Abstract:
A method of handling grey water and optionally at least a portion of the black water for disposal from vehicles such as boats, recreational vehicles or rural dwellings such as cottages, camps and the like, not having direct access to sewer systems, involves the treatment of such waste water with ozone. A batch system is used whereby a predetermined quantity of water to be treated is captured in a treatment tank. A circulating pump withdraws water from the tank and pushes the water along a treatment conduit, the conduit containing an ozone/water mixer and returns the water to the treatment tank. The treatment conduit has a discharge valve that is maintained in a closed position for a selected period of time. Ozone is fed to the ozone/water mixer from an ozone generator which is advantageously fitted with an air pump to pressurize the feed gas.

Description:
This application is a continuation-in-part of application Ser. No. 09/533,261 filed Mar. 22, 2000, now U.S. Pat. No. 6,402,945 issued Jun. 11, 2002. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a method and apparatus for the treatment of water. The water treatment method and apparatus may be applied to fluids such as grey or black water to be treated prior to discharge or raw water to be treated prior to consumption. 
     BACKGROUND OF THE INVENTION 
     In the field of grey/black water disinfection, great efforts are continuously being made to reduce the quantity and concentration of pollutants found in grey/black water being discharged into rivers, lakes, surface and ground water supplies, etc. This is evidenced by more and stricter government regulations and requirements relating to grey/black water treatment processes and discharges. The quantities of human wastes requiring treatment are constantly and rapidly increasing. In the field of potable water purification, available surface and ground water sources are rapidly deteriorating due to pollution caused by contaminates generated by a growing population and their careless use of water and improper disposal of waste products. 
     Many methods exist for the treatment of grey/black water. Biological or chemical disinfection of the grey/black water to neutralize the harmful micro organisms within grey/black water are common methods employed to reduce bacteria loading found in grey/black water. Biological disinfection of grey/black water requires large tanks for micro organisms to consume the biological waste contained within the grey/black water. Chemical disinfection of grey/black water is not acceptable for water based communities and activities. 
     Many methods also exist for the purification of potable water which include the use of chemical disinfectants, microfiltration and ultra violet radiation. The most commonly used disinfectant is chlorine and when water containing organic material and compounds is chlorinated, a range of carcinogenic trihalomethanes is generated and considerable contact time is required for effective disinfection. When microfiltration is used to remove biological contaminants, the filtering devices require constant and regular servicing. When ultra-violet radiation is used to make water potable, the effectiveness is limited by the clarity of the water being treated. These physical and chemical factors place severe limitations on these methods of disinfection in recreation facilities. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, a method for treating water to reduce bacteria, viruses, parasites and spores prior to discharge comprises the steps of collecting a predetermined quantity of water to be treated in a treatment tank and thereafter mixing with the predetermined quantity of water to be treated, ozone. The selected quantity of water to be treated is mixed with the ozone for a selected period of time. Thereafter the mixed water is discharged to waste. 
     In accordance with the invention, there is a system for treating water for discharge. The water is treated to reduce bacteria, viruses, parasites and spores in the water prior to discharge of the water. The system comprises collecting a predetermined quantity of water Q to be treated in a treatment tank and thereafter mixing ozone with the quantity of water to be treated by injecting ozone through an injector as the water to be treated passes through the injector. The method further includes mixing the predetermined quantity of water with the ozone for a selected period of time and preventing any additional water to be treated from entering the treatment tank while the predetermined quantity of water is mixed with ozone. The selected treatment time is less than five minutes. 
     In a preferred embodiment of the invention, a method for treating waste water involves carrying out such treatment in accordance with process parameters given by the formula:        T   =     I3Q   0                            
     wherein T is the treatment time in hours, O is the amount of ozone generated in milligrams per hour, I is the amount of ozone injected per liter of water being treated as the water passes the ozone injector and Q is the batch size of the water to be treated, in liters. In a particularly preferred embodiment of the invention, the amount of ozone injected into the predetermined quantity of water to be treated is at least 1.25 milligrams per liter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be discussed in association with the following drawings, which illustrate preferred embodiments of the invention. 
