FIELD

[0001] This disclosure relates to process and apparatus for treating secondary or tertiary effluents from municipal wastewater treatment plants, particularly for potable or non-potable re use.

BACKGROUND

[0002] Clean and safe water is crucial for human civilization. Over the past few decades, the rapid growth of population and urbanization and the impacts of climate change on water accessibility have continuously increased the pressures on existing drinking-water resources and resulted in the necessity to identify new or alternative sources of drinking-water. The world population is projected to pass 9.6 billion by 2050 while urban population is anticipated to grow to 6.3 billion. Concurrently, climate change has brought droughts and flooding which are also increasing pressure on water supplies.

[0003] The idea of Day Zero has been introduced to emphasise the need for managing water consumption as tightly as possible by persuading water consumers into reducing usage. Day Zero, as it’s called, is the start of water limiting and the day private taps will be switched off - literally - with large numbers of households and businesses having to go to local collection sites to draw water. One reaction to avoid this situation is to decrease vulnerability to population growth and climate change impacts by increasing resilience, diversity, adaptability and sustainability of drinking-water supplies. The development of new and preferably more climate independent water resources in close proximity to major population centres should be a priority. Potable reuse and, in coastal areas, seawater desalination meet this definition.

[0004] Seawater desalination is a viable water source alternative for coastal areas of the world. Seawater desalination process is the removal of salt and impurities from seawater to produce fresh water. Seawater is forced under high-pressure through special membranes with ultra-small pores to separate salt, bacteria, viruses and other impurities. Seawater desalination process provides a climate independent source of water for critical human needs and economic development. It is an effective way to secure water supplies against the effects of climate change, a growing population and drought. However, the process requires significantly more energy than existing conventional water treatment processes, making it expensive and additive to greenhouse gas emissions. In addition, it is not suitable for inland communities or areas separated from coastal regions by significant elevation. Furthermore, about half of the water that enters the plant from the sea becomes fresh drinking water and the brine discharge has negative impacts on the environment. [0005] Potable reuse, producing safe drinking-water from municipal wastewater, is a climate independent approach to enhance flexibility, sustainability, resilience, and diversity of drinking- water resources. Potable reuse schemes have been established all over the world and the number of potable reuse schemes is increasing constantly as populations and pressure on water supplies continue to grow. Economically and practically, potable reuse compares favourably with seawater desalination. Potable reuse can produce large volumes of drinking-water from wastewater available from established collection systems in both coastal and inland locations. Additionally, it can decrease negative impacts of microbial hazards and in some cases nutrients from wastewater discharges on marine and freshwater environments. Total dissolved solid (TDS) concentration of municipal wastewater typically ranges between 0.1-1 g L ¹ while seawater TDS is normally above 35 g L ¹ which is 35 to 350 times greater. Thus, the energy consumption to remove TDS and provide clean water is significantly lower for potable reuse (0.4- 1.0 kWh m ³ ) compared to seawater desalination (3.0-3.4 kWh m ³ ).

[0006] Climate change results in more extreme weather events. Long droughts and high temperature make surface water sources such as lakes, rivers and catchments more exposed to algal blooms compromising water quality. Fish kills and other biota kills are becoming more frequent. Subsequently, water to be discharged into the environment and for environmental reuse requires more stringent quality, in particular reduction of organic content and nutrient (phosphorus and nitrogen). Potable reuse could be an effective strategy to reduce the organic content and nutrient released to the environment and subsequently minimise the occurrence of algal blooms.

[0007] Source wastewaters, e.g. secondary and tertiary effluents sourced from municipal waste water treatment plants, are very poor quality with high concentration of pathogenic microorganisms and the occurrence of a broad range of the hazardous chemicals in the water matrix.

[0008] Secondary treatment is biological treatment which includes a clarifier, and water exiting the clarifier is referred to as secondary effluent. Tertiary treatment utilises a sand or mixed media filter, and water exiting is termed tertiary effluent. See, for example, Metcalf & Eddy, AECOM (2014), Wastewater Engineering: Treatment and Resource Recovery, 5 ^th Ed., McGraw Hill Education, New York, NY 10121.

[0009] Thus, treatment of wastewater for reuse is typically a complex action comprising advanced treatment processes such as high pressure membrane-based processes, ozone treatment, advanced oxidation based on UV and hydrogen peroxide and UV disinfection. Advanced treatment processes are generally more expensive than conventional water treatment processes and requires a high level of technical expertise and understanding.

[00010] High-pressure membrane-based processes such as reverse osmosis (RO) and nanofiltration (NF) are highly efficient advanced treatment processes for removal of most pathogens and organic contaminants from the water matrix. Up of 99% of salinity could be removed from water by RO membranes and even greater removal of pathogens are expected. Nano filtration is less effective to eliminate the salinity but will remove considerable quantities of higher valent ions like sulphate. However, RO and NF are quite expensive processes owing to the required high pressures and related energy costs. More importantly, a considerable part of the water is rejected in the form of a concentrated brine stream. For coastal potable treatment plants, the brine stream is often discharged into the aquatic environment but for inland communities brine disposal is a challenging matter. Membrane separation does not take out of the environmental cycle chemicals or contaminants of emerging concern (CEC) such as pharmaceuticals and endocrine disruptors. Large amounts of CEC enter the water cycle through household sewage. Membranes separate most of them into the concentrate but do not degrade these chemicals. Their effective removal remains an issue.

