RECYCLE, REUSE AND RECOVERY TECHNOLOGY WASTEWATER, BIOSOLIDS & WASTE MANAGEMENT

Transcription

1 RECYCLE, REUSE AND RECOVERY TECHNOLOGY WASTEWATER, BIOSOLIDS & WASTE MANAGEMENT Applications of Immersed Membrane Bioreactor Technology for Advanced Wastewater Treatment & Water Reuse in the Caribbean by James W. Hotchkies, P.Eng. Vice President Land Development Systems, ZENON Environmental Inc., 3239 Dundas Street West, Oakville, Ontario L6M 4B2 Canada Tel: ext FAX: September 2003

2 ABSTRACT While Immersed Membrane Bioreactor (IMBR) technology is a relatively recent approach to advanced wastewater treatment & reuse in the Caribbean, it has been applied extensively throughout North America & Europe for over ten years. In fact, in many parts of North America, IMBR technology is the preferred approach for many wastewater treatment & reuse applications, particularly for resorts, casinos, office buildings & schools in environmentally sensitive regions or where water supply is limited. However, the technology is now being applied throughout the Caribbean, with three IMBR plants in operation one for over three years two under construction and a significant number under consideration. Increasingly, we are starting to recognize the consequences of indiscriminate wastewater discharge and the serious implications of fresh water shortages. As a result, throughout the Caribbean & around the world, the treatment of wastewater to reuse quality has become one of the most critical issues of water management. The technology that is leading this introduction of IMBR systems within the Caribbean is the ZeeWeed membrane bioreactor. Developed by Canada s ZENON Environmental Inc., the ZeeWeed MBR is the most extensively used MBR technology in the world, with installed systems from less than 1,000 USgpd (4 m 3 /d) to over 12 mgd (50,000 m 3 /d), in locations from Singapore to Scotland. In application after application, it is the most cost-effective solution for both thorough wastewater treatment and optimum water reuse. Based around ZENON s immersed ZeeWeed membrane, the process treats highly variable and high-strength wastewater to the most advanced quality levels possible and, as a result, maximizes the potential for water reuse. With over 400 installations around the world, ZENON is the world leader in MBR technology and has set the standard for advanced wastewater treatment and water reuse. Using specific case studies of plants now operating in the Caribbean in the USVI & Barbados this paper will provide a technical overview of the ZeeWeed MBR process and discuss key factors that are critical to successful application of the technology in this region. From this experience, the paper will also discuss how specific project feedback has enhanced the designs of the two plants now under construction one in Barbados & one in the BVI and several other plants under design. In particular, the paper will discuss materials of construction, equipment selection and automation philosophy. Page 2 of 10

3 BACKGROUND Globally, water has become a critical commodity and is now recognized as a finite and valuable resource. In a world that has come to realize the consequences of indiscriminate wastewater discharge and the serious implications of fresh water shortages, the treatment of wastewater to advanced discharge standards or reuse quality has become one of the most critical issues in global water management. Nowhere is this more important than throughout the Caribbean basin, where many islands have severely limited water supplies and where the rapid growth of tourism has stressed the wastewater attenuation capacity of the environment to its limits. The problems facing many project developers or communities are, however, complex & varied:! Existing wastewater treatment plants if they exist may be overloaded or under-designed, or may be unable to handle the new, increased flows that are being generated.! Water costs are escalating rapidly or the supply of potable water is limited, and high quality reuse water is becoming increasingly attractive.! The space available to expand an existing plant or to construct a new treatment facility is extremely limited, or land costs are high.! The flow rate, composition and/or strength of the wastewater are highly variable, either on a daily or a seasonal basis, and conventional technology plants are unable to cope.! The initial wastewater flows in a new development are small but may increase by as much as an order of magnitude in the future.! Treated effluent will be discharged into a sensitive environment, where nutrient reduction or pathogen removal are critical requirements.! The location is relatively remote, perhaps with a limited availability of operating personnel, and a simple, reliable & easy-to-maintain solution is required. For these and other, challenging applications from Barbados to the Balkans, from Scotland to Singapore the ZeeWeed immersed membrane bioreactor (MBR) technology has become the preferred solution. Established in 1980, ZENON was a pioneer in the development of immersed membranes and MBR technology for wastewater treatment and water reuse. Today, with over 400 installations, ZENON has the largest base of installed MBR capacity in the world. With individual system capacities from less than 1,000 USgpd (4 m 3 /d) to over 12 USmgd (50,000 m 3 /d), ZENON is the world leader in MBR technology and has set the standard for advanced wastewater treatment and water reuse. The ZeeWeed MBR Solution A combination of the toughest and most reliable ultrafiltration (UF) membrane available, with a high-strength activated sludge process, the ZeeWeed MBR system is the proven solution for difficult-to-treat wastewater, demanding effluent targets and water reuse. Page 3 of 10

