The Science of Biosolids Recycling

The scientific process depends on critical peer review and debate. Modern biosolids recycling policy and practice rests on a body of scientific research, review, and debate conducted for over 30 years. A large proportion of government and university scientists working with biosolids have come to believe that biosolids recycling in accordance with current laws and best management practices represents "negligible risk" (this is the finding of the 1996 National Research Council review of the federal biosolids program; see below).

Still, there will be (and should be) robust discussion regarding new angles in the practice of recycling biosolids and other residuals. We at NEBRA believe that this robust scientific analysis and debate will lead to even better practice and policy.

Below are the key documents that provide an overview of the scientific basis for biosolids management, including biosolids application to soils. These documents, including U. S. EPA risk assessment and two reviews by expert panels of the National Research Council of the U. S. National Academies of Science, represent the scientific consensus on this topic.

Today, some research continues on the traditional research topics in this field: trace elements of concern (heavy metals), pathogens, and priority organic chemicals. But while those topics have, by now, been quite thoroughly addressed in the scientific literature, there are new topics of interest:

• What are the impacts of traces of chemicals in wastewater and biosolids that come from pharmaceuticals and personal care products (PPCPs)?
• What is the potential for land application of Class B biosolids to create bioaerosols that might impact neighbors?
• What are the impacts of particular treatment technologies, including possible triggering of bacteria reactivation and regrowth in some Class B biosolids?
• How do biosolids generate malodors and what process controls can be adopted to stop this from happening?
• In what ways can biosolids be used for energy production?
• What are the carbon emissions from various biosolids management processes, and how can biosolids management programs minimize those emissions and maximize efficiency and sustainability?

Federal EPA Risk Assessment & Reviews of Biosolids Recycling

The Part 503 Regulations

The U.S. Environmental Protection Agency (EPA) published regulations for biosolids at 40 CFR Part 503 in accordance with the Clean Water Act. Details about the 503 rule are available in A Plain English Guide to the EPA Part 503 Rule. The full risk assessment process that led to the final standards found in the 503 regulations can be accessed here: A Guide to the Biosolids Risk Assessments for the EPA Part 503 Rule.

Use of Reclaimed Water and Sludge in Food Crop Production (1996)

This is the first of two National Academy of Sciences expert panel reviews of the federal biosolids Part 503 regulatory program. It concluded…

"In summary, society produces large volumes of treated municipal wastewater and sewage sludge that must be either disposed of or reused. While no disposal or reuse option can guarantee complete safety, the use of these materials in the production of crops for human consumption, when practiced in accordance with existing federal guidelines and regulations, present negligible risk to the consumer, to crop production, and to the environment." (National Research Council: The Use of Reclaimed Water and Sludge in Food Crop Production," National Academy of Sciences, 1996, p.13.)

Biosolids Applied to Land: Advancing Standards and Practices (2002)

In 2000, the U.S. Environmental Protection Agency (EPA) asked the National Academy of Sciences to "review information on the land application of sludge and evaluate the methods used by the U.S. EPA to assess risks from chemical pollutants and pathogens in sludge." The Academy convened another National Research Council (NRC) panel that released its final report, Biosolids Applied to Land: Advancing Standards and Practices, in July, 2002. This report found:

"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. There have been anecdotal allegations of disease, and many scientific advances have occurred since the Part 503 rule was promulgated. To assure the public and to protect public health, there is a critical need to update the scientific basis of the rule to (1) ensure that the chemical and pathogen standards are supported by current scientific data and risk-assessment methods, (2) demonstrate effective enforcement of the Part 503 rule, and (3) validate the effectiveness of biosolids management practices" (from Summary, page 3, prepublication copy).

In September, 2002, Dr. Thomas Burke, Chair of the panel that wrote the report, issued a statement clarifying the panel's findings. "First, we found no evidence of an urgent public health risk from exposure to land-applied biosolids, based on our review of the scientific literature. Currently, there are no studies documenting adverse health effects from land application of biosolids, even though land application has been practiced for years. But this finding was tempered by the fact that few studies are available on human exposure to biosolids, and that, even when they are investigated locally, there are no means of tracking health allegations nationally."

