Abstract:
According to the invention there is provided a tertiary effluent treatment process for reducing the phosphate levels in effluent. The process comprises the steps of delivering effluent from a wastewater treatment plant to a primary filter, delivering the filtered effluent to a series of two or more phosphate removal filters, delivering the filtered phosphate-depleted effluent to a treated water tank as treated water, delivering the filtered phosphate-depleted effluent from the treated water tank to a discharge tank as treated water; and, discharging the treated water from the discharge tank as required. Each phosphate removal filter comprises a plurality of polymer-based beads having nano-particles of iron oxide coated thereon. The advantage of using a series of two or more phosphate removal filters is that the process can deliver a final effluent containing specific pre-determined levels of phosphate that may be as low as 0.01 mg/L of effluent, but will in all cases be below 1 mg/L. The series of two or more filters also allow the process to accommodate variations in the phosphate content of the effluent without affecting the level of phosphate in the discharge, and, the system can be retro-fit to the end of any type of existing waste water treatment plant or can be integrated into a new facility.

Description:
INTRODUCTION 
       [0001]    This invention relates to an effluent treatment process and an assembly for carrying out the effluent treatment process. More particularly, the present invention relates to an effluent treatment process and assembly for carrying out that process on final effluent that has already undergone prior treatment preferably in a biological effluent treatment plant. In particular, the invention is particularly designed to remove phosphorus from treated effluent to a level less than 0.02 mg/Litre. 
         [0002]    Throughout the following description, it should be understood that the term “phosphate” can refer to either a composition comprising phosphorus or to the chemical element phosphorus itself, and, that any reference to “phosphate” should be interpreted as such. 
         [0003]    A significant challenge facing local authorities is to ensure that adequate effluent treatment facilities are provided for both new and existing housing developments in remote areas where connection to a centralised effluent treatment plant is either uneconomical or impractical and dedicated effluent treatment facilities for the housing development are provided. The effluent, including but not limited to raw sewage, from the housing development must be handled in a very careful and comprehensive manner to ensure that no threat is posed to the residents or to the environment. It is desirable to treat the effluent to such a degree that the majority of the treated effluent may be released as surface water and the maximum amount of harmful substances from the effluent are captured and disposed of subsequently in a safe manner. 
         [0004]    A particular problem with known processes is that treated effluents still typically contain high levels of phosphate, suspended solids, chemical oxygen demands (CODs) and biological oxygen demands (BODs) which are harmful to the environment. Phosphate can be particularly harmful as high levels of phosphate in water systems leads to eutrophication of the water system which will encourage the growth and decomposition of oxygen-depleting plants such as algal bloom, and result in harm to other organisms including fish. As a result of these environmental concerns, many countries, including Ireland, the United Kingdom, other European countries and the USA, have set the limit for total phosphorus concentrations in discharges of wastewater treatment plants at 1 mg/Litre or in some cases even less. 
         [0005]    Several effluent treatment processes comprising phosphate treatment stages have been proposed to date. Phosphate treatment is conventionally carried out using one of two principal methods. The level of phosphate is reduced by a chemical precipitation or by an enhanced biological removal method. The biological removal method tends to be favoured as it has a lower overall operating cost, when compared with the chemical precipitation method, however, the biological removal method may not be as reliable and cannot achieve the same levels of phosphate removal as a well-run chemical precipitation method. 
         [0006]    There are problems with both of these existing methods. Both methods are largely unreliable when the level of phosphorus is required to be reduced below 1 mg/Litre. Phosphorous occurs in wastewater as organic phosphorous derived from food. The average content of phosphorous in crude wastewater is said to be about 10 mg/L. Following primary and secondary treatment of the crude wastewater in primary and secondary effluent treatment plants. Following a typical biological treatment of sewage, which reduces levels of BOD by 90%, the residual level of phosphorous in the effluent stream will be from 2.5 mg/L to 17.5 mg/L depending on the levels of phosphate in chemicals used in the primary and secondary treatment plants. New legislation requires that the residual level of phosphorous in the effluent stream be below 1 mg/Litre or 2 mg/Litre in some cases. 
         [0007]    The existing methods using the biological and chemical methods are incapable of adjusting to fluctuating levels of phosphate in the effluent as the methods are typically set up to introduce a predetermined amount of the biological or chemical substance into the effluent as the effluent flows through the treatment stage. 
         [0008]    Furthermore, existing methods do not allow for the recovery of the phosphate once it has been removed from the effluent. Phosphate can be used in a number of by-products, such as in fertiliser, to great effect, and the recovery of the phosphate removed from the effluent will allow for the incorporation of the phosphate into by-products which is efficient and financially advantageous. 
