A method for decomposing peroxides in contaminated wastewaters

Abstract

Disclosed herein is a method for decomposing a peroxide contaminant in a wastewater. The method comprises contacting the fluid with a catalytic media comprising manganese dioxide, iron oxide and silicon oxide.

Description

A METHOD FOR DECOMPOSING PEROXIDES IN CONTAMINATED WASTEWATERSField of the Invention

[0001] The present invention relates to methods for decomposing peroxides in peroxidecontaminated wastewaters and, in particular to decomposing hydrogen peroxide in wastewater streams from semiconductor manufacturing plants.Background of the Invention

[0002] Wastewaters produced by many industrial processes contain peroxides (commonly hydrogen peroxide) which, due to their antimicrobial attributes, poses a threat to microorganisms which are crucial for biological water treatment processes. Elevated concentrations of peroxides cause negative impacts on wastewater treatment plant efficiency and also pose environmental pollution risks. Thus, it is necessary to remove peroxides from industrial wastewaters before further treatment by biological processes.

[0003] For example, semiconductor production requires significant water usage, resulting in substantial wastewater production, especially during microchip fabrication and packaging stages, where intensive cleaning is required. The wastewater from these cleaning processes contains a considerable amount of hydrogen peroxide.

[0004] Peroxides are intrinsically unstable and slowly undergo spontaneous degradation over time. However, this spontaneous degradation is not compatible with the time requirements of industrial wastewater processing, and a number of techniques have been proposed to accelerate the degradation of hydrogen peroxide in industrial wastewaters. Most of these techniques involve the use of chemical reagents which, whilst effective in decomposing the peroxides, result in undesirable by-products (e.g. which themselves need to be removed before discharge, or which necessitate the use of specialised / complicated equipment). Furthermore, the effectiveness of such reagents can be diminished over time and in the likely event of the wastewater containing other contaminants.

[0005] There is therefore a need for alternative processes to remove peroxides (such as hydrogen peroxide) from peroxide-containing wastewaters (e.g., semiconductor manufacturing wastewater). Ideally such processes would be adaptable for treating large volumes of wastewater having a wide pH range and which contain a diverse range of organic and inorganic contaminants. Ideally, such processes would also maintain their effectiveness in the presence of these contaminants for extended durations.Summary of the Invention

[0006] The present invention provides a method for decomposing a peroxide contaminant (e.g. hydrogen peroxide) in a wastewater. The method comprises contacting the wastewater with a catalytic media comprising manganese dioxide, iron oxide and silicon oxide.

[0007] The inventors have discovered that a catalytic media which is indicated for removing heavy metals (e.g. arsenic, manganese and iron) from drinking water, and which is contraindicated for use with wastewaters containing oxidants such as hydrogen peroxide due to degradation issues, can, in fact, be used to quench hydrogen peroxide from semiconductor manufacturing wastewater. The catalytic media used in the present invention is based on natural mineral media, with the iron and silica oxides combining with the manganese dioxide to enhance the ability of the catalytic media to bond with and decompose peroxides such as hydrogen peroxide. This combination of metal oxides has surprisingly been found to significantly enhance the decomposition efficiency, making the process far more effective than methods using individual components (e.g. manganese dioxide), and thus enabling a high volume of wastewater to be treated in a commercially relevant timeframe. Furthermore, an enhanced durability of the catalytic media during the quenching process has been observed, suspected to be imparted by the combination of metal oxides, thus extending the media’s lifespan over commercially relevant timeframes. The inventors believe that these discoveries will enable their method to be used for decomposing peroxides in large volumes of wastewater in a relatively short timeframe.

[0008] In some embodiments, the catalytic media may comprise between about 70 wt% and 80 wt% manganese dioxide, between about 5 wt% and 30 wt% iron oxide and between about 10 wt% and 15 wt% silicon oxide. References to percentages throughout this patent specification are percentages by weight of the catalytic media (or other composition). The word “about” is intended to be understood as up to ±5% of the stated value.