     FIG. 1 illustrates a system embodying a first aspect of the invention; 
     FIG. 2 illustrates a system embodying an alternate aspect of the invention; 
     FIG. 3 illustrates an alternative embodiment of a portion of the system of FIG. 1; 
     FIG. 4A illustrates a first arrangement of parts of a portion the system of FIG. 1, and 
     FIG. 4B illustrates an alternate arrangement of the parts of the portion of the system of FIG. 1 illustrated in FIG.  4 A. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The term “grey water” is used in this description and in the claims to describe water which is not human sewage but results from use by humans such as in washing and the like. The term “grey water” can encompass effluent from sinks, showers and the like. The term “black water” is used in this description and claims to refer to water in which human sewage is a significant component. Black water normally results from effluent from toilets and the like. 
     The term “potable water” is used in this description and claims to refer to water which is fit for human consumption. 
     The term “raw water” is used in this disclosure and claims to refer to ambient liquid such as may be found in surface water comprising lakes, rivers, streams and the like, and in addition, ground water such as may be contained in wells, whether dug or drilled, as well as run off water such as collected rain water and the like. The term “raw water” is intended to cover all liquids other than water which is primarily either grey water or black water. 
     The term “disinfection” as used in this disclosure and the claims, refers to treatment of water to reduce bacteria, viruses, parasites and spores content of the water. In the case of use of the term “disinfection” with grey water or black water, the term is intended to encompass reducing the bacteria, viruses, parasites and spores content of the water to a level acceptable for discharge to the intended environment, whether that be on land or into other surface water. In connection with the term potable water, the term “disinfection” is intended to encompass reducing the bacteria, viruses, parasites and spores content of raw water to the state that the water, after treatment, is suitable for human drinking consumption. 
     The embodiment of the water treatment system illustrated in FIG. 1 is illustrated generally at  10 . The principal components of the system include a treatment tank  20 , a solenoid controlled discharge valve  30 , a controller  80 , and an ozone generator  40 . Preferably, the system includes a collection tank  60  for collecting water to be treated. Optionally, the system may also include a black water collection tank  70 . 
     The water treatment system  10  includes a treatment conduit  22  comprising withdrawal conduit  24  and a return conduit  26 , a circulating pump  28 , and a treatment mixer  42 . The system  10  further comprises a supply conduit  44  and a vent conduit  46 . The system  10  also includes a discharge conduit  32 , and an air inlet  41 . 
     The valve  30  includes a solenoid for controlling the position of the valve  30 . 
     The collection tank  60  includes an inlet  62 , a transfer pump  64  and a transfer conduit  66  which advantageously includes a check valve  68 . 
     The embodiment illustrated in FIG. 1 is particularly adapted for use in vehicles having relatively reduced space for collection of grey water and advantageously black water. Such vehicles may include recreation vehicles, water vessels and the like. It should be understood, however, that while the invention is discussed in association with its application to a marine vessel, the system is equally applicable to use in land based mobile vehicles such as recreational vehicles and the like and also to fixed installations such as in buildings not having connection access to sewage treatment systems such as rural properties, cottages and the like. 
     Water to be treated is collected by suitable piping from all sinks, showers, washing facilities and the like and directed to the water inlet  62 . Water to be treated continues to enter the collection tank  60 . The transfer pump  64  may be located in the bottom of the water collection tank  60  and may be operated by means of a float switch or the like. Upon operation of the transfer pump  64 , water collected in the collection tank  60  is transferred via the transfer conduit  66  through the check valve  68  to the treatment tank  20 . The transfer pump  64  will operate until such time as a determined quantity of water is contained within the treatment tank  20 . The treatment tank  20  includes a high level sensor  82  which may be a float which is connected to the controller  80  by input line  84 . The volume of the treatment tank  20  as determined by high level sensor  82  defines a selected volume Q 1  of water to be treated. 
     When the high level sensor  82  senses that the volume Q 1  of the water is in the treatment tank  20 , the controller  80  shuts off the transfer pump  64  via line  86  to ensure that no additional water to be treated is added to the treatment tank  20 . As a further option, the transfer conduit  66  may include a solenoid controlled valve  69  controlled by controller  80  through line  88  to ensure no gravity flow from collection tank  60  to treatment tank  20 . 
     Once the treatment tank  20  has been filled with quantity Q 1 , the controller will cycle the circulating pump  28  which is connected to the controller by line  90 . Upon operation of the circulating pump  28 , liquid will be circulated through the treatment conduit  22 . Liquid will be withdrawn through withdrawal conduit  24  to the pump  28  by valve  30  and through return conduit  26  to the tank  20 . The valve  30  is positioned at all times during treatment to direct flow from the withdrawal conduit  24  into the return conduit  26  and prevent flow through the discharge conduit  32  until opened by controller  80 . 
