Improving leachate quality and optimizing CH and NO 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 (CH) and nitrous oxide (NO) emissions during aeration. In this study, the effects of three pre-aeration strategies on leachate quality variations and CH and NO 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 CH emissions (9234.3 mg) and resulted in a longer emission period (95 days). HIA generated the least cumulative CH emissions (4297.6 mg) and shortest emission period (65 days) due to organic matter loss during aeration. NO 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 NO emissions (2884.6 mg) and experienced a longer emission period (179 days) compared to CMA (2281.6 mg; 151 days). LIA had the longest NO emission period (209 days), but had the lowest cumulative NO emissions (1486.3 mg). CH and NO 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 CH recovery; and late LIA may reduce NO emissions.