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Vermistabilisation, the use of earthworms in the treatment of waste materials, is a process in which valuable resources are recovered from wastes as earthworm biomass and vermicompost while, at the same time, the potential for pollution is reduced. In the first study, feedlot cattle manure was applied to earthworm beds to assess the potential for production of earthworm biomass and vermicompost under field conditions. A second study examined the changes to several agricultural wastes under controlled laboratory conditions. The field experiments demonstrated that vermistabilisation was effective in the recovery of valuable resources from feedlot cattle manure with substantial improvements to pollution indices. The process was most effective when manure was applied as a 10 - 15 cm layer onto earthworm beds, applications greater than 15 cm exhibiting no earthworm activity. Deeper layers retained the chemical characteristics of the initial manure, particularly its anaerobic status, which were not conducive to earthworm penetration. Earthworm biomass was produced and extracted at 4.9% (dry basis) of the mass of the original manure and represented 7, 18, 7 and 2% of the initial carbon, nitrogen, sulfur and phosphorus. The initial (dry) mass of manure was reduced by 30% and the residual matter (vermicompost) was greatly improved in its physical and chemical properties. The conversion of manure to vermicompost resulted in a pH shift toward neutral, a reduction in electrical conductivity, a large increase in oxidation potential and significant reductions in potentially polluting water-soluble matter. The improvements in electrical conductivity and sodium absorption ratio, however, were due to a large loss of sodium and potassium into the underlying bedding during vermistabilisation. This is a particular problem of feedlot cattle manure with its relatively high sodium content (1.0-1.5%) and large-scale operations would need to contain any leachate for treatment or disposal. Laboratory trials examined the effects of earthworms on several waste materials without additives (such as bulking agents or adsorbants) and in the absence of earthworm bedding. Several of the materials were toxic to earthworms while most did not support earthworm growth. Little change occurred in wastes with very high C:N ratios or with high lignin contents. |
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