A study was performed by the Orange County Environmental Protection Division to test the feasibility of vermicomposting as a viable method for obtaining United States Environmental Protection Agency (USEPA) Class A pathogen stabilization in domestic wastewater residuals (biosolids).
The study was conducted at the City of Ocoee's Wastewater Treatment Facility in Ocoee, Florida. The City of Ocoee's Class B biosolids were used as the earthworm substrate. Two rows of biosolids were heavily inoculated with USEPA's four human-pathogen (pathogen) indicators,
fecal coliform, Salmonella spp., enteric virus and helminth ova. The row that served as the test was seeded with earthworms, Eisenia foetida. The quantity of E. foetida was calculated at a 1:1.5 earthworm biomass to biosolids ratio (this is for a 24-hour period) and then
adjusted for the amount of days in the test period. The results of testing indicated that all of the pathogen indicators in the test row realized a greater reduction than in the control row within 144 hours. In this time, the test row samples showed a twenty-one fold reduction in fecal
coliforms; the control row only had a five-fold reduction. The test row samples showed a twenty-eight fold reduction in Salmonella spp.; the control row had a sixteen-fold reduction. The test row samples showed a fifteen-fold reduction in enteric virus; the control only had a six-fold
reduction. The test row samples showed a sixfold reduction in helminth ova; the control row only had a one-fold reduction. The USEPA required three to four-fold reduction in the indicator organisms was statistically obtained. These results suggest that vermicomposting may be used as an
alternative method for stabilization of Class A biosolids eliminating the need for traditional pre-composting.
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