A greenhouse gas source of surprising significance: anthropogenic CO emissions from use of methanol in sewage treatment.

The impact of methanol (CHOH) as a source of anthropogenic carbon dioxide (CO) in denitrification at wastewater treatment plants (WWTPs) has never been quantified. CHOH is the most commonly purchased carbon source for sewage denitrification. Until recently, greenhouse gas (GHG) reporting protocols consistently ignored the liberation of anthropogenic CO attributable to CHOH. This oversight can likely be attributed to a simplifying notion that CO produced through activated-sludge-process respiration is biogenic because most raw-sewage carbon is un-sequestered prior to entering a WWTP. Instead, a biogenic categorization cannot apply to fossil-fuel-derived carbon sources like CHOH. This paper provides a summary of how CHOH use at DC Water's Blue Plains Advanced Wastewater Treatment Plant (AWTP; Washington, DC, USA) amounts to 60 to 85% of the AWTP's Scope-1 emissions. The United States Environmental Protection Agency and Water Environment Federation databases suggest that CHOH CO likely represents one quarter of all Scope-1 GHG emissions attributable to sewage treatment in the USA. Finally, many alternatives to CHOH use exist and are discussed.