Young specimens of Eisenia andrei, weighing 200–250 mg live weight, were obtained from a
stock culture maintained in the laboratory at a temperature of 25°C in cow manure. Sewage
sludge biosolids were obtained from a wastewater treatment plant in Fresno, CA. Sixty earthworms
were placed in 2 litre plastic dishes and supplied 100 g of a mixture of sewage sludge
with paper, cardboard, grass clippings, pine needles, sawdust and food wastes (1:1 dry weight)
with the bulking materials chopped and sieved (< 2 mm). Aged sewage sludge (two weeks old)
was used as control. The worms were supplied with additional 100 g of the different mixtures
every week for the duration of the experiment which ended when weight losses of the earthworms
were detected (6 weeks). Three replicates for each treatment were established. The
weight of the worms (with full alimentary tracts), clitellum development and cocoon production
(determined by hand-sorting) were measured weekly. To compare the growth rates of E.
andrei in the different mixtures, it was necessary to find a common denominator for compari-
son. To achieve this, the growth rate (mg weight gained day-1 worm-1) was calculated and the
maximum weight achieved was divided by the number of days required to reach the maximum
weight.