     The ozone generator  40  is a commercially available ozone generator. A particularly suitable equipment for a marine application is the ozone generator sold by A. H. Simpson Industries Limited of Ontario, Canada, under the model designation SW400. The ozone generator  40  draws in ambient air through the inlet  41 . To enhance efficiency of the ozone generator, the inlet  41  advantageously directs the ambient air through a dryer  43 . The air is then fed to the ozone generator  40  so that ozone is generated. The ozone generated then passes along the supply conduit  44  to the inlet point of a treatment mixer  42  located in the return conduit  26 . Preferably the treatment mixer is a venturi injector. A suitable venturi injector is the equipment sold by Mazzei Injector Corporation of California, U.S.A., under the model designation 384. The controller  80  turns on the ozone generator  40 , which is connected by line  92 , when the circulating pump  28  is cycled. 
     Under the effect of the circulating pump  28 , liquid to be treated is continuously withdrawn from the treatment tank  20 , circulated through the withdrawal conduit  24  where it passes by the valve  30  and into the return conduit  26 . The passage of the liquid by the treatment mixer  42  draws ozone into the liquid to be treated thereby ensuring delivery of ozone to the fluid circulating in the treatment conduit and ensuring intimate mixing of ozone with the liquid travelling along the treatment conduit. 
     The treatment of water in accordance with this invention is a batch system. The volume of water to be treated is determined by the volume of the treatment tank  20 . The designated volume of water to be treated, Q 1  is thus circulated by the circulating pump  28  continuously through the treatment mixer  42 . The circulating pump  28  and the ozone generator  40  operate for a predetermined period of time T 1  to ensure that a suitable supply of ozone is injected into the liquid to be treated and to provide suitable contact between the ozone and all of the liquid to be treated. 
     After a designated period of time, T 1  of operation of the circulating pump  28 , the controller  80  moves valve  30  to the discharge connect position by means of control line  94 . At this time, the circulating pump  28  then withdraws liquid from the treatment tank  20  and discharges that liquid through the discharge conduit  32 . The circulating pump  28  continues to run until the treatment tank  20  is emptied. Emptying of the treatment tank  20  is sensed by a low level sensor  96 . A signal is passed through line  98  to controller  80 . The controller then stops the pump  28  and the generator  40  and resets all controlled items ready to handle another batch. 
     Since this is a batch process, the amount of liquid Q 1  to be treated is known. The treatment time T 1  can also be set by the controller to ensure treatment for any desired length of time. The amount of ozone generated by the ozone generator  40  in time T 1  will also be known. As during the treatment, ozone is admixed continuously into the liquid being treated by the mixer  42 , sufficient contact time can be ensured to ensure treatment of the quantity Q 1  of water to any desired level. The volume of the treatment tank  20  can be configured to meet whatever constraints drive the overall size of the equipment. Where the equipment is to be installed on a marine vessel, space may be at a premium and the batches treated may be relatively small batches in the order of 3 gallons. With a small volume of Q 1 , the treatment time T 1  may be relatively short, in the order of 3 minutes. Where space is not quite such a premium, then the treatment tank may be larger; with a larger treatment volume Q 1 , longer circulation times T 1  can be programmed into the controller to ensure satisfactory contact of the batch with the ozone to provide suitable treatment prior to discharge. One of the advantages of providing the collection tank  60  is the provision of additional storage of grey water prior to treatment. Thus, if a shower is being used, the grey water from the drain may be collected at any convenient flow rate which is not subject to the batch treatment limitation, Q 1  and T 1 . The size of the grey water collection tank will be determined by desired interim storage capacity and the treatment parameters of time and quantity. The process can be repeated continuously to treat a total amount of water which is larger than the batch size Q. Thus quantities of size 2Q and larger can be treated by repeating the method on a new batch as many times as required. 
