Effect of physical parameters on the decolorization of multiple synthetic textile dyes by bacteria recovered from dye contaminated soil and water

Abstract

Textile wastewater is a complex mixture of many contaminating materials. These include a high concentration of salts, acids, heavy metals, organochlorine-based pesticides, pigments, dyes etc. Dye is the first pollutant to be recognized in wastewater and many synthetic dyes are toxic, mutagenic and carcinogenic in nature. This makes dyes imperative to be removed from textile wastewater. Current physicochemical textile dye removal methods are less efficient and expensive. Bioremediation through utilization of synthetic dye degrading bacteria can be considered as an effective aid to the clean-up process. The present study attempts to decolorize eight synthetic textile dyes: Novacron Brilliant Blue C-B, Novacron Dark Blue S-GL, Novacron Navy S-GI, Novacron Turquoise GN, Novacron Super Black-G, Novacron Ruby S-3B, Avitera Brilliant Yellow SE and Novacron Yellow S-3R by newly isolated bacterial strains from dye contaminated soil and water. Dye decolorizing ability of bacteria was screened on Nutrient broth containing mixed dyes. Effects of different physical parameters like dye concentration, temperature, pH, agitation and seed culture concentration on the dye degrading ability of selected isolates were tested. The potential isolates were selected for BiOLOG identification. Pseudomonas aeruginosa (S9A6) exhibited to be the most promising amongst the isolated bacteria for decolorizing synthetic dyes, followed by Bacillus cereus/thuringiensis (S1A6). Pseudomonas aeruginosa was tested further for effects of mixed dye concentration and the repeated addition of dye aliquots up to four cycles. The decolorization obtained in this study was expressed in percentages with Pseudomonas aeruginosa, S9A6 having up to 98.5% decolorization of Novacron Super Black-G, 98.4% of Novacron Yellow S-3R, 98.3% of Novacron Dark Blue S-GL, 97.4% of Novacron Navy S-GI, 96.7% of Novacron Ruby S-3B, 94.2% of Novacron Brilliant Blue C-B and 88.6% decolorization of six synthetic dye mixture for 100 ppm of dye concentration when incubated under stationary condition at 37°C for 72 hours. However, there was no observable color difference for Novacron Turquoise GN and Avitera Brilliant Yellow SE by any of the isolated bacteria. The prime candidate Pseudomonas aeruginosa also exhibited very good ability to decolorize repeated additions for six individual dyes up to the fourth cycle without supplementation of additional nutrients, which is remarkable criteria for commercial applicability of it in textile effluent treatment.