Indian Journal of Chemical Technology Vol. 15, November 2008, pp. 604-612 Submerged membrane bioreactor system for municipal wastewater treatment process: An overview Neha Gupta, N Jana & C B Majumder* Department of Chemical Engineering, Indian Institute of Technology, Roorkee 247667, India Email: email@example.com Received 27 September 2007; revised 20 September 2008 The submerged membrane bioreactor (SMBR) is a promising technology for wastewater treatment and water reclamation. This paper provides an overview of wastewater treatment in a submerged membrane bioreactor process with a special focus on municipal wastewater systems. SMBRs predict more than 95% organic removal with relative short hydraulic retention times (HRTs) of 1-8 h and NH3 removal of more than 90% in the municipal wastewater treatment. It achieves 30% more removal of organic matter than activated sludge process. The COD can be reduced by 95%. Nitrification was complete and up to 82% of the total nitrogen could be denitrified. Nitrification/ denitrification is sensitive to the feed quality, such as dissolved oxygen (DO) concentration, temperature, organic loads, inorganic/ organic compounds and pH. The feed water composition, membrane geometry/configuration, membrane materials, and hydrodynamic effects are responsible for membrane fouling. These drawbacks can be reduced by maintaining turbulent conditions, operating at critical flux, and by selection of a suitable fouling resistance membrane material. Membrane washing is performed when the permeability is less than 10% of initial permeability. The reactor performance and the stability of the process and the membrane capacity are also discussed. Details of the various methods for washing are also included. Keywords: Submerged membrane, Bioreactor, Wastewater treatment, Nirification, Hydrarulic retention time Recently developed and one of the most promising bioreactor (Fig. 1). For municipal applications, it is newer technologies is the membrane bioreactor expected that the hollow-fiber submerged (MBR) consisting of both a biological stage and a configuration would be useful for medium-to-large membrane module, a process involving membrane size plants. For small-to-medium size plants, plate- filtration combined with biological treatment. In a and-frame technologies would have an advantage, membrane bioreactor solid/ liquid membrane filtration whereas larger applications could be designed with occurs either within the submerged configuration or secondary/tertiary treatment followed by membrane externally through recirculation of bioreactor subject filtration and ultrafilteration. to pressure drop across the membrane. Submerged For the submerged configuration, membranes act in membrane bioreactor has been gaining lots of the aeration basin as filter and improve the biological attentions for wastewater treatment for its better treatment of the effluent. In the external system1, the effluent quality and lower sludge production amount of permeate flux varies between 50 and 120 compared to conventional activated sludge processes. L.h−1.m−2 and transmembrane pressure (TMP) is in the This paper presents an overview of the submerged range of 1-4 bar. In the submerged configuration, the membrane bioreactor technology suitable to treat the permeate flux is removed by suction which limits municipal wastewater. A comparison of the transmembrane pressure at about 0.5 bar. The membrane bioreactor to conventional wastewater submerged configuration appears to be more treatment processes has been made and the economical based on energy consumption for two characteristics of the submerged membrane bioreactor main reasons: no recycle pump is needed since are discussed. aeration generates a tangential liquid flow in the vicinity of the membranes. Furthermore, the operating Membrane module characteristics and comparison conditions are much more feasible in an external with an activated sludge system membrane bioreactor system because of the lower For a bioreactor, there are two types of values of the transmembrane pressure and tangential configurations for the membrane module: the velocities. Lesjean et. al.2 established design membrane can be placed either outside or inside the parameters of submerged membrane bioreactor GUPTA et al.: SUBMERGED MEMBRANE BIOREACTOR SYSTEM: AN OVERVIEW 605 Fig. 1 — Bioreactor system (a) submerged