[00011] Water treatment systems for water reuse regularly comprise disinfection processes to deactivate pathogenic microorganisms (bacteria, viruses, protozoa, and helminths). While high- pressure membrane-based processes such as NF and RO provide removal of microorganisms, disinfection mostly refers to processes used to inactivate microbial pathogens such as UV light irradiation which is highly effective against pathogenic microorganisms. However, operational and energy costs are extremely high for UV light irradiation process. Energy consumption for inactivation of bacteria and protozoa is acceptable but becomes less acceptable when it comes to inactivation of viruses.

[00012] When it comes to degradation of dissolved organic matter and CEC through Advanced Oxidation Processes (AOP) the UV/H2O2 process uses less energy than other AOP processes and has met with adoption success. Still, energy consumption remains high and could be well in excess of 10 kWh/m ³ of treated water. Accordingly, there is an ongoing challenge to develop innovative technologies for water reclamation, including potable reuse schemes, which treat and disinfect water in a cost-effective and efficient manner.

[00013] The Applicant’s Australian Patent Application No 2016232986, the contents of which are hereby incorporated herein by reference, relates to a water treatment process for treating raw water sources such as groundwater and surface water. The process includes a pre-oxidation step (a) and advanced catalytic oxidation steps including a coagulation step and separation of flocculated solids. This process was recently evaluated for disinfection performance in agreement with requirements included in World Health Organization Drinking (WHO) Water guidelines and Australian Drinking Water Guidelines (ADWG). The process achieved required disinfection performance without the aid of any specific disinfectants used for water disinfection.

[00014] This process is less effective in treatment of wastewater with more complex and higher level of contamination such as secondary or tertiary effluent of municipal wastewater treatment plants. Municipal wastewater secondary effluent contains heavy metals, higher levels of CEC, higher level of nutrients, larger microbial contamination and typically has an unpleasant smell atypical of surface and groundwater.

[00015] In view of the foregoing, it would be desirable to identify new processes for treating secondary or tertiary effluent of a municipal wastewater treatment plant.

[00016] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgement or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

SUMMARY

[00017] The present disclosure pertains to a more efficient and cost effective water treatment process for treating and disinfecting wastewaters from municipal wastewater treatment plants, i.e. secondary or tertiary effluents, with a preferred objective of producing potable water.

[00018] Accordingly, in one aspect, the present disclosure provides a process for treatment of wastewater of a municipal waste water treatment plant comprising the steps of:

(a) adding to a, typically odoriferous, secondary or tertiary effluent to be treated, an inorganic oxidising metal salt and oxygenating the water for a time effective for oxidising a portion of contaminants;

(b) raising the pH of the water from oxidation step (a) for coagulating suspended and colloidal solids;

(c) flocculating contaminants in the water from step (b) using a cationic flocculant;

(d) clarifying and separating a product sludge from water from step (c); and

(e) subjecting the water from step (d) to catalytic oxidation and catalytic advanced oxidation (CO-CAO) in at least one bed reactor to oxidise residual inorganic contaminants and degrade organic contaminants, degradation of organic contaminants being catalysed by metal ions from the inorganic oxidising salt added in step (a).

[00019] Step (a), a conditioning step, is advantageously conducted under pressure with oxygen or oxygen enriched air being introduced to the water through a suitable injection means or diffuser, such as a bubble diffuser. Desirably, conditioning step (a) is conducted in enclosed reactor(s) including a headspace with oxygen content target controlled substantially above 21 vol. % oxygen. Preferably, oxygen content target is above 50 vol. % oxygen, more preferably above 75 vol. % oxygen and most preferably above 85 vol. % oxygen. The injection means or diffuser is most conveniently communicated with an oxygen generator, conveniently a pressure swing adsorption generator which can produce 90% to 93% oxygen concentration. According to Henry’s law, the oxygen content in the headspace of the tank could, for example and desirably, approach 90 vol. % and consequently the dissolved oxygen in the water could increase, for example approaching 30 mg/L oxygen under favourable conditions. Oxygen flow from the oxygen generator and through the injection means or diffuser is controlled to meet the oxygen content target described above. Under such conditions, volatile organic contaminants are stripped off and in part oxidised.

[00020] In embodiments, the inorganic oxidising metal salt may comprise one or more of iron or aluminium salts. Advantageously, the inorganic oxidising salt is an iron salt such as ferric and/or ferrous chloride. Ferric chloride may be selected to provide optimum results according to the process. The Applicant has not, so far, identified a metal salt with comparable performance to ferric chloride and the selection cannot be considered routine. In particular, manganese salts are not suitable for this purpose. Addition of ferric chloride in step (a) lowers the pH, as ferric chloride solutions, as used herein, are highly acidic. Target pH for optimal coagulation performance is 3.5 to 6, preferably about 4. Oxidation and attachment of organic matter to ferric hydroxide formed during oxidation step (a) is most effective at pH about 4.

