[0001] This disclosure generally relates to a process and apparatus for treatment of water for drinking and, particularly, to treatment of pre-treated drinking water of substandard quality to acceptable quality at point of entry and point of use.

BACKGROUND

[0002] Water may be of substandard quality when it leaves a water treatment plant or water may be contaminated downstream in the distribution network. Such water is nevertheless referred to herein as “pre-treated” water, typically containing some free chlorine. Municipal drinking water in developed world countries is usually supplied at the household level compliant with drinking water quality standards. In most other countries, the water at the tap in the house is not always suitable for drinking. This may be due to physical characteristics of the water and contamination with minerals, organic compounds and pathogens. Thus, for disinfection at the household level, water is often boiled. Boiling water consumes a large amount of energy. In addition, destruction of some of the pathogens needs a longer time than typical boiling and heavy metal contamination and toxicity is increased. During the boiling process, dissolved oxygen is displaced by water vapor which reduces metals to a more toxic form. Consequently, water becomes more corrosive and dissolves metals from the water boiling device, providing another potential source of contamination. For example arsenic, if present in the water, will be reduced from As(V) to the very toxic As(III).

[0003] For removal of other contaminants, water may be filtered through various types of filters such as contaminant absorbent materials and membrane filtration units. Disinfection through boiling may be replaced with pathogen separation through reverse osmosis and disinfection by ultraviolet irradiation. The essential difference in the developed world is that the distribution network between the water treatment plant and a consumer household is of much better quality and undergoes complex and regular service and maintenance. This results in a relatively high cost of drinking water. With the rapid population growth of cities and aging of the water distribution networks, many problems associated with maintaining water quality result and the cost of water distribution increases. Water losses from distribution networks are often higher than 20%. There is no perfectly sealed drinking water distribution network. Pipe bursts are a common problem. In particular, in older large cities there could be thousands of water pipe bursts and leaks per year. The water distribution networks cost much more than the water treatment plants to which they are connected. To reduce costs and reduce the amount of service and maintenance required by a water distribution network, a better option might be to distribute water of lower quality standard through the water supply network and treat it to drinking water quality standard close to the point of use: a “point of use” may be a point where the water is used for drinking, cooking, bathing and/or other purposes. Another treatment option is to treat at a point of entry: a “point of entry” being a point where water enters a community or community structure, for example a household, apartment block, community of households, commercial and institutional building

[0004] Pipe bursts, leaks and water supply interruptions may lead to serious contamination of the drinking water, from surrounding contaminated soil and leaking sewerage pipes. When there is no pressure in the drinking water distribution pipes, at leaking points, contaminated water from the surroundings enters the water pipes. Overall, the type of contaminants are very broad and dangerous to human health: pathogens, heavy metals, toxic substances and substances which may cause unpleasant taste and odour of the water. In addition, the corrosion of pipes and fittings of the distribution network can add heavy metals to the water. Another problem is that, in most cases, the disinfectant residual for the distribution network is chlorine. Chlorine reacting with dissolved organic matter in the water forms so-called disinfection byproducts (DBPs) detrimental to human health, many of them are known carcinogens. Common disinfectant additives typically form undesirable disinfection by-products. Disinfection by-products are regulated and have to be monitored and their concentration has to be kept lower than accepted maximum contaminant limit. Many of the disinfection by-products do not have a threshold for absolute safe limit. Moreover, they are regulated in isolation and combined health effects of multiple disinfection by-products and other contaminants acting together is not well researched and understood. Hence, over the years, maximum contaminant (including DBPs) limits are decreased more and more by health regulators as research into identifying new health risks progresses.

[0005] Current water treatment devices at point of entry and point of use are based on filtration and membrane separation processes, complemented by ultraviolet irradiation. For point of entry, a typical configuration of the treatment system is with one or two stage reverse osmosis. Description of a typical process follows. The water from the municipal supply is released into a buffer storage tank by opening an electrically operated valve. Then the water is pumped and filtered through a sand filter followed by a granular activated carbon filter. The granular activated filter is needed for removal of free chlorine which could cause oxidative deterioration of reverse osmosis membranes. The activated carbon filter also captures some of the heavy metals and dissolved organic matter. Further, there is an inline cartridge filter with 10 microns resolution for protecting the membranes from particulate damage. A pressure booster pump feeds the water to the reverse osmosis membranes. The reverse osmosis permeate water is finally disinfected using ultraviolet irradiation. A disinfectant may be added to the water for safe storage and distribution. A chemical cleaning system for membranes is also needed. Single stage reverse osmosis has usual water efficiency of 20% while two stage reverse osmosis plants could reach 50% efficiency or more. Thus, a large amount of water is discharged to sewer as reverse osmosis concentrate. While turbidity of the membrane permeate is very good, cost of raw water wasted is high along with potential costs of contaminants in the reverse osmosis concentrate. Besides direct cost of supplied water, often there is an extra 80% charge on volume used to cover fees for discharge to sewer. Monitoring the condition of the granular activated carbon filter is difficult. When the activated carbon is saturated, it has to be replaced. Often, due to no residual disinfectant in the water at the bottom of the filter, bacterial colonies develop and cause problems with water taste and water disinfection. Unfortunately, reverse osmosis also excessively demineralizes water and removes elements essential to human health such as calcium and magnesium. Desalination impairs the palatability of the water. Remineralisation is often used but is difficult and limited in what it can achieve.

