Vermicomposting : from microbial and earthworm induced effects in bacterial sanitation to the chemistry of biodegradation under batch or continuous operation

Vermicomposting is a mesophilic organic waste management practice in which earthworms interact with the microbiota to drive the stabilization of organic matter. Earthworms influence the microbial populations both directly and indirectly through grazing, ingestion and digestion of organic matter and deposition of castings and modifications of the physico-chemical parameters of the substrate. Under continuous operations, distinct patterns in the dynamics of pH, organic carbon, total nitrogen, total and labile sugars content of the vermicompost were distinguished. At the beginning, there was an accumulation of organic matter whose degradation rate increased after the initiation phase. No equilibrium state with stabilizing physico-chemical parameters could be distinguished during continuous operations, but interruption of feeding led to a decrease in total sugars, organic carbon, total nitrogen and pH. Elimination of bacterial pathogens from the vermicompost is primarily attributed to the indigenous microbiota and in a minor proportion to earthworm mediated effects; abiotic factors may modulate survival patterns but they are thought to play an indirect or secondary role. Different operational modes (batch vs. continuous) and varying earthworm densities did not affect E. coli survival. We showed that vermicompost contained both opportunistic bacterial pathogens and antagonists. Vermicompost is an organic waste management technology which can safely be conducted in domestic settings, provided that recommended management guidelines are followed. Further research is necessary to ensure that different species of bacterial pathogens are reduced to safe levels during vermicomposting, and future research efforts should be directed towards sanitation mechanisms