Assessing the spatial and temporal variability of greenhouse gas emissions from different configurations of on-site wastewater treatment system using discrete and continuous gas flux measurement

[摘要] Global emissions linked to wastewater treatment are estimated to account for up to 1.5 % of total greenhouse gas (GHG) emissionsglobally. However, few studies have measured GHG emissions from domestic on-site treatment systems (DWWTSs) directly. In this study, two DWWTSs weremonitored for 446  d and  >  42 000 gas flux measurements were conducted using both discrete spot measurements and continuous flux chamberdeployments. The observed GHG fluxes from biological activity in the soil and water phase were found to be highly spatially and temporally variableand correlated to environmental factors, water usage patterns and system design. In total, the results show that a septic tank discharging effluentinto a well-designed soil treatment unit is estimated to emit a net 9.99  kg - CO 2 eq . cap - 1 yr - 1 , with approximately 63 %,27 % and 10 % of the total CO 2 -equivalent net emissions in the form of CO 2 , CH 4 and N 2 O ,respectively. Emissions from the septic tank surface contributed over 50 % of total emissions and tended to be strongly underestimated byone-off discrete measurements, especially when episodic ebullitive events are to be considered. Fluxes from the soil treatment unit (STU) stemmedfrom both the soil surface and the vent system. Soil fluxes were mostly influenced by temperature but peaked regularly under conditions of rapidlychanging soil water content. Vent fluxes were mostly governed by effluent, quality and a low number of high-emission events were responsible for themajority of total observed vent emissions. Owing to the strong overall spatial and temporal heterogeneity of observed fluxes from DWWTSs across allmodules, future studies should focus on continuous deployments of a number of flux chambers over discrete measurements to accurately assess GHGemissions from on-site systems. This study also provided insights into managing GHG emissions from DWWTSs by different system configuration design,as well as indicating that the current IPCC emission factors for CH 4 and N 2 O significantly overestimate emissions foron-site wastewater treatment systems.

[学科分类] 大气科学