Optimising a novel biofilm-based process using Neurospora discreta for enhanced treatment of lignin-rich wastewater

Paper and pulp mills generate substantial volumes of wastewater containing lignin-derived compounds that are challenging to degrade using conventional wastewater treatment methods. This study presents a novel biofilm-based process for enhanced lignin removal in wastewater using the fungus Neurospora discreta, which effectively degrades lignin and forms robust biofilms at the air–liquid interface under specific conditions. The process was optimised using the Taguchi design of experiments approach, and three factors including pH, copper sulphate concentration, and trace element concentration were evaluated at three levels. Experimental data were analysed against three responses: lignin degradation efficiency and the activities of two ligninolytic enzymes (polyphenol oxidase and versatile peroxidase). The results indicated that wastewater pH was the most significant parameter affecting lignin degradation efficiency and enzyme activities. Over 70% lignin degradation was achieved at pH levels of 5 and 6 with copper sulphate concentrations above 4 mg/L, while degradation efficiency drastically dropped to 45% at a pH value of 7. Reversed-phase high-performance liquid chromatography analysis demonstrated the effects of the three factors on the polar and non-polar components of lignin in wastewater, revealing a clear decrease in all peak areas after treatment. Additionally, significant relationships were observed between biofilm properties (including porosity, water retention value, polysaccharide content, and protein content) and lignin removal efficiency. This study also reported for the first time the presence of versatile peroxidase, a ligninolytic enzyme, in Neurospora sp.