Greenhouse gas emissions from home composting of organic household waste

The emission of greenhouse gases (GHGs) is a potential environmental disadvantage of home composting. Because of a lack of reliable GHG emission data, a comprehensive experimental home composting system was set up. The system consisted of six composting units, and a static flux chamber method was used to measure and quantify the GHG emissions for one year composting of organic household waste (OHW). The average OHW input in the six composting units was 2.6-3.5 kg week-1 and the temperature inside the composting units was in all cases only a few degrees (2-10 oC) higher than the ambient temperature. The emissions of methane (CH4) and nitrous oxide (N2O) were quantified as 0.4-4.2 kg CH4 Mg-1 input wet waste (ww) and 0.30-0.55 kg N2O Mg-1 ww, depending on the mixing frequency. This corresponds to emission factors (EFs) (including only CH4 and N2O emissions) of 100-239 kg CO2-eq. Mg-1 ww. Composting units exposed to weekly mixing had the highest EFs, whereas the units with no mixing during the entire year had the lowest emissions. In addition to the higher emission from the frequently mixed units, there was also an instant release of CH4 during mixing which was estimated to 8-12% of the total CH4 emissions. Experiments with higher loads of OHW (up to 20 kg every fortnight) entailed a higher emission and significantly increased overall EFs (in kg substance per Mg-1 ww). However, the temperature development did not change significantly. The GHG emissions (in kg CO2-eq. Mg-1 ww) from home composting of OHW were found to be in the same order of magnitude as for centralised composting plants.