membrane, and (b) external membrane system (plate-and-frame and hollow fiber) which Table 1 — Design parameters of submerged membrane indicated that the hollow fiber membranes are bioreactors35 economical to use in submerged membrane bioreactor Membrane/module type Unit Plate-and- Hollow (Tables 1 and 2). Overall, the membrane bioreactor Frame fiber offers following advantages over the traditional (Flat sheet) (Bundles) activated sludge system: Net flux L/h.m2 15-25 20-30 Recommended MLSS G MLSS/L 10-15 10-15 (i) Energy consumption and capital costs for Fraction of aerobic volume % 30-10 10-40 fabrication and maintenance are lower for occupied by membrane submerged system. Energy consumption Kwh/m3 0.3-0.6 0.3-0.6 (membrane system only) (ii) The volume of the aeration tank can be reduced Cost m−2 High Medium since a higher concentration of biomass can be pH range - 1-12 2-11 stored in the bioreactor. T0 residence °C <60 <40 (iii) The traditional secondary clarifier is replaced by a membrane module. This module is more microbial process using porous carrier has been compact and the quality of rejected water is applied in view of high concentration culture of independent of the variations of sludge settling microbes5 or multifunctional microbial reaction such velocity. as simultaneous removal of carbonaceous and (iv) The membrane bioreactor allows the biomass nitrogenous substances from municipal wastewater6, 7. concentration to be higher than for traditional treatment plants. Jefferson et. al.3 utilized a Carbonaceous removal 20 g.L−1 biomass concentration while Yamamoto The membrane bioreactor is characterized by a et. al.4 utilized 30 g.L−1 in membrane bioreactor, complete retention of the biomass inside the whereas conventional processes utilize biomass bioreactor because of the use of membrane separation, concentration of less than 5 g.L−1 in order to which controls and increase the sludge retention time avoid problems inherent to settling of (SRT), and is a significant operational factor for the concentrated flocs. biological process being independent from the (v) The process can be run at high solids retention hydraulic retention time (HRT). High SRT enables time, which favours the development of slow one to increase the sludge concentration and the growing micro-organism and ultimately lead to applied organic load, thereby increasing the pollutant better removal of refractory organic matter and degradation. The organic decomposition rate making the system robust to load variations and decreases while the sludge retention time increases. A toxic shocks. small reduction in COD consumption is observed in the bioreactor with short sludge retention times. In the Biological activity of submerged membrane membrane process, COD removal remains constant at module 95% whatever may be the sludge retention time. Membrane processes have been extensively studied Dufresne et. al.8 were the first to undertake a for biological wastewater treatment. Retained comparative study of the traditional activated sludge 606 INDIAN J. CHEM. TECHNOL., NOVEMBER 2008 process (ASP) and the membrane bioreactor. This bioreactor system and aerated biological filters for study confirmed that the performance of membrane gray water recycling. Once again, the membrane bioreactor is better than that of conventional activated bioreactor system was found to be more efficient in sludge processes, especially for COD removal and the removal of biological oxygen demand, turbidity solid suspension separation. Jefferson et. al.9 carried and coli forms. out study of the performance of a membrane GUPTA et al.: SUBMERGED MEMBRANE BIOREACTOR SYSTEM: AN OVERVIEW 607 Table 2 — Examples of membrane types and characteristics used in submerged MBR system Membrane Membrane Pore size Wastewater Reference geometry characteristics (µm) Hollow MF- - Municipal 36 fiber polypropylene and synthetic Hollow MF 0.1 Municipal 20 fiber Hollow Zenon 0.1 Municipal 16 fiber MF- 0.2-0.4 17 polysulphone Flat MF- 0.4 Domestic 16 polyethylene Hollow MF- 0.1 Municipal 27 fiber polyethylene Plate MF- 0.4 Municipal 27 polyolefin Hollow Hydrophilic 0.1 Municipal 11 fiber polyethylene Hollow Polypropylene 0.1 Synthetic 12 fiber municipal Hollow Polyethylene 0.1 Municipal 15 fiber Plate and Polysulphone 0.4 Domestic 6 frame Polypropylene 0.5-5 Domestic 6 nonwoven Flat MF- 0.4 Municipal 37 hollow polyolefin