The effect of bacterial contamination on the heterotrophic cultivation of Chlorella pyrenoidosa in wastewater from the production of soybean products.

This study examined the impacts of bacteria on the algal biomass, lipid content and efficiency of wastewater treatment during the heterotrophic cultivation of Chlorella pyrenoidosa. Our results showed that soybean-processing wastewater can enhance the accumulation of lipids in algal cells and thus raise the lipid yield in the pure culture. The bacteria coexisting with algae improved the degradation of total nitrogen (TN), total phosphorus (TP), glucose and chemical oxygen demand (COD). Although the biomass productivity of algae was not significantly affected, the total algal lipid content and lipid production rate were slightly reduced when bacteria coexisted with algae. The difference in the compositions of the medium is presumed to be the main contributing factor for the variation in total lipid content in presence and absence of bacteria. The TN, TP, and COD decreased during the assimilatory process undertaken by C. pyrenoidosa, and the removal efficiency of TN by bacteria depended on the type of nitrogen species in the medium. Additionally, the apparent interaction between the bacterial and algal cultures varied with the changes in experimental conditions. Algae could compete with bacteria for the carbon and energy sources, and inhibit the growth of the bacteria in the presence of high organic matter concentration in the medium.