Enhanced carbon, nitrogen and phosphorus removal from domestic wastewater in a novel anoxic-aerobic photobioreactor coupled with biogas upgrading

•Biogas scrubbing enhanced TN and P-PO43− recovery via biomass assimilation.•Nitrification was limited by IC in the absence of biogas supply.•Biogas scrubbing maintained pH below inhibitory levels during the light period.•Biogas upgrading supported an efficient nitrification-denitrification process.•Biomass recycling resulted in unialgal cultures with high settling rates.

This work evaluated the performance of an innovative anoxic-aerobic algal-bacterial photobioreactor coupled with biogas upgrading for the treatment of domestic wastewater via nitrification-denitrification. The process, which incorporated a biomass settling step followed by recycling to the anoxic tank, was operated at a hydraulic retention time of 2 days, a sludge retention time of ≈11 days under a 12 h/12 h light/dark irradiation cycle at 392 μE m−2 * s−1. An increase in the removal efficiency of TN from 38% to 81%, NH4+ from 39% to 97%, and P-PO43− from 59% to 64% were recorded when additional CO2 was supplied to the photobioreactor via biogas scrubbing, which supported an almost complete nitrification of the NH4+ to NO3− and promoted microalgae growth (with the subsequent enhancement in N and P assimilation). TOC removal remained constant at 90 ± 2% regardless of the addition of CO2, while the effluent biomass concentration averaged 26 ± 12 mg TSS/L. A DGGE-sequencing analysis of the bacterial community revealed the occurrence of 10 phyla, Proteobacteria being the dominant phylum. Finally, the morphological characterization of the microalgae population dynamics revealed a gradual dominance of the genus Scenedesmus, which accounted for 94-100% at the end of the experiment.

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