Comparative analysis of sterile and non-sterile solid-state bioprocessing using Lichtheimia ramosa for agro-industrial waste valorization.

Abstract

This study investigated the biotechnological potential of Lichtheimia ramosa in the solid-state bioprocessing (SSB) of various agro-industrial and agricultural residues under both sterile and non-sterile conditions. Decomposing wood sawdust was used as the primary substrate, supplemented with different co-substrates including wheat bran, animal manures, slaughterhouse sludge, dairy wastes, apple pomace, and urea. The 28-day SSB experiments revealed significant changes in substrate composition, with notable increases in nitrogen content (up to 34.58 % in non-sterile wheat bran treatment) and corresponding reductions in C:N ratios, indicating enhanced organic matter mineralization. Enzymatic activity profiles demonstrated L. ramosa's robust lignocellulolytic capabilities, with substrate-specific enzyme induction patterns observed. Under sterile conditions, wheat bran supplementation yielded the highest enzymatic activities, with CMCase reaching 0.71 U/g, β-glucosidase 0.82 U/g, and amylase 7.85 U/g. In non-sterile systems, cooperative microbial interactions were evident, with xylanase activity peaking earlier (2.31 U/g at day 7) than in sterile conditions, suggesting preferential hemicellulose degradation by the mixed microbiota. The study revealed that system sterility, substrate composition, and nitrogen source interactively influenced hydrolysis efficiency and enzyme production. Wheat bran, slaughterhouse sludge, and fresh dairy solids emerged as the most effective co-substrates for optimizing bioconversion processes. These findings highlight L. ramosa's versatile biocatalyst potential for waste valorization, with sterile systems recommended for targeted lignocellulase production and non-sterile systems beneficial for organic waste mineralization.