The Benefits of Biosolids

August 8, 2018 | Blog, General RCAP News

Written by: Jim Jones

What are biosolids and what are the benefits of utilizing land application of biosolids? Biosolids are a nutrient-rich organic soil-like residue of materials that are removed from the mechanical treatment of wastewater. When these raw solids have undergone additional treatment to kill pathogens and additional processes that stabilize the solids, they are then called biosolids. Once they reach the stage of “Biosolids”, they are ready for recycling and can be applied as a fertilizer to improve and maintain productive soils and stimulate plant growth. This means that the bacteria used in the wastewater treatment process is captured from the water and digested or treated to make it safe to apply to farmland. Solids generated from the wastewater treatment process must be disposed of in a safe method. The land application of biosolids is widely regarded as the best management practice for many wastewater utilities that have biosolids to dispose of.
Why should biosolids get land applied? There are many benefits to land applied biosolids, including:

• Increased crop production
• Biosolids contain nutrients like nitrogen and phosphorus that crops can use
• Reduced soil erosion
• Reduced topsoil runoff
• Boosted soil water holding capacity, which protects against drought
• Protected water quality as organic nitrogen and phosphorus are less likely to leach into groundwater compared to commercial fertilizer
• Reduced demand for commercial petroleum-based fertilizers and the energy needed to manufacture it
• Using a recycled product like biosolids does not deplete non-renewable resources such as phosphorus.
• Increased soil organic matter
• Increased soil microbial activity
• Reduced farm production costs for fertilizers and provides other economic incentives
• Can be used to reclaim mine lands and other poor producing soils
• Can be used to increase forestry production by enriching forestland
• Conservation of landfill space, extending the life of existing landfills

Hauling biosolids at sunset in Mankato, MN


There are two types of biosolids: Class A and Class B biosolids. Biosolids are given one of these two designations based on the process is used to significantly reduce pathogens. Pathogens are reduced in the treatment plant as they undergo physical, chemical, and biological processing. The number of pathogens remaining in the biosolids will determine the Class. Class A Biosolids have reduced pathogen levels to virtually none. Class B Biosolids are treated so that they contain significantly reduced numbers of pathogens but are not necessarily free of pathogens. Class B Biosolids are treated in a way that they have fewer pathogens than typical animal manure. Because the treatment standard for Class B Biosolids does not require eliminating pathogens entirely, certain site restrictions are required when land applying them. 

Pressed biosolids at Hot Springs, SD.


Who manages biosolids? Certified operators and managers of wastewater treatment systems manage and are responsible for, the land application of biosolids. Biosolids cannot be applied at a rate that is higher than the maximum level of nutrients the crops grown on the application site take up. The rates that different crops can take up nutrients have been studied for years and each crop has a maximum amount of nutrients it can use. Many states publish fertilizer agronomic rates with recommendations for crops typically grown in that state. In addition, operators follow requirements for meeting suitable soils, slopes, hydraulic loading limits, and separation distances when applying biosolids. Biosolids field appliers are subject to more stringent soil conservation and soil erosion control practices, nutrient management, and recordkeeping and reporting requirements than farmers who use only chemical fertilizers or manures. Good biosolids managers implement best practices for biosolids production, processing, transportation, storage, and final use or disposal. 

Biosolids ready for land application in Mankato, MN


The EPA and State Agencies enforce the rules and regulations on biosolids use. Rules are designed to protect human health and the environment. Rules include site setbacks on the application and limiting human exposure to the application site. Site restrictions are necessary to allow time for any remaining pathogens to die off through the natural soil treatment processes. Biosolids, when managed properly, will meet strict quality criteria and the application rates will help improve, replenish, maintain healthy soil, and provide nutrients that increase crop yields. Biosolids can provide farm producers with over $100 per acre of organic fertilizer. Farm producers use biosolids primarily to reduce their use of fertilizers. Land applied biosolids that do not exceed the crop uptake rate are beneficial. It is the most cost-effective, environmentally sound, and efficient way to recycle solids from the wastewater stream.

More than half of all the biosolids created in the United States are land applied. Other disposal options include landfilling and incineration. Typically, neither landfilling nor incineration can be completed more economically than the land application of biosolids. Without the land application of biosolids, the many soil benefits listed above cannot be achieved.

This article was submitted by RCAP’s Midwestern Region, MAP. To learn more about MAP, visit map-inc.org