This 2002 NRC report can be downloaded here or it may be purchased in paperback book form from the National Academy of Sciences--order here (you can laso read the report on-line at that webpage).

In 2003, EPA responded to a petition that urged a moratorium on the use of biosolids on soils.  The petition cited several cases that they claimed indicated harm from biosolids.  In its response, EPA refuted the claims of the petitioners, undermining their allegations with contrary evidence from each case they cited.  EPA's response is available here.

Current Topics of Interest

What are the impacts of traces of chemicals in wastewater and biosolids that come from pharmaceuticals and personal care products (PPCPs) and other sources?

Ned Beecher, Executive Director of NEBRA, summarized current knowledge of PPCPs in wastewater and biosolids in the Fall 2008 edition of the New York Water Environment Association journal Clearwaters. Click here to download.

The Water Environment Association of Ontario (WEAO) published literature reviews on the fate and significance of microconstituents in biosolids in 2001 and 2010.  See the WEAO website biosolids committee pages to learn more and download the reports. 

What about possible public exposure to pathogens from Class B biosolids applied to land?

Since the late 1990s, there has been concern and research regarding the possibility that pathogens and/or other emissions from Class B biosolids land application activities or biosolids composting facilities may cause health impacts to neighbors. (Note that there are few concerns about Class A biosolids, because they have been treated so levels of pathogens are similar to background soils or less.) 

Research has found measurable health impacts in workers at confined feeding operations (e.g. hog farms) and compost facilities that process food waste, yard waste, and/or wastewater solids (sewage sludge). Apparently, exposure to high levels of organic dusts for extended periods of time - such as at composting facilities - can trigger measurable health impacts in some people.

The effects of exposure to unstabilized or Class B biosolids - which contain viable pathogens and may generate bioaerosols and dust - are not as clear.  Research regarding the health of workers at wastewater treatment facilities, who are most highly exposed to unstabilized wastewater solids, has not generally found significant health impacts.  Such workers are generally not considered to be in hazardous work conditions.  Still, those managing large volumes of Class B biosolids or unstabilized wastewater solids (including workers at wastewater treatment facilities) are advised to use personal protective equipment, wash hands frequently, and avoid hand-to-mouth contact during work (see http://www.cdc.gov/NIOSH/docs/2002-149/2002-149.html).) 

There are reports in newspapers and on the internet of health impacts - mostly resipiratory and headaches - to neighbors of Class B land application sites.  However, research showing a causal relationship between Class B biosolids and the health impacts is lacking (see, for example, this 2002 literature review from Québec: http://www.biosolids.org/docs/24902.pdf).  Often, intense malodors are also present when impacts are reported, and there is evidence that odors cause physiological impacts (for example, see http://jeq.scijournals.org/cgi/content/full/34/1/129).  This complicates the situation.

Researchers at the University of Arizona have collected air samples at Class B land application sites during actual land application activities around the country (http://wqc.arizona.edu/publications/index.htm).  They conclude that risks to neighbors from bioaerosols from Class B land application are minimal.  However, most of their work was conducted in the dry southwest, where conditions are not conducive to pathogen survival.

A health study of neighbors to permitted land application sites in Ohio published in 2008, appeared to find health impacts (see http://www.ohiowea.org/owea/residuals/HealthSurveyResidents08.pdf).  However, the study's conclusions were subsequently challenged (see http://www.ohiowea.org/owea/residuals/FINALToledo%20Review08.pdf) and the authors released a clarification (http://www.biosolids.org/docs/University%20of%20Toledo%20Biosolids%20Fact%20Sheet%20on%20Health%20Survey%20Study_2008.pdf).  

Research continues regarding this aspect of Class B biosolids land application.  Given the hundreds of biosolids land application programs around the continent, many of which have been ongoing for a decade or more, and relatively few complaints of health impacts, this concern seems to be minimal and possibly localized.  In the meantime, those managing Class B biosolids are required by all Northeast state and provincial regulations to maintain setbacks from neighbors for all Class B biosolids management activities, and public access to Class B land application sites is restricted.  In recent years, there have been few complaints in this region.