Long-Term Nitrogen Management in Bioreactor Landfills

Abstract

One scenario for the long-term nitrogen management in landfills is ex-situ nitrification followed by denitrification in the landfill. The objective of this research was to measure the denitrification potential of actively decomposing and well decomposed refuse. A series of 10-L reactors that was actively producing methane was fed 400 mg NO3-N /L every 48 hr for19 to 59 days. Up to 29 nitrate additions were either completely or largely depleted within 48 hr of addition and the denitrification reactions did not adversely affect the refuse pH. Nitrate did inhibit methane production but the reactors recovered their methane-producing activity with the termination of the nitrate addition. In well decomposed refuse, the nitrate consumption rate was reduced but was easily stimulated by the addition of either acetate or an overlayer of fresh refuse. Addition of a high acetate to nitrate ratio did not lead to the production of NH4+ by dissimilatory nitrate reduction. Although the population of denitrifying bacteria decreased by about five orders of magnitude during refuse decomposition in a reactor that did not receive nitrate, rapid denitrification commenced immediately with the addition of 400 mg NO3-N/L. These data suggest that the use of a landfill as a bioreactor for the conversion of nitrate to a harmless byproduct, nitrogen gas, is technically viable.