Patent Publication Number: US-2010116650-A1

Title: Removal of contaminants from a fluid

Description:
This invention relates to an electrocoagulation unit, and a fluid treatment apparatus including an electrocoagulation unit, for removing contaminants from a fluid. 
     It is often necessary to remove contaminants from a fluid, especially water, to render the fluid suitable for further use or discharge into the environment. Contaminants can include metal ions such as arsenic, chromium, copper, cadmium, nickel, lead, and zinc, suspended solids such as silt and clay, dissolved organic compounds, hydrocarbons, dyes, and phosphates. 
     One way of removing contaminants from a fluid involves adding a chemical additive to the fluid to cause a chemical reaction between the contaminants and the additive such that the contaminants and the chemical additive coagulate into larger particles, which can be removed from the fluid. 
     One drawback with the use of chemical additives is the creation of a large quantity of residual material that must be disposed of following treatment of a fluid. 
     As an alternative to the use of chemical additives, it is known to electrolytically treat a contaminated fluid so as to remove contaminants from the fluid in a process called electrocoagulation. 
     An electrocoagulation unit causes suspended contaminants in a contaminated fluid to coagulate together through the application of an electrical current to the fluid via a plurality of electrodes. This method of removing contaminants reduces the amount of residual material generated. 
     Through the use of different electrode configurations, or electrodes of different materials, it is possible to remove contaminants differing in nature and composition. 
     However, in conventional electrocoagulation units, it is difficult to alter the configuration of the anode and cathode electrodes. Consequently, such units generally employ an electrode arrangement that is suitable for removing a wide range of different contaminants from fluids so that the unit may be used with any contaminated fluid. This results in relatively inefficient electrocoagulation units since the electrode arrangement is not specifically chosen for any one specific contaminant. 
     There is a need therefore for a more flexible electrocoagulation unit that is readily configurable to deal efficiently with differently contaminated fluids. 
     According to a first aspect of the invention there is provided an electrocoagulation unit, for removing contaminants from a fluid, comprising:
         an electrode chamber, which in use has a top and a bottom, the chamber having a fluid inlet at or towards its bottom and being in fluid communication with at least one discharge conduit towards its top to direct fluid from the chamber towards a fluid outlet; and   an electrode module removable through the top of the electrode chamber and including at least one support body supporting a plurality of electrodes,   the electrode chamber and the electrode module co-operating with one another to restrict the flow of contaminated fluid to regions within the electrode chamber adjacent active surfaces of the electrodes.       

     The electrode module being removable through what, in use, is the top of the electrode chamber means that an operative can remove the electrode module directly from the electrode chamber without having to remove any seals or drain the electrode chamber. 
     The operative is then able to replace the electrode module with an electrode module having a different configuration of electrodes, or a different type of electrodes. It is thereby possible to provide an electrode module prepared for use with a fluid containing a specific contaminant, or to provide an electrode having a large active electrode surface area, and thereby maximise the efficiency of the electrocoagulation unit. 
     In addition, restricting the flow of contaminated fluid to regions within the electrode chamber adjacent active surfaces of the electrodes ensures that all contaminated fluid passing through the electrode chamber is acted upon to remove contaminants therefrom, thereby further improving the efficiency of the electrocoagulation unit. 
     Preferably the or each support body includes a first support member extending through each electrode. 
     The inclusion of one or more first support members conveniently secures the electrodes relative to one another and creates an electrode module that a user is able readily to handle. 
     Optionally adjacent electrodes are spaced from one another by at least one spacer member. 
     Such an arrangement ensures that a user is able easily to vary the spacing between adjacent electrodes through the use of one or more spacers having a desired thickness. As a result a user is able readily to adjust the configuration of the electrode module according to, for example, the viscosity of the contaminated fluid, the size and concentration of suspended solids within the contaminated fluid, or the rate of creation of suspended contaminants within the fluid. 
     In a preferred embodiment of the electrocoagulation unit the or each first support member passes through one or more corresponding spacer members. This arrangement retains the or each spacer member relative to the electrodes and so aids assembly of an electrode module. 
     In another preferred embodiment of the invention the electrodes extend laterally so as to lie adjacent to the electrode chamber. The inclusion of such electrodes helps to inhibit the flow of contaminated fluid between inactive edges of the electrodes and the electrode chamber in order to improve the efficiency of the electrocoagulation unit. 
