A system for purifying the water in a plurality of pools

Abstract: A pool water purifying apparatus and system comprising a filtering means that uses ceramic filters, a disinfecting means and an adsorbing means and, optionally, an ultrafiltration means as an additional filtering means, and are capable of removing not only bacteria but also viruses so that the water purified by this apparatus and system may be as clean as potable water. Such an extremely high efficiency of water purification achieved by the apparatus and system can be maintained over a prolonged period since both the filtering and adsorption means can be cleaned by backwashing. The purifying apparatus is compact but it can be made further compact and allows for simpler installation work if the individual means of purification are integrated into a unitary assembly. The purifying system permits the water in a plurality of pools having different water temperatures to be purified efficiently with a single unit of the purifying apparatus.

Description: BACKGROUND OF THE INVENTION This invention relates to a method of cleaning porous ceramic filters that is applicable to filtration equipment that is capable of effectively removing organics, inorganics and other impurities from pool water and other kinds of contaminated water. The invention also relates to a circulating purification apparatus and a pool water purifying apparatus that use a circulating system which, with the aid of backwashable porous ceramic filters, is capable of effectively removing organics, inorganics and other impurities from circulating water such as pool water and other kinds of contaminated water. The invention also relates to a system of purifying pool water using those apparatus. More particularly, this invention relates to an apparatus for purifying pool water in a circulating manner which, after being assembled in a factory, can be divided into components that can be transported on vans and other vehicles and that can be reassembled on an installation site by connecting them to a desired layout of external piping in a very simple way. The invention also relates to a pool water purifying apparatus that can be used with an ultrafiltration means to insure high performance over an extended period. The invention also relates to a pool water purifying apparatus that is an integral assembly of a porous ceramic filter, an adsorptive purifier, a disinfecting means and other purifying means, and even an ultrafiltration means and which yet is compact and can be installed by simple work. The invention further relates to a system for purifying the water in a plurality of pools including outdoor pools, indoor pools and whirlpools. The term "pools" as used herein includes not only ordinary swimming pools but also whirlpools installed in sports clubs, Kurhaus (spa houses) and healthcare facilities, as well as various kinds of health promoting hot tubs and spas. With the growing concern for physical fitness, many people prefer swimming as an exercise of the whole body that helps promote their health and relieve psychical stress and today an increasing part of the population, irrespective of age and sex, frequently go to swimming pools. In order for people to enjoy swimming in a safe and clean condition, pools must be kept clean, particularly in terms of water quality, and as the use of swimming pools increases, the performance requirements of purifying facilities that determine the quality of pool water are becoming increasing stringent. This is particularly true with indoor pools which are supposed to be used in all seasons because sweat, hair and other foreign matter originating from the human body are potential sources of bacterial growths that contaminate the pool water and deteriorate its quality. Filtration equipment available today adopts various methods to purify pool water. A common method is based on the combination of filtration and disinfection with chlorine or its compounds. Recently proposed methods are disinfection with ultraviolet rays and treatments with ozone. New filter media have also been proposed as substitutes for sand and they are porous filter media exemplified by ceramic filters and activated carbon (see Japanese Patent Application (kokai) No. 143917/1988 and Japanese Patent Application Nos. 311319/1988, 311320/1988, 126035/1989 and 126036/1989). One of the filter media that are drawing particular attention for application to facilities for purifying pool water is a porous ceramic filter. Porous ceramic filters have a three-dimensional network of extremely fine filtering spaces that are advantageous for application to pools, particularly to indoor pools, and are capable of effectively trapping organic matters such as oils excreted from the human body that have cannot be removed with existing filters. The concept of prior art pool water filtering equipment that employs porous ceramic filters is shown in Fig. 4. A cylindrical porous ceramic filter 700 (hereunder referred to simply as "ceramic filter 700") is closed on its top with a lid 702 and fixed in the center of a hollow