Advanced Oxidation Processes (AOP)

© Fraunhofer IGB

Oxidative water treatment (AOP, advanced oxidation processes) is understood as processes for chemical water treatment in which hydroxyl radicals are formed. These highly reactive radicals are available for chemical decomposition reactions and react with organic or inorganic substances that are not easy to break down biologically. They can be formed by adding oxidative substances such as ozone and hydrogen peroxide, or by introducing energy by means of UV radiation, ultrasound or electric current via inert electrodes as well as by a combination of these processes.

At present, catalytic, photochemical, and electrochemical processes as well as plasma processes for oxidative water treatment are investigated at Fraunhofer IGB. Various experimental set-ups for continuous, semi-continuous and batch trials are available for this purpose.

Application areas

AOP processes are always used when a biological decomposition is not feasible or cannot be carried out efficiently, for example because the contaminations contain persistent substances. Also, AOP processes are the method of choice when the process wastewater has a toxic effect on the microorganisms of a biological purification stage or occurs extremely discontinuously. The energy required for operating the system can be provided by electricity from renewable sources such as solar and wind power.

Example: Quantification of methylene blue degradation

A problem in the field of oxidative wastewater treatment is the formation of degradation by-products, some of which are hazardous or are not sufficiently evaluated toxicologically. However, the formation of toxic by-products can be avoided in almost all cases by choosing suitable process parameters. In order to quantify the reaction mechanisms and degradation products of various AOP methods in the AOP research facility, tests with the model substance methylene blue (C16H18Cl N3S) were carried out. In addition to the decoloration (measurement at 664 nm), the formation of by-products was observed using HPLC, coupled with UV and mass spectrometry. In a comparison of anodic oxidation, ozone treatment und UV treatment, the ozone treatment turned out to be the best method for this wastewater model.

Example: Decoloration of organic dyes by UV / H2O2 and anodic oxidation

As models for real wastewater from the textile industry, a dissolved organic dye and a particulate organic dye were discolored by more than 90 percent – until the liquids were transparent to the human eye. The study also served to determine the most energy-efficient process parameters and compared the decomposition products produced by each method.

Example: Life extension of metalworking fluids

In several projects we investigated whether the efficient reduction of microbial contamination in cooling lubricant emulsions can be achieved by means of ultrasound or ultrasound in combination with specific AOP processes. Depending on the type and concentration of the microbial contamination we were able to achieve a sustained reduction, without impairing the quality of the cooling lubricant.

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Advantages

  • Complete mineralization of pollutants possible
  • Staff savings and increased reliability
  • No increase in salinity, which enables recirculation
  • No disinfection by-products – in particular no halogenated compounds
  • Less handling of hazardous chemical agents
  • Little or no sludge formed
  • Hygienic outflow water
  • Robust process – discharge criteria can be met reliably
  • Available quickly – standby operation possible
  • Suitable for varying quantities and qualities of wastewater

 

 

AOP research facility

We offer our AOP pilot plant for the development of optimized treatment processes. Modular units (ozone generator, ozone reactor, UV reactor, ultrasonic units, electrolytic cells) can be freely combined.

 

Reactor for the elimination of micropollutants in wastewater by oxidation

The degradation of man-made pollutants in low concentrations, so-called organic trace substances or micropollutants, is increasingly gaining priority in water treatment. In Switzerland, the corresponding expansion of larger wastewater treatment plants is already mandatory, in California and other industrialized regions it is partly implemented as a precautionary measure.

 

Combination and integration of oxidative and electrolytic processes

Oxidative and adsorptive processes such as electrophysical precipitation can be combined, depending on the problems to be solved. By doing this, results can be achieved that exceed the sum of the results of the individual processes. A further advantage of these processes is that they are suited to standby operation and can be switched on or off at any time. Integration into existing plants and automation including autonomous operation or remote control are feasible without any problems. Continuous online logging of organic carbon (TOC, total organic carbon) can be effected, enabling requirement- based and thus energy-optimized treatment.