     Preferably each inactive surface includes a cover member secured thereto so as to lie between the given inactive surface and the electrode chamber. Securing one or more cover members in this manner inhibits the flow of contaminated fluid over each inactive surface, and so further helps to improve the efficiency of the electrocoagulation unit. 
     An electrocoagulation unit according to a further preferred embodiment of the invention includes a support body that defines a hollow conduit in which the electrodes are located and through which contaminated fluid flows. This arrangement allows the support body to effectively protect the inner surface of the electrode chamber from contact with the contaminated fluid, thereby reducing the build up of suspended contaminant deposits in the electrode chamber and thus helping to ensure that the electrode module is readily removable from the electrode chamber. 
     The electrode module may be removably located in the electrode chamber such that the support body spaces the electrodes from an inner surface of the electrode chamber. 
     Spacing the electrodes from the inner surface of the electrode chamber prevents the electrodes coming into contact with the inner surface of the electrode chamber and so reduces the likelihood of the electrodes becoming wedged within the electrode chamber as a result of a build up of suspended contaminant deposits. Wedging of the electrodes within the electrode chamber would inhibit removal of the electrodes from the electrode chamber and so make it difficult to reconfigure the electrocoagulation unit. 
     The support body may be located adjacent to each inactive surface of the electrodes. This allows the support body to restrict the flow of contaminated fluid to pass over the active surfaces of the electrodes only, thereby increasing the efficiency of the electrocoagulation unit. 
     Optionally the support body includes two co-operable body portions, which are separable from one another. This arrangement allows an operative to disassemble the electrode module in order to replace a damaged or worn electrode. 
     In a preferred embodiment, the support body includes at least one side member, the or each side member lying between the two body portions. Such an arrangement provides a convenient way of arranging the support body adjacent the inactive surface of a given electrode. 
     In another preferred embodiment, the or each support body is or includes a non-conductive material. Particularly desirable non-conductive materials include PVC and recycled plastics. 
     The electrodes may be formed from or include one or more of the following: aluminium, steel, stainless steel, copper, graphite, reticulated vitreous carbon and a dimensionally stable alloy. Each of these materials is effective at dealing with different contaminants. 
     Preferably the electrode module further includes at least one second support member, which passes through alternately spaced electrodes. The inclusion of one or more second support members provides the electrodes with additional support when the electrode module is removed from the electrode chamber. 
     Optionally the electrode module includes a handle secured to at least one second support member to facilitate removal of the electrode module from the electrode chamber. 
     The electrocoagulation unit may further include a DC power source electrically coupled to the electrode module. 
     In another preferred embodiment, the electrode module includes a pair of connecting members, each connecting member engaging two or more differing electrodes to define an electrical connection therebetween and being electrically coupled to the DC power source. Such a feature simplifies the connection of an electrical power supply to a group of electrodes. 
     In a further preferred embodiment, the or each discharge conduit includes at least one weir member lying between the transfer outlet and the discharge outlet. The provision of one or more weir members increases the size of the interface between the contaminated fluid and, e.g. air, in the discharge conduit, thereby improving the exchange of gas, e.g. oxygen, with the contaminated fluid. 
     In one embodiment, the or each weir member includes a plurality of perforations. The inclusion of a plurality of perforations helps to reduce the likelihood of any gas generated during electrocoagulation becoming trapped underneath a respective weir member. 
     Optionally the or each discharge conduit includes an aeration member for introducing a gas into any fluid flowing through the given discharge conduit. This enhances the exchange of gas with the contaminated fluid. 
     The or each discharge conduit may define a helical path. Such an arrangement maintains a laminar flow of fluid discharged from the electrode chamber. This further promotes the coagulation of suspended contaminants in the fluid and so helps to improve the efficiency of the electrocoagulation unit. 
     Preferably the electrocoagulation unit further includes at least one hydrogen collector. In this way the electrocoagulation unit is able to remove and harvest any hydrogen generated therein. 
     In one embodiment, the fluid inlet may include at least one inlet member, the or each inlet member including at least one inlet aperture, the or each inlet aperture being directed away from the electrode module to initially direct fluid away from the electrode module. Such an arrangement induces a laminar flow in the fluid flowing through the electrode chamber which results in more efficient operation of the electrocoagulation unit, i.e. less power or less active electrode surface area required to treat a given volume of fluid. 