cylindrical housing 704. An entrance line 708 for introducing water from a pool 706 is connected to the left side wall of the housing and an exit line 710 for recirculating filtered water to the pool 706 is connected to the center of the bottom of the housing 704. A line 712 for introducing filter aids is connected to the right side wall of the housing 704; an air vent 714 is provided on top of the housing 704; and a drain line 716 is connected to the bottom of the housing 704 in a position outside the ceramic filter 700. A back wash line 718 for cleaning the ceramic filter 700 is provided as a branch from the exit line 710. The process of filtering the water in the pool 706 with the filtration equipment shown in Fig. 4 proceeds in the following manner. First, the air vent 714, a valve 720 on the back wash line 718 and a valve 722 on the drain line 716 are closed. Then, a valve 724 on the entrance line 708 and a valve 726 on the exit line 710 are opened and a circulating pump 728 is driven so that the water in the pool 706 circulates through a loop consisting of the entrance line 708, housing 704 and exist line 710 in that order. In short, as the water passes through the ceramic filter 700 in the direction a of a solid arrow, impurities in it are removed by filtration and clean water is returned to the pool 706. As this process of water filtration continues, filter cake builds up on the outer surface of the ceramic filter 700 and clogs its extremely fine voids. If this condition occurs, the filter efficiency will decrease and, in an extreme case, it becomes necessary to replace the whole unit of expensive ceramic filter 700 but this means an extremely high cost since a number of filter units are usually employed. To avoid this problem, it is necessary to clean the ceramic filter 700 periodically by removing the filter cake deposited on its outer surface. Cleaning of the ceramic filter 700 is conventionally performed by backwashing in which a "jet stream" consisting of a mixture of cleaning water and air is supplied at high speed through the back wash line 718 in such a way that the jet stream coming into the ceramic filter 700 passes through it to go outside as indicated by an unfilled arrow b . As shown in Japanese Patent Application (kokai) No. 2252/1973, the back wash line 718 is furnished with a large air tank 729 filled with a large amount of air compressed to a comparatively high pressure and a flush tank 730 partly filled with cleaning water A to one third of its capacity. When a valve 732 provided between the two tanks is opened, the large amount of compressed air in the air tank 729 is jetted into the flush tank 730, where it is mixed with the cleaning water to produce an accelerated jet stream which is introduced into the ceramic filter 700. The process of backwashing for cleaning the ceramic filter 700 in the apparatus shown in Fig. 26 starts with stopping the circulating pump 728, closing the valves 724 and 726 and opening the valves 720 and 722. This completes the preconditioning step. Then, the valve 732 is opened, whereupon the large amount of compressed air in the air tank 729 is jetted into the flush tank 730 and the resulting accelerated jet stream flows through the back wash line 718 in the direction of arrow to come into the ceramic filter 700 through which it passes (for backwashing) in the direction indicated by an unfilled arrow b and, after dislodging the filter cake and other deposits on the outer surface of the filter 700, the jet stream leaves the housing 704 via the drain line 716. Since the voids in the ceramic filter 700 are extremely small, the jet stream used for backwashing is required to have a very high flow rate, namely, high cleaning pressure, in order to insure efficient cleaning of the filter. To this end, the air tank 729 must be filled with a large amount of highly compressed air but then the air tank 729 and, hence, the overall filtration equipment, becomes bulky to increase the initial investment cost. Further, the ceramic filter 700 must be backwashed at an adequate cleaning pressure for a comparatively long period in order to insure positive cleaning of the filter. However, as described above, the prior art backwashing apparatus forms a jet stream using the highly compressed air contained in the air tank 729 of a predetermined capacity, so the cleaning pressure drops in a very short time after it peaks Hence, in order to maintain the necessary cleaning pressure for a desired period of time, not only a very large air tank 729 but also a high-performance system for filling with compressed air is necessary. In addition, the cleaning water must be supplied in a large volume. These result in a further increase in the equipment and running costs. Existing apparatus for filtering pool water and industrial water are commonly equipped with many tanks including filtration tanks and disinfection tanks and fluids to be filtered such as pool water and contaminated water must be circulated through those tanks. To meet this need, a circulating system is constructed by interconnecting those many