City of Grand Junction and Mesa County's Collaboration to Compost Biosolids and Food Waste - Pilot and Feasibility Study

APPLICABILITY Biosolids management often includes incineration, landfilling, or limited land application. However, biosolids contain high quality nutrients essential to plant growth and including them as a feedstock in the composting process can produce a quality compost product with limitless land application possibilities. Mesa County owns and operates a composting facility which primarily composts carbon-rich yard waste; a necessary ingredient for composting biosolids. Mesa County and the City of Grand Junction collaborated on an evaluation of the feasibility of composting biosolids and food waste at the Mesa County Composting Facility. The evaluation included a pilot study and an assessment of current and future feedstocks, capital needs, operational logistics, and the return on investment potential of adding these two feedstocks. The evaluation found that composting biosolids would improve the facility's ability to cover their operational costs through the revenues generated from tipping fees and the sale of a nutrient dense compost product. In addition, diversion of biosolids from the landfill to the compost facility was shown to substantially reduce greenhouse gas (GHG) emissions. As part of the evaluation, a survey of local compost users was conducted to understand the market potential of compost made with biosolids. It was recommended that outreach and education measures be taken to strengthen the local market. DEMONSTRATED RESULTS AND OUTCOMES Evaluation Background and Goals Driven by sustainability goals, facility capacity constraints, and a state led initiative to divert organic materials from landfills, Mesa County (County) and the City of Grand Junction (City) collaborated on an evaluation of composting biosolids and food waste at the Mesa County Composting Facility (the Facility). The Facility currently uses windrow composting to compost yard waste, and is interested in expanding its operation to include food waste and biosolids. The City currently disposes of biosolids at the landfill and is interested in the environmental benefits of composting biosolids. Methodology This evaluation studied the technical and financial feasibility, as well as the environmental benefits and risks, of composting biosolids and food waste at the County Facility. Additionally, the City conducted a biosolids composting pilot at an alternative composting facility to understand the process of composting biosolids. The evaluation included: - A site capacity and feedstock quantity analysis. - A business-case evaluation to determine the tipping fees and compost sale prices required for revenues to cover expenses. - An analysis of the GHG quantities generated when landfilling biosolids versus composting them. - A survey of local compost users. - An assessment of odors and process risks and mitigation tactics. Results For the baseline scenario, the capacity and feedstock quantity analysis determined that there is sufficient capacity and yard waste to compost food waste and biosolids with a Facility expansion (Figure 1). In the worst-case scenario, there would be a yard waste shortage, which could be addressed by expanding collection, purchasing woodchips, or diverting a portion of biosolids to another composting facility. The business-case evaluation included an evaluation of the capital and operating costs (Figure 2) for the expanded Facility over a 20-year life-cycle. Using tipping fees and compost sale prices from nearby composting facilities it was determined that revenues would be enough to cover the capital and operating costs if the Facility was expanded and composted yard waste, biosolids, and food waste. However, if only yard waste and food waste were composted, revenue would decrease substantially, making it difficult for the Facility to recover its costs. Since the Facility needs to expand to accommodate increasing yard waste quantities, this finding is a strong financial driver to co-compost biosolids and food waste. A GHG analysis using the BEAM*2022 model determined that GHG emissions could be reduced by 60 metric tons carbon dioxide equivalents (CO2e) per year by diverting biosolids from the landfill to the Facility. While the business-case and GHG evaluations demonstrated substantial financial and environmental benefits, composting biosolids and food waste poses odor and process risks. To address those risks, the County may consider switching to aerated static piles, gradually introducing food waste and biosolids into its composting program, and covering rows with a biofilter layer. A market survey of local compost users indicated that users are interested in purchasing compost from yard waste and food waste, but there is hesitancy around biosolids. To address this hesitancy, a public outreach campaign should be developed to inform the public about the quality and benefits of biosolids compost. The municipalities may also consider implementing a policy requiring each entity to purchase biosolids compost for use in its parks and on new developments. Outcomes This evaluation determined that it is feasible for the Mesa County Composting Facility to compost food waste and biosolids, given the right market and regulatory drivers, successful management of odor risks, and outreach to develop the local biosolids compost market. RELEVANCE TO AUDIENCE In many states, landfills are considered super emitters of greenhouse gases, and many communities are implementing, or plan to implement, policies requiring diversion of organic wastes from landfills. Driven by potential regulatory requirements, as well as sustainability and GHG emission reduction goals, many agencies are considering composting biosolids and food waste along with their yard waste. This presentation would benefit agencies that currently compost, or are interested in composting, biosolids and food waste. Attendees will benefit from the pilot study by gaining a better understanding of how to compost biosolids, the feedstocks required, and the environmental benefits of composting biosolids. Attendees will benefit from the business-case evaluation by gaining a better understanding of the technical operation and financial aspects of composting these feedstocks. Future composters must consider not only the feedstocks but also the market for the finished product. Attendees will gain an understanding of the measures needed to address potential process and market risks to ensure the successful implementation of this sustainable biosolids management strategy. Additionally, many wastewater treatment facilities and waste management facilities are run by, or in partnership with, a municipality. This study demonstrates the intra-agency partnership that is often needed to meet individual agency goals.