Photocatalytic membrane modules for drinking water purification in domestic and community appliances

Abstract

In the present paper, the performance of a pilot plant for domestic use was investigated, able to operate continuously, and in which tap water was fed (inorganic carbon IC: 81.6±0.5 ppm; total organic carbon TOC content: 1.52±0.02 ppm). This plant produced 130 L/d of purified water. The tap water was first subjected to a prefiltration by a membrane microfiltration unit, followed by filtration through a membrane immobilising activated carbon, then through a reverse osmosis membrane, at a transmembrane pressure of 4 bar, and finally through a photocatalytic membrane unit, constituted by a metallic membrane, onto which the semiconductor and its photopromoters were present as a 3–4 μm thick surface layer, directly produced on the nanotechnologically treated surface of this membrane, irradiated at a power of 9.6 W in the range of optical absorption by semiconductor. Efficiency of these operations was compared by carrying out parallel experiments, using two other commercial plants (I and II), in which the photocatalytic treatment was not provided for. All the three plants were able to soften the tap water down to 6–8ppm IC, but, as regards TOC, (I) yielded a purified water still containing 1.12±0.05 ppm of organic carbon, and (II) 0.908±0.0095 ppm, while the TOC content of water purified in the pilot plant of present work was lowered down to 0.06±0.02 ppm. In order to compare further efficiency of these plants, a simulated feed solution was treated, containing 3.05 ppm of humic acids, or 2.16 ppm of atrazine, or 4.23 ppm of symazine. Reverse osmosis, which was present in all the three kind of plants examined, even if coupled with active carbon adsorption, was not able to remove entirely contamination due to organic micropollutants. This goal, on the contrary, was successfully achieved by the plant fitted with the photocatalytic membrane unit, particularly by considering that this plant showed substantially the same abatement efficiencies of plants (I) and (II), if the photocatalytic unit was switched off.