         [0009]    A further problem with the existing methods is that many of the methods produce large volumes of sludge which is expensive to dispose of in a secure and safe manner. 
         [0010]    Known phosphate removal filtering systems are described in WO2007/131522 (BIOPTECH HOLDING AB) and EP0607019 (STEP THREE). Both of these effluent treatment filtering systems describe a primary filter for removing suspended solids from wastewater, followed by one or more further filtering stages to further purify the wastewater, wherein one of the further stages is a phosphate removal filter. It is important to note that only one filtering stage in each of the systems disclosed in these prior art documents is used to filter out phosphates. Such an arrangement has been found to lead to problems when varying amount of phosphates are present in the wastewater. Due to the varying amounts of phosphate, the proposed solutions may not always be sufficient to reduce the phosphate levels to below 1 mg/Litre. Both of the prior art documents describe a phosphate removal filtering stage which uses a sorbent material such as Opoka rock or Alumina. Such sorbent materials are not always ideal for reducing the phosphate levels to below 1 mg/Litre. 
         [0011]    It is an object of the present invention to provide an effluent treatment process and assembly for carrying out the process that overcomes at least some of the problems with the known processes. In particular, it is an object of the present invention to provide an effluent treatment process and assembly for carrying out a process that removes high levels of phosphate from the effluent without any of the above-mentioned problems 
       STATEMENTS OF INVENTION 
       [0012]    According to the invention there is provided a tertiary effluent treatment process comprising the steps of delivering effluent from a wastewater treatment plant to a primary filter to remove suspended solids and particles having a diameter greater than 5 microns from the effluent; delivering, at a predetermined rate, the filtered effluent to a series of two or more phosphate removal filters, each phosphate removal filter comprising a plurality of polymer-based beads having nano-particles of iron oxide coated thereon; delivering the filtered phosphate-depleted effluent to a treated water tank as treated water; delivering the filtered phosphate-depleted effluent from the treated water tank to a discharge tank as treated water; and, discharging the treated water from the discharge tank as required. 
         [0013]    The present invention comprises a unique ability to deliver a final effluent containing specific pre-determined levels of phosphate that may be as low as 0.01 mg/L of effluent, but will in all cases be below 1 mg/L due to the use of the series of two or more phosphate removal filters. 
         [0014]    Moreover, the process can accommodate variations in the phosphate content of the effluent without affecting the level of phosphate in the discharge, and, the system can be retro-fit to the end of any type of existing waste water treatment plant or can be integrated into a new facility. The ability to guarantee such low levels of phosphate is required in some jurisdictions by legislation, and the above arrangement allows the effluent treatment process to meet the new legislative requirements regardless of the phosphate levels in the effluent. 
         [0015]    Furthermore, due to the set-up of the system, the removal of phosphate from the effluent is achieved without increasing the overall level of sludge produced by the waste water treatment plant, and, phosphate is removed in a manner that will allow it to be recovered in pure form for future use. Thus, the system can be adapted to any scale of treatment plant, and, the system can be utilised to remove phosphate from other water-based solutions, for example industrial effluent or drinking water. 
         [0016]    A further advantage is that the system of preparation of the effluent ensures that the phosphate absorption filters operate under optimum conditions, and, the system also advantageously uses a phosphate removal medium which can be regenerated once it has absorbed its capacity of phosphate. 
         [0017]    By having such a process, a large proportion of the effluent may be released as surface water with the minimum risk to the environment. The primary filter will trap a significant portion of harmful particles before the effluent is passed through the series of two or more dedicated phosphate removal filters once the majority of harmful particles have already been removed from the effluent, thereby allowing highly effective removal of phosphate from the effluent. Once treated in this manner, the phosphate and other contaminant-depleted treated effluent may be discharged, preferably as surface water. 
         [0018]    This process may reduce the overall cost of handling the effluent as the vast majority of harmful materials are successfully removed from the effluent without subsequent processing being required. Furthermore, the process allows for significant amounts of phosphate to be removed from the process allowing the resulting treated effluent to be discharged as surface water or into the environment without the treated effluent posing a significant danger to the environment. Furthermore, the treated effluent could be reused as grey water or non-potable water in a domestic or other environment. 
         [0019]    In a further embodiment, the process further comprises the step of backwashing at least one of the two or more phosphate removal filters with treated water from the treated water tank at pre-determined backwashing intervals. 
         [0020]    Such a backwashing process has not been known with phosphate removal filters until now. The inclusion of such this process allows relatively large suspended particles larger than 5 microns that either passed through the primary filter, or that were created after the primary filter due to the joining of smaller suspended particles, to be backwashed out of the phosphate removal filters. This increases the operable working time for the phosphate filters. 
