Newsletter - July 1999
WEAO jointly sponsors a federal and provincial technology evaluation/demonstration project
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| Tony Ho (second from right) was present on site when the septic tanks were buried. |
WEAO signed a Memorandum of Understanding in October, 1998 to jointly sponsor a technology evaluation/demonstration study with Environment Canada's Great Lakes 2000 Cleanup Fund (GL2000CUF), Ontario Ministry of Environment (MOE), Sand Filtration Inc. (SFI), Wilkinson Heavy Precast Ltd., and McMaster University. The study also received endorsement from the Town of Minto (formerly Village of Clifford) to allow the use of their sewage treatment plant (STP) for the study, and from the Ontario Clean Water Agency (OWCA), which operates the Village of Clifford STP, to assist in the study.
The study objectives are to evaluate the performance, reliability, design and operating conditions and costs of using septic tanks, plus recirculating sand filters, to treat municipal sewage for small communities. Study results will also be useful to optimize the design and operation of intermittent sand filters which are being used in a number of Ontario municipalities to polish their sewage lagoon effluent.
About 20% of the Ontario population living in small rural communities rely on private septic tanks and tile fields to treat and dispose of their sewage. Quite a number of these communities reported that the septic tank and tile field systems in their communities failed due to aging and led to basement flooding and/or groundwater contamination. Some of these failed systems can be remedied by replacing the old tile fields with new ones but not in all cases, due to poor local soil conditions or insufficient lot sizes as per the MOE guidelines. Where new tile fields cannot be used, sanitary sewers and a new STP have to be constructed or a long main sewer trunk line has to be constructed to convey sewage to an existing STP in a neighbouring municipality for treatment.
In 1997/98, MOE approved $16 million for seven small communities to remediate failed septic tank and tile field systems. Actual remediation costs are much higher since MOE only provided a portion of the remediation costs. It is essential, therefore, to develop a more cost-effective solution.
In 1997, GL2000CUF, MOE and McMaster University conducted a study to investigate technologies that could be used to remediate problematic septic tank and tile field systems and to provide cost-effective sewage treatment in small communities.
Based on literature review, followed by site visits to facilities in Wisconsin, the study reported that septic tank followed by recirculating sand filter would be a cost-effective technology. This technology has been successfully used for several years in a number of communities in Wisconsin. This technology is operated year-round and produces tertiary effluent quality. It is easy to construct, operate and maintain. There is no mechanical equipment required other than pumps and timers to control the septic tank effluent application rate onto the recirculating sand filters and recirculation rate.
Furthermore, the observations made in Wisconsin indicated that, to prevent freezing and to reduce filter plugging by solids and vegetation, coarser media (2 to 5 mm) should be used for the sand filter, and the septic tank effluent should be applied to the sand filter frequently, e.g. hourly. Some filters in Wisconsin were operated continuously for six months or longer without resting.
A similar technology, "intermittent sand filter", is being used in Ontario to polish and/or provide nitrification for sewage lagoon effluent. The intermittent sand filters in Ontario use fine media (0.2 to 0.5 mm), and the lagoon effluent is usually applied to the filter once or twice per day to build a head of 15 to 20 cm above the filter at the beginning of each application cycle. The intermittent sand filters become plugged after 15 to 30 days of operation. The plugged filters have to be rested for a period of 15 days or longer to restore their performance.
In 1998, GL2000CUF, MOE, McMaster University and WEAO agreed that a pilot plant demonstration study is necessary to fine-tune the design and operation of the septic tank and recirculating sand filter technology for Ontario application. The demonstration project will also be useful for technology promotion. SFI and Wilkinson were invited to join the study because of their expertise and willingness to make contributions to the study.
The pilot plant consists of four parallel trains. It is being built in the Village of Clifford STP and will be completed by July. Experimental studies will be conducted over a two-year period to determine the effects of media size, dosing frequency, recycle ratio, and mass/hydraulic-loading rates on effluent quality. The effect of chemical addition for phosphorus removal on sludge generation and septage haulage will also be monitored.
An interim report will be published after one year of study. Both the interim and final report will be available to the public, consultant companies and municipalities.
WEAO is responsible for coordinating the study, review of the study results and technology transfer and promotion. McMaster University has the responsibility of study design, data collection, analysis and reporting. The other partners made financial and in-kind contributions to the study. All partners believe that a multi-partnership arrangement is a useful model for future studies to leverage each other's resources and expertise.
Tony Ho, MOE