[0006] Small capacity water treatment devices are typical for point of use, commonly installed in the kitchen to treat water for drinking and cooking. There are two main types of point of use treatment systems. The most widespread type is based on use of single stage reverse osmosis membranes; and the second type is based on use of ultrafiltration membranes. Using ultrafiltration membranes, water treatment efficiency is improved but there are limitations in removal of viruses and removal of dissolved undesirable or toxic elements and substances. A description of one typical process follows. Water is made available for treatment by opening an electrically operated valve. Then the water passes through a mesh type pre-filter with resolution of 40 microns or larger. This is to trap large particles consisting of scale substances, rust, sand and alike. A pressure reducing valve may follow the pre-filter to protect the water treatment device from excessive pressure in the water distribution network. The corresponding function of the sand filter in larger systems is taken by a cartridge filter made of polypropylene or other synthetic materials and having filtration resolution of 10 microns or more. Downstream from the cartridge filter, there are one or two activated carbon filters. The first one is a granular activated carbon filter with filtration resolution of around 5 microns and the second one is an activated carbon block filter with resolution around 1 micron. The purpose of these filters is the same as that of the granular activated carbon filter in larger system. Free chlorine is removed to protect the reverse osmosis membrane and other contaminants are adsorbed, improving water quality. After removing the chlorine, often bacteria grows in the second filter. A pressure booster pump is used to feed water to the reverse osmosis membrane unit. The flow rate of the reverse osmosis unit is small. An air bladder hydraulic accumulator stores permeate for delivering larger water volumes in short time when needed. The elastic membrane in the accumulator is porous. Bacterial colonies develop in the porous material and often cause bad taste of permeate water. Another activated carbon filter is added downstream from the pressurised storage tank to correct water taste. This filter may also contain silver particles incorporated into carbon structure so that some disinfection is also provided, though noting that silver itself can be a toxin at sufficient level. Final disinfection is done through ultraviolet irradiation.

[0007] Arguably, the best water quality, when using current devices for treating municipal piped water (MPW), is obtained through devices based on reverse osmosis. However, there are a number of shortcomings of such devices. First, the water efficiency of point of use and small capacity point of entry systems is close to 20%. 80% of the water is wasted through discharge to drain. Demineralized water is not good for human health, and does not have a pleasant taste. Demineralized water changes the taste of the food cooked with such water by dissolving a significant amount of minerals from the food with further nutritional impacts. Many of the components in current devices correct a water quality issue but add new ones. Then, another component is added downstream from the first one to correct the new problem. This leads to complexity and high cost of water produced.

[0008] The Applicant’s Australian Patent Application No. 2016232986, the contents of which are incorporated herein by reference, relates to a water treatment process suitable for treating water, for example groundwater or surface water, which includes a pre-oxidation step (a) and advanced catalytic oxidation steps including a coagulation step and separation of coagulates. Pre oxygenation of water with air or oxygen is required prior to step (a) where there is high chemical or biological oxygen demand. This process has been recently evaluated for disinfection performance by third party specialists in agreement with World Health Organization directions and guidelines contained in the document “Evaluating Household Water Treatment Options: Healthbased targets and microbiological performance specifications, WHO 2011”. In the document Table 1, Performance requirements for HWT technologies and associated log 10 reduction criteria for “interim”, “protective” and “highly protective” defines the log 10 removal requirements for three classes of pathogens: bacteria, viruses and protozoa. Highest defined level is “Highly protective” and the process was found to achieve the required log reduction for this level. This was achieved without the aid of any specific disinfectants such as chlorine, chloramine, ozone or other disinfectants used for water disinfection. This process is therefore effective but less suited for the treatment of substandard water due to cost and efficiency considerations.

[0009] In view of the foregoing, it would be desirable to identify new processes for treating water from a prior water treatment process, where the prior water treatment process affords water of a substandard quality for drinking.

[00010] 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

[00011] The present disclosure is directed to a water treatment process and apparatus suitable for treating pre-treated water, where the pre-treated water is of substandard quality, in an efficient and cost effective way.

[00012] In one aspect the present disclosure provides a process for treating water produced from a prior water treatment process comprising the sequential steps of:

(a) in a first vessel a first oxidation step comprising contacting water from a prior water treatment process with an inorganic oxidising salt for a time effective for oxidising a portion of contaminants in said water from said prior water treatment process;

(b) in a second vessel subjecting water from step (a) to a further oxidation step for oxidising residual oxidisable contaminants, said oxidation being catalytic oxidation catalysed, in combination, by:

(i) inorganic oxidising salt left in solution after oxidation step (a); and

(ii) a solid phase catalyst comprising a granular catalytic material for oxidising residual oxidisable contaminants.

[00013] In embodiments, the water produced from a prior treatment process meets one or more of the following conditions:

• Turbidity < 30 NTU (nephelometric turbidity units)

• Colour < 40 PCU (platinum cobalt units)

• Suspended solids < 10 mg/L

• Total heavy metals < 5 mg/L

• Chemical Oxygen Demand < 20 mg/L

• Total Organic Carbon < 8 mg/L • Free chlorine < 5 mg/L.

[00014] In some embodiments, the water from the prior treatment process meets all of these conditions.

[00015] In embodiments, the turbidity of the water from the prior treatment process is less than about 20 NTU, or less than about 10 NTU, or less than about 5 NTU, or less than about 1 NTU. In alternate embodiments, the turbidity of the water from the prior water treatment process is from about 0.05 to about 30 NTU, or from about 0.1 to about 20 NTU, or from about 0.1 to about 10 NTU, or from about 0.1 to about 5 NTU, or from about 0.1 to about 1 NTU.

[00016] In embodiments, the colour of the water from the prior water treatment process is less than about 30 PCU, or less than about 20 PCU, or less than about 10 PCU, or less than about 5 PCU, or less than about 2 PCU. In alternate embodiments, the colour of the water from the prior water treatment process is from about 1 PCU to about 20 PCU, or from about 1 PCU to about 10 PCU, or from about 1 PCU to about 10 PCU, or from about 1 PCU to about 5 PCU, or from about 0.5 PCU to about 5 PCU.

[00017] In embodiments, the amount of suspended solids in the water from the prior treatment process is less than about 9 mg/L, or less than about 8 mg/L, or less than about 7 mg/L, or less than about 6 mg/L, or less than about 5 mg/L, or less than about 4 mg/L, or less than about 3 mg/L, or less than about 2 mg/L, or less than about 1 mg/L. In alternate embodiments, the amount of suspended solids in the water from the prior treatment process is from about 1 mg/L to about 10 mg/L.

[00018] In embodiments, the total heavy metals in the water from the prior treatment process is less than about 4 mg/L, or less than about 3 mg/L, or less than about 2 mg/L, or less than about 1 mg/L, or less than about 0.5 mg/L. In alternate embodiments, the amount of heavy metals from the prior water treatment process is from about 0.01 mg/L to about 5 mg/L.