tanks via pipes. The circulating system used in existing filtration apparatus is not only used for recirculating the fluids but also equipped with a bypass line, a wash line and a backflow line that permit the interior of tanks to be washed and which, if necessary, permit the circulating fluids to bypass certain tanks or flow backward. A prior art circulating system that has these capabilities is shown by 800 in Fig. 5 and comprises the following components: tanks 802a, 802b and 802c; an inlet pipe 804a and an outlet pipe 806a that are connected to each tank; a main pipe 808 that is directly connected to pipes 804a and 806a; switch valves 810a and 812a provided on the main pipe in two opposite positions with respect to the junction with the inlet pipe 804a; and a switch valve 814a provided on the outlet pipe 806a (those pipes and valves constitute a circulation line 816); a bypass line 818 formed of a separate bypass pipe 820; and a switch valve 822a provided on the bypass pipe 820 in positions that correspond to the respective tanks 802a, 802b and 802c in such a way that the main pipe 808 is connected to the bypass pipe 820 in two opposite positions with respect to the switch valve 822a. Because of this layout, the circulation line 816, bypass line 818 and a backflow line 824a can be selectively activated depending on the need. Another prior art circulating system is shown by 850 in Fig. 6. A first tank 852a has an outlet pipe 856a that is fitted with a switch valve 854a and which is connected to a main pipe 862 which in turn is connected to an inlet pipe 860b that is fitted with a switch valve 858b and which is connected to a second tank 852b, whereby a circulation line 864 is formed. A bypass line 868 is formed of a separate bypass pipe 866. The circulation line 864 and the bypass line 868 are interconnected by a pipe 870a which is fitted with a switch valve 872a. The bypass pipe 866 is also fitted with a switch valve 874a in a position that corresponds to the first tank 852a. The second tank 852b is connected to a third tank 852c in the same manner as described above to form both a circulation line and a bypass line. When these circulating systems are to be applied to a circulating filtration apparatus, it is necessary to provide not only a bypass pipe in addition to the main pipe but also the number of switch valves that permit the circulation line, bypass line and backflow line to be selectively activated increases. As a result, the number of components increases to make the layout of the overall equipment too complicated and costly to realize a compact system. Furthermore, great complexity is involved in controlling the switch valves for selectively activating the various lines. When a new pool is to be constructed, the installation of a purifying apparatus on the site is desirably performed as simply as possible and completed within the shortest possible period so that the progress of other building operations including the construction of the pool itself will not be retarded. This is also true with the case of replacing an existing pool water purifying apparatus with a new one. Particularly in the case of indoor pools which are supposed to be used in all seasons, meeting that need is important for shortening the "closing time". Ideally, a purifying apparatus as assembled in a factory is transported to the construction site where it is installed and connected to the pool or drain facilities. In fact, however, apparatus for purifying pool water, in particular those of high performance which have an excellent purifying capability, are bulky and involve various kinds of difficulty such as the need to use large a transportation means. Further, the purifying apparatus is to be used with proper connection being made not only to the pool but also to drain and water supply facilities on the site, so various devices and pipes associated with the purifying apparatus must be fabricated to insure good match with those facilities. Therefore, in practice, it is considerably difficult to transport the pool water purifying apparatus in the same condition as it was assembled in a factory and to place it on the installation site. Therefore, the conventional practice currently adopted is to assemble a filtration device, a disinfecting device and other individual components of the pool water purifying apparatus, transport them separately to the installation site and combine them into a complete system. However, the pool water purifying apparatus is usually installed in a fairly narrow limited place and, as already mentioned before, it comprises many components including various kinds of disinfecting and adsorbing devices and a complicated piping system is necessary to interconnect these components. Further, the use of machines and tools such as a crane and a hoist is also limited for working on the installation site. Under these circumstances the on-site operation of installing the purifying apparatus is time-consuming and difficult to accomplish. In existing purifying apparatus, especially one that adopts filtration equipment using ceramic