         [0021]    In a further embodiment, the process further comprises the step of backwashing at least one of the two or more phosphate removal filters only with treated water from the treated water tank at pre-determined backwashing intervals. 
         [0022]    By storing the treated water in the treated water tank, rather than delivering the treated water directly to the discharge tank to run off as surface water immediately, the treated water may be advantageously used in this backwashing process which will reduce the cost of operating the effluent treatment process. 
         [0023]    In a further embodiment, the process further comprises the steps of testing the effluent and determining one or more effluent properties; analysing the determined effluent properties to detect if the effluent is suitable to be further treated by the effluent treatment process; and, returning effluent with unsuitable effluent properties to the wastewater treatment plant for further processing prior to redelivery of this further processed effluent back to the primary filter; or, passing effluent with suitable effluent properties on to be further processed by the effluent treatment process. 
         [0024]    By returning effluent with unsuitable effluent properties to the wastewater treatment plant for further processing prior to redelivery of this further processed effluent back to the primary filter, effluent having unsuitable properties for efficient operation of the phosphate removal filters may be rejected, thus increasing the working life of the filtering medium, a plurality of polymer-based beads having nano-particles of iron oxide coated thereon, in the phosphate removal filters. 
         [0025]    In a further embodiment, the one or more effluent properties comprises the phosphate level of the effluent. 
         [0026]    In a further embodiment, the one or more effluent properties comprises the volume of effluent. 
         [0027]    In a further embodiment, the one or more effluent properties comprises the amount of bacteria in the effluent. 
         [0028]    In a further embodiment, the one or more effluent properties comprises the level of turbidity of the effluent. 
         [0029]    In a further embodiment, the one or more effluent properties comprises the amount of silica in the effluent. 
         [0030]    In a further embodiment, the process further comprises the steps of testing the phosphate level of the treated water in the discharge tank and delivering a predetermined amount of effluent from an output of the primary filter directly to the discharge tank, by-passing the series of two or more phosphate removal filters, until the phosphate level of the treated water has increased to a desired level; and, discharging the treated water having the desired phosphate level from the discharge tank. 
         [0031]    This step will allow unnecessary treatment of the wastewater to be avoided by controlling the system to deliver treated water with a predetermined level of phosphate from the discharge tank, regardless of the varying phosphate levels in the effluent. 
         [0032]    In a further embodiment, the process further comprises the steps of regenerating the plurality of polymer-based beads in at least one of the two or more phosphate removal filters by flushing the phosphate removal filter with a dilute alkaline solution, and subsequently flushing the phosphate removal filter with a brine and carbon dioxide (CO 2 ) solution in order to reduce the pH levels of the plurality of polymer-based beads in the phosphate removal filter back down to an acceptable level; collecting the flushed dilute alkaline solution that is output from the phosphate removal filter in a sedimentation tank, and, allowing the collected solution to settle over a predetermined settlement period; and, extracting the dilute alkaline solution from the sedimentation tank to re-circulate through the phosphate removal filters. 
         [0033]    In a further embodiment, the process further comprises the steps of making up the dilute alkaline solution with at least part treated water from the treated water tank and part re-circulated dilute alkaline solution from the sedimentation tank. 
         [0034]    By storing the treated water in the treated water tank, rather than allowing the treated water to be delivered to the discharge tank and run off as surface water immediately, the treated water may be advantageously used to make up the dilute alkaline solution which is used in the regeneration process of the filter medium in the phosphate removal filters. This will greatly reduce the cost of operating the effluent treatment process. 
         [0035]    In a further embodiment, the process further comprises the step of adding chlorine to the filtered effluent prior to delivering the filtered effluent to the series of two or more phosphate removal filters. 
         [0036]    In a further embodiment, each of the plurality of polymer-based beads comprises a plurality of cavities and channels so as to form a sponge-like constitution, whereby substantially all of the surfaces in the cavities, in the channels and on the exterior of the bead are coated with nano-particles of iron oxide. 
         [0037]    The advantage of using the polymer-based beads having a sponge-like constitution is that a large amount of nano-particles of iron oxide may be coated on the large surface area available as a result of the sponge-like constitution. The nano-particles of iron oxide offer high capacity, high surface area and rapid kinetics properties. Thus, the polymer based beads impregnated with iron oxide nano-particles are seen as a particularly effective substance for removing the phosphate from the effluent, and furthermore, they allow for relatively simple backwashing and achieve good longevity in service. 
