Municipal wastewater treatment by semi-continuous and membrane algal-bacterial photo-bioreactors

Abstract

Conventional wastewater treatment systems demand a high cost mechanical aeration. Using algal-bacterial systems helps to reach a cost-efficient treatment method by eliminating mechanical aeration, since algae produce the oxygen needed for treatment process. In this study, two groups of experiments were performed for domestic wastewater treatment processes. For the first group, semi-continuous microalgae-bacterial photo-bioreactors were cultivated. Chlorella Vulgaris and activated sludge (AS) were used as microalgae and bacterial inoculums, respectively. The effect of different algae and AS ratios on the chemical oxygen demand (COD), N-NH4+ and P-PO43− removal was studied. The removal efficiency of COD was above 93 % for the three tested algae and AS inoculum ratios (5:1, 1:1, and 1:5). The reactor with algae: AS inoculum ratio of 5:1 achieved the highest final N-NH4+ and P-PO43− removal efficiencies (88.0 ± 1.0 % and 84.0 ± 1.0 %, respectively). Furthermore, the highest biomass concentration (1.96 g L-1 from initial amount of 0.3 g L-1) was observed in the reactor with algae: AS ratio of 5:1. The ratio of 5:1 (algae: AS) was found as the optimum ratio which promoted the cooperation between microalgae and AS for nutrient removal. For the second group of experiments, the optimum ratio of 5:1 (algae: AS) was used in a membrane bioreactor, and the results showed that this reactor enhanced the final removal efficacies from 88 to 98 % and from 84 to 89 % for N-NH4+ and P-PO43-, respectively.