Evaluation of ozonation and electro oxidation treatment for the removal of organics and salt recovery from RO reject from leather industries: Sustainable approach for the management of contaminated salt in CETPs

The management of RO reject from Common Effluent Treatment Plants (CETPs) treating leather industrial waste streams is a challenging task due to the presence of high levels of chlorides and sulphates. The application of conventional biological and chemical oxidation treatment is limited. Hence, the present study aims to treat RO reject waste stream (RO-RWS) from CETPs by applying Advanced Oxidation Processes (AOPs) like ozonation, ozonation + H 2 O 2 and electrooxidation techniques to achieve maximum organic removal efficiency. AOPs such as Ozonation (Oz), Ozonation with H 2 O 2 (Oz-HP) and Electro-oxidation using TiO 2 and Graphite electrodes (EO TiO2+Graphite ) treatment systems eliminated 45 %, 54 % and 92.8 % of Chemical Oxygen Demand (COD) and 32 %, 38 % and 78.7 % of Total Kjeldahl Nitrogen (TKN) respectively from RO-RWS at high Total Dissolved Solids (TDS) environment. COD and TKN removal of RO-RWS by Electrooxidation treatment followed pseudo- first order kinetics with rate constants of 1.61 × 10 −2 min −1 and 3.91 × 10 −3 min −1 and R 2 values 0.9904 and 0.9885 respectively. SEM along with EDX analysis clearly reveal that the salts recovered from Electrooxidation treated RO-RWS show better crystallinity than the salts recovered from untreated RO-RWS. Cyclic voltametric and electrochemical impedance spectroscopic analyses confirmed the oxidation of organics in RO-RWS. The outcome of these experiments has shown that AOPs have promise for handling leather industry RO-RWS, which can significantly lessen the environmental effect of tanneries and contribute to circular economy. • TiO 2 and Graphite electrodes were highly effective to treat high TDS wastewater. • Electro-oxidation removes 92 % of organics and 77 % of nitrogen from wastewater. • SEM-EDX analysis have confirmed the purity of MAP crystals. • Cyclic voltammetry and Impedance analysis confirmed the oxidation of organics. • Approximately 4 % of salts recovered from the treated RO reject waste streams.