Patent Description:
There is an increasing demand on the availability of clean water as a natural resource throughout the world. Access to clean water is a requirement in all areas of society, ranging from domestic dwellings and agriculture to disaster areas and areas with a high risk of drought. With an increasing population, more strain is being placed on the availability of clean water in many areas around the world.

A large amount of contaminated water is generated by each household every day. Some of this wastewater originates from toilets and may be subject to faecal contamination. This wastewater is classified as black water and is generally treated in a sewage treatment facility. On the other hand, wastewater from all other sources (e.g. from sinks, baths, showers, kitchen, harvested rain water and laundry) is classified as greywater. By treating this mildly contaminated greywater, it can be re-used for applications such as toilet flushing, landscape and agricultural irrigation.

Various methods for treating greywater are known. For example, the greywater can be filtered and treated with chlorine to prevent bacterial growth. Other methods include UV treatment, and treating the greywater with hydrogen peroxide in combination with UV treatment.

<CIT> describes a water treatment system and method, which involves electrolysis to treat water.

<CIT> describes a method for treating wastewater using a catalytic wet oxidation process with a Pt-Pd/Al2O3 and a Cu/Al2O3 catalyst at a process temperature of <NUM> to <NUM> to produce hydroxyl radicals.

<CIT> relates to the use of catalyst compositions, comprising preferably gold and palladium, to produce a hydrogen peroxide solution.

The present invention provides a water treatment process comprising:.

Also described herein (not part of the invention) is a water treatment apparatus comprising.

The contaminated water may be wastewater, for example, greywater. Other examples of contaminated water that may be treated using the process of the present disclosure include river water, rain water, seawater and/or brackish water. In a preferred embodiment, the process and apparatus described herein may be used to treat greywater. For example, the process and apparatus may be used to treat greywater from a domestic or commercial sources to produce treated water that can be stored and recycled for use (e.g. for toilet flushing, landscape and agricultural irrigation, washing and cleaning).

In an alternative embodiment, the process and apparatus described herein may be used as part of a water purification process, for example, as a disinfection step. Examples of purification processes include wastewater treatment, desalination and sewage treatment processes.

By reacting hydrogen and oxygen in the presence of the catalyst and the contaminated water, oxidative species can be generated in situ to reduce the level of biological contaminants in the contaminated water. Examples of oxidative species include hydrogen peroxide and free radicals e.g. generated during or as a result of the reaction of hydrogen and oxygen in the presence of the catalyst. Examples of radicals that may provide an oxidative effect include those formed during formation or upon decomposition of hydrogen peroxide e.g. hydroxyl and hydroperoxy species. These radicals may have a disinfectant or antimicrobial effect.

Without wishing to be bound by any theory, the reaction between hydrogen and oxygen in the catalyst may produce effective amounts of oxidative species, for example, hydrogen peroxide, which perform an antimicrobial function. This is surprising as prior art methods of direct hydrogen peroxide production generally require the reaction between hydrogen and oxygen to be carried out in the presence of an organic solvent medium (e.g. methanol) to generate hydrogen peroxide in appreciable amounts. In the present invention, the oxidative species (e.g. hydrogen peroxide and/or radicals) are generated in situ. Accordingly, their local concentration at the catalyst's surface may be high, enhancing their antimicrobial effect on contaminants in the surrounding contaminated water medium. The in situ generation of oxidative species (e.g. radicals) also avoids the need for storing pre-formed hydrogen peroxide. Hydrogen peroxide needs to be stabilised with stabilising agents when stored and this reduces its potency as an oxidising agent. By generating hydrogen peroxide in situ, a disinfectant effect can be achieved without the need for stabilisation; the potency of the antimicrobial effect is thus enhanced.

Hydrogen and oxygen react in the presence of the catalyst and contaminated water to generate radical species in situ, which reduce the levels of biological contaminants in the contaminated water. These oxidative radical species may include radical species that are formed on route to the formation of hydrogen peroxide and/or are generated as a result of the decomposition of hydrogen peroxide in the presence of the catalyst. The radical species include hydrogen radicals and may include oxygen-containing radicals. These hydrogen radicals (H·) may be formed on route to the formation of hydrogen peroxide in the presence of the catalyst and/or as a result of the decomposition of any hydrogen peroxide generated in the presence of the catalyst.

Without being bound by any theory, it is believed that, by reacting hydrogen and oxygen in the presence of the catalyst and contaminated water, a greater flux of radical species (e.g. hydrogen radicals) can be achieved. Such species can react with contaminants in the water, thereby providing an antimicrobial effect.

