In this study, Chlorella vulgaris (C. vulgaris) were cultured in cell culture flask supplied with intermittent CO2 enriched gas. The impact of CO2 concentration (from 1% to 20% v/v) on the growth of C. vulgaris cultured in domestic wastewater was exploited in various perspectives which include biomass, specific growth rate, culture pH, carbon consumption, and the removal of nitrogen and phosphorus compounds. The results showed that the maximum microalgal biomass concentration, 1.12 g L-1, was achieved with 10% CO2 as a feed gas. At 20% CO2 the growth of C. vulgaris suffered from inhibition during initial 1.5 d, but acclimated to low pH (6.3 in average) with relatively higher specific growth rate (0.3-0.5 d-1) during subsequent culture period. After the rapid consumption of ammonium in the wastewater, an obvious decline in the nitrate concentration was observed, indicating that C. vulgaris prefer ammonium as a primary nitrogen source. The total nitrogen and phosphorus decreased from 44.0 mg L-1 to 2.1-5.4 mg L-1 and from 5.2 mg L-1 to 0-0.6 mg L-1 within 6.5 d under the aeration of 1-20% CO2, respectively, but no significant difference in consumed nitrogen versus phosphorus ratio was observed among different CO2 concentration. The kinetics of nutrients removal were also determined through the application of pseudo first order kinetic model. 5-10% CO2 aeration was optimal for the growth of C. vulgaris in the domestic wastewater, based on the coupling of carbon consumption, microalgal biomass, the nutrients removal and kinetics constants.
Keywords: Carbon dioxide; Chlorella vulgaris; Nutrient removal; Specific growth rate; Wastewater treatment.
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