Abstract:
A water purification method and system, wherein a source of ultraviolet light is disposed relative to the vessel containing the water to be purified for directing ultraviolet light along a major axis of the vessel, and the water is illuminated with the ultraviolet light. One of the systems includes a vessel containing the water to be purified, at least one ultraviolet lamp, external to the vessel, and at least one collimaor for collimating ultraviolet light radiated by the at least one lamp, wherein the light illuminates the water along a major axis of the vessel, Preferably, the lamp can be operated in one or more of the following three modes: continuous constant intensity; quasi cw intensity; and/or pulsed intensity.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to water purification  
         BACKGROUND OF THE INVENTION  
         [0002]    It is generally well known that it is necessary to kill or inactivate micro-organism (e.g. bacteria, viruses) to purit water. One method of killing or inactivating bacteria and viruses is through the usage of ultraviolet light (UV). Prior art UV systems use a single or multiple longitudinal mercury (Hg) lamps which are either low or medium pressure. Refer to prior art FIG. 1 which shows a low pressure Hg lamp system  10 . A lamp  12  is enclosed by a protective quartz sleeve  14  and the assembly of lamp  12  and quartz sleeve  14  is immersed in a treatment chamber  16 . The water  20  flows parallel to the major axis of lamp  12 . The light  18  from lamp  12  (caused by the excited Hg) radiates perpendicular to the major axis of lamp  12  and the intesity of light  18  drops as  1 /x. The variable x ranges from 0 to R, where R is the radial distance from lamp  12  to the wall of treatment chamber  16 . The intensity per is unit area relationship can be described as:  
         I        (   x   )       =       I   0          [       e     -   ax       -     1   x       ]                             
 
           [0003]    where:  
           [0004]    I o  is the intensity of light  18  per unit area on the envelope of lamp  12 ;  
           [0005]    I is the intensity of light  18  per unit area at a distance x from lamp  12  along the radial distance; and  
           [0006]    A is the absorption coefficient of water  20  (including turbidity)  
           [0007]    The second factor Io/x, which is due to geometrical considerations contributes more significantly to the intensity drop and limits effective light penetration more than the first factor I o e −ax  which is based on the Bear-Lambert&#39;s law.  
           [0008]    Prior art FIG. 2 shows the intensity profile of lamp  12  as a function of x.  
           [0009]    The limitations of prior art UV systems include: a) the associated maintenance cost for cleaning the quartz sleeve  14  from contamination by water deposit such as salts; b) the inefficiency in treating high turbidity water sources—with higher turbidity, one needs higher power to effect purification, however the level of penetration of light  18  is reduced due to the intensity drop as a function of radial distance; c) the large footprint (i.e. system size); d) the low electrical efficiency—because of the drop of intensity as a function of radial distance, one needs to increase lamp radiation so as to reach the minimum required intensity at a desired distance from lamp  12 ; and in certain systems e) the large number of lamps needed for sufficient radiation.  
           [0010]    All of the drawbacks listed above are encountered with conventional low-pressure longitudinal Hg UV lamps, and generally discourage consideration of UV for treating very high volume effluents.  
           [0011]    The more advanced systems use medium pressure Hg lamps with a continuum and poly-spectral emission in the range of 200-300 nanometers (“nm”). Medium pressure systems have smaller footprint and better electrical efficiency—but still are housed by quartz envelops which require frequent service.  
           [0012]    In a paper by LaFrenz entitled “ High Intensity Pulsed UV for Drinking Water Treatment ”, Proc. AWWA WQT Conference, Denver, Colo., November 1997, a pulsed system for drinking water treatment is described. The system uses a medium pressure longitudinal mercury lamp located inside the processing chamber, which provides about 2 times the peak power in pulsed operation than in DC operation.  
         SUMMARY OF THE INVENTION  
         [0013]    It is an object of the invention to overcome the inherent limitations of prior art UV systems.  
           [0014]    It is another object of the invention to eliminate the need for a protective quartz sleeve.  
           [0015]    It is yet another object of the invention to increase the efficiency of the water treatment by lowering the intensity drop per unit area.  
           [0016]    It is yet another object of the invention to increase the efficiency of the water treatment through the delivery of higher peak power in a quasi cw mode or a pulsed operation.  
           [0017]    It is yet another object of the invention to increase the efficiency of the water treatment, by introducing strong turbulence and mixing action in the irradiated zone, with minimal blocking and/or interfering with the passage of the UV radiation.  
           [0018]    A preferred embodiment of the system of the present invention includes a collimated high pressure Hg-Xe lamp (continuum plus poly-spectra in the 200-300 nm range) which is external to the processing chamber. A single lamp can deliver up to five kW in average electrical power.  
