paper

MEMBRANE BIOREACTORS FOR INDUSTRIAL WASTEWATER TREATMENT: APPLICABILITY AND SELECTION OF OPTIMAL SYSTEM CONFIGURATION

Paul M. Sutton

P.M. Sutton & Associates, Inc. 45 Bradford Lane, Enfield, NH 03748

ABSTRACT The membrane biological reactor (MBR) configuration has proven to be optimal for treatment of many industrial wastewaters when treatment efficiency is an important consideration. Since installation of the first large, U.S., full scale MBR system for industrial wastewater treatment at the General Motors plant in Mansfield, Ohio in the early 1990s, use of membranes for biomass-effluent separation in biological systems has gained wide appeal both in this country and internationally. Industrial applications have ranged from nitrogen removal from food processing wastewaters to use of the technology to deal with complex organics in wastewaters originating from the production of pharmaceuticals and the manufacture of polymeric membrane materials. Historically, low membrane flux, low permeability, limited membrane life and high membrane costs hindered broad application of the MBR technology. The membrane industry, including independent research and development organizations and system suppliers, invested considerable effort to overcome these limitations over the past decade. The result has been a dramatic increase in the number of new commercial system embodiments of the MBR configuration offered by suppliers and a rapid acceleration in the use of the technology for treatment of industrial wastewaters and other aqueous streams. MBR systems can be categorized according to the location of the membrane component. Until recently, the immersed or internal membrane MBR was typically more cost-effective than the external membrane MBR particularly in the treatment of larger wastewater flows. The technical advantages of the external membrane configuration, and recent significant membrane and system design advances resulting in reductions in operating power costs, have translated to broader application of this configuration. External membrane MBRs have recently been designed to treat wastewater flows as high as 3785 m3/day. KEYWORDS Industrial wastewater, bioreactors, membranes. INTRODUCTION

The ideal bioreactor configuration for treatment of organic (e.g., measured as COD) or inorganic (e.g., ammonia, nitrate) contaminants present in industrial wastewaters will operate efficiently (i.e., at a high contaminant volumetric removal rate) while achieving the design performance objective (i.e., contaminant percent removal or effluent quality requirement). Bioreactor systems such as the conventional activated sludge system, sequencing batch reactor system and trickling filters although typically designed for operation at a lower volumetric removal rate, are often

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Copyright 2006 Water Environment Foundation. All Rights Reserved©

selected for applications under site conditions where space constraints are not a factor and/or other conditions which render the systems acceptable. The membrane biological reactor (MBR) configuration has proven to be optimal for treatment of many industrial wastewaters when treatment efficiency is an important consideration. Since installation of the first large, U.S., full scale MBR system for industrial wastewater treatment at the General Motors plant in Mansfield, Ohio in the early 1990s (Knoblock et al., 1994), use of membranes for biomass-effluent separation in biological systems has gained wide appeal both in this country and internationally. Industrial applications have ranged from nitrogen removal from food processing wastewaters to use of the technology to deal with complex organics in wastewaters originating from the production of pharmaceuticals and the manufacture of polymeric membrane materials. Historically, low membrane flux (i.e., permeate production per unit of membrane area), low permeability (i.e., flux per unit of transmembrane pressure or TMP), limited membrane life and high membrane costs hindered broad application of the MBR technology. The membrane industry including independent research and development organizations and system suppliers, invested considerable effort to overcome these limitations over the past decade. The result has been a dramatic increase in the number of new commercial system embodiments of the MBR configuration offered by suppliers, and a rapid acceleration in the use of the technology for treatment of industrial wastewaters and other aqueous streams. The purpose of this paper is to provide a general procedure for determining when the MBR configuration is optimal for treatment of an industrial waste stream and a framework for selecting the optimal commercial MBR system embodiment. The approach will be illustrated by full scale case studies. BIOREACTOR SYSTEM SELECTION CRITERIA Biological treatment is considered Best Available Technology for many industrial wastewaters. An objective methodology needs to be followed to support the decision before selecting the bioprocess technology option versus physical and/or chemical treatment for treating a particular industrial wastewater. For example, in the treatment of an industrial wastewater stream contaminated with one or more organics, the methodology may take the form of a decision chart similar to that depicted in Figure 1. If the procedure results in the conclusion a high efficiency aerobic, anoxic or anaerobic bioprocess is optimal for treatment of the wastewater, a number of alternative bioreactor configurations are commercially available and selection of the ideal configuration will be dictated by performance requirements and other major technical and economic factors. In many cases the MBR configuration will represent an ideal reactor choice. HIGH EFFICIENCY BIOREACTOR ALTERNATIVES The ideal bioreactor configuration for treatment of organic or inorganic contaminants present in industrial wastewaters or other aqueous streams will operate efficiently while achieving the design performance objective. Other major factors important to consider beyond efficiency and

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Figure 1 – Simplified Version of Decision Chart to Select Alternatives for Treatment of an Organic Contaminated Aqueous Stream

No Yes Yes No Yes No Effluent No Yes Yes No No Yes No

performance when selecting a bioreactor configuration for treatment of a specific aqueous stream, include the following.