     In circumstances such as marine vessels and the like there will still be required, holding tanks for black water. Black water emanating from the vessel&#39;s toilet will need to be collected in a black water collection tank  70 . As the primary constituent of such black water will be human sewage, this will normally be stored in the tank and subsequently pumped out in available pump out stations. However, in order to extend the capacity of the black water holding tank  70 , the black water holding tank may be arranged so that an overflow conduit  72  may be arranged to permit liquid above a certain level in the black water holding tank  70  to flow over by gravity into the grey water collection tank  60 . Liquids at the top of the black water collection tank  70  may be, in essence, not substantially different than the content of the grey water input and thus may be suitable for treatment in the batch system discussed above. Sediment or other non liquid constituents of the black water holding tank  70  would, however, be retained in the lower reaches of the black water holding tank where they will remain until pumped out at a sanitary pump out station. By providing an over flow of the black water holding tank  70  for the liquids at the upper reaches of the black water holding tank, the effective capacity of the vessel between required pump outs may be extended by treating the upper surface liquids in the grey water treatment system. 
     Advantageously the treatment system  10  also comprises an ozone vent conduit  46 . The vent conduit  46  communicates from the top of the treatment tank  20 , ultimately to the discharge conduit  32 . As ozone is continuously introduced into the batch during the operation of the circulating pump  28 , gas pressure may build up in the treatment tank  20 . Any ozone building up in the treatment tank  20  is then vented to the discharge conduit  32  ensuring that a continuous fresh supply of ozone from the generator  40  will be introduced into liquid being treated through the treatment mixer  42 . Advantageously, the ozone conduit vent  46  may be directed to the collection tank  60 . Thus, any ozone from conduit line  46  will achieve slight pretreatment and deodorization in the collection tank  60 . The collection tank  60  is vented, in turn, through conduit  46 A to the discharge conduit  32 . Check valves  47 A and  47 B ensure no back flow in vent conduit  46  and  46 A respectively. Also, as shown diagrammatically, the vent conduit  46 A contains a vertically upwardly directed run  48  to prevent inadvertent draining of collection tank  60  directly to discharge conduit  32  which might occur while a vessel is moving through wave action or other motion. 
     FIG. 2 illustrates a modified version of the treatment system shown in FIG.  1 . The treatment system in FIG. 2 is essentially similar to the treatment system shown in FIG. 1 with the addition of a potable water treatment system utilizing the same ozone generator. Similar parts of the system  110  shown in FIG. 2 corresponding to those in FIG. 1 have been given like numbers with the prescript 1. Thus, ozone generator  140  in FIG. 2 corresponds to ozone generator  40  in FIG.  1 . 
     Accordingly, the water treatment system  110  as shown in FIG. 2 comprises a collection tank  160 , treatment tank  120  and ozone generator  140 . The circulating pump  128  circulates liquid to be treated through the withdrawal conduit  124  and through return conduit  126 . The return conduit  126  includes a treatment mixer  142 . After treatment for the set time the valve  130  in the treatment conduit  122  is opened by controller  180  so that the circulating pump  128  discharges through the discharge conduit  132 . Advantageously a black water collection tank  170  is fluidly connected to the collection tank  160  by an overflow conduit  172 . The transfer pump  164  transfers liquid from the collection tank  160  through the transfer conduit  166  by check valve  168 , into the treatment tank  120 . 
     The system  110  includes a potable water treatment system illustrated generally at  175 . In the system  110  illustrated in FIG. 2, the supply conduit  144  comprises a second conduit  144 A for delivery of ozone from the ozone generator to the potable water system  175 . 
     The potable water treatment system comprises a raw water inlet system  177 , check valve  179 , a filter  181 , a supply pump  183 , a supply mixer  185 , a retention and air release tank  187  and a carbon filter  189 . The supply mixer  185  may be similar to treatment mixer  142  and treatment mixer  42 . The potable water treatment system  175  comprises a potable water outlet  191  which may be connected to taps, tanks or other desired sources of drinking water within the facility in which the system  110  is installed. 
     The potable water purification system  175  commences to operate upon operation of the supply pump  183 . The supply pump  183  may be cycled by demand such as with a manually operated switch such as a foot switch or the like. When the supply pump  183  operates the controller receives a signal through line  193  and the ozone generator  140  is also turned on to supply ozone. Raw water from ambient such as a lake, river, or stream, in the case of a boat, or a well or other suitable surface water at a cottage or rural dwelling, is drawn through the raw water inlet  177 . The check valve  179  prevents any back flow. The raw water is first passed through a filter  181  to remove any gross particles in the water prior to entry into the supply pump. The supply pump  183  then forces the water to be treated through the supply mixer  185 . The supply mixer draws the ozone from the generator  140  and ensures mixing and contact with the raw water. The tank  187  provides a facility for releasing any gases or ozone contained in the water for collection in the tank  187 . A final “polishing” of the water is achieved by passing the water through the carbon filter  189 . In addition, the carbon filter  189  converts any ozone molecules in the raw water to oxygen molecules. After passage through the filter  189  the water is delivered to the source of drinking water. 
