,M.,2002.Performance of a bioreactor with

submerged membranes for aerobic treatment of municipal waste water.Water Research36(2),413e420.

Rotthauwe,J.H.,Witzel,K.P.,Liesack,W.,1997.The ammonia monooxygenase structural gene amoa as a functional marker: molecular?ne-scale analysis of natural ammonia-oxidizing populations.Applied and Environmental Microbiology63(12), 4704e4712.

Siripong,S.,Rittmann,B.E.,2007.Diversity study of nitrifying bacteria in full-scale municipal wastewater treatment plants.

Water Research41(5),1110e1120.

Song,K.-G.,Choung,Y.-K.,Ahn,K.-H.,Cho,J.,Yun,H.,2003.

Performance of membrane bioreactor system with sludge

ozonation process for minimization of excess sludge

production.Desalination157(1e3),353e359.

Trussell,R.S.,Merlo,R.P.,Hermanowicz,S.W.,Jenkins,D.,2006.The effect of organic loading on process performance and membrane fouling in a submerged membrane bioreactor treating municipal wastewater.Water Research40(14),2675e2683.

Urakawa,H.,Kurata,S.,Fujiwara,T.,Kuroiwa,D.,Maki,H., Kawabata,S.,Hiwatari,T.,Ando,H.,Kawai,T.,Watanabe,M., Kohata,K.,2006.Characterization and quanti?cation of

ammonia-oxidizing bacteria in eutrophic coastal marine

sediments using polyphasic molecular approaches and

immuno?uorescence staining.Environmental Microbiology8

(5),787e803.

Yang,S.,Yang,F.,Fu,Z.,Lei,R.,https://www.360docs.net/doc/bf11632926.html,parison between

a moving bed membrane bioreactor and a conventional

membrane bioreactor on organic carbon and nitrogen

removal.Bioresource Technology100(8),2369e2374.

Yoon,T.I.,Lee,H.S.,Kim,C.G.,https://www.360docs.net/doc/bf11632926.html,parison of pilot scale performances between membrane bioreactor and hybrid

conventional wastewater treatment systems.Journal of

Membrane Science242(1e2),5e12.

w a t e r r e s e a r c h44(2010)3313e3320 3320