     According to another aspect of the invention there is provided a fluid treatment apparatus, for removing contaminants from a fluid, comprising at least one electrocoagulation unit according to any of Claims  1  to  13  and a separation unit wherein the electrocoagulation unit and the separation unit are fluidly connected in series. 
     This arrangement of fluid treatment apparatus shares the advantages of the electrocoagulation unit of the invention. 
     Preferably the fluid treatment apparatus includes an electrocoagulation unit including an electrode module having stainless steel electrodes. One benefit of including an electrocoagulation unit which includes an electrode module that has stainless steel electrodes, is that such an arrangement is particularly effective at removing small amounts of aluminium from a fluid passing therethrough. 
     Optionally the separation unit is or includes a settling tank. A settling tank provides a convenient and cost effective way of removing suspended contaminant particles. 
     Preferably the separation unit is or includes an air filter including a diffuser for generating a stream of gas bubbles to urge any suspended contaminant particles to a surface of the fluid flowing through the separation unit. Such an arrangement provides a convenient way of removing relatively lightweight contaminant particles. 
     The separation unit may include an aspirator to suck suspended contaminant particles from an exposed fluid surface into a collection vessel, a skimmer to skim suspended contaminant particles from an fluid exposed surface into a collection vessel, or a decantor to decant suspended contaminant particles from an exposed fluid surface into a collection vessel. 
     Any of the foregoing features allow for the effective removal of any suspended contaminant particles from an exposed surface of the fluid. 
     Another embodiment of fluid treatment apparatus may further include a series connected hydrogen peroxide unit having an anode and a cathode. The inclusion of a hydrogen peroxide unit helps to oxidise organic compounds, which may cause oxygen demand, so as to allow for the removal of such compounds from a fluid. 
     Optionally the anode and the cathode are or include reticulated vitreous carbon. The provision of a reticulated vitreous carbon anode and cathode helps to maximise the active electrode surface area, and thereby improve the efficiency of the electrocoagulation unit. 
     Alternatively the anode is or includes a dimensionally stable electrode alloy and the cathode is or includes reticulated vitreous carbon. The use of a dimensionally stable electrode alloy helps to prevent electrode degradation. In addition, it is possible to tailor the choice of dimensionally stable alloy so that the gaseous products produced during electrocoagulation enhance the overall electrocoagulation process. 
     In one embodiment, the hydrogen peroxide unit includes at least one aeration member located upstream of the anode and cathode. The inclusion of an aeration member helps to ensure saturation of the fluid passing through the hydrogen peroxide unit with, e.g. oxygen. 
     In another embodiment, the hydrogen peroxide unit includes a sacrificial anode for releasing Fe 2+  ions into the fluid passing through the hydrogen peroxide unit. 
     In an alternative embodiment, the fluid treatment apparatus includes a fluid conduit between at least one of the electrocoagulation units and the hydrogen peroxide unit to allow the transfer of Fe 2+  ions from the or each electrocoagulation unit to the hydrogen peroxide unit. 
     The presence of Fe 2+  ions in the hydrogen peroxide unit improves the rate of degradation of organic compounds, which allows for the removal of such compounds from the fluid, without the need to chemically add coagulating agents, such as iron salts. 
     Optionally the fluid treatment apparatus further includes a series connected silver ionisation unit. The inclusion of a silver ionisation unit provides residual disinfection of the fluid passing therethrough. 
     Preferably the fluid treatment apparatus further includes a power supply module including at least one of the following: a vehicle engine and a renewable energy source. The inclusion of such a power supply module allows for the provision of a portable fluid treatment apparatus. 
