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In recent years, there has been political concern and public outcry over the land application of biosolids, especially Class B biosolids. In Florida, several counties, including DeSoto, Sarasota, Martin, and Okeechobee, have either banned or severely limited the land application of Class B biosolids within their jurisdiction. Others, such as St. Lucie, Hernando, and Putnam Counties, are following suit. The U.S. Environmental Protection Agency (EPA) and the Florida Department of Environmental Protection (FDEP) have conducted various sessions to discuss the current regulations regarding the land application of biosolids. In 2000, EPA asked the National Research Council (NRC) to conduct an evaluation of the EPA's current regulations and standards regarding the land application of biosolids, as presented in 40 CFR 503. The NRC committee concluded that, “There is no documented scientific evidence that the part 503 rule has failed to protect human health. However, additional scientific work is needed to reduce persistent uncertainty about the potential for adverse human health effects from exposure to biosolids” (NRC 2002).

Gainesville Regional Utilities (GRU) is committed to the protection of human health, the environment, and the positive public perception of biosolids land application. In an effort to demonstrate the success of a properly run Class B land application operation that meets all of the federal and state requirements, GRU initiated a comprehensive seasonal study to determine the pathogen reduction capabilities of their land application site. The primary objectives of the study were to evaluate the effectiveness of GRU's biosolids land application program and provide scientific evidence that the current federal and state requirements for Class B biosolids are adequate for protecting human health in a properly managed treatment and disposal operation.

The first phase of this comprehensive study was completed in the summer of 2003, with the second phase of the study completed in the spring of 2004. During each phase of the study, biosolids were applied under both surface and subsurface application methods. Soil samples were taken in various depths, both before and after application over a 30-day period, and analyzed for fecal coliforms, Salmonella sp., enteric viruses, viable helminth ova, Giardia lamblia, and Cryptosporidium sp. Fecal coliforms were used as an indicator species and sampled more frequently than other species throughout each phase of the study.

During the summer season, test results indicated that the fecal coliform levels were below the lower limit of detection within one week of application, regardless of the application method (surface application versus subsurface injection) and the depth of the sample. During the spring season, the fecal coliform levels were below the lower limit of detection within 2 weeks of application, regardless of the application method and the depth of the sample. Salmonella sp. exhibited similar destruction rates to the fecal coliforms during both phases of the study.

The levels of the additional four pathogens, enteric viruses, viable helminth ova, Cryptosporidium sp. and Giardia lamblia, were examined before application, at application, and at the end of the 30-day period. During both sampling events, these pathogen levels were not detectable at the end of the 30-day period, with the exception of viable helminth ova. During both sampling events, helminth ova were present at application and at significantly reduced levels after the 30-day period. During the summer of 2003 sampling event, helminth ova were also present in the background samples.

In an effort to increase the quality of the biosolids, GRU is currently conducting additional helminth ova testing to identify the source and develop a pre-treatment strategy for reducing helminths in the biosolids.

Document Type: Research Article


Publication date: 2005-01-01

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