To investigate light transmission and cells affinity to CO2, Chlorellavulgaris was attached to microfiltration membrane that laid on the solidified BG11 medium compared to that in suspended cultivation mode in this study. The results showed that C. vulgaris showed a 30.4% higher biomass production (103 g m(-2)) in attached than in suspend system. The upper layer of biofilm with a thickness of 41.31 mu m (the corresponding areal density of 40 g m(-2)) was effectively illuminated under light intensity of 120 mu mol m(-2) s(-1) and more than 40% of the microalgal cells were in light even the areal density was high to 100 g m(-2). While only 2.5% of the cells were effectively illuminated in the suspended cultivation system. Furthermore, microalgae cells in biofilm showed a higher affinity to CO2 compared with that in suspension, and CO2 saturation point of microalgae cells in biofilm was 1.5% but 4.5% in suspension. (C) 2016 Elsevier Ltd. All rights reserved.