Coming Full Circle: Diverted MSW Organics to RNG Fuel for Refuse Trucks in Mesa, AZ

As anaerobic co-digestion of municipal wastewater with food waste and fats, oils, and grease (FOG) becomes more widely implemented, developing a understanding of the effects co-digestion will have on the system, as well as developing a comprehensive investigation into the potential benefits - financial and environmental - is crucial to determining whether implementation will be advantageous. In collaboration with the Arizona State University Biodesign Swette Center for Environmental Biotechnology, several limits of digestion were developed and tested during bench scale digestion study. The bench scale study sets the precedence for the dynamic model; as well as pushed the limits to better understand the limits, indicators, and operational challenges of co-digesting commercial food waste and fats, oils and grease (FOG). The presented case study illustrates the use of dynamic modelling to evaluate several scenarios with variable quality of commercial food waste and FOG; quantity of waste a digestion system is feasibly able to accept; and the potential monetary and environmental benefits under various different biogas end uses. Based on modelling results, accepting 44 tons/day of unprocessed food waste and 10,000 gallons/day of unprocessed FOG can increase biogas production from 130 to 280 scfm. Compared to beneficial biogas end uses such as cogeneration, for the WRP it was both financially and environmentally advantageous to upgrade the biogas to compressed natural gas for the City’s existing compressed natural gas (CNG) vehicle fleet.