Biological removal of phosphorus and denitrification of waste water - by addn. of easily degradable organic acids during denitrification-anaerobic stage

摘要

In the biological elimination of P, combined with nitrification and denitrification of waste water, easily degradable organic acids are added to the denitrification/anaerobic stage, these acids being liberated during the anaerobic treatment of the raw waste water. The space loading for N breakdown is 30 vols.% for denitrification and 70% for nitrification, with 300% recirculation of the activated sludge resulting from the aerobic stage of the denitrification stage, at the same time as the P elimination. Later clarification and removal of excess sludge are carried out by the process of an activated sludge plant; excess sludge may be removed before the settling step in the later clarification, to avoid unwanted recycling of P in the later clarification. The ratio of recycled sludge is 80%. The sludge level in the pre-clarification is held constant at 0.6 m, when easily degradable organic acids are liberated in an anaerobic process (acid fermentation). The sludge is mixed by means of a plate or propeller pumps. Excessive thickening of the sludge is prevented by briefly pressing in air, e.g. through a sand trap jet, before withdrawal of the sludge. ADVANTAGE - Eutrophication of watercourse is limited, in a cheaper, simple process.