The removal of the trivalent chromium from the leather tannery wastewater: the optimisation of the electro-coagulation process parameters

The capacity of the electro-coagulation (EC) process for the treatment of the wastewater containing Cr³⁺, resulting from a leather tannery industry placed in Medellin (Colombia), was evaluated. In order to assess the effect of some parameters, such as: the electrode type (Al and/or Fe), the distance between electrodes, the current density, the stirring velocity, and the initial Cr³⁺ concentration on its efficiency of removal (%RCr⁺³), a multifactorial experimental design was used. The %RCr³⁺ was defined as the response variable for the statistical analysis. In order to optimise the operational values for the chosen parameters, the response surface method (RSM) was applied. Additionally, the Biological Oxygen Demand (BOD₅), the Chemical Oxygen Demand (COD), and the Total Organic Carbon (TOC) were monitored during the EC process. The electrodes made of aluminium appeared to be the most effective in the chromium removal from the wastewater under study. At pH equal to 4.52 and at 28°C, the optimal conditions of Cr³⁺ removal using the EC process were found, as follows: the initial Cr³⁺ concentration=3,596 mg/L, the electrode gap=0.5 cm, the stirring velocity=382.3 rpm, and the current density=57.87 mA/cm². At those conditions, it was possible to reach 99.76% of Cr³⁺removal, and 64% and 61% of mineralisation (TOC) and COD removal, respectively. A kinetic analysis was performed in order to verify the response capacity of the EC process at optimised parameter values.