NITROGEN REMOVAL FROM DIGESTER SUPERNATANT - COMPARISON OF CHEMICAL AND BIOLOGICAL METHODS

Physical/chemical elimination of ammonium from digester supernatant wi th magnesium-ammonium-phosphate (MAP) precipitation and with air strip ping is investigated in pilot scale and compared with separate intermi ttent denitrification, denitrification in wastewater treatment and in tertiary filtration. MAP-precipitation is feasible but most expensive due to required chemicals as well as dewatering and drying of the prec ipitate. Air stripping is slightly cheaper, but still more expensive t han biological treatment due to the complex process, cost of chemicals and reconditioning of the ammonium sulfate solution to a fertilizer p roduct. In nutrient removal plants the additional nitrogen from the di gester supernatant can be eliminated by increasing the anoxic volume o r using a carbon source. Denitrification with methanol will be the che apest solution with today's methanol price. If digester supernatant in hibits nitrification substantially or if the anoxic zone is too small for organic carbon addition a separate intermittent denitrification wi th addition of a carbon source, as used in some treatment plants in Sc andinavia, might be a good solution. Copyright (C) 1996 IAWQ.