Worm Species

In most locations, the facilities required for the vermistabilization procedure will be similar to an underdrained sand drying bed enclosed in a heated shelter. Studies at Cornell University evaluated four earthworm species: Eisenia foetida, Eudrilus eugeniae, Pheretima hawayana, and Perionyx excavatus. E. foetida showed the best growth and reproductive responses, with temperatures in the range of 68 to 77°F (20 to 25°C). Temperatures near the upper end of the range are necessary for optimum growth of the other species. Worms are placed on the bed in a single initial application of about 0.4 lb/ft2 (2 kg/m2) (live weight). Sludge loading rates of about 0.2 lb/ft3/wk (1000 g of sludge volatile solids per m2 per wk) were recommended for liquid primary and liquid waste-activated sludge (Loehr et al., 1984). Liquid sludges used in the Cornell University tests ranged from 0.6 to 1.3% solids, and the final stabilized solids ranged from 14 to 24% total solids (Loehr et al., 1984). The final stabilized sludge had about the same characteristics regardless of the type of liquid sludge initially applied. Typical values were as follows:

• Chemical oxygen demand = 606-730 g per kg TS

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