A program of batch, continuous-flow, and field pilot tests have been conducted to measure the extent and stability of nitrification in kraft wastewater. Laboratory batch tests measured the extent and rate of ammonia removal from kraft wastewater. Controlled variables included aerated stabilization basin (ASB) location, temperature, pH, ammonia concentration, black liquor content, bicarbonate content, and presence of acclimated nitrifying bacteria. Findings were that (a) moderate wastewater temperature (22-35°C), pH near 7.3, and black liquor spill control prevented slowing of nitrification, and (b) provision of acclimated nitrifying bacteria (by appropriate recirculation methods) dramatically reduced the residence time needed for nitrification in kraft ASBs. Laboratory-scale, fixed-film, continuous-flow tests were used to investigate 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 could not respond quickly enough to substantially dampen out the effect on effluent quality.

A pilot 4-stage rotating biological contactor (RBC) was installed at an ASB to test the nitrification of kraft wastewater under actual process variations. The results during the 11-month run were: (a) the RBC demonstrated capability to consistently and substantially reduce NH4-N concentration below 1 mg/L, (b) about one month was needed to establish effective treatment, and (c) effective treatment was sustained at a maximum hydraulic loading rate of 0.11 m3/day per m2.

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