A study on the carbon footprint contributions from a large wastewater treatment plant

The present work analyses aspects of the carbon footprint of a large wastewater treatment plant in central Italy. The plant mainly consists of a traditional activated sludge system along with an anaerobic digester providing a partial contribution of energy to the management. An integrated approach was adopted to evaluate the environmental sustainability of the treatment plant in terms of carbon footprint. For the assessment different sources of greenhouse gas emissions such as nitrous oxide and carbon dioxide were considered: effluent, production and transport of natural gas, energy consumption, boiler, co-generator, substrate and endogenous decays. According to the methodology adopted, energy consumption, production and transport of natural gas and N2O emissions from the effluent were found the most contributing sources of greenhouse gases. Based on this, these sources are suggested as the most relevant ones on which wastewater treatment plant managers should pay more attention when taking actions for carbon footprint mitigation. Considerations on the role of CO2 of biogenic origin (specifically the one in the biogas) in terms of sequestration options demonstrate that the analysis in this field should not be limited to the calculation and comment of non-fossil contributions to the overall balance.