Membrane Separation Bioreactors For Wastewater Treatment
. , ·Crit,:cal Reviews in Environmental Science a/u} Technology, 30(1):1-48 (2000)Membrane Separation Bioreactors forWastewater TreatmentC. Visvanathan,1 R. Ben A;m, 2 and K. Parameshwaran 3lEnvironmental Engineering Program, Asian Institute of Technology, P.O. Box 4, KlongLuang, Pathumthani 12120, Thailand; Email: visu@ait.ac.th; 21nstitute National desSciences Appliquees de Toulouse, Complexe Scientifique de, Rangueil- 31 077, ToulouseCedex, France; 3Center for Membrane Science and Technology, The University ofNew South Wales, Sydney 2052, AustraliaABSTRACT: With continuing depletion of fresh water resources, focus has shifted more Lowardwater recovery, rense, and recycling, which require an extension of conventional wastewater treat menL technologies. Downstream external factors like stricter compliance requirements for wastewaterdischarge, rising treatment costs, and spaLial constraints necessitate renewed investigation of alter native lechnologies. Coupled with biological treatment processes, membrane technology has gainedconsiderable attention due to iLs wide range of applicability and the performance characteristics ofmembrane sysLems that have been established by various investigations and innovations during thelast decade. This article summ31izes research effons and presenLs a review of the how and why ofLheir development and applications. The focus is on appraising and comparing technologies on thebasis of their relati ve merits and demerits. Additional facts ar}d figures, especially regarding processparameters and effluent quality. are used to evaluate primary findings on these tcchnologics. Keyfactors such as {oading rates, retention time, cross-llow velocities, membrane types, membranefouling, and backwasbing. etc. are some of the aspects covered. Membrane applications in variousaerobic and anaerobic schemes are discllssed at length. However, the emphasis is on the use ofmembranes as a solid/liquid separator, a key in achieving desired effluent quality. Further, technol ogy development directions and possibilitjes are also explored. The review concludes with aneconomic assessmenL' of the technologies because one of the key technology selection criteria isfinancial viability.KEY WORDS: membrane bioreactor, membrane technology, solid/liquid separation, membrane airdiffusers, Inembrane fouling. backwashing. micro-porous membranes.I. INTRODUCTIONThe use of biological treatment can be traced back to the late nineteenthcentury. By the 1930s, it was a standard method of wastewater treatment (Rittmann,1987). Since then, both aerobic and anaerobic biological treatment methods havebeen commonly used to treat domestic and industrial wastewater. During thecourse of these processes, organic matter, mainly in soluble form, is converted into1064-3389/00/ .50 2000 by CRC Press LLC1
H2 0, CO 2 , NHt, CH 4 , NOi, NO] and biological cells. The end products differdepending on the presence or absence of oxygen. Nevertheless, biological cells arealways an end product, although their quantity vades depending on whether it isan aerobic or anaerobic process. After removal of the soluble biodegradable matterin the biological process, any biomass formed must be separated from the liquidstream to produce the required emuent quality. A secondary settling tank is usedfor the solid/liquid separation and this clarification is often the limiting factor ineffluent quality (Benefield and Randall, 1980).In recent years, effluent standards have become more stringent in an effort topreserve existing water resources. Recycling and reuse of wastewater for second ary purposes is on the rise due to dwindling natural resources, increasing waterconsumption, and the capacity limitations of existing water and wastewater con veyance systems. In both cases, achieving a high level of treatment efficiency isimperative.The quality of the final emuent from conventional biological treatment sys tems is highly dependent on the hydrodynamic conditions in the sedimentationtank and the settling characteristics of the sludge. Consequently, large volumesedimentation tanks offering several hours of residence time are required to obtainadequate solid/liquid separation (Fane et aI., 1978). At the sarne time, close controlof the biological treatment unit is necessary to avoid conditions that lead to poorsettleability and/or bulking of sludge. Very often, however, economic