    
    
     
       There now follows a brief description of preferred embodiments of the invention, by way of non-limiting examples, with reference being made to the accompanying drawings in which: 
         FIG. 1  shows a front elevational, partially sectioned, view of an electrocoagulation unit according to a first embodiment of the invention; 
         FIG. 2  shows an elevational, sectioned view from one side of the electrocoagulation unit shown in  FIG. 1 ; 
         FIG. 3  shows a plan view from above of the electrocoagulation unit shown in  FIG. 1 ; 
         FIG. 4  shows a plan view from below of the electrocoagulation unit shown in  FIG. 1 ; 
         FIG. 5(   a ) shows a perspective view of an inlet member; 
         FIG. 5(   b ) shows an elevational view from one side of the inlet member shown in  FIG. 5(   a ); 
         FIG. 6  shows a schematic, perspective view an electrocoagulation unit according to a second embodiment of the invention; 
         FIG. 7  shows a partially exploded, perspective view of the electrode module shown in  FIG. 6 ; 
         FIG. 8  shows a perspective view of the electrode chamber shown in  FIG. 6 ; 
         FIG. 9  shows a fluid treatment apparatus according to a first embodiment of the invention; 
         FIG. 10  shows schematic view of a settling tank; 
         FIG. 11(   a ) shows a schematic view of an air filter; 
         FIG. 11(   b ) shows a schematic view of a diffuser; and 
         FIG. 12  shows a schematic view of a hydrogen peroxide unit. 
     
    
    
     An electrocoagulation unit according to a first aspect of the invention is designated generally by the reference numeral  10 . 
     The first electrocoagulation unit  10  includes an electrode chamber  12 , which in use has a top  16  and a bottom  17 . The top  16  of the electrode chamber  12  is open which allows the electrocoagulation unit  10  to operate at atmospheric pressure. The electrode chamber  12  has two inlets  14  at its bottom  17  and is in fluid communication with two discharge conduits  22  towards its top  16  to direct fluid from the chamber  12  towards respective fluid outlets  24 . 
     In the embodiment shown, each discharge conduit  22  also includes a plurality of inclined weir members  26 , which lie between the top  16  of the chamber  12  and the associated fluid outlet  24 . Adjacent weir members  26  in each discharge conduit  22  are attached to opposite walls  28 ,  30  of the discharge conduit  22  so as to define a serpentine path through the discharge conduit  22 . Optionally the weir members  26  are slidably received in each discharge conduit  22 . 
     In other embodiments, the arrangement of weir members  26  may differ. For example, a plurality of weir members may adopt a chevron arrangement (not shown) within a given discharge conduit. A discharge conduit may also include one weir member which defines a helter-skelter or spiral path (not shown) within a given discharge conduit. 
     In still further embodiments of the invention, the or each discharge conduit may define a helical path. 
     In addition, other embodiments may include one or more discharge conduits that are larger in proportion to the electrode chamber  12  than those shown in  FIGS. 1 to 4 . 
     Each discharge conduit  22  also includes an aeration member (not shown) for introducing gas into each discharge conduit  22 . 
     The electrocoagulation unit  10  also includes a hydrogen collector (not shown). The hydrogen collector is preferably located above the top of the electrode chamber  12  so that it is able to remove and collect any gaseous product produced within the electrode chamber  12 , or either discharge conduit  22 . Collecting any gaseous product in this way enables subsequent recycling or re-use of the gaseous product. 
     The electrocoagulation unit  10  also includes a first electrode module  34  which is removable through the top of the electrode chamber  12 . The first electrode module  34  has a support body  36  that supports a plurality of electrodes  38 . 
     Other embodiments of electrocoagulation unit (not shown) may include a plurality of first electrode modules  34  located within an electrode chamber  12 . 
     In the embodiment shown in  FIGS. 1 to 4 , the support body  36  defines a hollow conduit  40  in which the electrodes  38  are located, and through which contaminated fluid (not shown) is able to flow. 
     Each electrode is essentially an elongate plate  42  with a truncated corner. The electrode plates  42  have a smooth surfaces which help to maintain a laminar flow of contaminated fluid through the electrocoagulation unit  10 . In other embodiments, it is envisaged that the electrodes  38  may be formed in different shapes. 
     Adjacent electrode plates  42  are spaced from one another and alternately form an anode  44  and a cathode  46 . The arrangement of electrode plates  42  shown, includes iron anodes  44  and aluminium cathodes  46 . 
     Other combinations of electrodes such as iron anodes and cathodes, and aluminium anodes and cathodes are also possible. In addition the anodes and/or cathodes may include steel, stainless steel, copper, graphite, reticulated vitreous carbon and/or a dimensionally stable alloy such as tantalum or titanium. The electrodes may also be formed from a substrate which is coated with titanium. 
