Shown under construction, Lakeview's permeate pump room is flanked by UF membrane platforms.
The ZeeWeed Access Platform (ZAP) moves along the top of the membrane tanks and eliminates the need for an overhead crane, membrane cassette lifting brackets and tank covers.
A service technician removes a ZeeWeed membrane module from a cassette on the ZeeWeed Access Platform.
A technician looks on as BACC tanks are filled with carbon during Lakeview's construction.
By the end of June, the world's largest immersed membrane ultrafiltration (UF) plant will be fully operational and will begin treating water for more than 700,000 people in the rapidly growing Region of Peel, Ontario, Canada. The 96 MGD (363 ML) expansion to the Lakeview Water Treatment Plant is the first large-scale operation to combine ozone and biologically active carbon (BAC) pretreatment with immersed ultrafiltration membranes in one of the most technologically advanced municipal water facilities.
The decision to expand the Region's 56-year old 148 MGD (560 ML/d) conventional treatment plant with advanced treatment technology was influenced by several factors, including the introduction of the Ontario Safe Drinking Water Act, the need to protect the aesthetic quality of the drinking water from periodic taste and odor episodes, space constraints at the site, future expansion capabilities, and the declining cost of membrane systems.
Evolving water regulations influence selection of treatment technology
Following the Walkerton, Ontario tragedy in 2000, where seven people died and hundreds became ill from drinking water contaminated with E. coli and campylobacter bacteria, the Ontario government created the Ontario Safe Drinking Water Act in 2002. As the Region of Peel began planning for upgrades and expansions to its water infrastructure, planners wanted to be sure they were making prudent decisions that reflected the evolving regulatory environment.
"We assembled a team of water experts to develop a Water Quality Master Plan for the Region," explains Mark Schiller, Director of Water and Wastewater for the Region of Peel. "Our objective was to examine emerging global water quality and regulatory trends, identify the risks facing the Region's water systems, and develop a proactive strategy that prepares us for future changes in Ontario. We wanted to be sure that our infrastructure upgrades would allow us to stay well ahead of the regulatory curve."
Lakeview's water challenges
Located along the north shore of Lake Ontario, the raw water intake for Lakeview WTP is in close proximity to the outfall of one of the Region's wastewater treatment plants. Although the lake generally offers very good quality water, the proximity of the pipes and the heavy use of this area of the lake as a waterway and recreational area can bring about adverse fluctuations in water raw quality such as higher levels of pathogenic organisms, elevated turbidity, and occasional taste and odor episodes.
"Lakeview's expansion gave us an opportunity to re-evaluate the treatment objectives for our water plants," says Mitch Zamojc, Commissioner of Public Works for the Region of Peel. "The preparation of our Water Quality Master Plan revealed that water quality issues in the Great Lakes would continue to increase and regulations would become more stringent. As a result, we decided to select technology for the expansion that would exceed the Ontario Safe Drinking Water standards."
In 2003, the Region of Peel worked with CH2M HILL to conduct an environmental assessment that compared 22 water treatment options. The results of the assessment revealed that a multi-barrier treatment process consisting of ozone, biologically activated carbon contactors (BACC) and ultrafiltration membranes could offer the best water quality, most consistent performance, smallest plant footprint, and favorable lifecycle costs.
Three membrane vendors with experience in large-scale drinking water plants were asked to participate in a pilot study to evaluate the effectiveness of two treatment schemes; ozone and BACC pretreatment followed by membrane filtration (OBM), and membrane filtration followed by ozone and BACC (MOB).
"There is limited full-scale experience with ozone, BACC and membranes operating together, and virtually none showing how effective this treatment train would be for water from the Great Lakes," Schiller says. "However, we knew that each of these technologies is well accepted and effective. Our pilot testing was a critical step to tell us which configuration would work best and the quality of filtered water that we could consistently count on."
