WO2002036499A2

WO2002036499A2 - Treatment of waste water and apparatus therefor

Info

Publication number: WO2002036499A2
Application number: PCT/GB2001/004809
Authority: WO
Inventors: Charles Michael Pratt; Ian Baker
Original assignee: Charles Michael Pratt; Ian Baker
Priority date: 2000-11-01
Filing date: 2001-10-29
Publication date: 2002-05-10
Also published as: AU2002212451A1; EP1334073A2; WO2002036499A3

Abstract

A water treatment apparatus for the treatment of waste water (2), including sewage material, is provided on a marine vessel for example a cruise ship. The apparatus comprises a filter (10) in the form of an submerged flat panel membrane bio-reactor unit or MBR (11) having an average effective pore size of less than 0.1 micron (100 nanometres) and an ionisation unit (12) including electrodes (48, 50), the unit (12) acting as a source of metal ions. The electrodes (48, 50) are formed from an alloy of silver, copper and zinc. In use, waste water (2) flows through the filter (10) and then the ionisation unit (12), so that the waste water is filtered and then infused with metal ions. The concentration of ions in the effluent water is at a concentration effective to disinfect the waste water (2) and provide a residual disinfecting action, the metal ions providing biocidal and/or fungicidal effects. The apparatus may be retro-fitted to a ship by means of a conversion kit.

Description

Treatment of waste water and apparatus therefor

This invention relates to the treatment of waste water. The invention is particularly, but not exclusively, applicable to the treatment of waste water in marine vessels such as ships and other marine structures such as oil rigs and/or platforms .

Marine vessels such as ships commonly discharge both "black water" and "grey water" directly into the sea. "Black water" is used herein to mean water including sewage and/or medical waste water. "Grey water" is used herein to mean waste water not containing sewage or medical waste water. Examples of grey water include the discharges from sinks, baths, showers, kitchens, and laundry water. "Waste water" is used herein to mean water including black or grey water or a mixture of black and grey water. The term water when used without further qualification may be used herein to cover waste water and/or water of a quality better than waste water, depending on the context . With increasing environmental concerns, it is desirous to improve the quality of overboard discharge. Moreover, regulations are, in many territories, in force (or about to be brought into force in the near future) , that prohibit the discharge of waste water that is below a certain standard. Many ships are equipped with existing waste water treatment plants that are unable to meet these standards. One way in which such ships avoid these problems is simply to hold black and grey water in tanks on the ship for subsequent discharge in an area that does not prohibit such activities. However, providing waste water tanks for storage of untreated waste water is wasteful of space and may be hazardous -.unless suitable precautions are taken. Many ships discharge waste water, especially grey water, in such areas without any further treatment . Ships also have a requirement for clean water, for example drinking water, that can be met in a variety of ways including, for example, bunkering in port, reverse osmosis, or flash distillation from seawater. Distillation and reverse osmosis are relatively expensive solutions and therefore bunkering is often the preferred means of providing a supply of clean water. However, water bunkering is also becoming increasingly expensive, and furthermore reliable sources of clean water may not be available in certain areas, for example in areas with low water resources. Water bunkering is increasingly becoming less viable for cruise ships operating in popular cruise areas, such areas commonly being warm and/or low in water resources.

It is also desirous to provide an improved apparatus and method of treating waste water on land as well as at sea. An object of the present invention is to provide an improved apparatus or method for treating waste water that is preferably able to mitigate one or more of the above-described problems . According to the present invention there is provided a water treatment apparatus for the treatment of waste water, the apparatus comprising a filter having an average effective pore size of less than 1 micron and a source of metal ions, wherein the apparatus is so arranged that in use the waste water flows through the filter and the waste water is infused with metal ions, the concentration of ions in the waste water being at a concentration effective to disinfect the waste water. Advantageously, the apparatus is arranged such that, in use, waste water is first filtered and then infused with metal ions.

The apparatus is able to convert waste water of a very poor standard to disinfected water. There is furthermore no need for the apparatus of the present invention to be provided with the hazardous disinfection chemicals that other conventional water treatment apparatus use. Use of an embodiment of the invention in a waste water treating process has been found to be effective against faecal coliforms, e. coli., herpes simplex, polio (type 1), salmonella, staphylococcus, and streptococcus.

It has been found that the combination of infusing water with metal ions and the use of filters having an average effective pore size of less than 1 micron is particularly advantageous when treating waste water, especially black water. The provision of such a filter facilitates the effective treatment of waste water with a lower concentration of metal ions than would be required without such a filter. In use, waste water flows from upstream of the filter, and then via the filter and the source of metal ions (their order depending on the particular arrangement in the apparatus) . Components of the apparatus may therefore be considered as being downstream or upstream of each other and such terms are used herein; the reader will appreciate however that such terms do not, unless otherwise clear from the context, imply that a fluid is flowing through the apparatus, when not in use .

In the present context, the disinfected water produced need not necessarily be potable. The use to which the disinfected water is to be put (such use may simply be to get rid of the water) will of course determine the criteria to be applied when assessing whether water is "disinfected" . By way of example, water may considered as having been sufficiently disinfected if its faecal coliform (FC) content is less than 300 counts per 100 ml (according to the standard 24Hr test) , its total suspended solids (TSS) is less than 150mg/litre or its biological oxygen demand (BOD) (according to the standard 5-day test) is less than lOOmg/litre. Advantageously, however the apparatus is arranged to produce disinfected water meeting at least one, and preferably all, of the following conditions: FC less than or equal to 250/100ml, TSS less than or equal to lOOmg/litre and BOD less than or equal to 50mg/litre. The apparatus may of course be configured to operate to much more stringent requirements, if necessary. For example, the apparatus may be arranged to produce disinfected water meeting at least one, and preferably all, of the following conditions: FC less than or equal to 20/100ml, TSS less than or equal to 50mg/litre and BOD less than or equal to 50mg/litre.

