Biosolids are the organic and mineral solids resulting from the treatment of wastewater at wastewater treatment plants. They are rich in nutrients such as nitrogen and phosphorus and contain other supplementary nutrients such as potassium, sulfur, magnesium, calcium, copper and zinc.

As evidence of the success of our wastewater treatment facilities, millions of pounds of solids are removed from municipal sanitary and storm water flows every year as part of the treatment process. These solids, often referred to as “sludge” before treatment, are managed to minimize environmental risk during recycling or disposal.

Sludge can be processed to reduce its volume or to enhance its physical characteristics, making it easier to handle and transport. It may also be further processed, to a quality level that makes the final product acceptable for beneficial reuse. The products resulting from this additional treatment are commonly referred to as biosolids.

Traditionally, sewage sludge and biosolids have been managed in a variety of ways. With proper de-watering and treatment, sludges can be landfilled, incinerated, directly land applied, or further processed into compost or fertilizer. Biosolids and biosolids products that are land applied are treated to minimize odors and to reduce or eliminate pathogens. In addition to the significant quantities of valuable crop nutrients they contain, they also provide organic matter that enhances soil quality.

In 1993, the U.S. Environmental Protection Agency implemented processing and utilization standards for biosolids. The Federal Rule, 40 CFR Part 503, “Standards for Use or Disposal of Sewage Sludge,” recognized that sewage sludge and septage from residential septic tanks must be properly managed to minimize the potential for negative environmental impact. The rule established standards for the treatment of sludges and septage, and for the evaluation of the quality of biosolids.

The quality criteria include standards for disease-causing microorganisms, trace metals such as lead and mercury, and other contaminants that could enter wastewater and wastewater solids through routine residential, commercial or industrial discharges. Through extensive risk analyses and assessments, the EPA determined maximum levels of these contaminants that would be allowed in land-applied biosolids.

In the 503 Rules, EPA established two levels of microbiological quality for biosolids: Class A, which is essentially pathogen-free and can be used without restriction; and Class B, which has the potential for very low levels of pathogens and can be used with reasonable site restrictions to protect the public from exposure.

Treatment processes that help to achieve these classifications include lime stabilization, composting, heat drying, and anaerobic digestion. From a quality perspective, the EPA determined that only a few metals, often referred to as heavy or trace metals, were present in biosolids at levels that warranted the establishment of environmental risk standards. They established screening concentrations, below which biosolids and biosolid products can be used without restriction. When both the microbiological and biosolids quality screening standards are met, the biosolids are referred to as Exceptional Quality or EQ.

In the United States, approximately 7.1 million dry tons of treatment plant solids are generated each year at over 16,000 municipal wastewater treatment plants. Local communities decide what type of treatment processes and management options they use. About 55 percent of the total solids produced each year are land applied as biosolids, with the remainder being incinerated or landfilled (Water Environment Federation, 2010).

With over 30 years of successful recycling experience, land application of biosolids has returned hundreds of thousands of tons of valuable nutrients to the land, improving soil quality, enhancing crop growth, and providing farmers and horticulturists with a cost-effective and safe alternative to commercial fertilizers.

Biosolids are used for growing food crops, feed crops for animal production, and fiber crops for textile and paper mills. They are in high demand for use in landscaping, construction of ball fields and golf courses, topsoil replacement, turf farming and similar horticultural activities. Beneficial use of biosolids provides an environmentally responsible way to close the loop on the wastewater treatment process.