fiber Hollow Polyethylene 0.1 Domestic 37 fiber Table 3 — Organic loading rates of different biological treatment processes of submerged membrane bioreactor32 Reactor Membrane Organic loading HRT Percentage Reference geometry rate kgBOD5 kgCOD (h) removal m−3 m−3 day−1 day−1 Activated Sequencing 0.08- - 12- 85-95 38 sludge batch 0.24 50 Process Conventional 0.32- - 4-8 85-95 38 0.64 Complete- 0.08- - 3-5 85-95 38 mix 1.92 High-rate 1.6-16 - 2-4 75-90 38 aeration Submerged Plate and 0.39-0.7 - 7.6 99 39 frame Hollow fiber 0.03- - 1 98-99 40 0.06 Plate and 0.005- - 8 98 14 frame 0.11 Hollow fiber - 1.5 0.5 87-95 13 Plate and - 0.45 8 88-95 41 frame 608 INDIAN J. CHEM. TECHNOL., NOVEMBER 2008 It has been reported that the membrane in a MBR to feed water quality determinants and operational contributes approximately 30% to the removal of parameters such as dissolved oxygen (DO), organic matter, this roughly equates to the insoluble temperature, organic loads, inorganic and organic fraction10, with the soluble fraction being removed via compounds, and pH. Nitrification can be maintained the active biomass. From Table 3, it can be seen that at higher rates with lower DO concentrations organic removal is often greater than 95% even with (<5 mgL−1). Denitrification, the reduction of nitrate to relatively short HRTs of 1-8 h (ref. 11-13). Organic various gaseous end-products such as molecular loading rates of MBRs are typically higher than nitrogen and nitrogen oxide, can proceed alongside conventional ASP, owing to the shorter HRTs nitrification if: (Table 3). Increasing organic loads to an ASP produces (i) Aeration is performed intermittently, increased heterotrophic activity, as organic matter (ii) Hydrodynamics are such that an anoxic area removal follows first-order kinetics, and this can be results, assumed to be the case in MBRs. Organic matters (iii) High organic loads are added allowing anoxic removal in MBRs appears not to be significantly micro-sites to develop within the flocs. affected by low temperatures, such as those between In aerobic MBRs denitrification can be achieved by 5 to 20°C, which may be due to the number of the addition of an anaerobic tank prior to the aeration heterotrophic bacteria in the biomass remaining tank, with conventional recycle17. constant, albeit with a decreased activity at lower temperatures14. Membrane modules fouling Membrane fouling is influenced by the chemical Nitrogen removal nature of the membrane and by the membrane Biological nitrogen removal has been done by operational parameters such as suction and bubbling. using membrane systems to concentrate the nitrifier in Hollow-fiber microfiltration membrane induces a reactor15,16. Small increase in the oxygen supply rate transmembrane pressure gradients, which have an and the improved nitrification rate17,18 facilitates the impact on flux rates. The magnitude of the flux growth of microbial flocs. In spite of such improved depends on the design of the hollow-fiber (length, nitrification capability in membrane processes, an internal diameter, permeability) and on the properties anaerobic denitrification reactor is still needed for of the cake. The structure of the membrane pores play achieving complete nitrogen removal. Nitrification a significant role on the fouling and the rougher the has been shown to be greater in an MBR than with a surface of the membrane faster the fouling by conventional ASP owing to the longer retention times attachment of colloids and the particulate matters on of the nitrifying bacteria (high sludge age, low food/ the membrane surface. microorganism ratio) and the smaller floc sizes, The limiting factor for further process development allowing slightly greater mass transport of nutrients is membrane fouling resulting from the following: and oxygen into the floc. MBRs achieve almost complete nitrification owing (i) Formation of a layer or cake on the membrane to the retention of the slow-growing autotrophic and/or the intrusion of molecules, colloids and bacteria. At nitrogen loads of 0.1 and 3.3 kg NH3 particles in the porous structure; m−3 day−1, ammonia removal is greater than 90%. As (ii) Preferential adsorption on the membrane with conventional processes, nitrification is sensitive surface. Fouling induces transmembrane flux Table 4 — Flux decline rate of selected submerged membrane bioreactors Membrane