Simultaneous nitritation, denitritation and phosphorus removal in an algal-bacterial consortium system treating low-strength mariculture wastewater

Mariculture wastewater is characterized by high salinity and low concentration of pollutants, which poses a great challenge to the conventional wastewater treatment processes. In this study, an algal-bacterial consortium process for simultaneous organic carbon, nitrogen and phosphorus removal from such wastewater was investigated in a red-blue (4:1) LED photo-sequencing batch reactor (PSBR). Simultaneous bacterial ammonium oxidation (70 %) and algal ammonium assimilation (30 %) was obtained in the photo phase. In the dark phase, a weak ammonium assimilation was also observed. In the PSBR with an influent COD/N of 5:1, the nitrogen removal pathway was identified to be simultaneous nitritation and denitritation probably due to low-rate oxygenation of algae at a light luminance of 500 lx. In addition, the average COD and phosphorus removal efficiencies reached 82.4 % and 68.2 % with a removal activity of 0.63 mg PO43--P/(L.d). High-throughput sequencing results showed that Nitrosomonus and Nitrospina were the dominant nitrifying genera using oxygen released by Cyanobacteria and Bacillariophyta. Therefore, it is feasible to efficiently remove nitrogen and phosphorus from mariculture wastewater by the algal-bacterial consortium, which opens a new window for the treatment of high-salinity and low-strength wastewater.