A rational procedure for estimation of greenhouse-gas emissions from municipal wastewater treatment plants

Municipal wastewater treatment may lead to the emission of greenhouse gases. The current Intergovernmental Panel on Climate Change (Geneva, Switzerland) approach attributes only methane emissions to wastewater treatment, but this approach may overestimate greenhouse gas emissions from the highly aerobic processes primarily used in North America. To better estimate greenhouse gas emissions, a procedure is developed that can be used either with plant-specific data or more general regional data. The procedure was evaluated using full-scale data from 16 Canadian wastewater treatment facilities and then applied to all 10 Canadian provinces. The principal greenhouse gas emitted from municipal wastewater treatment plants was estimated to be carbon dioxide (CO(2)), with very little methane expected. The emission rates ranged from 0.005 kg CO(2)-equivalent/m(3) treated for primary treatment facilities to 0.26 kg CO(2)-equivalent/m(3) for conventional activated sludge, with anaerobic sludge digestion to over 0.8 kg CO(2)-equivalent/m(3) for extended aeration with aerobic digestion. Increasing the effectiveness of biogas generation and use will decrease the greenhouse gas emissions that may be assigned to the wastewater treatment plant.