NITRIFICATION/DENITRIFICATION IN AN INTERMITTENT AERATION PROCESS FOR SWINE WASTE-WATER

Nitrogen removal by a methane fermentation plus activated sludge process with the intermittent aeration was presented based upon a full-scale pig farm experiment. Swine wastewater had a T-N/BOD ratio from 0.2-0.29. The BOD concentration input to the process ranged from 1050-1608 mg l(-1) and the T-N concentration from 273-350 mg l(-1). More than 90% of organic carbon was removed in each experimental run. Only small concentrations of NO3-N were found in the effluent and higher than 60% of the T-N and 73% of NH4-N which were loaded to the intermittent aeration tank was removed. The nitrogen balance of each run was calculated. Denitrification was estimated to be accountable for 45-90% of the T-N removed in the intermittent aeration tank. Denitrification rate increased as the BOD concentration increased (> 1300 The T-N removal percentage was a function mg l(-1)) of the T-N/BOD ratio of the influent. Although higher DO concentration (> 3 mg l(-1)) did not enhance the denitrification rate, nitrification did maintain at relative higher rates at a lower DO concentration (ave. 1.5 mg l(-1)). An operational condition of intermittent interval of aeration/nonaeration at 1:1 hr is better than that of the condition at 3:1 hr. As a result, T-N and NH4-N were removed up to 30% and 40% respectively, and the denitrification rate reached 79% in the intermittent aeration tank. An experimental run in a pilot plant on treating anaerobically pretreated swine wastewater was observed to verify simultaneous nitrification/denitrification. The results of the full-scale plant experimentation seem to be confirmed by those obtained from the pilot plant runs.