New insights into the microalgal culture using kitchen waste: Enzyme pretreatment and mixed microalgae self-flocculation

With the development of the catering industry, the output of kitchen waste increases significantly. To respond to the carbon neutral policy, this study proposed the technology of combining kitchen waste treatment and microalgae culture. The kitchen waste was pretreated by enzymatic hydrolysis, and the optimal composition and proportion of compound enzymes were investigated. The results showed that acid protease: α-amylase: glucoamylase: cellulase = 50:1:10:1 (enzyme activity ratio) was chosen as the most suitable compound enzymes according to the growth and water purification effect of Scenedesmus obliquus in the hydrolysate. To optimize the microalgae biomass accumulation especially high-value substances, microalgae harvesting, and water purification effects, mixed culture of microalgae was performed. Chlorella sp. HQ and Scenedesmus sp. LX1 were the best combination, in which the contents of lipid, polysaccharide, and protein were 8.78 ± 4.48%, 2.11 ± 0.14%, and 8.38 ± 0.12%, respectively. After combination, the flocculation rate reached up to 63.75 ± 1.08%, and the removal rates of chemical oxygen demand, total nitrogen, and total phosphorus were 88.54 ± 0.58%, 90.97 ± 4.73%, and 88.81 ± 4.75%, respectively. The above results indicated that the enzymatic hydrolysate of kitchen waste had a promising application prospect in microalgae culture, and self-flocculation of mixed microalgae had the potential to recover biomass. [Display omitted] •Pretreating kitchen waste with compound enzymes was beneficial to microalgae growth.•Protease: α-amylase: glucoamylase: cellulase = 50:1:10:1 was the optimal ratio.•Microalgae mixed culture improved biomass accumulation, harvesting and purification.•Chlorella sp. HQ and Scenedesmus sp. LX1 were the best combination of mixed culture.