[00021] In step (a), organic matter is partly oxidised and removed by adsorption on ferric hydroxide, though adsorption of organic matter takes place mostly in step (b) when pH increase precipitates ferric hydroxide where ferric chloride is the inorganic oxidising metal salt. Precipitation of ferric hydroxide also has the effect of co -precipitation of some of the inorganic contaminants and coagulation of colloidal matter.

[00022] The alkaline compound used for pH increase - desirably to pH range 7.5 to 8.5 - is, advantageously, magnesium hydroxide or hydrated dolomitic lime. Other alkaline compounds, have not been found to have the beneficial effects of magnesium hydroxide as found by the Applicant under the process conditions described herein, namely removal of odour from the effluent and its limited solubility above pH 9 which assists in reducing total dissolved solids. [00023] Coagulation step (b) is conveniently performed in baffled tank(s) with baffles defining compartments each provided with a mixer. Mixer speed may be controlled to optimise mixing or coagulation as required with mixer(s) of different compartments being desirably run at different speeds. Water entering a first compartment may have a mixer run at a higher speed to promote mixing. Second and/or subsequent compartments may have mixer(s) run at a lower speed to promote coagulation.

[00024] In step (c) the flocculation is achieved using a polymeric flocculant. In one embodiment, the flocculation vessel(s) are open to atmosphere to enable settling of floes.

[00025] Advantageously, the flocculant used in step (c) may be a cationic polymeric flocculant such as, for example, a cationic polyacrylamide.

[00026] In embodiments, the cationic polyacrylamide may be in solid form or in the form of an emulsion.

[00027] In embodiments, the cationic polymeric flocculant may have a molecular weight from about lxlO ⁶ Daltons to about 1.5xl0 ⁷ Daltons, or from about 2xl0 ⁶ Daltons to about l.lxlO ⁷ Daltons, or from about 3xl0 ⁶ Daltons to about l.OxlO ⁷ Daltons.

[00028] In embodiments, the cationic polymeric flocculant may have a mole charge from about 20% to about 80%.

[00029] Suitable cationic polymeric flocculants include cationic polyacrylamides such as EM640CT and FO4440SH available from SNF Inc.

[00030] This compares with the primary reliance on an inorganic manganese flocculant (e.g. MnOOH) formed in situ in the process of the Applicant’s Australian Patent Application No. 2016232986.

[00031] Clarification step (d) to produce a clarified water and a sludge may be performed using any type of clarifier, though an inclined plate type is convenient, and sludge is likewise separated by conventional means.

[00032] Clarified water, which still contains a range of undesirable contaminants including pathogens, is then subjected to further oxygenation to increase dissolved oxygen level in preparation for the CO-CAO step (e). Oxygen availability for the CO-CAO step is, highly desirably, further increased through oxygenation using an injection means such as a bubble diffuser, addition of an oxygen donor and, preferably, both. Control over oxygenation may be conducted in the same way as described for step (a), though contact time is typically less than for step (a). Such oxygenation is preferably conducted in a separate vessel to a CO-CAO reactor, the separate vessel also facilitating backwashing as a break tank.

[00033] A preferred oxygen donor is a permanganate, conveniently potassium permanganate, which introduces another metal catalytic to oxidation, manganese. The oxygen donor should not be too strong an oxidant to directly oxidise ammonia. Ammonia oxidation has high oxidant demand and is highly desirably avoided in the water treatment process described herein. Depending on the concentration, ammonia may be removed from the water in an additional treatment stage by break point oxidation and other conventional methods, such as ion exchange. The water before entering the CO-CAO bed reactor(s) should have the pH adjusted within a range of 6 to 9 and oxidation reduction potential (ORP) 400 mV or higher depending on pH. Similar considerations on ORP apply as in the Applicant’s co-pending International Patent Application No. PCT/AU2020/050857, with the contents of that document hereby incorporated herein by reference.

[00034] Following addition of the oxygen donor and oxygenation, where required, the water is then treated in catalytic oxidation and catalytic advanced oxidation reactor(s) containing beds of granular oxidation catalysts, preferably selected metal oxides for oxidation of inorganic contaminants and advanced oxidation of organic matter. Suitable catalysts include oxides of iron, manganese, aluminium, silica and titanium whether alone or in combination. Conveniently, step (e) involves two bed reactors in series. The first reactor preferably accommodates suspended solids at the top of the bed, for example by including a top layer of large size and lower density particles than the metal oxide catalysts. For example, anthracite or particles of inorganic material including inert packings may be used for the top layer.

[00035] Without wishing to be bound by theory, highly reactive species, including hydroxyl radicals, are generated through the catalytic decomposition of the oxygen donor and metal oxidation state transition as in Fenton like reactions. As a consequence of the ability of the catalytic reactor(s) to degrade organic matter, a high level of disinfection is achieved. The disinfection is achieved without addition of any specific disinfectant which is highly desirable or required where water must be discharged into the environment, to avoid serious damage to the biota in the environment.

