Patent Publication Number: US-2022211888-A1

Title: Metal working fluid decontamination apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to metal working fluid decontamination apparatus. 
     2. The Prior Art 
     Metal working fluids are fluids which are used to lubricate and/or cool metal work pieces in metal working operations such as machining, cutting and forming. 
     Conventionally, metal working fluids are formed by adding a concentrate to water. The most commonly used concentrates comprise oil and performance additives including an emulsifier, and when added to water form a semi translucent or milky white emulsion. 
     One alternative to a conventional metal working fluid is a fully synthetic metal working fluid, which comprises water and a water soluble synthetic concentrate which does not contain oil. Examples of fully synthetic metal working fluids include water-miscible metal working fluids. 
     In use, a tank of the metal working fluid is located on or close by to the machine performing the metal working operation. The metal working fluid is pumped from the tank to the workpiece. After lubricating and/or cooling the work piece during the metal working operation, the metal working fluid is collected and conveyed back to the tank. Over a period of time, the metal working fluid becomes contaminated by a range of contaminants, including metal particulates, air borne particulates, tramp oil and microbial contaminants such as bacteria. The contaminants present a risk to the health of the machine operatives and also reduce the effectiveness of the metal working fluid. 
     In practice, microbial contamination is of most concern, as it presents a serious health risk, and causes unpleasant odours. Water-miscible metal working fluids (MWFs) by their nature become colonised by bacteria living in the environment if not maintained properly. The majority of MWFs adapted bacteria belong to the  Pseudomonas  family and are Gram negative meaning their surface consists of a double surface membrane. Bacteria die off naturally due to limited availability of nutrients in the MWF and are killed by the addition of biocide and other additives in an endeavour to manage the MWF quality. Once cell death occurs, the outer surface membrane breaks down releasing immunologically active proteins and potential toxins into the MWF. The main one of concern, due to its known link to respiratory ill health, is endotoxin. Thus, microbial contamination results in poor and potentially unsafe working conditions for the operatives. 
     Conventionally, metal working fluid contamination requires that metal working fluids are replaced on a regular, periodic basis as they become contaminated, entailing disposal costs for the user. To extend the period of use before replacement, biocides are used to prevent or reduce the growth of bacteria. However, the biocides become depleted over time and increased use of biocides itself presents a health, safety and environmental concern. In addition, regulatory changes may limit the availability of biocides as tank side additives. 
     In this specification, the term “metal working fluid” is used to include fluids which are used in relation to metal working machinery, including cutting fluids, grinding fluids, drawing and forming fluids, coolants, component cleaners, press lubricants, corrosion inhibitors and degreasers. 
     In this specification, the term “micron” is used and means 1×10-6 m. Filters are commonly rated in microns. The rating relates to the size of the holes in the filter and thus the size of the particles which are trapped by the filter. Thus, a 50 micron filter traps particles of 50 microns or larger, while a 2 micron filter traps particles of two microns or larger. Filters can be further classified as “nominal” or “absolute.” A nominal 5 micron filter is one that traps 85 percent of particles of 5 microns and larger, while a 5 micron absolute rated filter will remove at least 98.7% of particles of 5 microns or larger. Bacteria range in size from 0.2 to 2 microns in width or diameter and from 1 to 10 microns in length for non-spherical specie.  Pseudomonas  bacteria is rod shaped, the rod being about 1 to 5 microns long and 0.5 to 1.0 micron wide. Thus, a 1-micron filter will remove most bacteria and cysts but only a proportion of  pseudomonas , while a 0.1 micron filter will remove substantially all bacteria, including  pseudomonas.    
     In this specification, all of the filter ratings given are absolute filter ratings unless otherwise stated. 
