WRF Project# 5307: Evaluation of Source Separated Organic Feedstock Pretreatment and Management Practices

INTRODUCTION This paper will provide the project approach and results for Water Research Foundation (WRF) Project# 5037 Evaluation of Source Separated Organic (SSO) Feedstock Pretreatment and Management Practices. The final report is scheduled for release in summer of 2022. SSO co-digestion with wastewater solids at Water Resource Recovery Facilities (WRRFs) offers promise to advance sustainability through beneficial reuse of the organic fraction of pre- and post-consumer waste streams (source separated organics), which would otherwise be disposed in landfills. Promoting SSO diversion from landfills to anaerobic digestion (AD) is predicated on SSO feedstock pretreatment to enhance the digestibility and conveyance of SSOs. This project, as funded by the Water Research Foundation, aims to comprehensively evaluate SSO pretreatment technologies with guidance from existing facilities to develop recommendations for SSO pre-treatment alternatives for utilities considering SSO diversion. The project has been divided into four tasks: 1.Task 1: Global Literature Review and Survey of Existing Technologies and Management Strategies 2.Task 2: Evaluation of Existing Technologies and Management Strategies 3.Task 3: Case Studies with a Wastewater Industry Focus 4.Task 4: SSO Pretreatment Analysis and Decision Tool This project provides guidance for utilities interested in SSO pre-treatment and co-digestion in order to: 1. Successfully build new or enhance existing SSO pretreatment and co-digestion programs, 2. Address challenges and opportunities involved with SSO pretreatment, 3. Identify SSO pretreatment requirements based on SSO feedstock quality and quantity, an 4.Determine capital and O&M costs and potential impacts on WRRFs. This Report will be published January 2023. APPROACH Information pertaining to SSO pretreatment was gathered from literature sources including conference proceedings, project reports, journal articles, and manufacturer documentation in conjunction with questionaries from utility and vendor partners, as well as case studies from domestic and international facilities. Using a four-task approach, information has been distilled into a literature review, fact sheets, case studies, and a SSO pre-treatment guidance tool. Further, this information has been compiled into a PowerBI dashboard. The compatibility and effectiveness of multiple SSO pretreatment technologies were evaluated with information gathered from currently operating facilities which informed the development of SSO pretreatment selection workflows. These workflows were constructed based on contaminant properties such as size and type to distinguish appropriate pretreatment technology selection. RESULTS AND FINDINGS Task 1. Global Literature Review Task 1 focused on gathering information related to the application of SSO pretreatment prior to AD which was assembled in a literature review. Results from the literature review were organized by features and capabilities of unit operations and processes (UOPs). Physical UOPs were the most frequently implemented SSO pretreatment technologies used for both initial and polishing steps as shown in Figure 1. In addition, package units were found to be very attractive for utilities seeking multiple technologies in series for efficient removal of numerous contaminants. A thorough list of pretreatment technology vendors was also provided as a reference for utilities planning pretreatment installations. Task 2. Existing Technologies and Management Strategies Evaluation Seventeen (17) utilities and technology providers, both in the US and abroad, were surveyed through the completion of a questionnaire inquiring about existing pretreatment facilities. The information gathered was summarized into factsheets (example shown in Figure 2) containing information such as process flow diagrams, facility details, lessons learned, and maintenance requirements. Major findings from Task 2 include: -Receiving pre-treated SSO is advantageous for controlling consistency and material quality. -Adequate storage should be provided at the receiving facility. -Removing contamination to the extent possible ensures that downstream equipment and digester(s) aren't adversely impacted by SSO. -Storing critical spare parts on site is recommended. Task 3. Case Studies Results Task 3 results contain insight from seven case studies focused on SSO pretreatment in the wastewater industry. Case studies provided detailed information related to each utility such as mass balances, facility financial information, construction characteristics, and anticipated maintenance schedules. Unit cost curves have been developed for the SSO pretreatment facilities (example shown in Figure 3) to provide an estimate of construction cost, O&M cost, biogas revenue, tipping fees, and inert disposal costs as a function of wet ton of waste. Overall, increasing facility size had decreasing unit costs due to economies of scale. Task 4. SSO Pretreatment Selection Guidance Much of the technology documentation accumulated through the literature review, database development, and case studies was instrumental in the development of multiple SSO pretreatment workflows to guide SSO pretreatment selection. Workflows created as part of Task 4 are structured by contaminant type, size, and physiochemical properties. For example, as shown in Figure 4, appropriate selection of metal and glass removal technologies is contingent on the material size and can be further distinguished by color, magnetism, mobility. DISCUSSION AND BENEFITS The collection of information provided in this study is vital for utilities considering SSO pretreatment by providing technology descriptions, financial information, process mass balances, and selection tools for utilities to functionally apply SSO pretreatment at existing or future anaerobic digestors. While previous studies have focused on AD optimization, there is limited information related to the nuances of SSO pretreatment operation and overall pretreatment effectiveness as discussed in this study. As facilities continue to push for more sustainable waste solutions, the application of SSO pretreatment technologies can be a cost-effective improvement in AD performance.