Synthetic textile dyeing wastewater treatment by integration of advanced oxidation and biological processes – Performance analysis with costs reduction

• Minimization of chemicals consumed in the Fenton reaction is achieved by coupling a SBR.
• Fenton + SBR allows reaching better removals: >99% for color and 83–98% for organic matter.
• Fenton + SBR leads to lower cost : 2.9, 7.5 and 14.8 €/m3 for polyester, cotton and acrylic effluents.
• Hydrogen peroxide has the greatest impact in the treatment cost.

Color and organic matter removals from acrylic, cotton and polyester dyeing wastewaters were evaluated by biological oxidation in a sequential batch reactor (SBR) and by integration of Fenton’s reaction with SBR. Raw and chemically oxidized pre-treated wastewaters were fed into the biological reactor during 10 cycles (i.e., up to pseudo-steady state conditions). Because the biological degradation did not allow obtaining effluents complying with the discharge limits, neither did the chemical oxidation per se, coupling the SBR after chemical oxidation was required. In the integrated chemical-biological process a new strategy was applied in the optimization of Fenton’s oxidation, consisting in the application of the optimum doses of Fe(II) and H2O2 (for biodegradability enhancement and maximization of color and DOC removals), but with the simultaneous objective of minimizing the operating costs. The integration of Fenton’s oxidation with a downstream SBR provides much better removal of organic matter (88–98% for COD, 83–95% for BOD5 and 91–98% for DOC, values depending on the particular textile effluent being used) and color (>99%) than the biological or chemical treatment alone could do. Besides, such an integrated treatment allows treated wastewaters to meet the discharge limits with a reduction of the operating costs, in the range 24–39% comparatively to Fenton’s oxidation alone.