Improving leachate quality and optimizing CH 4 and N 2 O emissions from a pre-aerated semi-aerobic bioreactor landfill using different pre-aeration strategies.

Landfill aeration efficiently accelerates municipal solid waste (MSW) stabilization. This method also impacts methane (CH4 ) and nitrous oxide (N2 O) emissions during aeration. In this study, the effects of three pre-aeration strategies on leachate quality variations and CH4 and N2 O emissions from three lab-scale pre-aerated semi-aerobic bioreactor landfills, which were filled with MSW, were investigated: low frequency and high frequency intermittent aeration (LIA and HIA) and continuous micro-aeration (CMA). Experimental results showed that these three strategies effectively reduced organic and N-based pollutants concentration in leachate. Compared with intermittent aeration (IA), CMA increased cumulative CH4 emissions (9234.3 mg) and resulted in a longer emission period (95 days). HIA generated the least cumulative CH4 emissions (4297.6 mg) and shortest emission period (65 days) due to organic matter loss during aeration. N2 O emissions were present at low levels in early stages for each bioreactor, and then, increased by 1-3 orders of magnitude in the later stages due to low influent carbon-nitrogen ratio. HIA resulted in maximum cumulative N2 O emissions (2884.6 mg) and experienced a longer emission period (179 days) compared to CMA (2281.6 mg; 151 days). LIA had the longest N2 O emission period (209 days), but had the lowest cumulative N2 O emissions (1486.3 mg). CH4 and N2 O emissions mainly occurred in the early and later stages of landfill stabilization, respectively. Therefore, the study proposes an optimized pre-aeration strategy for practical landfill aeration management: early CMA may promote rapid organic matter removal and effective CH4 recovery; and late LIA may reduce N2 O emissions.