Water resource recovery by means of microalgae cultivation in outdoor photobioreactors using the effluent from an anaerobic membrane bioreactor fed with pre-treated sewage

With the aim of assessing the potential of microalgae cultivation for water resource recovery (WRR), the performance of three 0.55 m3 flat-plate photobioreactors (PBRs) was evaluated in terms of nutrient removal rate (NRR) and biomass production. The PBRs were operated outdoor (at ambient temperature and light intensity) using as growth media the nutrient-rich effluent from an AnMBR fed with pre-treated sewage. Solar irradiance was the most determining factor affecting NRR. Biomass productivity was significantly affected by temperatures below 20 °C. The maximum biomass productivity (52.3 mg VSS·L−1·d−1) and NRR (5.84 mg NH4-N·L−1·d−1 and 0.85 mg PO4-P·L−1·d−1) were achieved at solar irradiance of 395 μE·m−2·s−1, temperature of 25.5 °C, and HRT of 8 days. Under these conditions, it was possible to comply with effluent nutrient standards (European Directive 91/271/CEE) when the nutrient content in the influent was in the range of 40-50 mg N·L−1 and 6-7 mg P·L−1.