Selection of the most suitable ultrafiltration membrane for water disinfection in developing countries

One of the most critical problems in developing countries is the lack of drinking water. People in these regions are supplied with surface water, which contains a significant amount of microorganisms that can cause several diseases. In fact, one of the main causes of infantile mortality is the high incidence of diarrhoeic diseases and other illnesses related to impure drinking water. Ultrafiltration (UF) is a pressure-driven membrane process that separates on the basis of size and can remove bacteria and viruses from water. Therefore, UF can be applied for disinfecting water, avoiding some illnesses or epidemics where people consume ultrafiltrated water. The Chemical and Nuclear Engineering Department of the Polytechnic University of Valencia in Spain is working in cooperation with a non-governmental organisation to develop a system to make water drinkable in a region of Ecuador. The system consists of an UF plant with one spiral-wound module, equipped with a pressure pump driven by a petrol engine. Before the application of the process, the UF plant has to be completely tested and fine-tuned in order to assure that it will successfully perform once in Ecuador. One of the stages of these preliminary tests was the selection of the most suitable UF membrane from the point of view of kind of material and cut-off, bearing in mind the following points: quality of ultrafiltrated water, performance conditions, membrane fouling and cleaning and maintenance conditions. This paper describes the preliminary tests carried out with different UF membranes to select the most suitable one for disinfecting surface water.

UF membranes made of different materials and with a cut-off within a range of 10 and 100 kDalton were found to be very successful from the point of view of bacteria removal from surface water with different microbiological contents. All the tested membranes showed bacteria rejection values of 100%, with no difference with regard to membrane material, membrane cut-off, working pressure or feed water characteristics. Thus, all the tested membranes can be successfully applied to water disinfection. In relation to permeability, tested UF membranes with a cut-off equal to or higher than 30 kDalton produced very similar permeate fluxes, but the permeability of the acrylonitrile membrane was even higher than the permeability of polysulfone membranes in some experiments. Thus, it can be said that acrylonitrile membranes are more suitable for treating surface water because of higher permeability performance and higher resistance to free chlorine.