     The system  110  provides a very compact system for use in vehicles where storage capacity is limited. As all incoming raw water is treated, the need to maintain large fresh water storage tanks on a vessel can be substantially reduced, if not totally eliminated. The amount of holding tank capacity for black water may be reduced and the opportunity for treatment of all grey water before overboard discharge will eliminate the need for substantial grey water holding capacity. 
     As set out above, the size of the batch of material to be treated, Q 1 , can be determined by the designer of such a system based on available space requirements. The treatment time T 1  is advantageously selected to ensure appropriate treatment of the waste water to meet applicable discharge regulations. The treatment need of grey water is often specified in terms of biological oxygen demand (BOD) and chemical oxygen demand (COD). Grey water will be wide ranging from waste water which has a very low BOD and low COD to waste water having a much higher BOD and a much higher COD. There are two additional factors which are advantageously considered when determining the treatment time T 1 . These include the amount of ozone that is available for mixing with the water being circulated by the circulating pump  28  and also the success in dissolving the available ozone in the water. The contacting of the available ozone with the water occurs initially in the treatment mixer  42 , but of course continues in the turbulence which occurs as the water is circulated through the treatment conduit  22 , the pump  28  and the treatment tank  20 . We have carried out tests for these features to determine preferred operating conditions of the system. 
     A first group of tests were carried out using dechloronized, deionized and filtered laboratory water as the water to be treated. This low demand test water has essentially no BOD nor COD. This low demand test water was then used in tests to determine the effectiveness of ozone injection and dissolving of the ozone in the water. The effectiveness was determined by measuring the residual ozone in the low demand water using a spectrometer. For these tests, a ozone generator available from A. H. Simpson as outlined above was used in the test system together with different sizes and numbers of injectors from Mazzei Injector Corp. 
     Surprisingly, the first batch of tests showed an unsatisfactory residual ozone created in the low demand water. Observed ozone levels generally were less than 0.5 mg/liter of low demand water. 
     Various steps were taken to attempt to increase the residual ozone amount. Ambient air typically contains about 20% oxygen with most of the remainder being nitrogen. Commercially available oxygen has much higher concentrations of oxygen depending on intended use. These include divers oxygen or medical oxygen intended for administration to human beings and commercial oxygen not intended to be administered to a human. These all may have oxygen contents of from about 40% up to almost 100%. As one test, the air inlet  41  was equipped with a supply of commercial oxygen. Using commercial oxygen produced increased residual ozone in the water circulating in the treatment conduit  22 . Also, as might be expected, increasing the processing time T also tended to increase the residual ozone in the water. 
     As an additional part of this testing program, a high demand (high BOD and COD) test fluid was created in the laboratory. Because of the high demand, it was felt that such tests would be a useful indicator to determine whether the required amount of ozone necessary to treat grey water or contaminated water was in fact available and dissolved in the water. The tests were carried out using commercial oxygen supplied to the inlet  41 . After running the system for times slightly less and slightly greater than 2 minutes, it was determined that the residual ozone in the high demand water being treated was either zero or only slightly above zero. This lack of residual ozone appears to indicate that all available ozone was consumed by the BOD and COD demand of the water and from this it may be inferred that insufficient treatment may have occurred. 
     In order to overcome the apparent limitations as set out in these first experiments, various techniques were tested. As stated above, providing a commercial oxygen supply rather than using ambient air, initially provides greater oxygen to the generator, thus resulting in more conversion to ozone and a greater quantity of ozone is available in supply conduit  44 . 
     Another aspect of solution of these observations was to obtain better mixing of the available ozone. While a single ozone injector is described and illustrated in FIG.  1  and labelled treatment mixer  42 , use of a plurality of injectors assists in both the flow of ozone into the treatment liquid and additionally mixing of the available ozone into the water to be treated. Thus, tests were carried out using a plurality of injectors operating in parallel to see if this would show increased levels of residual ozone in low demand water. Finally, consideration was given to using two circulating pumps in place of the single circulating pump  28  illustrated in FIG. 1, to provide enhanced circulation. Using pumps operating in parallel, a higher volume of flow of water through the treatment conduit  22  would be achieved. This, in turn, would produce higher vacuum in the treatment mixer or mixers, thus drawing more ozone into the system as well as assisting in mixing the ozone generated with the water being treated. 