           [0019]    According to the present invention, there is provided a method for purifying water contained in a vessel, including the steps of disposing a source of ultraviolet light relative to the vessel for directing ultraviolet light along a major axis of the vessel; and illuminating the water with the ultraviolet light.  
           [0020]    According to the present invention, there is also provided a water purification system, including: a vessel containing the water to be purified; at least one ultraviolet lamp, external to the vessel; and at least one collimator for collimating ultraviolet light radiated by the at least one lamp; wherein the light illuminates the water along a major axis of the vessel.  
           [0021]    According to the present invention, there is still further provided a water purification system, including: a vessel containing the water to be purified and including an inner chamber, wherein the inner chamber includes rotating fins for increasing turbulence; at least one ultraviolet lamp, external to the vessel; at least one electrical circuit to operate the at least one lamp in pulsed mode; at least one collimator for collimating ultraviolet light radiated by the at least one lamp; and at least one window through which light collimated by the at least one collimator enters the vessel; wherein the light illuminates the water along a major axis of the vessel.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:  
         [0023]    [0023]FIG. 1 shows a schematic of a prior art water purification system using a low pressure mercury lamp;  
         [0024]    [0024]FIG. 2 is an intensity profile for a single lamp in a prior art water purification system;  
         [0025]    [0025]FIG. 3 illustrates a schematic of a water treatment system according to an embodiment of the present invention;  
         [0026]    [0026]FIG. 4 shows an entrance window to a processing chamber according to an embodiment of the present invention;  
         [0027]    [0027]FIG. 5 illustrates a water purification system according to an embodiment of the present invention;  
         [0028]    [0028]FIG. 6 shows a light beam according to an embodiment of the present invention;  
         [0029]    [0029]FIG. 7 illustrates a water purification system according to an embodiment of the present invention;  
         [0030]    [0030]FIG. 8 shows a lamp according to an embodiment of the present invention;  
         [0031]    [0031]FIG. 9 a  shows an electrical circuit for continuous constant (cw) operation of the lamp according to an embodiment of the present invention;  
         [0032]    [0032]FIG. 9 b  shows an electrical circuit for quasi cw operation of the lamp according to an embodiment of the present invention;  
         [0033]    [0033]FIG. 9 c  shows an electrical circuit for pulsed operation of the lamp according to an embodiment of the present invention;  
         [0034]    [0034]FIG. 10 shows an energy measuring device according to an embodiment of the present invention;  
         [0035]    [0035]FIG. 11 illustrates a water purification system according to an embodiment of the present invention; and  
         [0036]    [0036]FIG. 12 illustrates a water purification system according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]    The present invention is of a water treatment system and method. Specifically, the present invention call be used to more efficiently treat contaminated wastewater.  
         [0038]    Referring now to the drawings, FIG. 3 illustrates an embodiment of a water treatment system  26  according to the present invention.  
         [0039]    Longitudinal illumination of water  38  in a processing chamber i.e. vessel  30  by a UV beam  28  allows a decreased intensity drop compared to prior art system  10 . UV beam  28  enters processing chamber  30  through one or more entrance windows  40  (see FIG. 4), preferably quartz or sapphire window(s), preferably coated with special UV transmitting polymer to avoid contamination. Because of the smaller size of window  40  compared to prior art sleeve  14  of FIG. 1, the contact area with water  38  is smaller. Therefore window  40  is less likely to get contaminated, and there is less cost and time to clean window  40  from contamination compared to sleeve  14 . Contaminated water  34  flows into chamber  30  and clean water  36  flows out of chamber  30 . Preferably, water  38  is flowing along the major axis of chamber  30 . Although in the embodiment of FIG. 3, water  38  flows in the opposite direction of the radiation of light  28 , in other embodiments, water  38  flows in the same direction or in both the same and opposite directions as the radiation of light  28 .  
         [0040]    The intensity drop in system  26  is attributed only to the absorbed and scattered light in the water and the micro-organisms. If I o  is the intensity of beam  28  at entrance window  40 , then the intensity I(x) of beam  28  at a distance x into chamber  30  is given by: 
           I ( x ) =I   o e −at   
         [0041]    where: “a” is the absorption coefficient of water  38  (including turbidity). Note that the larger contributing factor (geometrically related) to the intensity drop of prior art system  10  does not contribute to the intensity drop of system  26 , because of the usage of longitudinal illumination instead of transverse illumination.  
         [0042]    Using system  26  enables longer interaction time between UV beam  28  and water  38 , because of the lower intensity drop. A larger volume of water  38  can therefore be treated with the energy from UV beam  28 , thus increasing efficiency compared to prior art system  10 .  