1) The characteristics of the contaminants in question with respect to such factors as biotreatability (e.g., readily biodegradable by large consortium of bacteria, slowly biodegradable by selected bacteria), soluble versus colloidal contaminants, presence of particulates, contaminant volatility and the sorbable characteristics of the contaminants (e.g., adsorbable on granular activated carbon or GAC).

Organic Contaminants

Contaminants Biotreatable

Contaminants Filterable Or Adsorbable

Filtration (Macro, Micro, Ultra, Etc) Or Carbon

Adsorption

Pretreatment Required To Remove Floating Oils,

Heavy Solids Or Bio-Inhibitory Compounds

Oil-Water Separation And Clarification With Or Without Chemical

Addition

Contaminants Are Chemically

Oxidizable Or Reducible

Chemical Oxidation/ Reduction

Land/Space Constraint

Contaminants Are Strippable

Air Or Steam Stripping

Low Efficiency Aerobic, Anoxic Or Anaerobic

Bioreactor

High Efficiency Aerobic, Anoxic Or Anaerobic

Bioreactor

Contaminants are Recoverable Or Volume

Reduction Can Be Achieved

Evaporation, Ion Exchange Or

Extraction

Waste Destruction/ Off-Site Disposal

Incineration, Wet Air Oxidation, Deep Well

Injection, Etc.

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2) The ability to design and operate the bioreactor under the required and/or optimal biological process conditions for treatment of the contaminants (e.g., aerobic, anoxic or anaerobic conditions dictated by the required or ideal electron acceptor, mesophilic or thermophilic temperature conditions, complete-mix or plug-flow hydraulic conditions dictated by the relationship between contaminant concentration and rate of biotreatment).

3) The ability to control and regulate the biomass inventory in the bioreactor, maximizing the active fraction and preventing loss due to variable or inhibitory feed conditions or an adverse change in process operating conditions.

4) The mechanical simplicity of the bioreactor configuration, and the ease of operation and maintenance requirements for the system. These factors are significant in dictating bioreactor system capital and operating costs.

The volumetric efficiency of any biological treatment process is dependent on maintaining a high active biomass concentration in the reactor. Biological reactors can be classified according to the nature of their growth. Those in which the active biomass is suspended as free organisms or microbial aggregates can be classified as suspended growth reactors, whereas those in which growth occurs on or within a solid media can be termed supported growth or fixed film reactors. Reactors involving the use of a fixed film media located in a suspended growth reactor are termed hybrid reactors or integrated fixed film activated sludge (IFAS) reactors. The distinction between suspended and fixed film reactors is not always clear. The important distinction is whether the kinetics of the biological reactions occurring can be best described by equations appropriate for suspended or fixed film growth. The major bioreactor configurations commercially available and capable of operation under aerobic, anoxic or anaerobic conditions at higher volumetric loading rates, are categorized in Figure 2. Each of these bioreactor configurations (Figure 2) achieves efficiency by design of the reactor to maintain a high active biomass concentration. In the MBR configuration, a high concentration of biomass measured as volatile suspended solids (VSS) (i.e., normally greater than 10 g/l) is achieved by absolute retention of suspended matter with a particle size much smaller than that characterizing a bacterial cell (i.e., typically 0.3 to 0.5 microns) through use of a microfiltration or ultrafiltration membrane unit process. VSS concentration values in excess of 30 g/l have been maintained (Sutton et al., 2001) in external membrane based MBR systems (i.e., membranes located external to the bioreactor, and operated at high cross-flow velocity and transmembrane pressure or TMP values). The bioreactor VSS design concentration selected is normally dictated by membrane efficiency considerations (e.g., membrane permeability). MBR SYSTEMS Since development of the coupled activated sludge-membrane sewage treatment system by Dorr-Oliver in the late 1960s (Smith et al., 1969), MBRs have emerged as an alternative bioreactor configuration in cases where space and water resources are limited. Industrial wastewaters,

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Figure 2 – Commercially Available Aerobic, Anoxic or Anaerobic Bioreactor Configurations Considered Efficient1

which can be difficult to treat without long solids retention times (SRTs), and wastewater operations where settling and clarification problems are regularly encountered, are typical applications of MBR technology. With the development of more economical, efficient membrane components, MBR systems have become a feasible option for aerobic treatment of municipal and industrial wastewaters, and potentially for anaerobic treatment of municipal and/or low to medium strength industrial wastewaters. Specific advantages of MBR systems in the treatment of industrial wastewaters include the following.

