Distinctive correlations between cell concentration and cell size to microalgae biomass under increasing carbon dioxide

[Display omitted] •Class-specific responses observed in cell size and concentration under CO2 influence.•Size of Nostoc and Chlorella cells significantly increased from 6% to 52% at 20% CO2.•Presence of CO2 restricted cell divisions in Nostoc.•At 20% CO2, Nostoc (Cyanophyceae) doubled in length but not in cell concentration.•Chlamydomonas biomass positively correlated to cell concentration under CO2 influence. Carbon capture and storage (CCS) via microalgae cultivations is getting renewed interest as climate change mitigation effort, owing to its excellent photosynthetic and CO2 fixation capability. Microalgae growth is monitored based on their biomass, cell concentrations and cell sizes. The key parametric relationships on microalgae growth under CO2 are absent in previous studies and this inadequacy hampers the design and scale-up of microalgae-based CCS. In this study, three representative microalgae species, Chlorella, Nostoc and Chlamydomonas, were investigated for establishing key correlations of cell concentrations and sizes towards their biomass fluctuations under CO2 influences of 0% to 20% volume ratios (v/v). This revealed that Chlorella and Chlamydomonas cell concentrations significantly contributed towards increasing biomass concentration under CO2 elevations. Chlorella and Nostoc cell sizes were enhanced at 20% (v/v). These findings provided new perspectives on growth responses under increasing CO2 treatment, opening new avenues on CCS schemes engineering designs and biochemical production.