Can earthworms completely eliminate disease-causing organisms from human waste? A pilot project in Florida established conclusively that, after introducing earthworms into biosolids infected with E. coli, Salmonella, and other harmful organisms, the worms eliminated these pathogens, rendering the resulting material (vermicompost) safe for handling and application to plants.
Compost Science & Utilization (Winter 2001,Volume 9, Number 1) contains the landmark publication “The Effectiveness of Vermiculture in Human Pathogen Reduction for USEPA Biosolids Stabilization.” The publication of this study in a peer-reviewed scientific journal confirms the efficacy of earthworms in eliminating human pathogens in biosolids (wastewater residuals) to achieve Class A stabilization, the highest rating of the USEPA, an indication that the material has been rendered safe because it is virtually free of harmful organisms.
The Florida-based study was conducted in two phases, the first beginning in March 1996 at the city of Ocoee’s Wastewater Treatment Facility in Ocoee, Florida. The purpose of the study was to see if vermiculture offered a low-cost but effective means of stabilizing biosolids. Dr. Jim Smith, Senior Environmental Engineer and Pathogen Equivalency Commission (PEC) Chair for the USEPA indicated by personal communication to principal investigator Bruce R. Eastman of the Orange County Environmental Protection Division (OCEPD) that a three- to four-fold reduction in indicator organisms would be sufficient to warrant serious consideration of vermicomposting as an effective stabilization methodology. In fact, the tests indicated that all of the pathogen indicators were reduced to safe levels in as short a time as 144 hours. Significant reduction of all pathogens had been achieved through vermicomposting within the first three days (72 hours).
Why should anyone care that earthworms reduce pathogens in biosolids? There may be several reasons. First, according to the authors of this paper, “The obvious inherent environmental and health hazards of unstabilized human waste can be seen in the third world nations. Rampant diseases that have debilitating consequences are common for people living in these countries. Unstabilized or improperly stabilized biosolids are a real concern and the regulations regarding stabilization reflect this ongoing concern.” Vermicomposting biosolids may offer an immediate and effective, low-cost solution to third world nations concerned with handling these wastes.
Second, the considerable expense involved for many smaller-sized US communities to build wastewater treatment plants suggests vermicomposting may appear to be a viable and more affordable alternative. The cost-per-ton for handling these wastes is extremely high and vermicomposting may offer a lower-cost, but equally effective means of processing biosolids where volumes of material are manageable by a small work force where space is available to spread the material. Vermicomposting biosolids in major metropolitan areas may not be as practical, but the practice may be of significant benefit to many rural communities. Consider that in Florida alone there were 3,500 to 4,000 wastewater treatment facilities in 1997, but only nineteen were Class AA Type I and four Class A Type I. According to Eastman, “the vast majority of these [remaining] facilities generated a product below EPA Class A standards.” The authors of this study stated “The vermicomposting method is an inexpensive low-technological procedure for achieving results comparable to other more intensive and expensive USEPA biosolids stabilization methods.”
A third, and possibly the most important reason why this study has such importance is the fact that it has now been scientifically demonstrated that vermicomposting eliminates the need for thermophilic (heat) composting. USEPA regulations to stabilize biosolids are found in the Code of Federal Regulations, often termed the “Part 503 regulations.” There it states that biosolids material must be maintained in an in-vessel container at 55 degrees Celsius (131 degrees Fahrenheit) or higher for a minimum of three days. This time and temperature requirement is necessary for achieving destruction of human pathogens. (When non-containment systems are used the material must be turned five times over a period of 15 days, maintaining the same temperature requirement.) This study in vermicomposting now presents evidence for the fact that earthworms feed on pathogenic organisms and effectively clean up the potentially harmful material, rendering it safe for handling. The authors speak of “the elimination of pre-composting,” a process many believe is necessary to sanitize material even before vermicomposting. “Until recently,” the authors stated, “this step was thought to be necessary to eliminate pathogens before adding earthworms. However, this project confirms that the earthworms greatly reduce the pathogens from the biosolids during vermicomposting making the pre-composting unnecessary. The use of earthworms to vermicompost biosolids exceeded even the initial experimental expectations for pathogen reductions.”
Four indicator organisms were introduced (spiked) into biosolids material to ensure high levels before testing began: fecal coliforms, Salmonella spp., enteric virus and helminth ova. The material was laid out in two windrows, one designated as a test row containing earthworms and the other row designated the control row. After 144 hours the test row samples showed a 6.4-log reduction in fecal coliforms compared with the control row, which only had a 1.6-log reduction. The test row samples showed an 8.6-log reduction in Salmonella spp., while the control row had a 4.9-log reduction. The test row samples showed a 4.6-log reduction in enteric viruses while the control only had a 1.8-log reduction. The test row samples had a 1.9-log reduction in helminth ova while the control row only had a 0.6-log reduction. The full-scale project was scheduled to last for 90 days, but was terminated after 68 days because the earthworms consumed material at a rate up to 1.5 times their body weight each day.
Final analysis of the samples taken from the test row of vermicomposted biosolids indicated negative readings for E. coli, Salmonella spp., enteric virus and helminth ova. The authors concluded, “Based on experimental analyses from both the pilot and the full-scale operation, vermiculture can be used effectively as an USEPA process to treat pathogens and potentially produce Class A biosolids.”
What remains to be done? In order to approve vermicomposting as an acceptable PFRP (Process to Further Reduce Pathogens) USEPA will want to evaluate the results of standard operating procedures (SOPs) to be suggested in a future project. Investigators will need to determine such factors as how long (duration) biosolids material must be processed by earthworms and what biomass of earthworms must be present in a given quantity of biosolids (ratio of earthworms to unprocessed material) in order to achieve Class A stabilization.
Bibliographic citation for this article is as follows: Eastman, B.R., P.N. Kane, C.A. Edwards, L. Trytek, B. Gunadi, A.L. Stermer and J.R. Mobley. 2001. The effectiveness of vermiculture in human pathogen reduction for USEPA biosolids stabilization. Compost Science and Utilization, 9(1):38-49.
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For Further Reading:
See Casting Call, February 2000, Volume 4 Issue 5 for two articles on vermicomposting and biosolids: “Vermicomposting Biosolids: Earthworms Reduce Pathogens in Sewage Sludge,” and “Will Vermistabilization of Biosolids Make a Comeback? A Brief Review of US Efforts.” Also, see the interview with Bruce R. Eastman, Assistant Manager for the Orange County Florida Environmental Protection Division, in the book In Their Own Words: Interviews with Vermiculture Experts, ed. Peter Bogdanov, (Petros Publishing, Merlin Oregon), 2001, pp.161-184. Also available an an ebook from akgy.cn