[00036] Important for environmental discharge of water is colour, which should be as low as possible to allow sunlight to penetrate through the water and support photosynthesis of aquatic vegetation. Colour is substantially removed by the catalytic advanced oxidation step, to level comparable to other AOP. Furthermore, turbidity is decreased to level comparable with membrane filtration and RO separation. A problem contaminant for treatment of secondary effluent wastewater is phosphorus. When water is discharged into water bodies into the environment, the maximum contaminant limit for phosphorus should be 0.02 mg/L or less to avoid loading of the water body with nutrient and potential algal blooms. Phosphorus is known to be the trigger for algal blooms. Biological water treatment processes are unable to consistently comply with maximum contaminant limit for phosphorus. The process of this invention removes phosphorus mostly through direct reaction and catalytic reaction with iron in the CO-CAO reactor(s). Degradation of organic matter containing nitrogen in the CO-CAO reactor(s) results in removal of nitrogen as nitrogen gas. Nitrite is oxidised to nitrate and ammonia will typically pass through the system without change under the preferred oxidising conditions.

[00037] Removal of heavy metals is also critical for most of the use of reclaimed water and for environmental discharge. The CO-CAO step (e) removes heavy metals to very fine degree, in compliance with the required water quality as set, typically, by regulation.

[00038] The process may include a backwashing step for the CO-CAO reactor(s) to maintain efficient water treatment. Clarified water from clarification step (d) is conveniently used for backwashing. A disinfectant, conveniently chlorine or chlorine dioxide, may be introduced to water during the backwashing step.

[00039] In case total dissolved solids (TDS) requires to be decreased, an EDI or other suitable treatment step may be added following the CO-CAO step (e).

[00040] Typically, as a treatment for municipal waste water, the process may include a biological treatment step, such as aerobic or anaerobic digestion, for example in a membrane bioreactor (MBR), prior to step (a).

[00041] Another aspect of the present disclosure provides an apparatus, such as a plant, for treatment of wastewater of a municipal waste water treatment plant comprising:

(a) a conditioning stage for treating a, typically odoriferous, secondary or tertiary effluent with an inorganic oxidising metal salt and oxygenating the water for a time effective for oxidising a portion of contaminants;

(b) a flocculation stage for flocculating contaminants from the water from conditioning step (a) using a cationic flocculant;

(c) a clarification stage for clarifying and separating a product sludge from water from step (b); and

(d) a catalytic oxidation and catalytic advanced oxidation (CO-CAO) stage including at least one bed reactor for oxidising residual inorganic contaminants and degrading organic contaminants, degradation of organic contaminants being catalysed by metal ions from the inorganic oxidising salt added in conditioning stage (a).

[00042] Use of the water treatment process and apparatus of the present disclosure in the treatment of water for environmental discharge and for reuse, depending on required treated water quality and number of barriers needed for disinfection is very advantageous. The high-energy consumption step processes of a conventional treatment process train may be effectively replaced with a CO-CAO stage with the benefit of removing a broader range of contaminants at lower treatment cost. This process can replace UV disinfection, RO (reverse osmosis) membrane separation and UV/H2O2 advanced oxidation and avoid their attendant disadvantages as described above.

[00043] Further features and advantages of the present disclosure will be understood by reference to the following drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[00044] Figure 1 is a process diagram of a conditioning stage for treatment of secondary effluent of municipal wastewater in accordance with one embodiment of the present disclosure. [00045] Figure 2 is a process diagram of CO-CAO stage of treatment of secondary effluent of municipal wastewater following the conditioning stage shown in Figure 1.

[00046] Figure 3 is a block diagram providing examples of process treatment trains for water reclaiming and discharge into the environment incorporating processes in accordance with the present disclosure.

DETAILED DESCRIPTION

[00047] The following is a detailed description of the disclosure provided to aid those skilled in the art in practicing the present disclosure. Those of ordinary skill in the art may make modifications and variations in the embodiments described herein without departing from the spirit or scope of the present disclosure.

[00048] Although any processes and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure, the preferred processes and materials are now described.

[00049] It must also be noted that, as used in the specification and the appended claims, the singular forms ‘a’, ‘an’ and ‘the’ include plural referents unless otherwise specified. Thus, for example, reference to ‘flocculant’ may include more than one flocculants, and the like.

[00050] Throughout this specification, use of the terms ‘comprises’ or ‘comprising’ or grammatical variations thereon shall be taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof not specifically mentioned.

[00051] The following definitions are included to provide a clear and consistent understanding of the specification and claims. As used herein, the recited terms have the following meanings. All other terms and phrases used in this specification have their ordinary meanings as one of skill in the art would understand. Such ordinary meanings may be obtained by reference to technical dictionaries, such as Hawley's Condensed Chemical Dictionary 14th Edition, by R. J. Lewis, John Wiley & Sons, New York, N.Y., 2001.

