Comparative study of various decolorization processes for treatment of synthetic dyes

Abstract

Azo dyes constitute the largest and most diverse group of dyes used in commercial applications. These dyes are carcinogenic and mutagenic in nature, as well as also create an aesthetic problem, so these must be removed before their disposal into water bodies. Various methods are in use for the decolorization of azo dyes. Every method has its own shortcomings and drawbacks. In this study, a comparative study was conducted to get the maximum decolorization of synthetic azo dyes and industrial effluents. Photo-Fenton’s process, biological and sequential methods were utilized for the decolorization of synthetic and real wastewater having azo dyes. In biological method, experiments was performed with five locally isolated indigenous white rot species, for the selection of two white rot fungal cultures based on their maximal decolorization potential. Different fermentation conditions (dye level, pH, inoculums size, temperature, mediators and metal ions) and nutritional factors (carbon and nitrogen sources) were optimized to enhance the efficiency of white rot fungal cultures for dye decolorization. In Photo-Fenton,s treatment method, the optimization of different experimental parameters (pH, FeSO4, H2O2, temperature and effects of salts) was done to get maximum decolorization (90%) of dye under study. Sequential methods were also studied) to investigate their effectiveness in the present study. The effectiveness of all treatment technologies was evaluated by water quality assurance parameters such as COD, BOD, TOC, TSS, phenolic contents ant toxicity assey, by following the standard methods of treatments. All treatments under study showed a good potential towards decolorization as well as mineralization, however, Sequential treatments showed best potential towards decolorization (up to 97%) as well as mineralization (up to 90%) of synthetic azo dyes. The uv-visible and FTIR spectral studies have shown decolorization as well as mineralization of dyes under study. An economic analysis has shown as the cost in the chemical treatment (Photo-Fenton treatment is considered mainly due to the chemicals, thus at lower doses (it is applied as a pre-treatment step), operating cost of the treatment can be saved. It was also found, that as the sequential carried out at lower dose of chemicals, so sludge production was almost negligible and the dye wastewater after sequential treatments fall within the safer limits, hence dispose off such treated water not be hazardous. Thus the overall treatment chain of Photo-Fenton oxidation followed by aerobic biological treatment could be quite effective and economical option for the treatment recalcitrant compounds like azo dyes in pilot plant scale.