     The support body  36  includes a plurality of recesses  48 , each of which slidably receives and supports one side of a respective electrode plate  42  such that adjacent electrodes plates  42  lie substantially parallel to one another. Each end  50 ,  52  of each electrode plate  42  is exposed at either end of the support body  36 . 
     In a preferred arrangement, each electrode plate  42  is 4 mm thick and is spaced from an adjacent electrode plate  42  by 4 mm. Other arrangements may have different spacings according to the configuration of electrode plates  42  required to deal with a fluid containing a particular contaminant. Other arrangements may also include a different number of electrode plates  42 . 
     In the embodiment shown, the support body  36  includes two co-operable body portions  54 ,  56 , which are separable from one another. 
     The support body  36  includes two separate side members  60  that extend between the body portions  54 ,  56 , and lie adjacent an inactive surface  62  of each end electrode plate  42 . 
     Each body portion  54 ,  56  may also include an elongate web (not shown) extending toward the other body portion  54 ,  56 , and lying adjacent the inactive surface  62  of each end electrode plate  42 . 
     Preferably the support body  36  is made from PVC or another non-conductive material, such as a recycled plastic. 
     The electrode plates  42  are arranged such that a corner  66  of adjacent electrode plates lie on opposite sides of the electrode chamber  12 , as shown in  FIG. 1 . 
     The support body  36  also includes two second support members  64 . Each second support member  64  passes through a hole  68  in the corner  66  of alternate electrode plates  42 . In this way, one second support member  64  passes through the anodes  44 , and one second support member  64  passes through the cathodes  46 . 
     A handle (not shown) may be secured to each support member  64 . 
     The electrocoagulation unit  10  includes a DC (Direct Current) power source (not shown) that is electrically coupled to the first electrode module  34   
     The first electrode module  34  further includes two connecting members  70 . One connecting member  70  engages the corner  66  of each anode  44  so as to provide an electrical connection between the anodes  44 . The other connecting member  70  engages the corner  66  of each cathode  46  so as to provide an electrical connection between the cathodes  46 . 
     The first electrode module  34  is removably received in the electrode chamber  12  such that the support body  36  spaces the electrode plates  42  from an inner surface  18  of the electrode chamber  12 . 
     The inlet  14  of the electrode chamber  12  includes two inlet members  72 , each of which includes a plurality of inlet apertures  74 . Each inlet aperture  74  is directed away from the first electrode module  34  and so initially directs fluid away from the electrode module  34 , as shown in  FIGS. 5(   a ) and  5 ( b ). 
     In use, the electrode chamber  12  is substantially vertical. Contaminated fluid (not shown) enters the electrode chamber  12  via the pair of inlet members  72 . The arrangement of inlet apertures  74  initially directs the contaminated fluid away from the first electrode module  34 , which results in a laminar flow of contaminated fluid across the electrode plates  42  of the first electrode module  34 . 
     The hollow conduit  40  of the support body  36  inhibits the flow of contaminated fluid to inactive surfaces  62  of the electrode plates  42 , and the flow of contaminated fluid adjacent to the inner surface  18  of the electrode chamber  12 . This latter feature helps to eliminate the build up of contaminant particle deposits on the inner surface  18  and therefore helps to ensure that the first electrode module  34  remains easy to remove from the electrode chamber  12 . 
     Once the contaminated fluid has passed through the hollow conduit  40  of the support body  36  it is directed from the electrode chamber  12  to the discharge conduits  22 . 
     Each discharge conduit  22  may omit the plurality of weir members  26 , and so the contaminated fluid may flow straight through each discharge conduit  22  and leave the electrocoagulation unit  10  via the fluid outlets  24 . Such an arrangement preserves the Fe 2+  ions in the discharged fluid. 
     In a different mode of operation, or if the electro coagulation unit  10  is used to treat a different contaminated fluid, each discharge conduit  22  may include a plurality of weir members  26 . In this case the contaminated fluid directed from the electrode chamber  12  flows over the weir members  26  to facilitate the conversion of Fe 2+  ions to Fe 3+  ions. 
     Air or oxygen may be added via the aeration members to further facilitate this conversion. 
     The resistance across a sacrificial electrode (not shown), which has a lifetime similar to the electrode plates  42  in the first electrode module  34 , may be monitored to determine when to replace one or more of the electrode plates  42 . 
