Addition of earthworm castings reduces gas emissions and improves compost quality in kitchen waste composting

Abstract

In this study, we demonstrate that the addition of earthworm castings (EC) in kitchen waste composting reduces ammonia and greenhouse gas (GHG) emissions and improves compost maturity. Kitchen waste (KW) was mixed with sawdust at a ratio of 7:3 as the compost stock. Four treatments with different proportions of EC added (0%, 2.5%, 5.0%, and 7.5% on the basis of the initial kitchen waste mass) were designed and utilized in a composting process lasting 85 days. The results showed that the GHG and ammonia emissions were considerably reduced in the treatments with EC added. In addition, EC amendment prolonged the thermophilic stage and shortened the composting period. The addition of EC reduced ammonia, methane, and nitrous oxide emissions by 61%, 48%, and 94%, respectively, also indicating that nitrogen in the compost was conserved. Nitrogen and major nutrients were best preserved in the EC 7.5% treatment, which produced a compost product with a better nutrient profile. Furthermore, the total global warming potential of the KW composting process was reduced by 74% by using the mixture with EC. An effective reduction in GHG emissions was observed already with the addition of 2.5% EC, but a significant reduction in ammonia emissions was observed for the EC 7.5% treatment. Therefore, the results of this study suggest that EC is an effective additive in KW composting. More specifically, addition of EC at 7.5% of the initial KW mass was most recommendable for mitigating potential global warming effects and improving compost quality.