Pore Flux Pressure Time Flux decline Reference size rate configuration (µm) (m3m−2day−1) (bar) (days) (mday−2bar−1) Plate and 0.4 0.5 0.06 0.04 208 41 frame Plate and 0.4 0.1 0.7 0.2 0.79 14 frame Plate and 0.4 0.9 0.06 39 0.38 13 Hollow fiber 0.1 0.2 0.7 70 0.004 10 GUPTA et al.: SUBMERGED MEMBRANE BIOREACTOR SYSTEM: AN OVERVIEW 609 reduction; when the flux reaches a threshold declines exponentially with time to a semi-stable low value, membrane washing becomes necessary. value after a few hours. This decline is caused by concentration of retained material. The complexity of fouling is increased by Fouling also contributes to the increased pressure biological activity, and the progression in this field is drop and thus the permeate flux increases with it. The relatively slow18. presence of dissolved substances in the solution causes an accumulation of solutes on the retaining Permeate flux decline side of the membrane. This layer is less permeable to Permeate flux decline means decrease in flux and it water, resulting in higher osmotic pressure and the is influenced by a number of factors relating to the permeate pressure decline but with the increase in feed water (composition), the membrane (element fouling it rises due to the rise in trans membrane geometry/ configuration, pore size area and material pressure difference and permeate flux vary according composition), and operation (hydrodynamics)19. Flux to Eq. (3), decline rate is dependent on the fouling mechanisms of various membrane systems. For ultra filtration of J α Lv( P – σ Π ) … (3) colloidal species, there are three main mechanisms. where σ is the reflection coefficient, Π is the (i) Standard pore blocking model osmotic pressure difference and Lv is the solvent (ii) Pore blocking model and permeability coefficient. (iii) Cake build up model It can be concluded by Eq. (1) and Eq. (3) that the reduction of trans membrane pressure is due to the The permeate flux generally decreases with time effect of osmotic pressure20, but increases with increasing operating flux or pressure (Table 4). The flux of clean water across a J = P− σ Π /µR … (4) membrane with no materials deposited on the surface can be described by, Hirose et al.21 showed the existence of a linear relation between the surface roughness of membrane J = P/µR … (1) and flux, as it has been mentioned earlier that the permeate flux increases with the fouling. Surface where J is the permeate flux (m3/m2s), P is the roughness increases fouling due to the increase in the pressure drop across the membrane (N/m2), µ is the attachment of colloids and the particulate matters on absolute viscosity of the water (Ns/m2), R is equal to the membrane surface. They concluded that greater is total resistance of the membrane against the flux the membrane roughness, greater is the local (1/m). turbulence, wall shear stress and the permeate flux. In submerged membrane bioreactor the permeate R= Rm + Ri + Rc …(2) flux is made stable at particular value. There are also Rm= hydraulic resistance of the membrane (m−1) in two modes of operation - constant transmembrane pure water, pressure (TMP) or constant flux. In a constant TMP Ri= irreversible fouling resistance of the membrane operation, deposition and fouling cause a decline in (m−1) and flux that is initially rapid, but later becomes more Rc = resistance due to particle deposit at the gradual. For constant flux the effect of deposition and membrane surface and it increases with roughness of fouling is to increase TMP, which is initially gradual, membrane (m−1). but accelerates prior to cleaning. Constant flux is the preferred mode of operation for membrane A comparison of the resistance caused by fouling bioreactors because it ensures a steady throughput21. with the performance of the membrane was quantified Depending upon biomass concentration and the in terms of specific flux i.e. the permeate flux permeate flux variation, Vyas et. al.22 showed two produced per unit pressure applied (l/m2h bar). It was distinct zone, increasing the biomass concentration observed that initially fouling of the membrane from 0.65 to 2.5 g.L−1 a flux reduction, beyond surface causes a high rate of flux decline. Thus, 2.5 g.L-−1 the biomass concentration had no permeate flux decreases with the increase in significant effect on the membrane fouling and resistance of membrane due to fouling. The