By Kitty Gifford
The New York Soil Health Program has released a new policy brief examining the complex topic of biosolids—the solid byproduct of municipal wastewater treatment—and what their use means for soil health, sustainability, and public safety.
What Are Biosolids?
Biosolids, or sewage sludge, are semi-solid organic materials that remain after wastewater is treated. In New York State, about 16% of these biosolids are treated and applied to farmland as a soil amendment, providing nutrients and organic matter to support crop growth while reducing municipal disposal costs. However, despite their potential benefits, biosolids may also pose risks due to the presence of emerging contaminants such as per- and polyfluoroalkyl substances (PFAS), microplastics, pharmaceuticals, and other persistent pollutants that current regulations do not fully address.
Beneficial Use or Cause for Caution?
Under existing state and federal rules, biosolids are classified by the degree of pathogen reduction and the presence of select heavy metals. Yet, these classifications don’t account for many modern contaminants of concern. While some biosolids are deemed “exceptional quality” and are even sold for residential use, others, particularly those containing emerging pollutants, may carry long-term risks to soil, water, and human health.
The new policy brief calls for a precautionary approach to biosolid land application, urging stakeholders to weigh the benefits of nutrient recycling against the potential for environmental contamination.
Promising Solutions on the Horizon
One of the most promising strategies highlighted in the brief is pyrolysis—a process that heats biosolids in the absence of oxygen to destroy PFAS compounds and other pollutants. This process reduces risks and produces biochar, a carbon-rich material that can improve soil health and store carbon long-term. Field trials in New York suggest that biosolids-derived biochar can support crop yields similar to synthetic fertilizers, with research ongoing into soil property impacts.
Policy Considerations
To address these challenges and opportunities, the policy brief offers six considerations:
- Promote Safety in the Circular Bionutrient Economy: Cycling carbon and nutrients back to farms is important for sustainable waste management and reducing reliance on synthetic inputs. However, biosolids and other bioresources must be clean and safe for land application beyond only pathogen concerns. Risks and loading rates, based on bioaccumulation and soil testing, need to be further explored, and land application of biosolids should be restricted while the extent of the problem is fully investigated.
- Invest in Innovative Research and Pilot Programs: Prioritize innovative integrated systems level research (source-processing-application-value). Collaboration among organizations and agencies can better leverage resources and demonstrate new strategies. Pyrolysis has proven to be a promising technology for PFAS removal, and more community and regional scale demonstrations could support upscaling.
- Foster Educational Opportunities: Coordinated extension and outreach efforts to stakeholders is essential to understanding beneficial solutions. Increased support for educational programming will reduce misinformation and foster a more informed community.
- Support Efforts to Identify Contaminated Soils: Soil testing is needed on farms and within communities known to have applied biosolids or other possibly contaminated amendments. Similar to the Community Garden Soil Testing Program established by the NYS Department of Agriculture and Markets, this would facilitate enhanced remediation efforts while minimizing human and environmental harm.
- Update Biosolids Classifications: Biosolids classes should be updated to reflect the current science around contamination. Pathogen reduction and select toxic metal limits can no longer be the only measures of safety prior to a beneficial-use determination.
- Establish Protective Regulatory Thresholds for Emerging Contaminants: While no consensus exists within the scientific community regarding ‘safe’ limits for persistent organic pollutants in the human body and the environment, further efforts should be made to assess exposure risk and support the establishment of maximum soil concentration levels to aid in cleanup.
A Path Forward
As interest in recycling organic materials grows, it is essential that safety and sustainability go hand in hand. With more research, updated regulations, and coordinated outreach, biosolids could play a responsible role in improving soil health while minimizing unintended consequences.
Click here to read the full policy brief and access other New York Soil Health policy resources.