DE3884808T2 - The oxidation of organic substances in water. - Google Patents

Description

The present invention relates generally to the detoxification of hazardous materials and more particularly to the removal of organic compounds.

There is currently a critical national need to remove trace amounts of toxic organic compounds from groundwater, surface water, and industrial wastewater without releasing these compounds into the atmosphere or disposal sites. Currently, oxidation by combustion or chemical means is the only method to achieve true detoxification rather than mere transfer of these organic poisons to the atmosphere or other medium.

Combustion of dilute aqueous solutions of organic components is expensive due to the energy required for the evaporation of water. In addition, combustion can cause the formation of toxic byproducts such as dioxin derivatives in the exhaust gases. Chemical oxidation processes for treating contaminated water include the use of such substances as potassium permanganate, chlorine dioxide, chlorine, hydrogen peroxide, or ozone. In addition, oxidation can be enhanced by using ultraviolet light (UV) together with any of these substances, except permanganate.

Chemical detoxification processes are used commercially for wastewater and some groundwater. However, these processes have associated disadvantages. For example, potassium permanganate produces manganese dioxide as a byproduct during oxidation. Chlorine and in some cases chlorine dioxide forms chlorinated organic compounds. In addition, Hydrogen peroxide plus iron(II) sulfate (Fenton's reagent) produces a soluble and insoluble iron residue.

Ozonation without UV light partially oxidizes benzene derivatives to mono- and dibasic acids that are biodegradable, but it does not oxidize saturated halogenated compounds. Oxidation with hydrogen peroxide and UV light is useful for oxidizing a number of organic compounds, but in many cases the oxidation rates are significantly slower than when UV/O3 is used. While ozone combined with UV enhancement has proven cost-effective and practical for nonvolatile unsaturated chlorinated hydrocarbons and a number of benzene derivatives, certain saturated chlorinated and oxygenated compounds such as the ubiquitous pollutants methylene chloride and methanol have proven resistant to UV oxidation. Thus, there is a long-standing need for an efficient and practical method for removing a wide range of toxic organic compounds from water. Such a process should provide a means of detoxifying hazardous compounds that is both highly effective and cost-effective. The present application meets these requirements and also provides associated benefits.

US-A-4,512,900 describes a process for treating a liquid waste composition containing copper ions and an organic complexing agent for the copper ions, in which the concentration of the copper ions is reduced to less than about 8 ppm and then first contacting the water composition with H₂O₂ to destroy about 20 to about 60 wt.% of the total organic content and then contacting the resulting partially treated waste composition with an ozone-containing gas and irradiating the ozone-containing waste composition with ultraviolet light.

FR-A-2,303,766 describes a process for removing oxidizable material from polluted water by the addition of a peroxide, which may be hydrogen peroxide or ozone, characterized in that the action of the peroxide can be activated by irradiating the treated water with ultraviolet light.

According to the present invention, there is provided a process for oxidizing organic compound constituents such as halogen-containing and/or partially oxygenated hydrocarbon constituents in aqueous solution, the process comprising simultaneously exposing the aqueous solution to ozone (O₃), hydrogen peroxide (H₂O₂) and ultraviolet radiation (UV) in amounts sufficient to substantially reduce the amount of organic compound constituents in the solution.

The addition of hydrogen peroxide to the UV/ozone combination results in a greatly increased efficiency of oxidation. Such increased efficiency reflects a synergistic effect that can be related to the intermediate generation of O₃ or HO₂ radicals, which initiate rapid oxidation reactions.

In a preferred embodiment, water containing halogenated hydrocarbon contaminants is exposed to ozone, hydrogen peroxide and ultraviolet radiation simultaneously. The temperature of the sample can be raised above ambient temperature.

The aqueous solution treated according to the present invention can be, for example, groundwater, industrial wastewater or drinking water.

The method of the present invention can be used

(a) to provide a new and viable process for decontamination of waters containing hydrocarbons, halogenated hydrocarbons and partially oxidised hydrocarbons;

(b) to oxidise or partially oxidise these contaminants effectively and economically to simple compounds such as carbon dioxide, water and halides; and

c) to oxidise less toxic partially oxidised compounds such as aldehydes, dibasic organic acids and the like, depending on their nature, their toxicity, the source of disposal, be it a receiving water body such as a stream, river etc. or a biological treatment process either on site or at public treatment plants.

Other features and advantages of the present invention will become apparent from the following more detailed description which explains, by way of example, the principles of the invention.