4 At the heart of the system is the industry-leading ZeeWeed immersed UF membrane. Invented by ZENON in the early 1990 s, ZeeWeed has become the industry standard for hard-to-treat wastewater, offering a powerful combination of unique features:! ZeeWeed is an immersed, suction-driven, hollow fiber membrane. The ZeeWeed membrane module is a shell-less, rectangular frame of hollow fiber bundles, immersed directly in the mixed liquor of an aerobic reactor and connected to the suction side of a centrifugal pump. Under a gentle suction of 3-8 psi (20-60 kpa), treated water (permeate) is drawn through the pores of the membrane into the hollow core of each fiber and discharged from the system.! ZeeWeed is an outside-in hollow fiber membrane, where water flows from the outside of the fiber to the inside of the membrane. As a result, the inside of the membrane only sees clean, filtered water and is never subject to fouling or plugging.! With a nominal pore size of µm (0.1 µm absolute), ZeeWeed membranes reject all suspended and colloidal solids, including bacteria & most viruses. Any solids larger than this including the bacteria in the biomass are unable to pass through the pores and always remain on the outside of the hollow fiber.! ZeeWeed is a composite membrane, where the semi-permeable membrane is cast over a porous but tough, structural core to create the strongest, most durable & most flexible membrane available. Page 4 of 10

5 ! ZeeWeed is resistant to chlorine, in concentrations up to 2,000 mg/l. Any surface fouling that might occur over time, from an accumulation of organic material on the membrane, may be removed easily by an automated cleaning process with sodium hypochlorite (bleach), either in-situ or in a dedicated dip tank. Also, this chlorine resistance allows for easy disinfection of the membrane.! Using a low suction to move water through the membrane require considerably less energy than with the high positive pressure used in many other membrane processes. In ZENON s MBR process, the ZeeWeed membranes are installed directly in the aerobic section of the bioreactor, or in discrete membrane tanks that are hydraulically connected to the bioreactor. The membranes are immersed in the aerated mixed liquor and are connected to the suction side of a standard centrifugal pump. Wastewater is biologically degraded (digested) in the aerobic section of the bioreactor and recirculated continuously within the bioreactor or between the bioreactor and the membrane tanks. Paced to the inflow of raw wastewater to the system, treated permeate is drawn through the membranes & discharged from the system. Air is supplied to the system, from standard positive displacement blowers, and distributed to the process through a grid of fine bubble diffusers. Common or separate blowers provide a continuous supply of coarse bubble air scour to the membranes. On either a continuous or cyclic basis, the coarse-bubble airflow is introduced at the bottom of each membrane module, producing a vigorous turbulence that scours the external surface of the hollow fibers and moves the rejected solids away from the membrane surface. Wastewater is recirculated continuously from the bioreactor to the membrane tanks, at a rate of 8 times average day flow (ADF), by one or more submersible transfer pumps, and returned by gravity to the lead end of the bioreactor. This recirculation moves accumulated solids away from the membranes and creates a more uniform biomass. Modular MBR Schematic Wastewater influent Screening Concentrate or sludge MMBR Module Clean in Place tank Treated Water Permeate & Backpulse Pumps Mixed liquor Recirculation pumps Bioreactor Aeration Blowers Air Scour Blowers Page 5 of 10