[0009] In some embodiments, the catalytic media may be provided in the form of granules shaped like pellets or spheres. Such granules may, for example, have particle sizes ranging from about 0.1 mm to about 2 mm, measured across their largest dimension. Granules of the catalytic media have a larger surface area than the same metal oxides in powder form, due to their porous structure.

[0010] In some embodiments, the catalytic media may have a surface area of between about 3 m2 / g and about 13 m2 / g.

[0011] In some embodiments, the peroxide may have a concentration in the wastewater (i.e. pretreatment) ranging from about 0.1 g / L to about 50 g / L. In some embodiments, the peroxide mayhave a concentration in the effluent (i.e. post-decomposition) of no more than about 0.03 g / L peroxide.

[0012] In some embodiments, the contact time between the wastewater and catalytic media may be from about 10 to about 20 minutes.

[0013] In some embodiments, the wastewater may be part of a wastewater stream, for example a semiconductor manufacturing wastewater.

[0014] In some embodiments, decomposition may be caused to occur in a catalytic quenching reactor, in which a bed of the reactor comprises the catalytic media. In such embodiments, after decomposition, the treated wastewater may be collected from underneath the catalytic media bed (i.e. the bottom of the bed) whilst oxygen gas is vented off from the top of the quenching reactor. A flow rate of the wastewater through the media bed may also be controlled to ensure complete decomposition of the peroxide. In some embodiments, the quenching reactor may be periodically backwashed using an oxidant.

[0015] In some embodiments, multiple contacts between the wastewater and the catalytic media may be used in order to even further condition the end product (e.g. if an even further reduced amount of peroxide is required). For example, the treated wastewater may be contacted for a second time with a catalytic media comprising manganese dioxide, iron oxide and silicon oxide (i.e. in the catalytic quenching reactor). Such might be advantageous, for example, in applications where a polish step is required.

[0016] In some embodiments, the method may further comprise conditioning the wastewater before it is contacted with the catalytic media. Such conditioning may, for example, comprise one or more of the following: adjusting the pH of the wastewater, adjusting the conductivity of the wastewater, adjusting the oxidation-reduction potential (ORP) of the wastewater, and filtering the wastewater (particularly if its pH has been adjusted). A contact time between the fluid and any conditioners may be adjusted to provide for a desired level of conditioning.Brief Description of the Drawings

[0017] Features and advantages of the present invention will become apparent from the following description of embodiments thereof, by way of example only, with reference to the accompanying drawings, in which:

[0018] Figure 1 is schematic diagram illustrating a process for hydrogen peroxide destruction in accordance with an embodiment of the invention;

[0019] Figure 2 is schematic diagram illustrating a bench-scale system developed for testing an embodiment of the present invention;

[0020] Figure 3 is a graph showing peroxide quenching performance at 5 min contact time;

[0021] Figure 4 is a graph showing peroxide quenching performance at 10 min contact time;

[0022] Figure 5 is a graph showing peroxide quenching performance at 20 min contact time;

[0023] Figure 6 is a graph showing peroxide quenching performance in long-term operation at 15 min contact time; and

[0024] Figure 7 are graphs showing the removal efficiency of catalytic media at various pH values during performance of an embodiment of the present invention.Description of Embodiments

[0025] As described above, the present invention provides a method for decomposing peroxides such as hydrogen peroxide in wastewaters such as industrial wastewaters. In the method, the wastewater is contacted with a catalytic media comprising manganese dioxide, iron oxide and silicon oxide.

[0026] In the embodiments described in further detail below, the present invention is described in the context of decomposing hydrogen peroxide in a fluid in the form of a wastewater stream such as semiconductor manufacturing wastewater. It will be appreciated, however, that the method has more general applicability than this and might, for example, be used to decompose many different types of peroxide species in many different types of wastewaters.