[00052] Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within two standard deviations of the mean. ‘About’ can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from context, all numerical values provided herein in the specification and the claim can be modified by the term ‘about’.

[00053] Any processes provided herein can be combined with one or more of any of the other processes provided herein.

[00054] Ranges provided herein are understood to be shorthand for all of the values within the range. For example, a range of 1 to 50 is understood to include any number, combination of numbers, or sub-range from the group consisting 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42,

43, 44, 45, 46, 47, 48, 49, or 50.

[00055] Reference will now be made in detail to exemplary embodiments of the disclosure. While the disclosure will be described in conjunction with the exemplary embodiments, it will be understood that it is not intended to limit the disclosure to those embodiments. To the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the disclosure as defined by the appended claims.

[00056] Referring to Figure 1, there is schematically shown a municipal water treatment plant 1. The conditioning stage of water treatment plant 1 has the object of treating the secondary effluent of municipal wastewater for bulk removal of contaminants and partial degradation of organic matter preparing the water for second stage of treatment: catalytic oxidation and catalytic advanced oxidation (CO-CAO). Secondary effluent wastewater may be supplied from a storage tank used to store water from a secondary clarifier (following biological treatment) or water further filtered through dual or mixed media filters, all as commonly used in municipal waste water treatment plants.

[00057] With reference to Figure 1, secondary effluent water is pumped by centrifugal pump 10 to the oxygenation tank 80. Valve 20 is a sampling valve for collecting water samples to assess quality of the water entering the plant 1 for treatment. Pressure gauge 30 is a visual indicator of system pressure for the first part of the system leading to the oxygenation tank 80. Flowmeter 40 monitors the flow and through the plant control system, the information is used for adjusting the speed of pump 10 to maintain targeted programmed flow. The pH transmitter 50 is used to measure the inlet water pH and in conjunction with pH transmitter 150 regulates the pH to be achieved through the amount of ferric chloride to be dosed by the dosing unit 70. The target pH to be measured at pH transmitter 150 is 4 to optimise coagulation performance.

[00058] Turbidity transmitter 60 monitors the turbidity of the water to be treated. Depending on the quality of treated water, the dosage of ferric chloride may be increased so that higher turbidity water is dosed with more ferric chloride for coagulation. The oxygenation tank 80 is provided with a drain valve 90 to allow emptying of the tank for service cleaning. The oxygen tank 80 has internal baffles so that most of the water will overflow passing over the internal baffles 120 for good mixing. The baffles are provided at the bottom with removable covers to allow water to drain when draining the tank for cleaning. The oxygenation tank 80 is enclosed, communicating with the atmosphere through air filter 140.

[00059] The oxygen transmitter 130 measures the oxygen content of the gas in a headspace above the water level of oxygenation tank 80. The information is used, by the plant control system, to control the flow of oxygen supplied by the pressure swing adsorption (PSA) generator 100 into the water through fine bubble diffuser 110. Dissolved oxygen can be increased well above 15 mg/L, even to 30 mg/L, at which level oxidation of contaminants in the water of oxygenation tank 80 is highly efficient.

[00060] A pH transmitter is used to monitor the pH of water treated in the oxygenation tank 80 and to correct dosage of ferric chloride (for example as a 40% ferric chloride solution in water) to meet the pH target 4 through dosing unit 70. Sampling valve 160 is for collecting water samples to be analysed for assessment of water treatment through the oxygenation stage.

[00061] Dosing unit 170 is used for dosing magnesium hydroxide slurry (here at 10% w/v magnesium hydroxide) for raising the pH to target 7.5 to 8.5 and causing coagulation in step (b). Coagulation tank 180 has internal baffles 190 open at one end so that the water travels across each mixing and coagulation compartment defined by baffles 190 and including mixers 200. The output end of the tank 180 should be open to atmosphere to allow for gas release and avoid flotation of coagulated material.

[00062] Mixers 200 are provided with a variable frequency drive controlled by the plant control system. Mixer 200 in the first compartment is controlled to run at high speed for initial mixing of magnesium hydroxide slurry with the water. Mixers 200 in the second and subsequent compartments are run at lower speed suitable for coagulation. Tapered mixing may be used, decreasing the mixing speed towards the exit of the tank 180.

[00063] Valve 210 is used for draining the tank for cleaning. Sampling valve 220 is for collecting and assessing the quality of coagulated water. pH transmitter 230 monitors pH of coagulated water and the measurement is used for correcting the magnesium hydroxide slurry dosage through dosing unit 170.

[00064] Dosing unit 240 adds a polyacrylamide cationic flocculant for flocculation of coagulated solids. Mixing for flocculation is achieved through mixer 260. Precipitation of floes and separation of sludge happens in the inclined plate clarifier 270. Sludge collects at the bottom of the clarifier and is intermittently discharged by opening the electrically operated valve 280. The clarifier 270 to be used need not be an inclined plate type but can be of any other known type as known in the art.

