Coagulation-Flocculation - Fenton-Neutralization sequential process for the treatment of industrial effluent polluted with AB194 dye

A two-stage sequential treatment of lime-assisted alum Coagulation-Flocculation (CF) and Fenton-Neutralization (F–N) was applied to industrial textile wastewater (ITWW) highly contaminated with Acid Black 194 dye. Lime-assisted alum CF at optimal operating conditions ([Alum] = 16.09 g/L, [Ca(OH)2] = 5.16 g/L) provided a dye removal efficiency of 95 %, a COD removal of 63 %, a TOC elimination of 60 %, a total Cr concentration reduction of 94 %, with a total operating cost (TOpCCF) of 5.99 USD/m3. In the F–N treatment applied to the CF supernatant, the operating conditions were optimized through experimental design, response surface methodology and multi-objective optimization analysis. The optimized conditions were: for Fenton stage: Fe2+ dose = 1977 mg/L, H2O2 concentration = 3679 mg/L and initial pH = 2.31; for Neutralization stage: 4.63 g/L of slaked lime. They allowed reaching total decolorization, global COD and TOC elimination of ca. 89 % and 87 %, respectively, complying with current environmental regulations. Total operating costs, TOpCCF-F-N, were estimated at 13.66 USD/m3. A biodegradable (BOD5/COD = 0.51), non-toxic for Artemia salina, Cr-free, neutralized effluent was obtained. Furthermore, the value of Carbon Oxidation State increased from 0.14 (ITWW) to 3.56, indicating a significant improve in the degree of oxidation of organic substances originally present in the ITWW. The sequential CF-F-N process can be considered an efficient alternative for the treatment of industrial textile wastewater.