Single-step treatment of primary effluent by Galdieria sulphuraria: Removal of biochemical oxygen demand, nutrients, and pathogens

Our previous reports have documented a single-step algal process for removing biochemical oxygen demand (BOD5) and nutrients from primary effluent in batch mode. In the current study, we report results from continuous fed-batch operation of this algal system demonstrating consistent removal of BOD5 and nutrients as well as significant reduction of pathogenic bacteria from primary effluent. The active volume of the algal bioreactor under fed-batch operation was 700 L, of which, 400 L was discharged at the end of every cycle and replenished with fresh primary effluent to start a new cycle. Results from thirty such cycles run over 120 days, under varying influent loadings and ambient conditions, confirmed that the discharge standards for BOD5 and nutrients could be attained in a fed-batch cycle time of < 3 days. Typical volumetric removal rates of BOD5, ammoniacal nitrogen and phosphates over the 120 days were 16.5 mg/L-d, 6.1 mg/L-d, and 1.4 mg/L-d, respectively. Fecal and total coliform were also reduced to non-detectable levels within these three days.