• Slower growing organisms, such as nitrifying bacteria and those capable of degrading complex organics, can be readily maintained in MBRs.

• Largely unencumbered control of the SRT provides optimum control of the microbial population and flexibility in operation. Provides opportunity to consider design/operation of bioreactor at very short or very long SRT (e.g., 1 day or less, or greater than 30 days) as process requirements dictate versus concerns for achieving a flocculant biomass. A short SRT maximizes biomass production and its organic content which if the biomass is anaerobically processed, maximizes digester gas production and therefore its energy value. A long SRT favors aerobic digestion of biosolids, which may be attractive under certain circumstances.

Aerobic, Anoxic or Anaerobic Processes

IFAS Reactors Fixed Film Reactors Suspended Growth Reactors

RBC Activated Sludge System

MBBR Activated Sludge Systems

Fixed Bed Activated Sludge Systems

PAC Sequencing Batch Reactor Systems

PAC Activated Sludge Systems

FBR Systems UASB Systems Downflow or Upflow

PBR Systems

1 IFAS represents integrated fixed film activated sludge, MBBR represents moving bed biofilm reactor, RBC represents rotating biological contactor, PAC represents powdered activated carbon, MBR represents membrane biological reactor, UASB represents upflow anaerobic sludge blanket, PBR represents packed bed reactor and FBR represents fluidized bed reactor.

MBR Systems

MBBR Systems

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• High mixed liquor concentrations in the reactor allow wastewaters to be treated efficiently at long SRTs, minimizing biomass yield.

• More compact biological reactors are possible.

• Non-biodegradable compounds tend to be discharged with the sludge rather than with the treated water.

• Rapid initial process startup due to retention of all microbial seed material.

• Particulate, colloidal and higher molecular weight organics are retained for a period equivalent to the reactor SRT versus the liquid contact time or hydraulic retention time (HRT), providing maximum opportunity for biological degradation of these compounds.

• Eliminates concern for changing biomass settling characteristics (e.g., filamentous growth) and associated cost implications (e.g., polymer addition, chlorine addition to control filaments).

• Can be readily configured to achieve biological nitrogen and phosphorus removal if required. Ideal process configuration to promote removal of certain metals through external chemical addition, and retention of resulting salts and hydroxides.

• MBR systems can operate largely unattended except for occasional routine performance checks and maintenance of mechanical components.

• Represents an attractive technology for upgrading and/or expanding an existing activated sludge system plagued by clarifier performance problems or excessive operational needs, or where site constraints dictate against addition of new structures.

• Ideal first step in producing water for reuse through reverse osmosis. MBR System Configurations MBR systems can be classified into two major categories according to the location of the membrane component (Figure 3). The first category is normally referred to as the external membrane MBR configuration. This configuration typically involves the use of polymeric organic or inorganic membranes located external to the bioreactor. The first large, U.S., full scale MBR system for industrial wastewater treatment previously referenced, was an external membrane based system. In the late 1980s, Japanese researchers began to explore application of the MBR technology where the membranes were mounted directly in the biological reactor, immersed in the mixed-liquor (i.e., internal membrane MBR system), and the membrane permeate or biosystem effluent was withdrawn through the membranes by the use of a suction pump (Yamamoto et al., 1989). In 1998, the first large U.S., full scale internal membrane MBR system for treatment of industrial wastewater in the U.S. was installed at a food ingredients manufacturing plant in the Northeast (Cantor et al., 2000). External membrane configuration. In the conventional external membrane MBR systems, first introduced in North America (i.e., conventional external membrane MBRs), membrane filtration is achieved by creating a high shear condition in tubes or channels, typically at least 1.2

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cm2 in cross-sectional area, where the mixed-liquor solids are routed (i.e., lumen side of membrane) and extracting the permeate or effluent through the membranes. In the case of tubular membranes, operation at a high liquid cross-flow velocity (i.e., typically 2 to 5 m/sec) and a high TMP (e.g., greater than 210 kPa), results in membrane permeation. Typically, these conventional tubular membranes used in the MBR application have an inside diameter of at least 20 mm although commercial systems do exist involving 5.2 mm diameter tubes. Figure 3 – Simplified Schematics Depicting MBR Configurations External

