Hybrid Advanced Oxidation (HAO)

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UV-based and chemical oxidation processes are preferred treatment technologies for the elimination of emerging pollutants in drinking water and wastewater because of their flexibility, long-term stability, low costs, and controllability (cp. recent EU-projects as TECHNEAU, POSEIDON, THREE, NEPTUNE, RECLAIM WATER).

A number of European utilities in Switzerland, Germany and the Netherlands have considered implementing oxidation-based technologies to enhance the treatment capacity to remove emerging pollutants from resources and effluents. In industrialized countries where more than 90 % of the wastewater is treated in centralized waste water treatment plants, these plants represent a major point source for emerging pollutants and are therefore the best location for mitigation measures.

Oxidation of drinking and wastewater for disinfection purposes has a long tradition, but its benefits for emerging pollutant removal during wastewater treatment have only been recently tested (e.g. NEPTUNE, RECLAIM WATER). Results from pilot plants and the first full-scale application using post-ozonation revealed removal rates > 80 % for many emerging pollutants.  Therefore, the transfer of knowledge from the drinking water to the wastewater field and demonstration of the technology would be highly beneficial for technology uptake.

A main innovation is the combination of different oxidation processes and appropriate post-treatment technologies. For example, ozone is a selective oxidant that is particularly reactive towards functional groups with high electron densities, like those occurring in many emerging pollutants. The main disadvantage of the use of ozone in drinking water treatment is the formation of bromate in bromide-containing water. A combination of UV/H2O2, on the other hand, does not generate bromate, but requires 5-20 times more energy than an ozone process for a similar degree of emerging pollutant transformation.

A major drawback of oxidation processes is the inherent formation of oxidation byproducts from matrix components (e.g. aldehydes, ketones, carboxylic acids, for ozone, bromate and possibly NDMA) and the fact that emerging pollutants are not fully mineralized, resulting in transformation products (TPs).

DEMEAU will actively address and answer open questions in this field to foster implementation. Various oxidation processes (O3, O3/H2O2, UV/H2O2) and different post-treatment applications (e.g. sand filtration or biological activated carbon filtration) will be studied and compared to advance elimination efficiency and to eliminate oxidation by-products and transformation products. Biological activated carbon filters are well established in drinking water treatment, but applications in wastewater still have to be gathered, as is foreseen in DEMEAU.

DEMEAU's contribution to controlling these technologies at full-scale will improve the long-term stability and robustness of the processes, thereby facilitating the uptake of these technologies.