OPERATION WITH BIOLOGICAL NUTRIENT REMOVAL WITH STABLE NITRIFICATION AND CONTROL OF FILAMENTOUS GROWTH

Bromma WWTP is the second largest wastewater treatment plant in Stockh olm, Sweden. To meet new regulations regarding nitrogen removal the pl ant needs to be operated with nitrogen removal all year round; In prev ious years, severe bulking problems during the winter have made it imp ossible to maintain nitrification during colder temperatures. Microsco pic examination of the activated sludge has increased the understandin g of bulking. The bulking is mainly due to excessive growth of filamen tous organisms, mainly Microthrix parvicella. By operating the plant w ith a high F/M ratio and decreasing the FIM ratio when filamentous gro wth occurs, excessive growth of these organisms Can be-avoided. The ni trification rate is optimized by adjusting the concentration of mixed liquid suspended solids in the tanks so that the nitrification is comp lete and by operating the tanks at a DO concentration of 4 mg/l. By th is process strategy it is now possible to operate the plant with nitri fication all year round. (C) 1998 IAWQ. Published by Elsevier Science Ltd.