Sidestream Bioreactor Membrane Effluent Wastewater (membrane permeate) Air Addition Internal Bioreactor Effluent Wastewater (membrane permeate) Submerged Membrane Air Addition More recently, a Dutch company has developed an external membrane configuration for use in the MBR application, consisting of cross-flow membrane modules mounted vertically, and relying on the combination of air and liquid flow to create high shear inside tubular membranes which are 5.2 mm in size. In this case, the liquid velocity is approximately 0.5 m/sec, the air flow translates to an airflow velocity in the range from 0.3 to 0.5 m/sec and the operating TMP is typically less than 15 percent of that characterizing the conventional external membrane systems (Van’t Oever, 2005). Critical to the performance of these lower velocity, lower TMP membrane systems is a design allowing frequent membrane backpulsing (e.g., every 5 min) using the effluent permeate. Very recently, a German company introduced a lower velocity, lower TMP (versus conventional external membrane systems) configuration consisting of cross-flow, tubular membrane modules with 8 mm openings which are mounted horizontally, and rely on a combination of liquid flow (velocity approximately 1.2 m/sec) and frequent membrane

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backpulsing to maintain flux performance (Linden, 2006a). That is, no airflow is used inside the tubes to help achieve shear across the membranes. The capital and operating costs associated with the membrane component of an MBR system will be significantly affected by respectively, the value of the absolute permeate flux and the specific flux or permeability. Conventional external membrane systems typically operate in a flux range from 85 to 135 l/m2.h and at a TMP exceeding 210 kPa. The non-conventional, back-washable, lower velocity, lower pressure, air-liquid (i.e., air-lift systems) or liquid only based systems (i.e., non-conventional external membrane systems), typically operate in a flux range from 40 to 80 l/m2.h and at a TMP less than 30 kPa. Membrane supplier information and associated calculations imply the difference in absolute and specific flux values for the non-conventional versus the conventional external membrane system translates to a dramatic reduction in operating power cost. It can be expected the power cost associated with the non-conventional external membrane systems will be less than 10 to 20 percent of that of the conventional systems. The capital cost of the non-conventional external membrane systems is likely to be no more than 10 percent greater than the conventional system when all membrane system capital cost components (e.g., membranes, pumps, piping, controls, electrical, etc) are considered, despite the lower flux characterizing the systems. Internal membrane configuration. In the immersed or internal membrane MBR system (Figure 3), the membranes are directly submerged in the bioreactor mixed-liquor, preferably located in compartments or a separate tank coupled to the bioreactor to minimize membrane cleaning efforts. This configuration typically involves the use of polymeric membranes. The membranes are either vertically or horizontally oriented hollow fibers contained in a rectangular or tubular support structure, or vertically oriented flat sheets contained within a support structure. The mixed-liquor is located on the shell side of the membranes and the effluent is extracted into the lumen of the membrane. The driving force across the membrane is typically achieved by creating negative pressure on the lumen or permeate side of the membrane. The membrane component of this configuration involves substantially more membrane area per unit volume relative to the membrane component of the external MBR configuration, operates at a TMP typically 28 to 56 kPa and operates at an effective cross-flow velocity of less than 0.6 m/sec (Lei and Bérubé, 2004). Although the shear across the membrane fibers is increased by continuous or intermittent aeration and other methods are used in certain designs to minimize the build-up of solids on the membrane surface (e.g., frequent membrane backpulsing, intermittent permeation), the typical mean permeate flux characterizing these systems is less than 35 l/m2.h. Internal versus external configurations. Table 1 contains a summary of information comparing external and internal membrane MBR system configurations considering various technical and economic factors governing system selection. The external membrane configuration is preferred for a number of technical reasons. Despite these advantages, until recently the operating power cost associated with this configuration limited application to smaller wastewater flows (i.e., normally less than 380 m3/day). The development of non-conventional external membrane system designs will no doubt lead to much wider application of the external membrane MBR as the economics of the systems appear comparable to the internal membrane MBR configuration, at least up to flow rates approaching 1893 m3/day. To-date, at least 6, full scale, non-conventional external membrane, air-lift based MBR systems are in

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operation or under construction in the U.S. treating municipal wastewater or septage (Linden, 2006b). The largest system is designed to handle a wastewater flow of 3785 m3/day. Table 1 – Comparison of External and Internal Membrane Based MBR System Configurations

Comparative Factor External MBR Systems Internal MBR Systems

Membrane Area Requirement

Characterized by higher flux and therefore lower membrane area requirement.

Lower flux but higher membrane packing density (i.e., membrane area per unit volume).

Space or Footprint Requirements

Higher flux membranes with bioreactor operating at higher VSS concentration and skidded assembly construction, results in compact system.

Higher membrane packing density and operation at bioreactor VSS concentration of 10 g/l or greater translates to compact system.

