Since the early 1990s, the Township of Ernestown in eastern Ontario has been searching for a cost-effective approach to upgrading its Amherst (population 6,100) water system. The present treatment is limited to coarse screening and chlorination of Lake Ontario water. A 1991 Environmental Study Report (ESR) recommended the construction of a new conventional treatment plant on a "greenfield" site on the edge of the community. Lack of funding delayed the $14 million project.
Since the original ESR was prepared, two factors have significantly changed the course of the project. First, membrane technologies have evolved to the extent that they can be economically competitive with conventional treatment. Second, an aggressive leak detection program cut system leakage from 50 to 25 percent, thus reducing the plant capacity required.
In late 1995, CH2M Gore & Storrie Ltd. (CG&S) developed a conceptual design based on microfiltration (MF) technology that could reuse the existing Township site and services at substantial cost savings. This site option had been eliminated in 1991 due to insufficient space to accommodate conventional treatment. The Township retained CG&S to further evaluate the MF option and to complete an addendum to the 1991 ESR, reviewing all alternative plant sites and processes.
The Township and CG&S teamed together to conduct a pilot study evaluating two leading MF membrane technologies. The first was a unit from the Australian-based Memtec Group that used pressurized cartridge systems up to 35 psi. The second was a creation of Zenon Environmental, Burlington, Ohio, that used suction pressure up to -9 psi as the driving force for filtration.
The two pilot units were housed side by side in a modified highway trailer on the Township's existing pump station site and operated 24 hours a day. On-board instrumentation included three particle counters, three turbidimeters and a personal computer that collected and stored both raw water and treated water quality data.
Results were impressive. Turbidities consistently registered as less than 0.04 NTU and particle counts (>2 micron) showed up as less than five per mL. Comparatively, an AWWA Research Foundation study of 100 conventional treatment plants found that particle counts (>2 microns) for filtered water actually range from one to 650 per mL.
To date, Canada has only two municipal drinking water MF plants, a permanent facility in Rothsay, New Brunswick, that filters groundwater, and a temporary plant in Collingwood, Ontario, that filters surface water. A permanent plant is under construction at the latter location.