NO emissions from an intermittently aerated semi-aerobic aged refuse bioreactor: Combined effect of COD and NH-N in influent leachate.

The carbon-nitrogen ratio (COD/NH-N) is an important factor affecting nitrification and denitrification in wastewater treatment; this factor also influences nitrous oxide (NO) emissions. This study investigated two simulated intermittently aerated semi-aerobic aged refuse bioreactors (SAARB) filled with 8-year old aged refuse (AR). The research analyzed how differences in and the combination of influent COD and NH-N impact NO emissions in leachate treatment. Experimental results showed that NO emissions increased as the influent COD/NH-N decreased. The influent COD had a greater effect on NO emissions than NH-N at the same influent ratios of COD/NH-N (2.7 and 8.0, respectively). The maximum NO emission accounted for 8.82±2.65% of the total nitrogen removed from the influent leachate; the maximum level occurred when the COD was 2000mg/L. An analysis of differences in influent carbon sources at the same COD/NH-N ratios concluded that the availability of biodegradable carbon substrates (i.e. glucose) is an important factor affecting NO emissions. At a low influent COD/NH-N ratio (2.7), the NO conversion rate was greater when there were more biodegradable carbon substrates. Although the SAARB included the NO generation and reduction processes, NO reduction mainly occurred later in the process, after leachate recirculation. The maximum NO emission rate occurred in the first hour of single-period (24h) experiments, as leachate contacted the surface AR. In practical SAARB applications, NO emissions may be reduced by measures such as reducing the initial recirculation loading of NH-N substrates, adding a later supplement of biodegradable carbon substrates, and/or prolonging hydraulic retention time (HRT) of influent leachate.