The catalyst may be any catalyst that is suitable for the direct synthesis of hydrogen peroxide. Such catalysts are well-known and described in, for example, <CIT>, <CIT> and <CIT>.

The catalyst in the process of the invention comprises palladium and gold or palladium and tin.

Preferably, the catalyst is a bimetallic catalyst. For example, the catalyst may comprise an alloy of palladium and gold or palladium, gold and platinum. In a preferred embodiment, the catalyst comprises palladium and gold. The catalyst may comprise an alloy of palladium and gold. In one embodiment, the catalyst comprises palladium, in combination with tin.

The catalyst may be a supported catalyst. For example, the catalyst may comprise at least one metal deposited on a support. The total amount of metal in the catalyst may be less than <NUM> wt % of the catalyst, for example, less than <NUM> wt. % of the catalyst, or less than <NUM> wt. % of the total weight of the catalyst. In certain embodiments, the total amount of metal in the catalyst may be greater than <NUM> wt% of the catalyst, for example, greater than <NUM> wt %, or greater than <NUM> wt % of the catalyst. In certain embodiments, the total amount of metal in the catalyst may be <NUM> to <NUM> wt %, for example, <NUM> to <NUM> wt %, or <NUM> to <NUM> wt % of the total weight of the catalyst. In some embodiments, the total amount of metal in the catalyst may be <NUM> to <NUM> wt %, for example, <NUM> to <NUM> wt %, or <NUM> to <NUM> wt % of the total weight of the catalyst.

The total amount of palladium and gold may be less than <NUM> wt % of the catalyst, for example, less than <NUM> wt. % of the catalyst, or less than <NUM> wt. % of the total weight of the catalyst. In certain embodiments, the total amount of palladium and gold in the catalyst may be greater than <NUM> wt% of the catalyst, for example, greater than <NUM> wt %, or greater than <NUM> wt % of the catalyst. In certain embodiments, the total amount of palladium and gold in the catalyst may be <NUM> to <NUM> wt %, for example, <NUM> to <NUM> wt %, or <NUM> to <NUM> wt % of the total weight of the catalyst. In some embodiments, the total amount of palladium and gold in the catalyst may be <NUM> to <NUM> wt %, for example, <NUM> to <NUM> wt %, or <NUM> to <NUM> wt % of the total weight of the catalyst. In a preferred embodiment, the total amount of palladium and gold is <NUM> to <NUM> wt% based on the total weight of the catalyst.

Where two metals are used in the catalyst, the ratio of the first metal to the second metal may be <NUM>:<NUM> to <NUM>:<NUM>. In some embodiments, the first metal and the second metal may be transition metals. In other embodiments, the first metal may be tin and the second metal, for example, palladium. In one embodiment, where the catalyst comprises palladium and gold, the ratio of palladium to gold may be <NUM>:<NUM> to <NUM> :<NUM>, for example, from <NUM>:<NUM> to <NUM> :<NUM>, or from <NUM>:<NUM> to <NUM> :<NUM>, or from <NUM>:<NUM> to <NUM> :<NUM>, or from <NUM>:<NUM> to <NUM> :<NUM>, or from <NUM>:<NUM> to <NUM> :<NUM>, or from <NUM>:<NUM> to <NUM> :<NUM>, or <NUM> :<NUM>. Where two metals are used in the catalyst, the metals may be deposited on the support as an alloy.

As mentioned above, the catalyst may be supported. In certain embodiments, the catalyst support is an organic or inorganic support, for example, catalyst support selected from the group consisting of carbon supports, oxide supports and silicate supports, for example, from SiO<NUM>, TiO<NUM>, Al<NUM>O<NUM>, CeO<NUM>, Nb<NUM>O<NUM>, W<NUM>O<NUM>, ZrO<NUM>, Fe<NUM>O<NUM>, silica-alumina, molecular sieves and zeolites, and mixtures thereof. Suitable carbon supports are graphite, carbon black, glassy carbon, activated carbon, highly orientated pyrolytic graphite, single-walled and multi-walled carbon nanotubes. In certain embodiments, the catalyst support comprises or is an oxide support, for example, an oxide support selected from SiO<NUM>, TiO<NUM>, Al<NUM>O<NUM>, CeO<NUM>, Nb<NUM>O<NUM>, W<NUM>O<NUM>, ZrO<NUM>, Fe<NUM>O<NUM> and mixtures thereof. In certain embodiments, the catalyst support is an acidic catalyst support. Acidic catalyst supports include, for example, niobic acid support, heteropolyacid-based support, acid-treated carbon support, sulfated zirconia/silica support, and a support comprising an oxide other than zirconium oxide (e.g., silica) and a precipitate layer of zirconium oxide. Heteropolyacid supports include supports of the formula CsxH<NUM>·xPW<NUM>O<NUM>, where x is from <NUM> to <NUM>, which may be prepared by the addition of a Cs source, such as CsNO<NUM>, to aqueous H<NUM>PW<NUM>O<NUM>. In an advantageous embodiment, the catalyst support comprises or is SiO<NUM>. In another advantageous embodiment, the catalyst support comprises or is TiO<NUM>. In certain embodiments, the catalyst does not comprise carbon supports. In certain embodiments, the catalyst does not include a heteropolyacid support.

