COMBINING VERMICULTURE WITH TRADITIONAL GREEN WASTE COMPOSTING SYSTEMS

Freshly-shredded green waste (yard waste) was composted for 16 weeks u sing a mechanically-turned windrow system. The rate of organic matter stabilisation was determined by measuring the reduction in the volatil e solids content of the waste. Samples of the fresh material were also vermicomposted using Eisenia andrei (Bouche) and rates of growth and reproduction obtained which were comparable to published rates for oth er wastes. Vermicomposting for 8 weeks produced a material with a sign ificantly lower volatile solids content compared to composting fora si milar period (P < 0.01). A combined composting and vermicomposting sys tem was investigated by extracting partially-composted samples from th e compost windrow every 2 weeks and feeding these to E. andrei. Growth and reproduction were found to be positively correlated to the volati le solids content of the waste (P ( 0.01). Vermicomposting partially c omposted waste (2 weeks), for a further 6 weeks, reduced volatile soli ds content significantly more than for composting fresh waste for a we eks (P < 0.001). It is concluded that E. andrei is capable of attainin g good rates of growth and reproduction in fresh green waste and that vermicomposting can result in a more stable material (lower volatile s olids content) compared to composting. Combining vermicomposting with existing composting operations can also accelerate stabilisation compa red to composting alone. The duration of pre-composting will determine the subsequent rate of growth and reproduction of E. andrei. To ensur e that the vermicomposting system operates at maximum efficiency, pre- composting should be kept to a minimum, consistent with effective sani tisation of the waste. (C) 1997 Elsevier Science Ltd.