Biodegradation of Lignin from Pulp and Paper Mill Effluent: Optimization and Toxicity Evaluation

Abstract

The pulp and paper industry is usually coupled with pollution problems related to high lignin and its derivatives. Plant capacity of 60 m3 h−1 was able to produce 12 tons of lignin per month. Due to the xenobiotic properties and toxicity to all life forms including humans, removal of undesirable color and associated toxicity is crucial. This study deals with lignin estimation, quantification of toxicity, and uses bacterial consortia to investigate optimum conditions for lignin degradation of pulp and paper mill (PPM) effluent. Bacterial samples with the highest ligninase activity were screened from rotten stumps, tree trunks, and soil near them. The screening of effective consortium consortia was carried out based on maximum lignin degradation. Between the designed six consortia (C1, C2, C3, C4, C5, and C6), C1 was screened for the treatment of PPM effluent in a batch bioreactor. The 3-level, 3-factor Box–Behnken design (BBD) was used to observe the effects of various operating conditions and optimization of the process. In addition, the toxicity assay was also analyzed. The predicted model had R2 and Radj2 correlation coefficients of 0.9700 and 0.9564, respectively, which showed the trial results were close to the predicted values. Moreover, at the optimal conditions (volumetric flow rate = 250 mL/min, lignin concentration = 252.87 mg/L and reaction time = 156 min.) the biodegradation of lignin efficiency was 94.83%. In addition, a Vigna radiate L. assay confirmed the detoxification of PPM effluent after treatment with C1.