flux 610 INDIAN J. CHEM. TECHNOL., NOVEMBER 2008 permeate flux remained stable. Defrance et. al23 (usually associated with the biomass growth) and by reported similar results, the first zone with biomass decay. PMS must be regarded as one of concentration range of 0.8-1.5 g.L−1 and second zone, significant factor in the process of biological that is stabilization zone, of the fouling layer with treatment. PMS is classified as: concentration range of 1.5-5 g.L−1. When the (i) Utilization-associated product (UAP). concentration increases between 5 to 10 g.L−1, the (ii) Biomass-associated product (BAP). third zone corresponds to a flux decrease. This could be due to the suspension of rheological properties The UAP represents the PMS associated to the (increase of non-Newtonian viscosity). substrate metabolism and the biomass growth; the rate of production of biomass is proportional to the Critical flux substrate consumption rate. The BAP are PMS Field et al.24 were the first to introduce the concept associated with biomass death and biomass of the critical flux. The membrane fouling can be production is proportional to the concentration; the neglected below critical flux, and thus membrane BAP is a by-product of the endogenous respiration of cleaning is not required. It is important, therefore, to the cell mass. Because of the concentration of choose an adequate initial permeate flux or activated sludge in the reactor and the long sludge transmembrane pressure. retention times, it is impossible to ignore the Liu et. al.25 observed that the hydrodynamic formulation of the microbial products in the characteristics have a strong influence on liquid mass membrane bioreactor system. transfer of submerged membranes bioreactor. Critical The disposal of undesirable organic and mineral flux depends on hydrodynamics, particle size (it matter occurs with the help of flocculating bacteria, reaches very quickly for small particles), interaction which are the base of sludge. The biological flocs are between colloids and membrane and suspension disintegrated by circulation inside the membrane properties (pH, salinity and conductivity). bioreactor. Changes in the particle size and there The system hydrodynamics is also important in distribution modify the fouling properties of the determining the critical fouling point, as has been suspension; the presence of smaller particles, resulting demonstrated by Muller et al.26. The airflow rate due to the breakdown of the flocs increases the affects the liquid tangential circulation, which in turn membrane fouling. For an external type of membrane affects the transmembrane pressure; furthermore the bioreactor, the membrane fouling depends on the dimensions of the bioreactor also act on the liquid intensity of shear stress imposed on the bacterial flocs circulation. by the recycling pump. The pump breaks down the The various biological conditions within the reactor flocs, generating more of the colloidal particles and are supposed to act differently on membrane fouling. releasing the extracellular polymeric substances (EPS, It is, therefore, clear that a purely hydrodynamic principal compounds of the soluble organic matter) analysis is not sufficient to explain the fouling from the interior of the flock to the bioreactor. The problem. Ogoshi and Suzuki et al. 27 showed that in a bacterial suspension is composed of three fractions29: bioreactor membrane fouling can be neglected below (i) The soluble fraction critical flux, as low transmembrane pressure prevents (ii) The colloidal fraction an irreversible membrane fouling and a reduction in (iii) The particulate fraction the membrane cleaning frequency. Generally, there appears to be much corroboratory evidence from Washing and regeneration of membrane modules MBRs to support the critical flux hypothesis; many Effective washing requires an understanding of the submerged (plate-and-frame) plants run at <0.4 bar interaction between the fouling products and the TMP with no noticeable steady-state flux decline27. membranes as well as the effect of the washing procedures on elimination of the deposit. Membrane Concentration and sizes of the particles and flocs washing is performed when the permeability is less Barker et al.28 showed that the main part of the than 10% of initial permeability. Details of the soluble organic matter present in the effluents of