         [0038]    The invention is further directed towards a tertiary effluent treatment assembly comprising an inlet to receive effluent from a wastewater treatment plant, a primary sand filter to remove suspended solids and particles having a diameter greater than 5 microns from the effluent received from the wastewater treatment plant; a series of two or more phosphate removal filters to receive the filtered effluent, each phosphate removal filter comprising a plurality of polymer-based beads having nano-particles of iron oxide coated thereon; a treated water tank to receive the filtered phosphate-depleted effluent as treated water; a discharge tank to receive the treated water from the treated water tank; and, an outlet to discharge the treated water from the discharge tank. 
         [0039]    The invention is further directed to a tertiary effluent treatment process comprising the steps of delivering effluent from a wastewater treatment plant to a primary filter to remove suspended solids and particles having a diameter greater than 5 microns from the effluent thereby providing a filtered effluent; delivering, at a predetermined rate, the filtered effluent to a series of two or more phosphate removal filters, each phosphate removal filter comprising a plurality of polymer-based beads having nano-particles of iron oxide coated thereon thereby providing a filtered phosphate-depleted effluent; delivering the filtered phosphate-depleted effluent to a discharge tank as treated water, and discharging the filtered phosphate-depleted effluent from the discharge tank as required. 
         [0040]    In a further embodiment, the process further comprises the step of backwashing at least one of the two or more phosphate removal filters with filtered phosphate-depleted effluent from the discharge tank at pre-determined backwashing intervals. 
         [0041]    In a further embodiment, the process further comprises the step of backwashing at least one of the two or more phosphate removal filters only with filtered phosphate-depleted effluent from the discharge tank at pre-determined backwashing intervals. 
         [0042]    In a further embodiment, the process further comprises the intermediate steps of testing the filtered effluent and determining one or more filtered effluent properties; analysing the determined filtered effluent properties to detect if the filtered effluent is suitable to be further treated by the tertiary effluent treatment process; and, returning the filtered effluent with unsuitable effluent properties to the wastewater treatment plant for further processing; or, passing the filtered effluent with suitable effluent properties on to be further processed by the tertiary effluent treatment process. 
         [0043]    In a further embodiment, the process further comprises the intermediate steps of testing the filtered effluent and determining one or more filtered effluent properties; analysing the determined filtered effluent properties to detect if the filtered effluent is suitable to be further treated by the tertiary effluent treatment process; and, returning the filtered effluent with unsuitable effluent properties to the wastewater treatment plant for further processing; or, passing the filtered effluent with suitable effluent properties on to be further processed by the tertiary effluent treatment process. 
         [0044]    In a further embodiment, the one or more filtered effluent properties comprises the phosphate level of the effluent. 
         [0045]    In a further embodiment, the one or more filtered effluent properties comprises the volume of effluent. 
         [0046]    In a further embodiment, the one or more filtered effluent properties comprises the amount of bacteria in the effluent. 
         [0047]    In a further embodiment, the one or more filtered effluent properties comprises the level of turbidity of the effluent. 
         [0048]    In a further embodiment, the one or more filtered effluent properties comprises the amount of silica in the effluent. 
         [0049]    In a further embodiment, the process further comprises the steps of testing the phosphate level of the filtered phosphate-depleted effluent in the discharge tank and delivering a predetermined amount of filtered effluent from an output of the primary filter directly to the discharge tank by-passing the series of two or more phosphate removal filters, until the phosphate level of the filtered phosphate-depleted effluent has increased to a desired level; and, discharging the filtered phosphate-depleted effluent having the desired phosphate level from the discharge tank. 
         [0050]    In a further embodiment, the process further comprises the steps of testing the phosphate level of the filtered phosphate-depleted effluent in the discharge tank and delivering a predetermined amount of filtered effluent from an output of the primary filter directly to the discharge tank by-passing the series of two or more phosphate removal filters, until the phosphate level of the filtered phosphate-depleted effluent has increased to a desired level; and, discharging the filtered phosphate-depleted effluent having the desired phosphate level from the discharge tank. 
         [0051]    In a further embodiment, the process further comprises the steps of testing the phosphate level of the filtered phosphate-depleted effluent in the discharge tank and delivering a predetermined amount of filtered effluent from an output of the primary filter directly to the discharge tank by-passing the series of two or more phosphate removal filters, until the phosphate level of the filtered phosphate-depleted effluent has increased to a desired level; and, discharging the filtered phosphate-depleted effluent having the desired phosphate level from the discharge tank. 
         [0052]    In a further embodiment, the process further comprises the steps of regenerating the plurality of polymer-based beads in at least one of the two or more phosphate removal filters by flushing the phosphate removal filter with a dilute alkaline solution, and subsequently flushing the phosphate removal filter with a brine and carbon dioxide (CO 2 ) solution in order to reduce the pH levels of the plurality of polymer-based beads in the phosphate removal filter back down to an acceptable level; collecting the flushed dilute alkaline solution that is output from the phosphate removal filter in a sedimentation tank, and, allowing the collected solution to settle during a predetermined settlement period; and, extracting the dilute alkaline solution from the sedimentation tank to re-circulate through the phosphate removal filters. 