[00019] The heavy metals may comprise one or more metals having a density greater than 5 g/cm ³ . Examples of heavy metals include one or more transition metals.

[00020] In embodiments, the chemical oxygen demand of the water from the prior treatment process is less than about 15 mg/L, or less than about 10 mg/L, or less than about 5 mg/L. In alternate embodiments, the chemical oxygen demand of the water from the prior treatment process is from about 1 mg/L to about 20 mg/L, or from about 1 mg/L to about 15 mg/L, from about 1 mg/L to about 10 mg/L, from about 1 mg/L to about 5 mg/L

[00021] In embodiments, the total organic carbon in the water from the prior water treatment process is less than about 7 mg/L, or less than about 6 mg/L, or less than about 5 mg/L. In alternate embodiments, the total organic carbon in the water from the prior water treatment process is from about 1 mg/L to about 8 mg/L, or from about 1 mg/L to about 7 mg/L, or from about 1 mg/L to about 6 mg/L, or from about 1 mg/L to about 5 mg/L.

[00022] In embodiments, the free chlorine content of the water from the prior water treatment process is less than about 5 mg/L, or less than about 3 mg/L, or less than about 2 mg/L, or less than about 1 mg/L. In alternate embodiments, the free chlorine content of the water from the prior water treatment process is from about 1 mg/L to about 5 mg/L, or from about 1 mg/L to about 4 mg/L, or from about 1 mg/L to about 3 mg/L, or from about 1 mg/L to about 2 mg/L.

[00023] In embodiments, the free chlorine content of the water from the prior water treatment process is from about 0 1 mg/L to about 1 mg/L, or from about 0.2 mg/L to about 1 mg/L, or from about 0.3 mg/L to about lmg/L, or from about 0.4 mg/L to about 1 mg/L.

[00024] In embodiments, the turbidity of the water from the prior water treatment process is < 40 PCU; the suspended solids in the water from the prior water treatment process is < 10 mg/L; the total heavy metals in the water from the prior water treatment process < 5 mg/L; the chemical oxygen demand of the water from the prior water treatment process is < 20 mg/L; the total organic carbon in the water from the prior water treatment process is < 8 mg/L; and the free chlorine in the water from the prior water treatment process is < 5 mg/L.

[00025] In embodiments, the turbidity of the water from the prior water treatment process is < 1 PCU; the suspended solids in the water from the prior water treatment process is < 5 mg/L; the total heavy metals in the water from the prior water treatment process < 1 mg/L; the chemical oxygen demand of the water from the prior water treatment process is < 10 mg/L; the total organic carbon in the water from the prior water treatment process is < 5 mg/L; and the free chlorine in the water from the prior water treatment process is < 2 mg/L.

[00026] In any one of the herein disclosed embodiments, the free chlorine in the water from the prior water treatment process is from about 0.1 mg/L to about 1 mg/L.

[00027] As the water from the prior water treatment process, such as municipal piped drinking water, may have relatively low Chemical Oxygen Demand (COD) and low suspended solids content, preoxygenation with oxygen and air as well as flocculation, settling and discharge of suspended solids, metal hydroxides precipitates and hardness precipitates can be omitted with a saving in capital and operating costs. Operating costs, in particular, can be reduced through avoiding oxygen or air consumption as well as addition of flocculants or a focus on generating an in-situ flocculant. Capital costs can also be reduced as described below. [00028] Further, pre-treated water typically contains free residual chlorine intended for maintaining disinfection in the distribution network. As such, presence of free chlorine is typically, though not exclusively, an indicator of water pre-treatment. Other parameters such as suspended solids content, pH (expected within a range of 6.5 to 8.5, on the slightly alkaline side being typical to prevent corrosion in a water distribution network) and so on may be used as an indicator of water pre-treatment. The free chlorine, while in the distribution network, reacts with organic matter present in the water and/or with bacterial slime formed in a water distribution network producing toxic disinfection by-products and may compromise aesthetic aspects of water: turbidity, smell and taste. The level of free chlorine may vary from very low and up to less than one milligram per litre. Free chlorine is usually not greater than 1 mg/L. These water quality issues are addressed by the process as described here. Given the low COD and presence of free chlorine in feed water to step (a), and the role of free chlorine as an oxidant, oxygenation with a gas, prior to oxidation step (a) has little to no benefit and is neither required nor used in the process.

[00029] Despite the likely presence of free chlorine in feed water to the presently disclosed process due to prior or pre-treatment, a further amount of oxidant is typically required for contacting with water in step (a), which may be described as a conditioning step. A water-soluble oxidant, desirably containing both oxygen and a catalytic metal element - such as manganese, iron is desirably avoided in this application - is preferred. Permanganates are convenient oxidants for the application. Conveniently, potassium permanganate which also adds the metal catalyst, manganese, needed in the catalytic oxidation step (b), is used as oxidant in step (a). Conditioning or reaction time may be by correlated by measured organic matter degradation. The duration of step (a) may less than 60 minutes, or less than 30 minutes, or less than 20 minutes, or less than 10 minutes. Preferably between 5 and 15 minutes.

[00030] pH increase may be necessary, typically after addition of the oxidant because oxidation of organic matter in step (a) is more efficient at low pH. pH may require increase to ensure efficient performance of step (b).

[00031] In some embodiments, the inorganic oxidising salt in step (a) is a metal permanganate, preferably selected from the group consisting of potassium permanganate, sodium permanganate, barium permanganate, calcium permanganate and aluminium permanganate.

[00032] In some embodiments, the process further comprises sulphate removal and wherein said metal permanganate is selected from barium permanganate and calcium permanganate. [00033] In some embodiments, the presently disclosed process is conducted at ambient temperature and ambient or near ambient pressure. [00034] In preferred embodiments said inorganic oxidising salt is a permanganate salt and water introduced to catalytic oxidation step (b) has visible colouration due to presence of residual permanganate.

[00035] In preferred embodiments, the treated water from catalytic oxidation step (b) has no visible colouration due to the presence of residual permanganate.

[00036] In some embodiments chlorine is added to water for disinfection of treated water for storage and distribution after step (b).

