Aerobic decomposition of Chlorella salina in freshwater and saline conditions

Abstract

Aerobic decomposition of the estuarine unicellular green alga Chlorella salina CU-1 was studied in freshwater and saline cultures. Data obtained on suspended solids, COD, chlorophyll a and population growth of the bacteria as well as the regeneration of inorganic phosphorus and nitrogen from these decomposing cultures indicated that the rate and extent of decomposition were much greater in freshwater than in saline condition. It took 20 days and 50 days for decomposition to become evident in the freshwater culture and in the saline culture, respectively. The extent of decomposition as expressed in percent reduction of particulate COD was 77% in the freshwater culture and 48% in the saline culture. Regenerated inorganic phosphate accounted for 85% and 46% of the total original cellular phosphorus in the freshwater culture and in the saline culture, respectively. Nitrogen regeneration was a direct function of the amount of cellular decomposition. In the freshwater culture 88% and in the saline culture 63% of the original particulate organic nitrogen were converted to inorganic nitrogen. It was evident that the ability of C. salina CU-1 to exhibit facultative heterotrophy in saline condition, the mode of algae-bacteria interaction, and the density of the bacterial population in the decomposing algal culture were the factors leading to the observed differences in the pattern and duration of decomposition, as well as the extent and rate of inorganic nutrient regeneration in freshwater and saline environment.