[0027] Without wishing to be bound by theory, the inventors believe that the decomposition of hydrogen peroxide by the catalytic media occurs in the present invention via the reactions shown in Equations 1-4 (the catalytic media is referred to as “Met-O” in these equations, and elsewhere in the specification). The inventors believe that the breakdown of hydrogen peroxide occurs not solely via direct interaction with the surface of manganese and iron oxides, but also through a propagation reaction, involving intermediates such as hydroperoxide / superoxide anions in the solution. Indeed, the inventors have observed that decomposition of residual hydrogen peroxide in the wastewater continues even after separation from the catalytic media. In effect, the inventors believe that contact between the peroxide-laden wastewater and the catalytic media generates an autocatalytic reaction.H2O2 + [Met-O]OH [Met-O]OH-H2O2(1)[Met-O]OH-H2O2[Met-O] + «OOH + H2O (2)[Met-O] + -OOH [Met-O]H + O2 (gas) (3)[Met-O]H + H2O2 [Met-O]OH + H2O (4)

[0028] The catalytic media used in the present invention includes a mixture of manganese dioxide, iron oxide and silicon oxide. In some embodiments, the catalytic media may consist of these three components, although the effort required to obtain such a level of purity would need to be offset against the cost of doing so and the deleterious effects (if any) of minor amounts of any additional components.

[0029] The catalytic media used in the specific embodiments of the present invention described below was commercially obtained from Starke Aquacare Technologies and is primarily composed of 77 wt% MnCh, 10.86 wt% SiCh, 7.19 wt% Fe2O3. Small proportions (<1 wt%) of other species (e.g., CaO, K2O, S, and P) are used as additives during the manufacturing process and are also present, with the balance being other metal oxides and minor impurities.

[0030] Manganese dioxide is present throughout the media, making up to about 80% by weight of the total catalytic media. Without wishing to be bound by theory, the presence of iron and silica oxides, along with manganese dioxide, is thought to contribute to the ability of the catalytic media to bond with and decompose hydrogen peroxide. This combination of metal oxides has also been found to enhance the peroxide decomposition efficiency and make the process more effective than methods using individual components. This combination of metal oxides has also been found to enhance the durability and hence lifespan of the media. Table 1 shows some of the physical properties of this catalytic media.Table 1Parameter Unit Value / DetailColor - Black to dark brownParticle size mm 0.1-1.0Uniformity coefficient - <1.7Bulk density kg / m31900Moisture content % <1Acid solubility % <1Specific gravity - 4.5Hardness Mohs - 5-6

[0031] The inventors expect that catalytic media including between about 70 wt% and 80 wt% manganese dioxide, between about 5 wt% and 30 wt% iron oxide and between about 10 wt% and15 wt% silicon oxide will be effective.

[0032] Catalytic media having less than 70 wt% MnCh are likely to either reduce the quenching efficiency or increase the required contact time. Catalytic media having greater than 80 wt% MnCh are likely to increase the capital expenditure, with no appreciable increase in efficiency and a potential decrease in durability. In some embodiments, the catalytic media may include about 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt% or 80 wt% MnCh

[0033] Catalytic media having less than 5 wt% Fe2C>3 are likely to either reduce the quenching efficiency or increase the required contact time. Catalytic media having greater than 30 wt% FezOs are likely to increase the capital expenditure for no additional functional benefit. In some embodiments, the catalytic media may include about 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt% or 30 wt% Fe2O3

[0034] Catalytic media having less than 10 wt% SiCh are likely to reduce the mechanical stability of the media. Catalytic media having greater than 15 wt% SiCh are likely to increase the capital expenditure unnecessarily. In some embodiments, the catalytic media may include about 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt% or 15 wt% SiCh.

[0035] The catalytic media may be provided in any suitable form, bearing in mind that it needs to be able to physically interact with peroxides contained in the wastewater in order to decompose these contaminants.

[0036] As noted above, the catalytic media in mineral (i.e. granular) form has a greater surface area and greater durability than in its powder form. In some embodiments therefore, the catalytic media used in the invention comprises or consists of granules shaped like pellets or small spheres. The particle sizes may range from about 0.1 mm to about 2 mm, with an optimal size of between about 0.3 mm and about 1 mm, measured across their largest dimension. Approximately 90% of the catalytic media particles may fall within this preferred size range. Particle size analysis of the catalytic media can be conducted using standard methodologies for particle size distribution (e.g. sieve analysis).

