Life Cycle Assessment of management systems for sewage sludge and food waste: centralized and decentralized approaches

The aim of the present study has been to assess the environmental profile of an experimental decentralized waste management system which is based on the anaerobic codigestion of the organic fraction of municipal solid waste (OFMSW) and dewatered sewage sludge in small plants (annual capacity: about 3000 t coupled at a 75 kW CHP unit) distributed over the territory. Two scenarios have been analysed: with and without aerobic composting post-treatment. In so far as an environmental point of view is concerned, such scenarios have been compared with the past and the current approaches occurring in the case study area (NE Italy) and characterized by a strong centralization. Environmental performances of the different scenarios have been assessed through Life Cycle Assessment methodology. Our results indicate that the anaerobic codigestion of dewatered sewage sludge and OFMSW in small plants combined with composting post-treatment may offer an environmentally sustainable option of waste management in small communities. This is achieved by (1) a strong reduction in the distances and volumes transported by road, (2) low energy requirement for the process itself, (3) energy saving from CHP unit and (4) energy/resources saving from the compost produced by the digested matter. Also social advantages may be gained, such as increased public acceptability of waste treatment facilities and increased awareness among citizen on waste management issue. To note that these advantages are closely related to some key assumptions like the use of digested matter as fertilizer. Assumptions and work limits are discussed in the final section of the paper.