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Membrane Bioreactor Technology - An Overview

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Vaibhav Nautiyal
Vaibhav Nautiyal

Urban wastewater is usually treated using conventional activated sludge processes, which involve bacteria breaking down pollutants. Membrane bioreactors improve on this by using a membrane to filter out bacteria instead of gravitational settling. This allows for higher concentrations of bacteria and produces very high quality treated water that can be reused. Membrane bioreactors have several advantages over conventional treatment, including more compact systems and better treatment, but also have higher costs and challenges with membrane fouling.

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Presented By: Charu Sharma M.Tech- Environment Engineering Roll No- 07/ENV/PT/2010 Delhi Technological University
Urban wastewater is usually treated by conventional activated sludge processes (CASP’s), which involve the natural biodegradation of pollutants by heterotrophic bacteria (i.e. activated sludge) in aerated bioreactors. Activated sludge could be separated by gravitational setting. The treatment efficiency is usually limited by the difficulties in separating suspended solids (SS’s). The optimal sludge concentration is generally up to 5 g /l, which imposes large size of aerated bioreactor. Further treatment of sludge needs to be provided separately. Membrane bioreactor (MBR) is an improvement of the CASP, where the traditional secondary clarifier is replaced by a membrane unit for the separation of treated water from the mixed solution in the bioreactor.
Membrane Bioreactor Technology is based on Biological Treatment followed by membrane separation, system comprising of an intense activated sludge process with the biomass separation stage carried out by membrane cassettes located outside the aeration tank in a separate membrane tank. The Membranes replace the settlement stage in conventional activated-sludge systems and effectively revolutionize the process. The separation of biomass from treated water using membranes provides filtered quality final effluent, offering possibilities of re-use It allows very high biomass mixed liquor suspended solids (MLSS) concentrations to be developed in the bioreactor without the detrimental effects usually associated with traditional settlement techniques.
It is an intervening phase separating two phases and/or acting as an active or passive barrier to the transport of matter between phases. Electron microscope view of membrane surface Membrane Fibers
Membrane fibers have billions of microscopic pores on the surface . The pores form a barrier to impurities , while allowing pure water molecules to pass. Water is drawn through the pores using gentle suction .
Two main process configurations of biomass rejection MBRs are as follows: (i) Submerged or Immersed MBR (iMBR) In the submerged MBR (SMBR) process, the membrane is submerged directly in the aeration tank. By applying low vacuum or by using the static head of the mixed liquor, effluent is driven through the membrane leaving the solids behind. (ii) External / Sidestream MBR (EMBR) In the external MBR (EMBR), the mixed liquor is pumped from the aeration tank to the membrane at flow rates that are 20–30 times the product water flow to provide adequate shear for controlling solids accumulation at the membrane surface. The high cost of pumping makes EMBR system impractical for full-scale municipal wastewater treatment plants
STRUCTURE OF MEMBRANE UNIT
Process Configuration : Compact Layout
Normally, systems are built with two different compartments. The first section is the screening stage where the wastewater enters the unit. In this area; heavy solids are first separated subsequently traversing to another compartment which houses the membranes. The initial screening is of high importance, as the larger molecules (scum and grit) will not trap the surface of the membrane and lead to fouling. In the second compartment , the biological process takes place involving vigorous agitation, coming from air bubbles generated from a blower system. This acts to scour and clean the surface of the membrane to prevent buildup of material on the and also to provide sufficient oxygen concentration for biological action that supports growth of bacteria. Depending on how the system is designed to ensure efficient air to water oxygen transfer, the household MBR is capable to support up to 4000ppm of MLSS level while large-scale industrial wastewater treatment plant bioreactor scan handle up to 20000ppm. A complete unit usually comes equipped with a backflush system whereby discharged wastewater will now move counter flow from the permeate side back again to the system to dislodge trapped material accumulating on the surface. During this process, air scouring will still continue to run to help increase removal effeciency.
Membrane Bioreactor Technology - An Overview
Membrane Bioreactor Technology - An Overview
S.NO. PARAMETERS UNITS VALUES 1. BOD mg/l < 2 2. TSS mg/l < 1 3. Ammonical Nitrogen as NH3-N mg/l < 0.5 4. Nitrogen as TKN mg/l < 1 5. Fecal Coliform Count MPN/100ml <2 6. pH 6.8-7.8
The effluent quality of the MBR is listed in Table . It shows that the UMBR system can provide Good Quality effluent that is completely acceptable for reuse. The reclaimed water can be directly reused for municipal watering, toilet flushing and car washing. After the softening treatment, the reclaimed water can be used as a cooling water supply or processing water. Therefore, lots of urban wastewater can be effectively harnessed, and moreover, large quantities of water can be saved. As a result, the water industry would move towards a more sustainable future.
