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 1:1. while the other system used one of 3:1. Methanol was used as supplementary carbon source for denitrification. When operating temperature was decreased from 70 to 17 degreesC, 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 degreesC. With the temperature at 14 degreesC. 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 degreesC, 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. (C) 2001 Elsevier Science Ltd. All rights reserved.