BIOLOGICAL NITRIFICATION OF KRAFT WASTE-WATER

A program of batch, continuous-flow, and field pilot tests have been c onducted to measure the extent and stability of nitification in kraft wastewater. Laboratory batch tests measured the extent and rate of amm onia removal from kraft wastewater. Controlled variables included aera ted stabilization basin (ASB) location, temperature, pH, ammonia conce ntration, black liquor content, bicarbonate content and presence of ac climated nitrifying bacteria Findings were that (a) moderate wastewate r temperature (22-35 degrees C), pH near 7.3, and black liquor spill c ontrol prevented slowing of nitrification, and (b) provision of acclim ated nitrifying bacteria (by appropriate recirculation methods) dramat ically reduced the residence time needed for nitrification in kraft AS Bs. Laboratory-scale, fixed-film, continuous-flow tests were used to i nvestigate dynamic responses to changes in wastewater composition and flow. Results demonstrated that the nitrifying films were not 'damaged ' by 4- or 24-hour step increases in influent ammonia, but the films c ould not respond quickly enough to substantially dampen out the effect on effluent quality. A pilot 4-stage rotating biological contactor (R BC) was installed at an ASB to test the nitrification of kraft wastewa ter under actual process variations. The results during the Ii-month r un were: (a) the RBC demonstrated capability to consistently and subst antially reduce NH4-N concentration below 1 mg/L, (b) about one month was needed to establish effective treatment, and (c) effective treatme nt was sustained at a maximum hydraulic loading rate of 0.11 m(3)/day per m(2). (C) 1997 IAWQ.