ADVANTAGES OF MBR OVER OTHER TREATMENT PROCESSES The retention of all suspended matter and most soluble compounds within the bioreactor leads to excellent effluent quality capable of meeting stringent discharge requirements and opening the door to direct water reuse. The possibility of retaining all bacteria and viruses results in a sterile effluent, eliminating extensive disinfection that would be required otherwise and eliminate the corresponding hazards related to disinfection by products. It results in more compact systems than conventional processes significantly reducing plant footprint making it desirable for water recycling applications. The process is more compact than a Conventional Activated Sludge process (CAS), skipping three (3) individual processes of the conventional scheme. The feed wastewater only needs to be screened (1-3 mm) just prior to removal of larger solids that could damage the membranes. In addition it is easier to operate and maintain. It has a higher Nitrogen Removal rate than any other treatment process. Finally, it has a comparatively low sludge yield; thereby reducing the IOM cost of sludge handling
Notwithstanding the advantages of MBRs, the widespread implantation is limited due to its high costs, both Capital and Operating expenditure (CAPEX and OPEX), mainly due to membrane installation and replacement, and high energy demand. This high energy demand in comparison with a CAS, is closely associated with strategies for avoiding/mitigating membrane fouling (70% of the total energy demand for an iMBR) Another drawback of the iMBR is the fouling of membranes. Fouling is the restriction, occlusion or blocking of membrane pores or cake building by solids accumulation on the membrane surface during operation which leads to membrane permeability loss. Though, Traditional strategies for fouling mitigation such as air sparging, physical cleaning techniques (i.e backflushing and relaxation) and chemical maintenance cleaning have been incorporated in most MBR designs as a standard operating strategy to limit fouling. Also, Membrane fouling problems can lead to frequent cleaning of the membranes, which stop operation and require clean water and chemicals.
Membrane Bioreactor (MBR) Wastewater treatment system that include a biological aeration basin followed by membrane system - replacing traditional clarifiers Benefits Potential Reuse of effluent water Smaller bioprocess footprint Substantial reduction of effluent TSS Eliminate settling challenges associated with a clarifier Potential Limitations Refinery upsets could foul membranes resulting in accelerated rate in cleaning and replacement
About 200 MBR’s are currently in operation for various wastewaters, and 90% of them are employed in municipal treatment . In the application of MBR that is based on polymeric materials, the leading country is Japan, where most MBR systems are used for water recycling in buildings. As these organic membranes are normally sensitive to caustic cleaning reagents, the difficulty met with in cleaning is often encountered especially when the membrane module is seriously fouled during industrial operation . In order to overcome this difficulty, an MBR system equipped with ceramic membranes was first developed in France. It makes the cleaning of membrane easy and convenient in situ because these inorganic membranes possess a high degree of resistance to chemical abrasion and biological degradation. The membrane has a great chemical stability in a wide range of pH and temperature. In India, MBR systems are now being used for the treatment of domestic waste water from Hotel Industries , Residential townships and group housing complexes. Treated effluent is of much better quality that it is reused in gardening, flushing, Cooling and other cleaning purpose. Current Status
 
Pictorial Representation of 1 MGD MBR-STP at Akshardham In Delhi, there is a full fledged 1 MGD Sewage Treatment Plant based on MBR Technology for the Common Wealth Games Village near Akshardham Temple, Delhi. Installed by Delhi Jal Board.
The treated water is Reused for toilet flushing in the flats of the Akshardham Complex and also in its Chillers. Acoustic Enclosures are provided around blowers which help in reducing the noise level by about 5-10 dB . The Control System for the plant has been designed so as to be operated automatically . This Automatic provision is beneficial to department from an energy saving point of view. The entire plant is enclosed in a single building .
The treatment performance of the MBR is better than in conventional activated sludge processes. A high conversion of ammonium to nitrate (>95%) and constant COD removal efficiency (80-98%) was achieved, regardless of the influent fluctuations. Microbial analysis of permeate showed the absence of bacterial indicators of contamination and parasitical microorganisms. At the same time, the membrane presented over 98% efficiency in the elimination of viral indicators. The removal efficiencies of BOD, COD and NH3-N were ranged between 98.9–99.9%, 97.8–99.9% and 91.0–100%, respectively. The removal efficiency of COD was on the average as high as 97%, in which 85% was attributed to the bioreactor and the residual 12% a result of membrane separation. The average removal of NH3-N and SS could reached 96.2% and 100%, respectively. The pH of the effluent was increased by 20.1–39.2% of that of the influent.
