By Ian Pepper, The University of Arizona; Greg Kester, California Association of Sanitation Agencies; Nick Basta and Alyssa Zearley, Ohio State University and Ryan Batjiaka, San Francisco PUC

The organic solids remaining after sewage treatment are termed organic residuals or biosolids. Biosolids have been defined as: “Sewage sludge that has been treated to meet the land application standards in the Part 503 Federal Rule or any other equivalent land application standards or practices” (National Research Council, 2002). In the U.S., an estimated 14,748 Publicly Owned Treatment Works (POTWs) are used to treat sewage for 238.2 million people (U.S. EPA, 2016). Overall approximately 8 million dry tons of biosolids are produced annually with the largest plants (≃ 3300) generating more than 92% of the total biosolids (NEBRA, 2007). Beneficial reuse through land application presently accounts for 55% of available biosolids spread on 0.1 of available agricultural land. Interestingly these values have remained fairly constant over the past several years (NEBRA, 2007; Brooks et al., 2011; NBP, 2013). Though biosolids represent only a small fraction of total organic residuals produced relative to animal manures, they are the most processed, most regulated, most studied and most controversial, with respect to disposal and beneficial reuse.

In the early 2000s, there was intense interest and scrutiny of land application of municipal biosolids. This interest peaked in 2002 when the National Research Council of the National Academies published the report: “Biosolids Applied to Land: Advancing Standards and Practices.” One of the overarching findings of the report was that:

“There is no documented scientific evidence that the Part 503 rule has failed to protect public health. However, additional scientific work is needed to reduce persistent uncertainty about the potential for adverse human health effects from exposure to biosolids.”

During this time, environmental activism against land application in the U.S. and elsewhere was increasing, in part due to the above-stated overarching finding. The finding should be placed in context where any regulation intended to protect public health and the environment must always be dynamic and evolve with the science, and thus will always need additional scientific work to confirm their adequacy. While most land application programs have and continue to operate successfully with strong support, there is a small cross-section of environmental activists that oppose land application due to odors, but also due to fear. Most residential complaints about land application are fueled by the odor of biosolids produced during the land application process. Historically odors have been associated with disease, which can result in psychosomatic problems, and also real fear, as for example, concern about aerosolized human pathogenic viruses that could occur during biosolid application, and emanate to offsite communities. This has led to a national debate on the safety of land application.

Contaminants of concern have been identified as: metals; trace organics; pharmaceutical and personal care products including antibiotics; and microbial pathogens. Of these, concern over metals has decreased due to the concept of point source control, first introduced via the Clean Water Act of 1972 and the pretreatment program adopted in the 1980’s. However, concern about the other three classes of contaminants has increased, in some cases to the point of wide-spread attention, as exemplified by PFAS and antibiotic resistant bacteria.

land application via injection
Land application via injection

In June 2017, the US EPA Office of Inspector General began a review of the EPA’s Office of Water Regulations and oversight of the U.S. biosolids land application program. The review was finally released as an EPA Office of Inspector General (OIG) Report in November 2018. However, the report was a sensationalistic and apparently biased indictment of the EPA biosolids program, and implied that land application is unsafe until formal risk assessments have been conducted on 352 constituents identified in biosolids.

Due to concern surrounding the negative impact this report could have on land application, utilities, and biosolids stakeholders coordinated support to present a rebuttal to the report that is being prepared by members of a national group of land application experts, with scientific expertise in chemical and microbial contaminants. This group consists of members of the USDA federally funded Multi-state Research Project W4170: Beneficial Use of Residuals to Improve Soil Health and Protect Public and Ecosystem Health that provides a national knowledge base of information on land application. A preliminary, yet reassuring power point presentation of the rebuttal was presented at this year’s Biofest sponsored by Northwest Biosolids. The presentation can be accessed via the link below and provides information on the 352 constituents, and other allegations against land application that have accrued over the years. The formal rebuttal to the EPA Report will be released later this year.


Allegations Against Land Application – Fact vs. Fiction 

OIG Report - PFOA, PFOS, PFAS and Beneficial Use of Biosolids

Literature Cited    

Brooks, J.P., Brown, S., Gerba, C.P., King, G.M., O’Connor, G.A. and Pepper, I.L. 2011.  Land Application of Organic Residuals: Public Health Threat or Environmental Benefit? American Society for Microbiology, Washington, DC.

National Biosolids Partnership (NBP). 2013. Potential Uses of Biosolids.

NEBRA (Northeast Biosolids and Residuals Association) 2007. A national biosolids regulation, quality, end-use and disposal survey. Final Report, 20 July 2007.

NRC (National Research Council) 2002. Biosolids Applied to Land: Advancing Standards and Practices. National Academy Press, Washington, DC.

U.S. EPA (Environmental Protection Agency). 2016. Clean Watersheds Needs Survey 2012 – Report to Congress.