The City of Wooster, Ohio, through a public–private partnership, invested in a biosolids facility to process the waste sludge generated on site at the City’s municipal wastewater plant, as well as third-party septage, biosolids, and food wastes. This new facility, called the Water Resource Recovery Facility (WRRF), includes a traditional mechanically mixed thermophilic and mesophilic digestion regime with liquid sludge disposal via land application. The resultant biogas is used to power a 1.1-MW combined heat and power (CHP) system. By supplementing the anaerobic digesters with food wastes and other putrescible feedstocks, the City generates further revenue through tipping fees and additional biogas that is used to generate green electricity on site.

The City of Wooster faced multiple challenges in operating the WRRF, including the inability to correctly receive and clean third-party waste streams, an unreliable digestion process, a failing CHP system, and high liquid sludge disposal costs. The City hired RETTEW to help identify solutions to these challenges. RETTEW visited the site and developed the following plan to address the City’s needs:

• A safety upgrade to the WRRF, including the addition of biogas flow meters and safety equipment such as flame arresters and new flare
• A new waste depackaging system for third-party wastes
• New mixers for the anaerobic digesters to increase the digestion rate
• Conversion of some thermophilic digesters to mesophilic digesters
• A new biogas scrubbing system
• A new biosolids dewatering system and building.

These upgrades will save the City more than $1.25 million per year.