filters, fine particles in pool water and other kinds of water to be treated, such as organic matters with a particle size of 0.5 - 1 µm and above, as well as fine particulate organics including some bacterial species are removed by the filtration equipment and those bacteria which cannot be removed by the filtration equipment are disinfected with a disinfecting device, whereas malodor substances such as ammonia contained in sweat and dead bacterial cells are removed by an adsorbing device. The bacteria range approximately from 0.2 µm to 1 µm in size, so they can be effectively removed in the existing purifying apparatus by using ceramic filters and can be killed almost completely by means of the disinfecting device. However, viruses that cause serious diseases such as AIDS, hepatitis, influenza and Japanese B encephalitis are in the form of colloidal particles ranging from 0.01 µm to 0.2 µm in size and cannot be removed even if ceramic filters are used. Needless to say, ceramic filters are totally ineffective for removing smaller particles such as protein particles with a size of ca. 0.001 - 0.01 µm. With the growing concern of the public for health, the number of healthcare facilities including sports clubs, health resorts furnished with multi-purpose spas (hot tubs), Kurhaus (spa houses) and healthcare centers is increasing today. These healthcare facilities are furnished with many kinds of pools including swimming pools, Jacuzzi whirlpools such as and jet baths and various other spas and hot tubs, among which visitors can select suitable ones to meet their object. Since safety and cleanness are two absolute conditions that must be satisfied by healthcare facilities, it is necessary that the pools in those facilities be strictly checked for their cleanness, particularly the quality of pool water. To meet this need, the performance requirements of purifying facilities that determine the quality of pool water are becoming increasingly stringent and modern versions are designed to have better performance in a correspondingly large size. A pool water purifying apparatus is an expensive system that is generally composed of filtration equipment that removes various impurities such as dust and hair contained in pool water, adsorptive purifying equipment that removes oils and other fine impurities, disinfecting equipment that disinfects pool water, optional equipment that supplies filter aids to the filtration equipment, means of heating pool water (in the case of indoor pools and hot tubs), pipes that interconnect these many units of equipment, and a control unit that control these devices. A high-performance purifying apparatus is particularly expensive and large in size and its installation takes much time. However, filters and other purifying elements used in the existing purifying apparatus are susceptible to changes in temperature and other factors and the purifying capability of the apparatus will fluctuate or deteriorate to thereby make it impossible to purify different kinds of pool water by means of a single unit of the apparatus. Under these circumstances, Kurhaus and other facilities that use many pools require a number of expensive pool water purifying apparatus and it is sometimes necessary to install as many purifying apparatus as the pools used, and this renders the investment, construction and running costs of the purifying system only exorbitant. The situation may be better understood by the following example. Not all pools used in Kurhaus have the same water temperature. Swimming pools, even if they are indoor pools, have water temperatures of about 30°C whereas the water in Jacuzzi is about 40°C and hot tubs and spas have much higher water temperatures. However, the performance of existing purifying apparatus varies with the temperature of water and no single unit of purifying apparatus is capable of keeping a plurality of pools in a uniformly clean condition. Further, depending on size, the performance of existing purifying apparatus is such that it is difficult to purity the water in a plurality of pools and keep them clean. Therefore, more than one unit of purifying apparatus is necessary to cope with different water temperatures and, as a result, the overall cost of the purifying system and its running cost become exorbitant. It is an object of the present invention to provide a pool water purifying system that uses both a purifying apparatus equipped with porous ceramic filters and prefiltration units which are provided for different pools, which system is characterized in that many kinds of pools having different water temperatures can always be kept clean by a single unit of the purifying apparatus so that the equipment and ruaning costs of the system can be significantly reduced while providing ease of its installation. The above object is achieved by the subject matter of claim 1. In particular, the present invention provides a system for purifying the water in a plurality of pools having different water temperatures, which system has both a purifying apparatus that includes a filtering means using