         [0043]    As an example, the absorption coefficient of clear water at a wavelength of 250 nm for beam  28  is about 200 cm −1 . The decrease in beam intensity I(x) is less than 20% on an interaction length of 70 cm. Note that the treated volume of water is equal to the interaction length (from window  40  to maximum distance along the major axis of chamber  30  where intensity remains sufficient to treat water) multiplied by the cross-sectional area of chamber  30 .  
         [0044]    In order to achieve the longitudinal illumination, in certain embodiments of the present invention, a lamp (external to processing chamber  30 ) is used along with a collimator. The collimator changes the diverging light from the lamp (which is a point source) to parallel beam  28 . Examples of collimators include lenses or reflectors parabolic, spherical, etc.). Typically, reflectors are more efficient collimators than lenses because reflectors collimate light from all directions. In particular, parabolic reflectors are especially efficient collimators.  
         [0045]    Refer to FIG. 5, which shows a water treatment system  60  that is a particular embodiment of system  26  of FIG. 3. A parabolic mirror  52  is used as a collimator. A lamp  56  is placed at one of the focal points of collimator  52  in the vertical position, illuminating downwards. Because of the presence of lamp  56  within collimator  52 , beam  28  is collimated in a ring or doughnut shape (i.e. within the ring of the parallel beam of light, there is a dark inner hole). FIG. 6 illuminates an example of the shape of beam  28  corresponding to the embodiment of FIG. 7.  
         [0046]    Referring to FIG. 7, there is illustrated the water treatment system  62  which is a second particular embodiment of the system  26  of FIG. 3 with lamp  56  illuminating upwards.  
         [0047]    In preferred embodiments of the present invention, the processing chamber  30  is also ring shaped so as to conform to the ring shape of beam  28 . There is no water  38  (FIG. 3) contained in an inner chamber  32 . Window  40  (FIG. 4) therefore does not need to provide an opening to inner chamber  32 -note that window  40  in the embodiment of FIG. 4 only exists on the sides of inner chamber  32 . Inner chamber  32  is preferably utilized t improve the water purification process. For example in system  62  of FIG. 7, an anode  48  is placed at the lower end of in inner tube  32 , saving space (as will be described below). As another example, in order to improve the water purification process, in many embodiments, inner chamber  32  includes one or more rotating fins i.e. stirrers  42  for agitating water  38  to increase turbulence. The rotation mixes water  38 , avoiding any dead volume, and allowing beam  28  to reach more micro-organisms. Fins or stirrers  42  are preferably very thin so as to avoid blocking light  28  from interacting with water  38 . Processing chamber  30  does not interfere with the high flow rate of water  38  because chamber  30  has a large diameter (for example, in the range of 2 to 10 inches) and there is no pressure drop.  
         [0048]    Note that because the prior art system  10  included the lamp  12  and quartz sleeve  14  inside the processing chamber  16 , the system  10  could not utilize the inner space of chamber  16  to improve the water purification process, for example for placing the anode or rotating fins.  
         [0049]    Preferably, lamp  56  can be operated in one or more of the following three modes:  
         [0050]    a) continuous constant (cw) intensity (100% duty cycle)  
         [0051]    b) quiasi cw intensity with “moderate” square pulses superimposed on a simmer. The peak power is 2 to 3 times larger than in cw operation and there is a 33% -50% duty cycle (where duty cycle equals the ratio of pulse duration to pulse period). The simmer provides very low power, sufficient to keep the lamp operating but with light output almost zero.  
         [0052]    c) pulsed intensity with “high” narrow pulses superimposed on a simmer. The peak power is 5 to 20 times larger than in cw operation and there is a 5% -20% duty cycle.  
         [0053]    Higher peak power allows better penetration in high turbidity water and possibly more efficient disinfection effects. The pulsed intensity mode is therefore the most preferred embodiment.  
         [0054]    In preferred embodiments of the present invention, lamp  56  is an arc lamp. Arc lamps produce light by maintaining an electric arc across the gap between two conductors, for example two electrodes. Preferably, lamp  56  is a short arc lamp, where the tips of the two electrodes are only a few millimeters apart. Some short arc lamps have a third electrode for applying the starting pulse. Others have only two electrodes and require a triggering mechanism. Some short are lamps are designed for alternating current power (AC), and typically have two identical main electrodes. Most short arc lamps are designed for DC power and typically have two dissimilar main electrodes. Lamps designed for DC may be pulsed. Certain short arc lamps may have to be operated in a specific position so as to not overheat. The bulb of a short arc lamp is typically filled with mercury vapor, xenon (“Xe”), argon, or mercury-xenon.  
