Life cycle assessment of processes for the treatment of wastewater urban sludge: energy and global warming analysis

This study compares six wastewater sludge treatment scenarios applied to a 300,000 equivalent-inhabitant (eq. inh) wastewater treatment plant: agricultural spreading, fluidised bed incineration, wet oxidation, pyrolysis, incineration in cement kilns and landfill. The study focuses on energy and emissions contributing to global warming over the whole treatment life cycle. As a result, avoided burdens by coproducts are very important in terms of energy consumption and pollutants’ emissions. The energy balance suggests that incineration and agricultural spreading have the lowest non-renewable primary energy consumption. For global warming, incineration in cement kilns has the best balance; landfill and agricultural spreading the worst. Results are now being extended to digested sludges and to impacts on human health and ecosystems.