Wastewater Methanol Use: A Surprisingly Significant Scope-1 GHG Emission Source

Many wastewater treatment facilities use methanol as a carbon source to enable biological denitrification of nitrate produced from ammonia through nitrification. GHG reporting protocols fairly uniformly account for methanol combustion as a Scope-1 emission and manufacturing energy and emissions as a Scope-3 GHG source. Only ICLEI’s (2012) more-recently-published U.S. Community Protocol’s identifies a methodology to account for the liberation of anthropogenic carbon dioxide (CO2) emissions attributable to the addition of methanol. The prior oversight was likely attributable to a belief that CO2 produced through activated-sludge-process respiration is biogenic; raw sewage carbon being previously un-sequestered prior to entering a water resource recovery facility (WRRF). However, the biogenic categorization does not apply to fossil-fuel-derived carbon sources added for WRRF operations. This paper provides a case study as to the significance of these emissions using the Blue Plains Advanced Water Treatment Plant (AWTP) in Washington, DC where methanol CO2 represented 70% and 82% of the AWTP’s Scope-1 GHG emissions, before and after enhanced digestion upgrades, respectively.