different methods in chronological order of their biological treatment process is the produced microbial applications are as follows. soluble (PMS). PMS is composed of the organic compounds released by the metabolism of substrate Intermittent filtration GUPTA et al.: SUBMERGED MEMBRANE BIOREACTOR SYSTEM: AN OVERVIEW 611 The suction pump is switched off for approximately membrane clean with a 0.1% sodium hypochlorite 10 min, and then the filtration operation is reinitiated. solution. Cicek et al.33 showed that a ceramic During the intermittent filtration, the recirculation membrane required weekly cleaning for about 2 h pump continues to make the retentate circulate29. using 5.25% NaOCl heated to 60-80°C along with the concentrated nitric acid. Forward flush The filtration is stopped when the reactor is filled Membrane bioreactors design and operational up with pure water. Then, the water is recirculated for options 10 min without filtering. Membranes can be incorporated into the design of wastewater bioreactors as the solids / liquid separation Back flush stages into submerged membranes bioreactor (Fig. 1). Back flush consists of reversing the filtration In this case surface shear and/or backflushing are direction for 5 to 30s in every 30-60 min or in every applied to control cake formation and fouling. In the hour, possibly accompanied by the air sparing. Ognier submerged system the membranes are located in the et al.30 showed that the pure water was filtered in the mixed liquor tank, where bubbling is applied to opposite direction of the normal filtration operation produce surface shear and permeate flux is kept stable with a TMP of 0.5 bar. Marcucci et al.29 cleaned UF which ensure the TMP is < 1 atmosphere. There are membranes by backwashing for 90s at every 20 min also two modes of operation - constant TMP or under a TMP of 0.4 bar. When the hydraulic constant flux (Fig. 2). At constant TMP operation, performance markedly decreases, the membrane must deposition and fouling cause a decline in flux that is undergo chemical washing by acid and alkaline initially rapid, but becomes more gradual. For compounds. constant flux the effect of deposition and fouling is to Back pulsing increase TMP, which is initially gradual, but High-frequency back pulsing is different from accelerates prior to cleaning. Constant flux is the backwashing. High-frequency impulses (typically preferred mode of operation for membrane 0.1-2 Hz) can also be applied over a very short period bioreactors (MBRs) because it ensures a steady (nearly a second for microfiltration and ultrafil- throughput34. tration). High-frequency back pulsing can be Configuration of various submerged membrane performed every couple of seconds after a few bioreactor is as follows: minutes of filtration. The problem of this technique is Hollow- Fiber-Capillary that it requires high-pressure-resistant membranes30. • Very small diameter membranes (< 1mm). Chemical cleaning • Consist large number of membranes in a Generally in first step of chemical cleaning, module and self supporting. membrane is chemically cleaned with a slightly • Density is above 600 to 1200 m2/m3 (for diluted solution of nitric acid at room temperature. capillary membrane), up to 30000 m2/m3 (for Bouhabila et al.31 showed that in case of less hollow fiber membrane). permeability, membrane are soaked in chloride water • Size is smaller than other module for given (2000 ppm Cl2/L) for 24 h. performance capacity. Marakami et al.32 cleaned a submerged plate and • Process “inside-out”, permeat is collected frame configuration by employing a twice-yearly outside of the membrane. • Process “outside-in”, permeat passes into membrane bore. Plate and Frame • Structure is simple and membrane replacement is easy. • Similar to filter press. • Density is about 100 to 400 m2/m3. • Membrane is placed in a sandwich style with Fig. 2 — Constant TMP operation and constant flux operation [a feed sides facing each other. & b respectively] 612 INDIAN J. CHEM. TECHNOL., NOVEMBER 2008 • Feed flows from its sides and permeate comes membranes tend to have higher TMPs than out from the top and the bottom of the frame. membranes for a given flux, particularly at the • Membranes are held apart by a corrugated beginning of an operational cycle. spacer. Nanofiltration (NF) membranes have pores that are approximately 2 nm in size and retain