Technoeconomic Analysis of Alternatives to Biosolids Land Application

Introduction Biosolids management in 2026 proceeds under substantial regulatory uncertainty, largely driven by concern for per- and polyfluoro alkyl substances (PFAS) and the potential for PFAS in biosolids to increase health risks in food supplies. State actions vary here; Maine banned land application of biosolids outright1, while Minnesota and Michigan established a tiered approach for land application based on measured concentrations of PFOA and PFOS2. Massachusetts recently completed detailed studies on current and future biosolids management options3,4. Meanwhile, the U.S. EPA published an initial draft risk assessment for PFOA and PFOS in biosolids in late 20255. Amid these developments and ongoing media coverage, wastewater professionals and policymakers need to understand available alternatives to biosolids land application, what they look like applied at a regional scale, and how much they could cost. These costs also need to be detailed to understand how these potential costs could translate into increased utility operating expenditure and wastewater rates. This study uses Minnesota as a case study to evaluate technoeconomic impacts of transitioning currently land applied biosolids to either landfills or thermal treatment. The analysis scope included logistics, transportation, and ancillary infrastructure associated with landfilling or implementing regional thermal treatment facilities. Methods Land applied biosolids in Minnesota were established based on state data for 2018-2022. Landfill logistics evaluation was based on publicly available data on municipal solid waste landfills in Minnesota6. Two different scenarios were evaluated for centralized thermal treatment of all biosolids currently land applied in Minnesota: Scenario 1 with three facilities treating between 16 and 35 dry tons per day, and Scenario 2 with ten facilities treating between 3 and 15 dry tons per day. All facilities were assumed to be housed at existing wastewater treatment facilities. Thermal treatment evaluated were sewage sludge incineration, pyrolysis with thermal, and supercritical water oxidation (SCWO), selected based on having demonstrated removal of the majority of PFAS from solids 7,8 and existing installations at least at pilot-scale. Conceptual designs were for each treatment alternative, including transportation from individual WRRFs to regional facility, biosolids receiving, dewatering, thermal drying (pyrolysis only), additional building space, input energy and chemicals, residuals disposal, and fertilizer offsets incurred (Figure 1). Capital costs for each equipment component and annual operation and maintenance (O&M) quantities at regional facilities were established based on previously published cost curves4,9 and vendor input. Operational unit costs were based on publicly available cost data and previous project information, and transportation distances were estimated based on location data for individual WRRFs, landfills, and regional facilities. Thermal treatment processes were assumed to be autogenous if input percent solids met the following solids content by technology, based on vendor input: 90% for pyrolysis, 30% for incineration, and 15% for SCWO. Results Landfilling all biosolids currently land applied is expected to increase the rate of landfill use in Minnesota by 11%. Logistically, the area within 50 miles of Minneapolis has over 75% of reported available landfill capacity in the state but only about 20% of WRRFs land applying biosolids, a mismatch indicating that moving towards landfilling biosolids across the state would incur significant hauling costs and associated emissions. PFAS-inclusive treatment of current land applied biosolids at regional facilities in Minnesota is expected to cost between $0.4 and $1.0 billion over 20 years. Of the treatment options evaluated, pyrolysis with thermal drying had the highest estimated costs and energy expenditure. This is primarily because pyrolysis requires higher solids content for autogenous operation than incineration and SCWO, necessitating inclusion of thermal drying infrastructure for pyrolysis facilities. Estimated costs are higher for Scenario 2 with more small facilities than for Scenario 1 with fewer large facilities, primarily due to economy of scale associated with capital infrastructure. These treatment costs translate to regional tipping fees of $600 to $1,500 per dry ton, using a payback period of 20 years and assuming no external funding. In either landfilling or treatment scenario, biosolids in Minnesota would travel substantially farther than they do now. The majority of facilities land applying biosolids in Minnesota currently apply as liquid, and since hauling liquid biosolids requires four times as many trucks as hauling cake3, these facilities would need to evaluate whether or not to add a dewatering process prior to hauling to landfill or regional treatment facility. Those landfilling biosolids may need to add dewatering or find other fill materials to meet landfill consistency requirements. Other considerations for regional implementation of thermal biosolids treatment technologies include partnerships and coalitions needed to fund, build, and operate facilities, whether facilities would discontinue anaerobic digestion to support energy recovery, and reuse potential of residuals including biochar and ash.