The catalyst support may comprise at least <NUM> wt. % of the catalyst, based on the total weight of the catalyst, for example, at least <NUM> wt. % of the catalyst, or at least <NUM> wt. % of the catalyst, or at least <NUM> wt. % of the catalyst, or at least <NUM> wt. of the catalyst, or at least <NUM> wt. % of the catalyst, or at least <NUM> wt. % of the catalyst, or at least <NUM> wt. % of the catalyst, or at least <NUM> wt. % of the catalyst, or equal to or greater than <NUM> wt. % of the catalyst. In certain embodiments, the catalyst support comprises from <NUM> wt. % to up to but not including <NUM> wt % of the catalyst, for example, to <NUM> wt. % of the catalyst. In some examples, the support forms from <NUM> wt. % to up to but not including <NUM> wt % of the catalyst, or from <NUM> wt. % to <NUM> wt. % of the catalyst.

In a preferred embodiment, the catalyst comprises palladium and gold supported on an oxide support, for example, silica, silicate or TiO<NUM> support. The total amount of palladium and gold on the catalyst may be <NUM> to <NUM> wt %, for example, <NUM> to <NUM> wt %, or <NUM> to <NUM> wt % of the total weight of the catalyst. In a preferred embodiment, the total amount of palladium and gold is <NUM> to <NUM> wt% based on the total weight of the catalyst. The ratio of palladium to gold may be <NUM>:<NUM> to <NUM> :<NUM>, for example, from <NUM>:<NUM> to <NUM>:<NUM>, or from <NUM>:<NUM> to <NUM>:<NUM>, or from <NUM>:<NUM> to <NUM>:<NUM>, or from <NUM>:<NUM> to <NUM>:<NUM>, or from <NUM>:<NUM> to <NUM>:<NUM>, or from <NUM>:<NUM> to <NUM>:<NUM>, or <NUM>:<NUM>. The palladium and gold may form an alloy on the support.

The catalyst may be prepared by any suitable preparative method, preferably starting from suitable metal precursors. For example, the metal may be deposited onto the catalyst support in the form of metal oxides or metal ions, e.g., metal salt, by any known method to form a catalyst precursor. Where two metals are used (e.g. palladium and gold), the metals may be deposited simultaneously or sequentially, advantageously simultaneously. After deposition of the metal precursors onto the catalyst support, a catalyst precursor may be recovered by any suitable separation method, such as evaporation, filtration, decantation and/or centrifugation. The recovered catalyst precursor may be washed and dried, for example, at a temperature of between <NUM> and <NUM>, typically greater than <NUM>, for example, greater than <NUM>, and typically, less than <NUM>, for example, less than <NUM>, e.g., a temperature of from <NUM> to <NUM>. Drying may be conducted over a suitable period of time. The catalyst precursor may then be transformed into the corresponding catalyst via at least one of a heat treatment, reductive treatment, e.g., chemical reduction in the presence of a reducing agent, or electrochemical reduction. Heat treatment may be conducted a temperature of from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>. Heat treatment may be conducted under any type of atmosphere such as, for example, oxygen containing atmosphere, inert atmosphere or reducing atmosphere. In certain embodiments, the heat treatment may be conducted under air, oxygen, nitrogen, argon, hydrogen or mixtures thereof.

Any suitable reactor may be employed. For example, a stirred reactor, such as an autoclave equipped with stirring means, a loop reactor or a tube reactor. The process may be conducted batch-wise, continuously or semi-continuously. The process is preferably carried out continuously. The catalyst may be in the reactor as a fixed bed or fluidized bed.

