Use of bioreactor landfill for nitrogen removal to enhance methane production through ex situ simultaneous nitrification-denitrification and in situ denitrification

High concentrations of nitrate-nitrogen (NO3−-N) derived from ex situ nitrification phase can inhibit methane production during ex situ nitrification and in situ denitrification bioreactor landfill. A combined process comprised of ex situ simultaneous nitrification-denitrification (SND) in an aged refuse bioreactor (ARB) and in situ denitrification in a fresh refuse bioreactor (FRB) was conducted to reduce the negative effect of high concentrations of NO3−-N. Ex situ SND can be achieved because NO3−-N concentration can be reduced and the removal rate of ammonium-nitrogen (NH4+-N) remains largely unchanged when the ventilation rate of ARB-A2 is controlled. The average NO3−-N concentrations of effluent were 470 mg/L in ex situ nitrification ARB-A1 and 186 mg/L in ex situ SND ARB-A2. The average NH4+-N removal rates of ARB-A1 and ARB-A2 were 98% and 94%, respectively. Based on the experimental data from week 4 to week 30, it is predicted that NH4+-N concentration in FRB-F1 of the ex situ nitrification and in situ denitrification process would reach 25 mg/L after 63 weeks, and about 40 weeks for the FRB-F2 of ex situ SND and in situ denitrification process . Ex situ SND and in situ denitrification process can improve the methane production of FRB-F2. The lag phase time of methane production for the FRB-F2 was 11 weeks. This phase was significantly shorter than the 15-week phases of FRB-F1 in ex situ nitrification and in situ denitrification process. A seven-week stabilization phase was required to increase methane content from 5% to 50% for FRB-F2. Methane content in FRB-F1 did not reach 50% but reached the 45% peak after 20 weeks.