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Membrane Bioreactor Technology - An Overview

  • 1. Presented By: Charu Sharma M.Tech- Environment Engineering Roll No- 07/ENV/PT/2010 Delhi Technological University
  • 2. Urban wastewater is usually treated by conventional activated sludge processes (CASP’s), which involve the natural biodegradation of pollutants by heterotrophic bacteria (i.e. activated sludge) in aerated bioreactors. Activated sludge could be separated by gravitational setting. The treatment efficiency is usually limited by the difficulties in separating suspended solids (SS’s). The optimal sludge concentration is generally up to 5 g /l, which imposes large size of aerated bioreactor. Further treatment of sludge needs to be provided separately. Membrane bioreactor (MBR) is an improvement of the CASP, where the traditional secondary clarifier is replaced by a membrane unit for the separation of treated water from the mixed solution in the bioreactor.
  • 3. Membrane Bioreactor Technology is based on Biological Treatment followed by membrane separation, system comprising of an intense activated sludge process with the biomass separation stage carried out by membrane cassettes located outside the aeration tank in a separate membrane tank. The Membranes replace the settlement stage in conventional activated-sludge systems and effectively revolutionize the process. The separation of biomass from treated water using membranes provides filtered quality final effluent, offering possibilities of re-use It allows very high biomass mixed liquor suspended solids (MLSS) concentrations to be developed in the bioreactor without the detrimental effects usually associated with traditional settlement techniques.
  • 4. It is an intervening phase separating two phases and/or acting as an active or passive barrier to the transport of matter between phases. Electron microscope view of membrane surface Membrane Fibers
  • 5. Membrane fibers have billions of microscopic pores on the surface . The pores form a barrier to impurities , while allowing pure water molecules to pass. Water is drawn through the pores using gentle suction .
  • 6. Two main process configurations of biomass rejection MBRs are as follows: (i) Submerged or Immersed MBR (iMBR) In the submerged MBR (SMBR) process, the membrane is submerged directly in the aeration tank. By applying low vacuum or by using the static head of the mixed liquor, effluent is driven through the membrane leaving the solids behind. (ii) External / Sidestream MBR (EMBR) In the external MBR (EMBR), the mixed liquor is pumped from the aeration tank to the membrane at flow rates that are 20–30 times the product water flow to provide adequate shear for controlling solids accumulation at the membrane surface. The high cost of pumping makes EMBR system impractical for full-scale municipal wastewater treatment plants
  • 8. Process Configuration : Compact Layout
  • 9. Normally, systems are built with two different compartments. The first section is the screening stage where the wastewater enters the unit. In this area; heavy solids are first separated subsequently traversing to another compartment which houses the membranes. The initial screening is of high importance, as the larger molecules (scum and grit) will not trap the surface of the membrane and lead to fouling. In the second compartment , the biological process takes place involving vigorous agitation, coming from air bubbles generated from a blower system. This acts to scour and clean the surface of the membrane to prevent buildup of material on the and also to provide sufficient oxygen concentration for biological action that supports growth of bacteria. Depending on how the system is designed to ensure efficient air to water oxygen transfer, the household MBR is capable to support up to 4000ppm of MLSS level while large-scale industrial wastewater treatment plant bioreactor scan handle up to 20000ppm. A complete unit usually comes equipped with a backflush system whereby discharged wastewater will now move counter flow from the permeate side back again to the system to dislodge trapped material accumulating on the surface. During this process, air scouring will still continue to run to help increase removal effeciency.
  • 12. S.NO. PARAMETERS UNITS VALUES 1. BOD mg/l < 2 2. TSS mg/l < 1 3. Ammonical Nitrogen as NH3-N mg/l < 0.5 4. Nitrogen as TKN mg/l < 1 5. Fecal Coliform Count MPN/100ml <2 6. pH 6.8-7.8
  • 13. The effluent quality of the MBR is listed in Table . It shows that the UMBR system can provide Good Quality effluent that is completely acceptable for reuse. The reclaimed water can be directly reused for municipal watering, toilet flushing and car washing. After the softening treatment, the reclaimed water can be used as a cooling water supply or processing water. Therefore, lots of urban wastewater can be effectively harnessed, and moreover, large quantities of water can be saved. As a result, the water industry would move towards a more sustainable future.