The reactor includes an inlet for introducing contaminated water into the reactor, and an outlet for withdrawing treated water from the reactor. The inlet may be coupled to a source of contaminated water, for example, greywater from household or commercial waste. The outlet may be coupled to a storage unit or tank, for example, for storing treated water for re-use in, for instance, cleaning, washing, toilet flushing, landscape or agricultural irrigation (see below). Alternatively, the inlet may be coupled to a source of water that has been treated or is being treated as part of a water treatment process, such as a desalination process. The outlet may be coupled to a storage tank or further downstream water treatment unit (s).

The contaminated water may be introduced into the reactor continuously and the treated stream may be removed from the reactor continuously. A portion of the treated stream may be recycled to the reactor.

As described above, hydrogen and an oxygen-containing gas are introduced into the reactor, where the gas flows into contaminated water contained in the reactor. The hydrogen and oxygen-containing gas may be introduced by feeding (e.g. continuously) the gases through water present in the reactor. Alternatively, the gases may be introduced into the water upstream of the reactor inlet. The hydrogen gas and/or oxygen-containing gas may be introduced continuously e.g. in admixture with a suitable diluent. Suitable diluents include carbon dioxide. Carbon dioxide may also be desirable as it may dissolve in the contaminated water to form carbonic acid, which may have a stabilizing effect on any oxidative species produced upon contact with the catalyst. In a preferred embodiment, the hydrogen gas is introduced in admixture with air, which acts as a source of oxygen and as a diluent.

In a preferred embodiment, an electrolyser is used in combination with the reactor. The electrolyser may be in fluid communication with the reactor. According to one embodiment, the water treatment apparatus comprises a reactor as described herein and an electrolyser. The electrolyser may be used to produce the hydrogen that is fed into the reactor. Hydrogen may be produced by electrolysing water. This may be water (e.g. clean water) from a separate source. Alternatively, the water may be contaminated water, for example, a portion of the contaminated water that is fed into the reactor. In yet another alternative, a portion of the treated (e.g. disinfected) water produced in the reactor is withdrawn and fed to the electrolyser.

In one embodiment, a portion of water passing through the electrolyser is recycled.

As described above, the process of the present invention involves the reaction between hydrogen and oxygen in the presence of the catalyst and contaminated water. This reaction generates oxidative species in situ to reduce the level of biological contaminants in the contaminated water. Examples of oxidative species include hydrogen peroxide, and oxidative species formed upon decomposition of hydrogen peroxide e.g. hydroxyl and hydroperoxy species, which may also have an antimicrobial effect.

In embodiments not part of the present invention the reaction between hydrogen and oxygen is conducted at a temperature of from -<NUM> to <NUM>, for example, from -<NUM>, to <NUM>. According to the present invention the reaction between hydrogen and oxygen is conducted at a temperature of from -<NUM> to <NUM>, or from -<NUM> to <NUM>, or from - <NUM> to <NUM>, or from -<NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, or at a temperature of <NUM>, or <NUM>, or <NUM>, or <NUM>, or <NUM>.

The total pressure in the reactor (measured at <NUM>) may vary according to the reaction conditions, amounts of starting materials and the type of reactor. In certain embodiments, the total pressure in the reactor is from <NUM> to <NUM> MPa, for example, from <NUM> to <NUM> MPa, or from <NUM> to <NUM> MPa. In one embodiment, the total pressure in the reactor is <NUM> to <NUM> MPa, for example, <NUM> to <NUM> MPa or <NUM> to <NUM> MPa. In another embodiment, the total pressure in the reactor is <NUM> to <NUM> MPa.

The contact time with the catalyst may vary according to the reaction conditions and amounts of starting materials and may be adjusted accordingly. In certain embodiments, the reaction time is from <NUM> seconds to <NUM> hours, for example <NUM> second to <NUM> minutes.

Any source of hydrogen can be used in the process of this invention. Likewise, any source of oxygen can be employed, including air or pure oxygen. The hydrogen and oxygen-containing gas may be introduced using diluents, for example, nitrogen or carbon dioxide. In a preferred embodiment, hydrogen is produced by electrolysis, for example, in an upstream step and fed to the reactor with air. The air may act as a source of oxygen and a diluent.

In one embodiment, hydrogen is fed to the reactor as a mixture of hydrogen and air. The hydrogen may form less than <NUM> vol %, preferably less than <NUM> vol % of the mixture. In a preferred embodiment, the hydrogen may form <NUM> to <NUM> vol % of the mixture. The total pressure of the mixture that is fed to the reactor may be <NUM> to <NUM> MPa, for example, from <NUM> to <NUM> MPa, or from <NUM> to <NUM> MPa. In one embodiment, the total pressure in the reactor is <NUM> to <NUM> MPa, for example, <NUM> to <NUM> MPa or <NUM> to <NUM> MPa. In another embodiment, the total pressure in the reactor is <NUM> to <NUM> MPa.