[0037] The catalytic media used in this invention typically possesses a large surface area, providing for the rapid and efficient catalytic decomposition of hydrogen peroxide. At a particle size of 0.45-0.6 mm, the surface area of the catalytic media is approximately 3 m2 / g, while a smaller particle size of 0.3-0.45 mm significantly increases the surface area of the catalytic mediato around 13 m2 / g. The specific surface area of the catalytic media can be determined using a nitrogen gas BET surface area analyser.

[0038] The method may be used to treat any wastewater containing an industrially relevant amount of a peroxide, with the process conditions being adjusted based on the teachings contained herein and straightforward trials in order to achieve effective decomposition of the peroxide in the wastewater.

[0039] In embodiments where the peroxide is hydrogen peroxide and the wastewater is a semiconductor manufacturing wastewater, for example, the hydrogen peroxide would be expected to have a concentration in the range of about 0.1 g / L to about 50 g / L, more likely between 0.1 g / L and 10 g / L, and even more likely between 0.1 g / L and 1 g / L. Determination of hydrogen peroxide content in the solution can be performed using potassium titanium (IV) oxalate and known laboratory procedures.

[0040] After the present invention has been performed, the level of peroxide in the treated wastewater is dramatically decreased, even eliminated. For example, in some embodiments, after decomposition, the treated wastewater may contain no more than 0.03 g / L (30 ppm) peroxide. The amount of residual peroxide in the treated wastewater may be adjusted based on downstream requirements or government regulations. As noted above, the inventors have observed that any residual hydrogen peroxide tends to decompose even after it is no longer in contact with the catalytic media, and note that this may well also occur for other peroxides.

[0041] In performing the invention, the peroxide-containing wastewater and the catalytic media may be caused to come into contact using any suitable technique, examples of some being given below. The wastewater may be caused to remain in contact with the catalytic media for any length of time effective for achieving decomposition of the required amount of peroxide. For example, contact times of between about 10 and about 20 minutes (or even longer, up to about 30 minutes, for example) have been found by the inventors to be effective. Typically, the flow rate of the wastewater through the catalytic media would be controlled to ensure complete decomposition of the peroxide, although other parameters in the method could be adjusted to effect this.

[0042] In some embodiments, for example, decomposition may be caused to occur in a catalytic quenching reactor having a catalytic media bed that contains the catalytic media. Catalytic quenching reactors are well known and can be assembled by persons skilled in the art using readily available components. In such reactors the treated wastewater (i.e. after peroxide decomposition) can be collected from the bottom of the bed and the oxygen gas vented off from the top of the quenching reactor.

[0043] In some embodiments, multiple passes of the wastewater through the catalytic media bed / catalytic media may provide beneficial effects such as an even further enhanced reduction in peroxide levels.

[0044] Some peroxide-containing wastewaters may be fit for immediate processing using the present invention. Sometimes, however, it may be advantageous (or necessary) to condition the wastewater before it is contacted with the catalytic media. The peroxides in such a conditioned wastewater may, when presented to the catalytic media, decompose more rapidly or otherwise more efficiently than might otherwise have been the case. Pre-conditioning may also provide other advantages, such as the removal of other contaminants or an improved durability of the catalytic media.

[0045] Such conditioning may, for example, include adjusting the pH of the wastewater, adjusting the conductivity of the wastewater and / or adjusting the oxidation-reduction potential (ORP) of the wastewater. The wastewater may also be filtered to remove suspended solids, which might otherwise (chemically and / or physically) impede the method of the present invention. Any desired level of conditioning may be achieved by adjusting the contact time between the wastewater and the conditioned s), with simple trials being all that would be required to ascertain this.