     For the avoidance of doubt, in this specification, the term “at least a 20 micron filter” (or similar) means that the filter will filter out particulates at least down to 20 microns, and the term “no more than a 1.0 micron filter” (or similar) means that the filter does not filter out particulates below 1.0 micron (with the actual micron values adjusted accordingly as the reader will understand). 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided metal working fluid decontamination apparatus, the apparatus including: 
     an intake arrangement for metal working fluid; 
     a pump for providing, in use, flow pressure to the metal working fluid; 
     a decontaminator for reducing contamination in the metal working fluid; 
     an outlet arrangement for the metal working fluid; 
     whereby, the metal working fluid is a fully synthetic metal working fluid, which comprises water and a water soluble synthetic concentrate which does not comprise oil. 
     Possibly, the metal working fluid comprises, in a fresh (i.e. unused) condition, no more than 10% by weight of the synthetic concentrate, and may comprise no less than 2% by weight of the synthetic concentrate in the fresh condition. Desirably, the metal working fluid comprises, in the fresh condition, no more than 7% by weight of the synthetic concentrate, and may comprise no less than 5% by weight of the synthetic concentrate. 
     Possibly, the metal working fluid is, in the fresh condition, substantially transparent. 
     Possibly, the decontaminator comprises a filter arrangement, to reduce particulate contamination in the metal working fluid. 
     Possibly, the filter arrangement comprises a coarse filter for filtering particulates. Possibly, the coarse filter is at least a 20 micron filter, and may be no more than a 5 micron filter. 
     Possibly, the filter arrangement comprises a fine filter for filtering particulates. Possibly, the fine filter is at least a 20 micron filter, and may be no more than a 0.5 micron filter. 
     Possibly, the filter arrangement comprises a microbial filter for filtering microbial particulates, such as bacteria. Possibly, the microbial filter is positively charged. Possibly, the microbial filter is at least a 1.0 micron filter and may be no more than a 0.1 micron filter. 
     Possibly, the filter arrangement comprises the coarse filter, the fine filter, and the microbial filter in flow sequence. 
     Possibly, the apparatus comprises pressure gauges, which may be located upstream and downstream of the or each filter, possibly to indicate the pressure drop over each filter and thereby whether any of the filters need replacing. 
     Possibly, the decontaminator comprises an ultraviolet (UV) light treatment arrangement, possibly to reduce microbial contamination and possibly to reduce endotoxins in the metal working fluid. 
     Possibly, the UV light treatment arrangement defines a treatment passage along which, in use, the metal working fluid flows. Possibly, the arrangement includes a UV light source which is arranged to treat the metal working fluid as it flows along the passage. 
     Possibly, the UV light source operates at a wavelength of 185 to 400 nm. 
     Possibly, the UV light source comprises a low pressure UV light source, which may operate at a wavelength of 185 to 254 nm, and/or may comprise a medium pressure UV light source, which may operate at a wavelength of 200 to 400 nm. 
     Possibly, the UV light treatment arrangement includes passage walling, which may define the treatment passage. Possibly, the passage walling is substantially transparent, and may be formed of glass, possibly, quartz. 
     Possibly, the UV light treatment arrangement includes at least four UV light sources, which may be arranged around the passage walling, and may be equally spaced around the passage walling. 
     Possibly, the UV light treatment arrangement is arranged so that the, or one, or some, or each of the UV light sources is located within the treatment passage, so that, in use, the metal working fluid flows around the UV light source(s). Possibly, the UV light source(s) is (are) located within the passage walling, possibly on the inside of the passage walling, and, in use, the metal working fluid flows around the outside of the passage walling. 
     Possibly, the UV light treatment arrangement includes a flow disrupter, which, in use, alters the flow of the metal working fluid along the passage from laminar flow to turbulent flow. Possibly, the flow disrupter includes one or more static mixing elements. 
     Possibly, the apparatus includes a pH monitor, for monitoring the pH of the metal working fluid. Possibly, the pH monitor includes a detector, for detecting the pH of the metal working fluid. Possibly, the pH monitor includes a display, for displaying the pH of the metal working fluid. 
     Possibly, the apparatus includes a controller, which may include a display. Possibly, the pH monitor is in signal communication with the controller, possibly by wire or wirelessly. 