The ratio of hydrogen to oxygen-containing gas is <NUM>:<NUM> to <NUM>:<NUM>, preferably <NUM> : <NUM> to <NUM>: <NUM>, for example <NUM>:<NUM> to <NUM>:<NUM>. It may be advisable to employ H<NUM>:O<NUM> ratios with appropriate diluent pressure to avoid using explosive mixtures.

As discussed above, the hydrogen and/or oxygen may be produced by electrolysis of water. The wastewater treatment apparatus described herein may include an electrolyser that is coupled to the reactor.

The process of the present invention may be used to treat any contaminated water stream. As described above, the contaminated water stream may be a greywater stream. For example, greywater from domestic, commercial or industrial sources may be treated using the process of the present invention.

In an alternative embodiment, the process of the present invention may be used as one of many steps of a water treatment or water purification process, for example, a desalination process.

The contaminated water may be contaminated with microbial contaminants, for example, pathogens. The pathogens may be viable, vegetative, planktonic and/or sessile pathogens. The contaminated water may contain biofilm. In one embodiment, the contaminated water contains viable pathogens. Examples of pathogens that may be present include bacteria, viruses, fungi and protozoa. The level of microbial contamination may suitably be measured by quantifying the total viable bacterial load in a given sample. This may be achieved by standard techniques, which are well known in the art, such as, Total Bacterial Count (TBC) (also known as Heterotrophic Plate Count (HPC), Heterotrophic Colony Count (HCC), Aerobic Plate Count (APC), Total Plate Count (TPC), or Standard Plate Count (SPC)). Such methods represent a measure of viable microorganisms present in a sample that could grow aerobically or anaerobically on a suitable medium (e.g. agar) at selected incubation conditions (usually <NUM> and <NUM>, for 48hrs). Depending on the desired final composition of the water sample, useful variations of these methods can suitably comprise, for example, measuring the total amount of viable aerobic and anaerobic bacteria. Furthermore, typically, the presence or quantity of specific indicator organisms may also be assayed, which may include, for example, faecal coliforms, such as E. The quantities of bacteria are generally expressed as Colony Forming Units (CFU) per unit sample (e.g. CFU per unit volume). Where the contaminated water sample is contaminated with pathogens, for example including but not limited to bacteria, prior to treatment the water may typically have a total number of viable pathogens (e.g. bacteria) of between <NUM><NUM> CFU/ml to <NUM><NUM> CFU/ml. Advantageously, once treated, the water has a CFU/ml that is lower than its starting value. Where the contaminated water sample is contaminated with micro-organisms and/or pathogens, for example bacteria, depending on the total number of viable micro-organisms or pathogens in the untreated sample, treatment of the water sample may reduce the total number of viable micro-organisms or pathogens present in the water sample by at least <NUM><NUM> CFU/ml, at least <NUM><NUM> CFU/ml, at least <NUM><NUM> CFU/ml, at least <NUM><NUM> CFU/ml, at least <NUM><NUM> CFU/ml, at least <NUM><NUM> CFU/ml, at least <NUM><NUM> CFU/ml, at least <NUM><NUM> CFU/ml, at least <NUM><NUM> CFU/ml, at least <NUM><NUM> CFU/ml relative to an untreated control sample. The target CFU/ml may vary depending on the end use of the treated water. However, it may be possible to reduce the target CFU/ml of the water to less than <NUM> CFU/ml, or less than <NUM> CFU/ml.

Advantageously, where a water sample to be treated is contaminated with micro-organisms and/or pathogens, for example bacteria, treatment of the sample in accordance with the invention may reduce levels of the total amount of viable micro-organisms or pathogens in the sample relative to those of an untreated control sample. In particular, levels of the total amount of viable micro-organisms or pathogens in the treated sample may be reduced with respect to those of an untreated control sample by at least a <NUM> log<NUM> reduction, for example, at least a <NUM> log<NUM>, at least a <NUM> log<NUM>, at least a <NUM> log<NUM>, at least a <NUM> log<NUM> or at least a <NUM> log<NUM> reduction. Levels of the total amount of viable bacteria in the sample may be reduced with respect to those of an untreated control sample by up to a <NUM> log<NUM> reduction, for example, up to a <NUM> log<NUM>, up to a <NUM> log<NUM>, up to a <NUM> log<NUM>, up to a <NUM> log<NUM>, up to a <NUM> log<NUM>, up to a <NUM> log<NUM> or up to a <NUM> log<NUM> reduction.

