Colour removal and its mechanisms in textile wastewater treatment by UASB reactor system with anaerobic granular sludge

Abstract

Textile wastewaters generated from different stages of textile processing contain various toxicants orpollutants that are seriously harmful to natural aquatic environment when released without propertreatment. Although there are different methods, which can be adopted for the treatment of textilewastewater. biological approaches are considered as environmentally friendly, low cost and effectivemethods over other physico-chemical methods. In the present study, simulated textile wastewater(STW) prepared by mixing of three popular acid dyes (Acid blue 204, Acid red 131 and Acid yellow79) in synthetic wastewater was studied for the decolourization and removal of degradable organic inthe laboratory scale Upflow Anaerobic Sludge Blanket Reactor system with anaerobic granular sludgefor about five months at different organic and dye loading rates. The colour removal mechanismsunder .maerobic treatment were also examined since microbial colour removal occurs basically in twoways namely biological degradation, which is more important in textile wastewater treatment, andadsorption of dye molecules onto microbial biomass. Chemical oxygen demand (COD) removal ofacid red 131 (AR 131) containing STW was about 80% at 300 mg/l dye concentration and it was over89% in acid yellow 79 (AY79) dye containing STW under studied conditions. Although acid blue 204(AB204) showed a little inhibition over rnethanogenic consortia, about 93% of COD removal wasobserved at 100 mg/l dye concentration. Colour removal of AR 131 dye containing STW was 95% and.it was credited to biodegradation. Treatment of STW prepared using AY79 showed 95% colourremoval owing to biodegradation while AB204 was quite resistant to biodegradation by anaerobicrn icroorgan isms. Observed colour removal was merely due to the adsorption of dyes onto microbialgranules. Even though a little accumulation of volatile fatty acid (YFA) was observed in increaseddye concentrations, the detected values ofYFA, alkalinity and pH showed that those values were inthe range of desirable limits of anaerobic process. It seems that AR 131 and AY79 can be decolourizedalmost completely by UASB reactor system while AB204 cannot be decolourised since all colourremoval attributed to adsorption of dye onto microbial granules. It can be concluded that anaerobictechnology can be used for the treatment of textile wastewater containing different dyes as an alternativemethod over other methods. However, further study ofUASB reactor for the treatment of real textilewastewater is suggested to find out matrix effect of other chemicals present in real textile wastewaterbefore application to the real world situations.