Bioremediation of Kraft Lignin in Wastewater: Optimization of Temperature and Isolation of Valuable Compounds

Conventional methods for the treatment of complex lignin found in the pulp and paper mill effluent is a strenuous and expensive process. Microbial degradation is a promising technique to degrade lignin efficiently due to its adaptability and rapid growth of microbes in diverse environments. This study is focused on the isolation of potential ligninolytic bacterial strains from agricultural soil and decomposed wood sources for successful degradation of lignin present in the wastewater. Initially, 15 ligninolytic strains were identified and three dominant species, Staphylococcus lentus (SB5), Bacillus megaterium (RWB15) and Pseudomonas geniculata (RWP9) were isolated as per their growth tolerance pattern with different lignin concentrations. The lignin degradation study was carried out at different temperatures (25-45℃) with 1000 mg/l of feed lignin concentrations. The optimum degradation temperature of all the strains fell within the range 30-35℃. The maximum lignin degradation of SB5, RWB15 and RWP9 was identified as 89, 77 and 90% at the end of the 6th, 3rd and 7th day of biodegradation, respectively. There was a steep reduction of COD by all three microbes before attaining the stationary phase and thereafter COD reduction was sluggish due to the death phase. Besides, the microbes used in this study showed the transformation of lignin into valuable low-molecular by-products, vanillin, vanillic acid and adipic acid with their concentration being quantified as 28, 101 and 130 mg/l, respectively. This study shows the successful degradation of waste lignin and the recovery of valuable byproducts from waste streams.