Advantageously, where a water sample to be treated is contaminated with bacteria, for example E. coli, treatment of the sample in accordance with the invention may reduce levels of the total amount of viable bacteria in the sample relative to those of an untreated control sample. In particular, levels of the total amount of viable bacteria in the sample may be reduced with respect to those of an untreated control sample by at least a <NUM> log<NUM> reduction, for example, at least a <NUM> log<NUM>, at least a <NUM> log<NUM>, at least a <NUM> log<NUM>, at least a <NUM> log<NUM> or at least a <NUM> log<NUM> reduction. Levels of the total amount of viable bacteria in the sample may be reduced with respect to those of an untreated control sample by up to a <NUM> log<NUM> reduction, for example, up to a <NUM> log<NUM>, up to a <NUM> log<NUM>, up to a <NUM> log<NUM>, up to a <NUM> log<NUM>, up to a <NUM> log<NUM>, up to a <NUM> log<NUM> or up to a <NUM> log<NUM> reduction. According to preferred aspects of the invention, where a water sample to be treated is contaminated with bacteria, treatment of the sample in accordance with the invention may reduce levels of the total amount of viable bacteria in the water sample by between a <NUM> log<NUM> to <NUM> log<NUM> reduction, for example, a <NUM> log<NUM> to <NUM> log<NUM> reduction, preferably a <NUM> log<NUM> to <NUM> log<NUM> reduction relative to an untreated control sample.

Optionally, where a water sample to be treated is contaminated with micro-organisms and/or pathogens for example bacteria, treatment of the sample in accordance with the invention may reduce the total viable number of a particular target micro-organism or pathogen, for example a particular target bacterium (for example E. coli) or of selected indicators (For example, coliforms) in the sample relative to those in an untreated control sample in the same way as described above. Similarly, where a water sample to be treated is contaminated with one or more viruses, treatment of the sample in accordance with the invention may reduce the total number of active, intact or infective virus in the treated sample relative to an untreated control sample in the same way as described above.

In a preferred embodiment, the contaminated water is water that contains viable pathogens, for example, viable culturable and non-culturable pathogens. Once treated, the water may no longer contain viable pathogens, allowing the treated water to be stored for re-use.

Examples of pathogens that may be initially present in the contaminated water prior to treatment may include:.

In one embodiment, the rate of flow of the contaminated water, hydrogen and/or oxygen-containing gas is controlled at a rate dependent on e.g. the CFU/ml of the contaminated water stream that is introduced via the inlet and/or the treated water stream removed via the outlet of the reactor.

Water that is treated or produced according to the process described herein may be used for a range of applications. The treated water is disinfected and, advantageously, may contain little or substantially no viable pathogens. Accordingly, the treated water may be stored and used for applications including washing, cleaning, irrigation and toilet flushing.

The disinfected water may also be used for healthcare applications, for example, as a diluent for pharmaceutical formulations, for example, topical formulations and cleaning liquids, including contact lens liquids.

In some embodiments, the process of the present invention may be used as a step in a series of water treatment steps to produce e.g. potable water.

Au-Pd catalysts were prepared as described below.

For the preparation of <NUM>% Au-Pd supported catalyst, the required amounts of HAuCl<NUM>·<NUM><NUM>O and PdCl<NUM>/HCl solution (HCl concentration: <NUM>) were charged into a clean <NUM> round-bottom flask, the volume of the solution was adjusted using deionized water to a total volume of <NUM>, and the flask immersed into an oil bath on a magnetic stirrer hot plate. The solution was stirred at <NUM> rpm and the temperature of the oil bath was raised from room temperature to <NUM> over a period of <NUM>. At <NUM>, metal oxide support material [<NUM> TiO<NUM> (Degussa Evonik P25)] was added slowly over a period of <NUM>-<NUM> with constant stirring. The subsequent slurry was stirred at <NUM> for an additional <NUM>. Following this, the temperature of the oil bath was raised to <NUM> for <NUM> leaving a dry solid. The solid powder was ground thoroughly to form a uniform mixture. <NUM> of the sample was reduced at <NUM>/min under a steady flow of gas (<NUM>% H<NUM>/Ar) for <NUM> hours.

