The impact of seasonal variations about temperature and photoperiod on the treatment of municipal wastewater by algae-bacteria system in lab-scale

The co-cultivation of microalgae and bacteria has become an attractive approach for treating wastewater. This approach can achieve both cost-effective nutrient removal and biomass resource recovery. However, the development of full-scale algae-bacteria systems or enhanced pond systems has been limited, because of the complexity and changeability of environmental factors in this process. This study investigated the effects of seasonal variations about temperature and photoperiod on municipal wastewater treatment by algae-bacteria system in lab-scale. Nutrient removal, biomass growth, settling ability, and community structures were examined using cultures of Chlorella vulgaris, Scenedesmus obliquus, Spirulina platensis, and aerobic activated sludge in raw municipal wastewater. Results showed that the nutrient removal and biomass yield varied with seasonal conditions. High removal rates and biomass production percentages were achieved in summer and autumn conditions with aeration. The highest specific growth rate was 0.46 d−1; the highest total nitrogen removal rate was 2.34 d−1; and the highest total suspended solids removal efficiency was 96.3 ± 2.1% in summer conditions with aeration. The highest total phosphorus removal rate was 1.67 d−1 in the autumn season with aeration. An overall analysis indicated that Chlorella vulgaris and Scenedesmus obliquus, combined with bacteria (Proteobacteria, Firmicutes, Bacteroidetes, Chloroflexi) can effectively use different carbon, nitrogen, and phosphorus sources from wastewater in summer and autumn conditions. Further research should focus on methods for effectively and inexpensively improving nutrient removal and recovering biomass at low temperatures and with short photoperiods.