Recent studies have shown that many pharmaceutical substances can be detected in wastewater effluents. An increasing body of evidence indicates that antibiotics, hormones and antiepileptics are responsible for microbial resistance against active substances and feminisation of higher organisms, respectively [1]. Low concentration of pharmaceuticals ranging from nanograms to micrograms per litre may cause problems in municipal sewage treatment plants. Advanced Oxidation Processes (AOP) may offer appropriate measures and have therefore been investigated.

Photochemical and electrochemical Advanced Oxidation Processes (AOP/EAOP) are efficient oxidation operations for degradation of persistent pollutants such as pharmaceuticals, pesticides, substituted aromatic hydrocarbons, dyes and complexing agents. The UV/H2O2 -, UV/O3- processes and the Photo-Fenton process are representative photochemical AOPs. Anodic oxidation is an electrochemical AOP. Both technological groups generate reactive hydroxyl radicals (E°=2,80 V), which mineralize contaminants or at least convert pollutants into less toxic or biodegradable products.

The aim of the project is the comparison and documentation of approved photochemical and electrochemical processes for different substance classes. This catalogue should help to evaluate a proper technology for a specific application. Criterion for comparison is the potential of degradation and mineralization, as well as the specific energy consumption.

Several substances, the selection was mainly based on the properties of substituents, were investigated. All experiments were carried out with a start concentration of 500 ppm of the substance. Photochemical degradation was carried out in a Heareus Noblelight UV-reactor system (UV-RS-2), equipped with a 15 W mercury low-pressure lamp. Electrochemical degradation was performed in open cell electrolysis with diamond coated electrodes and 0.05 M Na2SO4 for conductivity. The results demonstrate different rates of mineralization and degradation related to the substituent of the model substance and the absorption properties in the UV Range. m-Cresol for example shows a higher rate of degradation than the complexing agent ethylenediaminetetraacetic acid because of the different absorbability at 254 nm. In general electrochemical experiments show a simultaneous degradation and mineralization whereas photochemical experiments show first degradation of the substance and then mineralization.

The paper summarizes the present status of research and experience.

[1] Marc-Olivier Buffle, Jochen Schumacher, Elisabeth Salhi, Martin Jekel, Urs von Gunten. Water Research 40 (2006) 1884 – 1894