Bioremedition of Textile Dye Wastewater using Exopolysaccharides produced by bacteria cultured from Cotton Gin Trash Soil

Abstract

Synthetic dyes possess high thermal and photo stability making color removal from textile wastewater difficult hence causing major water pollution problem. Exopolysaccharides (Eps) have attracted interest owing to their safety and possible application in bioremediation. The main objective of this research was therefore to extract bacterial Eps and assess their efficiency in bioremediation of Reactive Black 5 (RB5) textile wastewater in comparison with chemical coagulants. Specific objectives were: to optimize chemical coagulation of the wastewater; to isolate bacteria with Eps production capacity from cotton gin trash soils; to screen for Eps with activity on the wastewater; to optimize bioremediation of the wastewater by the Eps; to identify Eps-producing isolates, Eps and Eps-treated wastewater. The wastewater was collected from Rivatex while cotton gin trash soils were grab sampled from three ginneries in Meru, Kitui and Baringo. In this work, Polyaluminium Ferric Chloride (PaFC), Polyferrous Sulphate (PFS) and alum were optimized by varying pH (2-10) and doses; alum, 60-140g/L, PFS, 20-100mg/L and PaFC, 140-280mg/L. Eps-producers were isolated using nine different media. Nutrient Broth +Sucrose, Nutrient Broth+ Glucose and Glucose, Yeast Extract and Magnesium Sulphate (GPYMgSO4) were used to assess Eps activity on the wastewater. The broths were dosed with the wastewater, Eps from high (≥90%) producers and incubated at 30 oC, pH 7-8 for 72h. Eps that supported at least 94% dye removal were optimized in Molasses, Soya, Yeast Extract and Magnesium Sulphate (MSYMgSO4) broth by varying temperature, incubation time and molasses concentration. Eps that gave at least 80% dye removal were characterized by FTIR and GC-MS, isolates identified molecularly and the treated wastewater analyzed by UV-Vis and FTIR. Out of the nine media used, YEA, YEPD, NA+G and PDA were the most efficient in isolation of Eps producing bacteria. GPYMgSO4 supported growth of 50% of the isolates whose Eps had at least 94% dye removal. Three Eps gave at least 80% dye removal in MSYMgSO4 at 30 oC, 72h and 20g/L molasses optimal conditions which was comparable to that of PFS, 86%. The isolates were identified as Bacillus sp. (Baringo and Kitui) and Alcaligenes Faecalis (Meru). GC-Ms indicated that Bacillus sp. Eps were heteropolysaccharides while Alcaligenes Faecalis was homopolysaccharide. FTIR determined that the Eps mainly contained hydroxyl, carbonyl and carboxyl active groups that were associated to the dye binding by adsorption, since no new peaks were formed in the treated wastewater. UV-Vis confirmed the dye removal by the Eps that gave at least 80% efficiency by absence of the peak at 597nm in the treated wastewater. In conclusion, Eps produced by bacteria isolated from gin trash soil were found to possess capacity to remove at least 80% of RB5 from textile wastewater. MSYMgSO4 was found suitable to substitute GPYMgSO4 for production of the Eps. The Eps had comparable dye removal efficiency to that of PFS. Cotton gin trash soil is therefore recommended as a suitable source of Eps with at least 80% RB5 removal capacity using MSYMgSO4 at 30oC for 72h.The bacterial Eps are hence proposed as effective substitutes to the chemical coagulants.