constraintslimit such options. Even with such controls, further treatment such as filtration,carbon adsorption, etc. are needed for most applications of wastewater reuse.Therefore, a solid/liquid separation method different from conventional methodsis necessary.Application of membrane separation (micro- or ultrafiltration) techniques forbiosolid separ'ation can overcome the disadvantages of the sedimentation tank andbiological treatment steps. The membrane offers a complete banier to suspendedsolids and yields higher quality effluent. Although the concept of an activatedsludge proc'ess coupled with ultrafiltration was commercialized in the late 1960sby Don-Oliver (Smith et aI., 1969), the application has only recently started toattract selious attention (Figure 1), and there has been considerable developmentand application of membrane processes in combination with biological treatmentover the last 10 years.This emerging technology, known as a membrane bioreactor (MBR), offersseveral advantages over the conventional processes currently available. Theseinclude excellent quality of treated water, which can be reused for industrialprocesses or for many secondary household purposes, small footprint size of thetreatment plant, and reduced sludge production and beller process reliability.The pUl1Jose of this monograph is to provide a comprehensive review ofmembrane bioreactor technology. The application of membranes in different stagesof biological treatment processes, the histOlical development of membrane bioreatOl's,2
and factors affecting the design and performance of MBR processes are discussed.A number of case studies for each type of major MBR application along with somecost information on MBR processes is also presented.II. FEATURES OF MEMBRANE APPLICATION IN BIOLOGICALWASTEWATER TREATMENTAs our understanding of membrane technology grows, they are being appliedto a wider range of industrial applications and are used in many new ways forwastewater treatment. Membrane applications for wastewater treatment can begrouped into three major categories (Figure 2): (1) biosolid separation, (2) biomassaeration, and (3) extraction of selected pollutants. Biosolid separation is, however,the most widely studied and has found full-scale applications in many countries(Table 1). Use of combined night-soil treatment and wastewater reclamation atplant scale operations in buildings in Japan are examples of some successfulapplications, and in these cases membrane-coupled technology is considered astandard process (Yamamoto aDd Urase, 1997). Solid/liquid separation bioreactorsemploy micro- or ultrafiltration modules for the retention of biomass for thispurpose. The membranes can be placed in the external circuit of the bioreactor orthey can be submerged direclly into the bioreactor (Figure 2a).Asymmetric membranes consist of a very dense top layer or skin with athickness of 0.1 to 0.5 ).1111, supported by a thicker sublayer. The skin can be placedeither on the outside or inside of the membrane, and this layer eventually definesthe characterization of membrane separation.3
TABLE 1Commercial Scale Solid/liquid Separation MBR PlantsCompanyRhone Poulenc-TechSepDorr OliverThetfort SystKubota :0Mitsui Petrochemical IndustriesZenon Env Inc.Dorr OliverMembratekSITAIIyonnaise des ntryType of omesticHuman excretaIndustrialIndustrialIndustrialLandfill leachateIndustying or methanogenic bacteria and this results in greater flexibility ofoperation.3. Compact Plant SizeVolumetric capacities are typically bigh because a high sludge concentrationcan be maintained independently of settling qualities. HRTs as low as 2 h havebeen satisfactorilY applied (Chaize and Huyard, 1991), and fluctuations on volu metric loading have no effect on the treated water quality (Chiemchaisri et aI.,1993). For example, sludge concentrations between 25 and 30 kg/m 3 have beenachieved regularly as opposed to the more common 4 to 6 kg/m3 in the conven tional aerobic process (Yamamoto and Win, 1991). Moreover, tlle higher turbu lence maintained within the mixed liquor to prevent the membrane from foulingal.so prevents the flocculation of biosolids and keeps them highly dispersed. Ananalysis on the floc size distribution of MBR sludge and conventional activatedsludge indicates that the floc size in the MBR (a number of samples from differentMBR plants were analyzed) are very much smaller than 100 /lm and concentl'atedwithin a small range. On the