Novel vertical upflow multi-column configured membrane photobioreactor with a filtration control system for outdoor microalgae-bacteria cultivation, harvesting and wastewater reclamation

Abstract

Coupling cultivation and harvesting systems remain a challenge in scaling up microalgae-based technologies for wastewater reclamation. The integration of membranes offers alternative process configurations, but effective filtration control is required for sustainable operation. To overcome these issues, this study proposes a novel vertical upflow multi-column configured membrane photobioreactor (VUC-MPBR). In addition, a feedback control system was used to enhance filtration performance, in which the permeate flux was dynamically opti- mized by controlling filtration time within the filtration cycle. A pilot-scale unit (456 L) was constructed with five vertically arranged columns connected in parallel with a membrane tank for suspension recirculation. It was run outdoors for over 175 days treating secondary wastewater effluent. The upflow mode of operation enhanced solid separation, via sedimentation, which maintained the recirculating suspension at low concentrations (0.14–0.55 g/L). Furthermore, concentrated biomass reached 15.0–15.4 g/L at the bottom of the columns. COD and N-NH4 + removal efficiencies ranging from 48 % to 75 % and from 97 % to 98 % were recorded, respectively. This process configuration permitted stable operation at moderate supra-threshold flux (25.6 L/h m2) by using a conventional filtration strategy. This performance was further improved when a feedback control system was applied. Under optimal environmental conditions, continuous operation at large supra-threshold fluxes (50.6 ± 4.5 L/h m2) was achieved for over 500 h at low specific aeration demands (SADp = 6.6 ± 0.8 Nm3 air/m3 permeate). This study, shows that the VUC-MPBR can enhance filtration performance and biomass harvesting, thus repre- senting an alternative process configuration for microalgae-based wastewater reclamation