The removal of selected pharmaceuticals from a municipal membrane bioreactor secondary effluent with an electrochemical oxidation process

Abstract

Municipal secondary membrane bioreactor (MBR) wastewater effluent in South Africa (SA) contains various types of pharmaceuticals that form part of a class of chemical contaminants of emerging concern (CECs). These contaminants cause harmful influences on the natural environment. While typical tertiary remedy methods efficiently remove micropollutants, residues of these products exist in water masses at low concentrations, emphasising the need for additional treatment. Advanced, pioneering and sensitive analytical technologies are needed to identify their low concentration in complex matrices such as MBR secondary wastewater. Under these circumstances, electrochemical oxidation (EO) is a possible solution for removing pharmaceuticals. This study investigates the removal of inorganics and pharmaceuticals in secondary municipal MBR effluent. A lab-scale EO unit with Ti/Pt and Ti/ IrO2Ta2O5 electrodes was used. The EO process produced effluent discharge for recycling application. Three pharmaceuticals were selected, i.e., ibuprofen (IBU), carbamazepine (CBZ) and diclofenac (DCF). IBU and DCF are from the same pharmaceutical group, a non-steroidal anti-inflammatory drug (NSAID), while CBZ is from the anti-epileptic group. Ammonia and COD were also treated in this process. The electrochemical oxidation process with Ti/Pt and Ti/IrO2Ta2O5 electrodes was applied to treat the secondary municipal MBR effluent in a batch reactor at constant pH of 4 and a working volume of 3L. The electrolyte (NaCl) concentration and current density were varied at room temperature. At a current density of 10 mA/cm2 and 0.08M electrolyte anode, Ti/IrO2Ta2O5 showed better results than Ti/Pt for CBZ, DCF and IBU of more than 99% pharmaceutical removal. The inorganic ammonia compound was successfully removed at a maximum removal of 99% (Ti/IrO2Ta2O5 anode) and 75% (Ti/Pt anode). However, Ti/Pt has a maximum reduction of 86% for COD. A Response Surface Methodology (RSM) and central composite design (CCD) characterised the electrochemical oxidation experiments. Polynomial quadratic models were successfully developed to remove COD, ammonia, and colour. Their removal was found to be significant.