porous ceramic filters and that is connected to at least two of said pools and a prefiltration unit that is provided for each of said pools, the water in each of said pools being purified in ordinary situations by means of the prefiltration units provided for the respective pools but, as time passes by and/or if the water in a certain pool becomes excessively dirty, the operation of the prefiltration unit associated with that pool is shifted to the purifying apparatus, which then purifies the water in that pool. Preferably, said purifying apparatus additionally includes an adsorbing means, a disinfecting means and a circulating means, said purifying apparatus also includes an ultrafiltration means, said ultrafiltration means has a backwashing means, and said backwashing means is an ultrasonic cleaner. Each of said prefiltration units comprises an overflow tank that provides a temporary storage for the water overflowing the associated pool and that is divided into at least two vessels by a partition suspended from above, a filter for filtering the pool water stored in the most downstream vessel of said overflow tank, and a means of circulating the pool water. Preferably, the switching from said prefiltration units to said purifying apparatus is sequence-controlled automatically in accordance with a preset program, except that when the water in a certain pool becomes very dirty, the system leaves the sequence control and allows said purifying apparatus to purify the water in that pool in preference over the other pools and returns to said sequence control after the purification of the excessively dirty water in that particular pool with said purification apparatus has ended. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing the concept of a pool water purifying system using the apparatus of the present invention; present invention; Fig. 2 is a diagram showing the concept of an embodiment of the purifying apparatus used in the purifying system shown in Fig. 1; Fig. 3 is a diagram showing the concept of an embodiment of the prefiltration unit used in the purifying system shown in Fig. 1; Fig. 4 is a diagram showing the concept of a system for filtering pool water using a prior art method of cleaning porous ceramic filters; and Figs. 5 and 6 are block diagrams of the circulation systems used in prior art circulating filtration equipment. Fig. 1 is a diagram showing the concept of this pool water purifying system (which is hereinafter referred to simply as the "purifying system"). Although not described below, valves, cocks, three-way cocks, check valves, solenoid valves and other components may, of course, be provided as required for the piping and equipment of the purifying system shown in Fig. 23 in order to control the various flow paths of the pool water. The purifying system generally indicated by 610 in Fig. 1 is intended to purify the water in four pools 612A, 612B, 612C and 612D having different temperatures (the term "water" as it appears below without any qualifier shall refer to "pool water"). The system comprises a purifying apparatus 614 that is connected to the four pools for purifying the water in those pools, and four prefiltration units 616A, 616B, 616C and 616D that are connected to the respective pools for filtering the water in those pools. In the purifying system 610, the purifying apparatus 614 supplies each pool with purified water through a feed line 618 and receives the water from each pool after it passes through the prefiltration unit connected to that pool. Fig. 2 is a diagram showing the concept of the purifying apparatus 614. As shown, the apparatus 614 consists basically of a prefilter 622, a ceramic filter assembly 624, disinfecting tanks 626a and 626b, an adsorption tank 628, and a circulating pump 630. Needless to say, the purifying apparatus 614 may be of the unitary assembly type described in connection with the fifth aspect of the present invention. In the system shown in Fig. 1, the water in each pool is first passed through the associated prefiltration unit before it flows into the purifying apparatus 614 via the feed line 620. The water flowing into the apparatus 614 is first introduced, either by suction with the circulating pump 630 or by the "head" with respect to the pool under treatment, into the prefilter 622 where it is freed of hair, dust and other large impurities. Subsequently, the water flows into the circulating pump 630, leaves it and then flows into the ceramic filter assembly 624. The ceramic filter assembly 624 contains in it a plurality of cylindrical ceramic filters and the water, as it passes through these ceramic filters inwardly, is filtered and fine impurities such as oils excreted from the human body are removed. In addition, unlike the conventional filters, the ceramic filters do not depend on water temperature for their performance and hence are capable of efficient filtration of the water regardless of its temperature. In the purifying system 610 under consideration, ceramic filters are used in the purifying apparatus 614 and a prefiltration unit is provided