Feasibility of vermicomposting dairy biosolids using a modified system to avoid earthworm mortality

A laboratory study was conducted to examine the feasibility of vermicompost ing dairy biosolids (dairy sludge), either alone or with either of the bulk ing agents - cereal straw or wood shavings, using the epigeic earthworm - E isinea andrei. Earthworms added directly to these three substrates died wit hin 48 hours. A system was developed to overcome the toxic effect of unproc essed dairy biosolids. The substrates were placed over a layer of vermicomp osted sheep manure into which the earthworms were inoculated. Within two we eks, all earthworms were within the upper layer of substrate. Compared to s heep manure which is a favourable substrate for vermicomposting, the three substrates containing dairy biosolids were more effective in supporting ear thworm growth and reproduction. The final products obtained after 63 days o f vermicomposting had 39-53% less organic carbon than the initial substrate s. Organic fractionation indicated that vermicomposting increased the stabi lity of the materials to biological decomposition. The vermicomposts obtain ed from the three substrates with dairy biosolids had low heavy metal conte nts and electrical conductivities, and did not inhibit plant growth when co mpared with a commercial vermicompost in a bioassay.