- 1 METHOD FOR TREATING WASTEWATER Technical Field 5 The present invention generally relates to the treatment of wastewater to remove physical, chemical and biological contaminants. Background Art 10 Wastewater may be a waste or by-product of e.g. domestic or industrial water usage or mining operations. Wastewater also includes sewage. Wastewater is usually characterised by the different sorts of compounds that it contains. These can be broken into particulate (solid) and soluble (dissolved) groups. Within these groups are organic and inorganic compounds of different sorts. The performance of different wastewater 15 treatment processes is measured and compared through the percentage reduction of a number of these compounds through the treatment process train. Wetlands have been shown to provide a low energy, low cost solution for wastewater treatment. The stems, roots and detritus, form a physical framework for 20 bacteria to flourish, in a similar way to what occurs in fixed substrate Sewage Treatment Plants, but with a much larger surface area than what those alternative processes can provide. The treatment of wastewater by a process including a wetland is described in the applicant's own patent document AU2012234912, the entire contents of which are hereby incorporated by reference. 25 It is desirable to provide methods for treating wastewater that have good effluent quality outcomes and which provide this using less power, with less process complexity, and which are significantly easier and cheaper to operate. 30 Summary of the Disclosure Disclosed herein is a wastewater treatment process, the process comprising the steps of: (i) passing wastewater through a polymeric biological trickling filter to 35 produce pre-treated wastewater, wherein the polymeric biological trickling filter comprises surfaces defining voids, and wherein the voids comprise greater than 50 % of the total volume of the biological trickling filter; and 5457196_1 (GHMatters) P94994.AU - 2 (ii) passing the pre-treated wastewater to a wetland system planted with plants. The biological trickling filter can reduce e.g. the organic loading and/or the 5 ammonia content in the water passed into the wetland system. The pre-treatment of the wastewater in step (i) can allow for a reduction in the overall area of the wetland system and minimises the risk of ecological stress in the front end of the wetland. Without a biological trickling filter, the wetland may need more frequent "resting" times. Therefore, the pre-treatment step (i) can improve the overall efficiency of the wetland. 10 A biological trickling filter (sometimes referred to herein as just "filter") is a fixed-film biological treatment process. Wastewater flows over the filter surfaces upon which an active bacterial mass grows, using the wastewater as food for growth and respiration. The bacteria utilise the biodegradable organic material (both in soluble form 15 and as suspended solids,) in the wastewater and other contaminants in the wastewater, such as ammonia, as they grow and reproduce. The filter can be a large matrix structure comprising a number of channels and pathways through which the wastewater can flow. The trickle is effected by the surfaces 20 of the filter allowing the passage of wastewater under gravity i.e. from the top of the filter to the bottom. The channels or passageways within the filter can be tortuous in order to allow the wastewater to contact as many of the surfaces of the filter as possible. The more contact the wastewater has with the bacterial mass on the filter surfaces, the better. The filter may be an open structure with channels extending vertically and 25 horizontally and in any other direction. In one embodiment, the filter has cross-fluted channels. The filter used in the method provides significantly higher surface areas and void spaces than traditional stone filters. One advantage of increased reaction surface 30 area is increased oxygen transfer with the wastewater. The filter comprises surfaces (or walls) which define the voids (or passages or channels) in the filter. In one embodiment, the filter has active treatment surface areas of up to about 100, 150, 200 or 250 m 2 / m 3 of filter. In one embodiment, greater than about 50, 60, 70, 80, 90, 95 or 97 % of the filter comprises void spaces (as a % of the total volume of the filter). 35 Traditional trickling filters use large stone pieces as the media framework. Due to the physical shape of large stone pieces, stone media can only deliver voids in trickling filters of <50% and can easily block either at the surface or deeper into the 5457196_1 (GHMatters) P94994.AU - 3 media column. This limits oxygen transfer and hence reduces performance. Additional issues can also result such as hydraulic limitations (e.g. water doesn't drain through column), odours (due to poor oxygenation) and prevalence of filter flys and vermin. Polymeric (plastic) media has a much more open structure, overcoming these issues and 5 delivering better treatment outcomes with less maintenance problems. The filter can be made up of a number of individual or modular filter units packed or stacked together to provide the overall filter structure. Alternatively, the filter is one large unit pre-formed prior to use. 10 The filter can be made of any plastic material on which the bacterial mass will grow. The plastic material can be selected from polyethylene terephthalate (PET), polyethylene (low or high density), polyvinyl chloride and/or polypropylene. 