Detailed description of the preferred embodiment

The present invention provides a highly efficient and effective process for oxidizing organic compounds in aqueous solutions, which has particular application to oxidizing hydrocarbon contaminants in water. The process involves exposing the contaminated water to H₂O₂, O₃ and UV. When groundwater or wastewater contains significant concentrations of hydrocarbon contaminants such as methylene chloride or methanol, these compounds are difficult to oxidize by conventional processes. With the process of the present invention, the water is simultaneously exposed to H₂O₂₁ O₃ and UV. The process is effective for oxidizing a wide range of Spectrum of hydrocarbons, including halogenated and partially oxygenated hydrocarbons, whether aromatic or aliphatic.

Example I Oxidation of methanol

Samples of distilled water (Arrowhead Co., P.O. Box 2293, Los Angeles, CA 90051-0293) containing the equivalent of 200 mg methanol/liter were treated with various combinations of O3, H2O2, and UV. For each such sample, two liters of the aqueous methanol solution were placed in an 82 x 485 mm cylindrical Pyrex glass reaction vessel which was sealed at the top. UV light was provided by a centrally located low-pressure mercury arc lamp (G37T6VH) inside a 24 mm OD quartz envelope (both from Voltare Tubes, Inc.) (lamp power = 40 watts; ultraviolet output = 14.3 watts; tube diameter = 15 mm; tube material = quartz). The lamp assembly was suspended 15 mm above the bottom of the cylinder to allow space for a magnetic stirring bar.

Hydrogen peroxide was introduced into the reaction vessel through a port at the top. 0.7 ml of 30% H2O2 was added at 5 minute intervals for 20 minutes. Ozone was generated from welding grade oxygen using a Model 8341 ozonizer (Matheson Gas Products Company. Lindhurst, N.Y.). 2% ozone in oxygen was introduced at the bottom of the cylinder through a coarse glass fritted disk at a rate of 62 mg/min. The solution was stirred with a magnetic stir bar during oxidation. The effluent oxygen stream was passed through a solvent trap to collect deposited materials.

The rate of methanol oxidation was determined by gas-liquid chromatography (GLC) using a Model 340 ALP gas chromatograph manufactured by Antek Instruments, Inc., Houston, Texas. The oxidized methanol solutions were injected directly onto a 6 ft. x 1/8 inch stainless steel column containing 10% Pennwalt + 4% KOH on 80/100 mesh Gas Chrom R. The column was operated isothermally at 100ºC.

The results of the operations are shown in Table 1. The resulting decrease in TOC (total organic carbon) using the combination of UV, H₂O₂ and O₃ is more than ten times greater than that achieved with the treatment using UV, H₂O₂ or O₃ alone or in combinations of two of them.

Table 1 Oxidation of methanol

The methanol concentration was 200 ppm at time zero. The volume of methanol solution = 2,000 mL, the O3 concentration in the O2-O3 feed gas = 3.6%, O2-O3 flow to deliver 70 mM O3/30 min = 2.2 L/min. Oxidation conditions No. of runs Time (min) Oxidant dose Control

Example II Oxidation of methylene chloride

The oxidation of methylene chloride was carried out using the procedures of Example I, except that the feed samples contained 100 mg methylene chloride/L, the oxidation time was 25 min, and each water sample to be oxidized was 1800 mL. 0.15 mL of 30% H2O2 was added to the methylene chloride solution in the reaction vessel initially. Ozone was added at a rate of 5.2 mg/min. The rate of oxidation of the methylene chloride was determined by extraction with hexane and gas-liquid chromatography using a Varian Aerograph Model 144010-00 gas chromatograph equipped with an electron capture detector (63Ni). An aliquot of the oxidized water sample, diluted to contain no more than 10 ppm methylene chloride, was combined with 2 ml of high purity hexane (Burdick & Jackson, Muskegon, MI) in a 40 ml tube sealed with a screw cap lined with a Teflon septum. The contents of the tube were shaken vigorously for 1 min and, after phase separation, one μl of the hexane extract was withdrawn through the Teflon septum and injected onto a 10 m x 0.53 nm i.d. capillary column coated with FSOT Superox. 1.2 μm. The column was operated isothermally at 30°C. The results are given in Table 2. As in Example I, the lowest content of unoxidized methylene chloride was obtained in the experiments using UV, H₂O₂ and O₃ in combination.

Table 2 Oxidation of methylene chloride

Volume of oxidized CH₂Cl₂ solution = 1800 mL; O₃ concentration = 2%; O₂-O₃ flow to deliver 10 mM O₃/25 min = 0.5 L/min. Oxidation Conditions No. of Runs Time (min) Oxidant Dose CH₂Cl₂ Solution Found (ppm) Trap % Control

Example III Oxidation of wastewater from a wood product manufacturer

Oxidation of wastewater from a wood product manufacturer was carried out using the procedures of Example I, except that the feed samples contained 29,800 Pt-Co color units and each water sample to be oxidized was 1,900 mL. 1.15 mL of 30% H2O2 was fed at 5 min intervals for 20 min. Ozone was added at a rate of 40 mg/min. The oxidized wastewater samples were diluted as necessary to give the same color intensity.