     In subsequent testing, another avenue was explored in an effort to ensure suitable treatment. This included the use of larger ozone generators. Firstly, tests were done using a generator produced by the A. H. Simpson company which was rated as being capable of generating 400 mg of ozone per hour. A still larger A. H. Simpson generator capable of producing 800 mg of ozone per hour was then used. This step helped to increase the residual oxygen in the low demand water, but at increased cost for the larger ozone generator. 
     Tests which had been conducted were conducted using atmospheric air available in the laboratory where the tests were being carried out, or a supply of commercial oxygen available in the laboratory was used for input to inlet  41 . As beneficially increased results were occurring using commercial oxygen as the source of gas entering inlet  41 , avenues were then explored to determine whether there was sufficient oxygen available in the gas being drawn into the inlet  41 . As an experiment on this point, additional ducting was added to the inlet  41  so as to draw in outside air rather than indoor air available in the laboratory. This also gave increased residual ozone in the low demand water being tested. The outside air being drawn in had a higher relative humidity. This then showed that use of a dryer such as dryer  43  in inlet  41  gave much better production of ozone from the generator. Thus, in preferred embodiments, particularly when moisture laden air is drawn in to inlet  41 , a dryer is advantagously used. 
     As an additional step in enhancing the effectiveness of dissolution of the ozone generated, into the water being circulated, a surfactant was added to the low demand water. The use of a surfactant, when other test conditions remained the same, increased the residual ozone in the water being circulated. This indicates that the surfactant aids in the uptake of the ozone so that there is in fact a higher residual ozone content of the mixed water, thereby leading to enhanced treatment. The surfactant added more closely mimics grey water which will naturally contain surfactants in the form of detergents or other soaps, in most cases. 
     A test was then carried out on a laboratory created simulated highly contaminated water. The system as shown in FIG. 1, was operated using a Simpson ozone generator rated as being capable of producing 800 mg/hour of ozone. Three Number 3, Mazzei injectors operating in parallel were used. The Simpson ozone generator was supplied with pure oxygen available in the laboratory. The batch size was 10.9 liters or 2.40 imperial gallons. The system was operated for a processing time of just over 50 seconds with low demand water. First, the residual ozone in low demand water was measured at slightly over 1.5 mg/liter. A test was then run on this system with a simulated highly contaminated water. The water treated was generated in the laboratory to simulate water having a very high BOD and a very high COD typical of the highest levels of demand normally experienced when dealing with grey water and to make the test more severe, the test sample additionally contained a concentrated sewage from a sewage collection facility. 
     This highly contaminated water was then used to determine the percentage reduction which might be achieved in respect of the Total Coliform, Fecal Coliform and  E - coli  using the system described above. The amount of Total Coliform, Fecal Coliform and  E - coli  was analyzed before treatment and after treatment and the figures compared. Although severe, it is considered that this is an apt test to demonstrate the effectiveness of the system. The ozone introduced into the highly contaminated water will first be used up in satisfying the BOD and the COD. Any ozone remaining after satisfying these demands is then available to kill any bacteria, viruses, parasites and spors which may be present in the water to be treated. By determining the reduction in Total Coliform, Fecal Coliform and  E - coli , a useful measure of the effectiveness of the system is obtained. 
     The system was operated for 25 seconds in a first test, 53 seconds in a second test and 95 seconds in the third test on this highly contaminated water. When run for 25 seconds, the analysis of the treated fluid showed that  E - coli  had been reduced by 18%, Total Coliform did not show any significant reduction and Fecal Coliform had been reduced by 10%. This result shows insufficient treatment of the water. When the system was run for 53 seconds, the treated water showed that  E - coli  had been reduced 35%, Total Coliform count had been reduced by 37% and Fecal Coliforms had been reduced by 67%. This shows improved results, but this level is still likely to be insufficient to meet most discharge requirements. 
     When the system was operated for 95 seconds, analysis of the treated water showed that  E - coli  had been reduced by 99.40%, Total Coliform had been reduced by 99.67% and Fecal Coliform had been reduced by 94.60%. This is an excellent result. 
