Feasibility Studies on Integrated Treatment of Chromium Contaminated Water using Microbial Consortium and Hairy Roots of Nicotiana Tabacum

Abstract

Hexavalent chromium (Cr(VI)) contamination represents a critical environmental challenge in Odisha, given its status as a region abundant in chromite mines. The discharge of water from these mines into surface water bodies often contains Cr(VI) concentrations exceeding permissible limits. In response to this pressing issue, bioremediation emerges as a promising eco-friendly solution. By harnessing the natural processes of microorganisms to degrade or transform contaminants, bioremediation offers a potential means to mitigate Cr(VI) pollution effectively and sustainably. Chromium reducing bacterial cultures were isolated from the chromite mine soil. Five highly potent bacterial isolates were screened after acclimatization and identified using 16S rRNA sequencing. Three bacterial consortia namely CRC589, CRC580 and CRC489 were developed from the different combinations of screened bacterial isolates. The optimization of process parameters for achieving maximum Cr(VI) reduction involved two main methodologies. Initially, a conventional single-variable approach was employed to individually optimize factors such as carbon source, nitrogen source, pH, incubation temperature, inoculum size and inoculum age. Subsequently, to further investigate the interactive effects of key variables on Cr(VI) reduction, Box Behnken design within the framework of Response Surface Methodology was implemented. Optimization results revealed that the optimum temperature for all the three consortia was 35°C and optimum pH for consortia CRC589, CRC489 was 7 whereas pH 8.5 was known to optimal for CRC580. Batch and continuous studies for Cr(VI) reduction were conducted with consortiumCRC489. Cr(VI) reduction in the CSTR revealed that at the dilution rate of 0.01 h-1, the maximum reduction of 91 % and 80% was achieved at the initial Cr(VI) concentration of 10 mg/L and 25 mg/L respectively. Hairy roots were induced from Nicotiana tabacum through the infection of Agrobacterium rhizogenes MTCC 2364. Effect of various influencing factors on the hairy root induction such as co-cultivation period, infection time, Acetosyringone concentration and ultrasonication treatment was evaluated. Maximum of 36.35 % of transformation efficiency was achieved at 72 hours of co-cultivation period with 30 minutes of infection time. The supplement of 100 μM acetosyringone increased the transformation efficiency to 55.35 % with reduced number of days for root induction. Hairy roots were used to treat Cr(VI) solutions to understand the mechanism of action and to evaluate their efficiency for the chromium removal from varying chromium concentration. The effluent of CSTR study was treated with hairy roots and resulted in a Cr(VI) level below the permissible limit in the water with 99.28 % reduction. In addition to that the production of secondary metabolite from the hairy root under the influence of various Cr(VI) concentration was evaluated by HPLC. The production of nicotine, a secondary metabolite from N. tabacum was elicited significantly at the lower concentrations (2 mg/L and 5 mg/L) of Chromium.