ZeeWeed membranes selected
The pilot testing, designed and operated by CH2M HILL, was conducted over a six-month period at the existing plant from the spring to the fall of 2003. During the testing, the pilot systems experienced a variety conditions including a broad range of feedwater temperatures, prolonged taste and odor episodes (> three weeks) , and high turbidity feedwater (> 40 NTU) caused by summer storms and the tropical storm effects of Hurricane Isabel.
The testing revealed that the OBM train was the ideal configuration. Pretreatment with ozone and BACC, removed up to 90 percent of the organic foulants prior to membrane filtration, enabling the membranes to operate at higher fluxes for longer periods of time with fewer cleaning intervals. Overall, the OBM train consistently produced treated water with at least 4-log removal of Cryptosporidium, turbidity of less than 0.1 NTU and insignificant levels of disinfection byproducts.
"We were extremely pleased with the results of the pilot testing," says Schiller. "Not only were we able to gather the data we needed to optimize the treatment process, but the performance of the pilot proved that a large-scale plant, utilizing ozone, BACC and membranes, can handle any potential upset situation and will consistently deliver high quality drinking water no matter what the conditions might be in the lake."
The pilot study also evaluated the ability of each membrane technology to comply with the US EPA's Stage 2 Disinfectants and Disinfection Byproduct Rule (DBPR) and the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). Since Ontario water policy has historically reflected the regulatory framework of the United States, the Region of Peel wanted to be sure that the new treatment process could meet the latest EPA regulations.
Following the pilot study, each membrane vendor submitted technical and cost proposals that reflected both capital and 20-year operating costs. Once bids and pilot performance was evaluated, the Region of Peel selected ZeeWeed ultrafiltration membranes, manufactured by GE Water & Process Technologies.
Latest ZeeWeed membranes add almost 40 percent more capacity The original expansion plan for Lakeview WTP specified a capacity increase of 70 MGD (262 ML/d), based on surface area and permeability data supplied by vendors during the pilot testing and in the product bids. However, ZENON, which has since been acquired by GE Water & Process Technologies, also proposed its newest generation of ZeeWeed 1000 membranes with enhanced performance that offered greater expansion capabilities.
"A new manufacturing technique made it possible for us to dramatically increase the number of membrane fibers in each ZeeWeed module, resulting in much greater filtration surface area," explains Manwinder Singh, Global Product Management Leader at GE Water & Process Technologies. "We also added larger permeate ports in the modules to reduce pressure loss and increase flux rates. As a result, the membranes are substantially more efficient, leading to smaller plant footprints and lower capital and operating costs."
There were also changes to the way the membranes are aerated. Air is now more uniformly directed through the fiber bundle, providing a more efficient solids removal process from the fibers. "The new aeration method makes the modules more tolerant to solids, which reduces their susceptibility to fouling," Singh adds.
The Region of Peel decided to take advantage of the new membranes to add more treatment capacity to the current expansion, and reduce future expansion costs. The Region and CH2M HILL worked to develop an alternative design that increased plant capacity by 38.5 percent, from 70 MGD to 96 MGD, with only a small increase in plant footprint-less than seven percent. This adds redundant treatment capacity for the short term, but will facilitate expansions to increase Lakeview's capacity to 303 MGD (1150 ML/d) by 2013.
Most advanced large-scale treatment process
The treatment process will start by adding chlorine at the plant intake to control zebra mussels. The water will then be pre-screened and pumped to a feed header that can supply either the conventional treatment plant or the expansion. Water that is directed to the advanced treatment train will be treated with caustic to adjust the pH to a level that is acceptable for the BACC. Ozone, generated from liquid oxygen, will then be added to perform multiple tasks. Ozone provides 1-log inactivation of Cryptosporidium and also oxidizes organic compounds that cause taste and odor problems. Sodium bisulfite will be added to the ozone-contacted water for quenching prior to releasing it to the BACC. Peroxide can also be added for additional taste and odor control.
