ADVANCED CONTROL SYSTEM OF ACTIVATED SLUDGE PROCESSES USING IN-SITU AMMONIUM AND NITRATE PROBES

摘要

Nowadays, effluent quality of Wastewater Treatment Plants (WWTP) has to meet stringent environmental regulations. The aim of this study was to assess the dynamic control efficiency of nitrification and denitrification process using a pilot-scale intermittently aerated and fed bio-reactor (IAFB). On-line monitoring of nitrification and denitrification processes was achieved using in situ ammonium and nitrate probes and a programmable control system. The aeration requirements for organic carbon and ammonia oxidation were controlled by setting ammonia effluent concentration at 2, 3 or 4 mg L~(-1) NH_4~+-N. Denitrification phase length was set by reaching the lowest nitrate effluent concentration (1 mg L~(-1) NO_3~--N).The average nitrification time was 52 and 21 min for the oxidation of 6 and 3 mg L~(-1) NH_4~+-N, respectively. The denitrification period needed for the reduction of 6 and 11 mg L~(-1) NO_3~--N was 7 and 71 min, respectively. Two distinct nitrification rates (Nr), i.e. 0.15 ± 0.05 and 0.08 ± 0.03 g g~(-1) VSS d~(-1), were detected, depending on the initial ammonium concentration of the influent. Three denitrification rates (DNr) were observed during anoxic phase, which were equal to 0.43 ± 0.09, 0.09 ± 0.02 and 0.04 ± 0.02 g NO_3~--N g~(-1) VSS d~(-1). The control strategy of the activated sludge process resulted in COD, BOD, TKN, NH_4~+-N and NO_3~--N removal efficiencies of 90, 94, 89, 94 and 99%, respectively.