By Hans Peterson, Saskatchewan Research Council, Saskatoon
In an article entitled Biological Treatment of Public Water Supplies (Critical Reviews in Environmental Control, 1989) Rittman and Huck state:"The purpose of this review is to describe one of the important new tools that is being used to produce safe and pleasing drinking water as the requirements of new regulations and reduced chlorination come more and more into effect. That new tool is biological treatment, or the use of processes which contain microorganisms capable of carrying out reactions that improve the quality of the water. Today, water-supply practice in North America shuns the use of biological treatment because microorganisms are associated with disease transmission. Current practice in North America tries to kill microorganisms wherever possible. Nevertheless, biological treatment to provide a safe and high-quality drinking water is becoming relatively common in other parts of the world, especially in Western Europe".
For the past four years the Saskatchewan Research Council, together with Napier University of Edinburgh, Scotland, have worked on adapting and optimizing biological treatment processes for the treatment of prairie surface waters. During this time, SRC's Joanne Sketchell has completed her Ph.D. thesis on The Removal of Dissolved Organic Carbon and Disinfection By-products from Prairie Drinking Water Supplies. One of the major findings in this work is the clear suitability of biological processes to improve the quality of dugout waters.
Biological treatment requires enough microorganisms to carry out the required purification of the water. These organisms are living cells. They will remove organic compounds, such as those generating taste and odour, as well as those causing a brown colour in the water. Biological treatment will work better if it is operated continuously and enough time is given to the organisms to carry out their purification role. Different materials can be used to support these microorganisms, with the most common being sand and granular activated carbon (GAC).
The first use of slow sand filtration was by the Chelsea Water Company in London in 1829. Slow sand filtration (water moves through such filters 10 to 20 times slower than rapid sand filters) relies on the formation of a biological layer at the top of the filter. The filter does not become effective until this layer has formed.
In addition to removing dissolved organics, slow sand filtration can be very effective in particle removal. The American Water Works Association states:
As effective as sand filtration can be, it is possible to maintain much greater numbers of microorganisms if the support material is GAC instead of sand. It is therefore preferable to use GAC for the removal of dissolved organics.
Mainstream Bio-Manipulation Systems Ltd. has, with the support of the National Research Council, worked on adapting both the slow sand filtration and biological GAC filtration processes. Such treatment systems have been installed at three different sites across Saskatchewan.
One site has been in operation for one-and-a-half years and removal rates of turbidity, dissolved organic carbon, and colour have been good for both the sand filter and the biological GAC filter. Both have provided high quality household water with no colour or odour (removal rates of turbidity, dissolved organic carbon, and colour are consistently above 50%). For drinking water purposes, the water is polished by a reverse osmosis unit. At this site, all of the household water was hauled before installation of the biological treatment system. Based on successes like this one, it is anticipated that biological treatment will become one of the most common future treatment tools for dealing with surface waters on the Canadian prairie.