[00065] Clarified water flows into the break tank 290 needed because from time to time the water treatment through CO-CAO step (e) is interrupted for backwashing the catalytic reactors 580 and 640 shown in Figure 2. The break tank 290 is enclosed, communicating with the atmosphere through air filter 330. Oxygenation is applied at this stage for increasing dissolved oxygen needed for the CO-CAO stage. Oxygen is produced by the PSA generator 310 and released into the water through fine bubble diffuser 320. The oxygen concentration in the headspace above the water level in break tank 290 is monitored by transmitter 340. Oxygenation contact time required at this stage is much less than in the initial oxygenation stage when oxidation of organic matter is targeted. Suitable contact time required at this stage was found to be around 10 minutes.

[00066] Break tank 290 full level is confirmed by level switch 350. Then, water treatment in the conditioning section has to be stopped to prevent overflow. Level switch 360 confirms empty level of the break tank 290 and water processing through CO-CAO section then has to stop. Valve 370 is used to isolate water supply when the pump 400, in the CO-CAO section of Figure 2, needs maintenance. Turbidity transmitter 380 monitors turbidity of the conditioned water and is used to make correction to pH control and ferric chloride/magnesium hydroxide addition in the conditioning stage of the treatment. Valve 390 is a sampling valve for collecting water samples to assess quality of the water after clarification step.

[00067] With reference to Figure 2, there is shown one possible arrangement of the CO-CAO water treatment section of water treatment plant 1.

[00068] Centrifugal pump 400 is used to pump the water through this section for enabling: CO CAO treatment, backwashing and rinsing of the section. In the normal mode of CO-CAO treatment, the water is dosed with oxygen donor, here potassium permanganate, by dosing unit 440, then passed through reaction tanks 460 and 480 to allow for preliminary oxidation reactions to take place. The two reaction tanks are conveniently selected to be of the same internal diameter as CO-CAO reactors 580 and 640. Reaction tanks 460 and 480 are each bed reactors which have coarse sand beds of 260 mm height to achieve uniform speed of the water in the cross section of the reactors. This arrangement makes possible removal of any sediment or precipitate accumulated in the reactor tanks when the CO-CAO reactors are backwashed. There will be the same backwash speed in all tanks. After allowing for reaction time in tanks 460 and 480, the water passes through CO-CAO bed reactors 580 and 640 arranged in series. Dosing unit 690 adds residual disinfectant if needed, depending on the use of reclaimed water. Water downstream of reactor 640 is monitored for quality compliance and if it is outside acceptable parameters, the water is diverted to raw water storage. Otherwise, the water is sent to treated water storage and use, for example as potable water. Backwashing is done with clarified water. During the backwashing, speed of pump 400 is increased to deliver the backwash flow, usually higher than normal mode flow. Dosing unit 520 will also dose a disinfectant such as chlorine or chlorine dioxide to disinfect the catalytic beds of the respective reactors 580 and 640.

[00069] First, the catalytic reactor 580 is backwashed. Valves 550 and 570 change position and the water travels from bottom to top inside the reactor expanding the bed and entraining solids and precipitate. Water exiting the reactor is directed to waste by valve 550. Next, for backwashing reactor 640, valves 550 and 570 rotate back into normal mode position and valves 620 and 630 move into position for backwashing reactor 640. Water enters the reactor 640 through valve 630 and travels upwards inside the reactor, expanding the catalytic bed and entraining solids.

[00070] Spent backwash water is directed to waste by the valve 630. During backwashing of reactor 640, the reactor 580 is operated in normal mode and due to higher than normal mode the bed will be submitted to higher pressure drop and compaction. Thus, after backwashing reactor 640 a short one minute backwashing is done again for reactor 580 to expand the bed and reduce compaction. The reactor bed settles back after finishing backwashing. The water quality through the settled bed is not usually of the normal water quality and rinsing of the beds has to be carried out. For rinsing, the catalytic reactors 580 and 640 are operated in normal mode but the water is diverted to raw water storage by valve 730.

[00071] Rinsing is also conveniently used to displace the water containing disinfectant which may not be desired in the treated water storage tank. For example, chlorine disinfectant may be toxic to an aquatic environment when the water is discharged into the environment. It is possible to setup the backwashing system using stored treated water and dedicated pump, valves and plumbing as is often the case with filter backwashing in a conventional water treatment plant. [00072] Following functional description of the items in Figure 2, the pressure gauge 410 is a visual indicator of the total pressure of the CO-CAO section. Pressure transmitter 420 monitors total pressure of CO-CAO and in conjunction with pressure transmitter 610 is used to calculate differential pressure and trigger backwashing of catalytic reactor 580. Flow meter 430 monitors the flowrate and through this plant section and the control system compares the actual flow with set values for normal mode and backwash mode and adjusts the speed of the pump to maintain set flow.

