Reactive electrochemical membrane for the elimination of carbamazepine in secondary effluent from wastewater treatment plant

Abstract

This study evaluated the feasibility of the electrooxidation process using a sub-stoichiometric titanium oxides (TiOX) reactive electrochemical membrane (REM) as anode for the treatment of a secondary effluent from a wastewater treatment plant. The main objectives were to analyze (i) the degradation of a pharmaceutical pollutant, carbamazepine, added at a concentration of 100 µg L−1, (ii) the mineralization of the residual total organic carbon (TOC = 7 mg L−1), (iii) the formation of toxic by-products and (iv) the energy consumption of the REM process. Two main operating parameters were tested: the current density applied to the REM (74, 149 and 290 A m−2) and the flux of TOC passing through the membrane. The results revealed that the efficiency of the process was maintained above 70% of mineralization and >98% of degradation of carbamazepine until a limiting value of TOC flux was reached. The higher the current density, the higher the limiting value of the TOC flux above which the efficiency decreased. This trend was ascribed to the limitation from the amount of reactive species produced on the REM surface (current limitation instead of mass transport limitation at lower TOC flux). As the energy efficiency strongly increased when applying a higher TOC flux, it is therefore crucial to apply the process around this threshold value. This study also showed that it is possible to control the formation of toxic chlorine-containing by-products (ClO3−, ClO4−, AOCl) by decreasing the current density. This issue is particularly important for such effluents containing a significant amount of Cl− ions. By taking into consideration both advantages and drawbacks, optimal results were obtained with the lowest current density of 73 A m−2 and a TOC flux through the membrane of 4.41 g h−1 m−2 corresponding to 1.34 m3 h−1 m−2. These conditions allowed for >98% degradation of carbamazepine and 70% of mineralization with an energy consumption of 0.15 kWh g−1 of TOC removed (i.e. 0.74 kWh m−3 of treated wastewater).