Mechanism of pyrene remediation in soil by biochar-immobilized laccase

Pyrene accumulates in soil from a variety of sources, infiltrating the food chain and causing mutagenic and carcinogenic disorders in humans. Pyrene has since been effectively removed from soil using a variety of chemical and physical remediation techniques, but these approaches have a number of disadvantages, including being costly, time-consuming, labor-intensive, and producing secondary environmental pollutants. Therefore, this work employed an environmentally friendly and sustainable biological approach that utilized enzyme immobilization on biochar. Wheat straw biochar prepared by pyrolysis, followed by acid activation, and then laccase was immobilized on biochar using the cross-linked adsorption technique. Results showed that immobilized enzyme retained over 50% of enzyme activity at pH 3-7, 20-60 °C, and maintained over 50% relative activity after five cycles and 50 days of storage. Pyrene remediation reached 80.33% after 50 days of incubation while quadratic model indicated the remediation efficiency will increase over time, reaching 53.56%. Soil phenol oxidase, peroxidase, and dehydrogenase activities increased by 105.2-107.1%, 155.1-167.2%, and 104.8-157% respectively compared to control. Firmicutes, Actinobacteria, and Proteobacteria were the dominant phyla, while Bacillus, Lysinibacillus, Sedimentibacter, Brevundimonas, Christensenellaceae_R-7_group, Sphingobium, and Stenotrophomonas were the most abundant genera in immobilized enzyme treatments. These microbes involved in the degradation of pyrene and various organic contaminants in the soil. Thus, it may be concluded that laccase immobilization on wheat straw biochar is a green and sustainable method for pyrene remediation in soil, as well as suitable for agricultural and industrial applications.