This research work proposes an innovative water resource recovery facility (WRRF) for the recovery of energy, nutrients and reclaimed water from sewage, which represents a promising approach towards enhanced circular economy scenarios. To this aim, anaerobic technology, microalgae cultivation, and membrane technology were combined in a dedicated platform. The proposed platform produces a high-quality solid- and coliform-free effluent that can be directly discharged to receiving water bodies identified as sensitive areas. Specifically, the content of organic matter, nitrogen and phosphorus in the effluent was 45 mg COD·L−1, 14.9 mg N·L−1 and 0.5 mg P·L−1, respectively. Harvested solar energy and carbon dioxide biofixation in the form of microalgae biomass allowed remarkable methane yields (399 STP L CH4·kg−1 CODinf) to be achieved, equivalent to theoretical electricity productions of around 0.52 kWh per m3 of wastewater entering the WRRF. Furthermore, 26.6% of total nitrogen influent load was recovered as ammonium sulphate, while nitrogen and phosphorus were recovered in the biosolids produced (650 ± 77 mg N·L−1 and 121.0 ± 7.2 mg P·L−1).

Microalgae cultivation appears to be a promising technology for treating nutrient-rich effluents from anaerobic membrane bioreactors, as microalgae are able to consume nutrients from sewage without an organic carbon source, although the sulphide formed during the anaerobic treatment does have negative effects on microalgae growth. Short and long-term experiments were carried out on the effects of sulphide on a mixed microalgae culture. The short-term experiments showed that the oxygen production rate (OPR) dropped as sulphide concentration increased: a concentration of 5mgSL reduced OPR by 43%, while a concentration of 50mgSL came close to completely inhibiting microalgae growth. The long-term experiments revealed that the presence of sulphide in the influent had inhibitory effects at sulphide concentrations above 20mgSL in the culture, but not at concentrations below 5mgSL. These conditions favoured Chlorella growth over that of Scenedesmus.

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