The aim of this study is the presentation of novel water treatment systems based on ozonation combined with ceramic membranes for the treatment of refractory organic compounds found in natural water sources such as groundwater. This includes, firstly, a short review of possible membrane based hybrid processes for water treatment from various sources. Several practical and theoretical aspects for the application of hybrid membrane-ozonation systems are discussed, along with theoretical background regarding the transformation of target organic pollutants by ozone. Next, a novel ceramic membrane contactor, bringing into contact the gas phase (ozone) and water phase without the creation of bubbles (bubbleless ozonation), is presented. Experimental data showing the membrane contactor efficiency for oxidation of atrazine, endosulfan, and methyl tert-butyl ether (MTBE) are shown and discussed. Almost complete endosulfan degradation was achieved with the use of the ceramic contactor, whereas atrazine degradation higher than 50% could not be achieved even after 60 min of reaction time. Single ozonation of water containing MTBE could not result in a significant MTBE degradation. MTBE mineralization by O3/H2O2combination increased at higher pH values and O3/H2O2molar ratio of 0.2 reaching a maximum of around 65%.
Chromium (Cr(VI)) is a very toxic and carcinogenic element, which is widely present in groundwaters, mainly due to geogenic conditions. The limit of Cr(VI) in drinking water is expected to be reduced to 10 μg/L in both the USA and the European Union. Recent literature findings indicated that the most efficient process in reducing Cr(VI) levels to below 10 μg/L proved to be Cr(VI) reduction by Fe(II), by applying a molar ratio Fe(II)/Cr(VI) of around 9. In the present work, we investigated the reduction of Cr(VI) by Fe(II) in pipe flocculation reactors followed by filtration of insoluble products by microfiltration. The proposed technology involves re-circulation of a part of the sludge in the pipe reactors, in order to improve kinetics and efficiency of the process. The obtained results showed that with a Fe(II) dose of around 1 mg/L, Cr(VI) was reduced to below 10 μg/L, by even an initial concentration as high as 300 μg/L of Cr(VI), corresponding to a molar ratio Fe(II)/Cr(VI) of around 3, thus reducing the overall quantity of reductive reagents and of the produced sludge. This ratio was also confirmed by the XPS analysis, which also showed that Cr(VI) was reduced to Cr(III) and then precipitated either as Cr(OH) or associated with the produced iron oxides.
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