Life cycle analysis of the integration of a side-stream microalgae process into a municipal wastewater treatment plant

The integration of a microalgae culture in the traditional layout of wastewater treatment offers many potential synergies, which could lead to positive effects on the overall sustainability of the process. This study was performed in the context of the IMAP (Integration of MicroAlgal based Processes in wastewater treatment) Project and aims to investigate the environmental improvements associated to the integration of a microalgae side-stream process within an existing facility of municipal wastewater treatment in the surroundings of Milan. In this facility, microalgae open ponds will be fed with the supernatant from the digestate dewatering, rich in nutrients, and with the CO2 of the off-gas from the cogeneration engines. The produced biomass will be recirculated at the beginning of the water line where it will be co-settled with primary sludge and undergo anaerobic digestion generating extra biogas. A comparative Life Cycle Assessment between the future treatment (with the algal process) and the current one (without the algal process) was performed by considering twelve impact categories and three indicators related to energy impacts, water consumption, and land occupation. Primary inventory data collected from the algal pilot-scale plant installed at the facility were used. Results show that the new algal unit will allow improvements for the wastewater treatment system in 7 out of the 15 analysed indicators mainly thanks to electricity savings. The life cycle perspective was applied to a system that is currently in the early stages of development and so some recommendations were given to optimize its performance at the full-scale.