Abstract:A two-step process for the purification of molasses wastewater from the yeast industry was developed using a combination of active charcoal-based decolorization and mixotrophic cultivation of Chlorella pyrenoidosa in the effluent. The color removal effects of eight types of commercial active charcoal powders were compared, and the optimal color removal effect was obtained using No. 200 active charcoal powder at a concentration of 3.0% (m/V) and pH 3.00. The removal rates of color, chemical oxygen demand (COD), and total nitrogen (TN) were high: up to 98.96%, 54.50%, and 46.75%, respectively. The decolored effluent was then used for mixotrophic cultivation of C. pyrenoidosa. The final biomass concentration (2.29 g/L) and the removal rates of COD and total phosphate (TP) (72.41% and 79.36%) after 8 days’ cultivation were significantly higher (p<0.05) than those of the original wastewater without pretreatment. The total removal rates of COD, TN, and TP of this two-step process reached 87.82%, 68.26%, and 78.57%, respectively. These results indicate that the decolorization of wastewater by active charcoal can dramatically enhance the transparency and reduce the concentration of wastewater, and deep purification was realized by the subsequent mixotrophic cultivation of Chlorella pyrenoidosa. In conclusion, the two-step process developed in the current study is an optimized process combining high-efficiency wastewater purification and Chlorella cultivation.
