By Darrell Corkal and Rob May, PFRA, Hans Peterson, SRC, and Joanne Sketchell, Sask Water
Evert and Vonne Johnson of Davidson, Saskatchewan are currently treating groundwater for all in-house needs, using biological treatment to reduce high levels of iron, arsenic and manganese. The innovative treatment train is manufactured by Mainstream BMS, a Saskatchewan company located in Vanscoy. The project is an applied research effort funded by the producer, ADD Board 15, the Canada-Saskatchewan Agriculture Green Plan Agreement and the Saskatchewan Research Council. PFRA and Sask Water are also working on the project. The findings from the work will be beneficial for rural people who are seeking solutions to deal with difficult to treat groundwater supplies.
The biological treatment train is effective in reducing iron levels found in the source water from about 4.4 ppm (parts per million) to an average of about 0.07 ppm after treatment. On average, the sand filter removes 98% of the iron found in the source water. Iron is not a health-related problem but becomes an aesthetic problem for many groundwater users if the levels are higher than 0.3 ppm (with poor taste, staining of clothes and fixtures, etc.). The treatment system does not require chemicals but does require manual backwashing with air and water about once each month.
High levels of arsenic are a health-related problem in drinking water. The current Saskatchewan municipal drinking water objective for arsenic is 25 ppb (parts per billion). The level of naturally-occurring arsenic found in the Johnson's groundwater is about 30 to 35 ppb. The biological treatment train removes arsenic to a level of about 2 ppb in the sand filter with further reduction at the reverse osmosis unit.
Like iron, manganese objectives are set for aesthetic purposes. The objective is to have manganese below 50 ppb; otherwise, the water may cause staining of fixtures and laundry and have an undesirable taste. The Johnson groundwater has naturally-occurring manganese levels of about 325 ppb. After the sand and carbon filters, the manganese levels are lowered to 220 ppb, which is not enough to meet the desired objective. Levels are 2 ppb after the kitchen tap reverse osmosis unit. The biological treatment process to reduce manganese might be improved with system modifications.
Other parameters that require treating for the Johnson source water include high levels of hardness, sulphates and sodium.
A softener was installed to deal with the hardness. The sulphates and sodium are being reduced at the kitchen tap by the reverse osmosis membrane.
As with all equipment, good operation and maintenance procedures are required. Biological processes will operate for long periods of time with proper backwashing of the sand and carbon filters each month using an air and water backwash. The storage tank will likely require disinfection with chlorine at regular intervals, and softener equipment requires regular backwashing. The kitchen tap reverse osmosis could be subject to fouling if any of these maintenance procedures are not followed, or if the pre-treatment proves inadequate for the source water used. In addition, pre-filters for the reverse osmosis unit should be replaced every six months.
To contact the authors, write to PFRA, 105 North Rd., Saskatoon, SK S7N 4L5.
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