  • 14. ADVANTAGES OF MBR OVER OTHER TREATMENT PROCESSES The retention of all suspended matter and most soluble compounds within the bioreactor leads to excellent effluent quality capable of meeting stringent discharge requirements and opening the door to direct water reuse. The possibility of retaining all bacteria and viruses results in a sterile effluent, eliminating extensive disinfection that would be required otherwise and eliminate the corresponding hazards related to disinfection by products. It results in more compact systems than conventional processes significantly reducing plant footprint making it desirable for water recycling applications. The process is more compact than a Conventional Activated Sludge process (CAS), skipping three (3) individual processes of the conventional scheme. The feed wastewater only needs to be screened (1-3 mm) just prior to removal of larger solids that could damage the membranes. In addition it is easier to operate and maintain. It has a higher Nitrogen Removal rate than any other treatment process. Finally, it has a comparatively low sludge yield; thereby reducing the IOM cost of sludge handling
  • 15. Notwithstanding the advantages of MBRs, the widespread implantation is limited due to its high costs, both Capital and Operating expenditure (CAPEX and OPEX), mainly due to membrane installation and replacement, and high energy demand. This high energy demand in comparison with a CAS, is closely associated with strategies for avoiding/mitigating membrane fouling (70% of the total energy demand for an iMBR) Another drawback of the iMBR is the fouling of membranes. Fouling is the restriction, occlusion or blocking of membrane pores or cake building by solids accumulation on the membrane surface during operation which leads to membrane permeability loss. Though, Traditional strategies for fouling mitigation such as air sparging, physical cleaning techniques (i.e backflushing and relaxation) and chemical maintenance cleaning have been incorporated in most MBR designs as a standard operating strategy to limit fouling. Also, Membrane fouling problems can lead to frequent cleaning of the membranes, which stop operation and require clean water and chemicals.
  • 16. Membrane Bioreactor (MBR) Wastewater treatment system that include a biological aeration basin followed by membrane system - replacing traditional clarifiers Benefits Potential Reuse of effluent water Smaller bioprocess footprint Substantial reduction of effluent TSS Eliminate settling challenges associated with a clarifier Potential Limitations Refinery upsets could foul membranes resulting in accelerated rate in cleaning and replacement
  • 17. About 200 MBR’s are currently in operation for various wastewaters, and 90% of them are employed in municipal treatment . In the application of MBR that is based on polymeric materials, the leading country is Japan, where most MBR systems are used for water recycling in buildings. As these organic membranes are normally sensitive to caustic cleaning reagents, the difficulty met with in cleaning is often encountered especially when the membrane module is seriously fouled during industrial operation . In order to overcome this difficulty, an MBR system equipped with ceramic membranes was first developed in France. It makes the cleaning of membrane easy and convenient in situ because these inorganic membranes possess a high degree of resistance to chemical abrasion and biological degradation. The membrane has a great chemical stability in a wide range of pH and temperature. In India, MBR systems are now being used for the treatment of domestic waste water from Hotel Industries , Residential townships and group housing complexes. Treated effluent is of much better quality that it is reused in gardening, flushing, Cooling and other cleaning purpose. Current Status
  • 18.  
  • 19. Pictorial Representation of 1 MGD MBR-STP at Akshardham In Delhi, there is a full fledged 1 MGD Sewage Treatment Plant based on MBR Technology for the Common Wealth Games Village near Akshardham Temple, Delhi. Installed by Delhi Jal Board.
  • 20. The treated water is Reused for toilet flushing in the flats of the Akshardham Complex and also in its Chillers. Acoustic Enclosures are provided around blowers which help in reducing the noise level by about 5-10 dB . The Control System for the plant has been designed so as to be operated automatically . This Automatic provision is beneficial to department from an energy saving point of view. The entire plant is enclosed in a single building .
  • 21. The treatment performance of the MBR is better than in conventional activated sludge processes. A high conversion of ammonium to nitrate (>95%) and constant COD removal efficiency (80-98%) was achieved, regardless of the influent fluctuations. Microbial analysis of permeate showed the absence of bacterial indicators of contamination and parasitical microorganisms. At the same time, the membrane presented over 98% efficiency in the elimination of viral indicators. The removal efficiencies of BOD, COD and NH3-N were ranged between 98.9–99.9%, 97.8–99.9% and 91.0–100%, respectively. The removal efficiency of COD was on the average as high as 97%, in which 85% was attributed to the bioreactor and the residual 12% a result of membrane separation. The average removal of NH3-N and SS could reached 96.2% and 100%, respectively. The pH of the effluent was increased by 20.1–39.2% of that of the influent.