     Possibly, the pH monitor includes a logger, for recording the pH of the metal working fluid. Possibly, the pH monitor includes a transmitter, for transmitting the pH of the metal working fluid to a remote display and/or a remote logger or to the controller. 
     Possibly, the pH monitor is located downstream of the decontaminator. 
     Possibly, the pH monitor is located upstream of the decontaminator. 
     Possibly, the apparatus includes a plurality of pH monitors. Possibly, one monitor is located upstream of the decontaminator, and one monitor is located downstream of the decontaminator. 
     Possibly, the apparatus includes a pH adjuster, for adjusting the pH of the metal working fluid. Possibly, the pH adjuster is located in flow sequence after the decontaminator. Possibly, the pH adjuster includes a pH monitor for monitoring the pH of the metal working fluid. Possibly, the pH adjuster includes a dosing pump for dosing a pH adjustment fluid into the metal working fluid, to adjust the pH of the metal working fluid. Possibly, the pH adjuster includes a controller, which, in use, may control the operation of the dosing pump in accordance with the level of pH detected in comparison with a predetermined desired level of pH. 
     Possibly, the pH adjustment fluid comprises a pH raising fluid. 
     Possibly, the predetermined desired pH level is in the range 8.6-9.1. 
     Possibly, the intake arrangement includes a strainer, for straining out relatively large particles, such as metal swarf. 
     Possibly, the intake arrangement includes a suction tube, which may be located in or attached to a tank of metal working fluid. 
     Possibly, the outlet arrangement includes an outlet tube, which may be located in or attached to the tank of metal working fluid. 
     Possibly, the decontaminator includes a bypass flow line, to permit the metal working fluid to bypass the UV light treatment arrangement. Possibly, the decontaminator includes a bypass control valve arrangement for switching flow of the metal working fluid between a treatment condition, in which the metal working fluid flows through the UV light treatment arrangement, and a bypass condition, in which the metal working fluid flows through the bypass flow line. 
     Possibly, the decontaminator includes a pH monitor, for monitoring the pH of the metal working fluid. Possibly, the pH monitor is located upstream of the UV light treatment arrangement and may be located between the UV light treatment arrangement and the filter arrangement. 
     Possibly, the decontaminator includes a bypass controller which receives a pH signal from the decontaminator pH monitor. 
     Possibly, the bypass controller sends control signals to the bypass control valve arrangement to switch the flow between the treatment condition and the bypass condition. Possibly, the switching is dependent on the monitored value of the pH at the decontaminator pH monitor relative to a predetermined pH control value. 
     Possibly, if the monitored value of the pH matches or exceeds the predetermined pH control value, the bypass controller sends a control signal to the bypass control valve arrangement to switch the flow from the treatment condition to the bypass condition. 
     Possibly, if the monitored value of the pH is lower than the predetermined pH control value, the bypass controller sends a control signal to the bypass control valve arrangement to switch the flow from the bypass condition to the treatment condition. 
     Possibly, the predetermined pH control value is 8.5. 
     Possibly, the metal working fluid does not comprise a bactericide. 
     Possibly, the metal working fluid is for use as one or more of a cutting fluid, a grinding fluid, a drawing and/or forming fluid, a coolant, a component cleaner, a press lubricant, a corrosion inhibitor and/or a degreaser. 
     According to a second aspect of the present invention, there is provided method of decontaminating metal working fluid, the method including providing metal working fluid decontamination apparatus, the apparatus including: 
     an intake arrangement for metal working fluid; 
     a pump for providing, in use, flow pressure to the metal working fluid; 
     a decontaminator for reducing contamination in the metal working fluid; 
     an outlet arrangement for the metal working fluid; 
     whereby, the metal working fluid is a fully synthetic metal working fluid, which comprises water and a water soluble synthetic concentrate which does not contain oil. 
