WATER PURIFICATION PROCESS AND SYSTEM
Field of the Invention
This invention relates to a water purification process and system, and more particularly a process and system involving filtration and ultraviolet irradiation of a contaminated water supply.
Background of the Invention
The provision of safe, clean drinking water is one of the biggest challenges facing governments throughout the world. Most often the naturally occurring sources of water will have become hopelessly polluted, and cause chronic health problems amongst populations who are dependant on the water supply. There have been many efforts made towards alleviating the problem, including schemes as will now be described.
Most processes and systems of the filtration and irradiation type incorporated into town water mains supplies are utilised in the water line at the point of use, and involve passing water through a treatment system only once and delivering the water at mains pressure.
These known processes and systems involve passing the water through one or more (usually not more than three) water filtering cartridges followed by ultraviolet irradiation to provide bacterial control, or more simply ultraviolet irradiation and no filtration. These processes and systems have advantages in that the delivery of water is at mains pressure and does not need additional equipment, are usually uncomplicated and therefore easy for the user to service. However, the disadvantages are: (a) One pass only through the filters.
(b) Unless filters are situated at the dedicated point of use, or all water treated is used within a short time after passing through the filters, treated water
becomes easily contaminated because all residual disinfection medium has been removed (providing the filter or filters have been effective) .
(c) Where ultraviolet equipment is installed disinfection is doubtful unless the equipment has been given time to warm up to operating temperature, which is approximately 42 °C. Waiting time is from one to two minutes, but the user wants to have water at the turn of the tap and usually will not wait; furthermore the equipment cannot be left energised without water flow.
(d) Where ultraviolet equipment is installed without the benefit of prefiltration, the effectiveness of the ultraviolet irradiation is proportional to the optical clarity of the water passing through the equipment. (e) The filters can become clogged with bacteria.
One other known system, installed in a high rise hotel, services approximately 20 floors. The main lower floors of the hotel which contain the restaurants, bars and catering kitchens are not serviced by this system, rather are serviced directly from the town water main supply. The system is installed on one of the upper floors of the hotel and comprises the following:
(a) Mains water is passed through four activated carbon filters housed in glass reinforced plastic of 910 mm diameter by 1800 mm height and connected in parallel via pipework manifolds. Each filter has a service flow of 9.0-19.0 m3/h.
(b) Storage tank with holding capacity of 100,000 1 where water is deposited after passing through the filters. (c) Gravity feed water from the storage tank flows as required, into an ultraviolet treatment plant comprising three large single ultraviolet tube chambers of stainless steel stand 1300 mm high and are 200 mm in diameter. Each has a capacity to treat 22 m3/h of water. (d) Gravity feed water leaves the ultraviolet treatment plant and passes into the building service pipes to eventually arrive at the point of use.
This system is simple in nature and simple to maintain, and because of gravity feed requires no pumping equipment. However the disadvantages are:
(a) Cannot provide filtered water delivered to the point of use as a 100 percent disinfected quality potable water.
(b) Glass reinforced plastic material is not suitable for potable water. The mix of chemicals in the manufacture of the plastic are in fact toxic materials in so far as potable drinking water is concerned, and do not have a
World Health Authority approval for containment and contact with potable drinking water.
(c) Activated carbon material in unprotected filters are very vulnerable to bacterial invasion, and backwashing with water will not remove bacterial contamination.
(d) Activated carbon absorbs chlorine and other contaminates, and backwashing will not restore filter media to new condition.
(e) Activated carbon filters are not suitable for use as particle filters, and therefore no suspended solids are removed by this system.
(f) During backwash and rinse cycles, each filter requires ten minutes at 19.8 m3/h for backwash, and six minutes at 9.0 m3/h for the rinse cycle. (g) The system provides no treatment for water in storage, and unprotected storage tank hold the water, which after activated carbon filtration should contain no disinfecting chloramines residuals. The quantity of water is also too great to keep in a disinfected condition by radiation means, and as such stored water is subject to extreme bacterial and viral contamination.
(h) Treated water, after being subjected to ultraviolet irradiation may be unused for days (depending on hotel occupancy) , and stored in the reticulation pipes of the tower without movement, and as such is subject to bacterial contamination becoming low quality water.
One other known process and systems involves a reverse
osmosis process which provides a high purity water source and is ideal for pretreatment of ion exchange deionisation to make pure water. This combination is economically attractive and offers several technical advantages, and may also be used for water pretreatment for boiler feed, cooling tower makeup, and wash water of essentially zero hardness.
However, water produced by this process is vulnerable to bacterial contamination and has to be protected from bacterial contamination if it is not immediately used, although water produced by this method can be used as the supply source for the system of the present invention. Water produce by the reverse osmosis process, is not recognised as good tasting drinking water.
It is therefore an object of the present invention to provide a water purification process and system which is not subject to, or at least minimises, the disadvantages of the known purification processes and systems discussed above.
