Getting to Zero with Co-Digestion - Defining the Road to Energy Neutrality

摘要

As we continue our evolution towards resource recovery, more water utilities are seeking paths to "net zero" or energy neutrality. The electrical and thermal energy harnessed from anaerobic digestion of municipal sludge is typically insufficient for energy neutral status. Accepting sufficient external energy sources for anaerobic co-digestion with municipal sludge can increase digester gas production and on-site energy generation to satisfy a plant's energy needs. However, a quantitative and holistic assessment of the modifications required at individual facilities must be performed to determine the feasibility of meeting this goal. Site-specific characteristics, including digester capacity, proximity of supplemental feedstocks, power and heat demands, existing gas handling and energy generation facilities, and regulatory requirements must be considered. This paper outlines an approach to developing a road map for energy neutrality on a site-specific basis and presents a case study of how this approach was applied at the Union Sanitary District's Alvarado Wastewater Treatment Plant in Union City, California.