Biofouling reduction for improvement of depth water filtration. Filter production and testing

Water is a strategic material. Recycling is an important component of balancing its use. Deep-bed filtration is an inexpensive purification method and seems to be very effective in spreading water recovery. Good filter designs, such as the fibr ous filter, have high separation efficiency, low resistance for the up-flowing fluid and high retention capacity. However, one of the substantial problems of this process is the biofouling of th e filter. Biofouling causes clogging and greatly reduces the life of the filter. Therefore, the melt-blown technique was used for the formation of novel antibacterial fibrous filters. Such filters are made of polypropylene composites with zinc oxide and silver nanoparticles on the fiber surface. These components act as inhibitors of bacterial growth in the filter and were tested in laboratory and full scale experiments. Antibacterial/bacteriostatic tests were performed on Petri dishes with E. coli and B. subtilis. Full scale experiments were performed on natural river water, which contained abiotic particles and mutualistic bacteria. The filter performance at industrial scale conditions was measured using a particle counter, a flow cytometer and a confocal microscope. The results of the experiments indicate a significant improvement of the composite filter performance compared to the regular fibrous filter. The differences were mostly due to a reduction in the biofouling effect

Electret filters, production and properties; proceedings of the international workshop on electret filters, production and properties, Warsaw, Poland, January 29 and 30, 1999.

particulate matter from a gas stream. Rational design of the filtration process should be based on reliable prediction of the effluent concentration and pressure drop for a given set of operating conditions. Moreover, both of these main filter parameters vary in time when a fibrous structure becomes more and more loaded with deposits. Usually, fibrous filters with a very high porosity can assure a long Iife-time for a given level of pressure drop and filtration efficiency and therefore the basic issue is an improvement of the clean filter characteristics, that is an increase of filtration efficiency maintaining a low pressure drop. One of the promising methods is an application of electret fibers in the filter structure. Electret fibers have a "built-in" electric charge and they preserve this charge for a very long time. Due to the electret characteristics of the fibers, additional forces of e1ectrical nature act between them and particles. The collection of submicron particles is considerably improved. Efficient and highly porous electret filters of low flow resistance are preferably used in respirators, clean room filters and ventilating systems. To stimulate an interdisciplinary discussion, Warsaw University of Technology (Prof.dr.L.Gradon) and Delft University of Technology Dr.irJ.C.M.Marijnissen) organised a Workshop on "Aerosol Filtration in Electret Fibrous Structures". The Workshop was held in the historical Jablonna Palace near Warsaw, Poland, January 28-30, 1999. This Workshop tried to bring together different disciplines to get a complete view of electret formation, nonsteady-state filtration in electret filters, filter testing and industrial application of electrets. All this information is necessary to produce optimal structures of filters. This book contains the proceedings ofthe Workshop, and it includes an additional discussion on the application ofbiodegradable polymers for fibrous filters formation