Advantageously, the apparatus is so_^ arranged that the concentration of metal ions in the disinfected water is great enough to provide a residual disinfecting action. Such a residual disinfecting action is of particular advantage if the apparatus is to be used to produce disinfected water for storage. The concentration of metal ions in the disinfected water is preferably great enough to prevent a significant increase in one or more of the FC, BOD, and TSS of the water when stored in normal conditions (i.e. in an otherwise clean tank, vented to atmosphere, but covered to prevent contamination from debris) at an average temperature of about 25 degrees Celsius for 24 hours, and more preferably so that there is no significant increase when the water is stored for 7 days. The concentration of metal ions in the disinfected water is preferably sufficiently great that the water after having been stored in normal conditions at an average temperature of about 25 degrees Centigrade for a given period (either 24 hours or, more preferably, 7 days) can still be considered as being disinfected water. Metal ions, when used to provide a long term (for example greater than 48 hours) disinfecting action, have advantages over other methods for achieving the same result. For example, chemical methods such as chlorination may only provide effective disinfecting action over short-term periods (for example less than 48 hours) owing to the chlorine being released as chlorine gas from the water. Also, unlike other agents able to provide short-term or long- term disinfecting action the effectiveness of metal ions is not unduly affected by sunlight or temperature.

The apparatus advantageously includes a control unit that controls, or facilitates the control of, at least a part of the operation of the apparatus.

The control unit may be arranged to receive a signal that, in use, indicates the rate of flow of water through the apparatus. For example, one or more flow sensors may be connected to the control unit that enable the control unit to monitor the rate of flow of water through the apparatus. The or each flow sensor may be in the form of a flow meter. A flow sensor may for example be provided between the filter and the source of metal ions, or alternatively downstream of both the filter and the source of metal ions . The control unit may be able to control the rate of flow of water through the apparatus. For example, the control unit may be connected to one or more pumps and/or one or more valves controllable to vary the flow of the water through the apparatus. Whilst the filter of the apparatus may be arranged to filter the waste water under a gravity feed arrangement, one or more pumps, preferably suction pumps, are advantageously provided to effect the passage of waste water through the filter. Removing the need for a gravity feed arrangement may save valuable space . The ability of the metal ions to provide a disinfecting action depends on the concentration of metal ions in the water. The control unit is advantageously able to control, in use, the rate of supply of metal ions so as to control the concentration of supplied metal ions in the waste water. The concentration of metal ions needed to enable the apparatus to disinfect waste water varies according to the degree of contamination of the waste water. However, for most applications the concentration needed to disinfect filtered waste water is between 40μg/litre and 400μg/litre. Of course, if the waste water is exceptionally heavily contaminated the concentration of metal ions required to provide a sufficient disinfecting action might be greater than 400μg/litre.

The control unit may vary the flow rate of the water through the apparatus in dependence on an input representative of the rate of supply of metal ions into the water flowing through the apparatus, thereby ensuring a concentration of ions necessary to provide sufficient disinfecting action. Alternatively, or additionally, the control unit may vary the rate of infusion of metal ions in dependence on the measured flow rate of water through the apparatus to ensure a concentration of ions necessary to provide sufficient disinfecting action.

The control unit may perform one or more of the above- mentioned functions. One or more separate control units may be provided.

The source of metal ions advantageously includes a plurality of electrodes. The source of metal ions may, for example, include one or more pairs of electrodes connectable across a power source. The electrodes are preferably removably mounted in the apparatus . The electrodes may therefore be easily changeable for example for the purpose of changing the electrodes so as to be more suitable for treating a given type of waste water or simply for the purpose of renewing the electrodes.

The apparatus conveniently includes a power supply that is connected to the electrodes via constant current circuitry, which facilitates, in use, the control of the current passing between the electrodes. As indicated above, a control unit may be provided that is able to control, in use, the rate of supply of metal ions so as to control the concentration of supplied metal ions in the waste water. Given that the current passing through the electrodes provides an indication of the rate of metal ions infused into the water passing through the apparatus, an indication of the current can be used to control the concentration of metal ions provided to the water, if an indication of the flow rate is known. Alternatively, a sensor can be provided downstream of the source of metal ions, the sensor being able to provide a signal to a control unit indicative of the concentration of the metal ions in the water. The sensor may be connected to a control unit which is arranged to vary the flow rate of the waste water and/or the rate of supply of metal ions, in response to signals from the sensor, in order to ensure a concentration of ions necessary to provide sufficient disinfecting action. The electrode advantageously comprises therefore a substance, the concentration in the water of which can be measured downstream, in order to provide an indication of the rate of supply of ions into the water. For example, the electrode may comprise copper and there may be provided a copper ion sensor downstream of the source of ions, the copper ion sensor being connected to the control unit.

The source of metal ions is advantageously able to provide, in use, one or more of the following: silver ions, copper ions, and zinc ions. For example, in the case where the ions are provided by electrodes, the electrodes are preferably formed of an alloy or mixture comprising one or more of the following: silver, copper, and zinc. The apparatus preferably further comprises a further source of disinfecting material, the apparatus being so arranged that the waste water is infused with the material at a concentration effective to aid disinfection of the waste water. The further source of disinfecting material is preferably, but not necessarily, provided downstream of the filter. The source of disinfecting material may be provided upstream of the source of metal ions . Preferably the material comprises or consists of an oxidising agent such as chlorine or a material able to produce such an oxidising agent . In the case where the oxidising agent is chlorine, the chlorine is preferably provided at a concentration of one part per million to one part per billion (10⁹) . There may be more than one further source of disinfecting material provided in the apparatus .

As mentioned above, the further source of disinfecting material may be chlorine. The combined use of chlorination and metal ionisation improves the disinfecting power of the apparatus synergistically. In particular, the combination may reduce the bacteria and other organisms by an amount greater than the sum of the reductions afforded by the use of chlorination and ionisation individually at the same dosages. This allows reduced amounts of chlorine and metal ions to be used without a corresponding reduction in effectiveness. The metal ions have the advantage over chlorine however that chlorine has a tendency to evaporate out of the water over time (especially where the ambient temperature is relatively high) . The use of metal ions in combination with chlorine may provide an added benefit in that excess metal ions can produce a long-term residual disinfection effect.

