Trends in Membrane Filtration in Canada
The use of low pressure membrane filtration for the production of drinking water has grown astronomically over the last decade in both the United States and Canada.
By Simon Breese, Joe Gemin, and Mike Adkins
The use of low pressure membrane filtration for the production of drinking water has grown astronomically over the last decade in both the United States and Canada. This growth has been driven by a number of factors, including more stringent regulations for Giardia and Cryptosporidium in drinking water, but also the ever-declining cost of membranes, realized through ongoing research, and an increasingly competitive marketplace.
In addition to these factors, several drivers unique to the Canadian market have also had a strong influence on the growth of the membrane filtration market, and resulted in a growth rate that probably exceeds that seen in United States:
- Most important of these factors was the serious outbreak of E.Coli that occurred in the Town of Walkerton, Ontario in 2000, which ultimately resulted in the deaths of seven residents of the town, and caused widespread gastrointestinal disorders in the community;
- In the decades preceding this outbreak, drinking water quality had always been somewhat taken for granted by the Canadian public, as Canada is blessed with an abundance of high quality surface water sources. During this time, drinking water quality regulations were also significantly less stringent in most parts of Canada than they were in the United States, and as such, the regulatory drivers for advanced treatment did not exist;
- Many of Canada’s larger cities, and particularly the Greater Toronto area, are continuing to experience significant growth. Since Greater Toronto is bounded to the south by Lake Ontario, the growth has predominantly been northward, away from the Lake, and the most obvious source of drinking water. This has resulted in the desire to expand existing large water treatment plants along the Lake to allow this treated water to be conveyed northward to serve this growth;
- In the years preceding the Walkerton crisis, a Canadian company, Zenon Environmental Limited, of Oakville, Ontario, had quietly developed a revolutionary approach to membrane filtration, i.e. the ZeeWeed immersed membrane filtration system, which allowed for the membrane hollow fibers to be simply suspended in an open tank. This new development revolutionized the industry, by facilitating the conversion of existing conventional water treatment plants through the conversion of granular media filters or clarification basins.
Pictured is the vacuum pump room at Region of Peel Lakeview Water Treatment Plant. The plant will be the largest membrane plant in the world when the second stage of its expansion is completed.
With these conditions in place, the Walkerton crisis became a watershed event in the Canadian drinking water industry. Suddenly, both the general public and regulators alike took notice of the need for increased vigilance of drinking water quality, and pushed for the widespread adoption of more stringent regulations for Giardia, Cryptosporidium, and other pathogens previously unregulated in much of the country. In tandem with these changes, government funding of projects to upgrade existing water treatment plants rose to new highs.
With increasing pressure to upgrade plants to meet these new standards, to expand plants to meet increasing demand, and with the technology in place to readily convert existing plants to a technology better able to provide protection against waterborne disease, the conditions were perfect for this explosive growth to occur. What resulted was a sweeping change in the industry, and membrane filtration rapidly became an extremely attractive alternative for Canadian water purveyors strongly motivated to avoid a repeat of the events of Walkerton in their community.
In the wake of these changes, some of the largest membrane filtration systems in the world are already in operation, or are under design and construction in Canada. Although membrane systems by a number of membrane vendors are in operation across the country, GE / Zenon have been able to capture the majority of the larger water treatment upgrade/expansion Projects, partially by virtue of their strategic location. Such projects include:
- A 260 ML/d immersed membrane filtration retrofit recently completed at the Region of Peel’s Lakeview Water Treatment Plant, raising total plant capacity to 820 ML/d. As soon as this expansion was complete, the Region embarked upon a second, identical expansion, which will take total capacity to 1,080 ML/d. At the time of writing, this would make the Lakeview plant the largest membrane filtration system in the world;
- The Region of Peel is also in design of a 380 ML/d expansion to the existing Lorne Park Water Treatment Plant, to raise total plant capacity to 500 ML/d, by converting some of the existing granular media filters using GE/Zenon ZW-1000 immersed membrane modules;
- The City of Kamloops, British Columbia, constructed a new 160 ML/d water treatment plant using GE/Zenon ZeeWeed ZW-500 immersed membrane modules to treat the flashy Thompson River. The ZW-500 membrane is one of the earlier versions of the ZeeWeed membrane, with low membrane packing density, and therefore better suited to more turbid sources;
- The Region of Halton, Ontario, decided to build the new 55 ML/d Burloak water treatment plant, incorporating ZeeWeed ZW-1000 modules to treat Lake Ontario water for distribution to the communities of Oakville and Burlington, west of Toronto;
The remainder of this article focuses upon the new 115 ML/d City of Thunder Bay Bare Point Water Treatment Plant, designed by Earth Tech Canada, as a typical examples of a large Canadian membrane filtration project.
Thunder Bay Project
The City of Thunder Bay historically has been served by two water sources:
- The Loch Lomond supply, serving the southern areas of the City, and drawing from Loch Lomond, an upland, low turbidity, but highly colored source.
