Iron and Manganese Removal Using Slow Sand Filtration - Canadian Experience

A variation of traditional slow sand filtration (TSSF) is being used to remove iron and manganese from well water in two communities in Western Canada. A third plant will be commissioned late 2011. The new filtration technology is marketed as the Manz Polishing Sand Filter TM or MPSF. It was selected over competing technologies on the basis of its effectiveness in removing iron and manganese, ability to treat water with sulphate reducing bacteria and H2S, capital cost, operating costs, maintenance costs, energy consumption, chemical requirements, waste production, ease of operation, and reliability. The selection process included on‐site piloting. The ability of TSSF to effectively remove iron and manganese was recognized in the late nineteenth century. However, the use of TSSF for this purpose was considered impractical because of the need for frequent cleaning involving removal of fouled media (sand), a process known as scraping, and periodic media replacement, a process known as resanding of the filter bed. The design of the MPSF retained and improved on key elements of TSSF, responsible for its ‘polishing’ capabilities; and, the disadvantages of the TSSF were eliminated, including the onerous cleaning process that was replaced with a simple effective backwash process. Media is never removed or lost from the filter. A biological layer is not required for successful operation, allowing loading rates three or more times that of TSSF and a shallower filter bed resulting in a more compact filter design. The communities which chose to use the MPSF technology are small to medium in size. Two of the treatment plants provide 1,200 m 3 (314,184 gallons) of treated water per day and the third plant is will provide 2,400 m 3 (628,368 gallons) of treated water per day when commissioned. The well water treated in each of the communities was not considered under direct influence of surface water or GWUDI. One of the 1,200 m 3 plants treats water that has an elevated concentration of manganese with evidence of the presence of sulphate reducing bacteria (SRB) and H2S. This plant has been operating successfully for several years. The second 1,200 m 3 per day plant treats water with elevated concentrations of iron and manganese, SRB contamination and the associated presence of H2S. This plant has just been commissioned. The 2,400 m 3 per day treatment plant will treat water with significant concentrations of iron and manganese that appear to be naturally sequestered. Sodium hypochlorite is used to oxidize the iron and manganese and provide the necessary chlorine residual in

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