[0046] The pH of the wastewater can be conditioned by adjusting using an acid or an inorganic base. The choice of acid or base is flexible as long as it is strong enough to reach the desired pH, does not interfere with quenching efficiency, and does not impact the catalyst's activity. Suitable acids include sulfuric, hydrochloric, phosphoric, and nitric acids, while appropriate bases include sodium hydroxide (caustic soda), calcium hydroxide (lime) and potassium hydroxide. The inventors expect that wastewaters having a pH between about 2.5 to about 9.5 could be treated in the present invention, although wastewaters having a moderately acidic to neutral pH may be more effective in decomposing the peroxide without causing significant degradation of the catalytic media. Furthermore, wastewaters having a pH of less than 5 would typically need to be posttreated before they could be discharged into the environment in order to bring the pH up to an appropriate value. A pH of between about 5 and about 7 has been found by the inventors to be effective in the context of the semiconductor manufacturing wastewater described below. pH values of between about 5 to 8, 5 to 7 or 5 to 6 may also be appropriate in some situations.

[0047] If the ORP of the influent liquid is low (despite the presence of peroxide), its ORP may need to be increased to ensure advanced oxidation process can start and sustain. Species such as KMnO4, which is commonly used for increasing ORP in advanced oxidation processes, or NaOCl could be used to increase the liquid’s ORP. It is within the ability of a person skilled in the art todetermine an appropriate ORP for any particular wastewater. In the embodiments described in further detail below, for example, an ORP of above about 200mV is effective.

[0048] In some embodiments, the wastewater may be filtered before presenting to the catalytic media. Such filtration would remove suspended solids in the wastewater, which might otherwise foul the catalytic media and reduce its efficiency. Suspended solids may, for example, have formed in the wastewater due to a change in pH, and the combination of a pH change and filtration step may remove additional contaminants present in the wastewater. In alternative embodiments (or even in addition to a filtration step), a supernatant liquid may be drawn off from above settled solids, thus effectively separating suspended solids in the wastewater.

[0049] A specific embodiment of the method of the present invention will now be briefly described with reference to Figure 1. A summary of operational parameters of the catalytic quenching reactor is presented in Table 2. This embodiment relates to a process for the catalytic decomposition of hydrogen peroxide in semiconductor manufacturing wastewater, wherein the process comprises contacting the wastewater with the catalytic media.

[0050] The raw wastewater 1 is first conditioned 2, 3 before the decomposition process (i.e. exposure to the catalytic media) in order to have the wastewater present to the catalytic media having an optimal pH (i.e. by adding a pH adjustment agent), conductivity and ORP (i.e. by adding an oxidant). The feed water may need to pass through a contact tank 4 to increase the contact time between the raw water and the conditioning chemicals to maximise the treatment efficiency.

[0051] The conditioned wastewater 5 is then transferred through a catalytic quenching reactor 6 in which hydrogen peroxide in the wastewater is decomposed in the catalytic media bed 7. The treated water 8 is collected from the bottom of the bed and the produced oxygen gas 9 is vented off from the top of the quenching reactor 6.

[0052] The quenching reactor 6 may be periodically backwashed 10 using an oxidant solution 11 (e.g. NaOCl) to remove solids from the top of the media bed as well as to regenerate the catalytic activity of the catalytic media 7 after operation duration. Backwash waste can be removed from the quenching reactor 6 via line 12. A hydrogen peroxide quenching efficiency of 98-100% was observed by the inventors.Table 2Parameter Unit Value / DetailBed depth mm 600Maximum temperature °C 40 pH range - 3.0-9.5Reaction contact time min 10-20Service velocity m / h 12Backwash velocity m / h 50-70Bed expansion during backwash % 15-30Chemicals for backwash - NaOClLevel of chemical for backwash ppm 10-50Service hydrogen peroxide level ppm Up to 30,000

[0053] This method has been found by the inventors to be capable of treating wastewater effectively across a wide spectrum of hydrogen peroxide concentrations, without significant deterioration in catalytic efficacy, despite the presence of organic and inorganic impurities. The media experiences minimal mechanical wear, particularly at neutral pH, and does not leach problematic quantities of iron and manganese.

[0054] In these embodiments, the aqueous hydrogen peroxide-containing wastewater contacts the fixed bed of catalytic media packed in a filter vessel or column. The flow rate of the wastewater through the media bed is adjusted depending on various factors, such as the concentration of hydrogen peroxide in the influent, the complexity of the wastewater, and the acceptable residual level of hydrogen peroxide in the effluent. For example, the optimal contact time to achieve complete removal of hydrogen peroxide at 10 g / L (10,000 ppm) is between 10 and 30 minutes, preferably between 10 and 20 minutes.

