Exploring the potential of bacterial consortium for the treatment of paper mill effluent treatment through various treatment strategies and evaluation of their toxicity

Paper mill effluent containing kraft lignin (KL) and other toxic compounds poses serious environmental health concerns due to its potential for bioaccumulation. A prospective bacterial consortium is still needed for the remediation of paper mill effluent. Therefore, the current work aims to explore the potential of consortium, i.e. Bacillus cereus, B. paramycoides, and B. aryabhattai via different treatment strategies: batch, continuous, multipulse, and dissolved oxygen (DO) stat fed-batch for maximum detoxification of effluent under optimised conditions. A minimal salt medium containing 1.0 % glucose, 0.5 % ammonium nitrate, and pH 8.0 was the optimum condition for the consortium to degrade 1000 mg/L of kraft lignin in the effluent. Laboratory adaptation evolution (LAE) studies showed that the maximum number of bacterial generations was observed within 178 h at 5th cycle for 3000 mg/L kraft lignin. The maximum removal of KL, color, chemical oxygen demand (COD), biological oxygen demand (BOD), and total phenol by the dissolved oxygen stat fed-batch treatment strategy was 94 %, 86 %, 91 %, 90 %, and 97 %, respectively. Phytotoxicity testing of the consortium-treated effluent on Vigna radiata L., and Trigonella foenum-graecum L. revealed a reduction in phytotoxicity by -66 % and -68 %, respectively. The genotoxicity study on Allium cepa L. showed that the percent of aberrant cells with different chromosomal aberrations was decreased in consortium-treated effluent as compared to untreated effluent. This work provides a new insight and strategy for the paper mill effluent treatment at an industrial scale. Statement of environmental implication: The paper mill effluent contains various hazardous compounds; chlorinated phenols, dioxins, kraft lignin, and endocrine disrupting compounds, when discharge from industries without proper treatment. This effluent causes mutagenic, clastogenic, carcinogenic, and endocrine-disrupting mechanisms in flora and fauna. This study provides a comparative performance evaluation of different treatment strategies: batch, continuous fed-batch, multipulse fed-batch, and dissolved oxygen stat fed-batch, for paper mill effluent treatment using a bacterial consortium for maximum removal of kraft lignin, color, chemical oxygen demand, total phenol concentration, and quantified ligninolytic enzyme production. Treated effluent showed a lesser phytotoxic and genotoxic effect. Therefore, the results of this study are suitable for environmental restoration. Significance of study: Contrastingly, throughout this study, found that bacterial consortium have superior detoxifying qualities of paper mill effluent compared to pure cultures, via different treatment strategies: batch, continuous, multipulse, and dissolved oxygen stat fed-batch strategies under optimised conditions at lab scale. According to these results, such dissolved oxygen stat fed-batch strategy mediated treated effluent that promotes seed germination and showed a higher mitotic index of root cells of the plant in contrast to untreated effluent. Therefore, these treatment strategies are adequate, effective, and sustainable to reduce the significant pollution load in effluent.