Dual function filtration and catalytic breakdown of organic pollutants in wastewater using ozonation with titania and alumina membranes

摘要

Water recycling via treatment from industrial and/or municipal waste sources is one of the key strategies\udfor resolving water shortages worldwide. Polymer membranes are effective at improving the water quality\udessential for recycling, but depend on regular cleaning and replacement. Pure ceramic membranes\udcan reduce the cleaning need and last significantly longer in the same applications while possessing the\udpossibility of operating in more aggressive environments not suitable for polymers. In the current work,\udfiltration using a tubular ceramic membrane (�-Al2O3 or TiO2) was combined with ozonation to remove\udorganic compounds present in a secondary effluent to enhance key quality features of the water (colour\udand total organic carbon, TOC) for its potential reuse.\ud‘Bare’ commercial �-Al2O3 filters (pore size\ud∼0.58 �m) were tested as a microfiltration membrane and\udcompared with the more advanced catalytically active TiO2 layer that was formed by the sol–gel method.\udThe presence of anatase with a 4 nm pore size at the membrane surface was confirmed by X-ray diffraction\ud(XRD) and N2 adsorption. Filtration of the effluent over a 2 h period led to a reduction in flux to 45% and\ud60% of the initial values for the �-alumina and TiO2 membrane, respectively. However, a brief dose (2 min)\udof ozone at the start of the run resulted in reductions to only 70% of the initial flux for both membranes. It\udis likely that the oxide’s functional property facilitated the formation of hydroxyl (OH•) or other radicals\udon the membrane surface from ozone decomposition which targeted the breakdown of organic foulants\udthus inhibiting their deposition. Interestingly, the porous structure therefore acted in a synergistic, dual\udfunction mode to physically separate the particulates while also catalytically breaking down organic\udmatter. The system also greatly improved the efficiency of membrane filtration for the reduction of\udcolour, A254 (organics absorption at the wavelength of 254 nm) and TOC. The best performance came\udfrom combined ozonation (2 min ozonation time with an estimated applied ozone dose of 8 mg L−1)\udwith the TiO2 membrane, which was able to reduce colour by 88%, A254 by 75% and TOC by 43%. It is\udclearly evident that a synergistic effect occurs with the process combination of ozonation and ceramic\udmembrane filtration demonstrating the practical benefit of combining ceramic membrane filtration with\udconventional water ozonation.