[00037] In some embodiments, the particle size of the granular catalytic material is between about 100 micron and 2000 micron, or between about 175 micron and about 1000 micron, or between about 250 micron and about 400 micron.

[00038] In some preferred embodiments step (b) is performed in an upflow reactor.

[00039] In some embodiments, an additional oxidant may be added after step (a) and prior to step (b) with minimum contacting time required as catalytic processes of step (b) decompose the oxidants to release oxygen which causes desired oxidation and degradation of remaining contaminants. Though a permanganate could again be used, a more suitable oxidant includes a compound which is both oxidising and disinfecting, such as a hypochlorite, conveniently sodium hypochlorite or calcium hypochlorite. The amount of sodium hypochlorite added depends on the nature of COD in the water. Sodium hypochlorite could be useful for oxidising inorganic part of the COD at low cost. This oxidant addition is also aimed at minimising upward increment in the concentration of disinfection by-products by not allowing a long reaction time of chlorine with organic matter. Contacting should be on the order of minutes not hours. With such control, minimal toxic disinfection by-products will be added by the process itself. Sodium and calcium hypochlorite are less expensive means to raise the ORP than further addition of potassium permanganate, an alternative option. The maximum dosage of hypochlorite added is desirably limited by the target level of disinfection by-products in the treated water. Other oxidants like hydrogen peroxide could, however, be used.

[00040] The process may include an electrochemical parameter, desirably oxidation-reduction potential (ORP), as a control parameter to monitor the occurrence of efficient catalytic advanced oxidation reactions to take place in catalytic reactor for reducing disinfection by-products. ORP is measured prior to catalytic oxidation step (b), and preferably prior to step (a), with adjustments being made to achieve a target ORP (or other electrochemical parameter). Desirably, treatment for water directed to step (b) has a target of about 500 mV oxidation-reduction potential (ORP) or higher. ORP is contributed by free chlorine in the raw water as well as oxidant additions (e.g. permanganate and hypochlorites, the latter typically being less expensive than permanganates) as described above. Oxidant additions to steps (a) and (b) are then balanced, as required to achieve targeted ORP, for instance 500 mV or higher. This may require an inverse relationship between additions of permanganate, where used, and hypochlorite, where used. That is, increasing dosage of permanganate should allow decrease of hypochlorite dosage for achieving required ORP before the catalytic reactor. A control system for the process conveniently makes the necessary ORP adjustments with benefits in minimising formation of disinfection by-products. Hypochlorite may be avoided if disinfection by-product levels must be strictly controlled. It may be substituted by potassium permanganate.

[00041] The value of ORP (or other selected electrochemical parameter) may be converted, as part of process control strategy to a free chlorine residual using a calibration based, conveniently, on experimental measurement. Alternatively, free chlorine could be measured directly in the feed water to the process. However, the measurement of free chlorine is more difficult and requires more expensive instrumentation and maintenance of the instrumentation. However, this may be justifiable for larger capacity water treatment plants.

[00042] The control strategy - together with the design of vessel(s), preferably bed reactors, used for catalytic oxidation step (b), for example through selection of catalyst bed volume - also controls permanganate addition to reduce or avoid visible colouration in product water due to presence of residual permanganate. pH adjustment may also form part of the control strategy, if pH differs from a near neutral target, with suitable acid or alkali being used for this adjustment - for example, though not limited to, hydrochloric acid and sodium hydroxide. This step may often be avoided because pH of pre-treated feed water is often in an acceptable pH range of 6.5 to 8.5 on introduction to step (a).

[00043] Catalytic oxidation step (b), which may be referred to as catalytic advanced oxidation, is desirably conducted in a bed reactor as described in more detail below, and has a polishing effect in removing contaminants through processes such as precipitating remaining iron and manganese as oxides or hydroxides, co-precipitation of heavy metals as oxides or hydroxides, degradation of dissolved organic material, degradation of chemicals which may affect water taste and a broad range of chemicals of emerging concern and inactivation and destruction of pathogens such as coliforms; as well as combinations of these. Any of these hazards may be introduced due to faults in a water distribution network or the initial water treatment. Under catalysed oxidizing conditions, highly reactive manganese radicals, such as manganyl radicals are generated together with hydroxyl ions through a Fenton type reaction scheme though not exactly the same since hydrogen peroxide or ozone are not necessary to be used in the described process. Use of permanganate will also tend to favour formation of sufficient manganyl and hydroxyl radicals to achieve co precipitation of the metals and other contaminant reduction processes which should be sufficient to achieve potable water standards. Potassium permanganate is unstable and at the surface of the metal oxide, it disproportionates into Mn(II) and Mn(IV). Background research indicates that alkaline conditions favour more formation of manganyl, Mn02+ over Mn2+. The intermediate reactions are complex and happen in a very short time. Where used, unreacted permanganate is required to be present in the water entering the catalytic reactor bed for the advanced catalytic oxidation process to take place. Presence of unreacted permanganate is conveniently indicated by the pink to violet colour of the water entering the catalytic reactor. The applicant found that for efficiency of the process to oxidise and degrade organic matter, the ORP has to be maintained high, higher than 400 mV, as noted in the industrial practice when using Fenton reagent. This result is achieved without recourse to physical oxidation methods such as through use of corona discharge or ultraviolet radiation steps. In addition, the Applicant has not found such radical stability to be an issue in effecting contaminant removal so addition of chelating agents such as polyamines and phosphate salts is not required.

[00044] Unreacted potassium permanganate is decomposed in the catalytic oxidation stage, the manganese precipitating as manganese hydroxide and manganese dioxide, this with dosage control, preventing colour contamination of treated water.

[00045] Addition of potassium permanganate to catalytic advanced oxidation could be as low as 0.5 mg/L and may be increased if disinfection by-products increase too much with the addition of hypochlorite, or water aesthetic characteristics are not satisfactory. Minimum recommended pH to target, before the catalytic reactor, is 7.

[00046] A bed reactor for catalytic oxidation requires periodic backwashing to remove precipitates. A disinfectant is desirably added during backwashing with sodium hypochlorite being preferred though not limiting on the process.