Reactions were performed in a continuous flow micro reactor. The reactor was constructed using Swagelok components with an internal diameter of <NUM>/<NUM> of an inch. Brooks gas flow controllers control the flow of either <NUM>% H<NUM>/CO<NUM>, <NUM>% O<NUM>/CO<NUM> or a combination of H<NUM> + O<NUM>/CO<NUM>. Water contaminated with E. coli was pumped through the system using an Agilent HPLC pump and the overall pressure of the reactor was controlled with a Swagelok back pressure regulator. The catalyst bed (when present) was submersed in a temperature controlled water bath and pressure gauges were positioned before and after the water bath to monitor pressure drops. Sampling was carried out using a gas liquid separator (GLS) (<NUM>) fitted with a valve and positioned before the back pressure regulator. In a typical reaction, <NUM> of catalyst was pelleted (diameter ~<NUM>-<NUM> micron) and packed into the micro reactor catalyst bed supported by glass wool. The reactor was typically cooled to <NUM> in the water bath. The system was pressurised to <NUM> bar (unless otherwise stated) with a H<NUM>:O<NUM> ratio of <NUM>:<NUM> unless otherwise stated. Total gas flows were kept at <NUM> min-<NUM> and once the reactor was fully pressurised, solvent was pumped through the system at a rate of <NUM> min-<NUM>.

An initial cell density of <NUM><NUM> CFU/ml was used to perform blank and control experiments using an empty reactor. <FIG> shows the observed E. coli cell density after one pass through the reactor system under different reaction atmospheres with and without the catalyst present. It was observed that when no catalyst was present and the reactor was operated at <NUM> bar with a flow of <NUM> min-<NUM> of either <NUM>% H<NUM>/CO<NUM>, <NUM>% O<NUM>/CO<NUM> or a combination of H<NUM> + O<NUM>/CO<NUM> the cell density decreased from <NUM><NUM> to <NUM><NUM> CFU/ml. The observed decrease of two orders of magnitude from the initial cell density irrespective of the atmosphere used may be due to either the effect of the pressure or the possible acidification of the working solution by dissolved CO<NUM>. However, in either case full inactivation of the bacteria was not achieved when no catalyst was present.

Analogous reactions were carried out in the presence of Au-Pd/TiO<NUM> catalyst (<NUM>), also shown in <FIG>. In the presence of CO<NUM> and H<NUM> a further reduction in cell density by an order of magnitude to <NUM><NUM> CFU/ml is achieved relative to the equivalent experiment without catalyst present. This could indicate that the catalyst itself has some intrinsic antibacterial activity which could arise from the presence of Au or Pd nanoparticles. The reaction carried out in the presence of <NUM>% O<NUM>/CO<NUM> further reduced the cell density to <NUM><NUM> CFU/ml which indicates that oxidative environments in the presence of the catalyst are effective for destruction of bacteria.

When the reaction was carried out in the presence of both H<NUM> and O<NUM> no live bacteria were observed in the reaction effluent, even in the undiluted reaction sample, and no H<NUM>O<NUM> was observed in the effluent. This indicates that in situ generated H<NUM>O<NUM> and/or radicals are effective in removing high levels of bacterial contamination, up to <NUM><NUM> CFU/ml, from the water stream (e.g. by generating oxidative species through the activation of O<NUM> and H<NUM> to generate either H<NUM>O<NUM> or subsequent hydroxyl and hydroperoxy species, through the synthesis and decomposition of H<NUM>O<NUM>). These reactions were carried out at <NUM> bar total pressure of the reactant gases. Analogous reactions carried out at <NUM> bar total pressure with the same gas flow rates showed identical results indicating that there is sufficient H<NUM>O<NUM> produced at this lower pressure to inactivate <NUM><NUM> CFU/ml.

Further experiments shown in <FIG> demonstrate that when using <NUM> bar total pressure and <NUM> min-<NUM> total gas flow of <NUM>% O<NUM>/CO<NUM> and <NUM>% H<NUM>/CO<NUM> was capable of complete inactivation of <NUM><NUM> CFU/ml from the solution. This highlights the efficiency of the H<NUM>O<NUM> system for the inactivation of bacterial contaminants from a wastewater stream.

