Potential of wastewater treatment using a concentrated and suspended algal-bacterial consortium in a photo membrane bioreactor

Current algal-bacterial consortia require hydraulic retention times (HRTs) of up to 2-10 days for wastewater treatment. The application of a photo membrane bioreactor (PMBR) culturing an algal-bacterial consortium should significantly reduce the HRTs, which has not been attempted before. A low light intensity, 200 μmol/(m2·s), was applied in a PMBR. The results showed that ammonium was almost completely removed and the removal efficiency of chemical oxygen demand was 90% when the HRT was as low as 24 h and mechanical aeration was not applied. Ammonium-oxidizing bacteria and algae approximately equally shared the ammonium in the reactor. Phosphate reduction was approximately 3 mg PO43−-P/L.h. A light intensity of up to 600 μmol/(m2·s) did not inhibit algal activity. The complete removal of ammonium resulted in a decline in the chlorophyll a concentration. Nevertheless, the reactor performance remained stable. Heterotrophic bacteria, autotrophs, algae and phosphate-accumulating organisms coexisted and functioned in the reactor. Furthermore, a sustainable flux of 15 L/m2.h enabled operating the filter of the PMBR at a transmembrane pressure as low as 4 kPa. Considering the stable pollutant removal performance and significant reduction in HRT, this PMBR has the potential to be applied in wastewater treatment.