6 Typically, the lead end of the bioreactor is designed as an anoxic (zero dissolved oxygen) zone. This is used to assist with ph control in standard systems and for denitrification in applications where extremely low levels of total nitrogen (TN) are required in the effluent stream. The process may also be enhanced easily for phosphorus reduction. The addition of a metal salt, such as ferric chloride or alum, will precipitate the phosphorus in solution and this now suspended solid will be unable to pass through the membrane pores. Unlike a conventional system, however, where a significant volume of metal salt is required to precipitate, coagulate & flocculate the phosphorus into readily settleable particles, the ZeeWeed MBR process only requires for formation of a pin-floc that will be blocked by the fine size of the membrane pores. In the ZeeWeed MBR system, the ZeeWeed membrane is a complete physical barrier to any suspended solids and completely replaces the clarification and sand filtration processes found in a conventional activated sludge process. Solids are completely separated from the treated wastewater by the membrane and there is never any need to settle sludge. This yields a number of very positive results:! With no need to settle sludge, the bioreactor in a ZeeWeed MBR system operates at MLSS concentrations of 10-15,000 mg/l. This is 3 to 4 times higher than possible with a conventional activated sludge system, and dramatically improves the removal of both soluble and particulate biodegradable material in the waste stream.! Highly variable wastewater (flow and/or concentration), a condition that causes serious upset problems in a conventional system, has absolutely no effect on the smooth operation of a ZeeWeed MBR system.! With no need to settle sludge, the continuous monitoring of sludge characteristics is no longer required. As a result, a ZeeWeed MBR system is easy and inexpensive to operate and maintain, and may require only 3-4 hours per week of operator attention. Over the last two decades, the ZeeWeed MBR has become the industry standard MBR technology for the treatment of municipal sewage, industrial wastewater, landfill leachate, as well as for the treatment of effluent from residential and commercial developments, recreation facilities, hotels and resorts, shopping centers and other, similar land development projects:! ZeeWeed membranes can be installed in almost any existing wastewater treatment plant, converting it to a high-efficiency MBR process and increasing treatment capacity by up to 500% in the same footprint.! With a process efficiency of greater than 98% reduction in BOD & TSS, coupled with the absolute barrier provided by the ZeeWeed membrane, effluent will always meet the highest discharge or reuse quality standards.! The modular construction of ZeeWeed allows developers to start with the smallest capacity required & then add more capacity (modules) as demand grows.! With no clarifiers or tertiary filters, and operating with a significantly more efficient biomass, a ZeeWeed MBR system requires as little as 1/10 th of the space required by a conventional activated sludge plant. Civil construction costs are slashed and significantly less valuable property is lost to non-revenue producing activities.! The ZeeWeed MBR technology is simple, elegant and thoroughly reliable. The process is fully automated and designed to operate in almost any environment. The plants may be monitored & controlled via modem from thousands of miles away. Page 6 of 10

7 The Caribbean Experience At a five-star USVI resort, the existing, 15-year-old treatment plant was unable to handle the increased wastewater flows of the expanded hotel & could not achieve the newer, more demanding effluent standards. The resort recognized the need to upgrade the existing plant but the situation posed several challenges:! There was no alternate location for wastewater disposal and the plant could not be taken out of service while it was upgraded.! The hillside location of the plant prohibited the construction of any more treatment tanks.! The plant access road made mobilization for heavy construction extremely difficult. Using the ZeeWeed MBR technology, the plant capacity was tripled without adding any treatment tanks. Furthermore, the unique design developed for this project allowed installation of the membranes while the plant continued to process wastewater. The treated water exceeds DPNR and EPA s standards for reuse. An added benefit of this system is that it reduces the amount of sludge that must be hauled and dramatically reduces the odours at the facility. The upgraded plant was able to treat an average annual flow of 100,000 USgpd (400 m 3 /d) with a peak flow of over 200,000 USgpd (800 m 3 /d). After three years of flawless operation, with 100% of the treated water being used for landscape irrigation, the plant is being further expanded by the simple addition of extra membrane modules. At a luxury resort on the West Coast of Barbados, a major expansion of the facility required a complete reassessment of the hotel s wastewater treatment capability. The hotel s existing wastewater treatment system, comprising an underground aerobic treatment system, was unable to provide adequate treatment when conditions were less than perfect. In particular, the system experienced problems during shock loading events or during low flow periods both typical conditions for a Caribbean resort and was unable to produce a reuse quality treated water on any consistent basis. After evaluating several alternatives, the resort decided to install a ZENON Modular Wastewater (MWW) treatment system to handle the additional flow from the expanded facility. Designed for an initial flow of 9,000 USgpd (36 m 3 /d), the system can be expanded to an ADF capacity of 12,000 USgpd (48 m 3 /d) by the simple addition of another membrane module. Page 7 of 10

8 During peak periods, the system is able to handle flows in excess of 20,000 USgpd (80 m 3 /d). All of the treated wastewater is used for irrigating the extensive gardens of this exclusive resort. MWW Schematic Wastewater influent Concentrate or sludge MWW Module Permeate Pump Clean in Place tank Treated Water Bioreactor Backpulse Pump Mixed liquor recirculation pump Aeration Blower Air Scour Blower At this location, the MWW system employs discrete biological treatment and membrane separation units. The biological treatment is performed in an underground, aerated process vessel, of fibreglass construction. Submersible grinder pumps transfer mixed liquor to the MWW membrane unit, at a rate of 4 times ADF, from where the stream flows by gravity back to the bioreactor. Centrifugal pumps pull permeate through the ZeeWeed membranes under suction and deliver treated water to the reuse storage tank. After a year of successful operation, an analysis of the treated wastewater demonstrated nondetectable total coliforms in the sample. The permeate is crystal clear & has been applied extensively throughout the resort for landscape irrigation. Intended for applications with average design flows between 3,000 USgpd (12 m 3 /d) and 25,000 USgpd (100 m 3 /d), the MWW system is an easily installed, pre-engineered unit that offers clients the lowest cost MBR platform available. Page 8 of 10

