Factors Regulating the Growth of Algae in Continuous Culture in Diluted Secondary Sewage Treatment Plant Effluent and Subsequent Biodegradability

Heterogeneous algal cultures were grown in laboratory continuous culture in continuous flow, completely mixed chemostats in secondary sewage treatment plant effluent diluted to give an ammonia nitrogen concentration of 10 mg/1. Variables were lighting, pH, carbon dioxide availability, and hydraulic residence time. Optimum growth occurred under pH 7.0, excess CO2, and continuous lighting conditions. The availability of artificially supplied excess CO2 greatly increased the mass (standing crop) at steady-state over that produced under otherwise identical conditions for all residence times studied. For the case of excess CO2 availability, the nitrogen concentration in the algal cells regulated growth rather than the concentration of nutrients in solution. A mathematical expression was hypothesized to describe this phenomenon and was confirmed by the experimental results. Under dark-aerobic conditions, the algal cultures exerted a two-stage BOD, the second stage apparently beginning after the death of the algal cells. Longer chemostat residence times during growth produced cultures with lower percentage biodegradability. Carbon dioxide enriched growth conditions produced cultures with lower percentage biodegradability than cultures grown in a carbon dioxide deficient medium