Studies On Decolorization Of Azo Dye Wastewater Under Methanogenic Conditions

Anaerobic biological treatment of Reactive red 2 was discussed in this paper. The effects of biomass,carbon source and dye concentration on decolorization were studied as well as the effect of dye concentration on the sludge Methanogenic activity. Meanwhile, decolorization efficiency and the COD, pH, VFA in the anaerobic baffled reactor (ABR) were analyzed with different dye concentration and HRT. The mechanism of decolorization for the Reactive red 2 in the anaerobic condition was also discussed. The results were shown:1. From the batch experiments, the anaerobic bioreactor have acquired higher decolorization for the dissolvable Reactive dye and could remove the COD effectively. The higher biomass in the reactor, the more removing efficiency of the dye was obtained, but it was not proportional between them. Decolorization efficiency was higher with higher carbon source concentration. The initial decolorization rate was increased with the dye concentration. By compare the Methane production of different dye concentrations, it could be concluded that the reactive red 2 or its productions had inhabition to the methanogenism. The decolorization of reactive red 2 under methanogenic conditions was considered to be second kinetics reaction.2. The decolorization and COD removing efficiency were perfect with ABR treating dye wastewater.Under the fixed Influent Organic load, the decolorization declined from 94% to 50% as as the increasing of dye concentration from 100mg/L to 900 mg/L,while COD removing efficiency from 93% to 60%. The pH was always between 6.3～7.5 and the VFA concentrations maintained below 100 mg/L when the dye concentration was under 700 mg/L. While the dye concentration was higher than 700 mg/L, the pH of the first compartment of ABR reduced to 6.0, and the VFA concentration of effluent increased to 200 mg/L.Under the fixed Influent Organic load and dye concentration, the decolorization declined from 75% to 50% as the decrease of HRT, and COD removing efficiency from 90% to 80%.The pH and the VFA concentration of the effluent maintained 6.6～6.7 and below 100 mg/L, respectively. The ORP of four compartments was between -360～380mv, therein, the ORP of first compartments was the lowest and the final the highest.3. Reactive red 2 could not be served as the carbon and energy source for the methanogenisms. Thus extra carbon source should be added to ensure the decolorization of reactive azo dyes. In the ABR, the dye absorbed to sludge first, and then the azo bond cleaved on the work of azo-reducing enzyme which was produced by anaerobic bacterial. Aniline and the o-aminohydroxynaphthalene (AHN) derivative were conferred to be the main productions of decolorization under methanogenic conditions according to spectrum analysis. Aniline and the o-aminohydroxynaphthalene derivative couldn't be mineralized absolutely under anaerobic conditions.