Treatment efficiency and membrane fouling of a lab-scale anaerobic membrane bioreactor treating dilute municipal wastewater

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1 Loughborough University Institutionl Repository Tretment efficiency nd membrne fouling of lb-scle nerobic membrne biorector treting dilute municipl wstewter This item ws submitted to Loughborough University's Institutionl Repository by the/n uthor. Cittion: NGA, T.T.... et l, Tretment efficiency nd membrne fouling of lb-scle nerobic membrne biorector treting dilute municipl wstewter. IN: Shw, R.J., Anh, N.V. nd Dng, T.H. (eds). Sustinble wter nd snittion services for ll in fst chnging world: Proceedings of the 37th WEDC Interntionl Conference, Hnoi, Vietnm, September 2014, 7pp. Additionl Informtion: This is conference pper. Metdt Record: Version: Published Publisher: c WEDC, Loughborough University Rights: This work is mde vilble ccording to the conditions of the Cretive Commons Attribution-NonCommercil-NoDerivtives 4.0 Interntionl (CC BY-NC-ND 4.0) licence. Full detils of this licence re vilble t: Plese cite the published version.

2 37th WEDC Interntionl Conference, Hnoi, Vietnm, 2014 SUSTAINABLE WATER AND SANITATION SERVICES FOR ALL IN A FAST CHANGING WORLD Tretment efficiency nd membrne fouling of lb-scle Anerobic Membrne Biorector treting dilute municipl wstewter T. T. V. Ng, V. D. Cnh, M. Kobyshi & S. Wkhr, Vietnm REFEREED PAPER 2067 The study ims to investigte the ppliction of nerobic processes coupled with membrne filtrtion for treting dilute municipl wstewter in Hnoi city (COD: mg/l, BOD 5 : mg/l, NH 4 - N:14-35 mg/l). A lb-scle Anerobic Membrne Biorector (AnMBR) with flt sheet, polyvinylidene fluoride membrnes (nominl pore size=0.4µm; totl filtrtion re=0.09 m 2 ) ws operted t different HRTs (48 hours, 36 hours, 24 hours, 12 hours, 8 hours nd 6 hours) for 560 dys with COD loding rtes up to 1.58 kg/m 3.d t room tempertures (from C). The biomss ccumulted reched 8gMLVSS/L by the end of the opertion period. No noticeble voltile ftty cids (VFAs) were detected regrdless of HRT vritions. The AnMBR system mintined reltively constnt TrnsMembrne Pressure (TMP). The results showed tht physicl retention of orgnics by the MF membrne plyed significnt role in chieving good nd stble performnce (removl rte for TSS: %, COD:70-90%, nd BOD: 72-88%) t wide rnge of tempertures. Introduction The nerobic tretment of low strength or dilute wstewters, such s domestic sewge, hs strted to ttrct much ttention, which t present is lrgely treted by erobic processes. Two mjor fctors re of concern with the ctivted sludge process, high sludge production nd high operting cost ssocited with ertion. Anerobic tretment offers mny benefits compred to erobic tretment such s low energy consumption, low sludge production, nd useful methne production (Bek et l., 2006). However, high biomss inventory nd long hydrulic nd solids retention times (SRT) re needed to chieve efficient tretment, prticulrly for dilute wstewter due to low biomss yield. In ddition, the effluent qulity of nerobic system is poorer thn the erobic one. These limittions hve prevented wide ppliction of nerobic technology for treting such wstewter. Therefore, different strtegies hve been developed to chieve long SRT in the rector such s nerobic contct process, nerobic filter, up-flow nerobic sludge blnket (UASB) rector, expnded grnulr sludge bed (EGSB), nerobic fluidized bed rector nd nerobic sequencing btch rector. Such rector configurtions mintin significntly longer SRT irrespective of HRT. The UASB nd EGSB processes hve been widely dopted mong ll these rector configurtions due to their superior performnce (Munritis nd Grigoropoulos, 2002). However, those systems require meticulous process control to chieve nd mintin sludge grnultion. Membrne coupled nerobic biorectors hve been pplied s one lterntive to cope with tretment chllenges. It could produce excellent effluent qulity in terms of suspended solids, chemicl oxygen demnd (COD) nd pthogen count, nd there is possibility of reuse nd recycling of the treted effluent for non-potble purposes. A typicl nerobic membrne biorector include: nerobic rector which ply role s digester nd membrne modules which cn either submerge or plce outside of the rector. The membrne modules work s brrier to retin ll of the biomss in the rector effectively nd help to mintin long sludge retention time (SRT) irrespective of short HRT. Therefore, the key dvntge of AnMBR system is to decouple hydrulic retention time (HRT) nd SRT in order not only to chieve high 1