     Possibly, the apparatus includes any of the features described in any of the preceding statements or following description. Possibly, the method includes any of the steps described in any of the preceding statements or following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:— 
         FIG. 1  is a schematic view of metal working fluid decontamination apparatus; 
         FIG. 2  is a sectional schematic view through a UV light treatment arrangement of the apparatus of  FIG. 1  as indicated by arrows II-II in  FIG. 1 ; 
         FIG. 3  is a sectional schematic view of another UV light treatment arrangement; and 
         FIG. 4  is an end view of the UV light treatment arrangement of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  show metal working fluid decontamination apparatus  10 . The apparatus  10  includes: an intake arrangement  40  for metal working fluid  42 ; a pump  16  for providing, in use, flow pressure to the metal working fluid  42 ; a decontaminator  50  for reducing contamination in the metal working fluid  42 ; and an outlet arrangement  34  for the metal working fluid. 
     The metal working fluid  42  is a fully synthetic metal working fluid, which comprises water and a water soluble synthetic concentrate which does not comprise oil. The metal working fluid  42  is non-combustible. 
     In one example, the metal working fluid  42  could comprise, in a fresh (i.e. unused) condition, no more than 10% by weight of the synthetic concentrate, and could comprise no less than 2% by weight of the synthetic concentrate in the fresh condition. In another example, the metal working fluid  42  could comprise, in the fresh condition, no more than 7% by weight of the synthetic concentrate, and could comprise no less than 5% by weight of the synthetic concentrate. 
     The metal working fluid  42  is, in the fresh condition, substantially transparent. 
     In one example, the pump  16  could be a self-priming centrifugal pump. In other examples, the pump  16  could be a positive displacement pump. 
     The decontaminator  50  comprises a filter arrangement  60 , to reduce particulate contamination in the metal working fluid  42 . 
     The filter arrangement  60  comprises a coarse filter  62  for filtering particulates. In one example, the coarse filter  62  could be at least a 20 micron filter (i.e. filters out particulates at least down to 20 microns), and could be no more than a 5 micron filter (i.e. does not filter out particulates below 5 microns). 
     The filter arrangement  60  comprises a fine filter  64  for filtering particulates. In one example, the fine filter  64  is at least a 20 micron filter (i.e. filters out particulates at least down to 20 microns), and could be no more than a 0.5 micron filter (i.e. does not filter out particulates below 0.5 microns). 
     The filter arrangement  60  comprises a positively charged microbial filter  66  for filtering microscopic particulates, which could include metal particles such as brass and microbial particles such as bacteria. In one example, the microbial filter  66  could be at least a 1.0 micron filter (i.e. filters out particulates at least down to 1.0 micron), and could be no more than a 0.1 micron filter (i.e. does not filter out particulates below 0.1 micron). 
     In the example shown, the filter arrangement  60  comprises the coarse filter  62 , the fine filter  64 , and the microbial filter  66  in flow sequence. 
     All of the filters  62 ,  64 ,  66  could comprise replaceable filter cartridges or filter bags. 
     The apparatus  10  comprises pressure gauges  32  which are located upstream and downstream of each of the filters  62 ,  64 ,  66 , to indicate the pressure drop over each filter  62 ,  64 ,  66  and thereby whether any of the filters  62 ,  64 ,  66  need replacing. 
     The decontaminator  50  comprises an ultraviolet (UV) light treatment arrangement  20 , to reduce microbial contamination and endotoxins in the metal working fluid  42 . 
     The UV light treatment arrangement  20  defines a treatment passage  38  along which, in use, the metal working fluid  42  flows. The arrangement  20  includes a UV light source  26  which is arranged to treat the metal working fluid  42  as it flows along the passage  38 . 
     In one example, the UV light source  26  operates at a wavelength of 185 to 400 nm. The UV light source  26  could comprise a low pressure UV light source, which could operate at a wavelength of 185 to 254 nm, and/or could comprise a medium pressure UV light source, which could operate at a wavelength of 200 to 400 nm. 
