| Recycled landfill leachate is often characterized by its high ammonia content, which can be nitrified in an aerobic bioreactor. This research investigates the capability of landfill bioreactors to remove nitrate by denitrification with a focus on utilizing the methane flow as a carbon source. Eight lysimeters that contained synthetic municipal solid waste were operated for 510 days to demonstrate the feasibility of converting nitrate, at concentrations between 20 and 2000 mg/L, to nitrogen gas.; The results show that the landfill as a bioreactor is capable of denitrifying this wide range of nitrate concentrations with an efficiency up to 100%. At low nitrate concentrations (20–100 mg-N/L), denitrification was feasible with high efficiency in young and mature landfills, without affecting landfill activities (i.e. extent of waste degradation). However, denitrification with high nitrate concentrations (800–2000 mg-N/L) was associated with less gas production and hence less waste degradation. As the nitrate concentration increases, this effect also increases. In addition, at high nitrate concentrations, the denitrification efficiency decreases as the landfill ages due to carbon deficiency. The results also suggest that the carbon deficiency causes incomplete denitrification.; The use of methane as a carbon source for denitrification was not detected during the early stages of the landfill life. In mature landfills, methane gas enhanced denitrification efficiency, even at high nitrate concentrations (1500 mg-N/L).; Finally, testing was conducted to evaluate the kinetics of denitrification supported by methane or leachate. Results show that denitrifiers can grow on leachate, and consume nitrate at a rate faster than when growing on methanol. Denitrifiers were able to grow on methane, but at a much slower rate. |
