City of Rock Hill, South Carolina - Biosolids Market Assessment

Background and Project Goals: Material Matters conducted a Biosolids Market Study on behalf of the City of Rock Hill (the City), to assist in evaluating biosolids products generated by selected technologies under consideration for the Manchester Creek Wastewater Treatment Facility Plant (MCWWTP). The City initiated the study to better understand the demand for various biosolids products in the region and identify outlet options and associated costs. The MCWWTP generates an average 20,000 wet tons of dewatered solids annually, managed via landfill disposal and incineration. The dependability of the existing solids management options for the City have proven to be a challenge in recent years, with loads turned away during routine and unscheduled outages at the incinerator and trucks turned away at the landfill gate despite having established contracts for disposal. While the incinerator has been cost-effective management option at $40 per wet ton tipping fee, the landfill tipping fees nearly doubled from $34 to $62 per wet ton between 2016 and early 2019. The purpose of the market assessment was to evaluate short-term opportunities and long-term solids handling and management solutions for possible implementation at the treatment plant. Short-term options were identified as alternatives that could be implemented within an 18-month period. Therefore, these options focused on identifying alternate third-party contracts available to the City to provide additional reliability via increased end-use outlets. Long-term options were identified as alternatives that would require more than an 18-month window to implement. Each of the long-term options require significant capital investment. The technologies proposed in the different options: conventional digestion, thermal hydrolysis process (THP), and thermal drying. Project Approach: Potential short-term outlets included landfill disposal, incineration, off-site composting, and land application. Long term outlets considered for the assessment included bulk agriculture, forestry, sod production and soil blending (Figure A-1). Material Matters identified, contacted, and interviewed more than 40 potential outlets including representative of landfills, incinerators, off-site processing facilities, and other outlets within approximately 100 air-mile radius of the MCWWTP. Program costs for biosolids management (transportation and final disposition) were evaluated through two major biosolids distribution pathways: via Full-Service Providers (FSP) and a Self-Managed Program (SMP). FSPs are biosolids management companies (or similar) responsible for processing (e.g., dewatering, composting, etc.) and/or marketing and distribution of the final biosolids product. Figure A-2 illustrates the important components to consider for each type of program: transportation, beneficial use coordination, permitting, marketing, recordkeeping, and regulatory reporting. Interviews were conducted with regional FSP companies to obtain information about product preferences and outside-the-gate program costs (those incurred for transport, final disposition, and product management.) Project Findings: In the short term, maintaining the existing process and producing an unstabilized cake appears to have the greatest flexibility. The City's current management options of landfill disposal (outside-the-gate costs of $54 to $92 per wet ton or $1.1 to $2.0 million per year) and incineration ($40 per wet ton or $880,000 per year) are cost effective; however, they are not always reliable. Material Matters identified a unique opportunity for off-site processing of unstabilized cake, an outlet not explored previously by the City. The outlet is a biosolids composting facility in North Carolina that has capacity to process all the solids generated at MCWWTP. This option offers greater reliability despite a higher outside-the-gate annual cost of $63 to $97 per wet ton or $1.4 to $1.5 million per year (Figure A-3). The City elected to engage with the compost facility and is currently using as a reliable outlet. For long-term options (those requiring processing upgrades and capital investment), the bulk agriculture market appears to be well established within 100 miles of the MCWWTP and is favorable for a low odor product. Both Class B mesophilic anaerobic digested cake and Class A/EQ products (cake, compost and dried) are seen favorably. The market assessment revealed that use in bulk agriculture can be a cost-effective management option through either a Full-Service Provider (FSP) or Self-Managed Program (SMP). For cake products, regardless of meeting Class A/EQ or Class B requirements, the outside-the-gate costs range between $20 and $40 per wet ton or $130,000 to $400, 000 per year. Projected annual management costs for the alternative products and management types is summarized in Figure A-4. Use of biosolids in the local forestry market, topsoil manufacturing, or other specialty markets is not well established and will require effort to educate and market the product. Management of Class A/EQ compost or digested dried products have potential to yield a net revenue of up to $5 per wet ton in if the product is high quality (low odor, consistent, available when needed) and is actively marketed.