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

[Display omitted] •Immobilized Chlorellavulgaris showed worse growth than that of suspended cells.•Carbon-dependent pattern of immobilized cells was changed during NH4+-N uptake.•Regulation of C/N ratio was crucial for NH4+-N uptake of mixotrophic cells.•High carbon was needed for growth whereas high nitrogen for amino acid synthesis. Nitrogen recycling by microalgae has aroused considerable attention. In this study, immobilized Chlorellavulgaris 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.