The effect of decreased ambient temperature on the biological nitrification and denitrification of a high ammonia landfill leachate

This research investigated the nitrogen removal capabilities of a pre- and post-denitrification process, when treating sanitary landfill leachate containing an ammonia concentration of over 2200 mg N/L, at operating temperatures down to 10°C. The treatment system employed is generally known as a 4-Stage Bardenpho process. Two parallel systems were operated throughout the study; each system had an aerobic solids retention time of 20 days and an external recycle ratio (return activated sludge) of about 3:1. During the entire experimental period, one system used an internal recycle ratio of about 4:1, while the other system used one of 3:1. Methanol was used as supplementary carbon source for denitrification. When operating temperature was decreased from 20 to 17°C, an approximate 15% decrease in denitrification was immediately experienced within both systems, with no noticeable affect on nitrification. This was an unexpected result. Subsequently, the temperature was further decreased to 14°C, and finally to 10°C. With the temperature at 14°C, aerobic wasting was also stopped and methanol loading was progressively decreased to match actual denitrification requirements. At 10°C, both systems suffered major nitrification and denitrification inhibition. Changes in operating parameters, such as a decrease in influent ammonia and methanol loading, as well as an increase in ambient temperatures, from 10 to 15°C, did not significantly improve overall system performance, within a reasonable time frame. Both denitrification and nitrification problems were mainly attributed to decreased ambient temperature, although other possible factors were noted; at project completion, about 50% of the incoming ammonia was being removed across the system.