     Alternatively the voltage required to maintain a predetermined current through the electrode plates  42  may be monitored to determine when one or more of the electrode plates  42  needs replacing. 
     An operative may remove the first electrode module  34  from the electrode chamber  12  simply by lifting the first electrode module  34  out of the top  16  of the electrode chamber  12 . The operative does not have to remove any seals and/or plates and covers in order to remove the first electrode module  34 . 
     Once removed, the operative can replace the first electrode module  34  with another first electrode module  34 , which may have a different configuration and/or electrodes  38  formed from a different material, for example. The other first electrode module  34  may be, e.g. more efficient for treating differently contaminated fluid, or have electrode plates  42  with a greater active surface area so as to be able to deal with a greater throughput of contaminated fluid within the fixed volume of the electrode chamber  12 . 
     Alternatively, the operative can replace a damaged or worn first electrode module  34  with an identical first electrode module  34 . 
     The operative may also repair/replace one or more electrode plates  42  of a removed first electrode module  34  before returning the first module  34  to the electrode chamber  12 . 
     A second electrocoagulation unit according to a second embodiment of the invention is designated generally by the reference numeral  210 , as shown schematically in  FIG. 6 . 
     The second electrocoagulation unit shares some features with the first electrocoagulation unit  10 , and these are designated using the same reference numerals. 
     The second electrocoagulation unit includes a second electrode module  234  which is shown in partially exploded form in  FIG. 7 . The first and second electrode modules  34 ;  234  have some features in common with one another, and these are designated using the same reference numerals. In addition, the first and second electrode modules  34 ;  234  are interchangeable with one another. 
     The second electrode module  234  includes five support bodies  36 , each support body  36  including a first support member  236  which extends through each electrode  38 . One form of first support member  236  is a bolt  238  and a corresponding nut  240 , which may be formed from nylon. However, differing numbers and other types of first support member are also possible. 
     Adjacent electrodes  38  in the second electrode module  234  are spaced from one another by five first spacer members  242 . Each first spacer member  242  corresponds to a given first support member  236  which passes therethrough to secure the first spacer member  242  relative to the electrodes  38 . Other embodiments may include a different number of first spacer members  242  between adjacent electrodes  38 . 
     As a result it is possible easily to vary the spacing between adjacent electrodes  38  by varying the thickness or number of first spacer members  242  interposed between the adjacent electrodes. 
     In the second electrode module  234  shown the first support members  236  and the first spacer members  242  are electrically non-conducting. 
     Each electrode  38  in the second electrode module  234  extends laterally so as to lie adjacent to the corresponding wall  244  of the electrode chamber  12 . 
     Each inactive surface  62  of the electrode plates  42  in the second electrode module  234  includes a cover member  246  secured thereto so as to lie between the inactive surface  62  and the corresponding wall  244  of the electrode chamber  12 . This inhibits the flow of contaminated fluid over each inactive surface  62 . 
     The second electrode module includes two second support members  64  which pass through two second spacer members  248 . 
     In the second electrocoagulation unit  210 , the second support members  64  and second spacer members  248  also electrically interconnect alternate electrode plates  42  to define a group of anodes  44  and a group of cathodes  46 . 
     A fluid treatment apparatus according to another aspect of the invention is designated generally by the reference numeral  80 . 
     The fluid treatment apparatus  80  shown in  FIG. 9  includes two electrocoagulation units  10 ;  210  connected in series with a hydrogen peroxide unit  82 , which, in turn, is connected in series to a separation unit  84 . Each electrocoagulation unit  10 ;  210  may include a first and/or a second electrode module  34 ;  234   
     A third electrocoagulation unit (not shown) may include an electrode module  34 ;  234 , which has stainless steel electrode plates  42 . 
     Other preferred arrangements of fluid treatment apparatus (not shown) include:
         (i) two series connected electrocoagulation units  10 ;  210  connected in series with a separation unit  84 , which in turn is connected in series to a hydrogen peroxide unit  82 ;   (ii) a first electrocoagulation unit  10 ;  210  connected in series to a hydrogen peroxide unit  82 , which is connected in series to a second electrocoagulation unit  10 ;  210  connected in series to a separation unit  84 ; and   (iii) a hydrogen peroxide unit  82  connected in series to two series connected electrocoagulation units  10 ;  210 , which are connected in series to a separation unit  84 .       