[0055] The hydrogen peroxide destruction process is effective across a wide pH range. However, it is optimal when the wastewater pH is above 5, 6 or 7, and ideally below 10, with a more specific range of between about 5 and about 7. Operating the method below pH 5 may cause an increased rate of degradation of the catalytic media and, as described above, necessitate additional treatments before discharge. Operating the method above pH 10 may lead to the wastewater having an undesired ORP and might adversely affect the catalytic media (e.g. metal hydroxyl precipitates may be caused to form on the surface of the catalytic media). The process achieves high efficiency and stability within these pH parameters. Under these specified conditions, the hydrogen peroxide destruction process is particularly efficient, while the catalytic media shows a particularly highcatalytic activity as well as chemical and mechanical stability.

[0056] The hydrogen peroxide removal process can occur at any pressure, as long as the generated molecular oxygen can escape. The release of oxygen gas formed in the system is mandatory to ensure a stable operation and effective treatment of the system. Ideally, this process is performed at atmospheric pressure (101.3 kPa). However, it can also be conducted within a pressure range of 10 kPa to 101.3 kPa, or even above 101.3 kPa. The process is usually carried out at temperatures between 10°C and 50°C, preferably between 10°C and 40°C, and most preferably between 20°C and 35°C.

[0057] Under optimal conditions, the process of the present invention can be capable of quenching hydrogen peroxide effectively, even completely from the solution. Consequently, the wastewater treated with the catalytic media typically contains no more than 30 ppm (0.03 g / L) of hydrogen peroxide, with typical levels being below 10 ppm and often under 5 ppm. This allows the treated wastewater to be suitable for direct biological treatment. Furthermore, due to no introduction of significant amounts of manganese or iron into the water, the treated wastewater can be reused for other applications where needed. This reusability is particularly beneficial in regions with limited water resources.

[0058] The catalytic media used in the embodiments of the present invention described herein has demonstrated a mechanical and catalytic stability over long-term operation. In the inventors’ preliminary experiments, the hydrogen peroxide quenching efficiency remained stable at above 99% after more than 6 days. Furthermore, negligible mechanical erosion of the catalyst was observed during the quenching process.ExamplesExample 1 - Model wastewater

[0059] A series of experiments was conducted to demonstrate the effectiveness of using the catalytic media described above (i.e. that purchased from Starke Aquacare Technologies) to quench hydrogen peroxide in a model wastewater. A bench-scale testing system was constructed for this purpose, as shown in Figure 2. The system includes three tanks (i.e. feed (TNK-001), backwash (TNK-002), and treated water (TNK-003) tanks), two peristaltic pumps (i.e. feed (PMP- 001) and backwash (PMP-002) pumps), a catalytic quenching reactor (CQR-001) where the quenching process occurs, an air release valve (ARV-001) to vent off the gas formed during the reaction, two pressure gauges (PG-001, PG-002) to monitor the changes in pressure throughoutthe tests, and a gas counter (GCT-001) to monitor the gas production from the system. The design allows the system to be operated in four different modes (i.e., filtration, backwash, rinse, and drain).

[0060] In these experiments, 168 mL of the catalytic media was used to fill up a clear uPVC column. The hydrogen peroxide-containing model wastewater was passed through the column at different flow rates corresponding to the desired contact times. All experiments were performed at ambient temperature. The hydrogen peroxide concentration in the solution before and after treatment was measured by potassium titanium (IV) oxalate solution.Test 1 - Quenching performance at 5 min contact time

[0061] This test was conducted to investigate the peroxide quenching efficiency of the catalytic media at 5 min contact time. The detailed testing conditions are presented in Table 3.Table 3Parameter Unit ValueInitial H2O2 level ppm 10,000Solution pH - 7Media bed volume mL 168Flow rate mL / min 33.6Contact time min 5

