Liquid purification or separation – Processes – Utilizing electrical or wave energy directly applied to...
Patent
1998-02-23
2000-01-25
Hruskoci, Peter A.
Liquid purification or separation
Processes
Utilizing electrical or wave energy directly applied to...
204237, 204248, 204269, 204293, 205745, 205760, 205751, 210764, 210765, 210101, 210169, 210192, 210206, 210253, C02F 1467
Patent
active
060174617
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to water purification systems.
Water supplied by public utilities is normally treated to reduce the micro-organism content to safe levels. However, in many water-using systems, it is possible for micro-organisms to grow. Among the conditions which favour this are the maintenance of water in static form (so that micro-organisms can build up), warmth, light. and the possibility of the accumulation of contaminents on which the micro-organisms can feed.
The control of such micro-organisms in water is therefore often of major importance. In swimming pools, the control of algae is required for both safety and esthetic reasons, in air conditioning systems, the control of bacteria such as Legionella pneumophile is a well-known requirement; and in commercial and industrial water systems (and especially in hospitals and similar establishments) which distribute water for cooking, drinking, and/or washing purposes, there is also often a need for active control of micro-organisms.
Various techniques for water purification in such systems are known.
One known technique consists of the introduction of suitable metal ions into the water. In particular, silver ions are an effective bactericide and copper ions are on effective fungicide. Suitable ion concentrations are typically in the region of 0.01 to 1 ppm (parts per million). The technique is sometimes termed electronic water purification, as such ions can be introduced into the water electrolytically, by using anodes of silver and copper. This is typically achieved by recirculating the water to be treated through a chamber containing the anodes, though in some situations the water may be treated as it is introduced into the system.
This technique has certain advantages over other techniques such as the addition of chemical biocidal compounds. In suitable circumstances the metal ions are maintained indefinitely in the water until an organic mass such as bacteria and algae absorbs them, and their concentration is normally low. However, this technique suffers from various disadvantages, since it is dependent on a variety of factors which influence the efficiency of ion production. These factors include the chemical make-up of the water, its pH, the levels of other metals present, the presence of any organic matter, and any chemical reactions that have taken place. All of these can have a considerable effect on the measurable results. Some will affect ion production rate dissimilarly for the different metals (eg silver and copper) of the anodes. Others will cause chemical conversion, drop-out of ions, or absorption of the metals.
Considering some of these matters in more detail, if the circulation over the anodes is not sufficient, released hydrogen may not be cleared; this may result in the formation of gas pockets in the chamber, and there are potential formations of chemical combinations on the anodes which inhibit ion release. In hard water areas, scale tends to build up on the anodes, inhibiting ion release. With very hard water, such as in a poorly maintained swimming pool, the hardness may also, in combination with high pH (high alkalinity) causing over-saturation of the water, result in the copper falling from its ionic state. Also, if chlorine is present in the water, especially at the levels accepted as good practice in swimming pools, copper chloride and other salts can build on the anodes; this is noticeable on the non-ionizing faces of the anodes, especially when the circulation rate is low. The water temperature also effects the contact time for silver ions to kill bacteria; in hard water the kill time for Legionella pneumophila is reduced by 60% for a temperature rise from 20.degree. C. to 39.degree. C.
In addition, the efficacy of the metal ions depends on a variety of factors. Thus the hardness (level of calcium) in the water affects the time taken to kill micro-organisms; for hardness in the range 0-400 ppm, the time for a 99.9% kill increases by about 200 g for each 10 ppm increase in hardness at 20.degree. C., pH 7.0. For c
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Garvey Ernest Sydney
Reid Randolph Euan Irvine
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