Characteristics of CO2, CH4 and N2O emissions from a multi-soil-layering system during wastewater treatment

In the present study, characterization of greenhouse gas emissions, such as CO2, CH4 and N2O, from a multi-soil-layering (MSL) system during wastewater treatment was conducted, using a laboratory scale system (width 50 x depth 10 x height 120 cm). Net fluxes of CO2, CH4 and N2O from the system were in the range of 21.2-48.0 g m(-2) day(-1), -66.4-0.02 mg m(-2) day(-1) and 41-246 mg m(-2) day(-1), respectively. Carbon dioxide emission generally increased as the air temperature increased. The net flux of CO2 was not appreciably different among the treatments, even though the hydraulic loading rates (HLR) differed widely. These findings indicated that the decomposition of organic matter loaded through wastewater was more efficient in the low HLR treatments. Mean CH4 emission was lower than the amount of CH4 brought by the influent. Methane was consumed in the MSL system during most of the study period, and the consumption tended to be more efficient in the treatments at high HLRs. Wastewater quality was not markedly related to the characteristics of the CO2 and CH4 emissions. Nitrous oxide was mainly released into the treated water as dissolved gas. Nitrous oxide emission per 1,000 L of wastewater decreased as the HLRs increased in the wastewater containing a high level of contaminants (HWW), while in the case of wastewater containing a low level of contaminants (LWW), such a decrease in the emission was not observed. Mean N2O conversion rates of the LWW treatments ranged from 1.10 to 1.79% and were higher than those of the HWW treatments, which ranged from 0.19 to 1.95%. Nitrous oxide emission could be reduced in the HWW treatments.