most species, Following design equation can be used to design a except for certain monovalent ions and low molecular single SMBR: weight organics. They are rarely applied to MBRs Sludge retention time (SRT) can be defined as, because of their high hydraulic resistance, but they SRT = (Total mass of organism in the reactor)/(Total may be of interest in niche applications. mass of the organism leaving the system per day). Membrane materials are either organic polymers or SRT can be calculated by the following equation: inorganic, i.e. ceramics. The relatively high cost of SRT = V.X/Q.X = V/Q …(5) inorganic membranes puts them at a disadvantage in wastewater MBRs, where low cost components are where V is the reactor volume; X is the biomass required. When inorganic membranes have been concentration in the reactor; Q is the wastage flow evaluated they have usually involved high flux rate per day. operation (promoting fouling) and high energy input. Certain physical and chemical properties of S = Ks µm−( kd + 1/SRT)]/(kd + 1/SRT) ...(6) membranes favour their use in MBRs. These are: where So and S are the initial and substrate (i) Hydrophilicity — it is well known that concentration at time t respectively, and µm, kd, Ks are hydrophilic polymers are less prone to fouling biokinetic coefficients. by biosolids and biosolutes. This favours Death rate constant kd, and yield (y) can be cellulosic materials, but does not preclude more determined by using following equation, hydrophobic materials such as polyolefins and fluoropolymers. Q/X.V (So− S ) = [(1/SRT). (1/Y)] + [kd / Y] ...(7) (ii) Robustness — the material should be resistant to chemical cleaning agents and able to handle Membrane characteristics cyclic stresses, particularly if blow-back or The primary role of the membrane in a SMBR is to bubbling are applied. provide a barrier against suspended solids, but mixed (iii) Modest cost — as mentioned previously many liquor from the bioreactor is often a complex mixture. applications require low cost components. The removal or partial removal of other species is (iv) Ease of fabrication — some materials are more possible, but it is dependent on the choice of readily processed into microporous barriers or membrane34. extruded into hollow fibers than others. Microfiltration (MF) membranes have pore sizes down to 0.1-0.2 microns. They provide high removals The choice of polymer is a compromise, but those of suspended solids including most bacteria, as well generally favour include polyolefins, polysulphone as partial removal of viruses and macro solutes. The and polyvinylidene35. principle macro solute in the liquor is extra cellular Module characteristics polymeric substance (EPS) produced by bacteria, and The module design defines how the membranes are this is removed by adsorption and gradual retention as arranged or housed and also provides the fluid the membranes foul. Thus, MF membranes provide management, i.e. distribution of feed across the partial biochemical oxygen demand (BOD) removal membrane surface. The design also determines other (i.e. primarily suspended solids), which is retained in characteristics such as the relative energy demand, the the bioreactor. Membranes have low TMPs for a ability to handle suspended solids, ease of cleaning given flux when unfouled, but this can be gradually and replacement and the packing density. Table 2 lost because of fouling. summarizes these characteristics for a range of Ultrafiltration (UF) membranes have pores ranging module concepts - the contained modules are used in from 0.1 microns down to less than 5 nm. These external loop arrangements. The standard MBR membranes provide high removals of virus and (direct membrane filtration of mixed liquor) requires a reasonable removals of EPS. As a result they help to module that can handle suspended solids, has a retain BOD, which is maintained in the bioreactor. UF relatively low energy demand and can accommodate GUPTA et al.: SUBMERGED MEMBRANE BIOREACTOR SYSTEM: AN OVERVIEW 613 reasonably high membrane packing densities. These 12 Churchouse S, Personal Communication, 1998. requirements tend to exclude tubular modules, 13 Chiemchaisri C & Yamamoto K, Membrane Sci, 87 (1994) 119. contained hollow fibers and the spiral wound module, 14 Kishino H, Ishida H, Iwabu H & Nakano I, Desalination, 106 suggesting the use of contained flat sheet systems or (1996) 115. submerged membranes35. 