Mixing starch wastewaters to balance nutrients for improving nutrient removal, microalgae growth and accumulation of high value-added products

Abstract

Unbalanced nutrients limited the starch wastewater (SW) treatment and nutrient recovery by microalgae. The higher carbon content in SW resulted in a nutritional imbalance for the growth of microalgae. While, the anaerobic wastewater with less organic content made up for this shortcoming. Mixing the two could improve the C/N ratio of wastewater, promoted the synthesis of microalgal biomass and the purification effect of wastewater. In this study, five species of microalgae (Chlorella sp. HQ, Scenedesmus sp. LX1, Tribonema sp., Anabaena sp. and Anabaena flos-aquae) suitable for growth in SW were compared, and the optimal microalgae (Chlorella sp. HQ) was selected out to be cultured in corn SW (CSW), modified SW (MSW), anaerobic wastewater (AW) and their mixtures. The results showed that the subculture biomass of Chlorella sp. HQ in CSW increased from 2.15 to 2.61 ​g/L. In mixed wastewater, CSW ​+ ​MSW ​+ ​AW improved the biomass of microalgae with CSW as a culture medium by 0.3-fold (to 2.79 ​g/L), and the algal density was as high as 1.57 ​× ​10⁷ ​cells/mL. In addition, 75.49% of chemical oxygen demand (COD), 62.00% of total nitrogen (TN), 76.47% of total phosphorus (TP), and 56.57% of ammonia nitrogen (NH₄⁺-N) were removed by microalgae. The yields of lipids, polysaccharides, and proteins were 1.34, 1.76, and 1.09 times (0.90 ​g/L, 0.30 ​g/L, and 1.19 ​g/L) that of CSW as a culture medium, respectively. These results implied that mixing different sections of SWs to balance nutrients levels for microalgae cultivation and wastewater treatment could be an efficient and economical mode.