Effect of pre-composting and vermicomposting on compost characteristics

The aim of this study was to determine the effect of thermophilic pre-composting followed by vermicomposting on compost characteristics compared with thermophilic pre-composting and windrow composting. Source segregated household waste was thermophilically composted (14 days) to sanitise the waste. Organic matter and nitrogen losses were 9% and 5% respectively. The waste was then matured (84 days) using either vermicomposting beds (n = 5) or composting windrows (n = 5). At the end of the 98 days processing there was a significantly greater mass (P < 0.01) of fine particles (<10 mm) in the vermicomposting beds (65.3% m:m) compared with the compost windrows (36.9% m:m) suggesting enhanced fragmentation of the paper-based feedstock components by the earthworms. When screened, the windrow compost (<10 mm) contained significantly higher (P < 0.01) concentrations of total N, P and K and total Cu (P < 0.01), Pb (P < 0.001), Ni (P < 0.05) and Cd (P < 0.01). Significantly higher levels of electrical conductivity (EC) 3.08 mS.cm (P < 0.001) and water-soluble K 6366 mg kg−1 (P < 0.01) were recorded for the windrow compost compared with the vermicompost (1.78 mS.cm; 3328 mg kg−1). The vermicompost NO3 concentration (2660 mg kg−1) was significantly higher (P < 0.05) than for the windrow compost (1531 mg kg−1). In a programme of plant response tests based on B.S.I. PAS 100 (2005), the screened (<10 mm) vermicompost and windrow compost performed comparably when formulated into growing media based on equalising EC levels.