Vermicomposting of sewage sludge:: Effect of bulking materials on the growth and reproduction of the earthworm Eisenia andrei

The effect of different residual bulking agents (paper, cardboard, grass clippings, pine needles, sawdust and food wastes) in mixtures with sewage sludge (1:1 dry weight) on the growth and reproduction of Eisenia andrei, Bouche 1972 was studied in small-scale laboratory experiments with batches of sixty earthworms. The maximum weight achieved and the highest growth rate were attained in the mixture with food waste (755+/-18 mg and 18.6+/-0.6 mg day(-1) respectively) whereas the smallest size and the lowest growth rate was achieved in the mixture of sewage sludge with sawdust (572+/-18 mg and 11+/-0.7 mg day(-1) respectively). The earthworms showed much higher reproductive rates in the paper and cardboard mixtures (2.82+/-0.39 and 3.19+/-0.30 cocoons earthworm(-1) week(-1) respectively) compared to the control with sewage sludge alone (0.05+/-0.01 cocoons earthworm(-1) week(-1)).