         [0053]    In a further embodiment, the process further comprises the steps of making up the dilute alkaline solution with at least part filtered phosphate-depleted effluent from the discharge tank and part re-circulated dilute alkaline solution from the sedimentation tank. 
         [0054]    In a further embodiment, the process further comprises the steps of regenerating the plurality of polymer-based beads in at least one of the two or more phosphate removal filters by flushing the phosphate removal filter with a dilute alkaline solution, and subsequently flushing the phosphate removal filter with a brine and carbon dioxide (CO 2 ) solution in order to reduce the pH levels of the plurality of polymer-based beads in the phosphate removal filter back down to an acceptable level; collecting the flushed dilute alkaline solution that is output from the phosphate removal filter in a sedimentation tank, and, allowing the collected solution to settle during a predetermined settlement period; and, extracting the dilute alkaline solution from the sedimentation tank to re-circulate through the phosphate removal filters; and, making up the dilute alkaline solution with at least part filtered phosphate-depleted effluent from the discharge tank and part re-circulated dilute alkaline solution from the sedimentation tank. 
         [0055]    In a further embodiment, the process further comprises the steps of regenerating the plurality of polymer-based beads in at least one of the two or more phosphate removal filters by flushing the phosphate removal filter with a dilute alkaline solution, and subsequently flushing the phosphate removal filter with a brine and carbon dioxide (CO 2 ) solution in order to reduce the pH levels of the plurality of polymer-based beads in the phosphate removal filter back down to an acceptable level; collecting the flushed dilute alkaline solution that is output from the phosphate removal filter in a sedimentation tank, and, allowing the collected solution to settle during a predetermined settlement period; and, extracting the dilute alkaline solution from the sedimentation tank to re-circulate through the phosphate removal filters; and, making up the dilute alkaline solution with at least part filtered phosphate-depleted effluent from the discharge tank and part re-circulated dilute alkaline solution from the sedimentation tank. 
         [0056]    In a further embodiment, the process further comprises the steps of regenerating the plurality of polymer-based beads in at least one of the two or more phosphate removal filters by flushing the phosphate removal filter with a dilute alkaline solution, and subsequently flushing the phosphate removal filter with a brine and carbon dioxide (CO 2 ) solution in order to reduce the pH levels of the plurality of polymer-based beads in the phosphate removal filter back down to an acceptable level; collecting the flushed dilute alkaline solution that is output from the phosphate removal filter in a sedimentation tank, and, allowing the collected solution to settle during a predetermined settlement period; and, extracting the dilute alkaline solution from the sedimentation tank to re-circulate through the phosphate removal filters; and, making up the dilute alkaline solution with at least part filtered phosphate-depleted effluent from the discharge tank and part re-circulated dilute alkaline solution from the sedimentation tank. 
         [0057]    In a further embodiment, the process further comprises the step of adding chlorine to the filtered effluent prior to delivering the filtered effluent to the series of two or more phosphate removal filters. 
         [0058]    In a further embodiment, each of the plurality of polymer-based beads comprises a plurality of cavities and channels so as to form a sponge-like constitution, whereby substantially all of the surfaces in the cavities, in the channels and on the exterior of the bead are coated with nano-particles of iron oxide. 
         [0059]    The invention is further directed towards a tertiary effluent treatment process comprising the steps of delivering effluent from a wastewater treatment plant to a primary filter to remove suspended solids and particles having a diameter greater than 5 microns from the effluent thereby providing a filtered effluent; delivering, at a predetermined rate, the filtered effluent to a series of two or more phosphate removal filters, each phosphate removal filter comprising a plurality of polymer-based beads, each bead comprising a plurality of cavities and channels so as to form a sponge-like constitution, whereby substantially all of the surfaces in the cavities, in the channels and on the exterior of the bead are coated with nano-particles of iron oxide, thereby providing a filtered phosphate-depleted effluent; delivering the filtered phosphate-depleted effluent to a discharge tank as treated water, and discharging the filtered phosphate-depleted effluent from the discharge tank as required. 
         [0060]    A tertiary effluent treatment assembly comprising an inlet to receive effluent from a wastewater treatment plant, a primary sand filter to remove suspended solids and particles having a diameter greater than 5 microns from the effluent received from the wastewater treatment plant; a series of two or more phosphate removal filters to receive the filtered effluent, each phosphate removal filter comprising a plurality of polymer-based beads having nano-particles of iron oxide coated thereon; a treated water tank to receive the filtered phosphate-depleted effluent as treated water; a discharge tank to receive the treated water from the treated water tank; and, an outlet to discharge the treated water from the discharge tank. 
     