     The UV light treatment arrangement  20  includes a UV light treatment unit  56  which includes passage walling  36  which defines the treatment passage  38 . In the example shown, the passage walling  36  is in the form of a tube  24 . The passage walling  36  is substantially transparent, and could be formed of glass. In one example, the passage walling  36  is formed of quartz. In the example shown, the unit  56  includes four UV light sources  26 , which are equispaced around the passage walling  36  to provide even 360° illumination of the passage walling  36  and which treat the metal working fluid  42  as it flows along the passage  38 . 
     The UV light treatment unit  56  includes a housing  22 , in which the UV light sources  26  and the passage walling  36  are located, and which could be formed of a corrosion resistant metal such as stainless steel or aluminium. 
     The UV light treatment unit  56  includes a flow disrupter  44 , which is located in the passage  38  and, in use, alters the flow of the metal working fluid  42  along the passage  38  from laminar flow to turbulent flow. The flow disrupter  44  includes one or more static mixing elements  46 , which could be spiral type plastic elements. 
     In one example, the length of the passage  38  is approximately 800-1200 mm and the diameter is 20 mm. The flow rate of metal working fluid  42  is approximately 20 to 40 l/min and the energy consumed is 75-400 W. 
     The apparatus  10  includes a plurality of pH monitors  30 A,  30 B for monitoring the pH of the metal working fluid  42 . Each pH monitor  30 A,  30 B includes a detector  52 , for detecting the pH of the metal working fluid  42  and could include a local display  54 , for displaying the pH of the metal working fluid  42 . 
     The apparatus  10  could include a controller  70 , which could include a local display  54 . Each of the pH monitors  30 A,  30 B could be in signal communication with the controller  70 , either by wire or wirelessly, as indicated by partial dashed lines  74 . 
     In the example shown, one pH monitor  30 A is located upstream of the decontaminator  50  and another pH monitor  30 B is located downstream of the decontaminator  50 . This permits monitoring of the alkalinity levels of the metal working fluid  42  before and after passing through the decontaminator  50 . 
     The apparatus includes a pH adjuster  80 , for adjusting the pH of the metal working fluid  42 . The pH adjuster  80  is located in flow sequence after the decontaminator  50 . In one example, the pH adjuster  80  includes a pH monitor  30 C for monitoring the pH of the metal working fluid  42 . The pH adjuster  80  includes a dosing pump  28  for dosing a pH adjustment fluid  82  (which could be stored in a container  86 ) into the metal working fluid  42 , to adjust the pH of the metal working fluid  42 . 
     In the example shown, the pH adjuster  80  includes a controller  84 , which, in use, controls the operation of the dosing pump  28  in accordance with the level of pH detected by the monitor  30 C, in comparison with a predetermined desired level of pH. 
     The pH adjustment fluid  82  comprises a pH raising fluid. 
     In some examples, the detector  52  of the downstream pH monitor  30 B could comprise the monitor  30 C of the pH adjuster  80 . 
     In some examples, the monitor  30 C and/or the controller  84  of the pH adjuster  80  could comprise, or be in signal communication with, the controller  70 , either by wire or wirelessly, as indicated by partial dashed lines  74 . 
     The intake arrangement  40  includes a strainer  14 , for straining out relatively large particles, such as metal swarf. The intake arrangement  40  includes a suction tube  12 , which could be located in or attached to a tank  18  of the metal working fluid  42 . 
     The outlet arrangement  34  includes an outlet tube  92 , which could be located in or attached to the tank  18  of the metal working fluid  42 . 
     The decontaminator  50  includes a bypass flow line  48 , to permit the metal working fluid  42  to bypass the UV light treatment unit  56 . The decontaminator  50  includes a bypass control valve arrangement  58  for switching flow of the metal working fluid  42  between a treatment condition, in which the metal working fluid  42  flows through the UV light treatment unit  56  and a bypass condition, in which the metal working fluid  42  flows through the bypass flow line  48 . 