other hand, floc size from conventional activatedsludge processes varied from 0.5 to 1000 /lm (Zhang et aI., 1997). The smallerHocs from MBRs could stimulate a higher oxygen and/or carbon substratemass transfer and thus higher activity levels in the system. Zhang and co-workers(1997) also found that nitrification activities in MBR processes averaged 2.28 gNHrN/kg MLSS.h, which was greater than in conventional processes (0.95 gNHrNlkg MLSS.h). Also, there is an enormOUS saving in space with MBRsbecause there is no need for secondary settling devices and post-treatment toachieve reusable quality.4. High Rate DecompositionTreatment efficiency is also improved by preventing leakage ofundecomposedpolymer substances. If these polymer substances are biodegradable, they can bebroken down with a reduction in the accumu lation of substances within the9
".treatment process. On the other hand, dissolved organic substances with lowmolecular weights, which cannot be eliminated by membrane separation alone, canbe broken down and gasified by microorganisms or converted into polymers asconstituents of bacterial cells, thereby raising the quality of the treated water. Forexample, the permeate from microfiltration of screened raw sewage (feed averageBODs 230 mg/l) had an average BODs of 93 mg/l. This was mainly the solublepOltion of the influent BOD 5 , although it showed 99% removal of suspended solidsand 5.8 log removal of fecal coliforms (Johnson et al., 1996). In contrast, mostMBR studies indicate the effluent BOD 5 is below 5 mg/l (Parameshwaran andVisvanathan, 1998; Buisson et al., 1997; Trouve et aI., 1994). Due to the highbiomass concentration and the fact that bio-oxidation is an exothermic process,temperature increase can be maintained at the maximum activity lemperature level.Maximum growth rates are about five times higher than the activity commonlyobserved in activated sludge systems. Based on cubic meter of reactor volume,combining high activity with high biomass concentration results in conversionrates 10 to 15 limes higher than conventional conversion rates (Buisson et al.,1997), an especially useful feature in cold climates.5. Low Rate Sludge ProductionStudies on MBR indicate that the sludge production rate is very low (Table 2).Chaize and Huyard (1991) have shown that for treatment of domestic wastewater,sludge production is greatly reduced if the age is between 50 and 100 days. LowFIM ratio and longer sludge age in the reactor is generally used lo explain this lowproduction rate.Pradelie (1996) demonstrated that the viscosity of sludge increases with age,eventually limiting the oxygen transfer in the MBR system. Therefore, he recom mends limiting the MLSS concentrate to 15 to 20 gil for effective oxygen transfer.It was also .noted that with increased age there was greater difficulty in sludgedewaterability, which could be attributed to excess amount of cellular polymerformation (Parameshwaran, 1997; Erikson el aI., 1992).It is also anticipated that micrological activity can be modified with increasedsludge age, but little published information is available on the subject. The initialmicroscopic observation (Praderier, 1996; Pliankarn, 1996) on microorganismpopulation indicates that with increased sludge age, reduction in filamentousbacteria increased rotifers and nematodes.6. Disinfection and Odor ControlIn this membrane filtration process, the removal of bacteria and viruses can beachieved without any chemical addition (Pouet el aI., 1994; Langlais et aI., 1992;Kolega et aI., 1991). Because all the process equipment can be tightly closed, noodor dispersion occurs. Comparison of conventional biological processes andMBR is shown in Table 3 and depicts the advantages discussed above.10
TABLE 2Comparison of Sludge Production in Conventional Activated SludgeProcess (ASP) and MBR Process Treating Domestic WastewaterType ofProcessSRT (d)ASPASPASPMBRMBRMBR10-2014332525 50SludgeproductionRef.0.7-1 kg MLSS/kg BOD50.7 kg MLSS/kg BOD50.6 kg MLSS/kg 80050.53 kg MLVSS/kg BOD50.26 kg SS/kg BOD50.22 kg MLSS/kg BOD5Hsu and Wilson, 1992E.I.A,1994E.I.A, 1994Trouve et aI., 1994aTrouve et aI., 1994bTakeuchi et aI., 1990Wi th the exception of wastewater reuse, membrane separation acti vated sludge'processes have not been widely used. Obstacles to more widespread use include: High capital and operating costsCunent regulatory standards can be achieved by conventional treatment processLimited experience in use of membranes in these application areasLack of interest by the membrane manufacturersMembranes will only find greater application in the wastewater industry if theycan achieve the required regulatory standards or better at the same or less costTABLE 3,Comparison of Operating Data for Conventional, Extended Aeration ASP,and AS/UF Treatment ProcessesProcessesParametersSystem reactor volumeInfluent BODSystem MLSSOrganic loading rateVolumetric loading rateReactor dissolved oxygenSludge retention timeRe-circulation ratioHydraulic retention 50-10012-24Unit1m'g/Img/Ikg BOD/kg.MLSS.dkg BOD /m 3 .dmg/Id%hFrom Smith et aI., 1969.11
