Calculating the cost of gas emissions from wastewater: calculating carbon tax liabilities from wastewater treatment and biosolids stockpiling

Under the Federal Government's proposed carbon tax legislation, a price will be placed on emissions of greenhouse gases including methane (CH4 ) and nitrous oxide (N 2 0). These two gases are substantially emitted during wastewater treatment. We outline how to calculate emissions of CH4 and N 2 0 from wastewater and sludge treatment processes. Further, we provide an example calculation for emissions of methane from sludge pan-drying and biosolids stockpile storage, using data on organic degradation from a large metropolitan treatment plant located in Melbourne. A cumulative total of 6.874ft of C0 2 e per t of biosolids was estimated to be emitted, after one year of pan-drying and three years' stockpiling of biosolids. This would incur tax of $174.59ft at a carbon price of $25.40/ tC0 2 e or $378.05 at a price of $55. These figures do not include emissions from the "liquid train" of wastewater treatment, or any N2 0 emissions.