Bioreactor and Membrane Component Design and Operation Dependency

Bioreactor can be designed and operated under optimal conditions including those to achieve biological N and P removal, if required.

Design and operation of bioreactor and membrane compartment or tank are not independent. High membrane tank recycle required (e.g., recycle ratio 4) to limit tank VSS concentration build-up.

Membrane Performance Consistency

Less susceptible to changing wastewater and biomass characteristics.

More susceptible to changing wastewater and biomass characteristics requiring alteration in membrane cleaning strategy and/or cleaning frequency.

Recovery of Membrane Performance

Off-line cleaning required every 1 to 2 months. Simple, automated procedure normally requiring less than 4 hours.

Off-line “recovery” cleaning required every 2 to 6 months. A more complex procedure requiring significantly more time and manual activity, at least on occasion may be required (i.e., physical membrane cleaning).

Membrane Life or Replacement Requirements

Results to-date imply an operating life of 7 years or more can be achieved with polymerics prior to irreversible fouling. Operating life of ceramics much longer.

Results to-date imply an operating life of 5 years may be possible prior to irreversible fouling and/or excessive membrane physical damage.

Full Scale Application Status

Conventional membrane based systems have a very long track record. Few non-conventional systems in operation in the U.S.

Full scale application widespread in the U.S.

Economics Non-conventional designs translate to comparable power costs. Comparable capital cost at least at lower wastewater feed rates (e.g., approaching 1893 m3/day).

Power and capital cost advantage at higher wastewater feed rates.

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Industrial Wastewater Treatment MBR System Suppliers The first large, U.S., full scale external and internal membrane MBR systems for treatment of industrial wastewater were installed in the 1990s, as previously referenced. In both cases, Zenon Environmental, now part of General Electric (General Electric-Zenon Environmental) provided the membrane system. Since that time, there has been a rapid escalation in the application of the MBR technology for industrial wastewater treatment in North America and elsewhere. The rapid market growth has resulted in MBR system product offerings from a number of suppliers (Table 2) who in the past offered conventional biological treatment systems or equipment and/or membrane systems, for industrial wastewater treatment. Most of the suppliers have focused their efforts on the supply of internal membrane MBRs, recognizing the power cost advantage of this configuration versus the conventional external membrane MBR. Shaw Environmental are rather unique in the marketplace in that they offer a number of high efficiency bioreactor configurations for treatment of industrial wastewaters and other contaminated aqueous streams containing more difficult to degrade compounds. In recent years, they have installed a number of conventional external membrane or internal membrane MBRs. They are now focused on supply of non-conventional external membrane MBRs recognizing the technical advantages of the configuration and the comparable economics with respect to internal membrane MBRs (Linden, 2006b). General Electric-Zenon Environmental and environmental companies affiliated with Kubota, to-date are the leaders in the supply of MBR systems for industrial wastewater treatment. ADI Systems represents Kubota for industrial wastewater treatment in North America and to-date have four, full scale internal membrane MBR systems either installed or under construction (Cocci, 2006). Future Developments The increased focus of membrane suppliers on the MBR application is likely to result in more cost-effective system embodiments of the technology as improvements are made in the efficiency of the membrane component. Additional future developments are likely to include the emergence of cost-effective anaerobic MBR systems and alternative MBR configurations in which membranes are used for other purposes than simply biomass-effluent separation. Membrane component efficiency. The volume of industrial and municipal wastewater treated by MBR systems worldwide is estimated to be growing by 20 percent per year (Le-Clech et al., 2005). As with any new technology, unforeseen design and operating issues arise as experience is gained. Identifying the issues form the user’s perspective and proposing solutions was the focus of MBR technology articles published in 2003 and 2005 (Sutton, 2003; Le-Clech et al., 2005). Not surprising the major issues identified related to the short and long term operating efficiency of the MBR membrane component. Basic research and membrane component development efforts have led to the introduction of membranes tailored to this application and resulted in other approaches focused on the objective of achieving and maintaining a high, absolute membrane flux and membrane permeability. The recent development of a specifically formulated, long chain cationic polymer to enhance the flux performance of polymeric

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Table 2 – Partial Listing of External and Internal Membrane MBR System Suppliers to North America For Industrial Wastewater Treatment

External Membrane MBR System Suppliers Internal Membrane MBR System Suppliers

General Electric – Zenon Environmental • Major supplier of conventional membrane based

systems. • Manufacture and supply membranes, membrane

modules and complete MBR systems. • Access to non-conventional designs through GE

relationship with X-Flow BV. Shaw Environmental

• MBR system supplier utilizing conventional and non-conventional membrane based systems but focused on supply of non-conventional systems (Linden, 2006b).

