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The Big Industry of Domestic Sewage Sludge and the Scientific Data Needed to Steer a Polarized Debate
06/05/2009
In 1988, the U.S. government banned ocean disposal of domestic sewage sludge. With limited options for disposal, the Environmental Protection Agency (EPA) looked for sustainable options for reuse. Today, 60% of the nearly 8 million dry tons of domestic sewage sludge produced each year is applied to agricultural lands as soil amendments. While the EPA has deemed this practice safe, health complaints from residents living near application sites have caused concerns to the contrary – that land application of treated sewage sludge, termed “biosolids,” may present hazardous human exposure to pathogens.According to associate professor of environmental and chemical engineering, Jordan Peccia, the EPA’s standards for ensuring safe land application of biosolids were developed for “environmental regulation expedience” – meaning they were based on the best available technologies, best knowledge, and available funding at the time. “The EPA didn’t know the pathogen content of biosolids, how many and what types of pathogens were present, how it becomes aerosolized, how it moves into a house and out of a house, how a person responds to it,” says Peccia. Unfortunately, this lack of information has limited the use of aerosol models to adequately assess off-site exposure during application.
Through grants from the Water Environment Research Foundation and National Science Foundation, Peccia’s team of researchers has focused on categorizing aerosols from biosolids. Currently, the U.S. Environmental Protection Agency (EPA) classifies biosolids as those which are pathogen free (class A), and those which contain pathogens (class B), based on indicator content (i.e., fecal coliforms) and/or the technologies used for treatment. The reality is that class A is not pathogen free. The problem, according to Peccia, is that these regulations are based on incomplete studies. Only recently, have researchers begun to compare the various treatment methods to understand how pathogens are removed, the adequacy of indicators for estimating pathogen content, and the presence of other relevant airborne pathogens that may survive treatment methods.
In the January 2009 issue of Applied and Environmental Microbiology, Jordan Peccia and doctoral student, Emily Viau, presented a survey of biosolids from over 30 different treatment facilities, producing class A and class B biosolids, that provides the necessary pathogen concentrations to add to the biosolids aerosol risk and pathogen exposure analysis, while clarifying the effectiveness of the indicators used in the U.S. EPA land application regulations, as well as the effectiveness of class A treatment methods.
Through modeling, measurement, and molecular biology source tracking, they had previously concluded that exposure to airborne pathogens from biosolids can occur up to 500 feet from the application area. The question remained whether or not this exposure is harmful. With this recent study, investigating different pathogen concentrations, they are able to begin to address this question.
Is there an easy solution? “Moving to methods of class A biosolids is going to be much better than using class B biosolids,” says Peccia. “There are two options. You can either use a higher quality, or class A, biosolid or you can apply at a farther distance.” But, that doesn’t solve the problem completely, says Peccia. “Class A is a little bit better, but it still has pathogens in it.”
Biosolids is a big industry and their use has created a polarized debate. Peccia’s group is unique in that they have refused to choose sides, and focus instead on using science to fill in the data that the EPA was missing when it first developed its standards. “Eventually, the EPA is going to have to take this on again and make a decision,” says Peccia. “Our hope is that our science plays a role in helping them make that decision.”
For additional information on this research, please visit the Peccia Research Group website.
For more information, contact Thea Reilkoff, SEAS Director of External Relations at (203) 432-4244 or thea.reilkoff@yale.edu.