[00047] Water from catalytic oxidation treatment step (b) is conveniently directed for storage or distribution to users with disinfectant additions and pH adjustment being made if necessary to reach a pH range 6.5 to 8.5 with target pH 7. Due to the catalytic oxidation, in particular, disinfectant additions should not cause any appreciable formation of disinfection by-products due to prior degradation of most dissolved organic matter through steps (a) and (b) of the process. Water treated by catalytic oxidation has very low to no disinfectant. A preferred disinfectant to be added prior to distribution is chlorine dioxide. Sodium hypochlorite, calcium hypochlorite or chlorine gas could also, less preferably, be used. Downstream from the catalytic reactor the content of organic matter is very low and what is not degraded is of more refractory nature, very little reacting with chlorine to form disinfection by-products. Little disinfectant should be needed because most of the matter that could react to consume disinfectant has been already degraded; however, residual disinfectant for storage and distribution provides further assurance that treated water is pathogen free.

[00048] If ammonia, nitrate or hardness present an issue in the pre-treated water, a step may be included to remove these contaminants. Ion exchange is one option and an ion exchange step (c) may follow catalytic oxidation step (b), prior to disinfectant dosing for the distribution network as described above. This is a synergetic integration because treated water fed to an ion exchange step contains a very low and safe oxidant amount (no need for dedicated chlorine removal), low level of biodegradable organic matter, is well disinfected and well clarified. As a result, ion exchange resin filters may be operated more efficiently and at lower cost. For large treatment systems, other methods for removal of ammonia, nitrate and hardness may be used.

[00049] The process may be used to treat a pre-treated water whenever it is substandard. However, the process is suitable to provide consumers with further assurance of water quality and the process is also suitable for treating water on a bypass basis when there are faults in operation of a prior water treatment plant.

[00050] In another aspect, the present disclosure provides an apparatus for treating water produced from a prior water treatment process said apparatus comprising:

(a) at least one first vessel for performing a first oxidation step comprising contacting water from a prior water treatment process with an inorganic oxidising salt for a time effective for oxidising a portion of contaminants in said water from said prior water treatment process;

(b) at least one second vessel for subjecting water from step (a) to a further oxidation step for oxidising residual oxidisable contaminants, said oxidation being catalytic oxidation catalysed, in combination, by:

(i) inorganic oxidising salt left in solution after oxidation step (a); and

(ii) a solid phase catalyst comprising a granular catalytic material for oxidising residual oxidisable contaminants.

[00051] Desirably, one vessel is used for each of steps (a) and (b) allowing for a simpler plant design and lower cost.

[00052] The at least one vessel in stage (a) need not be configured as a settler, since a pre treatment would typically remove issues with suspended solids as precipitation reactions for pre- treated water should not produce substantial quantities of sludge. An in-line tank would typically be suitable for this vessel allowing a saving in capital cost.

[00053] Catalytic oxidation may be conducted in a range of vessels including bed reactors, column reactors or filter beds. The at least one vessel in stage (b) is conveniently a bed reactor. Such beds would comprise a granular catalytic material to further (i.e. in combination with catalytic metal ions and hydroxyl radicals) catalyse the catalytic oxidation process. Favoured catalytic materials are granules consisting of silica or alumina supported metal oxides or mixtures of metal oxides selected from the group consisting of manganese oxide (green sand and others), manganese dioxide, iron oxides, aluminium oxides, titanium dioxide, perovskite and rare earth oxides. The maximum content of the catalytic component is about 10 wt% of the total weight of a catalytic granule. Catalytic materials may be arranged in layers in possible combination with other materials which assist filtration of oxidation products from water. Examples of such materials include silica sand and filter coal.

[00054] Other catalysts that could be used include zeolites and electrically conductive catalytic materials where granular activated carbon is typically used as a support for a metal. Catalytic elements for such case include noble metals (platinum, gold, silver and nickel) and copper.

[00055] In any case, a combination of catalysts in solution and solid phase is effectively used in the catalytic oxidation reactor.

[00056] As alluded to above, the volume of the granular catalyst bed is selected to efficiently enable catalytic oxidation whilst controlling permanganate levels - in combination with control over permanganate addition - to reduce or avoid visible colouration in product water due to presence of residual permanganate.

[00057] If inadequate or irregular water supply pressure is a problem, the apparatus may include a pressure booster pump, coupled with a buffer storage tank if required. Feed water is desirably directed through a feed pipe to the at least one vessel of stage (a), the feed pipe may be connected to a water distribution network from water treatment plant(s) with treated water quality issues on a regular or intermittent basis. In the case of intermittent water quality issues, the feed pipe may be closed by a valve or valve system when water quality is acceptable and opened when there are water quality issues.

[00058] The apparatus may include a separation stage for removal of contaminants such as ammonia and nitrate. An ion exchange stage is preferred for this purpose.

[00059] The apparatus may conveniently be located adjacent or at the point of entry to, or point of use of, water to a community or community structure. [00060] The water treatment process and apparatus of the present invention allows for efficient post-treatment of water to compensate for water quality issues caused by an ineffective pre treatment or faults within a water distribution network, whether formed by pipes, containers or other means. In this way, contaminant levels can be reduced by a simplified flow scheme and apparatus at a high level of efficiency, including efficiency of 95% and above.

[00061] 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

[00062] Figure l is a process diagram of a water treatment apparatus constructed and operated in accordance with one embodiment of the present disclosure.

[00063] Figure 2 is a process diagram of a water treatment apparatus constructed and operated in accordance with another embodiment of the present disclosure.

DETAILED DESCRIPTION

[00064] 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.

[00065] 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.

[00066] 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 ‘permanganate’ may include more than one permanganates, and the like. [00067] 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.

[00068] 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. [00069] 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’.

[00070] Any processes provided herein can be combined with one or more of any of the other processes provided herein.

[00071] 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.

[00072] 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.

[00073] The water treatment apparatus or plant 1 shown in Figure 1 has the object of treating municipal piped water in a case where the municipal piped water supply is not frequently interrupted and the pressure is maintained above 100 kPa. Water treatment apparatus 1 relies on municipal piped water line pressure to flow through the system which performs treatment and the auxiliary operational functions such as backwashing of a catalytic reactor described below. Common to point of entry water treatment devices is manual valve 10 which could be closed to isolate the device from the water supply for performing service and maintenance. During normal operation of the device this valve 10 is open.

