Removal of nitrogen and phosphorus by Chlorella sorokiniana cultured heterotrophically in ammonia and nitrate

The growth rate of biomass and removal characteristics of nitrogen and phosphorus were examined using nitrate and ammonia as nitrogen sources for batch cultures of the heterotrophic microalgae, Chlorella sorokiniana. The initial nitrogen concentrations examined were 10, 20, 40, 80 and 160 mg-N l−1. The results show that a nitrate concentration of 80 mg-N l−1 as a nitrogen source provided the maximum growth rate and greatest removal of nitrogen and phosphorus, while the growth rate decreased with decreasing ammonia concentration. The maximum growth rate and removal amounts of nitrate and phosphorus were 0.48 d−1, 32.6 mg-N and 5.9 mg-P, respectively, with 80 mg NO3-N l−1. With ammonia as a nitrogen source, the maximum growth rate and removal amounts of nitrogen and phosphorus were 0.6 d−1, 79.2 mg-N and 5.9 mg-P, respectively, with 160 mg NH3-N l−1. When ammonia was used as a nitrogen source, removal rates of nitrogen and phosphorus were higher than those with nitrate. However, the pH decrease caused by ammonia affected the growth of Chlorella sorokiniana, resulting in a lower yield of biomass than when using nitrate as a nitrogen source.