3 sludge concentrtion in the system but lso to decrese rector size. This high-rte nerobic technology therefore my lso work with low strength wstewter which hve limittion with conventionl nerobic tretment due to slow growth rte of nerobic microorgnisms. Previous studies elucidted the potentil of AnMBR for the tretment of low strength wstewter t mbient temperture (Ho et l., 2007). Hnoi s sewerge network is combined system which ws initilly developed for urbn flooding prevention, nd then grdully receive municipl wstewter. Most urbn residents of Hnoi hve flush toilet with connection to the septic tnk from which the effluent (septic) is dischrged into sewers nd semi-open dringe cnls (e.g To Lich River, Kim Nguu River nd Set River) before flow into the Red River. As the collection system hve no Combined Sewge Overflows (CSOs) nd with lrge proportion of open cnls in the network, wet wether conditions re expected to hve big impct on the delivered wstewter composition nd flow. A recent study by World Bnk (2013) reveled tht BOD concentrtion of wstewter in collection network in Hnoi City vries lrgely from less thn 50 mg/l to bove 250 mg/l with the lower rnge ws observed in the riny seson (from July to September). The objective of this study is to investigte the ppliction of n nerobic membrne bio-rector for the tretment of dilute wstewter like municipl wstewter in Hnoi. The focus ws to investigte the optimum opertion prmeters to chieve good removl efficiency while minimize bckwshing or chemicl clening of the membrne modules. Methodology Lbortory experimentl setup A lbortory-scle nerobic membrne biorector (AnMBR) with 5L of working volume were run t mbient temperture (see Figure 1). The nerobic rector ws equipped with biogs collection system nd blower for keeping the sludge in the suspension nd membrne scouring effect using gs generted from the system. Other equipments re the TrnsMembrne Pressure (TMP) sensor nd dt logger, nd level sensors to control permete flow rte. A flt sheet, polyvinylidene fluoride (PVDF) with nominl pore size of 0.4µm nd totl filtrtion surfce re of 0.09 m 2 (supplied by KUBOTA Coopertion, Jpn) ws plced submerged inside the rector tnk. Figure 1. Schemtic of the lb-scle AnMBR 2

4 Feed wter ws tken from n equliztion tnk in Kim Lien Wstewter Tretment Plnt (WwTP). The rw wstewter qulity is shown in Tble 1. Seeding sludge (1.5 g/l) ws obtined from the mesophilic nerobic digester in Yen So municipl wstewter tretment plnt. The AnMBR system hs been operted for bout 560 dys t different hydrulic retention times. The verge HRTs for the entire system were 48 hours, 36 hours, 25 hours, 12 hours, 8 hours nd 6 hours. The membrne flux ws mintined t 0.03, 0.08, 0.12, 0.24 nd 0.36 m 3 /m 2.dy; nd orgnic loding rte ws therefore 0.31, 0.54, 0.95, nd 1.58 kgcod/m 3.dy respectively. There ws no sludge withdrwl except for the sludge nlysis. No chemicl clening ws ttempted during the entire experiment. Tble 1. Influent wstewter qulity in Kim Lien Wstewter Tretment Plnt Wter prmeters Rnge (mg/l) Averge (mg/l) BOD 5 (mg/l) COD (mg/l) TSS (mg/l) NH 4-N (mg N/L) TKN (mg N/L) T-P (mg/l) Ft nd Grese (mg/l) <30 - Alklinity (mg CCO 3/L) >100 - ph Smple nlysis DO, ph, temperture of feed, feed nd permete flowrte in nerobic tnk were mesured dily by portble meters. Wstewters nd mixed liquor were lso smpled on times per week nd nlyzed for chemicl oxygen demnd (COD), Biologicl Oxygen Demnd (BOD) totl nitrogen (T-N), mmoni nitrogen (NH 4 - N), dissolved oxygen (DO), Mixed Liquor Suspended Solid (MLSS) nd Mixed Liquor Voltile Suspended Solid (MLVSS), Voltile Ftty Acids (VFA). The concentrtions of COD, T-N, NH 4 -N, MLSS nd MLVSS were nlysed following Stndrd Method (APHA 2003) nd HACH methods with the pproprite kits nd DR 2800 Spectrophotometer (HACH Compny, USA). A wet-test gs meter ws used to mesure biogs. Gs composition nd methne gs ws nlyzed using test kit GAC25 (Jpn). Results nd discussions AnMBR performnce nd tretment efficiency t mbient temperture The rector hs been operted t different hydrulic retention times (48 hours, 36 hours, 24 hours, 12 hours, 8 hours, nd 6 hours) for period of bout 560 dys (from June 2012 to December 2013) t mbient room tempertures from C. Seeding sludge ws obtined from the nerobic digester in Yen So municipl wstewter tretment plnt. Since the digester hs just been put in opertion, MLSS concentrtion of the sludge ws still low, rnging from mg/l. The results showed tht sludge concentrtion hve been incresed stedily when incresing of feed flow rte over experimentl period nd reched 8000 mg/l t the end of the Phse 6 with the HRT is of 6 hours ccordingly. It lso indictes no sludge wshout in the system. Although ph in the AnMBR system ws not controlled, the ph levels in the rector did not ffect nerobic degrdtion of orgnics. VFAs profiles indicted tht cetic cid ws the predominnt VFA in the rector. Propionic nd butyric cid were not detected. Biologicl removl rte ws clculted by the difference between influent COD nd mixed liquor COD divided by the influent COD, while physicl removl rte ws the difference between the totl COD removl rte nd the biologicl removl rte. The concentrtion of COD in feed nd permete, removl efficiency re 3