15 Ueda T & Hata K, Water Res, 33(12) (1999) 2888. 16 Bouhabila E H, Ben Aim R & Buisson H, Desalination, 118 (1998) 315. Conclusion 17 Mignani M, Nosenzo G & Gualdi A, Desalination, 124 The nitrogen removal in the membrane bioreactor (1999) 287. system is about 30% higher than conventional 18 Sakairi M A C, Yasuda K & Matsumura M, Water Sci treatment process. The nitrogen removal is not solely Technol, 34 (1996) 267. due to microbial nitrification/ denitrification but also 19 Shimizu Y, Okuno Y I, Uryu K, Ohtsubo S & Watanabe A, Water Res, 30(109) (1996) 2385. due to assimilation derived from microbial growth. 20 Mulder M, The Netherlands, 2nd edn (Kluwer Academic The alkalinity of the suspension can cause the Publishers), 1996. precipitation as a cause of the system instability, even 21 Hirose M, Ito H & Kamiyama Y, Membrane Sci, 121 (1996) if the system works in sub critical conditions. COD 209. 22 Vyas H, Bennett R J & Marshall A D, Int Dairy, 10 (2000) removal efficiency in the submerged membrane 855. bioreactor could be maintained at over 95% regardless 23 Defrance L, Jaffrin M Y, Gupta B, Poullier P & Geaugey V, of STR. Submerged membrane systems, run at low Bioresource Technol, 73 (2000) 105. TMP, achieve a steady-state flux that does not decline 24 Field R W, Wu D, Howell J A & Gupta B B, Membrane Sci, over the time after the initial fouling period; this is 100 (1995) 259. 25 Liu R, Huang X, Wang C, Chen L & Qian Y, Process hypothesized to be due to sub-critical flux. Critical Biochem, 36 (2000) 249. flux decreases with increase of STR, indicating that 26 Muller E B, Stouthamer A H, Van Verseveld H W & membrane fouling has started to occur even at low Eikelboom D H, Water Res, 29 (1995) 1179. flux condition. Membrane fouling in the presence of 27 Ogoshi M & Suzuki Y, Water Sci Technol, 41(10-11) (2000) 287. microorganism is linked to microbial products, 28 Barker D J, Mannucchi G A, Salvi S M & Stuckey D C, concentration, and sizes of the particle. The Water Res, 33 (11) (1999) 2499. membrane fouling rate increases with STR, due to 29 Marcucci M, Nosenzo G, Capannelli G, Ciabatti I, Corrieri D large amount of foulant. These strategies of & Ciardelli G, Desalination, 138 (2001) 75. membrane washing or backwashing are proposed in 30 Ognier S, Wisniewski C & Grasmick A, Desalination, 146 (2002) 141. order to maintain a stable permeate flux in the 31 Bouhabila E H, Aim R B & Buisson H, Sep Purif Technol, membrane bioreactor systems. 22-23 (2001) 123. 32 Marakami T, Usui J, Takamura K & Yoshikawa T, Water Sci Technol, 41(10-11) (2000) 295. References 33 Cicek N, Winnen H, Suidan M T, Wrenn B E, Urbain V & 1 Fane A G, Filtr Sep, 39 (5) (2002) 26. Manem J, Water Res, (1998) 1553. 2 Lesjean B, Rosenberger S, Schrotter J C & Recherche A, 34 Madec A, Buisson H & Aim Ben R, Proceedings of World Membrane Technol, 8 (2004) 5. Filtration Congress 8, UK. 1(199-202) (2000). 3 Jefferson B, Laine A L, Judd S & Stephenson T, Water Sci 35 Chang S & Fane A G, J Membrane Sci, 2 (221-231) (2003) Technol, 41(1) (2000) 197. 184. 4 Yamamoto K, Hiasa M, Mahmood T & Matsuo T, Water Sci 36 Semmens M J, Qin R & Zander A K, Water Work, 81(4) Technol, 21(4-5) (1989) 43. (1989) 162. 5 Gander M A, Jefferson B & Judd S J, Water Sci Technol, 37 Huang X, Gui P & Qian Y, Process Biochem, 36 (2001) 41(1) (2000) 205. 1001. 6 Shin H S & Park H S, Water Sci Technol, 23 (1991) 719. 38 Marrot B, Barrios-Martinez A, Moulin P & Roche N, 7 Xing X H, Inoue T, Tanji Y & Unno H, Biosci Bioeng, 87 Environ Progress, 23(1) (2004) 59. (1999) 372. 39 Jun B, Miyanaga K, Tanji Y & Unno H, Biocheml Eng, 14 8 Dufresne R, Lavallee H C, Lebrun R E & Lo S N, Pulp Pap (2003). Mag Can, 99(2.III) (1998) 51. 40 Urbain V, Manem J, Mobarry B, De Silva V D G, Stahl D & 9 Jefferson B, Laine A, Brindle K, Judd S & Stephenson T, Rittman B E, Sympo Environ Biotechnol: 94th Event of the Proc Water Environt 98: Maintaining the Flow, 41(1) (2000) European Federation of Biotechnol, (1997). 197. 41 Jefferson B, Laine A L, Judd S & Stephenson T, Water Sci 10 Yoon S H, Kim H S, Park J K, Kim H & Sung J Y, Water Sci Technol, 41(1) (2000) 197. Technol, 41(10-11) (2000) 235. 11 Huang X, Lui R & Qian Y, Process Biochem, 36 (2000) 401.
Pages to are hidden for
"Submerged membrane bioreactor system for municipal wastewater"Please download to view full document