Developments in Filter Technology for Appropriate Water Treatment
Water is increasingly a precious resource, so suitable treatment of municipal or industrial waste water is vital to realize maximum water recyclability, while reducing the use of valuable drinking water, processed at a high cost. Efficient treatment of used, or non-potable water is important to reduce costs, and to enable companies to satisfy self-imposed or legislated environmental targets.
Using filtration to remove solid contaminants is a vital element in the water treatment process. The contaminants can be inorganic or organic particles, or mud; and may be waste products of industrial processes - in the case of used water - or may be particles found in river water or sea water extracted for industrial use.
For both cases filtration media has been subject to severe demand from the nature of contaminants present in water. Any sand or grit present will considerably increases the abrasiveness of the water being used, posing significant physical challenges on the materials employed in the filtration process.
The filtration process becomes unreliable when the erosion effects reach such high levels that the filter fails, so it should be made of materials strong enough to bear the harsh abrasives present in the water.
It is also necessary to consider the chemical effects of the water being processed through the filtration media. Process water may contain aggressive chemicals, or could be highly alkaline or acidic, all of which is a result of how the water has been previously used. Any chemical additives can corrode and cause damage to the filter, eventually affecting the process of filtration itself.
The filtration media's ability to ensure the process water has a good flow through the membranes should be considered. This characteristic, called flux property, is important to allow a good flow of the process water at the desired rate. However, the water flow should not be at a rate so high it impacts the filtration process quality, or builds up system pressure to the extent that machinery, including the filter, is damaged.
Undetected or premature filter failure can have huge implications for other processes in addition to filtration, leading to gradual or complete damage to downstream plant and equipment, bringing water processing to a complete halt. Other processes may be impacted, and all production areas can halt due to lack of water. Any form of failure causes a subsequent delay in water processing until replacing the filter.
The selection of filter materials is crucial because of these reasons. In addition, inappropriate filter specifications can reduce filter life, unnecessarily increase the pumping pressure, which results in higher energy usage, costs and environmental footprint.
Conventionally, filter materials preferred by specifiers for such applications have been either metallic or polymeric. However, neither are able to provide the required performance levels in the three key areas: chemical resistance, mechanical resistance and flux properties.
This factor and the quest for increased reliability and additional capacity in water processing have made filter manufacturers explore alternative materials to satisfy the three requirements, without any change in the quality of filtration.
Two new ceramic materials have been developed recently for use in filtration media. Ceramics are non-metallic and inorganic materials, made up of a metal and a non-metal, and are formed by heating and the subsequent cooling. They have a better stiffness and strength in comparison to polymers or metals. Alumina (Al2O3) allows the formation of fine pore sizes, which is vital when purity is of importance. Silicon carbide (SiC) has better resistance to corrosion and abrasion, making it ideal for treating water consisting of aggressive particles or chemicals.
As well as these three properties, filter specifiers should also consider the materials that have to be removed from the media, the design – generally the option is between a flat filter or tubular filter – and the cost of the system. The new material should be compatible with other equipment in order to provide optimal filtration performance. Some ceramic filter suppliers are now providing complete systems, consisting of a membrane layer and a carrier.
Specifiers now have many choices for a durable solution that provides uniform filtration performance with a prolonged service life.
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