15 The wastewater can be passed to the filter by any means including pumping or pouring. The wastewater is preferably evenly distributed over the top of the filter. The wastewater can be delivered by large rotating arms that extend across the entire diameter of a substantially cylindrical shaped filter. It should be understood, however, that the filter can be of any shape and flows could be distributed with fixed downward 20 sprays. The rate at which wastewater is passed to the filter (dosing rate) can be controlled so as to ensure that substantially all of the filter surfaces remain substantially wet. If the surfaces dry out, the bacterial population thereon can diminish. The dosing 25 rate can be varied by any means. The dosing rate can be varied by changing the speed of rotation of the rotating arms which can deliver the wastewater or by controlling the delivery pump. To keep the filter wet, a minimum flow rate through the filter structure could be 30 in the range of from about 5 to about 600 L/s, but lower flow systems can be achieved. The dosing rate will change depending upon the type of effluent and size of the filter. The dosing rate can be up to about 5, 10, 20, 50, 100, 200, 500, 700 L/s with flow rates of 5L/s to 700L/s. Effluent flow can be recirculated back over the filter to maintain the desired wetting rate, to balance hydraulic flows, or to dilute influent concentrations of 35 contaminants. The bacteria of the filter surfaces can be allowed to develop naturally over time. However, it can be advantageous to inoculate the filter surfaces with the desired 5457196_1 (GHMatters) P94994.AU - 4 bacteria prior to use in the wastewater treatment process. The filter can be inoculated with the bacterial mass by contacting the surfaces with bacterial cultures. The surfaces of the filter can be contacted directly with colonising cultures for example by introducing bacterial liquor into the influent. The bacteria can be provided in an 5 inoculation liquid that is trickled over the filter surfaces. There can be many different types of bacteria on the filter surfaces. In some embodiments, one or more bacteria are selected according to the characteristics of the wastewater to be treated. If the wastewater contains ammonia, one or more strains of bacteria that can metabolise ammonia can be selected. During use of the filter, more or other bacterial masses can 10 develop. The bacterial mass can comprise chemoautotrophic and/or heterotrophic bacteria. Heterotrophic bacteria need organic carbon as their main source of food. Bacterial food in a wastewater is often characterised as 5 day Carbonaceous 15 Biochemical Oxygen Demand (cBOD). Bacteria are able to quickly and easily use the soluble cBOD, and removal of this wastewater fraction in a filter is expected to be very high - of the order of greater than about 60, 70, 80 or 90 %. As noted above, the bacterial mass can also comprise bacteria that can use small 20 amounts of other nutrients such as ammonia and phosphorus for growth and respiration. Specialised groups of bacteria that use inorganic carbon and ammonia as their main food source can also grow in the filter. The removal of ammonia will occur through the process of nitrification. 25 The type of bacteria that colonise the filter can change in the direction of wastewater flow. At the top or uppermost portion of the filter, the bacteria can comprise heterotrophic bacteria which use the soluble cBOD. As the cBOD content of the wastewater is reduced, bacteria towards the bottom or lowermost portion of the filter can change in type to become those which metabolise nutrients (e.g. chemoautotrophic). 30 The metabolism of nutrients can include the metabolism of ammonia to nitrates. As a result, the ammonia content of the wastewater can be reduced by the filter. Nitification bacteria are typically slower growing and more environmentally sensitive than hetrotrophic bacteria which consume carbon. Consequently, nitrifiers tend to only flourish when there is limited carbon available for the heterophic bacteria 35 to consume (e.g. BOD<20mg/L). Stone media trickling filters are not usually efficient at nitfiying for several reasons: 1) the filters struggle to get organics to <20mg/L; 5457196_1 (GHMatters) P94994.AU - 5 2) nitrifiers require aerobic conditions, which can be restricted deeper into the bed depth of stone media systems; 3) stone media does not deliver high surface areas, which are needed by nitrifiers because of the slower reaction kinetics. 5 Plastic media trickling filters are able to overcome these issues. Wastewater compounds such as inorganic carbon or other inorganics such as metals will not be substantially removed by the filter. 10 Higher organisms can also live in the filter. The higher organisms can include nematodes, rotifers and/or filter flies. The higher organisms can graze on the bacteria and each other, and help to limit the biofilm thickness. This new bacterial mass, along with the higher organisms that make up the ecology of the filter system, can be 15 periodically sloughed off the filter, primarily through a flushing process, and can be discharged. The wastewater that has trickled through the filter is collected as pre-treated wastewater. The pre-treated wastewater can be collected in pipes and/or channels which 20 direct the wastewater to the next stage in the treatment train. The pre-treated wastewater has a reduced organic matter loading. The pre-treated wastewater from the filter can have a Biochemical Oxygen Demand (BOD) of less than about 30, 40 or 50 mg/L BOD The ammonia content of the pre-treated wastewater can be controlled to be less 25 than about 10mg/L, if required. The pre-treated wastewater can be subject to further treatment in a clarifier and wetland system. The wetland system is in fluid communication with the filter. 