5 Concentrtion (mg/l) efficiency shown in Figure 2 nd Tble 2. The COD level in the feed wter vried from less thn 50 mg/l to 470 mg/l, with verge vlue of 172mg/L. With this rnge of COD vlues, the feed wter could be clssified s low strength or dilute wstewter. As shown in the Figure 2, the removl rte for COD ws not good in the first 111 dys (R1, HRT 48 hours) with COD level in permete rnged up to 100 mg/l. This strt-up period could be considered n cclimtiztion stge for the microbil communities. In the next 180 dys (R2 nd R3), the COD removl rte remin unstble, rnging from 40% to 97%. During these periods, the MLSS concentrtion in the rector ws incresed but still low of less thn 4000 mg/l. When HRT chnged to 12 hours (R4), the removl rte become more stble, rnging from 70% to 90%. The COD removl rtes remined quite stble nd high in the next 85 dys with HRT of 8 hours. The MLSS concentrtion reched nerly 6100 mg/l t the end of Run 5. During these periods, COD in the permete vried but lwys less thn 100 mg/l with n verge of 39.2 mg/l. This vlue ws lower thn the dischrge limit of 50 mg/l (Ntionl Technicl Regultion for Domestic Wstewter Dischrge, QCVN14:2008/BTNMT, pplied for ctegory A - wter bodies using for domestic wter supply). The BOD concentrtion in the permete ws lso stble nd less thn 30 mg/l, indicting AnMBR system ws effective in the tretment of orgnic mtter. After dy 420 th, when the HRT chnged to 6 hours (R6), COD removl rte ws getting fluctuted nd COD in the permete ws higher thn the previous run, rnging up to 90 mg/l. Throughout the opertion t different hydrulic retention times, COD removl rtes from low vlue of 31.8% to high of 98.4 % could be obtined by the rector, with COD in the permete fluctuted but minly less thn 100 mg/l, which meet the dischrge stndrd QCVN14:2008/BTNMT, Ctegory B (wter bodies using for other wter usge purposes thn domestic wter supply). The system chieved the best nd stble removl efficiency for COD nd BOD t HRT of 8 hours, with COD in the permete stisfied the consent pplied for Ctegory A COD influent COD effluent COD removl rte R1 R2 R3 R4 R5 R6 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% dys Figure 2. COD profiles in feed nd permete nd removl efficiency in AnMBR system The chnge in the mmonium concentrtion in feed nd permete during opertion is shown in Tble 2. Rw wstewter hve mmonium concentrtions of bout 3-30 mgn/l. Ammonium concentrtion in permete showed higher rnge of bout 4-67 mgn/l, which ccount for 80-95% of TKN level. The results indicted tht mmonium is the min nitrogen component nd exists stbly in the nerobic environment. It lso showed tht AnMBR system is ineffective in treting nitrogen compounds in wstewter to chieve the current dischrge requirements, highlighting the need of further processes to reduce its residul nitrogen levels to meet stringent Vietnmese wstewter dischrge stndrds (QCVN14:2008/BTNMT). 4

6 Tble 2. Style: Summry of AnMBR opertion nd tretment efficiency Run R1 R2 R3 R4 R5 R6 Operting conditions HRT (hours) Opertion time (dys) ORL (kgcod/m 3.d) Flux (m 3 /m 2.d) Ambient temp ( o C) Effluent COD (mg/l) ( ) b ( ) b ( ) b ( ) b ( ) b ( ) b NH 4-N (mgn/l) (4-27) ( ) ( ) ( ) ( ) ( ) TKN (mg/l) ( ) ( ) T-P (mg/l) ( ) ( ) ( ) ( ) ( ) ( ) ph Biogs CH 4 content (%) Totl gs yield (L/d) ( ) b ( ) b ( ) b ( ) b ( ) b Note: : verge vlue b: (min-mx) vlue - : n/ Biogs genertion Biogs volume is collected nd mesured dily. Experimentl results showed tht very limited mount of gs could be collected t different hydrulic residence time (from 48 to 6 hours HRT). Therefore we could not estimte the CH 4 yield from system lthough the COD removl rte ws good nd stble. Experimentl results lso show tht verge methne content in some period of opertion time could chieved up to 30 % (Tble 2). The results showing mjority of biogs nd methne is lost from the system. The gs lekge control ctivities hve been tightly controlled in the system so the resons could be possibly: i) COD is utilized for sulphte reduction; nd/or ii) the gs dissolved in the wter nd hve been wshed out of the rector with permete through the membrne. This observtion lso coincides with findings from the previous studies (Ho nd Sung, 2010). The loss of methne from the system, especilly when lrge-scle 5