[00074] Next in line, downstream from valve 10, is another common item called a prefilter. The pre-filter 50 is provided with stainless steel mesh of filtration resolution of 40 microns or larger, up to a few hundred microns. The role of the mesh is to retain large solid particles such as scale and rust coming from the water distribution network. The bowl of the pre-filter 50 is clear so that the accumulation of a relatively small volume of particulates at the bottom of the filter bowl can be seen. Periodically, the manual valve 40 is opened for a short time to discharge the accumulated sludge in the pre-filter mesh 30. The pre-filter 50 can also be dismantled for cleaning the mesh. [00075] Pressure gauge 20 shows the pressure at the inlet to the water treatment plant 1. This pressure has to be higher than the pressure shown by pressure gauge 70 downstream from the pressure reducing valve 60. As shown in Figure 1, the set downstream pressure of the pressure reducing valve is 200 kPa. If municipal piped water supply has a pressure lower than 200 kPa, then the pressure reducing valve 60 will be completely open and when feed water is not flowing through, the pressure shown by pressure gauges 20 and 70 is the same. At the same time, the solenoid valves 90 and 100 are both closed.

[00076] The pressure switch 80 is used for signalling low line pressure, lower than 100 kPa, under which the water treatment apparatus 1 could not be operated at all. One such situation is when the water supply is interrupted. Solenoid valve 90 opens for normal water treatment. Flow is regulated through the orifice plate restrictor 120 and kept constant due to constant pressure controlled by valve 60. The water flow rate will decrease progressively as the catalytic bed in the catalytic reactor 320 accumulates precipitate. The flow is monitored by flowmeter 210. At a selected flow rate, lower than nominal set, backwashing of catalytic reactor 320 may be initiated. Backwashing may also be initiated based on differential pressure between pressure measured by pressure transmitter 190 and pressure transmitter 360.

[00077] Solenoid valve 100 in conjunction with orifice plate restrictor 110, control the flow for backwashing the catalytic reactor 320. During a backwashing process, solenoid valve 90 is closed. The flowmeter 210 monitors and confirms the backwash flow. If the flow is not within target limits then the size of the orifice plate 110 is adjusted accordingly.

[00078] ORP transmitter 130 measures the oxidation-reduction potential (ORP) of the raw municipal supplied water and the value is converted to an equivalent of free chlorine in the feed or raw water. For example, samples of feed water can be spiked with sodium hypochlorite, then both free chlorine and ORP are measured allowing a correlation between ORP and free chlorine to be derived for use by the process control system which can include an electronic control unit of conventional type with inputs from the various transmitters, in particular ORP transmitter 130, as described here.

[00079] The free chlorine value 140 is used for calculation of an amount of potassium permanganate to be added by dosing unit 150 and dosage of sodium or calcium hypochlorite by dosing unit 230 under control of the control system as a response to input transmitter signals as described herein. Potassium permanganate provides catalytic metal, manganese, for the catalytic reactor 320 which performs partial oxidation of organic and inorganic matter and provides part of the oxygen for the catalytic reactor 320. [00080] An amount of potassium permanganate to be dosed by dosing unit 150 depends on ORP level of the raw water (as measured by ORP transmitter 130), COD of the water and level of disinfection by-products found in the treated water. In order to decrease disinfection by-products specific to chlorine reacting with organic matter, the dosage of potassium permanganate has to be increased while dosage of hypochlorite has to be decreased, maintaining the same ORP ahead of the catalytic reactor 320. This ORP value is not less than 400 mV. If the pH of the finished water is not within drinking water guidelines, then pH correction chemical (whether acid or alkali) will be dosed through dosing unit 160. This will rarely be the case. In general, dosing unit 160 is not expected to be necessary.

[00081] Reaction tank 170 has a typical retention time of 10 minutes to allow, for the most part, oxidation reactions with potassium permanganate to be completed. Reaction tank 170 can be conveniently a filter container used for sand filters with a small bed of coarse silica sand, around 260 mm. This will allow the water to rise with uniform speed distribution across the section of the reaction tank 170. At the top of the reaction tank 170, there is an air release valve item 180.

[00082] Pressure transmitter 190 monitors the overall system pressure and is used in conjunction with pressure transmitter 360 to determine the differential pressure drop over the catalytic reactor 320. At a set differential maximum pressure, backwash operation is triggered by a control system for the water treatment plant 1. The backwash removes precipitate accumulated in the catalytic reactor 320 by directing the water flow upwards, from bottom of the catalytic reactor 320. The water exiting the catalytic reactor 320 flows to waste. The process is the same as for sand filter or mixed media filters. The pressure gauge 200 is for visual indication of the system pressure and verification of pressure value. The pressure indicated by the pressure gauge 200 and pressure transmitter 190 should be the same. The water treatment plant 1 operates at a water speed of 20 m/h through the catalytic reactor 320 while treating the water. This speed and corresponding flow will decrease as precipitate accumulates in the catalytic reactor bed. A minimum water flow rate value is set for triggering backwash, in addition to differential pressure trigger of backwash by the control system. Flow meter 210 is used for flow monitoring. Flow meter 210 is also used to monitor the amount of water processed by the plant 1 and based on this, to manage operation and maintenance required for the plant.

[00083] Sampling valve 220 is for sampling the water and assessing water quality parameters following the addition of oxygen donor chemical and reaction time allowed in reaction tank 170. Chemical dosing unit 230 is also used for dosing disinfectant, typically sodium hypochlorite, during backwashing of the catalytic reactor 320. Sodium hypochlorite is also used to raise the ORP. Maximum usage is determined by the level of disinfection by-products as measured by conventional analytical techniques. When a maximum acceptable limit of disinfection by-products is reached, ORP can be further increased by increasing dosage of the oxygen donor chemical such as potassium permanganate.

