Ozone is an allotrope of oxygen, containing 3 oxygen atoms. Ozone is a light blue gas at room temperature and pressure, and its solubility in water is 9.2mlO3/L, which is higher than oxygen (42.87mg/L). It is purple-blue when the dissolved concentration in water is higher than 20mg/L. Ozone has strong oxidizing properties, with a redox potential of 2.07V, which is only lower than F2 (3.06V) in single substances. Ozone can directly mineralize the residual macromolecular, long-chain, and difficult-to-biodegrade organic matter in wastewater into carbon dioxide and water, and partially decompose it into small molecular biodegradable substances, destroy the structure of non-biodegradable organic matter, reduce toxicity, and increase the B/C ratio, thereby ensuring the treatment effect of subsequent biochemical methods.
Ozone is widely used in industrial wastewater treatment. There are two main ways for ozone to interact with organic matter in aqueous solution: one is the direct oxidation of ozone molecules; the other is the strong oxidation of •OH hydroxyl radicals produced after ozone is decomposed.
Traditional ozone oxidation technology is mainly based on direct oxidation, which has poor mass transfer effect, extremely high selectivity, low ozone utilization rate, and high investment and operating costs.
Ozone catalytic oxidation technology is to add transition metal ions into the oxidation system, which can produce a significant catalytic effect on ozone oxidation, catalyze the self-decomposition of ozone in water, increase the concentration of •OH produced in water, and thus improve the ozone oxidation effect.
Currently, catalytic ozone processes are divided into two types: homogeneous ozone oxidation and heterogeneous ozone oxidation. Homogeneous ozone oxidation refers to adding some soluble transition metal ions into water to achieve the effect of catalytic ozone oxidation. The catalyst of heterogeneous ozone catalysis exists in solid form, is easy to separate, and has a simple process, which not only avoids the loss of catalysts, but also reduces the cost of water treatment.
The commonly used catalysts in heterogeneous catalytic ozone engineering are mainly: metal oxides and composite metal oxides; metal oxides loaded on carriers; metals loaded on carriers; activated carbon or catalysts with activated carbon as carriers; porous materials, etc.
Among them, transition metal series oxides are widely used because of their relatively cheap prices, easy availability of raw materials, and high catalytic activity. Such as titanium oxide, iron oxide, manganese oxide, aluminum oxide, zinc oxide, copper oxide, nickel oxide, etc.
In heterogeneous catalytic ozone oxidation systems, there are generally three possible reaction mechanisms:
1. Ozone chemically adsorbs on the catalyst surface, generates active substances and then reacts with organic matter in the solution. This active substance may be •OH, or it may be other forms of oxygen.
2. Organic molecules are adsorbed on the catalyst surface through chemical bonds and further react with ozone in the gas or liquid phase. First, the organic matter will be quickly adsorbed on the catalyst carrier, and the oxide on the surface of the carrier will form some chelates with it, and then these chelates will be oxidized by ozone and •OH.
3. Ozone and organic molecules are adsorbed on the catalyst surface at the same time (complex action), and then the two react. Starting from the reduced catalyst, ozone will oxidize the metal, and the reaction of ozone on the reduced metal will generate •OH. The organic matter will be adsorbed on the oxidized catalyst, and then oxidized through electron transfer reaction to produce a reduced catalyst again. The organic matter will then be easily desorbed (desorbed) from the catalyst and then enter the bulk solution or be oxidized by •OH and ozone.
After the optimization of our full system, the production of hydroxyl radicals can be increased by 100%-300%, greatly enhancing the utilization rate of ozone oxidation.
Application of heterogeneous catalytic oxidation process
The heterogeneous catalytic oxidation process appears in the form of a heterogeneous catalytic oxidation reactor in the treatment of high-concentration organic wastewater, and different oxidants such as air, ozone, hydrogen peroxide, chlorine dioxide, etc. need to be added according to different water quality and environment. The addition of catalysts will accelerate the generation of OH hydroxyl radicals and the oxidation of organic matter. This process has been widely used in the pretreatment of difficult organic wastewater such as printing and dyeing, pharmaceuticals, papermaking and chemical industry in recent years. The heterogeneous catalytic oxidation process has a significant effect on CODcr removal, decolorization and improving the biodegradability of wastewater. For example, in the treatment of printing and dyeing wastewater, its decolorization efficiency is as high as 75%-95%, and it can remove 50%-80% of CODcr and increase the B/C ratio to more than 0.45. In the treatment of pesticide wastewater with CODcr exceeding 150,000, the multiphase catalytic oxidation process also shows extremely high efficiency. After 2 hours of reaction, its CODcr removal rate can reach more than 90%, and the properties of the wastewater have changed greatly. The most obvious is that the B/C ratio is increased from 0 to more than 0.3, and the biodegradability of the wastewater is enhanced, making it possible for the subsequent biochemical treatment to meet the discharge standards.
The catalytic oxidation material in the multiphase catalytic oxidation process has high stability, so the service life can reach more than five years, and the installation and operation are simple, and the operation is economical and reliable. The biggest advantage of this process is that it can be attached to any traditional treatment process, so it has unique advantages that other processes cannot match in the transformation of the original treatment process of high-concentration wastewater.
2: Advantages and application scenarios of ozone catalytic oxidation process
After most of the sewage has been treated by traditional biochemical treatment at the front end, most of the main biochemical indicators meet the national emission requirements. With the increasing requirements of national ecological and environmental protection, the national emission standards have been increasing year by year. At the same time, the national requirements for hazardous waste have been further tightened. The cost of treating hazardous waste is getting higher and higher, resulting in a significant increase in the unit treatment cost of the entire sewage system. This forces companies to find a suitable upgrading process without generating hazardous waste. Our ozone catalytic oxidation process just meets this requirement. Ozone oxidation is simple to operate, highly automated, and will not generate secondary pollution. There is no sludge, no sludge, no sludge, relatively low cost, decolorization, degradation of cod, increase of B/C ratio, deodorization, sterilization, and virus elimination. Ozone catalytic oxidation is mainly used in the upgrading and transformation of sewage processes, which does not generate secondary pollution and high-quality requirements.
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The project "Key Technologies and Equipment for the Treatment of High-Difficulty Chemical Wastewater and its Application" was awarded the First Prize for Environmental Technology Advancement in 2020 by the China Environmental Protection Industry
The "Key Technology and Application of Iron-Based Materials for the Synergistic Catalytic Oxidation Treatment of High-Difficulty Chemical Wastewater" has been awarded the Provincial Science and Technology Progress First Prize.
The "Leachate Treatment System for Direct Discharge to Meet Standards" has been awarded the Municipal Science and Technology Second Prize.
The "Zero Discharge and Resource Utilization Technology for High-Salinity Chemical Wastewater" was approved as part of the 2020 Municipal Science and Technology Development Plan. The project was selected for the Shandong Province Science and Technology-based SMEs Innovation Capacity Enhancement Program.
The "LEM Electrochemical + LDF Oxidation Combined Process Technology" and the "LCO Ozone Catalytic Oxidation Process" were respectively selected for the Municipal and Provincial Advanced Technology Directories for Water Pollution Prevention and Control.
Over 70 patents for independent intellectual property rights have been granted
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