Comparison of the chemical, physical and microbial properties of composts produced by conventional composting or...

The chemical, physical and microbial properties of thermophilic composts and vermicomposts were compared using the same municipal green waste-based feedstocks: (i) municipal green waste alone, (ii) 75 % municipal green waste/25 % green garden waste and (iii) 75 % municipal green waste/25 % cattle manure. Temperatures reached 37 °C during composting of municipal green waste alone but when garden waste or cattle manure were added, temperatures reached 47 and 52 °C, respectively. At the end of vermicomposting (using Eisenia fetida), the number of earthworms present was greater than that added for the cattle manure-amended feedstock but much less for both the garden waste and municipal green waste alone treatments. The products formed in all treatments generally fell within suggested maturity indices for composts. Greater organic matter decomposition occurred during composting than vermicomposting resulting in composts having a significantly lower organic C content and a greater content of total N, extractable Mg, K, Na, P, and mineral N, a higher EC and a lower C/N ratio than the vermicomposts. For all three feedstocks, vermicomposts had a lower bulk density and greater total porosity and macroporosity than composts. For the garden waste- and cattle manure-amended feedstocks, vermicomposts had a higher microbial biomass C than the composts and for all three feedstocks, basal respiration and metabolic quotient were greatest for vermicomposts. It was concluded that composting is a robust process suitable for treatment of a range of organic wastes but, because of the nutritional requirements of the earthworms, vermicomposting is a much less robust and was only suitable for the cattle manure-amended feedstock.