compared with present processes, or if regulations were to tighten further such thatconventional processes can no longer achieve the desired effluent quality.IV. FACTORS AFFECTING THE MBR PROCESS PERFORMANCEThe main aim of memhrane-coupled bioreactors is to improve the efficiencyof the biological process step such that high-quality effluent is obtained. Becausebiological treatment and membrane separation are rather distinct processes, thecombined MBR process is relatively complex. To optimize the MBR process,many parameters have to be considered. These include solid concentrations. sludgeage, and tbe hydraulic retention time (HRT) in the biological step as well as the fluxrate, material costs, and the energy cost of the membrane separation. The treatmentand disposal of the waste sludge also needs to be considered. Comparisons 'madeon the waste sludge properties of the conventional activated sludge process and theMBR process indicates that dewatering of MBR waste sludge is difficult comparedwith the conventional process. This has been attributed to higher organic mattercontent and excess production of extracellular polymers (Parameshwaran, 1997).As all these parameters are interrelated, optirnizatioll is complicated. For example,an increase in slUdge concentration can enhance the biological stage. However,when sludge concentration exceeds a certain limit, the penneation flux rapidlydeclines due to a dramatic rise in the viscosity of the sludge mixture (Pradelie,1996). An increase in sludge concentration can also affect the gas transfer efficiency, and the energy requirements for the aeration therefore increase will (Praderie,1996).Permeation nux of membrane filtration is affected by the raw materials of themembrane and its pore size as well as operational conditions such as the pressuredriving force, the liquid velocity/turbulence, and the physical properties of themixed liquo ' being filtered (Tables 4 to 6).A. Type of MembraneSelection of the membrane module plays an important role on the membraneflux achieved. Membranes can be categorized according to the materials used(organic or ceramic), membrane type (microfiltration or ultrafiltration), moduletype (plate and frame or tu bular or hollow fiber), filtration surface (inner skin orouler skin), as well as the module status (static or dynamic membranes). All arebeing tested and many combinations have been considered. There are, however,overlaps and omissions in the combinations considered largely due to poor communication among international researchers,The flux will vary depending on the combination considered. For example,submerged hollow fiber membrane modules (external skin) show the lowest fluxof 3.5 JJm 2 .h, while ceramic microfillers show the highest of 100 l/m2 .h (Tables 4lo 6). Smooth surface membranes (ceramic) offer more resistance to cake layer12
TABLE 4Characteristics and Operating Conditions of Aerobic MBR Process (Membrane in External Circuit)Membrane configurationMembrane malerialUF(plale andframe)Noncell uloseorganic-Pore size (Dalton/jlm).WFiltration area (m2 )Cross lIow velocity (m/s)Transmembrane pressure(kPa)Temperature (0G)MLSS' (kg/m3 )Flux (Um2 ,h)Frequency of cleanl ngReference15Smith el aI., 19691969IndustrialMembrane configurationUFhollow fiberOrganicMixed-liquor suspended solids.Unit (IIm2 astewater typeMembrane malerialPore size (Dallon/jlm)Filtration area (m2 )Cross flow velocity (m/s)Transmembrane pressure (kPa)Temperature (0G)MLSS' (kg/m')Flux (1/m 2 .h)Frequency or cleaningReferenceSyntheticDomesticWastewater type2140307.5-12.450Hare el aI.,1990--251/hAudic,1986UF(plate andframe)Polysulfonelcellulose50,000MF(hollow 93.7:t 0.880-100-205-40-Chaize andHuyard, 72190-39030-3820-2823-701/hSalo and Ishi, Krauth and 38520-800.12.2-3.6200-25020304.8-11.420Suwaet aI., 1992Bailey1994-Trouveel aI., 1994cSour vegetablecanningUF plateand framePolysulfone1-5150-400MF/UFMullerel al.,1995Ice amic0.20.06-1025474024LObbeckeel aI., 1995Scott and uro,1993UF(tUbular)276-4045LObbeckeet aI., 1995
