Solids management at a crossroads

Published on by in Case Studies

Cleaning our nation’s wastewaters inevitably leads to waste solids and, for the last half century, landfilling, incineration and land application have been the dominant outlets for these products. Regulatory trends historically have impacted the relative allocation to each outlet however, and before the promulgation of new federal rules for land application in 1993, most solids were managed via landfilling or incineration. Those rules (40 CFR 503) drove a trend that continues today, with most solids now land applied for beneficial use in the U.S.

The sustained dominance of beneficial use reflects two key drivers in solids management: resource recovery and climate change mitigation. Biosolids — wastewater solids treated to allow their application for agricultural and urban landscape uses — have long been valued as a source of renewable nutrients for the soil. The organic matter they contain also is a major reason they are beneficial as a soil amendment. Land-applied biosolids improve drought resistance, soil structure and microbial communities. From a climate change perspective, biosolids offset greenhouse gas intensive fertilizer production, sequester carbon in the soil and, when applied to the land instead of disposed in landfills, reduce greenhouse gas emissions (methane) from landfills.

Today, however, land application is facing unprecedented challenges. While the long-standing prevalence of this practice appears to be in question — other outlets are facing challenges as well.

For the past twenty years, biosolids land application has been the dominant outlet for WRRF solids.

For the past twenty years, biosolids land application has been the dominant outlet for WRRF solids.

 

Pressures across all solids outlets 

Land application is currently limited in some areas by phosphorus restrictions, but emerging contaminants are a broader concern, especially per- and polyfluoroalkyl substances (PFAS). These ubiquitous compounds can be found in food packaging, textiles, cosmetics, firefighting foam and other sources. They enter wastewater influent through industrial discharges, landfill leachate and residential contributions. Conventional water resource recovery facilities (WRRFs) do not destroy these compounds, so PFAS are found in liquid effluents and solids from WRRFs.

PFAS management is a priority for U.S. Environmental Protection Agency (EPA), which set forth a multi-year plan to address these compounds in its PFAS Strategic Roadmap, with actions and activities focused on source reduction, remediation and research. With respect to biosolids land application, a PFOA and PFOS risk assessment is expected to be published in a draft in summer of 2024 and finalized by the end of 2024. The risk assessment does not establish limits, per se, but is a step on the path to setting limits for these compounds if risk management analyses by EPA indicate limits are warranted.

The roadmap also set forth EPA plans, now included in a final rule, to include PFOA and PFOS as hazardous substances under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA). This action has raised concerns not only for land application, but for landfilling as well. A primary concern is that both WRRFs and landfills are PFAS “receivers,” and the amount of PFAS exiting these facilities in effluent, solids or leachate is driven by the concentrations coming in via influent or landfill wastes. Burdening these facilities with PFAS control costs under CERCLA would deviate from the “polluter pays” principle on which CERCLA was founded.

EPA has noted that utilities are not an enforcement focus for this rule, but potential third-party litigation is still a dominant concern. To address these concerns, utilities and landfill owners are exploring legislative remedies that reflect their role as PFAS receivers. For land application, utilities are looking to exemptions currently within CERCLA that protect activities such as permitted releases, recycling activities and normal fertilizer use, as well as the domestic sewage exclusion.

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