The filter preferably has an average effective pore size of less than 0.5 micron and more preferably less than 0.1 micron. The filter may be configured such that it allows particles of a size less than 0.01 microns to pass through the filter during use. The filter may have an effective pore size less than even 0.01 microns, and may for example have an effective pore size of the order of a few nanometres. Preferably, however, the notional pore size is between 0.01 and 0.1 microns. The filter may be a mechanical filter. The filter is preferably a membrane bio-reactor (MBR) . The filter may be a submerged MBR. The filter is preferably in the form of a flat panel filter. The filter could alternatively comprise one or more hollow fibre membranes, for example, in the form of tubes. Most MBR filters are designed for use in an environment that allows a biomass to grow and be sustained in the region of the filter surface, the biomass aiding the disinfecting action of the filter and also, over time, reducing the effective pore size of the filter. Thus, such MBRs rely to a certain extent on the biomass being sustained. However the biomass layer is susceptible to damage, especially when the quality of the waste water changes. The disinfecting ability of such MBRs can therefore be unpredictable. However, when coupled with a source of metal ions according to the present invention, such problems are greatly mitigated. The source of metal ions is advantageously downstream of the MBR so that the ions do not significantly affect the integrity of any beneficial biomass on the MBR. MBR components are commercially available, for example from Kubota Corporation (Japan) and Toray Corporation (Japan) . The filter may, for example, be formed of ceramic material, of stainless steel or of wound fibres. MBRs may include filters made from polymer fibre.

The apparatus preferably comprises further filtering apparatus provided upstream of the filter, the filtering apparatus being able to remove particles having a size greater than 3mm. Thus the risk of the finer filter getting clogged or damaged by large particles is greatly reduced. The filtering apparatus is preferably configured to allow particles having a size less than 1mm to pass through. The further filter may thus have an effective pore size of between lmm and 3mm. If the effective pore size were less than 1mm, there could be risk of clogging (depending, of course, on the nature of the filtering steps, if any, carried out upstream) . There may be provided a pre-disinfection tank upstream of the filter.

The apparatus advantageously comprises cleaning apparatus arranged to further disinfect or clean the water. The cleaning apparatus may be provided in addition to, or instead of, the further source of disinfecting material referred to above. The cleaning apparatus may comprise one or more of the following: UN disinfecting unit, carbon filter, zeolite filter, a unit providing an oxidising agent (for example a chlorination unit) , and metal ion removal unit (or means for removing metal ions) . The cleaning apparatus may be provided upstream or downstream of the source of metal ions . In the case where the cleaning apparatus is capable of reducing the disinfecting action of the provided metal ions (for example, if it were capable of removing the metal ions, such as the case where the cleaning apparatus is in the form of a carbon filter or zeolite filter) , it may be preferable for the cleaning apparatus to be provided upstream of the source of metal ions, so that the disinfecting action of the metal ions is not prematurely reduced. In the case where the cleaning apparatus is an oxidising unit or a UN disinfecting unit, the cleaning unit may be provided downstream, but is preferably provided upstream of the source of metal ions. The cleaning apparatus may for example be in the form of a post treatment unit. In the case where the cleaning apparatus includes a means for removing metal ions, the cleaning apparatus may be arranged downstream of the source of metal ions so that it may remove excess metal ions introduced by the source of metal ions . The metal ions may be removed by any suitable means including, for example, chemical means, electrolytic means, or means including a granulated activated carbon filter. Preferably, the metal ions are removed immediately before (and preferably as late as is practically possible) the disinfected water is used for its intended purpose. The apparatus may include more than one cleaning apparatus arranged to further disinfect or clean the water.

If the disinfected water produced by the apparatus is to be used as drinking water, it is of course preferable that the water has no significant taste or odour. In such cases, the metal ion content is preferably low enough not to impart a taste detectable to the average person. It may for such purposes be necessary for the apparatus to be able to remove excess metal ions as described above. The apparatus conveniently includes an inlet and an outlet. The inlet may be connected to a source of waste water for treatment. In use, further apparatus may receive disinfected water supplied from the outlet. The outlet may be a discharge outlet for discharging the treated water. Power may be supplied to the apparatus by any suitable source. For example, electric power may be supplied by means of solar power, wind power, water turbine or a conventional generator.

The present invention also provides a method of disinfecting waste water comprising the steps of filtering the waste water to remove particles having a size greater than 1 micron and infusing the waste water with metal ions effective to disinfect the waste water, whereby the method converts the waste water into disinfected water. The step of infusing the waste water with metal ions is preferably performed after the step of filtering the waste water.

The method is of particular advantage when the waste water is of a poor quality. For example the waste water may have an FC greater than 1000/lOOml, TSS greater than 500mg/litre and/or a BOD greater than lOOmg/litre. The quality of the waste water may be very poor, for example having an FC greater than 10 , 000/lOOml, TSS greater than lg/litre and/or a BOD greater than 200mg/litre.

Preferably, substantially all particles bigger than 1 micron are removed. Preferably, the filtering step removes particles having a size greater than 0.1 micron. Of course, whilst the method may be performed such that particles greater than 0.1 micron in size are removed, there may be some, preferably relatively very few, particles greater than 0.1 micron in size that are not removed by the filtering step. The step of filtering the wastewater preferably removes substantially all particles greater than 0.1 micron in size. The filtering step may remove particles having a size of the order of nanometres .

The waste water is preferably filtered to remove particles having a size greater than 3mm before the fine filtering step is performed. The pre-filtering of the waste water reduces the likelihood of clogging or damage of any means provided to effect the fine filtering step.

Advantageously, the concentration of metal ions infused into the filtered waste water is great enough to provide a residual disinfecting action.

