Sustainable treatment of “high-maintenance” industrial wastewater
Industrial wastewater in the chemical industry is often polluted. Evonik will in future utilize the environmentally compatible, resource-conserving Fenton reaction, involving hydrogen peroxide supplied by Evonik Active Oxygens, for pretreatment purposes at its Marl site.
Great things have happened at Marl Chemical Park, Evonik’s largest site in Germany. A new plant complex for manufacturing high-performance plastic, Polyamide 12, is “the largest capacity enlargement in Evonik’s recent history,” says Jörg Gisselmann, Head of Environmental Operations in Marl. And therefore, probably the largest and most spectacular “new addition” to the massive chemical park in the Ruhr region ever. Sections of the plant have been in operation since January 2021, while further expansion of manufacturing capacity in Marl is now good to go.
Pretreatment of heavily polluted industrial wastewater
However, industrial production also generates industrial wastewater. Normally polluted process water can be purified in a wastewater treatment plant. In such plants, a screen first of all removes solids and suspended matter, and then pollutants are decomposed by bacteria. This is usually the most effective method of treating contaminated process water.
But some industrial wastewater – especially in the chemical and pharmaceutical industries – is heavily contaminated by organic and inorganic pollutants, such as aromatic compounds, hydrocarbons, amines and others. “This wastewater can’t be biodegraded in a wastewater treatment plant,” says Philipp Christ, Operations Assistant at Evonik Active Oxygens. “The bacteria are unable to do that job. That is why this wastewater has to be pretreated, before it is piped into the treatment plant.” If new wastewater flows are added to an industrial site, e.g. as a result of a new production facility, it is important to scrutinize them.
In the past, heavily polluted industrial wastewater was often incinerated – an expensive and energy-intensive process that negatively impacted on the environment. Alternative processes were therefore developed to break up the large, tough-to-degrade molecules in the wastewater to enable them to then be degraded by bacteria. These are mainly the so-called AOP (advanced oxidation processes) methods, which work on the basis of hydrogen peroxide (H2O2) or ozone. H2O2 is a highly effective oxidant that’s produced and sold by Evonik Active Oxygens. Given that this chemical decomposes into water and oxygen during the reaction, no harmful by-products remain, as with other oxidants.
Hydrogen peroxide is a key component of the Fenton reaction
These AOP methods involve hydrogen peroxide being catalyzed by additional components like ultraviolet light or – as in the Fenton reaction – iron salts, in order to increase the oxidation effect. Combinations of components are also an option. Under certain conditions, the catalyzation of H2O2 results in the formation of so-called hydroxyl radicals, which have a very high oxidation potential. These break up the complex, tough-to-degrade molecules, which then become small, water-soluble and biodegradable. “So, what remains are small organic fragments, such as acetic acid or lactic acid, which are then metabolized by the bacteria in the wastewater treatment plant,” Christ explains.
The various AOP methods are suitable for different applications. Fenton performs well in sustainability and cost terms by comparison:
- UV light is unsuitable for turbid wastewater, because it does not penetrate deep enough. Furthermore, the lamps consume energy and need to be replaced regularly.
- Ozone is produced at high energy input, it is also expensive to procure and the operation of ozone generators is energy-intensive.
- Fenton plants are expensive to install, but they cost significantly less to maintain than the alternatives. Feedstocks are readily available and environmentally compatible.
Evonik and Fenton
The Fenton reaction is not new: it was discovered way back at the end of the 19th century by Henry John Horstman Fenton. It has been continuously adapted and refined since then.
Fenton plants are used worldwide, especially in the petrochemicals industry and in the manufacture of pharmaceuticals. Evonik itself is not a provider of Fenton plants, but partners with manufacturers. The Group supplies hydrogen peroxide for Fenton plants operated by other companies, and has its own plants in Rheinfelden and more recently in Marl.
Besides, Evonik chemists conduct tests to enhance the processes and adapt them to different wastewater types – in collaboration with manufacturers too. A few years ago, for example, a team from Active Oxygens succeeded in modifying the Fenton reaction by adjusting the reaction parameters to enable it to be used resource-efficiently in the production of hydrogen peroxide.
Extensive data analyses and series of large-scale tests
However, the type of wastewater and its constituents determine which AOP method is the most effective. Therefore, only testing helps. Those responsible in Marl know this too. They started looking for the right method to pretreat these additional wastewater flows. Scientists from TU Berlin were also involved in the extensive data analyses and series of large-scale tests. “The whole thing took a year,” says Gisselmann. “In the end, we opted for Fenton. Fenton provides the widest coverage for our applications, when you consider environmental as well as technical and commercial factors.”
So, the Evonik Business Line responsible – Energy and Utilities – planned and built a Fenton plant for around 15 million euros, which is expected to require about 2,250 metric tons of hydrogen peroxide a year. The operators of the plant will obtain this primarily from Evonik’s Delfzijl site in the Netherlands.
Expertise provided by Evonik Active Oxygens
Those responsible at Evonik in Marl obtained the necessary expertise from the hydrogen peroxide experts working for the Evonik Active Oxygens Business Line. This Business Line produces and sells hydrogen peroxide in a wide range of concentrations.
Furthermore, Evonik Active Oxygens has already been operating a Fenton plant at the Rheinfelden site in southwestern Baden-Württemberg, near the Swiss border, since the end of 2017. Here, it was a similar story back then: capacity enlargements had resulted in a new type of wastewater that had to be handled. After weighing up the alternatives, those responsible opted for the Fenton process.
“We are not operating your classic Fenton process here, but one that specialists in a laboratory in Hanau have enhanced and tailored exactly to our needs,” says Christ. “And it works – in terms of impact, costs and sustainability.”