     In another test the system was operated first using atmospheric air as an input to the ozone generator and second using commercial oxygen as an input to the ozone generator both for 100 seconds. When the system was operated for 100 seconds using atmospheric air as the input to the ozone generator, analysis of the treated water showed that the  E - coli  had been reduced by 99.962% and the total Coliform had been reduced by 99.880%. When the system was operated for 100 seconds using commercial oxygen as the input to the ozone generator, analysis of the treated water showed that the  E - coli  had been reduced by 99.997% and the total Coliform had been reduced by 99.992%. This is a significant result. 
     The results of these tests do show, as indicated above, that the time of treatment T 1  is a significant factor in producing a satisfactory treatment level. The test using the system operating as explained above for a time of 95 seconds shows excellent treatment of the highly contaminated water, a result which would permit overboard discharge from a marine vessel in accordance with most discharge regulations. Such a system is thus able to treat a batch of approximately 10.9 liters of highly contaminated water in just over one and a half minutes. 
     As the system described above in connection with these tests has been demonstrated to operate successfully, further tests were then carried out to optimize the system components. Tests were performed utilizing a series of larger generators from the A. H. Simpson company. While these tests indicate slightly increased residual ozone in low demand water, the increase in available ozone did not appear to offset the increased cost of providing a larger generator. Surprisingly, during these tests, it was ascertained that a factor in the amount of ozone produced arises from the fact that the ozone system as explained above was not pressurized. Ozone is supplied in the treatment conduit as outlined in FIG. 1 by reason of the negative pressure developed by the treatment mixer  42 . The treatment mixer  42 , being of the venturi type, produces a suction pressure which draws the ozone into the treatment mixer. An advantageous modification of the structure illustrated in FIG. 1 is illustrated in FIG.  3 . The inlet  41  for the ozone generator  40  includes a dryer  43  and an air pump  45 . The air pump  45  thus pressurizes the feed to the ozone generator  40 . Using pressurized air, satisfactory residual ozone was produced in the fluid to be treated when determined by using a sample fluid having little or no BOD and COD. Pumping air into the ozone generator gives successful results using fresh ambient air so that commercial oxygen which otherwise would increase cost of operation is not required. 
     Another surprising aspect that developed during such testing, is the role played by the arrangement of the batch treatment tank. FIGS. 4A and 4B show diagrammatically, two different arrangements of the batch treatment tank. In FIG. 4A, the return conduit  26  enters the treatment tank  20  at the upper regions of the tank substantially adjacent to the high level sensor  82 . In FIG. 4B, the return conduit  26  enters the treatment tank  20  substantially below the level of the fluid in the tank adjacent to the low level sensor  96 . With the arrangement of the return conduit  26  adjacent the upper region of the treatment tank as shown in FIG. 4A, it was noted that additional flow of gas was achieved in supply conduit  44 . With the return conduit  26  located adjacent the lower region of the treatment tank as shown in FIG. 4B, there was less flow in the supply conduit  44 . However, the flow of greater amounts of ozone in supply conduit  44  with the configuration of FIG. 4A did not lead to increased residual ozone in the water to be treated. In fact, the greatest residual ozone level was achieved with the arrangement shown in FIG.  4 B. Operating the device as illustrated in FIG. 4A using atmospheric air rather than pressurized air to the inlet  41  showed an increased flow in supply conduit  44  of 4.75 cubic feet per hour, but a residual ozone in the low demand water of only 0.23 mg/liter after 96 seconds cycle time. Using the same equipment, but with a bottom feed to the treatment tank  20  as illustrated in FIG. 4B, the flow rate in supply conduit  44  was observed to have fallen to 3 cubic feet per hour. However, after the same processing time, the residual ozone in the low demand water had increased to 0.39 mg/liter. These figures appear to indicate that returning the water from the treatment mixer  42  to the bottom of the batch treatment tank  20  further assists in dissolving the ozone into the water where it is available for treating the water. 