By comparing the rate of E. coli killing by H<NUM>O<NUM> addition alone with the rate of killing after passing thorough the reactor, even taking the difference in pressure into account, it was observed that reacting H<NUM> and O<NUM> in situ was much more efficient. <NUM> ppm of added pre-formed H<NUM>O<NUM> takes <NUM> to completely eliminate <NUM><NUM> CFU/ml of E. The microreactor system employed in this example eliminated all viable bacteria from a <NUM><NUM> CFU/ml solution during the residence time of the liquid passing over the catalysts. This will be of the order of seconds meaning that the in situ approach much more efficient than adding commercially produced H<NUM>O<NUM>. This could arise from a number of factors including the difference in stability between stabilized commercial H<NUM>O<NUM> and unstabilized synthesized H<NUM>O<NUM> or the catalytic decomposition of H<NUM>O<NUM> over the catalyst bed during synthesis.

Experiments were then carried out using a gas feed comprising <NUM>% H<NUM>/air to simulate a gas feed that could easily be generated by water electrolysis on potential applications sites. To carry out this experiment the H<NUM>:O<NUM> ratio was adjusted from <NUM>:<NUM> to <NUM>:<NUM>. It has previously been shown that deviation from a stoichiometric H<NUM>:O<NUM> ratio leads to a decrease in the amount of H<NUM>O<NUM> synthesized. Also the removal of CO<NUM> as a diluent is likely to destabilize the H<NUM>O<NUM> synthesized by removal of the carbonic acid from the working solution. However, in this application the greater instability may be beneficial in generating reactive intermediates. Reactions were carried out at various pressures between <NUM> and <NUM> bar to investigate if inactivation of E. coli could be carried out at lower pressures. <FIG> shows that from a starting solution containing <NUM><NUM> CFU of E. coli a small degree of inactivation is seen at pressure below <NUM> bar. At <NUM> and <NUM> bar total pressure full inactivation is observed. Promisingly, this demonstrates that full inactivation of <NUM><NUM> CFU/ml of E. coli can be carried out using a dilute hydrogen feed and synthetic air as diluent. Gas flow rates have also been shown to have marked effects on the disinfection effect (<FIG>). At higher gas flow rates, the mass transfer between gas and liquid is increased, but probably more important is the increase in the rate of mass transfer through the liquid layer surrounding the catalyst surface.

To compare the efficiency of in situ vs ex situ inactivation of bacteria by H<NUM>O<NUM>, reactions were carried out passing solutions containing E. coli with various amounts of H<NUM>O<NUM> through the reactor system containing the AuPd catalyst under a pressure of synthetic air. Solutions of E. coli and H<NUM>O<NUM> were mixed immediately prior to being pumped into the reactor to minimise any cell death. The results shown in <FIG> demonstrate that when solutions containing initial E. coli concentrations of ~<NUM><NUM> CFU/ml with <NUM>-<NUM> ppm H<NUM>O<NUM> were passed through the reactor complete inactivation was not observed, with <NUM><NUM>-<NUM><NUM> CFU/ml remaining in solution at the exit of the reactor. Starting from a similar concentration by utilising in situ H<NUM>O<NUM> generated from <NUM>% H<NUM> in air full inactivation of viable cells was observed.

In this Example, electron paramagnetic resonance (EPR) spectroscopy was carried out on an aqueous solution containing commercially available hydrogen peroxide as it was passed over an AuPd catalyst. As a comparison, ESR spectroscopy was performed on an aqueous solution containing bubbled hydrogen and oxygen gas as it was passed over an AuPd catalyst. The results are shown in <FIG>.

In the case of commercial hydrogen peroxide, hydroxyl (·OH) spin trap adducts were observed resulting from the generation of OH or a decomposition of the hydroperoxt (·OOH) spin trap adduct. When using hydrogen gas and oxygen gas, the EPR revealed the presence of a higher concentration of the oxygen based spin trap adducts and also the presence of hydrogen (H·) radicals, which were not observed when using pre-formed hydrogen peroxide. These initial results suggest that, by using hydrogen and oxygen, a greater flux of radical species can be achieved as a result of either generating high local concentrations of hydrogen peroxide which is decomposed, or that radicals are formed in the steps leading to hydrogen peroxide synthesis which are active against the microorganisms that are present. When no catalyst is present, no radical signals are present and the presence of a radical trap within the reaction gases suppresses antimicrobial activity.

Claim 1:
A water treatment process comprising:
contacting contaminated water with a catalyst, wherein the catalyst comprises palladium and gold or palladium and tin;
introducing hydrogen and an oxygen-containing gas into the contaminated water, wherein the ratio of hydrogen to oxygen-containing gas is <NUM>:<NUM> to <NUM>:<NUM>; and
reacting hydrogen and oxygen at a temperature of from -<NUM> to <NUM> in the presence of the catalyst and the contaminated water to generate radical species that react with contaminants in the water, wherein the radical species include hydrogen radicals.