7 implementtion, not only to loss of biogs resources, but lso bring negtive effects to the climte since the globl wrming potentil of methne is round 21 times higher thn for CO 2 (Jeho nd Shihwu, 2010). TrnsMembrne pressure nd membrne fouling Throughout the experiment, the chnge in TrnsMembrne Pressure (TMP) cross the submerged membrne in the rector ws monitored by digitl vcuum guge. If the TMP vlue greter thn 20 kp, the membrne ws considered in the fouling mode nd the filtrtion of membrne ws stopped temporry for membrne clening. For the first 420 dys, the TMP ws lwys less thn 2 kp, nd no membrne clening ws required. But fter the HRT chnged to 6 hours, significnt jumps in the TMP vlues were observed severl times (see Figure 3) nd membrne clening with citric cid ws needed. It is noted tht membrne fouling occurred when the feeding tube ws clogged (on Dy 445 th, 480 th, 492 t h); the membrne then become exposed since the permete pump continued to operte. The increse of flowrte could be reson for these unstble conditions. After the system ws restrted with the clened membrne, the TMP returned to low vlue of less thn 2kP, indicting the clening process is effective. Over the course of 550 dys of opertion, the sludge concentrtion ws grdully incresed but still remined low (MLVSS ws less thn 8000 mg/l t the end of experiment period). One dvntge of n AnMBR system treting dilute municipl wstewter is it could mintin low suspended mixed liquor sludge concentrtion in the rector which help prevent membrne fouling. The results suggested tht HRT of 8 hours would be good since the system showed stble performnce with high removl rte of orgnic mtter while minimize membrne clogging. R1 R2 R3 R4 R5 R6 C2 C1 C3 Figure 3. Flux nd TMP vritions during the entire experimentl phse Note: C1, C2, C3 indicte membrne ws tken out for clening by citric solution (8-10%). Conclusions A lbortory-scle nerobic membrne biorector (AnMBR) ws run over for bout 560 dys to investigte the efficiency nd membrne fouling in treting low strength domestic wstewter in Hnoi. Results showed tht t different hydrulic retention time nd orgnic loding, high nd stble removl efficiency of orgnic mtter COD (70-90%) nd suspended solid TSS (95-98%) were chieved. Nitrogen content (TN, NH 4 -N) in the treted wter ws lmost fmilir with untreted sewge, suggesting nerobic processed coupled with membrne filtrtion does not remove nitrogen. In order to meet the current dischrge consent for domestic wstewter (QCVN14:2008/ BTNMT), the permete from AnMBR system needs to be undergone nitrifiction processes for mmoni removl. The results show tht AnMBR technology is suitble for treting domestic wstewter in Vietnm conditions. Treted wstewters were of good qulity nd fit with WHO guidelines for griculturl reuse (WHO, 2006). In ddition, AnMBR bring smll footprint dvntge which is very pplicble in smll urbn res nd hving difficulties in sludge tretment. 6

8 Acknowledgements This study ws conducted under the reserch project finnced by Vietnm Ministry of Eduction nd Trining (B ) References Arki, N., Hrd, H., Popultion dynmics of methnogenic biofilm consortium during strt-up period of nerobic fluidized bed rector. Wter Sci. Technol. 29, Bek, S.H., Pgill, K.R., Aerobic nd nerobic membrne biorectors for municipl wstewter tretment. Wter Environ. Res. 78, Ho J. Khnl, S.K. Sung, S., Anerobic membrne biorector for tretment of synthetic municipl wstewter t mbient temperture. Wter Sci. Technol. 55, Jeho H nd Shihwu S. Methnogenic ctivities in nerobic membrne biorectors (AnMBR) treting synthetic municipl wstewter. Bioresource Technology 101 (2010) Munritis I. D. nd Grigoropoulos S. G. Low-strength wstewter tretment using n nerobic bffled rector Wter Environment Reserch, 74 (2002) WHO (2006). WHO guidelines for the sfe use of wstewter, excret nd greywter. Volume 2: Wstewter use in griculture World Bnk (2013). Vietnm urbn wstewter reviews Contct detils Trn Thi Viet Ng 55 Gii Phong Rod, Hnoi, Vietnm Tel: Fx: Emil: ng.trn.vn@gmil.com 7