TABLE 5Characteristics and Operating Conditions of Aerobic MBR Process (Submerged Membrane)Wastewater typeMembrane configuration.j::oMembrane materialPore size {tIm)Fillration area (m')Transmembranepressure (kPa)Temperature (0C)MLSSa (kg/m 3 )Flux {11m 2 h)Frequency of ticSyntheticIndustrialDomestic0.940MFHollow fiberPolyethylene0.10.313MFHollow fiberPolyelhylene0.1-0.24-108MFHollow fiberPolyethylene0.10.2727MFHollow fiberPolyethylene0.10.680MFHollow fiberPolyethylen e0.10.640MFHollow fiberPolyethylene0.10.320-80MFHollow 51829-3112-146/14/27Takeuchiet aI., 1990Yamamotoel aI., 1991Benitez el aI.,et aI., 1995Parameshwaranet al., 1998MFHollow fiberPolyethylene0.1Yamamotoel aI., 1989Chiemchaisri.Chiemchaisriet al . 1992, 1993 et aI., 1992, 1993-
TABLE 6Characteristics and Operating Conditions of Anaerobic MBR ProcessWastewater typeMembraneconligurat,onWheat starchBreweryMFplale andUFUF(tllbular)kameMembrane malerialPore sl4e(Dallonl m)Filtralion area (m')Cross flowPulpHighandstrength SSpaperMFMF(hollow(P and F)DistilleryMFSyntheticIndustrialUF(P and F)UF(tubular)High slrengthMFUFUF2 x ne0.4540,0000.0120.4421.5150160PolysulfonePVDF3 x 10'0.1202 x 6.91537.5-113.315b-16.2512.510,0000.12 x 10'54--0.22velocity (m/s)Transmembranepressura (kPa).t1ITemperalure (0G)MlSS' (kg/m')Flux (Vm 2.h)Frequency 01 35--4525sJ6-7 min.1/2-3 eylrid andMiamiKitamura,Halland Ross,Razi,19911991el aI., 1992el aI., 1994Broockmann,et aI., 19911994et aI., 199519921994Mixed-liquor suSpended solids.Mixed-liquor volahle suspended solids, MLVSS.1995
Therefore, a solid/liquid separation method different from conventional methods is necessary. Application of membrane separation (micro-or ultrafiltration) techniques for biosolid separ'ation can overcome the disadvantages of the sedimentation tank and biological treatment
Membrane bioreactors with their great capabilities in semi-selective separation are promising options for making a breakthrough in lignocellulosic biorefinery processes. Therefore, in this thesis, different membrane modules and immersed membrane bioreactors (iMBRs) set-ups were developed and applied to take advantage of this long- matured
tivated sludge process and membrane technology has been recognized as a technology for advanced wastewater treatment. In membrane bioreactor technology, the membrane separation technology and bio- organic combin a-tion are new technologies of wastewater treatment. It utilizes membrane separation activated sludge and bio-
2. Bioreactors: 2.1 In-Process control (IPC), determination of plant cell growth: 2.2 Illumination 2.3. Types of bioreactors for plant cell suspension culture 2.3.1 Re- and multi usable bioreactors for plant cell suspension culture: 2.3.2 Single-use and disposable bioreactors for plant cells and tissue cultures
the bulk phase through the membrane into the permeate stream (Di et al., 2017). 3. Membrane Integration on chip It is crucial to apply a membrane (i.e. material and type) that best fits the targeted application. Membrane properties differ from one membrane to another and they greatly affect the overall membrane separation efficiency.
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A MEMBRANE SEPARATION TECHNIQUE NAGARAJU M Ph.D. Scholar Dept. of PHP&FE . Case study Membrane fouling Conclusion References 2 . MEMBRANE SEPARATION TECHNIQUES Membrane separation is a technology which selectively separates (fractionates) materials via pores . Pharmaceutical Industries Purification and concentration of products Automobile .
membrane separation technology and bioorganic combination of new wastewater treatment technology. It uti-lizes membrane separation activated sludge and bio chemical components of the reaction cell. Organic molecules . (MBR) treating chemical synthesis-based pharmaceutical wastewater. The pH of the MBR effluent was found in a narrow range of 6 .
MONDAY 11TH JANUARY, 2021 AT 6.00 PM VENUE VIRTUAL MEETING Dear Councillors, Please find enclosed additional papers relating to the following items for the above mentioned meeting which were not available at the time of collation of the agenda. Item No Title of Report Pages 1. FAMILY SERVICES QUARTERLY UPDATE 3 - 12 Naomi Kwasa 020 8359 6146 naomi.kwasa@Barnet.gov.uk Please note that this will .