Statement of the Invention
The invention therefore envisages, in broad conceptual terms, a water purification process in which water to be purified is firstly filtered and subjected to ultraviolet irradiation before being supplied to a storage tank from, and to, which it is periodically recirculated through a further filtering and ultraviolet irradiation system to repurify the stored water.
The invention also envisages a system or plant for carrying out the process of the present invention.
Therefore, the invention can be said to reside in a method for the purification of contaminated water, comprising the steps of:
passing a supply of the contaminated water through a first purification system having filter means and ultraviolet irradiation means to purify the water; storing the purified water in a storage tank; and periodically recircμlating the stored water from, and back to, the storage tank through a second purification system having filter means and ultraviolet irradiation means to periodically repurify the stored water.
The invention can also be said to further reside in apparatus for the purification of contaminated water, comprising: a first purification system having filter means and ultraviolet irradiation means through which a supply of contaminated water passes to be purified; a storage tank which receives and stores the purified water from the first purification system; and a second purification system connected in recirculating fashion to the storage tank which receives water stored in the tank and returns the water to the tank after it periodically passes through filter means and ultraviolet irradiation means to repurify the stored water.
Description of the Drawing and a Preferred Embodiment
A preferred embodiment of the invention will now be described with reference to the accompanying figure, which is a schematic illustration of an embodiment of a system constructed in accordance with the invention.
The system of the embodiment is intended to provide a consistent, high pressure supply of water to establishments such as motels, hospitals, laboratories and food processing factories. It could also provide a centralised source of purified water for a population who otherwise have only very poor quality water.
Referring then to Figure 1, it can be seen that there
is a supply of contaminated water, which could be either from a town water supply or from some other source such as a river or reservoir. The supply water is initially passed through a non-return valve 1 which functions to prevent water from escaping the system. The contaminated water then passes through a pressure limiter 3 adapted to prevent excessively high pressure surges in the system, before passing through a solenoid blocking valve 4.
The supply water is then treated before passing to the storage tank 6. The type and configuration of the treatment depends on the chemical and microbiological make¬ up of the supply water. The treatment is firstly a filtration directed to removing micro-organisms and particulates such as silt, dirt, rust, fine colloids, and to reduce organic contaminants, chlorines and chloramines. The filtration process is achieved by a series of filters 5. The filters may typically be of the activated charcoal cartridge type. The filters have step-wise reducing pore size down to 0.8 microns, which results in less chance of clogging and a lower opportunity for breakthrough' by micro-organisms. Even so, it is quite acceptable to have only the one filter stage. Ultraviolet disinfection is then performed to reduce bacterial numbers in the supply water typically to be less than 1 organism per ml, and is achieved by the ultraviolet modulator 2 to produce purified water which is passed to the storage tank 6.
The storage tank 6 is enclosed and lined with an inert material, while the air space contains air which has been subjected to ultraviolet radiation. The purified water in the storage tank 6 is stored for the purpose of reticulation for use. As will become apparent from what follows, the purified water is also subject to periodical recirculation for the purpose of repurification.
In use for reticulation, purified water is drawn from the storage tank 6, passing a non-return valve 14 to a
centrifugal pump and in-line pressure tank 7. The pump/tank 7 provides the requisite supply pressure at the faucets 15 of the ring main 13 to allow the purified water to be drawn off. Reticulation is facilitated by a series of conduits 9 which are normally closed to flow by a solenoid valve 8. With the solenoid valve 8 closed, the pump 7 pressurises the conduits 9 to the desired operating pressure. As noted, water can be drawn off by any one of many faucets, and as water is removed a sensor on the pump 7 or within a conduit 9 senses the drop in water pressure and activates the pump 7 to effect repressurisation to the desired delivery pressure. Preceding the points at which water is drawn from the ring main 13, the water passes through a series of filters 10 and an ultraviolet modulator 11 where further purification or polishing takes place.
The filters 10 may be of the same type as those referred to above, or may be specifically chosen in accordance with the requirements of the end user. As the water level in the storage tank 6 decreases with reticulation it will be replenished from the mains supply by appropriate control over the solenoid valve 4.
Considering now the recirculation function. According to a determinable time sequence, the solenoid valve 8 periodically activates to allow recirculating flow, whereafter the resulting drop in pressure in the conduits 9 causes the pressure sensor to activate the pump 7 and recirculate pump water from and back to the storage tank 6. During recirculation the water is subjected to still further bacterial control as it passes through a further ultraviolet modulator 12 before passing back into the storage tank 6. That is, independently of water being drawn off for reticulation, the water in the tank 6 is regularly drawn from the storage tank 6 and recirculated to provide regular filtering and bacterial control. In most cases the time period for which the solenoid valve 8 is opened will allow the whole volumetric content of the storage tank 6 to recirculate, thereby repurifying all the
stored water. The time between recirculation events may typically be 20 minutes, thereby to avoid reinfection or problems in taste of the stored water which results from lack of oxygena ion.
It is to be understood that the invention includes any modifications that would be envisaged by a person skilled in the art and which do not depart from the spirit of the invention, and any such modifications are to be considered within the scope of the invention.