- Lake Superior, a very high quality source, low in turbidity and organics;
Membrane modules are loaded into one of the five trains at the Bare Point Water Treatment Plant.
Both of these sources were previously supplied unfiltered, but eventually the City constructed treatment facilities on both sources, constructing the 60 ML/d Bare Point direct filtration plant in 1974 on the Lake Superior supply, and eventually a 27 ML/d “emergency” membrane filtration facility in 1994 using ZeeWeed ZW-500 modules to treat the Loch Lomond source, in response to a Cryptosporidium “scare”.
Armed with several years of operating experience with the membrane filtration system at Loch Lomond, the City then decided to upgrade and expand their larger plant, the 60 ML/d Bare Point WTP, to increase total capacity to 115 ML/d through the construction of 55 ML/d of new membrane filtration capacity, with the intent of consolidating all supply through this facility, allowing the “temporary” facility at Loch Lomond to be decommissioned.
Early in the design of the Bare Point upgrade, several potential membrane vendors were considered for the supply of the equipment, however GE/Zenon was selected as the preferred vendor on the basis of their proposal to re-use the existing ZW-500 membranes from the Loch Lomond plant at Bare Point, which allowed them to offer a significant reduction in base cost.
Around that same time, GE/Zenon were beginning to develop modified versions (the ZW-650 and ZW-1000) of their immersed membrane modules, which allowed for tighter packing of the membranes within the same module size. Over the course of the Thunder Bay project, several versions of the Zenon modules became available to greatly increase packing density, and therefore both the filtration capacity per unit area, and the potential for cost reduction. While these tighter packing densities render the membrane modules less tolerant to solids loading, it was thought that use of these membranes on the high quality Lake Superior water would not pose a challenge from a fouling perspective, and so each new version in turn was considered in design.
It was ultimately decided therefore that the membranes in service at Loch Lomond would be scrapped, and the plant decommissioned once the expansion was complete at Bare Point. Two distinct alternatives were originally considered for the expansion:
Option 1: Retain the existing 60 ML/d direct filtration plant, and construct a new 55 ML/d membrane filtration plant
Option 2: Convert the existing direct filtration plant to membrane filtration, and construct new tankage as required to complete a complete conversion of the plant to membrane filtration, with a total capacity of 115 ML/d;
After pricing was received for both options through a public tendering process, the city decided that it was their preference that the plant be converted entirely to membrane filtration, and so a third option was introduced, involving the construction of an entirely new 115 ML/d membrane filtration plant, and decommissioning the direct filtration plant once construction was complete.
Tender pricing for this new option showed that it was markedly more expensive to undertake the retrofit of the existing plant, compared to construction of a new plant, and it was therefore decided to construct a new 115 ML/d membrane plant. The construction contract was awarded in June 2004. Key design criteria for the plant are as follows (Table 1):
One of the unique aspects of the Thunder Bay design is the elimination of the standby membrane train commonly used in the design of membrane systems. This relies upon the provision of an adequate supply of spare parts, including membrane modules and permeate pumps, to allow the complete replacement of any major item within a matter of hours. While it demands vigilance on the part of the operators, the resulting savings were substantial.
With raw water quality from Lake Superior being generally excellent, the system is designed to be normally operated without coagulation pre-treatment. However, on occasion, short duration spikes in raw water true color can occur as high as 50 TCU. As such, the plant has been designed to allow polyaluminum chloride (PACl) coagulation, up to a maximum dose of 5 mg/L.
The plant was commissioned in February 2007, and has been performing very well since then, typically producing water in the 0.02 – 0.06 NTU range. Total project cost was of the order of Cdn $45 million.
What does the Future Hold?
To a very real extent, the Walkerton crisis has played a seminal role in driving the Canadian drinking water industry towards membrane filtration on a large scale. With major expansions already in the planning stages for some of these large membrane plants, this trend is unlikely to subside in the immediate future.
However, while these new projects have moved forward very quickly over the course of a few years, the membranes have continued to develop very rapidly even within the lifespan of individual projects. For example, over the course of the Thunder Bay project, three discrete versions of the GE/Zenon membrane were released into the marketplace, and in turn were considered for incorporation into the project.
While it is fair to say that low pressure membrane filtration in general is now widely considered a robust and mature technology, the rapid evolution of the technology has driven the industry in Canada to the point that these newer generation membrane modules are being installed on a significant scale with limited long term O&M data from full scale plants to substantiate economic evaluations used in the selection of the membranes. We believe that more work is necessary to benchmark the long term performance and O&M cost of these newer membrane filtration technologies against the cost of other approaches to treatment (including older generation membranes as well as conventional treatment), to facilitate informed treatment decisions by water purveyors and consultants alike in the years to come.
About the Authors:
- Simon Breese, M.A.Sc., P.Eng., is Technical Practice Leader, Drinking Water, for Earth Tech in Kitchener, Ontario.
- Joe Gemin, P.Eng., is Senior Project Engineer for Earth Tech in Kitchener. Mike Adkins, P.Eng., is National Director, Water & Wastewater, for Earth Tech and is based in Vancouver, B.C.