[0062] The results demonstrated that 5 min contact time was not sufficient to continuously quench peroxide completely at a very high initial level of hydrogen peroxide (Figure 3).Test 2 - Quenching performance at 10 min contact time

[0063] This test was conducted to investigate the peroxide quenching efficiency of the catalytic media at 10 min contact time. The detailed testing conditions are presented in Table 4.Table 4Parameter Unit ValueInitial H2O2 level ppm 10,000Solution pH - 7Media bed volume mL 168Flow rate mL / min 16.8Contact time min 10

[0064] The results demonstrated that 10 min contact time was sufficient to quench peroxide completely at a very high initial level of hydrogen peroxide (Figure 4). No residual hydrogen peroxide was detected in the effluent at any time.Test 3 - Quenching performance at 20 min contact time

[0065] This test was conducted to investigate the peroxide quenching efficiency of the catalytic media at 20 min contact time. The detailed testing conditions are presented in Table 5.Table 5Parameter Unit ValueInitial H2O2 level ppm 10,000Solution pH - 7Media bed volume mL 168Flow rate mL / min 8.4Contact time min 20

[0066] The results demonstrated that 20 min contact time was sufficient to quench peroxide completely at a very high initial level of hydrogen peroxide (Figure 5). No residual hydrogen peroxide was detected in the effluent at any time.Test 4 - Long-term quenching performance at 15 min contact time

[0067] This test was conducted to investigate the long-term peroxide quenching efficiency of the IWI catalytic media at 15 min contact time. The detailed testing conditions are presented in Table6.Table 6Parameter Unit ValueInitial H2O2 level ppm 10,000Solution pH - 7Media bed volume mL 168Flow rate mL / min 11.2Contact time min 15

[0068] The results demonstrated no decrease in the catalytic activity of the IWI media in longterm operation at 15 min contact time (Figure 6). Complete removal of hydrogen peroxide was achieved using the catalytic media in long-term operation. (Figure 6).Example 2 - Semiconductor manufacturing wastewater

[0069] An industrial wastewater from a semiconductor manufacturing plant was obtained in order to establish the utility of the present invention with complex wastewaters from commercial sources. The time period between production of the wastewater and the inventors’ experiments was in the order of weeks, over which time the H2O2 self-decomposed. The wastewater was therefore spiked with H2O2 to reach 10,000 ppm (the value likely to be present in freshly produced wastewater) before the experiments described below. Relevant parameters of the wastewater are set out below in Table 7. The wastewater was also found to contain Cu, Al, Fe and Co cocontaminants.Table 7Parameter Unit ValueInitial H2O2 level (spiked) ppm 10,000Solution pH - 0.65ORP MV 451.1Conductivity pS / cm 17,050TDS mg / L 9,660

[0070] In these experiments, the wastewater was treated in a preconditioning step before its delivery to the bench-scale testing system. Specifically, two batches of wastewater were adjusted to a pH of 5 and 7 using sodium hydroxide. Subsequently, any precipitate that formed was filtered from the wastewater and the resultant solution was delivered to the reactor. The same catalytic media and bench-scale testing system described in Example 1 were used. The columns were operated with a 20 min contact time and for 10 bed volumes (BV). A sample for H2O2 was taken at each BV and, after 10 BV (i.e. Cycle 1), the column was backwashed using 50 ppm NaOCl, ready for operating again for another 10 BV (i.e. Cycle 2).

[0071] The results of these experiments can be seen in Figure 7. After the wastewater was treated as described above, H2O2 was removed completely after two cycles of 10 BV at pH 7, with an initial concentration of 10,000 mg / L and 20 min contact time. At pH 5, removal efficiency reached 87% after the first 10 BV and remained stable at 84% after the second cycle.

[0072] Similar experiments were carried out using the same wastewater, but in which the H2O2 content was spiked to 30,000 ppm. Almost complete decomposition of the H2O2 was achieved, with the treated wastewaters containing <30ppm H2O2 at both pH 5 and pH 7 (a removal efficiency of 99.9%, results not shown).

