Green biocatalyst for decolorization of azo dyes from industrial wastewater: Coriolopsis trogii 2SMKN laccase immobilized on recycled brewer's spent grain.

This study presents an innovative approach for the reuse and recycling of waste material, brewer's spent grain (BSG) for creating a novel green biocatalyst. The same BSG was utilized in several consecutive steps: initially, it served as a substrate for the cultivation and production of laccase by a novel isolated fungal strain, Coriolopsis trogii 2SMKN, then, it was reused as a carrier for laccase immobilization, aiding in the process of azo dye decolorization and finally, reused as recycled BSG for the second successful laccase immobilization for six guaiacol oxidation, contributing to a zero-waste strategy. The novel fungal strain produced laccase with a maximum activity of 171.4 U/g after 6 days of solid-state fermentation using BSG as a substrate. The obtained laccase exhibited excellent performance in the decolorization of azo dyes, both as a free and immobilized, at high temperatures, without addition of harmful mediators, achieving maximum decolorization efficiencies of 99.0%, 71.2%, and 61.0% for Orange G (OG), Congo Red, and Eriochrome Black T (EBT), respectively. The immobilized laccase on BSG was successfully reused across five cycles of azo dye decolorization process. Notably, new green biocatalyst outperformed commercial laccase from Aspergillus spp. in the decolorization of OG and EBT. GC-MS and LC-MS revealed azo-dye degradation products and decomposition pathway. This analysis was complemented by antimicrobial and phytotoxicity tests, which confirmed the non-toxic nature of the degradation products, indicating the potential for safe environmental disposal.