[00084] Catalytic reactor 320 contains a bed of granular metal oxide catalyst. Typical catalysts are iron oxides, manganese oxides, aluminium oxides and titanium oxide or a mixture of metal oxides. Most such oxides could be corroded by water with highly acidic pH and low ORP anoxic water. The pH is monitored by instrument 240 and ORP is monitored by instrument 250 with the control system adjusting pH and ORP as required to prevent water contamination by corrosion. A sufficiently high ORP is required for the water entering the catalytic reactor 320 in order for the water treatment process to perform efficiently. ORP less than 400 mV is not desirable.

[00085] Sampling valve 260 is used to sample the water entering the catalytic reactor 320 and verify main water parameters important for efficient catalytic or advanced oxidation. These are ORP, pH, suspended solids and oxygen demand. The advanced oxidation reactor 320 has the purpose of degrading organic material and has limited capacity in retaining suspended solids and precipitated solids. The oxygen demand of the water is checked against the oxidation capacity provided by the dissolved oxygen and oxidation to be provided by the added oxidants: potassium permanganate and sodium hypochlorite (which may be substituted by potassium permanganate if trihalomethanes (THMs) levels require strict control).

[00086] Valves 270 and 280 control the water flow direction through the catalytic reactor 320. In normal operating position as shown in Figure 1, the water passes through the catalytic reactor 320 from top to bottom, with water being subjected to catalytic oxidation in the catalytic bed inside the catalytic reactor 320.

[00087] At the bottom of the catalytic reactor 320, there are collector pipes with slots through which water enters and rises through a central pipe and out of the catalytic reactor 320. For backwashing the catalytic reactor bed, the position of the valves 270 and 280 changes. The water enters the reactor through valve 280, then flows down the central pipe and out of the collector pipes at the bottom of the catalytic reactor 320. Further, the water flows upwards expanding the catalytic bed and entraining suspended solids accumulated in the catalytic bed. Water exits the catalytic reactor 320 and through valve 270 with the backwash spent water being directed to waste or treatment for sludge thickening and dewatering. The sight glass 310 is used to observe turbidity of spent backwash water and adjust duration of the backwashing. Sampling valve 290 is for collecting water processed through the catalytic reactor 320 for analysis. [00088] Pressure downstream from the catalytic reactor 320 is visually indicated by pressure gauge 300 and monitored by pressure transmitter 360. The pH transmitter 360 monitors the pH at the output of the catalytic reactor 320 and, if needed, pH could be corrected by adding more pH correction chemical (acid or alkali) through dosing unit 160 though pH is expected to remain in an acceptable range 6.5-8.5 throughout the process. Transmitter 340 monitors water conductivity. A large change in conductivity indicates a change in raw water quality which may require water treatment process adjustment by the control system or is an indication of deviation in the chemical addition which the control system may check as a possible chemical dosing fault.

[00089] The chemical dosing unit 350 is used for addition of disinfectant providing residual disinfectant for the water distribution network, as little disinfectant is present in water flowing from catalytic reactor 320. The preferred disinfectant is chlorine dioxide because the disinfection capacity of chlorine dioxide does not diminish with increase in pH in the pH range 6.5 to 8.5 used for potable water.

[00090] By difference, disinfection with chlorine decreases by around 50% at pH 7.5 compared to pH 6.5 and decreases rapidly with further upward increment in pH. Chlorine dioxide is less aggressive to metals and materials in the water distribution networks than chlorine, displaying a low risk of corrosion. The disinfection by-products generated by chlorine dioxide in water are not carcinogenic nor of high toxicity. Addition of chlorine dioxide to the water treated through the process described herein generates mostly chlorate. Chlorate does not display any significant toxicity in the concentration generated by addition of chlorine dioxide in the range recommended for residual in the distribution network. Consequently, in many countries, there are no regulatory limits for chlorate in drinking water. Chlorate is also a mild disinfectant and degrades in time with its chlorine content converted to chlorides.

[00091] The concentration of chlorine dioxide and disinfection capacity in the finished water are monitored through transmitter 370. Precise chlorine dioxide concentration can be measured in water sampled from sampling valve 380. Through the backwashing process, part of the water exiting the catalytic reactor 320 contains some amount of suspended solids. This suspended solids containing water is directed for a few minutes to waste by valve 390. Valve 390 will also direct the water to waste if the monitoring and control systems determine that the water may be out of specification and not suitable for drinking.

[00092] Under a normal mode of operation, valve 390 directs the water to the finished water storage tank 400. The design and flow through the finished water storage tank 400 should be such that a minimum hydraulic retention time of water is achieved before the water enters distribution network for use as potable water. The retention time in the finished water storage tank 400 is determined based on pathogen contamination risk assessment and in relation with chlorine dioxide concentration to achieve a minimum necessary, so-called CT value. The CT value is calculated by multiplying the disinfectant concentration in mg/L by the contact time, T in minutes.

[00093] The finished water storage tank 400 is provided with level monitoring. In Figure 1, level switch 410 confirms tank 400 is full and stops the water treatment plant 1. Level switch 420 confirms that the tank 400 is empty and typically has the function to protect the water distribution pump (not shown) from running dry. The water distribution pump is connected to the tank through valve 430.

[00094] With reference to Figure 2, the process fluid diagram shown for water treatment apparatus or plant 1 is for the case where the municipal piped water supply has interruptions and low pressure, decreasing temporarily to lower than 100 kPa a common condition in developing countries.

[00095] In this case, a buffer storage tank 570 is used to store raw water and a pump 620 is needed to provide the operating pressure and flow. In a manner similar to the embodiment described in Figure 1, the water supply is filtered for removal of coarse solids by pre-filter 540. Connection to the water supply is through manual valve 510 and the water supply is open or shut off using normally closed solenoid valve 520.