Preferably, the metal ions are provided by electrolytic action. The electrolytic action may be provided by two or more electrodes across which a potential difference is applied. Advantageously, the potential difference applied across the electrodes is varied so that a desired current is passed between the electrodes. Constant current circuitry may for example facilitate the control of the current flowing between the electrodes.

Preferably, the polarity of the electrodes is periodically reversed. Periodically reversing the polarity can have the benefit of reducing the build up of unwanted deposits, for example lime-scale, on the electrodes. The period between reversing the polarity is conveniently, but not necessarily, a substantially constant period. The time between reversing the polarity is preferably between 60 and 240 seconds, and is more preferably between about 90 seconds and 180 seconds.

The ions infused into the water advantageously comprise one or more of the following metal ions : silver ions, copper ions, and zinc ions. The ions infused preferably comprise at least 60% silver ions. Silver ions are known to have good biocidal properties.

Advantageously, the metal ions include copper ions. Copper ions are known to have good fungicidal properties. Preferably both silver and copper ions are infused, there being more silver ions than copper ions . The ions may for example be provided at a ratio of between 1.5:1 to 6:1 (silver to copper ions) .

Preferably silver, copper and zinc ions are all infused, there being more silver than either zinc or copper ions. The presence of zinc ions aids the holding of the silver ions in suspension. Zinc ions may also aid fungal disinfection. There are preferably fewer zinc ions than copper ions.

When electrodes are provided to infuse the water with ions, the electrodes are preferably formed of an alloy or mixture that includes not less than 60% silver, by weight. The alloy composition may be Ag>50%, Cu<50%, Zn<20%, preferably Ag>70%, Cu<20%, Zn<20%, and more preferably Ag>80%, Cu<10%, Zn<10%. By way of example, the ratio of weights of the metals for an application where fungicidal disinfection is more important might be 60% Ag : 40% Cu : 0% Zn, whereas the ratio of the metals for an application where biocidal disinfection is more important might be 80%Ag : 15% Cu : 5% Zn. The method advantageously includes a step of adding oxidants to the water, for example by chlorinating the water, at a concentration effective to aid disinfection of the waste water. If the water is subsequently stored, the chlorination may be performed in such a way that residual free chlorine is released over time during storage, thereby providing a residual disinfecting action.

The method may include a step of storing the disinfected water. Such a step may be advantageous when for example the method is performed on a marine structure or a marine vessel, for example a ship. The disinfected water may for example be stored for later discharge once the ship is in a location suitable for discharging the water.

Above it is mentioned that the method may be so performed that the concentration of metal ions in the disinfected water is great enough to provide a residual disinfecting action. Having excess metal ions present in the disinfected water, is particularly advantageous when storing the resultant water, in that the metal ions assist the prevention of the disinfected water significantly deteriorating in quality over time. If the stored water is to be discharged, for example into the sea, such excess metal ions may removed immediately before discharging the water. Such a step is of particular benefit when water is to be discharged into areas with regulations prohibiting the discharging of water with a metal ion content over a given level (for example in areas such as New York Harbour or over mussel beds) .

The method may further include a step of discharging the water. The method may additionally or alternatively include a step of reusing the water. Such steps may be performed in addition to a step of storing the disinfected water. For example, if the method is performed on a marine vessel the disinfected water may be stored and thereafter reused as technical water. The method is of particular advantage when performed at sea and especially when performed on a ship or other marine vessel or a marine structure. In the past, marine sanitation devices have relied on settlement to separate out suspended solids. Relying on settlement, especially on a moving ship, to separate out suspended solids is often not satisfactory.

Also, such prior art methods often only treat the resulting effluent (excluding the settled solids) with high levels of chlorine before discharging overboard. The amount of chlorine required to provide the required disinfecting effect is often not adequately controlled. The present invention may provide an improved method that mitigates such problems. The method may be particularly suited for use on a ship, especially where submerged MBR filters are used in the step of filtering, because of the potential saving of space that might otherwise be taken up by treatment apparatus .

Whilst the present invention is particularly advantageous when effected at sea it may also be put to advantage on land. For example, the method of the present invention may include a step of using the disinfected water for irrigation, in particular spray irrigation. If irrigating crops, for example, spray irrigation provides a convenient means of distributing water to the crops. However, if the water is not clean the spraying of the water can be particularly undesirable, as disease or pollutants for example can easily be spread over a large area. It is therefore beneficial when spraying water in this manner if the water is first disinfected.

The disinfected water produced by the invention may be used in many other ways. For example, the disinfected water may be treated further, for example, to produce potable water. The step of further treating the disinfected water may for example comprise removing metal ions from the water. The method may also be used in relation to the preparation of food and/or drink, where waste products require disinfecting treatment, such as wash water to allow re-use of the water. The method may for example have application in the brewing industry.

The method may of course be performed using an apparatus according to any aspects of the present invention as described herein. Also the apparatus of the present invention may be configured to be suitable for performing the method according to any aspects of the present invention as described herein. There is also provided a water treatment installation including an apparatus according to any »aspects of the present invention as described herein. The water treatment installation may for example include a source of waste water for example stored in tanks .

The present invention yet further provides a method of improving an existing water treatment installation, the existing installation comprising a filter having an average effective pore size of less than 1 micron arranged in use to provide filtered waste water, the method including the steps of connecting in series with the filter an ionisation unit including a source of metal ions, and connecting a control unit to the treatment installation for controlling the concentration of metal ions infused into the waste water so that the concentration is effective to disinfect the waste water. The ionisation unit is preferably connected downstream of the filter. The ionisation unit does not necessarily need to be connected directly to the filter, in that further components may be positioned between the ionisation unit and the filter. The existing water treatment installation may include an existing control unit, in which case the method preferably includes a step of replacing the existing control unit, the replacement control unit being configured to control not only the concentration of metal ions infused into the waste water, but also the operation of the installation. The method is preferably performed to produce a water treatment installation including an apparatus according to any aspects of the present invention as described herein. The present invention also provides a conversion kit comprising an ionisation unit and a control unit for use in the method of improving an existing water treatment installation described above .

