Decomposition of phenols in water by high energy radiation and other advanced oxidation processes

Within the scope of this thesis the decomposition of phenol and catechol (500 μM) has been studied by high energy radiation (Gamma- radiation, electrons) as well as by other advanced oxidation processes (UV/H2O2, UV/TiO2, Ozone). The degradation process was investigated and evaluated on the basis of the degradation rates, product formation (HPLC), degree of oxidation (COD), mineralization (TOC) and detoxification. Gamma radiolysis experiments proved that the presence of oxygen during irradiation is essential for an effective removal of organic compounds. Using air saturation, a 65 % TOC reduction could be achieved at a dose of 12 kGy and detoxification at 6 kGy.To investigate the influence of inorganic water components experiments were carried out in distilled water (DW) and drinking water of Vienna and Seibersdorf, (WLW, SLW). It could shown, that the different degradation rates found, could be mainly attributed to the different initial pHs of waters. For phenol the pH range of maximal degradation is ∼ 5.5-6.5. For total removal of phenol and catechol in DW and WLW doses from 5 kGy up to 6 kGy and in SLW 9 kGy up to 12.5 kGy are required. The combined process electron/ozon (EB/O3) is the most powerful technique, using irradiation with electron beams, for phenol and catechol destruction as well as for mineralization and detoxification. For total degradation 7-10.5 kGy and 16-27 mg O3 dm-3 are required. Under this condition a 25-40 % mineralization and a total detoxification was obtained. The efficiency of the UV/H2O2 process was studied as a function of the H2O2 concentration. An optimal degradation rate was achieved with a ratio (ppm) of substrate : H2O2 = 0.02. In contrast to ionizing radiation, where only indirect oxidation via OH radicals take place, in the case of UV/TiO2 the substrates are also oxydized directly by valence band holes of the semiconductor. The rate of decomposition is slow, but it correlates well with mineralization. At the time of total substrate removal, the TOC reduction is 80-90 %. The removal of phenol and catechol by ozone was studied in distilled water (pH 5.6) and Viennese drinking water (pH 8.2). For both of them the decomposition at pH 8.2 is faster than at pH 5.6 due to radical chain reactions. In comparison to the other methods the rates of degradation and mineralisation are distinctly lower. The most efficient processes are the combination EB/O3 and the photoxidation UV/H2O2. Ionizing radiation, however, has the advantage of a much broader application field. In contrast to the photooxidation this method enables the remediation of dyestuffs, suspensions and sludges. (author)