Isolation and Characterization of Aspergillus niger AZ2 from Pulp and Paper Mill Effluent that Degrade Lignin under Alkaline Conditions.

The pulp and paper industry produces and discharges substantial amounts of wastewater containing hazardous substances, including lignin, necessitating their treatment before release. This study explores the lignin-degrading capabilities of a newly isolated fungus, designated as strain AZ2, from a black liquor sample. The fungus was identified as Aspergillus niger AZ2 through colony morphology, microscopic examination and sequencing of the internal transcribed spacer (ITS) region. The degradation of lignin by A. niger AZ2 was evaluated by measuring lignin reduction, color removal, and ligninolytic enzyme activity in a medium containing alkali lignin. The maximum laccase and lignin peroxidase activities were recorded as 1.57 U/mL and 1.26 U/mL, respectively, on the 5th day. The lignin degradation was noted as 63.5%, accompanied by a color reduction up to 65.6%, after 05 days of incubation at 30 °C and pH 8.0. The degradation process was further supported by trends in fungal biomass growth and ligninolytic enzyme production. Fourier transform infra-red (FTIR) spectroscopy and scanning electron microscopy (SEM) analysis revealed notable alterations in functional groups and surface morphology throughout the degradation process. Lignin degradation products were detected through gas chromatography-mass spectrometry (GC-MS), including key low molecular weight compounds such as 3-methoxyphenol, vanillin, and fumaric acid. This study presents A. niger AZ2 as a novel fungal strain exhibiting remarkable ligninolytic activity under alkaline conditions, a characteristic not widely explored in this specie. To the best of our knowledge, this is the first comprehensive study integrating FTIR, SEM, and GC-MS analyses to elucidate its lignin degradation potential. The findings suggests that A. niger AZ2 efficiently breakdown lignin in alkaline environment, positioning it as an eco-friendly and promising candidate for lignin degradation applications.