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Eisenmann develops, designs, and installs custom-made systems for water purification, waste water treatment, and water recycling for nearly all areas of production and service. This includes a large variety of industries such as surface treatment companies, disposal and cleaning plants, the chemical industry, power plants, the printing industry, metal processing plants, the food industry, the pharmaceutical industry and many others. Here, the patented FENTOX – process will be reviewed.
Generally, organic compounds should be degraded in a biological step. However, many organic compounds coming from industrial productions show hardly any biodegradability and are even toxic. Moreover, high salt concentrations or elevated temperatures as well as high seasonal variations in the flow or the concentration hamper the biological treatment that needs stable conditions for an efficient treatment. Consequently, alternative treatment systems have to be taken into account.
In 1894 Mr. Fenton discovered, that the reaction of iron(II) with hydrogen peroxide in aqueous solution shows a strong oxidation ability. Later it was shown, that this is due to the formation of reactive OH-radicals. The reaction can be described as follows:
Fe2+ + H2O2 + H3O+ => Fe3+ + OH• + 2 H2O
The reaction occurs under acidic conditions. OH-radicals are formed, which further react with organic compounds.
Eisenmann optimized this reaction for the oxidative treatment of industrial waste water using laboratory scale batch and continuous tests as well as pilot scale test units. Especially, the reaction conditions were optimized focusing on the best reactor design, temperature, amount of catalyst, as well as pH. As reactor design, a multistage dosing of hydrogen peroxide in a reactor cascade showed the best results. After acidification, temperature adjustment, and dosing of iron(II), hydrogen peroxide is dosed before the first reactor. The main reaction occurs in the first reaction chamber. Mixer, foam reducing circulation and air injection stabilize the process. Before the water is fed to the second reaction chamber, hydrogen peroxide is dosed again. Thus, the reaction is enhanced, achieving a higher reduction in COD while catalyst consumption remains low. A detailed analysis showed that two consecutive reactors are the optimum in terms of investment costs, and operation costs, as further consecutive reactors do only have minor positive influence on the total COD reduction efficiency.
Usually, a water sample is analysed. COD values between 1,000 mg/L and 15,000 mg/L are preferable for the large scale application. The oxidation ability is tested in batch tests. Important factors are the buffer capacity, chemicals consumption, optimum iron/hydrogen peroxide ratio in relation with the treatment goal. The heat formation as well as foam production is investigated. Finally, the amount of neutralisation agent applied and sludge formed is determined. With the received data, first process data is achieved and applied in a continuous plant. Here, fine tuning is achieved and an up scale, based on the experience in other projects carried out.
So far, Eisenmann has set up several plants mainly for the detoxification of waste water coming from chemical production. The volume flow varies in the range between 1.5 and 15 m³/h. COD reduction is in a range between 65 and 90% depending on the waste water characteristics. AOX is removed by more than 95%.
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