Indigenous microalgae biomass cultivation in continuous reactor with anaerobic effluent: effect of dilution rate on productivity, nutrient removal and bioindicators.

Effluents from municipal wastewater treatment have been long recognized as suitable media for the cultivation of microalgae biomass. However, few studies report data concerning biomass productivity in continuous reactors using unsterilized wastewater effluents. This study focuses on indigenous microalgae strains that grow with native bacteria and are applicable for biomass production and tertiary wastewater treatment in continuous growth mode. Initially, five Chlorophyta strains were isolated and grown in batch mode to single out a potential inoculum for the experiments in continuous growth mode. The isolate sp. L06 was selected and evaluated based on five dilution rates from 0.1 to 0.5 day on continuous growth reactor using unsterilized secondary effluent as culture medium. Maximal volumetric biomass productivity of 283 mg L day was achieved at 0.3 day without CO addition or air bubbling. Carbohydrates were the major fraction of the dried biomass, followed by proteins and then lipids. The highest removal rates of total nitrogen and phosphorus from the liquid phase were 13.0 and 1.4 mg L day, respectively, and were obtained at 0.4 day. The maximal decay rate for (2.9 day) was achieved both at 0.3 and 0.4 day. Conclusively, sp. L06 cultivation in unsterilized secondary effluent can be adjusted depending on the objective: for biomass production, a dilution rate of approximately 0.3 day is recommended; and for tertiary treatment a rate of 0.4 day is suggested.