NITRIFICATION REACTIONS IN TREATMENT OF SUPERNATANT FROM DEWATERING OF DIGESTED SLUDGE
Separate nitrification of the reject water from dewatering of digested sludge has been studied at the Bromma sewage plant in Stockholm. Experimental studies were carried out in an SBR pilot plant. It was shown that a very high nitrification rate could be obtained in the reactor, about 30-40 g NH^-N/kg MLVSS, h. During the nitrification process, nitrite was accumulated in the reactor until ammonium nitrogen was depleted. When all ammonium had been oxidized all nitrite could be completely oxidized to nitrate. By use of multivariace methodology it was shown that nitrite accumulation was primarily caused by the initial concentration of ammonium and secondly by the oxygen concentration. The nitrification rare was strongly dependent on the oxygen concentration. The strong dependence of nitrification rates on the oxygen concentration makes the process easy to control by for instance measurements of oxygen concentration, air flow and pH.