After ozonation, the water will travel by gravity to the deep-bed activated carbon filters for removal of organics and taste and odor control. The BACC will also act as a roughing filter for turbidity removal. From the BACC, the water will flow by gravity to the membrane filtration tanks. Lakeview will have 12 membrane process trains, each consisting of a 14,500-gallon (55,000 L) tank that can hold up to seven ZeeWeed membrane cassettes. Eleven of the trains will operate at all times, with the twelfth train operating on demand, whenever one of the others is taken out of service for cleaning, scheduled maintenance or testing.
The ZeeWeed membrane cassettes will be immersed directly into the membrane tanks, and will filter water using low-energy vacuum applied to the fibers. ZeeWeed ultrafiltration membranes operate in an outside-in flow pattern and draw permeate into the fiber through microscopic pores, collecting clean water inside the membrane and then directing it to permeate headers at the top of each cassette. The membranes form a physical barrier to virtually all suspended particles such as turbidity, and pathogens, and guarantee a minimum of 4-log removal of Cryptosporidium and turbidity of less than 0.1 NTU 100 percent of the time. Suspended solids and pathogens remain in the process tank and are drained to the lake during the backpulse process, which occurs at 18-minute intervals.
Permeate from the membranes will have chlorine and fluoride added before flowing to the plant's 6.7 million gallon (25 ML) reservoir, which will collect permeate from both the conventional plant and the expansion. A new high lift pumping station will pump the treated water from the reservoir to the distribution system. Optimum membrane permeability will be maintained through a regiment of proven cleaning methods that ensure high performance and low energy consumption for water production.
ZAPping out membrane cassettes
Another first for Lakeview is the introduction of the ZeeWeed Access Platform, or ZAP, which will be used to install, remove, and service membrane cassettes. ZAP is a rolling platform that moves along the top of the membrane tanks and eliminates the need for an overhead crane, membrane cassette lifting brackets, and separate tank covers, which have been standard equipment for ZeeWeed plants until now. It is equipped with a cassette lifting system, additional lighting, and ample workspace for membrane maintenance and repairs.
Peel implements innovative membrane monitoring
With more than 250 million fibers contained in approximately 7,500 membrane modules to manage and monitor, the Region of Peel along with CH2M HILL and GE is developing a Membrane Integrity Verification and Management Program (MIVMAP) to ensure water quality and regulatory compliance. The program is based on the log-removal value (LRV) framework defined in the LT2ESWTR and the US EPA Membrane Filtration Guidance Manual.
"Ontario's regulatory framework still specifies turbidity as the only standard for measuring the effectiveness of filtration processes-there is no standard for membrane integrity testing," says Schiller. "Our MIVMAP will monitor membrane integrity with a three-tier system that can detect integrity breaches as small as three microns. It will give us a much higher resolution of our system operation than just turbidity measurements alone."
A direct, pressure-based integrity test will be automatically conducted on each train every 24 hours and will be able to verify greater than 5-log Cryptosporidium removal. Each membrane cassette will also be monitored with a turbidimeter, and each train of six cassettes will be monitored by a particle counter.
"Water is an essential service, but most people take it for granted," says Oliveira. "Most people don't think about the technology and processes used to treat water, that's why some private water companies can scare them into questioning the safety of their water. The Region's outreach program is designed to educate people about what we do to make sure that their water is clean and safe."
More membranes in Peel's future
The Region is also in the process of planning another plant expansion-this time to its Lorne Park WTP. Membranes are the preferred option for a 101 MGD (380 ML/d) expansion, and are currently under review as part of the environmental assessment for the expansion. A decision is expected later this year. The Region is also considering membrane bioreactor technology for wastewater treatment plants in some northern areas. Sensitive receiving bodies and limited space at some wastewater treatment sites make MBRs an ideal choice for the future projects.
"The Lakeview expansion and our future membrane projects put the Region of Peel at the forefront of advanced treatment solutions for municipal infrastructure," Zamojc says. "We're proud to be setting the benchmark for large-scale projects and leading the municipal water industry into a new age of superior water quality and dependable public health protection at an affordable cost."