PARIS -- The deterioration of natural water resources and the change in standards for water quality are leading to the development of membrane technology in the treatment of drinking water. Today in France, industrial facilities based on this method are functioning, such as at Vigneux-sur-Seine outside of Paris, where Suez-Lyonnaise des Eaux has installed its Cristal¨ technology in a 1.95 million cubic ft/day treatment plant. Vivendi, formerly Compagnie Generale des Eaux, the country's other major water treatment company, is building a 7.1 million ft3/day plant near Paris that will use nanofiltration membranes.
One claims to serve 88 million people, the other 73 million: Vivendi and Suez- Lyonnaise des Eaux are neck-and-neck in the water industry worldwide, as they are in France. Neither company has direct competitors in France that can offer such comprehensive service in the water sector. Over the years they have broadened their role as producers and distributors of drinking water to include the collection and treatment of waste water. Today their areas of development also include the management and protection of resources.
To respond to the diversity of international demand, both companies have a number of subsidiaries and links with numerous partners, in industry and with universities. Vivendi, for example, has research groups in the United States, Great Britain, and Australia, and collaborates with the University of Hong Kong.
In 1998, Suez-Lyonnaise des Eaux reorganized its research resources with the creation of two new centers. Based in the town of Le Pecq in the Paris region, Cirsee remains its main site. In Newcastle in the United Kingdom, the Northumbrian Lyonnaise Technology and Research Center (NLTRC) is more particularly concerned with the management of the infrastructure of networks for the distribution of mains and waste water. In Kuala Lumpur, the capital of Malaysia, the Asian Technology and Research Network (Astran) coordinates the work of several research centers in the Asia-Pacific region, specializing in the development of innovative technologies for water resource management.
The first research on the use of filtration membranes in the field of drinking water started in 1985, within the framework of the European Eureka and Esprit programs. Numerous tests were carried out over several years on small-scale systems before proceeding to larger installations. The advantages of using membranes are now well known. These thin, semi-permeable materials hold back a wide range of micropollutants, such as pesticides and pathogenic organisms, and make it possible to reduce the use of chemical reagents. Depending on their pore size, membranes can be used for microfiltration, ultrafiltration or nanofiltration.
Nanofiltration
Vivendi chose nanofiltration to meet the needs of the Syndicat des Eaux d'lle de France, the organization responsible for supplying drinking water to Paris and its suburbs, in its project for the expansion of its Mery-sur-Oise treatment plant. Approximately 7.1 million cubic ft/day of surface water will be treated by passing it through nanofiltration membranes. It is scheduled to enter service at the end of 1999.
An experimental nanofiltration unit (99,000 cubic ft/day) is already in operation at this site and supplies the inhabitants of the town of Auvers-sur- Oise. Nanofiltration is used for purifying drinking water, and replaces both ozonation and filtration over activated carbon. The extremely fine pores of the membrane act as a physical barrier to many substances dissolved in the water, which is injected into the membrane and circulates in a spiral towards its center. By tangential filtration, under the effect of a large pressure difference between the two faces of the membrane, some of the water passes through the membrane, leaving behind most of the material that it originally contained. Left behind are micropollutants such as pesticides, organisms most resistant to the usual disinfectants, and also organic matter likely to encourage the development of bacteria in water distribution systems. This softened water then needs to be remineralized. Nanofiltration has also shown good results on water containing sulfates, which has been proven at a purification facility in Jarny, in eastern France.
Immersed Membranes
Other developments relate to the use of ultrafiltration membranes which consist of hollow fibers that are directly immersed without a pressure casing. Filtration takes place inwards from the outside of the membrane. This technique is known as Biosep¨ and has just been installed by OTV, a subsidiary of Vivendi, in a small unit supplying drinking water to the town of Ocana on the Mediterranean island of Corsica.
Ultrafiltration And Powdered Activated Carbon
In 1997, at Vigneux-sur-Seine, Suez-Lyonnaise des Eaux installed its Cristal¨ purification technology to supply 1.95 million cubic ft/day of water to some 200,000 inhabitants in the southeastern region of Paris. The Cristal technology combines ultrafiltration membranes with powdered activated carbon, with the water to be treated coming from the Seine River. After clarification and oxidization, it is mixed with activated carbon and then injected under pressure through ultrafiltration membranes.
The water passes through the minute pores which trap micropollutants (bacteria, viruses, pesticides and other organic matter). Combining the two techniques makes it possible to remove particles down to 0.01 micron in size as well as smaller material that is adsorbed by the activated carbon. Only mineral salts, essential for good taste and the balance of the water, can succeed in passing this barrier. The disinfectant properties of membranes make it possible to reduce the quantity of chlorine used in the plant by a factor of ten.
These membranes were developed in the city of Toulouse in southwestern France by Aquasource and manufactured by Degremont, two subsidiaries of Suez- Lyonnaise des Eaux. They provide three acres of filter surface divided into 224 modules. Each module consists of 15,000 hollow porous fibers, measuring 4.3 feet in length, grouped in seven bundles.
Fifty plants using membranes have been built by Degremont to date. The total capacity installed by Suez-Lyonnaise des Eaux in 1999 should reach 12.4 million cubic ft/day. Although this still only represents 5 percent to 10 percent of production, taking all water purification technologies into account, growth is accelerating, since the number of units has nearly doubled over the last four years.
To increase the performance of this technology, work is being carried out on the configuration of the modules. Instead of being tangential the filtration method could be a barrier membrane, thus reducing the circulation of water. The use of easily interchangeable disposable membranes is also being considered. The objective is to reduce the cost of membrane technology to that of conventional processes (about $5/ft3/day) for large industrial plants that handle at least 35 million cubic feet of water per day.
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