    
     
       DETAILED DESCRIPTION OF THE INVENTION 
         [0061]    The invention will now be more clearly understood from the following description of some embodiments thereof given by way of example only, in which: 
           [0062]      FIG. 1  is a diagrammatic representation of a first effluent treatment process assembly according to the present invention; and, 
           [0063]      FIG. 2  is a diagrammatic representation of a second effluent treatment process according to the present invention. 
       
    
    
       [0064]    Referring to  FIG. 1 , there is shown an effluent treatment assembly, indicated generally by the reference numeral  100 , comprising a waste water treatment plant  101  from which partially treated sewage coming is collected in a sump  102 . The partially treated sewage is delivered by a pump  103 , at a pre-determined rate, through a conduit  104  to a primary filter  105 . The effluent may be analysed, to determine flow rate, pH level, turbidity and phosphate content en route to the primary filter  105  or directly subsequent to the primary filter  105 . If the effluent does not meet the required criteria, control valves (not shown) will divert the effluent back to the primary wastewater treatment plant  101 . The user may select the levels of the above mentioned criteria, and based on these selected levels of the criteria, the effluent may be diverted back to the primary wastewater treatment plant  101 . 
         [0065]    The effluent will be passed through the primary filter  105 , which in the present embodiment is a sand filter, although it is envisaged that other types of filters may be used instead of the sand filter, to a series of phosphate removal filters  106 ,  107 ,  108  which reduce the level of phosphate in the water. The effluent is passed through a conduit  109  to the plurality of phosphate removal filters  106 ,  107 ,  108 . The phosphate removal filters  106 ,  107 ,  108  each comprise a phosphate removal medium of polymer based beads impregnated with iron oxide nano-particles. 
         [0066]    Three phosphate removal filters  106 ,  107 ,  108  are shown in  FIG. 1 , however, any number of filters greater than one may be used dependent on factors including but not limited to the flow rate of the effluent to be treated; the volume of phosphate removal media within each filter  106 ,  107 ,  108 ; the level of phosphate in the effluent; the required contact time of the effluent with the phosphate removal media within each filter  106 ,  107 ,  108 ; the required interval between back washing procedures for each filter  106 ,  107 ,  108 ; the required interval between regeneration procedures for each filter  106 ,  107 ,  108 ; and, the level of redundancy which may be required in the effluent treatment assembly  100  to allow continuous operation whilst some of the filters  106 ,  107 ,  108  are either being backwashed or regenerated. The use of the three filters  106 ,  107 ,  108  allows one or more of the filters to be backwashed or regenerated whilst the remaining filter or filters continue to operate as normal. This allows the effluent treatment assembly  100  to operate continuously without having to stop for maintenance to be carried out. 
         [0067]    Once treated, the effluent is passed through an outlet conduit  110  to a treated water tank  111  where it is held for possible future as a backwashing agent, or, as part of regeneration solutions. The treated water that is not used in the backwashing or regeneration processes, both of which are described below, is delivered to the discharge tank  129  to be discharged as surface water. 
         [0068]    The phosphate removal medium has a certain capacity to absorb phosphate after which it must be regenerated. That is to say, the phosphate removal medium has to be flushed out with a dilute alkaline solution, acting as a regeneration solution, to remove the accumulated phosphate from the phosphate removal filters  106 ,  107 ,  108 . The effluent treatment assembly  100  incorporates a mixing tank  112 , in which the dilute alkaline solution is prepared by mixing the chemicals with treated water from the treated water tank  111 . The chemical solution is delivered to each of the filters  106 ,  107 ,  108  as required under pressure produced by a pump  113 , along a conduit  114 , controlled by a system of associated valves (not shown). The selection of which of the filters  106 ,  107 ,  108  is to be regenerated may be achieved manually or automatically by a controller  128 . The dilute alkaline solution along with the phosphate removed from the filters  106 ,  107 ,  108  passes along a conduit  115 , to a sedimentation tank  116 , where the phosphate settles, after further treatment, in the form of sludge at the bottom of the sedimentation tank  116  and may be subsequently pumped to the wastewater treatment plant  101  via a conduit  117 . Alternatively, the phosphate may be recovered from the sludge in the sedimentation tank  116  for use as a fertiliser for example, and, the dilute alkaline solution may be recovered from the sedimentation tank  116  to be re-circulated through the filters  106 ,  107 ,  108  again. 
         [0069]    After rinsing the phosphate removal medium in the filters  106 ,  107 ,  108  with the dilute alkaline solution, the phosphate removal medium in the filters  106 ,  107 ,  108  must be rinsed with a brine and CO 2  solution in order to bring the pH level in the filters  106 , 107 , 108  back to within an ideal operating range. The brine and CO 2  flushing system comprises a mixing tank  118 , delivery pump  119 , a delivery conduit  120 , and return conduit  121  to the wastewater treatment tank  101 , complete with associated valves and controls (not shown). The brine and CO 2  solution may be prepared by mixing the constituent components with treated water from the treated water tank  111 . 
