Combining vermiculture with traditional green waste composting systems

Freshly-shredded green waste (yard waste) was composted for 16 weeks using a mechanically-turned windrow system. The rate of organic matter stabilisation was determined by measuring the reduction in the volatile solids content of the waste. Samples of the fresh material were also vermicomposted using Eisenia andrei (Bouché) and rates of growth and reproduction obtained which were comparable to published rates for other wastes. Vermicomposting for 8 weeks produced a material with a significantly lower volatile solids content compared to composting for a similar period (P < 0.01). A combined composting and vermicomposting system was investigated by extracting partially-composted samples from the compost windrow every 2 weeks and feeding these to E. andrei. Growth and reproduction were found to be positively correlated to the volatile solids content of the waste (P < 0.01). Vermicomposting partially composted waste (2 weeks), for a further 6 weeks, reduced volatile solids content significantly more than for composting fresh waste for 8 weeks (P < 0.001). It is concluded that E. andrei is capable of attaining good rates of growth and reproduction in fresh green waste and that vermicomposting can result in a more stable material (lower volatile solids content) compared to composting. Combining vermicomposting with existing composting operations can also accelerate stabilisation compared to composting alone. The duration of pre-composting will determine the subsequent rate of growth and reproduction of E. andrei. To ensure that the vermicomposting system operates at maximum efficiency, pre-composting should be kept to a minimum, consistent with effective sanitisation of the waste.