Synergistic coupling of microalgae and corn cob residue biochar for enhanced lipid production and heavy metal removal from waste leachate and corn cob hydrolysate

Waste leachate (WL) contains a high content of heavy metals, which not only harms the environment but also wastes the resources it contains. In this study, corn cob hydrolysate was added to WL to cultivate microalgae for lipid production, and the corn cob hydrolysate residue was prepared into biochar to remove high concentrations of heavy metals in WL, while simultaneously achieving WL purification and bioenergy recovery. The results showed that the biomass and lipid yield of microalgae cultured in WL by adding 15% corn cob hydrolysate increased from 0.54 ± 0.06 g/L and 111.45 ± 10.49 mg/L in the control group to 1.66 ± 0.02 g/L and 351.15 ± 16.40 mg/L, respectively. Moreover, 62.1%-85.3% of ammonia nitrogen and 81.6%-97.7% of total phosphorus were absorbed by microalgae for growth. With the addition of 15% corn cob hydrolysate, the microalgae scavenged 41.1% of the intracellular reactive oxygen species level by mobilizing the antioxidant systems such as superoxide dismutase, catalase, peroxidase, and reduced glutathione, which reduced the oxidative damage caused by WL to the microalgae. Microalgae coupled with corn cob residue biochar removed 77.7% Cr3+, 78.1% Cu2+, 89.6% Fe3+, 99.6% Mn2+, 77.1% Ni2+, and 93.1% Zn2+. The surface of the biochar became a pipeline pore-like structure and contained more functional groups, which provided more sites for the adsorption of heavy metals. This study lays a theoretical foundation for the simultaneous treatment and resourcing of WL, the whole-component utilization of corn cob as well as the practical production of microalgae biodiesel.