• Purchase membrane components from others. Have or are developing definitive agreements with membrane component suppliers.

Koch Membrane Systems • Supplier of conventional membrane based systems. • Provide membrane components for construction of

complete MBR Systems. PMC BioTech

• MBR system supplier utilizing conventional membrane based systems.

• Focused on thermophilic biotreatment. Purchase membrane components or systems from others.

Dynatec Systems • MBR system supplier utilizing conventional and non-

conventional membrane based systems. • Purchase membrane components from X-Flow BV.

General Electric – Zenon Environmental • Major supplier. • Manufacture and supply membranes, membrane

modules and complete MBR systems. • GE-Ionics MBR activity will be halted. Previously

Ionics through Mitsubishi offered horizontally oriented hollow fiber design (Novachis, 2006).

Shaw Environmental • Supplier of complete MBR systems through

relationships with membrane component suppliers. Dorr-Oliver Eimco/Enviroquip

• Supplier of complete MBR systems through relationship with Kubota who manufacture and supply membranes and membrane modules.

• Flat sheet design. ADI Systems

• Supplier of complete MBR systems through relationship with Kubota who manufactures and supplies membranes and membrane modules.

• Flat sheet design. Koch Membrane Systems

• Supplier of membrane systems through purchase of Puron AG.

• Provide membrane components or systems to others for construction of complete MBR Systems.

• Vertically oriented hollow fiber design. Smith & Loveless

• Supplier of complete MBR systems. • Focused on supply of standard, pre-engineered,

smaller systems. • Flat sheet design.

ITT Advanced Water Treatment • Supplier of complete MBR systems utilizing ITT

affiliated companies equipment components (e.g., Sanitaire aeration equipment).

• Vertically oriented hollow fiber design. Veolia Water

• Supplier of complete MBR systems. • Manufacture and supply membranes and membrane

modules and complete MBR system. • Offer both vertically oriented hollow fiber and flat

sheet design. Siemens - US Filter

• Major supplier. • Manufacture and supply membranes and membrane

modules through Memcor. Supply complete MBR systems.

• Vertically oriented hollow fiber design.

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membranes used in internal membrane MBRs is an example of a positive research outcome (Livingston and Trivedi, 2006). Anaerobic MBR systems. In 1982, Dorr Oliver introduced an anaerobic MBR system for treatment of industrial wastewaters (Sutton et al., 1983). Pilot study results indicated the technology held great promise for treatment of high strength wastewaters provided improvements could be made in membrane efficiency. Since that time, a number of anaerobic MBR research and development studies have been completed (Sutton et al., 2004). The results of these studies and recent work completed under a Water Environment Research Federation project (Hall et al., 2006), imply ceramic membranes may be a good choice in the anaerobic MBR application due to evidence of less membrane fouling and the ability to rigorously clean the membranes without concern for negatively affecting membrane life. CeraMem Corporation is providing membranes to researchers and MBR system suppliers who are exploring ceramics for this MBR application (Bishop, 2006). Alternative MBR configurations. Direct treatment of industrial wastewaters containing complex organics in microbially hostile environments (e.g., high salt concentration) is often impractical (e.g., need for excessive wastewater dilution). Extractive membrane biological reactors (EMBRs) may provide an attractive alternative to physical-chemical processes for treatment of these wastewaters. The EMBR uses membranes to separate the waste stream form a biological liquid solution which contains suspended organisms and/or is in contact with organisms attached as a biofilm to the membranes. In alternative but similar systems, the membrane is used to transfer pure oxygen or another gas from the lumen side of the membrane to the liquid solution containing the contaminants and the organisms which form a biofilm on the membrane. The membrane biofilm reactor (MbfR) system currently being commercialized by Applied Process Technology (Rittman, 2006a), represents a system embodiment of this alternative MBR configuration. In the system, hydrogen gas is transferred through hollow fiber membranes representing an electron donor for autotrophic bacteria that reduce nitrate, and other oxidized contaminants such as perchlorate and selenate (Rittman, 2006b). Selected Full Scale Applications Wastewaters from production of membrane materials. The application of membranes for environmental control, including use in the MBR application, has seen a dramatic increase in the last 10 years. Membrane suppliers have responded by expanding their existing and/or building new manufacturing facilities. The production of polymeric membranes results in the release of a variety of complex organic compounds typically including, dimethylformamide (DMF), n-methyl pyrrolidone (NMP), polyvinylpyrrolidone and glycerin. These organic nitrogen compounds often are present in the wastewaters at very high concentrations (e.g., DMF at 30,000 mg/l). Biological treatment of these wastewaters requires close control of the reactor SRT and other process conditions, favoring the MBR configuration. Typically, biological treatment of polymeric membrane production wastewaters results in the release of ammonia as an end product of organo-nitrogen metabolism. At high concentrations, the un-ionized form of ammonia can be quite toxic. Higher pH values shift the ammonia/ammonium ion equilibrium toward the un-ionized form. Nitrite is produced from

