From pilot-scale validation to life cycle assessment: Towards sustainable wastewater treatment with an enhanced rotating algal biofilm reactor.

The transition of municipal wastewater treatment plants towards energy-neutral, resource-efficient facilities is a cornerstone of sustainable urban management. However, selecting core technologies with verifiable low-carbon and resource-recovery credentials remains a critical challenge. This study addresses this gap by piloting and comprehensively assessing an enhanced rotating algal biofilm (RAB) reactor as a viable core unit. Through microalgae-activated sludge co-inoculation, the system achieved efficient nutrient removal at a commercially viable 24-h hydraulic retention time, reducing direct CO2 emissions by 72.6% while producing valuable biomass (37.7 g/m2/day). A subsequent life cycle assessment (LCA) of a scaled-up process (20,000 m3/d), which was designed based on pilot data to integrate the enhanced RAB with necessary downstream units, confirmed its superior environmental profile compared to conventional A2/O and MBR processes. Crucially, the biodiesel production pathway was identified as optimal, with sensitivity analysis revealing its potential for net negative carbon emissions under optimal summer conditions and with cleaner electricity grids. Furthermore, the environmental merit of this pathway was found to be highly dependent on regional grid cleanliness, providing a clear decision-making framework for technology selection based on local contexts. This work delivers a validated, resource-recovering technology option and a robust, data-driven guide for environmental managers overseeing the sustainable transformation of wastewater infrastructure.