Veris Environmental provides the following CSU publication, quick links and overview in our mission to inform, educate and provide transparency to the local communities we serve.
This information and the services we provide are thanks to decades long work done by many who look to future generations and work every day to improve the environment those generations will inherit.
Everything You Wanted to Know about Biosolids Recycling
Biosolids Recyling Quick Links
Biosolids supply N, other plant nutrients and organic matter to soils.
Necessary steps in a biosolids application program include:
- File a Letter of Intent with the Colorado Department of Public Health and Environment (CDPHE).
- Meet all CDPHE requirements regarding trace elements and pathogens.
- Apply biosolids at “agronomic rates.”
- Develop a soil-management program that includes periodic soil and plant sampling and analyses.
Households, businesses, and industries produce wastewater. Biosolids are by-products of the wastewater-treatment process. Farmers, land-reclamation specialists, landscapers and home Gardeners have used these primarily organic materials for over seven decades in the United States.
The Colorado Department of Public Health and Environment (CDPHE) and the U.S. Environmental Protection Agency (EPA) encourage and regulate recycling of biosolids on crop- or rangeland, since they contain plant nutrients and organic matter that can improve production as well as soil conditions.
The CDPHE (1993) defines biosolids as:
“The accumulated residual product resulting from a domestic wastewater treatment works. Biosolids does not include grit or screenings from a wastewater treatment works, grease, commercial or industrial sludges, or domestic or industrial septage.”
Applications Required to Meet Agronomic Rates
A key aspect of EPA and CDPHE regulations requires application of biosolids at an agronomic rate. The CDPHE (1993) defines agronomic rate as:
“The rate at which biosolids are applied to land such that the amount of nitrogen required by the food crop, feed crop, fiber crop, cover crop or vegetation grown on the land is supplied over a defined growth period, and such that the amount of nitrogen in the biosolids which passes below the root zone of the crop or vegetation grown to groundwater is minimized.”
Biosolids Properties & Safety
Biosolids can exhibit a wide array of physical and chemical traits. Depending on the extent of dewatering or drying, the solids content of biosolids can range from less than 5 percent to more than 90 percent. Chemical characteristics of biosolids vary between treatment plants and, to a limited extent, within the same plant over time.
New, aggressive pretreatment programs at the source of generation have dramatically reduced metal concentration in biosolids over the last two decades, minimizing the possibility of environmental damage.
Biosolids are treated to eliminate pathogens (disease- causing organisms) that may reside in wastewater. EPA and CDPHE (1993) require domestic wastewater treatment plants to reduce pathogens and diminish the attraction of insects and animals before biosolids are applied. (See Also, EPA Control of Pathogens Information)
Common Treatments in Colorado
In Colorado, anaerobic (without air) and aerobic (with air) digestion are the most common methods used to treat and stabilize biosolids. Digestion destroys pathogens through heat and attack by beneficial microorganisms (e.g., anaerobic bacteria); it also reduces odors. Municipalities use composting, heat drying and other techniques to further reduce pathogens and stabilize the material.
Fertilizer and Soil Amendment Value
Frequently, biosolids promote physical changes in soil that are more significant than the plant nutrients they supply. Most Colorado soils contain less than 1.5 percent organic matter.
Biosolids can serve as a source of organic material that improves soil tilth, water-holding capacity, structure development and stability, and air and water transport, and can ultimately decrease soil erosion potential.
Cropland & Rangeland Application
The greatest challenge in using biosolids for beneficial reuse on crop- and rangeland is to prevent NO – leaching to groundwater. As biosolids’ nutrient value may vary depending on the form (i.e., liquid, dewatered or dried), determining the correct agronomic rate remains a challenge.
However, if the agronomic rate is applied under non-irrigated (dryland) cropping in our semi-arid environment, where water table depths generally are over 100 feet deep, the potential for groundwater contamination is negligible. Under irrigated conditions, if agronomic rates of biosolids based on site specific soil-test and crop-management information are applied, groundwater contamination with NO3-N should not occur. Annual monitoring of residual soil NO3-N levels will help guard against groundwater pollution.
Society can benefit if we can safely recycle the plant nutrients and organic material that constitute biosolids.
Land application of biosolids for beneficial use poses no health or environmental threat if CDPHE and EPA guidelines for trace elements and pathogens are followed and proper soil management is practiced.
Public education should continue to develop trust between all parties.
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