The present invention yet further provides a marine structure or a marine vessel, for example a ship, including a water treatment installation including an apparatus according to any aspects of the present invention as described herein. The invention is particularly advantageous when the marine vessel is a ship designed to carry more than 100 persons (for example passengers and crew), for example, a cruise ship. The invention is of course of benefit in smaller applications at sea, and can provide cost benefits when used on a marine structure or vessel accommodating at least 10 persons.

Embodiments of the invention will now be described, by way of example only, with reference to the drawings, in which:

Figure 1 is a schematic flow diagram illustrating the principles of a first embodiment of the invention; Figure 2 is a schematic flow diagram illustrating the principles of a second embodiment of the invention; Figure 3 is a schematic diagram illustrating in further detail the second embodiment of the invention; Figure 4a shows a component of the embodiment of Figure 3 in more detail; Figure 4b shows a part of the component shown in Figure 4a in more detail and Figure 5 is a schematic diagram illustrating a further embodiment of the invention.

Figure 1 shows as a flow diagram a first embodiment of the present invention, which may or may not be provided on a ship. Waste water 2 is passed sequentially through a filter 10, which may be in the form of an MBR, and then an ionisation unit 12. The filter unit is capable of removing particles down to approximately 0.1 micron. The particulates removed may include protozoa, some bacteria, and some chemical compounds. If the filter is in the form of an MBR, the MBR may facilitate the biological treatment of the water, whereby the BOD, COD and Ammonia content may be significantly reduced.

The ionisation unit 12 includes one or more channels through which the water passes. The channels house electrodes consisting of silver, copper and possibly zinc. Thus the first embodiment illustrates a method of treating water, in which the water is first filtered to remove particles greater than a predetermined size (preferably 0.1 micron), and is then infused with metal ions effective to produce disinfection. In use, a potential difference is applied across the electrodes to cause a current to flow across the water as it flows through the channels. Metal ions are thereby caused to be infused into the water, the ions having a disinfecting effect. The output from the ionisation unit 12 is of a quality that complies with IMO (International Marine Organisation) requirements (as at 1st November 2000) . Furthermore, the output also complies with the Marine Equipment Directive 96/98/EC (as modified by Directive 98/85/EC) . The output may thus be discharged 17 into, for example, estuarine or coastal waters. Alternatively, the output water could be re-cycled 15 for use as technical water. It will be understood that the term "technical water" includes water of a quality suitable for use as boiler feed water, or water suitable for use in other technical processes, but not of a standard high enough to be potable. If potable water is required the output water can, after analysis of the quality of the water, be fed to a further cleaning/disinfecting unit 19, which may be in the form of a conventional disinfection unit. The further cleaning/disinfecting unit 19 may treat the water with one or more of the following: chlorine, ozone, hydrogen peroxide (H₂0₂) , bromine, UN radiation, potassium permanganate and iodine .

In the case where the invention according to the first embodiment is on a ship, the disinfected water may be chlorinated and then stored in storage tanks on the ship for re-use as technical water. Any residual free chlorine will evaporate inside the storage tanks. The ionisation continues to provide residual disinfection, once the chlorine has evaporated, however.

The synergistic effect of the combined use of chlorination and ionisation improves the "kill rate" ; that is it reduces the bacteria and other organisms by a greater percentage than chlorination or ionisation individually at the same dosages. This allows reduced amounts of chlorine and metal ions to be used without a corresponding reduction in effectiveness .

The combination of ionisation and chlorination according to this aspect of the first embodiment allows the recommended contact time for either ionisation or chlorination alone (of about 30 minutes) to be reduced to around a few minutes, without prejudicing the anti-bacterial effects necessary to allow legal overboard discharge. The volume capacity of any post treatment vessel facilitating such contact time may also be greatly reduced.

The first embodiment of the invention could be used in many different applications in addition to marine uses. For example, the first embodiment may be used to treat the liquid outflow from a conventional sewage treatment such as a septic tank, which may be of particular interest in a land based application. Photo-electric cells could also be used as a power source in remote locations. Also, the embodiment of the first invention could be used to treat suitable raw water (i.e. water not contaminated with isotopes, poisonous metals or harmful chemical compounds) from a river, lake, spring or well to produce water of a potable standard.

Figure 2 shows as a schematic flow diagram a second embodiment of the invention, where the apparatus is provided on a cruise ship. Grey water is held in a grey water holding tank 20. Black water is held in a black water holding tank 21. The black and grey water is drawn via a 3mm strainer 24, which is used to remove extraneous matter greater than 3 mm in size, and then through an MBR 11 by a suction pump 38. The water then passes to a further disinfecting unit 13 and then to an ionisation unit 12.

The further disinfecting unit 13 is a chlorination unit. The benefits of the additional use of chlorination are described above with reference to Figure 1. Treated water at the outlet 41 of the apparatus (i.e. after the water has passed through the ionisation unit 12) may be used, stored, discharged, and/or processed further according to requirements. The water may for example be passed through a yet further disinfection/cleaning unit 19. The water may be discharged overboard 17. The water may be reused 15 as technical water. The water may optionally be- stored in storage tanks 23 before being subjected to any of the aforementioned processes. Also, the water could be subjected to more than one of the aforementioned processes. As indicated above the outlet 41 could be connected to a further disinfection/cleaning unit 19. The further disinfection/cleaning unit 19 (or post treatment unit) may be in the form of a conventional disinfection unit for producing potable water. The further disinfection/cleaning unit 19 in this embodiment is however in the form of a residual disinfecting unit. So that bacteria may be made non-viable, there is a requirement for the bacteria to be in contact with the metal ions for a sufficient time. The residual disinfecting unit is therefore configured to ensure that there is sufficient contact time in view of the water flow rate. The residual disinfecting unit includes a conduit, or series of chambers, having a flow path length long enough (or a volume large enough) that the time taken for water to travel through the unit at normal flow rates is about two or three minutes. This time is long enough for the water to be further disinfected by a residual disinfecting action provided by excess metal ions in the water. Flow sensors (not shown) are provided to ensure that the water remains in the residual disinfection unit for a given length of time (for example, at least 3 minutes) .

