Background: The daily use of water causes its degradation and must be reclaimed to protect the environment. Wastewater treatment plants (WWTPs) have environmental burdens associated with energy consumption and sludge management. These burdens are linked, for instance, to energy consumption and sludge management. To diminish the environmental impact of the WWTPs, solutions like the developed one in the LIFE B2E4sustainable-WWTP project (B2E) arose. The B2E solution seeks to decrease some of the WWTP burdens by managing in situ the sludge generated in the WWTP through a gasification stage, valorising the syngas obtained in a cogeneration engine to produce both thermal and electrical energy. This reduces both the environmental impacts and costs derived from the sludge treatment by an external entity, being a self-sustainable solution in terms of energy. The B2E solution is designed for midsize WWTPs (10,000 and 100,000 PE), the majority of the European WWTPs.

Methods: The Life Cycle Assessment (LCA) was selected to evaluate the environmental performance of the B2E system. Six impact categories were analysed under the environmental footprint methodology (EF 3.0): climate change, freshwater ecotoxicity, freshwater eutrophication, human toxicity (cancer and non-cancer) and resource use (fossils). To check if the B2E solution reduced the environmental burdens, a comparison with a baseline (BS) system, typically implemented in midsize WWTPs, was performed.

Results: The B2E system showed an environmental improvement compared to the BS in the six studied impact categories. The largest difference was observed in both human toxicity (cancer and non-cancer) impact categories. Their impacts were 99% lower compared to the BS. The reduction of the environmental impact for the rest of the categories ranged between 19% and 48%.

Conclusions: These results demonstrate from an environmental point of view that the B2E system has the potential to be implemented in midsize WWTPs in the near future. However, the technology should confirm these results under an operational environment to test the whole system by obtaining only representative primary data, which would enable future implementation strategies towards more efficient and sustainable WWTPs.

biosolid thermal valorisation, energy saving, sludge management, sludge gasification, syngas production