for each of the pools to be treated; because of this arrangement, the water in a plurality of pools having different water temperatures can be highly purified with a single unit of the purifying apparatus, thereby reducing the investment and running costs of the whole purifying system. The water leaving the ceramic filter assembly 624 flows into the disinfecting tanks 626a and 626b for disinfection purposes. The disinfecting tanks 626a and 626b, which disinfect the water by the combined application of ozone and ultraviolet radiation, are each furnished with an ultraviolet lamp and an ozone lamp. The water is vigorously agitated by bubbling with ambient air and, at the same time, ozone is generated by irradiation with the uv lamp. The combination of the generated ozone and the exposure to uv radiation provides a very effective means of disinfecting the water in the purifying apparatus 614. The disinfected water then flows into the adsorption tank 628. The adsorption tank 628 is packed with activated carbon and zeolite, which adsorb bacteria and other microorganisms that have been decomposed in the disinfecting tanks 626a and 626b, whereby those impurities are rejected from the water. The water leaving the adsorption tank 628 is supplied into each pool via the supply line 618. In the purifying apparatus 614 shown in Fig. 2 a filter aid tank 631 is connected to the ceramic filter assembly 624. Thus, in the case shown, the means of filtering the pool water is composed of the prefilter 622, ceramic filter assembly 624, and a filter aid supply means including the filter aid tank 631. The filter aid tank 631 consists of two vessels, one being filled with a mixture of water and a powder filter aid (e.g. diatomaceous earth) and the other being filled with a mixture of water and a fibrous filter aid (e.g. pulp fibers). The purifying apparatus 614 is also equipped with a unit 632 for backwashing the ceramic filter assembly 624. Since the purifying system 610 under discussion uses the purifying apparatus 614 having the construction described above, it is capable of purifying and disinfecting the water to to a level that has been unattainable by the prior art, whereby the water in various pools can be held in a very clean condition. Needless to say, the system may be furnished with auxiliary tanks, heat exchangers, etc. as required. In ordinary situations, the purifying system 610 purifies the pool water by means of the prefiltration units connected to the respective pools of interest. The pools and the associated prefiltration units incorporated in the system shown in Fig. 23 have basically the same construction, so the following description which centers on pool 612A and prefiltration unit 616A should also apply to the other pools and prefiltration units. Fig. 3 is a diagram showing the concept of pool 612A and prefiltration unit 616A. Pool 612A comprises basically a tank 634, a a heat exchanger 636 connected to a boiler and other components, a NaOH and Cl supplier (not shown), etc. The pool water is held at a predetermined temperature by being passed through the heat exchanger 636 as required in a circulation mode. Prefiltration unit 616A which purifies the water in pool 612A comprises basically an overflow tank 637 which provides a temporary storage for the water overflowing the tank 634, a carbon filter tank 638 that filters the water stored in the overflow tank 637, and a pump 640 which is a means of circulating the water in pool 612A. The overflow tank 637 has a suspended partition 642 that divides the interior of the tank into two vessels, an upstream vessel a and a downstream vessel b . The water flowing through an overflow line 644 is admitted into vessel a , whereas vessel b is connected to the carbon filter tank 638. Impurities in the pool water may be removed by filters as exemplified by dust and hair but equally abundant are those impurities which are lightweight and float on the water, as exemplified by oils excreted from the human body. Therefore, if the overflow tank 637 which is partitioned in the way described above is used, most impurities can be captured in the upper part of vessel a while the water in the lower part of the vessel b is admitted into the carbon filter tank 638 and this insures that the water in pool 612A is kept clean without operating the purifying apparatus 614 in all instances. Another advantage of the overflow tank 637 is that the water stored in it can be used to adjust the volume of the water in pool 612A, thereby eliminating the need of providing a balancing tank which has been indispensable to the existing pools for controlling the quantity of pool water. The impurities collecting in the overflow tank 637 may be removed at a later stage when the water in pool 612A is purified with the apparatus 614. The carbon filter tank 638 uses carbon filters to remove dust and other impurities that will not float on the surface of the water. Carbon filters are filter media that are capable of trapping ordinary fine particles and hair, dust and other unwanted impurities are removed by such carbon filters. It