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ammonia in the presence of dissolved oxygen by the action of the nitrifying bacteria, Nitrosomonas. Typically, the nitrite formed is rapidly oxidized to nitrate by the action of Nitrobacter but if process conditions are not suitable for the growth of Nitrobacter, nitrite can accumulate. Based on laboratory pilot studies, it was found in order to treat these wastewaters and obtain near complete organic carbon removal, the ammonia concentration in the bioreactor had to be controlled below approximately 3500 mg/l, a specific SRT had to be maintained (i.e., minimum and maximum respectively, near 5 and 10 days) and the reactor pH had to be controlled in the range from 5.0 to 5.5, based on operation at a temperature in the 35° to 40°C range (Sutton and Togna, 2005). A full scale internal membrane MBR system was designed and installed in the U.S. based on these process boundary conditions. Wastewaters from the manufacture of food products. Since installation in 1998 of the first large, U.S., full scale internal membrane MBR system for treatment of wastewater from the former Nestle food ingredients manufacturing plant in New Milford, CT (Cantor et al., 2000), a number of suppliers have provided MBR plants to treat food processing wastewaters. The Nestle referenced MBR system was designed to achieve over 90 percent total nitrogen removal in the treatment of a wastewater with maximum nitrogen and COD concentrations exceeding respectively, 800 and 12,000 mg/l. Start-up of the MBR system began in early 1999. To-date, the MBR system has run successfully, undergoing various modifications and upgrades over the years. The Nestle application represents use of the MBR technology to upgrade an existing activated sludge system treating a food products wastewater. It was the first large, full scale internal membrane MBR system installed in the U.S. for treatment of industrial wastewater, as previously noted. The membrane system was provided by General Electric-Zenon Environmental. The company claims it is now in the process of designing what will be the largest MBR system in North America for treatment of industrial wastewater (Novachis, 2006). In this case, an existing biological system treating wastewater from the production of mainly starch based products is being expanded to handle an increase in COD load. The production plant owned by Tate & Lyle is located in Lafayette, Indiana. The internal membrane MBR system is being designed to handle a wastewater flow of 10,790 m3/day containing a COD of approximately 5000 mg/l. It is worthwhile noting the largest external membrane MBR system in North America to the knowledge of the writer, will also treat wastewater from the manufacture of food products. General Mills is installing the MBR system at their plant in Covington, GA as a pretreatment step prior to reverse osmosis, with the objective of producing water for reuse (Linden, 2006b). The plant, currently under construction, is designed to treat a wastewater flow of 1893 m3/day. Dynatec Systems is providing the MBR system teaming with Aquabio of Worcester, UK. Thermophilic bioprocess application. The advantages of aerobic, thermophilic versus mesophilic biotreatment of high strength industrial wastewaters, normally include higher volumetric reaction rates and a decrease in excess biomass production. A major disadvantage of the process is thermophilic organisms do not flocculate very well leading to biomass particles with poor settling characteristics. Use of membranes for biomass-effluent separation addresses this issue. All full scale aerobic thermophilic MBRs installed to-date involve the use of external polymeric membranes. The external polymer membranes systems currently commercially

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available, tend to be able to withstand higher operating temperatures versus the internal membrane system designs. PMC BioTec is the leader to-date in the supply of full scale thermophilic MBR systems (Rozich, 2006) although systems have been provided by others (Togna et al., 2003). CONCLUDING REMARKS The following conclusions can be made regarding the use of MBRs for treatment of industrial wastewaters.

• The MBR technology has proven optimal for treatment of many industrial wastewaters.

• The external membrane MBR configuration is preferred versus the internal membrane configuration, for a number of technical reasons.

• Recent membrane and system design advances have resulted in comparable economics for external versus internal membrane MBRs over a much broader wastewater flow rate range.

• Future developments are likely to include the emergence of cost-effective anaerobic MBR systems and full scale application of alternative MBR configurations in which membranes are used for other purposes than simply biomass-effluent separation.

