The isolation and degradation characteristics of lignosulfonate-degrading aerobic bacterial strains

Lignin is a refractory organic compound with complex structure. For promoting the recycling of lignocellulose, we need to study the microbial degradation mechanism of lignin in mitigating pollution caused by pulp and paper-making black liqour. In this research five aerobic bacterial strains utilizing lignosulfonate as a sole carbon and energy source were isolated from activated sludge in a pulp and paper mill. A strain with better degradation efficiency was then selected to investigate the effect of temperature, pH and C/N ratio on its growth and degradation performance. Moreover, changes of functional groups and elemental compositions in residual lignosulfonate and the metabolic products were analyzed to speculate the degradation mechanisms. The results showed that all five bacterial strains were capable of degrading lignosulfonate, with Sphingobacterium sp. HY-H showing the best performance. The optimal conditions for strain HY-H were determined by Taguchi's orthogonal matrix method to be initial pH of 7.0, temperature of 30 oC, and C/N ratio of 5:1. Under these conditions, the lignosulfonate degradation capacity of strain HY-H (initial lignosulfonate concentration of 1 g L-1) could reach 30.6% after 5 days. During the process, contents of phenolic hydroxyl and methoxyl groups decreased, but those of carbonyl, carboxyl and sulfonate groups increased. The results indicated that lignosulfonate is degraded to carbon dioxide via oxidation of α-hydroxyl groups, cleavage reaction of β-O-4, demethylation and decarboxylation. The strain HY-H could effectively degrade lignosulfonate, thus having a great application prospect for the biotreatment of pulp and paper-making wastewater.