Characterization & application of dye decolonzing metal tolerant bacterial community for treatment of textile waste-water

Abstract

Bioremediation of colored textile wastewater loaded with dyes and metals is a matter of great concern due to the hazardous risks associated with their untreated discharge into water bodies. The present study was conducted to isolate and characterize dye decolorizing metal tolerant bacterial strains for treatment of textile wastewater. For this purpose, 220 metal tolerant bacteria isolated from textile wastewaters coming from different textile industries in Faisalabad were tested for their potential to decolorize four different reactive dyes viz. reactive red 120 (RR120), reactive black 5 (RB5), reactive orange 16 (RO16) and reactive yellow 2 (RY2). Based on the potential to decolorize RR120, RB5, RO16 and RY2 in the presence of a mixture of four heavy metals (Cr, Cd, Zn, Pb), four bacterial strains viz. ZM17, ZM130, ZM160 and ZM183 were selected for subsequent studies. These strain were identified following the amplification, sequencing and bioinformatics analyses of their 16SrRNA, and were named as Raoultella sp. ZM17, Pseudomonas aeruginosa strain ZM130, Pseudomonas sp. ZM160 and Pseudomonas sp. ZM183. The selected bacterial strains were found to have varying levels of tolerance against the presence of different heavy metal ions in the media. Moreover, the decolorizing potential of these isolates was found to be decreased with an increase in the initial dye concentration. Furthermore, the interactive effects of four input variables including salt content, pH, C source concentration and level of multi-metal mixture on decolorization of RB5 by the selected bacterial strains were examined following response surface methodology (RSM) statistical modeling. All the four strains were also found capable of simultaneously removing Cr(VI) and all the reactive azo-dyes under study. However, the strain ZM130 was found to be the most efficient among these strains. The strains ZM17 and ZM183 were also found to harbor a dye decolorizing azoreductase Azr gene, whereas, a cadmium tolerant czcABC gene was found to be amplified from the DNA of the strains ZM130, ZM160 and ZM183. Enzymatic analyses of the strain ZM130 indicated that azo-reductase and tyrosinase activities were absent in this strain, however, this strain exhibited considerable activity of laccase and NADH-DCIP reductase activity during the decolorization of RR120. While testing the applicability of the strain ZM130 for treatment of synthetic wastewater, efficiency for color and COD removal of this strain was found to be favored and better in the anaerobic batch bioreactor as compared to aerobic batch bioreactor system. However, presence of yeast extract significantly increased the potential of ZM130 for color and COD removal with attached growth of microbial culture. The potential of the most efficient dye decolorizing metal tolerant bacterial strain Pseudomonas aeruginosa ZM130 for treatment of synthetic colored wastewater containing both RB5 (300 mg L-1) and hexavalent chromium (25 mg L-1) was also tested in vertical soil columns bio-augmented with this strain using sterilized and non-sterilized soil. It was interesting to note that the highest level of color, COD and Cr(VI) removal (˃90%) was achieved in the treatments where the soil columns were bio-augmented either with the sludge alone or the sludge along with ZM130 followed by the strain ZM130 along with addition of yeast extract. Based on the findings of the present study, it might be concluded that the selected bacterial strains, particularly Pseudomonas aeruginosa strain ZM130, harbor a varying but highly considerable potential for bioremediation of different xenobiotic compounds including dyes and heavy metals. Hence, this strain could be used to develop the bio-treatment systems (bioreactors) for addressing the problem of azo-dyes and metals in the wastewater.