The process is electronically managed by a control unit 25. The control unit 25 has a control panel (not shown) allowing an operator to monitor and alter the processing of the waste water 2.

The control unit 25 receives inputs from a water flow meter 27 arranged after the MBR 11 and the ionisation unit 12. (The flow meter could of course be positioned elsewhere along the flow path, for example at a position between the MBR 11 and the ionisation unit 12) . The control unit is also connected to the suction pump 38 and is thus able to vary the rate of flow of water through the apparatus. The control unit 25 is also able to control the current flow passed between the electrodes of the ionisation unit 12. The rate of dissolution of metal ions into the flow depends on the current flow. The concentration of metal ions in the output water depends on the current and on the flow rate of water. The control unit 25 is arranged to control the concentration of metal ions in the output water by varying the current in dependence on the rate of flow of water as measured by the control unit 25. The control unit 25 may alternatively or additionally be connected to a sensor (not shown) provided downstream of the ionisation unit 12 able to provide an indication of the concentration of metal ions in the water. The sensor could for example sense the concentration of copper ions in the water.

The control unit 25 may, if additionally connected to such a metal ion sensor, be able by means of the sensor to check its control of the rate of dissolution of metal ions. The concentration of metal ions provided may be controlled by the control unit 25 on the basis of a simple feedback system making use of the measurements made by the sensor.

The quality of the filtered waste water at the output of the MBR unit 11 may, somewhat surprisingly perhaps, be within a predictable range irrespective of the original quality of waste water 2, particularly if an MBR with a healthy biomass is used. For example, it has been found during tests that the filtered water usually has a TSS of about 5mg/litre, a FC of about 5 counts per 100ml and a BOD of about 5mg/litre. Initially (on first use), the MBRs remove particles of 0.1 micron in size and above. During the first few days of use, the MBR will develop a biomass which can aid the disinfection properties of the apparatus. The MBR unit 11 may over time have a biomass that reduces the effective notional pore size to 0.01 microns.

The second embodiment of the invention has an ability to convert black water (the black water having an FC of about 8 x 10⁶/100ml, TSS of about 4 grams/litre and a BOD of about 600mg/litre) into disinfected water at outlet 41, the disinfected water having FC<1 count per 100ml, TSS<5 mg/litre and BOD<5mg/litre.

Figure 3 shows the second embodiment in greater detail . The overall layout of the second embodiment is described above with reference to Fig. 2. The features shown in Fig.3, and not illustrated by Fig. 2, will now be described. (The control unit 25 is not shown in Fig. 3 for the sake of clarity. )

The black water tank 21 is connected via pumps 22a to the strainer 24 via a motorised valve 29, a flow restrictor 33 and a non-return valve 35 after which the flow path merges with the flow path from the grey water tank 20. The black water tank 21 is provided with a high level sensor (not shown) and a low level sensor (not shown) . The grey water tank 20 is connected via a pump 22b to the strainer 24 via a non-return valve 37 after which the flow path merges with the flow path from the black water tank 21. The waste water flow path then passes via the strainer 24 to a treatment tank 26 via a flow switch 36. The strainer 24 is provided with a bypass flow path 24a in order to facilitate cleaning. The treatment tank 26 houses two MBRs 11 which are connected in parallel in the flow path. For each MBR 11 inside the treatment tank 26 there is also provided an aerator (not shown separately) supplied with compressed air via a pipe 30 from an air pump 31. The use of an aerator is of particular advantage where the waste water to be treated contains a large amount of organic material, has a pH imbalance, or contains large numbers of pathogenic organisms. A pump 32 is provided to enable surplus residue to be transferred via a non-return valve 39 to a sludge storage tank 53 or discharge unit (not shown) . The treatment tank 26 is provided with a high level sensor (not shown) and a low level sensor (not shown) . The output flow paths from each MBR 11 merge and are connected to the suction pump 38 via a vacuum safety control switch 43. The treatment tank 26 is provided with a sample point 45. Downstream of the suction pump 38 there is provided the further disinfecting unit 13 (a chlorination unit in this case) and downstream of that there is provided a further sample point 47. The water flow path then passes to the ionisation unit 12, which is connected to an outlet via a further sample point 49 and a non-return valve 51.

The ionisation unit 12 is shown in further detail in Figure 4a, which shows that the flow through the unit is divided amongst a number of cells 46, each of which being in the form of a length of stabilised plastic tube of 50mm diameter capable of retaining a pressure of 15 bar. One cell 46 is shown in more detail in Figure 4b. Each cell 46 contains electrodes 48 and 50 connected to opposite poles of a power supply provided with current control circuitry. The electrodes 48, 50 in this embodiment each measure 125mm x 8mm x 35mm. The electrodes 48, 50 are formed of a tri-metal alloy of Ag 80%, Cu 10%, Zn 10%, which, when sufficient current is passed, releases metal ions into the water flow to produce disinfection of the waste water 2. The electrodes 48, 50 are substantially identical to each other. The power supply (not shown) is able to provide 2A at up to 50V. As mentioned above the control unit 25 varies the current in dependence on the required concentration of metal ions and on various other factors including for example the water flow rate as measured by the flow sensor 27. At low rates of flow the current is for example reduced by the control unit 25 so as to maintain a substantially constant number of ions deposited per second per unit volume of water. If the flow as measured by the flow meter 27 falls below a predetermined threshold the control unit 25 shuts down the apparatus. The shutting down of the apparatus includes stopping pumps 22a, 22b and suction pump 38.