[00073] Dosing unit 440 is used for dosing oxygen donor chemical, preferably potassium permanganate. Sampling valve 450 is used to take water samples and analyse quality of water before entering the reaction tanks 460 and 480. The reaction tanks 460 and 490 allow for preliminary oxidation to take place. Each reaction tank 460 and 490 is provided with an automatic air vent valve, 470 and 490. Pressure gauge 500 is a visual indicator of pressure before the CO CAO first reactor 580. Samples, to check water quality following pre-oxidation could be collected using sampling valve 510. Dosing unit 520 is used during backwashing to dose disinfectant. [00074] ORP of the water is monitored by ORP transmitter 530 and pH is monitored by pH transmitter 540. Most suitable is chlorine dioxide, though chlorine and other disinfectants may be used. Water entering the catalytic reactor 580 has a target ORP not less than 400 mV for efficient CO-CAO reactions to proceed. ORP can be increased by increasing flowrate of oxygen from the PSA oxygen generator and injected into the water through diffuser 320, as described with reference to Figure 1 and by increasing the oxygen donor dosage by dosing unit 440.

[00075] In addition, pH is adjusted within a suitable range. Regardless of the use of reclaimed water, the pH at this stage should not be lower than 6 otherwise damage of the catalytic bed could happen. The catalytic metal oxide material may dissolve into the water under excessive acidic conditions. Strong reducing conditions, ORP approaching zero or negative, can damage the catalyst. In the position as represented, valves 550 and 570 direct water to be treated in normal mode through the catalytic reactor 580.

[00076] Water enters the reactor at the top side and travels downwards through the catalytic bed. For backwashing the reactor, the position of the two valves is rotated 90 degrees and the water travels upwards through the reactor and is directed to waste. Item 560 is a sight glass to observe spent backwash water quality and adjust duration of backwashing. Backwashing can be stopped when the backwash spent water is clear enough as measured by sight or a turbidity transmitter. Pressure indicator 600 shows the pressure ahead of the second catalytic reactor 640. Pressure transmitter 610 monitors the pressure ahead of the second catalytic reactor. In conjunction with pressure transmitter 710, the differential pressure drop over the second reactor is calculated and backwashing is triggered when a set differential pressure value is reached.

[00077] Valves 620 and 630 are shown in normal mode of operation whereby the water travels through the catalytic bed, comprising granular metal oxide catalyst (a combination of iron, manganese, aluminium and titanium oxides as described above) and an anthracite top layer of large size and lower density particles than the metal oxide catalyst particles to accommodate suspended solids at the top of the bed, inside reactor 640, from top to bottom. For backwashing, the position of the valves is rotated 90 degrees and the water travels from bottom to top expanding the catalytic bed and entraining solids retained in the bed. Then, the spent backwash water is directed to waste by valve 620.

[00078] Water treated through CO-CAO reactors is checked for pH, conductivity and ORP to verify that is within desired quality limits. pH is monitored by pH transmitter 660, ORP is monitored by ORP transmitter 670 and conductivity is monitored through conductivity transmitter 680. The treated water does not contain residual disinfectant for storage and distribution. If needed a dosing unit 690 is added to the treatment train to inject disinfectant. Commonly, the disinfectant is a chlorine based chemical and free chlorine is monitored and used for disinfectant dosage control by free chlorine analyser 700. The main purpose of pressure transmitter 710 is to calculate differential pressure over the catalytic reactor 640 and trigger backwashing of catalytic reactor 640 when set value is reached. Sample of finished water could be collected at sampling valve 720. Valve 730 directs the treated water in normal mode of operation to storage for reuse. During rinsing mode or if the water is not of suitable quality for reuse, the valve 730 changes position and water is returned to raw water storage. [00079] With reference to Figure 3, block diagrams of preferred treatment trains incorporating CO-CAO for treatment of water for reuse and discharge into environment are shown by way of example. The acronyms used are:

EDI Electro Deionization

UF Membrane Ultrafiltration

DPR Direct potable reuse, drinking water production without further treatment, mixing or aquifer retention

[00080] Where the targeted nutrient is total nitrogen, this may conveniently be reduced through nitrification-denitrification. Enhanced biological nutrient removal can decrease total nitrogen to 5 to 10 mg/L and ammonia nitrogen to 0.7 to 3.0 mg/L. Further, in the tertiary and advanced treatment stage the processes and plant described herein will degrade organic matter and release organic nitrogen as nitrogen gas. Nitrite will be oxidised to nitrate. Removal of phosphorus is also economically removed in wastewater treatment plant 1.

[00081] Treatment train (a) of Figure 3 is an example of treatment of secondary effluent of municipal wastewater for DPR incorporating the water treatment processes as described herein. Addition of MBR accounts also for additional disinfection barriers which in case of DPR treatment systems should be three process barriers or more for each type of pathogens, which can be removed according to the processes and plant described herein

[00082] The processes of the various trains of Figure 3 have lower energy consumption than RO (reverse osmosis) and advanced oxidation of the UV/H2O2 type. RO and UV/H2O2 advanced oxidation are typical part of the more conventional water treatment train for DPR. At the same time, capital and operating costs will be lower and technical constraints, such as requirement for RO treated water to be re-mineralised and stabilized with elements essential to human health such as calcium and magnesium, may be avoided with reference to Table 2 below.

