Treatabality of azo dyes in anaerobic/aerobic sequential processes

II ABSTRACT In the framework of this Ph. D. thesis, the removal of azo dyes, which produced banned carcinogenic aromatic amines, was studied using batch anaerobic and continuous fed Upflow Anaerobic Sludge Blanket (UASB)/ Continuous Stirred Tank Reactor (CSTR) sequential reactor systems in synthetic, simulated and real textile wastewaters. Reactive Black 5, Direct Yellow 12, which are used in Izmir region, and Direct Brown 2, Direct Red 28 and Direct Black 38 which are banned azo dyes containing benzidine were degraded and decolorized rapidly at concentrations varying between 200 and 3200 mg/1. Meanwhile, the aromatic amines produced from the cleavage of azo bonds were accumulated in batch anaerobic conditions. The decolorization, and glucose-COD removals exhibited first order kinetics. The effect of operational conditions such as organic and dye loadings, hydraulic retention time (HRT), food to mass (F/M) ratio on the substrate removal rates, color removal efficiencies and methane gas productions was investigated in anaerobic (UASB)/aerobic (CSTR) sequential system using RB 5, DR 28 azo dyes, and DB 38 at a concentration varying between 0 and 3200 mg/1. It was found that HRT was more effective than the dye loading rates applied in UASB reactor for decolorization. The aromatics amines were effectively removed in CSTR reactor. Furthermore, the effect of co-substrate concentration (glucose) and alkalinity levels on the color removal of azo dyes was investigated. It was found the color of azo dyes was successively removed even if at lower substrate and alkalinity levels. The treatment of wool dyeing wastewater and a real wastewater taken from a Cotton Textile Mill were investigated in the same system. Color removal efficiencies varying between 80-91% and 40-77% were obtained in wool dyeing and cotton textile mill wastewaters, respectively, while the COD removal efficiencies were 83-96% and 39- 82% in whole system. In order to obtain the kinetic coefficients, the UASB reactor was operated with simulated wastewater containing desizing agents, dye, salts etc. atm six different HRTs. Stover-Kincannon and Grau second order substrate removal kinetics were found to be the more appropriate models in lab scale UASB reactor treating simulated textile wastewater. Finally, synthetic wastewater containing DB 38 and DR 28 azo dye of 3200 mg/1, was decolorized using the anaerobic/aerobic sequential reactor system in order to monitor the toxicity and the intermediate products through decolorization of DB 38, and DR 28 azo dyes. Azo dyes were mineralized and the toxicity was decreased under anaerobic/aerobic conditions. HPLC-DAD and GC-MS analysis showed that the azo dyes could be mineralized using UASB/CSTR sequential system.