         [0070]    The phosphate removal filters  106 ,  107 ,  108  accumulate particles which have passed through the primary filter  105 . Thus, the phosphate removal filters  106 ,  107 ,  108  are backwashed from time to time. Treated water from the treated water tank  111  is used to backwash the phosphate removal filters  106 ,  107 ,  108  and unclog the phosphate removal filters  106 ,  107 ,  108  by removing these particles at pre-determined intervals. The treated effluent is pressurised by a pump  122 , and delivered through a conduit  123 , with associated control valves (not shown) to each phosphate removal filter  106 ,  107 ,  108  as required. The backwashed treated effluent is returned by the conduit  121  to the waste water treatment plant  101 . 
         [0071]    The treated effluent in the discharge tank  129  may be mixed with effluent which has passed through the primary filter  105  and has by-passed the phosphate removal filters  106 ,  107 ,  108  along a conduit  124 , in order to produce a final discharge effluent containing a specific pre-determined phosphate content. 
         [0072]    In a further embodiment, the primary filter  105  may contain an anti bacteriological medium (not shown) to kill off any bacteria which might grow within the primary filter  105  or the phosphate absorption filter, causing malfunction or blockage. 
         [0073]    Furthermore, the primary filter  105  will need to be backwashed at pre-determined intervals, in order to remove any accumulated particles and thus maintain ideal operating conditions for the primary filter  105 . The backwash solution is delivered by a pump  125 , through a conduit  126 , from the treated water tank  111 . Having passed through the primary filter  105 , the backwash solution will be returned via a conduit  127  to the waste water treatment plant  101 . 
         [0074]    The effluent treatment assembly  100  may incorporate other means of controlling the growth of bacteria such as by the injection of chlorine or by exposure to ozone prior to the primary filter  105 . Ozone will cause flocculation of the remaining harmful particles in the effluent thereby facilitating their subsequent removal in the primary filter  105 . 
         [0075]    When the effluent treatment assembly  100  is operating at a plant where the final effluent is to include a specific content of phosphate which is higher than that pertaining after passage of the effluent through the phosphate filtration system, control valves may be installed which will allow an amount of the effluent to bypass the phosphate removal filters  106 ,  107 ,  108  along a conduit  124 , in order to add back a calculated amount of phosphate in line with the required limit. In this manner the removal of unnecessary amounts of phosphate will be avoided. 
         [0076]    Referring to  FIG. 2 , there is illustrated an effluent treatment assembly, indicated generally by the reference numeral  201 , comprising a pair of inlet pumps  203  and an inlet conduit  205  located intermediate a balance tank (not shown) and a primary filter  207 . The primary filter feeds a contact vessel  209 ,  211 , each of which has an ozone generator  213  and ozone injection apparatus  215  associated therewith. The effluent treatment assembly  201  further comprises a secondary filter  219 , a phosphate removal filter  221 , a storage tank  223  and a backwash pump  225  is associated with the storage tank  223 . A further phosphate removal filter backwashing assembly, indicated generally by the reference numeral  227 , is provided and comprises a caustic dosing system  229 , a brine and CO 2  dosing system  231 , a backwash clarifier  233  and a pH correction unit  235 . 
         [0077]    The caustic dosing system  229  comprises a caustic solution make-up vessel  237 , a caustic dosing unit  239 , a backwash pump  241  and a plurality of valves  243 . The brine and CO 2  dosing system  231  further comprises a CO 2  tank  245 , a brine solution make-up vessel  247 , a brine dosing unit  249 , a backwash pump  251  and a plurality of valves  253 . The backwash clarifier  233  further comprises a sludge pump unit  255  associated therewith. The assembly further comprises a divert valve  217  intermediate the contact vessels  209 ,  211  and the secondary filter  219  and the balance tank (not shown). The effluent treatment assembly further comprises a network of conduits connecting the various pieces of the assembly and valves that are operable to control the flow of effluent in the assembly. 
         [0078]    In use, effluent is delivered from a balance tank (not shown) to the primary filter  207  by the inlet pumps  203  and inlet conduit  205 . The effluent is filtered in the primary filter to remove suspended solids from the effluent. In the primary filtrations steps, the concentration of harmful substances is typically reduced from of the order of thirty parts per million (ppm) down to of the order of 10 ppm. After filtration, the filtered effluent is delivered through conduits to the contact vessel  209 ,  211  and ozone is added to the filtered effluent en route to the contact vessels. The ozone and filtered effluent are left in the contact vessel for a predetermined period of time, preferably between four and twenty minutes. Ideally, the ozone and filtered effluent are left in the contact vessel for a minimum of five minutes. Once the ozone and filtered effluent have been left in the contact vessel for a sufficient period of time, the ozone and filtered effluent mixture is monitored by an effluent quality unit (not shown) which monitors the quality of the effluent. If the effluent is not suitable for onward progression to the secondary filter, the effluent quality unit operates the divert valve  217  so that the filtered effluent and ozone mixture is returned to the balance tank (not shown). If the effluent quality unit detects that the ozone and filtered effluent is suitable for onward progression, the effluent quality unit operates the divert valve  217  so that the ozone treated effluent is delivered to the secondary filter  219 . The ozone acts as a flocculating agent for the filtered effluent causing many of the remaining harmful components to bind with each other to form larger components that may be filtered out of the effluent. Further suspended solids are removed from the ozone treated effluent in the secondary filter  219 . 