30 The wetland can convert nitrates in the pre-treated wastewater to nitrogen gas, which is dispelled to atmosphere. An advantage of reducing ammonia content before delivering the pre-treated wastewater to the wetland is that the conversion of nitrates to nitrogen can occur immediately in the wetland. This means the overall size of the wetland system can be reduced because the ammonia to nitrate reaction need not 35 substantially occur in the wetland system. The wetland system can comprise an artificial wetland system. The artificial wetland system may require about 6, 12, 18, 24 or 36 months to establish. 5457196_1 (GHMatters) P94994.AU - 6 To further reduce the organic or inorganic, suspended solid content of the water before passing it to the wetland system further pre-treatment step(s) can be undertaken. The pre-treated wasterwater can be passed through a clarifier. The clarifier can remove 5 suspended solids and phosphates if chemically dosed with alum or other suitable coagulant. The further pre-treatment step may comprise dilution. The pre-treated wastewater may be diluted with other relatively pure water, for example stormwater water. 10 The further pre-treatment step can comprise at least one pond. The pond can be a facultative pond. In one embodiment, the pre-treated wastewater from the filter can be passed to the facultative pond. In an alternative embodiment, the wastewater is treated in a facultative pond prior to being passed to the trickle filter. 15 The facultative pond may have algae that can at least in part normalise the pH of the liquid therein. The pond may have bacteria. The pond can have fixed carbon, for example dead organic matter or other complex molecules having carbon. The algae and/or bacteria may die and form the fixed carbon. The pond can be up to about 0.5m, Im or 2m deep at its deepest point. Greater depths may reduce the oxygen transfer and 20 capital and operational costs. The water can reside in the pond for an average of 3 days to 6 days. This may provide sufficient time for the bacteria and/or algae to grow and/or act. The pond can be open to the environment. This may allow chemicals, for example carbonates, in the water to equilibrate with the atmosphere. 25 The pond can be advantageous in the treatment process because it can moderate the flow of the pre-treated wastewater to the wetland. By moderated flow it is meant that the rate at which the pre-treated wastewater is delivered to the wetland is controlled. Sometimes there may be a sudden surge of water from operations which if not moderated may exceed the capacity of the corresponding system to treat. At other 30 times, the water flow through the system may drop below acceptable limits if not moderated. Insufficient impure water inflows into the system may be compensated by adding other water. The wetland can be a vertical or a horizontal wetland. The wetland can be 35 configured for horizontal flow. The wetland can be sloped at a gradient of about 0.1, 0.2, 0.4 or 0.5 %. 5457196_1 (GHMatters) P94994.AU The water residence time in the wetland can be on average 1 to 2 days. In an embodiment, the wetland is open to the environment. This may allow chemicals, for example carbonates, in the water to equilibrate with the atmosphere. The wetland may be sized for sedimentation. The wetland can have organic matter to which a bio-film 5 can bind. The wetland system may comprise first and second wetland units. The first wetland unit may be in fluid communication with the filter or the facultative pond if present. The second wetland unit may be in fluid communication with the first wetland 10 unit for receiving at least some of the water that has flowed through the first wetland unit. The water may be delivered to a first plurality of spaced apart regions within the first wetland unit. At least some of the water may be delivered to a second plurality of spaced apart regions within the second wetland unit. Each of the first and second wetland units may comprise at least one of a pipe arrangement, conduits, and manifold is that deliver the water at a plurality of spaced apart regions. The first wetland unit may have a smaller area than the second wetland unit. The first wetland unit may have less than half the area of the second wetland unit. The first wetland unit may be sized for at least one of sedimentation and sediment adsorption. The sediment substrate may oxidise a chemical in the water. The sediment substrate may be soil, or dead organic matter, for 20 example. In an embodiment, the first wetland unit may have an operating water depth of 50mm to 300mm. The system can comprise a third wetland unit which may comprise a filter cartridge. The filter cartridge may comprise bags of palletised material, for example 25 gravel. The filter cartridge may absorb heavy metals. The third wetland unit may be disposed between the first and second wetland units. The water passing out of the wetland can be treated. The treatment can include steps to reduce biological pathogens and/or to remove particulates. 30 The treatment includes the step of passing the water from the wetland to a membrane filter or pressure filter unit consisting of glass, sand or other. This unit filters at least some of the water that has flowed through the wetland system. In the context of this document, "membrane filtration" encompasses, but is not limited to, 35 nano-filtration, ultra-filtration, micro-filtration, and reverse osmosis. The membrane filter may comprise a reverse osmosis membrane. 5457196_1 (GHMatters) P94994.AU - 8 Other treatment steps that can be undertaken alternatively, or in addition to membrane filtration include sand filtration, UV light exposure, and contact with a disinfection agent. The disinfection agent can include chlorine, UV, or ozone. 