The results are shown in Table 3. Table 3 Oxidation of a wastewater to remove color components from a wood product manufacturer using UV, O₃,H₂O₂ Batch Operation Run No. Oxidation Conditions Oxidizer Dosage Dilution Required to Achieve the Same Color Intensity Feedstock

Example IV Oxidation of wastewater from a chemical plant

Wastewater from a chemical plant containing 700 ppm 1,4-dioxane, 1,000 ppm ethylene glycol and 1,000-5,000 ppm acetaldehyde was subjected to comparative oxidation using the combination of UV, H2O2 and O3. The operating steps were as given in Example I except that the reaction time was 120 min, 35 ml of 30% H2O2 was added gradually over the first 90 min and the rate of ozone addition was 205 mg/min. The decrease in 1,4-dioxane concentration was determined by gas-liquid chromatography as described in Example I except that the GLC column was operated isothermally at 140°C.

The results are given in Table 4. The combination of UV, H₂O₂ and O₃ resulted in a dioxane reduction that was two to five times higher than that achieved with UV and O₃. Table 4 Oxidation of a waste water from a chemical plant with UV/O₃/H₂O₂ in the laboratory 2000 ml volume, batch operation Run No. Time (min) Reaction conditions Dioxane found (ppm) Add H₂O₂ within 90 min.

Example V Oxidation of groundwater from a chemical plant

Comparative oxidations of groundwater containing a variety of organic compounds were carried out using UV, H2O2 and O3 and UV and O3. The operating steps were as described in Example 1 except that the time was 60 min, 3.2 ml of 30% H2O2 was added at the beginning of the oxidation and the ozone dose was 11 mg/min. The concentration of organic compounds in the feed and in the oxidized groundwater was determined by Montgomory Laboratories, Pasadena, CA using gas-liquid chromatography/mass spectrometry. The results are given in Table 5. Table 5 Oxidation of groundwater from a chemical plant using UV/O₃/H₂O₂ in the laboratory. Compound Feedstock (ppb) Vinyl chloride Methylene chloride 1,1-DCE 1,1-DCA Trans-1,2-DCE CHCl₃ 1,2-DCA TCE PCE Chlorobenzene Benzene Toluene Ethylbenzene Xylene Bromoform CHBrCl₂ ' 60 min. 27.5 mM O₃ (= 22 mg O₃/min/1.81) - 60 min. 11 mg O₃/min. (14 mM), 28 mM H₂O₂ (3.2 ml 30%) ND not detectable

Example VI Oxidation of wastewater from paint stripping

Wastewater from paint stripping containing methylene chloride was pretreated to remove chromate ion and paint particles. The pretreatment consisted of using sodium metabisulfite to reduce the chromate ion to Cr3+ and then adding sodium hydroxide and an anionic polymer solution to form a rapidly settling Cr(OH)3 precipitate. Three ml of 0.76% Na2S2O5 was added to 100 ml of the wastewater adjusted to pH 4. After 30 min, NaOH was added to pH 8.5 and then an anionic polymer solution was added to give 0.5 ppm of the anionic polymer. The precipitated Cr(OH)3 was filtered off and the filtrate was washed with UV/H2O2/O3. oxidized according to the procedures given in Example I, except that samples were obtained at 15 min intervals. The total oxidation time was 60 min, the volume of waste water was 1800 ml, the total H₂O₂ dose was 4.7 ml of 30% H₂O, and the ozone dose was 21.5 mg/min. The decrease in methylene chloride was measured as described in Example 11. Table 6 Laboratory test results with pretreated wastewater from paint stripping. Methylene chloride vs. reaction time Time (min) Methylene chloride (ppm) ND not detectable

Claims (8)

1. A process for oxidizing organic compound constituents in an aqueous solution, the process comprising exposing the aqueous solution to ozone, hydrogen peroxide and ultraviolet radiation in amounts sufficient to substantially reduce the amount of organic compound constituents in the solution. 2. The method of claim 1, wherein the aqueous solution is groundwater. 3. A process according to claim 1, wherein the aqueous solution is industrial waste water. 4. The method of claim 1, wherein the aqueous solution is drinking water. 5. Process according to one of the preceding claims, in which the aqueous solution contains halogen-containing and/or partially oxygen-enriched hydrocarbon components as components of organic compounds. 6. A process according to any one of claims 1 to 4, wherein the organic component is methylene chloride. 7. Process according to one of claims 1 to 4, in which the organic component is methanol. 8. A process according to any preceding claim, wherein the temperature of the aqueous solution is increased during the time it is exposed to the ozone, hydrogen peroxide and ultraviolet light.