     The decontaminator  50  includes a decontaminator pH monitor  30 D, for monitoring the pH of the metal working fluid  42 . The decontaminator pH monitor  30 D is located upstream of the UV light treatment unit  56 , between the UV light treatment unit  56  and the filter arrangement  60 . 
     The decontaminator  50  includes a bypass controller  72  which receives a pH signal from the decontaminator pH monitor  30 D. 
     The bypass controller  72  sends control signals to the bypass control valve arrangement  58  to switch the flow between the treatment condition and the bypass condition, dependent on the monitored value of the pH at the decontaminator pH monitor  30 D relative to a predetermined control value. 
     In some examples, the bypass controller  72  could comprise, or be in signal communication with, the controller  70 , either by wire or wirelessly, as indicated by partial dashed lines  74 . 
     The metal working fluid  42  could be for use as one or more of a cutting fluid, a grinding fluid, a drawing and/or forming fluid, a coolant, a component cleaner, a press lubricant, a corrosion inhibitor and/or a degreaser. 
     In Use 
     In use, the pump  16  is operated and draws the metal working fluid  42  from the machine tank  18  into the suction tube  12 . In a contaminated condition, from the machine tank  18 , the metal working fluid  42  is usually opaque. 
     The metal working fluid  42  flows through the strainer  14  and through the three stage filter arrangement  60  of the coarse filter  62 , the fine filter  64  and the microbial filter  66 . 
     After filtration, the metal working fluid  42  is substantially transparent. 
     The decontaminator pH monitor  30 D monitors the pH value of the metal working fluid  42  exiting the filter arrangement  60 . The bypass controller  72  compares the monitored value of the pH at the decontaminator pH monitor  30 D relative to a predetermined control value. 
     If the monitored value of the pH matches or exceeds the predetermined pH control value, the bypass controller  72  sends a control signal to the bypass control valve arrangement  58  to switch the flow from the treatment condition to the bypass condition. 
     If the monitored value of the pH is lower than the predetermined pH control value, the bypass controller  72  sends a control signal to the bypass control valve arrangement  58  to switch the flow from the bypass condition to the treatment condition. 
     In one example, the predetermined pH control value is 8.5. 
     In the treatment condition, the metal working fluid  42  flows through the UV light treatment unit  56 . As it does so, UV light from the UV light sources  26  illuminates the metal working fluid  42  to kill bacteria therein. The static mixing elements  46  of the flow disrupter  44  ensure the flow is turbulent flow to provide thorough treatment. 
     If the monitored value of the pH is higher than the predetermined pH control value (eg higher than 8.5), the bypass controller  72  sends a control signal to the bypass control valve arrangement  58  to switch the flow from the treatment condition to the bypass condition and the metal working fluid  42  does not pass through the UV light treatment unit  56 . In the bypass condition, the UV light treatment unit  56  can be switched off to save power. 
     The pH of the decontaminated metal working fluid  42  is monitored by the pH adjuster  80 . If the pH is below the predetermined desired level, the pH adjuster controller  84  operates the dosing pump  28  which doses the pH raising fluid  82  into the metal working fluid  42  to raise the pH of the metal working fluid  42 . The pH raising fluid  82  does not comprise a biocide. 
     In one example, the predetermined desired pH level is in the range 8.6-9.1. 
     The decontaminated and pH adjusted metal working fluid  42  then flows back to the machine tank  18 . 
     Upstream and downstream pH monitors  30 A,  30 B provide indication of the pH of the metal working fluid  42  before and after treatment. 
     In one example, the bacterial load in the metal working fluid  42  before treatment could be 106 CFU/ml (colony forming units per ml). After a period of treatment using the apparatus  10 , the Applicant has found that the bacterial load could be reduced to 103 CFU/ml. 
     The Applicant has realised that one of the properties of fully synthetic metal working fluids, namely transparency, can be utilised to permit UV light treatment. Conventionally, UV light treatment of metal working fluids has been unsuccessful, since most metal working fluids are usually emulsions with poor light transmission properties. Also, emulsifiers in the metal working fluid emulsify tramp oil from the machine which causes shadowing. Tests of emulsion metal working fluids have shown that penetration of UV light is 100% attenuated at 1 mm depth. 