         [0079]    Having passed through the secondary filter  219 , the twice filtered effluent is passed to the phosphate removal filter  221 . The phosphate removal filter preferably comprises a filter medium of polymer based beads impregnated with iron oxide nano-particles. After the secondary filtration and the phosphate removal filtration, the harmful component concentration is reduced further from above the order of 10 ppm down to of the order of better than 10 ppm, where the harmful components combine BOD, Suspended Solids and Phosphate, and, the amount of BOD is between 0 ppm and 5 ppm, the amount of Suspended Solids is between 0 ppm and 5 ppm and the level of phosphate is approximately 0.1 ppm, with a reduction in biological oxygen demand (BOD) and chemical oxygen demand (COD). The resulting phosphate and other contaminant-depleted treated effluent is then transferred from the phosphate removal filter  221  to the storage tank  223  from where the treated effluent may be sampled if desired before being discharged as surface water. 
         [0080]    The storage tank  223  is sufficiently large that it will keep a supply of treated phosphate and other contaminant-depleted effluent to backwash the primary and secondary filters. A backwash pump  225  and conduits  257  are connected intermediate the storage tank  223  and both the primary filter  207  and the secondary filter  219  to backwash the primary and the secondary filter with treated phosphate and other contaminant-depleted effluent. Further conduits  259  are provided from the primary filter  207  and the secondary filter  219  and lead to an effluent biological treatment plant (not shown). These conduits  259  carry the backwash from the primary and secondary filters to the effluent biological treatment plant (not shown). The effluent biological treatment plant is used to treat the backwash prior to delivering the treated backwash to the balance tank (not shown) for application of the currently described process to the backwash. Essentially therefore, the backwash will be treated in the same way as effluent passing through the system. 
         [0081]    The phosphate removal filter backwashing assembly  227  is used to backwash the phosphate removal filter  221 . A supply of treated phosphate and other contaminant-depleted effluent is supplied to the caustic solution make-up vessel  237  and the brine solution make-up vessel  247  by the backwash pump  225  and the conduit  257 . The caustic dosing system  229  and the brine and CO 2  dosing system  231  combine to provide a backwash to the phosphate removal filters. This backwash is then transferred to the backwash clarifier where the backwash from the phosphate removal filters has lime added to it and mixed with it. This mixture is allowed to settle in the backwash clarifier until a lime sludge and a clarified liquid are formed. The lime sludge is transferred to a lime sludge storage unit (not shown) and the clarified liquid is pumped to the effluent biological treatment plant. If necessary, the pH correction unit  35  may be used to alter the pH level of the clarified liquid if desired. 
         [0082]    Typically, in a well-run effluent treatment plant, effluent having a quality of 20 ppm BOD, 30 ppm Suspended Solids and 10 ppm Phosphate will be provided. Under those circumstances, the present invention would expect to produce a treated effluent quality better than 5 ppm BOD, 5 ppm Suspended Solids and 0.1 ppm Phosphate. Using the hereinbefore described effluent treatment process, the following results were found: 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 BOD 
                 SS 
                 P 
                 % P 
               
               
                   
                 mg/L 
                 mg/L 
                 mg/L 
                 removed 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Effluent to test rig 
                 9.20 
                 18.0 
                 2.44 
                   
               
               
                 Post sand filter 
                 2.00 
                 2.00 
                 2.00 
               
               
                 Post Phosphate removal 
                 0.10 
                 &lt;1.0 
                 &lt;0.02 
                 &gt;99.2 
               
               
                 filters 
               
               
                   
               
             
          
         
       
     
         [0083]    However, it will be understood that in certain circumstances, the quality of effluent that must be treated by the process according to the present invention may exceed the above amounts and accordingly the performance of the process and the quality of treated effluent will be affected. Similarly, the times required for treating the effluent with ozone may also have to be lengthened in order to ensure effluent of a sufficient standard is treated by the process according to the present invention. 
         [0084]    In this specification, the terms “comprise, comprises, comprised and comprising” and the terms “include, includes, included and including” are all deemed totally interchangeable and should be afforded the widest possible interpretation. 
         [0085]    The invention is in no way limited to the embodiments hereinbefore described but should be afforded the widest possible interpretation.