[00096] Pressure gauge 530 provides visual indication of pressure before the prefilter 540 and may be used to decide when the pre-filter 540 needs sediment discharge through valve 560 or needs cleaning of the filter mesh. Indicated pressure increases with increased level of solids accumulated in the pre-filter mesh 550. Level switch 580 confirms when buffer storage tank 570 is full and subsequently the plant control system closes solenoid valve 520 to prevent tank overflow. Level switch 590 confirms that buffer storage tank 570 is empty and prevents the pump 620 running dry. [00097] Manual valve 610 is used to collect samples for analysis. Pump 620 is connected to the buffer storage tank 570 through manual valve 610 used for disconnecting water supply when pump 620 needs replacement or service. The pressure required to operate the water treatment plant 1 is low. Pump 620, usually of centrifugal type, is selected to deliver the maximum flow for treating the water at not more than 200 kPa pressure. Another selection point is the flow rate needed for backwashing the catalytic reactor 860 at around 100 to 150 kPa. The selection of the pump 620 depends also on the pressure drop through the plumbing of the water treatment plant 1 and the additional pressure head to deliver the water to the finished water storage tank 940. [00098] Pressure gauge 630 provides visual indication of overall system pressure. The ORP transmitter 670 has the same function as ORP transmitter 130 in Figure 1. All downstream components and their function in Figure 2 are the same as in Figure 1. In terms of functionality, there is one difference to note that the flow rate through plant 1 in Figure 2 will not decrease when the pressure drop over the catalytic reactor 860 increases. This is because pump 620 is driven through a variable speed drive and the pump speed is adjusted automatically to maintain set flow rate independent of pressure. Flow rate is monitored by flow meter 750. Thus, triggering of backwash operation for the apparatus shown in Figure 2, is done through set point for differential pressure or on operating time. The backwash trigger for the water treatment plant 1 in Figure 1 could be in addition set at a point of minimal flow.

[00099] Following the process fluid diagram of Figure 2, the ORP transmitter 670 indirectly monitors the level of disinfectant in the raw water supplied to the plant 1 to allow correlation and adjustment of chemicals dosed through dosing unit 690 and 770. Sampling valve 680 is to sample water and measure water parameters prior to any chemical addition and treatment. Dosing unit 700 will dose pH correction chemical (acid or alkali) if needed. The reaction vessel 710 allows for oxygen donor reaction time (for example potassium permanganate as with the water treatment plant 1 of Figure 1) of typically 10 minutes. Valve 720 is an air release valve to vent air and gasses from the top of the reaction tank 710. Pressure transmitter 730 monitors system pressure before the catalytic reactor 860. This pressure is also visually indicated by pressure gauge 740. Flow meter 750 monitors the water flow for a particular mode of operation.

[000100] Sampling valve 760 is for sampling the conditioned water before final addition of hypochlorite upstream of the catalytic reactor 860. The important parameters for the conditioned water, pH and ORP, are monitored by transmitters 780 and 790. Final conditioned water can be sampled and tested through sampling valve 800. Valves 810 and 820 are shown in Figure 2 in the normal operating mode and will change position for backwashing the catalytic reactor 860. Functionality is the same as for corresponding items in Figure 1. Items 290 through to 430 in Figure 1 have the same functionalities as items 830 to 970 in Figure 2 and as described above with reference to Figure 1.

[000101] A pilot field testing plant operating in accordance with the process of the present disclosure, as point of entry water treatment apparatus for supplying an office building, shows the following capabilities. Water aesthetics are significantly improved. In an informal blind taste test, the treated water could not be differentiated from good quality bottled water. Although at the time of analyses the municipal piped water supplied was of overall good quality, comparative water quality data are provided in the Table below.

[000102] Chemical oxygen demand (COD) was measured following American Public Health Association (APHA) method 5220 B.

[000103] Colour was measured following APHA 2120 B.

[000104] Turbidity was measured following APHA 2130 B.

[000105] Total organic carbon was measured following APHA 5310 B.

[000106] Total heavy metals were measured following USEPA 6020.

[000107] Suspended solids were measured following APHA 2540 D.

[000108] Free chlorine was measured following APHA 4500-Cl D. [000109] There was an improvement in the water aesthetics. Colour, ammonia, total organic carbon and COD were decreased, though further ammonia reduction would be possible through including an ion exchange step. This is consistent with good appearance and taste of the treated water. The treatment process preserves fluoride, good for dental and skeletal health at the level measured in the treated water, 0.23 mg/L. Calcium and magnesium are essential to human health and were not significantly removed. This is a beneficial aspect of the process, not demineralizing the water indiscriminately as is the case with reverse osmosis.

[000110] Metals such as aluminium, cadmium, copper and nickel were decreased in concentration. Cadmium was present in the raw water at maximum acceptable limit according to more demanding country standards. Tin and zinc were increased in the distribution network but are far from any health concern at the level present in the tap water. Manganese is used in the process as catalytic metal and is added during treatment. Manganese is thought to be an essential element but is not recommended to exceed 0.050 mg/L.

[000111] In most countries, the total trihalom ethanes (THM) have a regulated maximum limit. The lowest level is presently 0.080 mg/L. Test data of treated water shows a total of 0.0376 which is a safe limit. Chloroform is not regulated in all countries as an individual component of THM. This is because chloroform is not understood to pose a health risk as with other THM. World Health Organization drinking water guidelines specify a maximum of 0.300 mg/L for chloroform. This is too high for many countries with more restrictive total THM. A small amount of chloroform was added due to addition of sodium hypochlorite in the treatment process but the addition is not significant. Overall THM were kept low also because the disinfectant added as residual for the distribution network was chlorine dioxide which has been shown to yield lower levels of disinfection by-products.

[000112] If needed, the process could be adjusted to decrease THM in the treated water. This could be achieved by completely eliminating addition of sodium hypochlorite, just using it during backwashing of the catalytic reactor 320, 860. In compensation for maintaining suitable ORP, the addition of potassium permanganate is increased.

[000113] When adding chlorine dioxide as disinfectant, the disinfection by-products generated are chlorite and chlorate. Of some health concern, chlorite should be kept in control to less than 0.7 mg/L or according to the particular country standard. In some countries chlorate is also regulated. Only chlorate was increased and at a limit lower than any country standard. No pathogenic bacteria of concern were detected in the raw water and the water at the tap. Disinfection performance of the process is compliant with WHO standards and addition of chlorine dioxide is a complementary barrier helpful to assurance that treated water is pathogen free while also providing residual for the distribution network.

[000114] The contents of all references and published patents and patent applications cited throughout the application are hereby incorporated by reference.

[000115] 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.