In use, the apparatus of the second embodiment operates in substantially the same way as the first embodiment, subject to the following comments. When the system is initially started up, pumps 22a and/or pump 22b are energised to transfer waste water 2 to the tank 26 and the air supply to pipe 30 is actuated. If the tank 26 fills to the level of the high level sensor, pumps 22a and 22b are stopped. Whilst the level in the tank is between the low and high level sensors, the suction pump 38 is operated to draw water from the MBRs 11 and to the ionisation unit 12. One or both of the pumps 22a, 22b that pump water from the tanks 20, 21 are restarted if the level in tank 26 falls to the low level sensor. As water passes through the ionisation unit 12, the control unit 25 controls the current passing between the electrodes 48, 50 in the cells 46 of the ionisation unit 12. The polarity of the electrodes 48 and 50 are reversed every 90 seconds to reduce the effects of scaling and plating and to equalise erosion of the plates.

The use of multiple tubular cells 46 is particularly advantageous. Manifolding and valve arrangements are used to match the number of cells 46 in use to the rate of flow of water to be treated. The apparatus may be configured to be positioned in small and/or awkwardly sized spaces, such as may be found in ship machinery spaces.

The water may be passed from the outlet 41 to various further units according to the particular application (as described with reference to Fig. 2) .

A third embodiment of the invention on a ship (not separately illustrated) is provided to produce potable water. The third embodiment of the invention is based closely on the second embodiment, but wherein the further disinfection/cleaning unit 19 is capable of producing potable water. In this third embodiment the further disinfection unit treats the water, by using known chemical or non chemical methods, to ensure that the output water is of a quality sufficient for drinking use. The further disinfection unit includes reverse osmosis (RO) equipment to deal with soluble salts or other chemical compounds that may be present in the water outputted at outlet 41. The combination of MBR and ionisation treatments provides a relatively sterile and low saltation index liquid for treatment by the RO equipment, thus lowering capital costs, increasing reliability and reducing maintenance .

Other modifications may be made to the second embodiment to suit given requirements. For example, the further disinfecting unit 13 (chlorination unit) may be in the form of a dispenser of any known suitable type for introducing, in a controlled manner, standard disinfections, for example iodine, into a flow of liquid. A fourth embodiment of the invention relating to the upgrading of existing marine black water treatment systems will now be described with reference to Fig. 5. Legislation may cause some existing treatment systems to fall short of required standards. By retro-fitting suitable apparatus (to produce a simplified version of the second embodiment of the invention) , the life of existing units may be extended without involving replacement or major re-fit work. Figure 5 shows existing equipment including a primary treatment tank 100 and a final treatment tank 102. The treatment tanks 100, 102 are connected by a pipe 54 to a discharge outlet 17. In use of the existing equipment, black water is treated by the tanks 100, 102 and immediately thereafter is pumped by a pump 104 into the sea via a solenoid valve 106 and the discharge outlet 17.

The conversion process includes severing the pipe 54 between the existing pump 104 and existing solenoid valve 106, and connecting to the pump 104 a filter unit 10, an ionisation unit 12, and a post-treatment unit 52. The output from the post-treatment unit 52 is then connected back^' to the solenoid valve 106. The filter unit 10 is provided with a backwash system, the backwash water being returned via pipe 55 to the primary treatment tank 100. The output of the post-treatment unit 52 is also connected via a junction 103 to the filter unit 10 to provide disinfected water for the purpose of backwashing. Between the junction 103 and the filter unit 10 there is provided a solenoid valve 108. A further solenoid valve 110 is provided in the water flow path downstream of the junction 103. A control unit (not shown) is arranged to receive inputs from the filter unit 10 and to send control signals to the ionisation unit 12 and the valves 106, 108, 110.

During normal use of the converted equipment, valves 106 and 110 are open and valve 108 is closed and the apparatus operates in a manner similar to that described above with reference to the second embodiment. The apparatus also includes a backwash system not described above. A sensor within the filter unit 10 provides a signal representative of the pressure therein. When a preset pressure is reached the control unit shuts valves 106 and 110 and opens valve 108 allowing the treated water to backwash the filter in the filter unit 10. The backwash water is then returned to the primary treatment tank 100. When the pressure within the filter unit 10 drops below a preset threshold, the control unit closes valve 108 and opens valves 106 and 110. The treated water is again then discharged outboard of the ship via discharge outlet 17. Valve 106 could alternatively be in the form of a non-return valve if desired. Other modifications and improvements may be made within the scope of the present invention. In particular, the invention may be of some advantage when the effective pore size is much greater than 0.1 microns. Further embodiments of the invention (not referring to the drawings) will now be described.

According to a fifth embodiment (not illustrated) of the present invention there is provided a water treatment system comprising a filter having a filter element suitable for removing particles above a predetermined size (the size possibly being as great as 400 microns, preferably less than 10 microns and more preferably being 0.1 microns); and a disinfection unit which comprises at least one cell having a pair of electrodes connectable across a power supply, the electrodes comprising one or more metals acting as a source of metal ions effective to disinfect water flowing through the cell from the filter and providing a residual disinfecting action.

According to a sixth embodiment (not illustrated) of the present invention there is provided a method of treating water, in which the water is first filtered to remove particles greater than a predetermined size (possibly being as great as 400 microns, preferably less than 10 microns and more preferably 0.1 micron) , and is then infused with metal ions effective to produce disinfection.

According to a seventh embodiment (not illustrated) of the present invention there is provided a disinfection apparatus for the disinfection of waste water, comprising at least one cell having a pair of electrodes connectable across a power supply, the electrodes comprising one or more metals acting as a source of metal ions effective to disinfect water flowing through the cell. Preferably, the water flowing through the cell is from a filter. Advantageously, the disinfection apparatus is used with Membrane BioReactor [MBR] technology (preferably able to remove particles greater than 0.1 micron) . Preferably, the electrodes are arranged to act as a source of metal ions effective both to disinfect and to provide a residual disinfection to the water flowing through the cell. The disinfection apparatus may be used in waste treatment plants, in which case further equipment is preferably provided prior to the electrodes to remove biological and solids components. There is also provided a water treatment system comprising a filter having a filter element suitable for removing particles above a predetermined size; and a disinfection apparatus according to this seventh embodiment of the invention connected to receive water from the filter and providing a residual disinfecting action.

