Leather tanning consists of many processes, most of which are carried out using water, in which variety of chemical compounds, mineral tannins (including chromium (III) salts) and vegetable tannins, dyes etc. are added. In combination with organic matter of animal origin it results in wastewater that is very difficult to treat. Coagulation and advanced oxidation processes are commonly used methods for the treatment of tannery wastewater.
The aim of this study was to pretreat tannery wastewater by removing organic compounds determined by COD. For their treatment, a coagulation process using iron (FeCl3) and aluminium (Al2(OH)5Cl) coagulants and advanced oxidation processes (AOPs) used of Fenton reagents were applied. Studies using the Fenton process were conducted applying different doses of iron (VI) sulphate (II) FeSO4 with a constant hydrogen peroxide H2O2 dose of 3000 mg/L. The type and the dose of the coagulant were the basic parameters of the coagulation process subject to optimization. Doses in the range of 1.0 - 6.5 mL/L were adopted. An even better reduction of organic compounds was obtained in a hybrid system: Fenton reaction and coagulation. In that case, the COD value in the pretreated wastewater was 4010 mg/L.