     A further disadvantage of emulsion metal working fluids is that filtration is limited to no lower than 10 micron as anything smaller can remove emulsion particles such as additives and oil, effectively disrupting the stability of the emulsion. 
     The Applicant has realised that fully soluble synthetic metal working fluids permit the use of finer filters, which can be used to remove microbial particles such as bacteria. 
     The Applicant has surprisingly found that the three stage filtration of the apparatus  10  is effective in providing a satisfactorily treated metal working fluid without, or with reduced, use of biocide and without requiring UV treatment. 
     However, the filters are not 100% effective in removing all microbial particulate. Hence, the UV treatment arrangement provides a cleaner, safer metal working fluid  42  which results in safer working conditions for operators, and longer filter life. 
     A further benefit is reduced use of biocide, with attendant environmental benefits, particularly on disposal. In fact, the Applicant has found that use of the apparatus  10  means that bactericide or biocide use in the metal working fluid is not required or greatly reduced. 
     The Applicant has further realised that pH provides an indication of bacterial load. A higher bacterial load will result in a lowering of pH. Thus by measuring pH, a measure of the bacterial load of the metal working fluid  42  can be obtained and hence health and safety risk can be assessed. In the apparatus  10 , this understanding is used to control flow through the UV light treatment unit  56 . At satisfactory pH levels (i.e. low bacterial load) the flow of the metal working fluid  42  is diverted through the bypass line  48 , thus saving energy. 
     Other Embodiments 
       FIGS. 3 and 4  show another embodiment of the invention, many features of which are similar to those already described in relation to the embodiment of  FIGS. 1 and 2 . Therefore, for the sake of brevity, the following embodiment will only be described in so far as it differs from the embodiment already described. Where features are the same or similar, the same reference numerals have been used and the features will not be described again. 
       FIGS. 3 and 4  show another UV light treatment arrangement  120 . The UV light treatment arrangement  120  includes a UV light treatment unit  56 . The UV light treatment unit  56  includes a housing  22  and passage walling  36 . The housing  22  and the passage walling  36  define a treatment passage  38  therebetween, along which, in use, the metal working fluid  42  flows. In the example shown, the passage walling  36  is in the form of a tube  24 , which is circular in cross-section. The passage walling  36  is substantially transparent, and could be formed of glass. In one example, the passage walling  36  is formed of quartz. 
     In the example shown, the unit  56  includes a UV light source  26 , which is located within the treatment passage  38 , within the passage walling  36 . In the example shown, the UV light source  26  is on the inside of the passage walling  36  and the metal working fluid  42  flows, in use, around the outside of the passage walling  36 . 
     In  FIGS. 3 and 4 , arrows F indicate the flow of the metal working fluid  42  and arrows L indicate the direction of the UV light transmission. Thus, in use, the metal working fluid  42  flows into the unit  56  and along the unit  56 , along the passage  38  between the housing  22  and the passage walling  36 . UV light is transmitted outwardly from the UV light source  26  through the passage walling  36  to treat the metal working fluid  42  in the treatment passage  38 . In this embodiment, the metal working fluid  42  flows around the UV light source  26 , maximising the efficiency of the UV light treatment arrangement  120 . 
     A flow disrupter  44  could be located in the treatment passage  38  as in the previous embodiment, or upstream thereof, to ensure the flow is turbulent and provide thorough treatment. 
     Other Modifications 
     Various other modifications could be made without departing from the scope of the invention. The apparatus and its various components could be of any suitable size and shape, and could be formed of any suitable material (within the scope of the specific definitions herein). 
     The apparatus  10  could be used to treat any mineral oil free cutting fluid or aqueous machine cleaner. 
     The apparatus  10  could be provided to be permanently fixed to a machine, built integrally into the machine (for example, as part of the machine filtration system) or temporarily connected to the machine. 