[0073] Described herein is a method for decomposing peroxides such as hydrogen peroxide in wastewaters such as semiconductor manufacturing wastewater. Advantageously, the present invention:• can be used to remove hydrogen peroxide from wastewater streams, enabling subsequent treatment using biological methods;• can be used to decompose hydrogen peroxide in a wide range of pH values, between 3 to 9.5, without causing long-term damage to the media; and• can be used to decompose hydrogen peroxide in 10 to 20 minutes, even for high concentration of 30,000 ppm (with a shorter timeframe if lower concentration).

[0074] In the claims which follow and in the preceding description of embodiments, except where the context requires otherwise due to express language or necessary implications, the word “comprise” and variations such as “comprises” or “comprising” are used in an inclusive sense, to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

[0075] It will be understood to persons skilled in the art of the invention that many modifications can be made without departing from the spirit of the invention. For example, it would be possible to add a copolymer with the polystyrene without changing the characteristics of the operation. Such modifications are deemed to be within the scope of the present invention.

[0076] Further embodiments of the invention will be apparent from the following description, and from the claims.

Claims

CLAIMS:

1. A method for decomposing a peroxide contaminant in a wastewater, the method comprising contacting the wastewater with a catalytic media comprising manganese dioxide, iron oxide and silicon oxide.

2. The method of claim 1, wherein the catalytic media comprises between about 70 wt% and 80 wt% manganese dioxide, between about 5 wt% and 30 wt% iron oxide and between about 10 wt% and 15 wt% silicon oxide.

3. The method of claim 1 or claim 2, wherein the catalytic media comprises about 77 wt% manganese dioxide, about 7 wt% iron oxide and about 11 wt% silicon oxide, with the balance being other metal oxides and minor impurities.

4. The method of any one of claims 1 to 3, wherein the catalytic media comprises granules shaped like pellets or spheres.

5. The method of claim 4, wherein the granules have particle sizes ranging from about 0.1 mm to about 2 mm.

6. The method of any one of claims 1 to 5, wherein the catalytic media has a surface area of between about 3 m2 / g and about 13 m2 / g.

7. The method of any one of claims 1 to 6, wherein the peroxide is hydrogen peroxide.

8. The method of any one of claims 1 to 7, wherein the peroxide has a concentration in the wastewater ranging from about 0.1 g / L to about 50 g / L.

9. The method of any one of claims 1 to 8, wherein, after decomposition, the wastewater contains no more than about 0.03 g / L peroxide.

10. The method of any one of claims 1 to 9, wherein a contact time between the wastewater and the catalytic media is from about 10 to about 20 minutes.

11. The method of any one of claims 1 to 10, wherein the wastewater is a semiconductor manufacturing wastewater.

12. The method of any one of claims 1 to 11, wherein decomposition is caused to occur in a reactor, wherein a bed of the reactor comprises the catalytic media.

13. The method of claim 12, wherein, after decomposition, treated wastewater is collected from underneath the catalytic media bed whilst oxygen gas is vented from the quenching reactor.

14. The method of claim 13, wherein the treated wastewater is contacted for a second time with a catalytic media comprising manganese dioxide, iron oxide and silicon oxide.

15. The method of any one of claims 12 to 14, wherein the reactor is periodically backwashed using an oxidant.

16. The method of any one of claims 12 to 15, wherein a flow rate of the liquid through the catalytic media bed is controlled to ensure substantially complete decomposition of the peroxide.

17. The method of any one of claims 1 to 16, wherein the method further comprises conditioning the wastewater before the wastewater is contacted with the catalytic media.

18. The method of claim 17, wherein the conditioning comprises one or more of the following: adjusting the pH of the wastewater, adjusting the conductivity of the wastewater, adjusting the oxidation-reduction potential (ORP) of the wastewater, and filtering the wastewater.

19. The method of claim 17 or claim 18, wherein the conditioning comprises adjusting the pH of the wastewater to a pH of between about 5 and about 7.

20. The method of claim 19, wherein the conditioning further comprises filtering a precipitate from the wastewater having a pH of between about 5 and about 7.

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