Sludge Quality

The sludge organics pass through the gut of the worm and emerge as dry, virtually odorless castings. These are suitable for use as a soil amendment or low-order fertilizer if metal and organic chemical content are within acceptable limits (see Table 9.16 for metals criteria). Only limited quantitative data are available with regard to removal of pathogens with this process. The Texas Department of Health found no Salmonella in either the castings or the earthworms at a vermistabili-zation operation in Shelbyville, Texas, that received raw sludge (Donovan, 1981). A market may exist for the excess earthworms harvested from the system. The major prospect is as bait for freshwater sport fishing. Use as animal or fish food in commercial operations has also been suggested, but numerous studies have shown that earthworms accumulate very significant quantities of cadmium, copper, and zinc from wastewater sludges and sludge-amended soils; therefore, worms from a sludge operation should not be the major food source for animals or fish in the commercial production of food for human consumption.

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