5 The water treated by the processes described herein can be collected and stored for later use. The water treated by the processes can be used immediately if desired. The water treated by the process can be Class A+ or Class A as defined by Australian standards. The size of the wetland system and the residency times and flow rates can be altered so as to achieve Class A+ or Class A quality water with the addition of suitable io disinfection. The water treated by the process can have a total nitrogen content of less than about 5mg/L or l0mg/L. 15 Brief Description of the Drawings Embodiments of the method will now be described, by way of example only, with reference with the accompanying drawings in which: Figure 1 shows a flow diagram of one embodiment of a method for treating 20 wastewater; Figure 2 shows the filter which can be used in the method of the invention. Detailed Description of Specific Embodiments 25 Figure 1 shows a flow diagram of one embodiment of a method for treating wastewater. The wastewater may originate from, for example, a sewage treatment plant although water from mining operation or coal seam gas extraction, domestic or industrial operations and generally any sources can also be treated. 30 The wastewater can first be passed through a screening plant where all gross solids greater than about 6mm, 12mm, or 24mm in dimension can be removed, washed, pressed and taken away for landfill disposal in a covered skip. After screening, the wastewater can flow by gravity through grit removal 35 facilities where small, heavy, solid particles (sand etc) are removed. This "grit" is washed and dewatered in a grit classifier and then taken away for landfill disposal in large bags or a skip. 5457196_1 (GHMatters) P94994.AU - 9 The wastewater is then pumped to the filter station. The filter station can comprise a number of high surface area plastic media trickling filters. These can be referred to as Biological Trickle Filters (BTF) (Sometimes referred to as just "filters") for biological treatment. Figure 2 is a close up view of a filter suitable for use in the 5 method. The channels in the filter are cross-fluted. The filter typically comprises a round tank filed with plastic media cut to shape. The void space within the plastic mediabody is 97%. The contact surface area is 144 m 2 /m 3 . In order to pass through the filters, the wastewater is distributed evenly over the 10 top surface of the plastic media filter by four (or six (or more)) large rotating arms, stretching the full diameter of the tanks, whose speed of rotation can be varied to change the "dosing rate". To keep the filter wet, a minimum flow rate through each filter is 5 L/s. 15 Once a day, the rate at which water is delivered to the filter is slowed down, which means higher intensity flows through the filter, effectively "flushing" old biomass off the filter modules to enable renewal of the biological growth that is transforming the incoming organic material in the raw sewage/wastewater. 20 The "trickled" wastewater (pre-treated wastewater) is collected on the floor of the filter station. The pre-treated wastewater can flow by gravity back to the pump station where, depending on the total inflow rates to the treatment plant, it is mixed with the raw influent from the grit chamber and recirculated to the top of the filter. The net outflow from the pump station is always equal to the main plant inflow, and the rate of 25 recirculation is inversely proportional to the ratio of this inflow to the design wetting rate. The pre-treated wastewater is clarified before passing it to the wetland system. The water is then treated by the wetland system. 30 In an optional step, the water that has passed through the wetland system is then passed through a membrane filter such as a ultrafiltration membrane. The treatment by the wetland system reduces the work that needs to be done by the membrane, increasing energy efficiency, reducing the impurity load on the membrane which further increases 35 the efficiency of the system, and preventing premature clogging of the membrane. The water can then be used for irrigation, industry, domestic applications or released to the environment or any other use as suitable. 5457196_1 (GHMatters) P94994.AU - 10 The effluent from the wetland is delivered to a disinfection plant. Due to the balancing effect of the wetland, the plant can be designed with a capacity of 5 L/s. Flows in excess of this up to 15L/s can be transferred to an Effluent Storage Pond. The disinfection system can be established with flexibility to either utilise different elements 5 of the disinfection independently. For example, should the surrounding area flood and treatment be pared back to base BOD/SS treatment through the trickling filter and clarifier, then effluent could be chlorinated and discharged to the Effluent storage pond without having to go through the membrane/UV. 10 It will be understood to persons skilled in the art that many modifications may be made without departing from the spirit and scope of the disclosure. For example, the pond may be replaced by a tank, dam, vessel or any suitable structure. The flow moderator may be integral with the wetland system. is In the claims which follow and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the system and method. 20 It is to be understood that a reference to background art or problem herein does not constitute an admission that the art or problem forms a part of the common general knowledge of a person of ordinary skill in the art, in Australia or in any other country. Such a reference is not intended in any way to limit the scope of the method as 25 disclosed herein. 5457196_1 (GHMatters) P94994.AU