should, however, be noted that filter media that can be used in the prefiltration units are by no means limited to carbon filters and various kinds of filters that are used in ordinary pool purifying equipment may be employed. The thus purified water is supplied to pool 612A by means of pump 640. The specific operations for purifying the water in pools 612A - 612D in the purifying system 610 are described below. In ordinary situations, the system is sequence-controlled automatically in accordance with a preset program for purifying (filtering) the water in prefiltration units 616A - 616D that are connected to the individual pools. The system's operation is described below with pool 612A being taken as an example. The water overflowing the tank 634 passes through the overflow line 644 to flow into vessel a in the overflow tank 637. As already mentioned, the interior of the overflow tank 637 is divided into two sections by the partition 642 suspended from above; thus, lightweight impurities such as oils excreted from the human body collect in the upper part of vessel a and only the clean water in the lower part of vessel a will move toward vessel b . The water moving to vessel b flows into the carbon filter tank 638 through line 645, either by the "head" or by the suction of pump 640. In the carbon filter tank 638, hair, dust and other impurities are removed by the carbon filters and the resulting clean water is returned to pool 612A though lines 646 and 648. If the temperature of the water is lower than a predetermined level, it is passed though the heat exchanger 636 before returning to tank 634; if the water temperature is equal to or higher than the predetermined level, the water bypasses the heat exchanger 636 and is directly returned to the tank 634. In ordinary situations, the purifying system 610 purifies the water by means of prefiltration units 616A - 616D connected to the individual pools 612A - 612D in the manner described above. If the continuous operation of the prefiltration units 616A - 616D for purifying the water exceeds a predetermined duration, or if it is found by sensor or some other suitable means that the water has become more foul than is permissible, the path of water circulation is shifted from the individual prefiltration units to the purifying apparatus 614 and enhanced water purification is performed. This mode of water purification is described below with reference to pool 612A. Suppose here that the continuous operation of prefiltration unit 616A for purifying the water exceeds a prescribed time or that it is found by a sensor or some other means that the water in pool 612A has become more foul than is permissible. Then, pump 640 is turned off, lines 645 and 646 are closed, a line 650 connecting to an entry line 620 is opened, and the water in the overflow tank 636 flows into the purifying apparatus 614 through line 650 and entry line 620. If the situation is such that the purifying apparatus 614 has been operated to purify the water in another pool, say, pool 612D, in a circulating manner, the entry line to the purifying apparatus 614 from the overflow tank in the prefiltration unit 616D associated with the pool 612D is closed simultaneously with the opening of lien 650, whereas the entry line for circulation from the pool 612D to the prefiltration unit 616D is opened. However, before all of the water from pool 612D that remains in the purifying apparatus 614 and in the associated lines has been returned to the pool 612D, the supply line from the purifying apparatus 614 to the pool 612D is not closed, nor is opened the line of circulation from the prefiltration unit 616D to the pool 612D. Consider here the case where the volume of water in the overflow tank 637 associated with pool 612A has become smaller than a predetermined level (e.g. the level of that water becomes lower than the partition 642) and where the purifying apparatus 614 is operating to purify the water in another pool, say, pool 612D, in a circulating manner. If, in this case, all of the water in pool 612D that remains in the purifying apparatus 614 and in the associated lines is returned to the pool 612D, then the line to the pool 612D connected to the feed line 618 is closed and, at the same time, a line 652 to the pool 612A which is connected to the feed line 618 is opened, whereupon highly purified water is supplied from the purifying apparatus 614 to the pool 612A. If the temperature of the water supplied from the purifying apparatus 614 is below a predetermined level, it may be passed through the heat exchanger 636 to be heated to the predetermined temperature before it is supplied to the tank 634. Needless to say, the operations of switching one line to another or those of opening and closing lines should preferably be conducted gradually enough to avoid "water knocking". The water flowing into the purifying apparatus 614 is first freed of dust and other large impurities by the prefilter 622 and then supplied into the ceramic filter assembly 624 where it is freed of fine impurities such as oils excreted from the human