Reducing mechanical aeration in membrane bioreactors by inoculation of algal cells into activated sludge biomass

The aim of this study is reduction of mechanical aeration (produced by air pumps) by introducing algal cells into the conventional membrane bioreactor (MBR) at no detriment of its other performances, e.g., purification efficiency and membrane fouling. The effect of aeration rates (3, 2, 1, 0.5 L min(-1)) and percentage of microalgae to total biomass (only activated sludge, 17 %, 33 %, 50 %) on the membrane fouling and purification efficiency of algae-sludge membrane bioreactors was studied. The results revealed that the introduction of algae cells into conventional MBR (C-MBR), with a suitable inoculation ratio (in this study, 50 % of total biomass), enables a 60 % reduction of mechanical aeration compared to conventional MBR, without weakening the purification efficiency and without increasing membrane fouling. The highest nutrients removal (NH4-N: 93.7 %, PO4-P: 32.4 %, TOC: 97.1 %) was measured when the highest amount of algae (50 % of total biomass) was inoculated, and the aeration intensity was on the level of 1 or 2 L min(-1) while the highest nutrients removal for C-MBR was achieved at 3 L min(-1). Moreover, the results indicates that by controlling the mechanical aeration it is possible to control growth rate of algae cells compared to bacteria cells and maintain a constant ratio of algae and bacterial biomasses in the MBR. As a result of this research, it is suggested that introducing algal cells to MBRs can enable significant reduction of mechanical aeration without compromising other performances.