Respiratory relationships of a symbiotic algal‐bacterial culture for wastewater nutrient removal

A continuous symbiotic algal‐bacterial system was developed consisting essentially of a mixed Chlorella ‐activated sludge culture which would efficiently remove nutrients from wastewater under aerobic conditions without supplementary aeration. Oxygen decline data were fitted to a mathematical model used to predict respiratory rates, photosynthetic oxygenation, and steady‐state oxygen concentrations. Stable relative biological populations and a dissolved oxygen concentration of about 2 mg/1 were maintained during steady‐state operation with daily harvesting of excess biomass. Respiratory and physiological relationships indicated that the carbon dioxide‐oxygen balance is a primary control that governs the steady‐state operation of a symbiotic algal‐bacterial culture. The close association of the algae and bacteria resulted in an algal‐bacterial floc with settled rapidly yielding a clear supernatant.