     If temporarily connected, (ie mobile) the apparatus  10  could be moved to different machines on a periodic basis. 
     If permanently fixed or integral, the apparatus  10  could be programmed to operate on a periodic basis eg a certain number of hours per day, and/or on certain days of the week or month. 
     If permanently fixed or integral, the coarse and fine filters  62 ,  64  of the apparatus  10  could be integrated into the machine filtration system. 
     The apparatus  10  could be used remote from the machine, to treat stored used metal working fluid. For example, the apparatus  10  could draw metal working fluid from one storage vessel (eg an Intermediate Bulk Container or IBC), and provide the decontaminated metal working fluid either back to the same IBC or to another IBC. 
     In another example, the apparatus  10  could include a pH monitor (not shown) which measures the pH in the machine tank  18  and the controller  70  could operate the apparatus  10  when the pH in the tank  18  falls below a predetermined level. 
     The intake arrangement  40  could include a coupling or connector, eg a camlock quick release connector (not shown), to connect to a fitting (not shown) on the tank  18 . Similarly, the outlet arrangement  34  could include a coupling or connector, e.g. a camlock quick release connector (not shown), to connect to a fitting (not shown) on the tank  18 . 
     The number of pH monitors could vary. The pH monitors could be standalone devices or linked to the controller or to another device. The or each or one or some of the pH monitors could include a logger, for recording the pH of the metal working fluid, and/or a transmitter, for transmitting the pH of the metal working fluid to a remote display and/or a remote logger or controller. 
     The apparatus  10  could include a different number of filters. The filters could be operated independently, so that the user can select which filters operate. For example, a bypass line could be provided for the microbial filter  66  and the pH of the metal working fluid  42  monitored at the exit of the fine filter  64 . If the monitored value of the pH matches or exceeds the predetermined pH control value, then the metal working fluid  42  could be directed along the bypass line, extending the life of the microbial filter  66 . 
     Any or all of the control valves, dosing pump and pH monitors could be manually operated. 
     The filters could be of any suitable type. 
     The UV light treatment arrangement could comprise any suitable number of UV light treatment units. The UV light treatment units could be of any suitable type and could comprise any suitable arrangement (including number, design and type) of passage walls, tubes, mixing elements and UV light sources, arranged in any suitable way. In one example, the UV light treatment arrangement could comprise a plurality of UV light treatment units which, could be arranged in parallel or, more desirably, in series. 
     In one example, the UV light source  26  could comprise both the low pressure UV light source operating at the wavelength of 185 to 254 nm, and the medium pressure UV light source, operating at a wavelength of 200 to 400 nm. The UV light sources  26  could be arranged in series. 
     Both the low pressure UV light source and the medium pressure UV light source operate to destroy bacteria (and hence reduce bacterial contamination) and oxidise endotoxins (and hence reduce toxicity). However, the Applicant has found evidence that the low pressure UV light source is more effective than the medium pressure UV light source in destroying bacteria, and the medium pressure UV light source is more effective than the low pressure UV light source in oxidising endotoxins. Ideally, therefore, the combination in series of both the low pressure UV light source and the medium pressure UV light source would appear to be most effective, but is relatively costly and requires a lot of space and therefore with the presently available technology can only be justified for large installations. 
     In one example, the flow disrupter could be located upstream of the treatment passage. 
     Any of the features or steps of any of the embodiments shown or described could be combined in any suitable way, within the scope of the overall disclosure of this document. 
     There is thus provided metal working fluid decontamination apparatus  10 . The apparatus  10  uses a combination of filtration and UV light treatment to decontaminate metal working fluids and reduces/eliminates the use of biocides. In comparison with conventional arrangements, costs are reduced, the health and safety risk is reduced and the working conditions of operatives are improved. The apparatus  10  is flexible in use to maximise energy efficiency. The reduction in use of biocides is a significant environmental benefit. The apparatus also reduces the frequency of disposal of the metal working fluid and hence operating cost, providing a further environmental benefit.