Role of heterotrophic nutrition in growth of the alga Scenedesmus obliquus in high-rate oxidation ponds

The green alga Scenedesmus obliquus readily adapted to heterotrophic growth in the dark, utilizing glucose as the sole carbon source. Heterotrophic cells differed significantly from photoautotrophic cells with respect to several physiological properties such as the rate of photoassimilation of CO2, rate of incorporation of glucose, and chlorophyll a concentration. Oxidation pond cells shared features common to both photoautotrophic and heterotrophic cells. Approximately 15 percent of oxidation pond algal carbon was derived from glucose assimilated directly without first being oxidized by bacteria. Bacteria seem to play a minor role in biological oxygen demand reduction in high-rate oxidation ponds, and their role is probably confined to degradation of biopolymers, thus producing substrates for algal consumption.