Post-tanning wastewater treatment using electrocoagulation: Optimization, kinetics, and settlement analysis

Abstract

Post-tanning process in the tannery industry generates complex wastewater. Continuous electrocoagulation (EC) with carbon-steel electrodes was used to treat synthetic/post-tanning wastewater. Research surface methodology, based on central composite design (RSM-CCD), was used for variables optimization and analysis of variance (ANOVA) to relate all parameters. Optimal variables were identified as initial pH 3.0, current density 6.4 mA m−2, initial dye concentration 125 mg L−1, NaCl concentration 1000 mg L−1, and inlet flow rate 176 mL min−1 to produce 71% dye removal, operational costs (OC) 0.05 US$ m−3, power consumption 1.3 kWh m−3, iron consumption 0.05 kg m−3, dye removal capacity per dissolved mg iron (qe) 4.3 mg Dye L−1 C−1 and total dissolved solids (TDS) removal 43.5%. Best process conditions were used to treat real post-tanning wastewater and resulted in carbon oxygen demand (COD) and TDS abatement (23% and 76%, respectively), as well as low OC (0.84 US$ m−3) and energy consumption (20.6 kWh m−3). Pseudo-first-order kinetic model was found fitting experimental results, having electrical energy per order (EEO) of 1 kW h m−1 order−1 with a higher k = 1.14 min−1. Scanning electron microscopy analysis suggested the presence of iron nanoparticles within the sludge. All input and output parameters resulted in statistically significant where TDS and qe were the most valued for effective pollutant removal optimization and prevention of TDS increase in treated water. The outcomes of this study suggest EC as a suitable treatment for post-tanning wastewater and further knowledge of steel-carbon EC reactor design and sludge reusing purposes.