     Based on all of the foregoing tests and experiments, various parameters and preferred operating conditions have been developed. Preferably, as this is a batch system, the selected time period should be less than 5 minutes. By processing each batch within a 5 minute time frame, the equipment can be kept relatively compact and yet will be large enough to handle relatively low flow rates as are typical in most applications. One of the principal advantages of the invention is the ability to ensure treatment to a particular level. In part, this arises because no additional water to be treated is permitted to enter the treatment tank once the treatment process is initiated. Thus, once the quantity Q of water is fixed by limiting any further inflow to the tank, the treatment parameters and conditions can be controlled by the equipment and the operating controller. It has been determined, that the biologicial oxygen demand plus the chemical oxygen demand of even the most severely contaminated water is in the order of approximately 1.00 mg of ozone per liter. With this amount of ozone injected into the water, the BOD and COD of the water will be fully satisfied. Thus, if a highly polluted test liquid is run through the system, and if sufficient ozone is supplied to the fluid so that a total of 1.00 mg of ozone per liter is supplied to the fluid, then subsequent testing may fail to detect any residual oxygen showing that all ozone supplied has been used up to meet the COD and BOD demand of the water. If this occurs, this will result in unsatisfactory treatment for bacteria, viruses, parasites and spores in such highly contaminated fluid. It has also been established that the density of ozone needed to reduce bacteria, viruses, parasites and spores by five logarithm in water to be treated is up to 0.25 mg of ozone per liter. Combining these two requirements, it can be shown that providing 1.25 mg of ozone per liter of fluid to be treated, will be sufficient to treat even very highly contaminated fluids to satisfy the BOD and the COD of the contaminated fluid, and to give a five logarithm reduction in bacteria, viruses, parasites and spores which may be present in that highly polluted water. Thus, a system which supplies at least that amount of ozone per liter of water will in almost all cases completely satisfy the BOD and COD of the water as well as give the desirable reduction in bacteria, viruses, parasites and spores. 
     This provides another parameter for sizing and controlling the equipment. Another aspect of the preferred embodiment of the process is to ensure appropriate mixing of the ozone provided with the fluid to be treated With the system as shown in the figures of this patent, a circulation pump is used to withdraw the water to be treated from the treatment tank and circulate the water through the treatment conduit and through the ozone injector. In order to ensure good mixing of the ozone with the water to be treated, we have determined that it is desirable that the pump provided be capable of pumping at a rate of at least 2Q per minute. This, in turn, means that if the selected time T is greater than one minute, then all of the fluid on average would be circulated through the injector twice. More preferably, it has been noted that good mixing occurs when a pump pumping at a rate of at least 2Q liters per minute operates for a long enough period of time T such that at least 3Q of water is passed through the treatment conduit and through the ozone injector. This effectively means that on average, all of the fluid to be treated passes through the ozone injector three times. This three-times passage helps to ensure proper mixing of the ozone with the water and effectively provides a slightly longer period of time within which to supply the ozone as compared to attempting to supply all of the necessary ozone in a single pass. 
     In accordance with a preferred embodiment of the process, the process is carried out such that the time T in hours is equal to I 3 Q over O where I is equal to the amount of ozone injected per liter of fluid as fluid passes through the ozone injector, Q is the batch size of water to be treated in liters and O is the amount of ozone generated in milligrams per hours. 
     Based on the above testing, a commercially effective arrangement involves the use of an air pump feeding a moderate sized ozone generator such as the Simpson generator rated at 800 mg/hr production, with the air pump moving a supply of fresh air drawn in through a dryer. The use of larger ozone generators does not seem to be cost justified. One Mazzei No. 8 mixer also appeared to be sufficient although a No. 6 injector may also be sufficient. Use of multiple parallel venturi injectors did not produce results sufficiently enhanced to offset the expense of the multiple injectors. Best results were achieved using a bottom feed to the treatment tank  20 . 
     From reviewing the above examples and description, it will be appreciated that a relatively compact system can be created for successful treatment of highly contamined water having very high BOD and COD and various pollutants to the point where the treated water is substantially enhanced before being discharged. The effectiveness of the system in treating contaminated water also shows that the system may be used in a combined system, for enhancing the quality of drinking water produced from raw water which may be available from a lake or on board the vessel or facility where the system is installed. 
     Although municipal regulations may not yet permit the discharge of black water after treatment in such system, the above tests with highly contaminated fluids show that even water having very high BOD and very high COD and other pollutants can be treated in the system in accordance with this invention. Such a system may be acceptable for treatment of the non-solids portion of black water or at least a portion of the contents of a black water holding tank. 
     While the system has been described in connection with preferred embodiments of the system, various changes and modifications to the system may be made. The full scope of the invention is to be determined by reference to the following claims.