A greenhouse gas source of surprising significance: anthropogenic CO 2 emissions from use of methanol in sewage treatment.

The impact of methanol (CH ₃ OH) as a source of anthropogenic carbon dioxide (CO ₂ ) in denitrification at wastewater treatment plants (WWTPs) has never been quantified. CH ₃ OH is the most commonly purchased carbon source for sewage denitrification. Until recently, greenhouse gas (GHG) reporting protocols consistently ignored the liberation of anthropogenic CO ₂ attributable to CH ₃ OH. This oversight can likely be attributed to a simplifying notion that CO ₂ 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 CH ₃ OH. This paper provides a summary of how CH ₃ OH 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 CH ₃ OH CO ₂ likely represents one quarter of all Scope-1 GHG emissions attributable to sewage treatment in the USA. Finally, many alternatives to CH ₃ OH use exist and are discussed.