Claims

Claims :

1. A water treatment apparatus for the treatment of waste water, the apparatus comprising a filter having an average effective pore size of less than 1 micron and a source of metal ions, wherein the apparatus is so arranged that in use the waste water flows through the filter and the waste water is infused with metal ions, the concentration of ions in the waste. ater being at a concentration effective to disinfect the waste water.

2. An apparatus according to claim 1, wherein the apparatus is so arranged that the concentration of metal ions in the disinfected water is great enough to provide a residual disinfecting action.

3. An apparatus according to claim 1 or claim 2 , wherein the apparatus includes a control unit that is arranged to receive a signal that, in use, indicates the rate of flow of water through the apparatus .

4. An apparatus according to any preceding claim, wherein the apparatus includes a control unit that is able to control the rate of flow of water through the apparatus .

5. An apparatus according to any preceding claim, wherein the apparatus includes a control unit that is able to control the rate of supply of metal ions so as to control the concentration of supplied metal ions in the waste water.

6. An apparatus according to any preceding claim, wherein the source of metal ions includes a plurality of electrodes.

7. An apparatus according to claim 6, wherein the electrodes are removably mounted in the apparatus .

8. An apparatus according to claim 6 or claim 7, wherein the apparatus includes a power supply that is connected to the electrodes via constant current circuitry, which facilitates, in use, the control of the current passing between the electrodes .

9. An apparatus according to any preceding claim, wherein the source of metal ions is able to provide, in use, one or more of the following: silver ions, copper ions, and zinc ions .

10. An apparatus according to any preceding claim, wherein the apparatus further comprises a further source of disinfecting material, the apparatus being so arranged that the waste water is infused with the material at a concentration effective to aid disinfection of the waste water.

11. An apparatus according to any preceding claim, wherein the filter has an average effective pore size of less than 0.1 micron.

12. An apparatus according to any preceding claim, wherein the filter is a membrane bio-reactor.

13. An apparatus according to any preceding claim, wherein the apparatus comprises further filtering apparatus provided upstream of the filter, the filtering apparatus being able to remove particles having a size greater than 3mm.

14. An apparatus according to any preceding claim, wherein the apparatus comprises cleaning apparatus arranged to further disinfect or clean the water.

15. An apparatus according to claim 14, wherein the cleaning apparatus is provided downstream of the source of metal ions and includes means for removing excess metal ions.

16. An apparatus according to claim 14, wherein the cleaning apparatus comprises one or more of the following: UV disinfecting unit, carbon filter, zeolite filter, and a unit providing an oxidising agent.

17. A method of disinfecting waste water comprising the steps of filtering the waste water to remove particles having a size greater than 1 micron and infusing the waste water with metal ions effective to disinfect the waste water, whereby the method converts the waste water into disinfected water.

18. A method according to claim 17, wherein the step of filtering the wastewater removes particles greater than 0.1 micron in size.

19. A method according to claim 17, wherein the waste water is filtered to remove particles having a size greater than 3mm before the step of filtering to remove particles having a size greater than 1 micron is performed.

20. A method according to any of claims 17 to 19, wherein the concentration of metal ions infused into the waste water is great enough to provide a residual disinfecting action.

21. A method according to any of claims 17 to 20, wherein the metal ions are provided by electrolytic action.

22. A method according to claim 21, wherein the electrolytic action is provided by two or more electrodes across which a potential difference is applied.

23. A method according to claim 22, wherein the polarity of the electrodes is periodically reversed.

24. A method according to claim 23, wherein the time between reversing the polarity is between 60 and 240 seconds.

25. A method according to any of claims 17 to 24, wherein the ions infused comprise one or more of the following metal ions: silver ions, copper ions, and zinc ions.

26. A method according to claim 25, wherein the ions infused comprise at least 60% silver ions.

27. A method according to any of claims 17 to 26, wherein the method includes a step of adding oxidants to the water at a concentration effective to aid disinfection of the waste water.

28. A method according to any of claims 17 to 27, wherein the method includes a step of storing the disinfected water.

29. A method according to any of claims 17 to 28, wherein the method includes a step of using the disinfected water for irrigation.

30. A method according to any of claims 17 to 29, wherein the method comprises a step of further treating the disinfected water.

31. A method according to claim 30, wherein the step of further treating the disinfected water is performed to produce potable water.

32. A method according to claim 30 or claim 31, wherein the step of further treating the disinfected filtered water comprises removing metal ions from the water.

33. A method according to any of claims 17 to 32, wherein the method is performed on a marine structure or marine vessel.

34. A method according to any of claims 17 to 33, wherein the method is performed using an apparatus as claimed in any one of claims 1 to 16.

35. Apparatus according to any of claims 1 to 16, wherein the apparatus is configured to be suitable for performing the method according to any of claims 17 to 33.

36. Water treatment installation including an apparatus according to any of claims 1 to 16 and 35.

37. A method of improving an existing water treatment installation, the existing installation comprising a filter having an average effective pore size of less than 1 micron arranged in use to provide filtered waste water, the method including the steps of connecting in series with the filter an ionisation unit including a source of metal ions, and connecting a control unit to the treatment installation for controlling the concentration of metal ions infused into the waste water so that the concentration is effective to disinfect the waste water.

38. A method according to claim 37, wherein the existing water treatment installation includes an existing control unit and the method includes a step of replacing the existing control unit, the replacement control unit being configured to control not only the concentration of metal ions infused into the waste water, but also the operation of the installation.

39. A method according to claim 37 or claim 38, wherein the method is performed to produce a water treatment installation according to claim 36.

40. A conversion kit comprising an ionisation unit and a control unit for use in the method according to any of claims 37 to 39.

41. A marine structure or a marine vessel including a water treatment installation according to claim 36.