     The separation unit  84  may be or include a settling tank  86 , as shown in  FIG. 10 . Fluid enters the settling tank  86  via a tank inlet  88  and exits via a tank outlet  90 . Contaminant particles  92 , e.g. sludge, may be removed via a tap  94  at the bottom of the tank  86  following settling. 
     A further separation unit  84  may be or include an air filter  96 , as shown in  FIG. 11(   a ). 
     The air filter  96  includes a filter inlet  98  through which contaminated fluid  99  enters the filter  96 , a filter outlet  100  via which fluid leaves the filter  96 , and an air inlet  102  through which a gas such as air or oxygen is introduced into the filter  96 . 
     The air filter  96  also includes a diffuser  104  which includes a plurality of fluid transmission pores  106 , together with a plurality of smaller, gas transmission pores  108 . 
     A gas, e.g. air, is fed into the diffuser  104  and generates a stream of bubbles  110  which rise through the contaminated fluid  99  and urge suspended contaminant particles  112  to a surface  114  of the fluid  99 . 
     Meanwhile, the larger fluid transmission pores  106  allow decontaminated fluid to pass through diffuser  104  to be collected via the filter outlet  100 . 
     The air filter  96  may also include an aspirator (not shown) for sucking the contaminant particles  112  from the surface  114 , a skimmer (not shown) for skimming the contaminant particles  112  from the surface  114 , or a decanter (not shown) for decanting the contaminant particles  112  from the surface  114 . 
     In each case the volume of collected contaminant particles  112  can be further reduced by evaporation or further treatment such as by filter press. 
     When treating fluid contaminated with dissolved organic carbon, or other organic based waste, it is desirable to include a hydrogen peroxide unit  82  in order to oxidise the organic contaminants in the fluid. 
     The hydrogen peroxide unit  82  includes a main chamber  116 , which contains an anode  44  and a cathode  46 . The anode  44  and the cathode  46  are made from blocks of reticulated vitreous carbon (RVC) in order to maximise the surface area of each electrode. 
     Alternatively, a dimensionally stable alloy (DSE), such as tantalum or titanium, can be used to form the anode  44 . 
     The hydrogen peroxide unit  82  also includes two aeration members  32  located upstream of the anode  44  and cathode  46 . Preferably each aeration member  32  includes a diffuser (not shown) with a relatively small pore size for generating small gas bubbles. In use the aeration members  32  help to ensure that the fluid passing through the hydrogen peroxide unit  82  is saturated with, e.g. oxygen. 
     The hydrogen peroxide unit  82  may also include a sacrificial anode (not shown) for releasing Fe 2+  ions into the fluid passing through the unit  82 . 
     Alternatively, the fluid treatment apparatus  80  may include a fluid conduit (not shown) between at least one electrocoagulation unit  10  and the hydrogen peroxide unit  82  for transferring Fe 2+  ions from the electrocoagulation unit  10  to the hydrogen peroxide unit  82 . 
     The presence of Fe 2+  ions in the hydrogen peroxide unit  82  helps to improve the rate of degradation of organic compounds and promote the formation of suspended contaminant particles, which can then be coagulated and removed from the fluid. 
     The fluid treatment apparatus  80  may also include a silver ionisation unit (not shown) connected in series at the downstream end of the apparatus  80 . 
     The fluid treatment apparatus  80  shown schematically in  FIG. 9  also includes a power supply module  118 , which provides power to the first and second electrocoagulation units  10  and the hydrogen peroxide unit  82 . The power supply module  118  may include a vehicle engine and/or a renewable energy source such as a cycle-driven dynamo, a photovoltaic cell and a wind turbine. The fluid treatments apparatus  80  may also be powered by mains electricity or a methane source. 
     Other embodiments of fluid treatment apparatus  80  (not shown) may be powered by mains electricity. 
     In addition, the fluid treatment apparatus  80  shown includes a fluid pump  120  for pumping contaminated fluid through the electrocoagulation units  10  and the remainder of the fluid treatment apparatus  80 . 
     The fluid treatment apparatus  80  may also include a gas pump  122  to supply the aeration members  32  with gas, e.g. air or oxygen.