[00083] Treatment train (b) of Figure 3 is an example of treatment of secondary effluent of municipal wastewater incorporating CO-CAO treatment processes as described herein. The use of reclaimed water is for a dual reticulation system with reclaimed water used for non-potable and other than cooking needs. Addition of MBR in the first stage of treatment is not usually needed. A high level of disinfection and overall removal and degradation of contaminants is achieved. [00084] Treatment train (c) of Figure 3 is an example of treatment of secondary effluent of municipal wastewater for water reclamation to be used for municipal irrigation with unrestricted access. The processes described herein will remove the frequent objectionable odour, disinfect the water to a level comparable with drinking water and remove heavy metals which could impact plant health and soil quality. Disinfection is a critical matter where the public has access to the irrigated area. Bacteria and viruses could be transported through air in aerosols from irrigation and viruses can survive for long time on wet and dry surfaces. Heavy metals removal is expected to be compliant with maximum contaminant limit for long term irrigation. Nutrient load, in terms of P and N, would also achieve compliant standards.

[00085] Treatment train (d) of Figure 3 is an example of treatment of secondary effluent of municipal wastewater for discharge into environmental water bodies. The major concern in this case is nutrient content of the discharged water which could, without appropriate handling, trigger algal blooms with serious consequences to the biota in the water body. Phosphorus is typically the trigger for algal blooms. The ratio of nitrogen to phosphorus for algae growth is around 16 to 1. If any of these elements are completely missing, then the particular element is the limiting factor or the algal growth would not take place at all. Treated water for discharge into an environment has stringent limits for both nitrogen and phosphorus. Water for discharge into an environment should be disinfected but should not contain significant residual disinfectant such as chlorine. Chlorine interferes with reproduction of most aquatic fauna. Heavy metals could be toxic and could bio accumulate in fish subsequently posing risk health to people consuming the fish. Excessive dissolved iron could damage the gills and skin of the fish precipitating on them and causing local oxidative damage because the mucous on the gills and skin is highly alkaline. Other metals such as aluminium and zinc could precipitate in fine particles which could accumulate on the gills and cause asphyxia and death of fish. The processes described herein can efficiently remove, potentially to undetected limit, phosphorus, degrade organic matter containing nitrogen, releasing it as nitrogen gas and generally degrade organic matter. Thus, the processes described herein limit the risk of eutrophication of the receiving water bodies. Heavy metals of concern are also removed. The water is disinfected without the use of any specific disinfectant and there is no residual chlorine in the treated water.

[00086] Possible use of CO-CAO process in treatment train for the use of reclaimed water is not limited to the examples shown in Figure 3. For example, reclaimed water may be used for cooling towers and industrial process water amongst other potential applications.

[00087] A validation study was conducted to measure output quality of water following treatment by the process operating at nominal operational conditions to remove and/or inactivate microorganisms seeded into municipal wastewater (secondary effluent) and also validate its performance for treating municipal secondary treated wastewater to produce recycled water. The logio reduction value (LRV) measured for each challenge test microorganism is summarised in Table 1. The LRVs measured are approximately equal to, or greater than, those required for Queensland Class A+ requirements (Department of Energy and Water Supply Queensland, 2008, Water quality guidelines for recycled water schemes) and the Australian Guidelines for Water Recycling (AGWR) dual reticulation requirements for recycled water (Natural Resource Management Ministerial Council. Environment Protection and Heritage Council Australian Health Ministers’ Conference, Canberra, Australia, 2006. Australian Guidelines for Water Recycling: Managing Health and Environmental Risks (Phase 1)) (Table 1). For the bacteria and viruses, the LRV measured across the treatment plant would achieve the Qld Class A+ and AGWR dual reticulation recycled water requirements.

[00088] To evaluate the capability of the process to treat wastewater for reuse applications, the properties of raw water sample (secondary effluent) and treated water sample were also investigated (Table 2). In comparison to the raw water sample, treated water has physical (e.g., true colour, turbidity, and suspended solids) and chemical (e.g., metals, P, N, organic contents) properties which meet regulations for water reuse. The significant reduction in P and organic nitrogen is beneficial to prevent algal blooms if the treated water is discharged to the environment. It was noted that the bad odour of water was absent after treatment by the process described herein.

[00089] TDS, ammonia and nitrite contents may be reduced for direct/indirect potable reuse of water by adding polishing steps such as RO (reverse osmosis) or END (electro nano diffusion). [00090] The contents of all references and published patents and patent applications cited throughout the application are hereby incorporated by reference.

[00091] It is understood that the detailed examples and embodiments described herein are given by way of example for illustrative purposes only, and are in no way considered to be limiting to the disclosure. Various modifications or changes in light thereof will be suggested to persons skilled in the art and are included within the spirit and purview of this application and are considered within the scope of the appended claims. For example, the relative quantities of the ingredients may be varied to optimize the desired effects, additional ingredients may be added, and/or similar ingredients may be substituted for one or more of the ingredients described. Additional advantageous features and functionalities associated with the processes of the present disclosure will be apparent from the appended claims. Moreover, those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the disclosure described herein. Such equivalents are intended to be encompassed by the following claims.