Immobilization altering the growth behavior, ammonium uptake and amino acid synthesis of Chlorella vulgarisat different concentrations of carbon and nitrogen

Nitrogen recycling by microalgae has aroused considerable attention. In this study, immobilized Chlorella vulgaris with 5-day mixotrophic cultivation to recover ammonium (NH4+-N) were systematically investigated under various sodium acetate (CH3COONa) and ammonium chloride (NH4Cl) concentrations, and evaluated by comparison with suspended cells. The results revealed that, unlike suspended cells, NH4+-N uptake by immobilized cells was not in direct proportion to chemical oxygen demand (COD) concentrations. The immobilized cells to NH4+-N uptake was all inferior to that of suspended cells, presenting the maximum rate of 68.92% in group of 30 mg/L NH4+-N and 200 mg/L COD. Free amino acids in immobilized cells such as glutamate (Glu), arginine (Arg), proline (Pro) and leucine (Leu) were more sensitive to NH4+-N assimilation, as higher values observed by suspended cells. Low carbon-nitrogen (C/N) ratio showed remarkable benefits to amino acid synthesis. These results could provide a reference for manipulating the algal system and biomass accumulation.

Automated summary

The study found that immobilized Chlorella vulgaris is less influenced by COD concentrations compared to suspended cells, with lower NH4+-N uptake rates than suspended cells. Specific nitrogen and carbon concentrations were found to be beneficial for amino acid synthesis.