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BIOSOLIDS_logoBiosolids are an organic fertilizer that is produced during wastewater treatment. During treatment, bacteria and other microbes break sewage down into simpler, harmless organic matter. This organic matter combined with microbial cell masses constitutes biosolids.

Land application of biosolids provides an excellent nutrient source for crops by providing soil with nitrogen, phosphorus, potassium, trace minerals and other nutrients vital to the production of healthy crops. Biosolids improve the physical, chemical and biological properties of soil by reducing soil erosion, increasing water-holding capacity, providing nutrients for plant growth, and providing food and energy necessary for promoting beneficial soil microorganisms. The application of biosolids reduces the need for chemical fertilizers. Improvements in treatment technologies continue to increase biosolids quality, providing even greater opportunities for this valuable resource.

Is it safe?

Yes it is safe! Hundreds of thousands of land applications have been conducted in the US over the past 80 years and there has never been substantiated adverse health effect. Similarly, 80 years of scientific research has demonstrated that biosolids recycling is safe. In addition, the University of Arizona collaborating with Pima County has conducted studies here in Tucson, on different aspects of biosolids for over 40 years. These studies, along with comprehensive compliance monitoring, contributed to the development of federal and state biosolids regulations published in 1993 that ensure that biosolids are safe. Pima County adheres to these regulations to protect public health and the environment. Biosolids have been approved by the U.S. Environmental Protection Agency (EPA) for land application as a beneficial fertilizer and soil amendment for use on farms and forests in all 50 states. Even though there are over 7 million tons of Biosolids beneficially used annually on the national level, these are applied on less than one percent of the nation's agricultural land.

What about heavy metals?

The risks of heavy metals in the U.S. have been greatly reduced by point source control that reduces metal inputs into sewage. In addition, as part of Federal 503 Monitoring rules, all biosolids that are to be land applied must be tested for heavy metals. Through very exhaustive research and testing, EPA has determined the maximum allowable amount of metals that are allowed in biosolids. These are known as “priority pollutants” and include arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc. Pima County ensures that the quality of our biosolids is well within these limits. In fact, Pima County performs regular testing of biosolids quality every month and the concentrations of metals are typically less than 10% of the maximum allowable limits. These results are summarized in an annual report that is submitted to both EPA and ADEQ.

What about germs and bacteria?

EPA 503 rules require that all biosolids meet certain treatment levels to assure the public that the material is safe for land application. Pima County verifies pathogen reduction meets acceptable limits to ensure compliance with all State and Federal regulations. There are tens of thousands of workers who have been working daily with sludge and Biosolids nationwide; there is no reported trend of abnormal incidence of occupational microbial injury among these workers.

What about odor?

Pima County takes great care to ensure that odors are not a nuisance to the public. EPA rules also address this through vector attraction reduction techniques dictating the type of treatment as well as land application methods. Timely covering the biosolids with soil reduces the potential for odor and vector attraction.

What about nitrogen?

The use of biosolids is regulated by the federal and state governments and has a long history of safe use as an alternative fertilizer. The land application of biosolids adheres to agronomic loading rates meaning that biosolids based nutrients cannot be applied to a field in excess of the ability of the designated crop to utilize. This limitation minimizes the potential for groundwater contamination.
Conversely, no regulatory limits exist for the amount of commercial fertilizer that can be applied to a field creating the potential for groundwater contamination from commercial based fertilizers.

Can people get sick from biosolids?

Substantial evidence from years of research and the widespread use of biosolids on farms supports the conclusion that humans do not get sick from the land application of biosolids. The National Academy of Sciences, in its review of current practices, public health concerns and regulatory standards, concluded that the use of biosolids in the production of crops presents “negligible risk” to humans, crop production and the environment.

Can biosolids spread pathogens through the air?

The overwhelming scientific research says NO! Extensive studies to determine whether biosolids can spread disease through the air have been documented via the University of Arizona’s Department of Microbiology and Immunology, and supported by the National Science Foundation Water Quality Center. Their conclusion: “…aerosolized microbes are rapidly inactivated during land application of Class B biosolids and present negligible risk to nearby communities…”

Can biosolids be used for mine reclamation?

Biosolids have been used successfully at mine sites to establish sustainable vegetation. Not only does the organic matter, inorganic matrix and nutrients present in the biosolids reduce the bioavailability of toxic substances often found in highly disturbed mine soils, but also regenerate the soil layer. Pima County has partnered with local mines for reclaiming abandoned mine sites with little or no topsoil. The biosolids application rate for mine reclamation is generally higher than the agronomic rate which cannot be exceeded for use of agricultural soils.

Can biosolids be used for composting?

Yes, biosolids may be composted and sold or distributed for use on lawns and home gardens. Most biosolids composts, are highly desirable products that are easy to store, transport and use.

Can biosolids be used to reclaim disturbed rangeland?

Biosolids have been found to promote rapid native soil cover, timber growth, allowing restoration and preservation of an important natural resource.

Are there different types of biosolids?

Class A refers to biosolids whose pathogen densities have been reduced to non-detectable levels. Due to this intensive pathogen reduction, handling and application of Class A biosolids are less restricted than for Class B. Biosolids with almost zero concentrations of metals, trace organics and pathogens, are termed “Exceptional Quality” biosolids. These can be safely handled and used by the general public and can be applied like any other registered fertilizer on lawns, gardens, parks and golf courses in urban areas based on soil nutrient recommendations for plant growth.
Class B refers to biosolids that have been treated to reduce pathogens (Salmonella sp. bacteria, and viruses) to levels that do not pose a threat to public health and the environment. Class B biosolids are commonly used as soil amendments and fertilizers on agriculture lands, pastures, forests and for the reclamation of disturbed lands such as roadsides and mine lands.

How are land application contractors selected?

Pima County selects qualified contractors through a competitive bidding process, beginning first with a request for proposal (RFP). Contractors submit applications, which are then reviewed based on performance requirements represented in the RFP. Price is only one of the many options reviewed by a municipality before choosing a contractor. Performance history, safety, and environmental compliance factors are also considered.

Will biosolids decrease my property value?

Biosolids application will not reduce the value or your property. Farmers who use biosolids are benefiting from a more cost-effective fertilizer option, helping the productivity and profitability of their operation. The more profitable in operation, the more likely the land will stay green, open, and productive, thereby increasing its potential value. Unproductive farms are, in most cases, quickly sold off for subdivision development. Keeping farms profitable maintains a locality’s rural character.

Glossary of Terms

PFAS in Biosolids - A Southern Arizona Case Study

In order to understand the effects of Per- and polyfluoroalkyl substances (PFAS) in land application of biosolids, RWRD partnered with the University of Arizona, Jacobs Engineers and the National Science Foundation and produced PFAS in Biosolids–A Southern Arizona Case Study, one of the largest studies of its kind ever undertaken.

U.S. Environmental Protection Agency EPA, Per- and Polyfluoroalkyl Substances (PFAS)
Arizona Department of Environmental Quality
North East Biosolids and Residuals Association PFAS & Biosolids
Northwest Biosolids Research Short Stories & Resource Library

California Association of Sanitation Agencies PFAS Overview
Mid Atlantic Biosolids Association
Virginia Biosolids Council

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