REFERENCES Cantor, J.; Sutton, P.M.; Steinheber, R.; Novachis, L. (2000) Industrial Biotreatment Plant Capacity Expansion and Upgrading Through Application of Membrane Biomass-Effluent Separation. Proceedings of the WEF 73rd Annual Conference & Exposition, Anaheim, CA. Bishop, B.A. (2006). Personal communication to P.M. Sutton. CeraMem Corporation, Waltham, MA, May. Cocci, A. (2006). Personal communication to P.M. Sutton. ADI Systems, Salem, NH, May. Hall, E.R.; Bérubé, P.R.; Sutton, P.M. (2006) Membrane Bioreactors for Anaerobic Treatment of Wastewaters. Project 02-CTS-4, Water Environment Research Foundation. Knoblock, M.D.; Sutton, P.M.; Mishra, P.N.; Gupta, K.; Janson, A. (1994) Membrane Biological Reactor System for Treatment of Oily Wastewaters. Water Environment Research, 66 (2), pp.133-139. Le-Clech, P.; Fane, A.; Leslie, G. (2005) MBR Focus: The Operators Perspective. Filtration & Separation, June pp. 20-23. Lei, E.; Bérubé, P.R. (2004) Impact of Membrane Configuration and Hydrodynamic Conditions on the Permeate Flux in Submerged Membrane Systems for Drinking Water Treatment. Proceedings AWWA Water Quality Technology Conference, San Antonio, TX.

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Linden, S. (2006a). Industrial MBR Issues. Novel MBR Technologies for Industrial Wastewater Treatment and Reuse, WEF Webcast, May. Linden, S. (2006b). Personal communication to P.M. Sutton. Shaw Environmental & Infrastructure, Stoughton, MA, May. Livingston, D.; Trivedi, H. (2006) Treating the Cause Not the Symptom. Membrane Technology, Supplement to Water & Wastes Digest, Spring, pp. 18-19. Novachis, L.N. (2006). Personal communication to P.M. Sutton. General Electric – Zenon Environmental, Oakville, Ontario, May. Pain, L. (2006). Personal communication to P.M. Sutton. ITT Aquious-PCI Membrane Systems, Milford, OH, May. Rittman, B.E. (2006a). Personal communication to P.M. Sutton. Arizona State University, Tempe, AZ, April. Rittman, B.E. (2006b) The Membrane Biofilm Reactor: The Natural Partnership of Membranes and Biofilm. Water Science & Technology, 53 (3), 219-226. Rozich, A.F. (2006). Personal communication to P.M. Sutton. PMC BioTech, Exton, PA, May. Smith, C.V.; Di Gregorio, D.O.; Talcott, R.M. (1969) The Use of Ultrafiltration Membranes for Activated Sludge Separation. Proceedings of the 24th Industrial waste Conference, Purdue University, Lafayette, Indiana, pp. 805-813. Sutton, P.M.; Li, A.; Evans, R.R.; Korchin, S. (1983) Dorr-Oliver’s Fixed Film and Suspended Growth Anaerobic Systems for Industrial Wastewater Treatment and Energy Recovery. Proceedings 37th Industrial Waste Conference, Purdue University, Lafayette, IN, Ann Arbor Science, Ann Arbor, MI, pp. 667-675. Sutton, P.M.; Mishra, P.N.; Roberts, J.A.; Abreu, L.; Gignac, P. (2001) Optimization of Oily Wastewater Membrane Bioreactor Treatment: Pilot to Full Scale Results. Proceedings of the Water Environment Federation 72nd Annual Conference & Exposition, Atlanta, GA, October. Sutton, P.M. (2003) Membrane Bioreactors for Industrial Wastewater Treatment: The State-of-the-Art Based on Full Scale Commercial Applications. Proceedings of the Water Environment Federation 74th Annual Conference & Exposition, Atlanta, GA, October. Sutton, P.M.; Bérubé, P.R.; Hall, E.R. (2004) Membrane Bioreactors for Anaerobic Treatment of Wastewaters – Phase 1 Report: Compilation/Review of Existing Literature. Project 02-CTS-4, Water Environment Research Foundation.

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Sutton, P.M.; Togna, A.P. (2005) Biological Treatment of Industrial Wastewaters and Other Contaminated Aqueous Streams: Selection of Bioreactor Alternatives. Proceedings of the Water Environment Federation 76th Annual Conference & Exposition, Washington, DC, October-November. Tonga, A.P.; Yang, Y.; Sutton, P.M.; Voight, H.D. (2003) Testing and Process Design of a Thermophilic Membrane Biological Reactor to Treat High-Strength Beverage Wastewater. Proceedings of the Water Environment Federation 74th Annual Conference & Exposition, Atlanta, GA, October. Van’t Oever, R. (2005) MBR Focus: Is Submerged Best. Filtration & Separation, June, pp. 24-27. Yamamoto, K.; Hiasa, M.; Manhmood, T.; Matsuo, T. (1989) Direct Solid-Liquid Separation Using Hollow Fiber Membrane in an Activated Sludge Aeration Tank. Water Science & Technology, 21, 43-54.

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