body. Subsequently, the water is disinfected by ultraviolet radiation and ozone in the disinfecting tanks 626a and 626b and thence supplied into the adsorption tank 628 for removal of bacteria and other fine impurities. The resulting clean water is supplied to pool 612A via lines 618, 652 and 648. When the purification of the water in pool 612A by means of the purifying apparatus 614 ends, the line of water purification is switched again to the prefiltration unit 616A and then switched to the prefiltration unit (616B, 616C or 616D) that is associated with another pool the water in which should be highly purified, as well as to the purifying apparatus 614. The switching between individual prefiltration units 616A - 616D and the purifying apparatus 614 may be sequence-controlled automatically in accordance with a preset timing chart or program or, alternatively, it may be conducted on the basis of the results of detecting the degree of fouling of the pool water with various sensors. If desired, the two control systems may be combined in such a way that the switching operations are sequence-controlled in ordinary situations but when the quantity of the water in a certain pool decreases or if it becomes very dirty for some reason such as the use of that pool by many bathers at a time, the water in that particular pool is first purified in preference over the other pools and the system is returned to sequence control after the purification of that water ends. The timing chart or program for sequence control may be constructed in an optimal way by performing preliminary experiments. Needless to say, such timing chart and program may be modified as appropriate for various factors such as the status of a specific operation of water purification. The pool water purifying system of the present invention is not limited to the particular embodiment described above and various other system arrangements may be adopted in accordance with such factors as the use and scale of the pools to be treated; for example, additional filtration tanks or disinfecting tanks may be added, or unnecessary components may be eliminated from the system, or an entirely different type of the purifying apparatus may be added to the system. In the embodiment described above, only one unit of the purifying apparatus is used but it should be noted that depending upon factors such as the number of pools to be treated and the scale of the purifying apparatus, more than one unit of the purifying apparatus may be used as required. As described above in detail, the pool water purifying system of the present invention has the advantage that the water in a plurality of pools having different water temperatures such as those used in a Kurhaus can be purified by a single unit of purifying apparatus and, therefore, the investment and running costs of the purifying system can be substantially reduced.

Claims: Apparatus (614) for purifying the water in a plurality of pools (612a, 612b, 612c, 612d) having different water temperatures, which apparatus has both a purifying section that includes a filtering means using porous ceramic filters (624) and that is connected to at least two of said pools and a prefiltration unit (616a, 616b, 616c, 616d) that is provided for each of said pools, the water in each of said pools being purified in ordinary situations by means of the prefiltration units provided for the respective pools but, as time passes by and/or if the water in a certain pool becomes excessively dirty, the operation of the prefiltration unit associated with that pool is shifted to the purifying section, which then purifies the water in that pool and wherein each of said prefiltration units comprises an overflow tank (637) that provides a temporary storage for the water overflowing the associated pool and that is divided into at least two vessels (a, b) by a partition (642) suspended from above, a filter (638) for filtering the pool water stored in the most downstream vessel (b) of said overflow tank, and a means (640) of circulating the pool water. An apparatus according to claim 1, wherein said purifying apparatus additionally includes an adsorbing means (628), a disinfecting means (626a, 626b) and a circulating means (630). An apparatus according to claim 1 or 2, wherein said purifying apparatus (614) also includes an ultrafiltration means. An apparatus according to any one of claims 1 to 3, wherein the switching from said prefiltration units to said purifying apparatus is sequence-controlled automatically in accordance with a preset program, except that when the water in a certain pool becomes very dirty, the system leaves the sequence control and allows said purifying apparatus to purify the water in that pool in preference over the other pools and returns to said sequence control after the purification of the excessively dirty water in that particular pool with said purification apparatus ended.

Inventors: YUGENGAISHA ATLAS
Applicants: YUGENGAISHA ATLAS
Application year: 1991
Main classification: B01D36
IPC codes: B01D29, B01D37, B01D63, B01D65, C02F1, B08B9, B01D61