         [0055]    The geometry of the short arc lamp is the most efficient for collimating the UV radiation. Preferably, a mercury-xenon high pressure short arc lamp is used which is the most efficient UV radiator among all short arc lamps, with the ability to radiate up to 15% of the electrical input as a UV radiation in the 200-300 nm range. The mercury-xenon high pressure short arc lamp can be operated in any of the three modes described above (cw, quasi, and pulsed). The mercury xenon high pressure short arc lamp can be pulsed efficiently and behaves very similarly to a pure xenon short are lamp. The mercury generally does not interfere or alter the electrical behavior of the lamp under pulsed conditions. It is the xenon which dictates the pulsed behavior. Suitable mercury-xenon short arc lamps for commercial use, available in the 100 to 5000 watts range, include UXM-101MD (1000 watts), UXM 2004 MD (2000 watts), and UXM 5000 MF (5000 watts), all by Ushio America of Cypress Calif.  
         [0056]    [0056]FIG. 8 shows an example of a short arc lamp that can be used as the lamp  56 , enlarged to clearly show the two electrodes, anode  48  and a cathode  50 . In this particular embodiment anode  48  of lamp  56  is large and bulky and cathode  50  of lamp  56  is thinner and has a needle shape.  
         [0057]    In the particular embodiment of system  60  of FIG. 5, anode  48  (here, the larger electrode) faces upwards. The dimensions of collimator  52  are determined by the shadow of anode  48  on reflector  52  so as to collect the maximum of the light emitted by lamp  56 . As an example, an eight-inch reflector  52  is illustrated in FIG. 5.  
         [0058]    In the particular embodiment of FIG. 7, anode  48 , again the larger electrode faces upwards (and as mentioned above is placed at the bottom of the inner chamber  32 ). System  62  also uses a collimator  64  that is a parabolic reflector the dimensions of collimator  64  are determined by the shadow of the cathode  50  (the smaller electrode) on collimator  64  so as to collect the maximum of the light emitted by the lamp  56 . The dimensions of collimator  64  can therefore be smaller than collimator  52  of FIG. 5. Note that power density is determined by watts/unit area. In both systems  60  and  62 , the power of lamp  56  is the same but in system  62 , the collimator  64  has a smaller unit area than the collimator  52  of system  60  and therefore the power density of system  62  is higher.  
         [0059]    [0059]FIG. 7 shows anode  48  placed at the bottom of the inner tube  32 , conserving space in system  62 . In other embodiments, for example where the lamp illuminates downwards as in FIG. 5, cathode  50  could be placed in inner tube  32 , to conserve space. In other embodiments, cathode  50  faces upwards and/or is the larger electrode.  
         [0060]    [0060]FIG. 5 also illustrates additional elements which are added to certain embodiments of system  60  including a stirrer motor  44  for operating stirrers or fins  42 , a handpiece  54  for holding collimator  52  to lamp  56 , a reflector mirror  46  for reflecting back the transmitted lights thereby increasing efficiency, and a cooling-down medium  57  for dissipating heat from anode  48 . The handpiece  54 , reflector mirror  46  and cooling unit  57  are not shown in FIG. 7 or in other figures (for example FIGS. 10, 11, and  12 ) representing other embodiments so as to not complicate the drawing, but the handpiece  54 , reflector mirror  46  and the cooling down medium  57  can be included in certain embodiments of system  62  and/or certain embodiments corresponding to FIGS. 10, 11, and  12 .  
         [0061]    Most of the existing commercial power supplies for xenon, argon, and krypton arc lamps (short, linear DC or flashlamps) are suitable for operation of lamp  56  in the three modes of cw, quasi cw, and pulsed, with minor modifications and adaptations for voltage and current.  
         [0062]    An example of a suitable commercially available electrical circuit in one unit which can operate lamp  56  is Part Number 891A-c manufactured by Analog Modules, Inc. of Longwood, Fla.  
         [0063]    Alternatively, the electrical circuits shown in FIGS. 9 a ,  9   b  and  9   c  can be used to operate lamp  56  in cw, quasi cw, and pulsed modes, respectively. The electrical circuits for cw, quasi cw, and pulsed operation of lamp  56  may incorporate commercial sub-circuits.  
         [0064]    [0064]FIG. 9 a  shows an example of an electrical circuit which can be used for cw operation of lamp  56 .  