9 Fully assembled at ZENON s Canadian manufacturing facility, the MWW system is designed to ship in a standard 20 ISO container and is ready for use once power is connected to the control panel. This reduces the complexity of the entire installation process significantly. As a result, the overall system becomes a very cost-effective and easily installed package. To date, the ZeeWeed MBR has been applied successfully in hundreds of projects around the world, from Arctic to equatorial climates. However, while the technology is effective on wastewaters from 1 o to 40 o C, the Caribbean offers some unique experiences and places some unique demands.! If you need it for the project, ship it with the equipment. o Unlike North America or Europe, equipment suppliers cannot assume that small, miscellaneous items can be obtained from local stock. Even basic items such as pipe fittings and motor starters may not be available at all on some islands and, if they have been overlooked in the initial plant shipment, will have to be shipped in from the mainland often at significant expense. o An adequate quantity of parts that are often consumed during start-up operations, such as seals, fuses, etc., should be included as part of the primary shipment. o Even miscellaneous items such as pipe hangers & fasteners that are readily available in a supplier s domestic market may not be available, and should be included as part of the project scope.! An electrical experience. o Specific brands of electrical hardware, often standard components for North American or European suppliers, may not be available on some islands. Suppliers should determine the brands of hardware available locally & change their designs to reflect this product Page 9 of 10

10 availability. Alternatively, sufficient shelf spare components should be supplied for all non-local items. o It should be assumed that all PLC components, such as spare I/O cards, are not available from local suppliers. Spare cards, or even an entire PLC should be included in the critical spares list. Provision should also be made for a secure local source of the project-specific PLC program. o Many islands experience wildly fluctuating or unstable (dirty) power. All control panel components should be protected from such power variability and/or sensitive hardware should be avoided. On many projects, VFD s are a source of unending problems & should be eliminated completely. o Daily temperature/humidity fluctuations may result in severe condensation problems in some electrical components, such as valve actuators. Assume that climate control is not available & design for the worst conditions anticipated, eg installing heaters in the actuators. o The 50 vs 60 Hz issue is obvious, but be careful that the equipment supplied is actually a true 50 or 60 Hz component and not just generally compatible with either.! Not always as specified. o Although not unique to the Caribbean, site services & construction details specified by suppliers may not always be installed or constructed as defined. It s just a lot more expensive to remedy problems in the Caribbean than in Connecticut. Suppliers should always check & recheck all critical site requirements before shipping parts & assemblies to the field. In the case of non-conformance, it may be significantly less expensive to change items at the factory than in the field.! A material difference. o The Caribbean offers some unique environmental challenges & is considerably different than the markets to which most suppliers send their equipment. PVC should be UVprotected; stainless steel should be marine-grade; carbon steel should be carefully coated & cathodically protected; galvanized parts should be avoided, etc. Suppliers need to recognize that the site may be very close to the sea & will often be exposed to 365 days of sunshine, and that all parts & equipment must be designed to operate in these conditions. o Equipment or system specifications should clearly articulate the need for suppliers to incorporate Caribbean-compatible materials into their designs.! Service & support. o Even the best made & most carefully designed equipment will require maintenance. Both the client & the supplier need to determine how & how fast parts can be replaced & equipment can be repaired. While major support may always require sending key personnel from a supplier s home base, clients should look for & insist on locallyavailable (at least within the region) service for most routine maintenance & repair activity. o In their domestic markets, equipment suppliers can often diagnose process problems via remote modem access. In the Caribbean, reliable telephone connections for complex data exchange may not be readily available & remote troubleshooting may not be possible. Clients should insist on the availability of trained, regionally-located service personnel.! Truly taxing. o Different islands can have dramatically different customs, excise & tax requirements, and most are radically different than those in most supplier s domestic markets. To avoid lengthy & costly delays at the port of entry, and major tax liabilities, equipment suppliers should research local requirements thoroughly. Page 10 of 10