Biosolids: Our Approach

Society has used biosolids as a soil amendment for as long as we have treated municipal wastewater. Land application has increased over the past 20 years, to the point where more than 50 percent of the sewage sludge produced in the United States is land-applied as biosolids. A longstanding issue remains, however: what is the best way to manage possible exposure to pathogens associated with land application of biosolids?

This WERF research will explore advancements in pathogen risk assessment. It will also bring forth the complementary and equally important science of risk communication practices. The research will lay out some risk assessment and communication options – all in a single, integrated process – for utilities, land appliers, regulators and local public administrators at the local, state and national level.

Researchers will use state-of-the-science data and assumptions for biosolids pathogens, and will access ongoing research on other important issues related to pathogens in general, and specifically to land application of biosolids. Other research is looking for more precise information on infectious doses; more reliable indicator organisms and analytical methods; and better information on the emergence of antibiotic resistant microorganisms. WERF will factor the latest information into future refinements of both the risk assessment and communication practices components of this project.

Quantitative Microbial Risk Assessment

Using risk-based methodologies as part of the Standards for the Use and Disposal of Sewage Sludge (Part 503), EPA developed maximum allowable levels for chemical contaminants in biosolids. They based maximum allowable levels of microbial contaminants on treatment-based performance – rather than risk levels – because pathogen risk assessment methodologies were not yet accepted for biosolids. The treatments cited in the Part 503 rule include general requirements, management practices, and operational standards for land application.

This research may help put pathogen risk assessment for biosolids into common practice.

Microbial health risk studies to date have predominantly focused on the fate of pathogens during treatment and in the environment. Through work on several related projects, WERF developed a quantitative pathogen health risks methodology for land application of biosolids, which offers one logical starting point for this research. Researchers will supplement that approach with other pathogen risk assessment methodologies.

Microbial risk assessment (QMRA) has four fundamental components:

• Hazard identification (also referred to as problem formulation) identifies pathogens and potential exposure pathways, including the types of illnesses that could occur.
• Exposure assessments estimate the quantity of pathogens (dose) to which individuals or populations are exposed.
• In a dose-response assessment, the dose is entered into a health effects model that quantitatively estimates the risk associated with a specific pathogen-exposure scenario, in this case the occurrence of illness/disease for an individual or target population.
• The risk characterization step then examines risk estimates for different pathogen exposure scenarios to provide an overall risk summary. The risk summary allows for the estimation of incremental increased risk above background risk.

Strategic Risk Communications

An integral and equally important aspect of this research is application of the best risk communications science and practices.

Effective strategic risk communications involve stakeholders from the outset and throughout the entire process. It provides purposeful interaction and appropriate information, and helps decision-makers and stakeholders make well-informed decisions leading to effective risk management.(Stakeholders are individuals, groups, or organizations that may affect, be affected by, or perceive itself to be affected by a potential risk.)

Strategic risk communications includes all communication content and interactions that can influence risk decisions and behavior.

• Such content may be included in announcements, warnings, and guidance documents.
• Content may appear in verbal statements, pictures, advertisements, publications, legal briefs, labels, warning signs, or other declarations.
• Content may describe risks or characterize their importance. It may also advocate actions regarding risks, hazards, and technologies, including ways to mitigate them.
• Interactions include everything from engaging individuals and/or groups in one-on-one or small group settings to broader and often more formal citizen engagement and consultation processes.

Effective risk communications must reflect the best available knowledge. Such knowledge should be selected for its relevance to decisions facing stakeholders and framed in terms that address their beliefs and feelings.