         [0065]    A DC current source  84  is connected to the anode of a diode  86  whose cathode is connected to an igniter  88 . Igniter  88  is connected on the other side to the anode of lamp  56 . An example of a suitable DC current source  84  includes commercially available Part Number C2577 manufactured by Hamamatsu Photonics K.K. (Japan). An example of a suitable igniter  88  includes commercially available Part Number 68920 manufactured by Oriel Instruments of Stratford, Conn.  
         [0066]    [0066]FIG. 9 b  shows an example of an electrical circuit which can be used for qiasi Cw operation of lamp  56 . A pulsed current source (0 to 120 Amps)  90  is connected to the anode of a diode  92  whose cathode is connected to the cathode of a second diode  93  and an igniter  96 . The anode of diode  93  is connected to a simmer DC  94 . Igniter  96  is connected on the other side to the anode of lamp  56 . An example of a suitable pulsed current source  90  includes commercially available Part Number 68920 manufactured by Oriel Instruments of Stratford, Conn. An example of a suitable igniter  96  includes commercially available Part Number 68920 manufactured by Oriel instruments of Stratford, Conn. (Pulsed current source  90  and igniter  96  are in same commercially available package by Oriel). An example of a suitable simmer DC  94  includes commercially available Part Number 861A manufactured by Analog Modules, Inc. of Longwood, Fla.  
         [0067]    [0067]FIG. 9 c  shows an example of an electrical circuit that can be used for pulsed operation of lamp  56 .  
         [0068]    A DC capacitor charging power supply  98  is connected to a pulse forming network  100  which is connected on the other side to the anode of a diode  102 . The cathode of diode  102  is connected to the cathode of a second diode  103  and to an igniter  106 . The anode of diode  103  is connected to a simmer DC  104 . Igniter  106  is connected on the other side to the anode of lamp  56 . An example of a suitable capacitor charging power supply  98  includes Part Number 8800 manufactured by Analog Modules, Inc. of Longwood, Fla. An example of a suitable pulse forming network  100  includes commercially available Part Number 8800 manufactured by Analog Modules, Inc. of Longwood, Fla. (Power sapply  98  and pulse forming network  100  are in same commercial package by Analog Modules). An example of a suitable simmer DC  104  includes commercially available Part Number 861A manufactured by Analog Modules, Inc. of Longwood, Fla. An example of a suitable igniter  106  includes commercially available Part Number 68920 manufactured by Oriel Instruments of Stratford, Conn.  
         [0069]    It should be evident that sub-circuits shown in any of FIGS. 9 a ,  9   b , and  9   c  may be separated into a larger number of sub-circuits or integrated into a fewer number of sub-circuits. It should also be evident that the circuits of  9   a ,  9   b  and  9   c  may be integrated with each-other so that two or less circuits may be used for all three modes (cw, quasi cw, and pulsed)  
         [0070]    In preferred embodiments of the present invention, an energy measuring device  112  is used to control the operation as shown in FIG. 10. Energy measuring device  112  is in one preferred embodiment a light sensitive detector, sensitive in the range of 200 nm to 300 nm, with an optical filter for selecting a sample of light  28  at an end of vessel  30 . An example of a suitable energy measuring device  112  includes commercially available ADV 5 UV Monitor manufactured by Trojan Technologies, Inc. of London, Ontario. Energy measuring device  112  is not shown in any other figures so as to not complicate the drawings but may be present in other embodiments.  
         [0071]    Note that stirrers  42  and stirrer motor  44  are not shown in FIG. 10 so as to not complicate the drawing. In most of the embodiments of the invention described above and below, stirrer motor  44  does not need to be placed in a specific position along vessel  30  but is placed where there is room and where motor  44  will not interfere with the rest of the water treatment system.  
         [0072]    Although one lamp in preferred embodiments of the invention provides the equivalent purification as provided by approximately ten lamps in conventional prior art systems, in certain preferred embodiments, more than one lamp may be used For example, refer to FIG. 11 which shows two lamps, lamp  120  illuminating downwards and lamp  122  illuminating upwards. Again stirrer motor  44  is not shown so as to not complicate the drawing. FIG. 12 shows two lamps  130  and  132  both illuminating in the same direction. Note that there is a darkened zone  134  to which light from lamps  130  and  132  does not reach, but water  38  flows freely in zone  134 . Although in FIG. 12, both lamps  130  and  132  are shown illuminating upwards, it can be appreciated that in another embodiment both lamps  130  and  132  illuminate downwards. In other embodiments, other configurations of two or more lamps may be used. In other embodiments, other orientations for axes aligning the system, for example horizontal or at an angle may be used rather than the vertical axis. The addition of extra lamps may necessitate additional windows, reflectors and/or electrical circuits.  
         [0073]    While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made without departing from the scope of the following claims: