How to globally reduce the greenhouse gas emissions from sewage systems?

A reliable and exhaustive measurement of the global greenhouse gas emissions from a given sewage plant must be performed prior to the implementation of any abatement measure. The method presented in this paper takes into consideration both the direct emissions but also the indirect ones generated by the plant activity and identified using a life cycle-type approach. Three examples of projects or realizations are presented in this paper to illustrate the different means of abatement of greenhouse gas emissions from a sewage plant in a global way. The first example concerns a project of abatement of the electricity consumption of a plant for sludges and fats digestion and biogas valorization. A 85% global abatement of CO2 emissions is obtained thanks to the substitution of the aerobic digestion process by an anaerobic one. The second example presents an optimization of the greenhouse gas emissions of the municipal sewage plant of Valenton (Paris region) thanks to a valorization of sludges as fertilizers and fuels and to the recovery of the process heat. The last example concerns the Seine-aval sewage plant which gathers several projects of improvement: setting up of a second biogas turbine, redesign of the heat loop, use of river transport for a significant abatement of greenhouse gas emissions. (J.S.)