GB2239452A

GB2239452A - Treating water with chlorine and ozone

Info

Publication number: GB2239452A
Application number: GB8929341A
Authority: GB
Inventors: Ian A Wray
Original assignee: Barr & Wray Ltd
Current assignee: Barr & Wray Ltd
Priority date: 1989-12-29
Filing date: 1989-12-29
Publication date: 1991-07-03
Also published as: GB8929341D0

Abstract

Treatment of chlorinated water to remove impurities utilises injection of ozone at a treatment station 13 to remove oxidisable impurities and subsequent passing of the treated water through a de-ozonising medium 14A to remove residual ozone. The ozone is injected on a discontinuous basis to enable the chlorine content of the water to penetrate the bed of de-ozonising medium for sterilisation thereof. Chlorine may be injected at 15. <IMAGE>

Description

METHOD OF WATER TREATMENT This invention relates to water treatment.

Treatment of water is known where the water is for potable purposes or where the water may be inadvertently consumed, as for example is the case with swimming pool water. Known treatments involve dosing the water with a suitable chlorine content and removing particulate and oxidisable impurities, the latter by ozone injection.

Chlorine prevents build-up of bacteria in the water.

It has however been found that there is a tendency for bacteria to build-up in the de-ozonising beds of the treatment station and it is an object of the present invention to provide a new and improved treatment process which obviates or mitigates this disadvantage.

According to the present invention there is provided a method of treating chlorinated water to remove impurities from the water, comprising delivering water to be treated to a treatment station having a bed of de-ozonising medium, injecting ozone into the water at the treatment station to remove oxidisable impurities and subsequently passing the treated water through the bed of de-ozonising medium to remove residual ozone from the treated water, wherein the improvement comprises injecting the ozone on a discontinuous basis to enable the chlorine content of the delivered water to penetrate the bed for sterilisation thereof.

Preferably the de-ozonising medium allows at least some of the chlorine content of the water to be retained in the purified water emergent from the treatment station. The medium may be a form of treated coal such as Hydroanthrazit or manganese dioxide. The de-ozonising bed may be associated with or form part of one or more filter beds for removing particulate water impurities.

It will be appreciated that in addition to oxidising oxidisable impurities ozone also oxidises chlorine and whereas conventional water treatment systems provided a chlorine injection system subsequent to the residual ozone removal this may not be required in accordance with the present invention since the discontinuous or intermittent injection of ozone permits, and is designed to permit, intermittent flow of chlorinated water through the bed.

Thus the water emergent from the treatment station contains chlorine, at least on an intermittent basis, and this is sufficient to disinfect the bed and prevent bacterial build-up.

The precise timing of the discontinuous basis of ozone injection is dependent upon a large number of factors, including flow rates, volumes, distances and bed thickness and requires to be evaluated on a case by case basis. It is believed that a typical discontinuous basis would be ozone on SO minutes; ozone off 10 minutes per hour.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawing.

In the drawing a water treatment plant 10 is associated with a swimming pool 11 which contains a volume of chlorinated water 12. Water is continuously drawn from pool 11 and delivered to plant 10 which comprises an ozonator 13, a vessel 14 (which may be a pressure vessel) incorporating filter and ozone removal beds 14A, 14B, 14C and a chlorine injector 15 the output from which is returned as pure water to the pool 11.

In accordance with the present invention ozonator 13 is controlled by an ON/OFF control signal 16 so that ozone injection is discontinuous. Vessel 14 has beds 14B, 14C, for example made of sand for filtering out non-oxidisable particulate material from the water and bed 14A for removal of residual ozone, bed 14A preferably being made of Hydroanthrazit or manganese dioxide.

When control signal 16 is continuously ON as in the prior art it has been found that the beds 14A, 14B, 14C tend to accumulate a bacteria build-up. It is believed that this arises because the ozone injection in addition to oxidising oxidisable impurities also oxidises the chlorine content of the water 12 whereas in accordance with the present invention when signal 16 is suitably discontinuous sufficient chlorine content reaches the lower parts of the beds 14A-14C to sterilise the beds 14A-14C, thus eliminating any bacterial problems.

Claims

1. A method of treating chlorinated water to remove impurities from the water, comprising delivering water to be treated to a treatment station having a bed of de-ozonising medium, injecting ozone into the water at the treatment station to remove oxidisable impurities and subsequently passing the treated water through the bed of de-ozonising medium to remove residual ozone from the treated water, wherein the improvement comprises injecting the ozone on a discontinuous basis to enable the chlorine content of the delivered water to penetrate the bed for sterilisation thereof.

2. A method as claimed in claim 1, wherein the de-ozonising medium allows at least some of the chlorine content of the water to be retained in the purified water emergent from the treatment station.

3. A method as claimed in either preceding claim, including the step of injecting chlorine subsequent to the residual ozone removal.

4. A method as claimed in any preceding claim, wherein the ozone is only injected for 50 minutes per hour and on a discontinuous basis.