Lidia Dąbek
Politechnika Świętokrzyska
Abstract
The removal of organic contaminants such as aliphatic and aromatic hydrocarbons, phenols and related compounds, halogenated compounds, polycyclic aromatic hydrocarbons, aldehydes, ketones, acids, detergents, fats, dyes etc. from water and sewage is still an interesting and significant problem in environmental engineering. Both household and industrial waste is a source of organic contaminants in the environment. Higher and higher requirements regarding treated waste that is directed to water or the ground require constant development of the waste treatment process. The literature data and implemented solutions indicate that more and more attention is now paid to the use of sorption and advanced oxidation processes for the removal of organic compounds.
The highest significance and application among available sorbents has activated carbon. The sorption properties of activated carbon are dependent on its porous structure, produced by the system of interconnected macro-, meso- and micropores as well as the chemical composition of the surface resulting from the presence of oxygen functional groups. Activated carbon is especially useful as sorbents of phenol and chlorophenol. It has been shown that the adsorption ability of activated carbon depends on the specific surface area, porosity and surface chemical composition. High affinity of phenol to the surface of activated carbon is related to the creation of donor-acceptor complexes between alkaline locations on the sorbent’s surface and the aromatic ring. Oxidation of activated carbon’s surface leading to increased acidity lowers the sorption capacity of activated carbon. While the presence of metals increases the sorption capacity of activated carbon in relation to phenol due to the donor-acceptor interaction of metal-electrons of π aromatic ring in the phenol particle.
Another method of successful oxidation of phenols is their oxidation especially with the AOP methods (Advanced Oxidation Processe)s. A characteristic feature of these methods is oxidation of generally all organic compounds to CO2, H2O and inorganic compounds with the use of the hydroxyl radical OH* (generated in the solution) of extremely high oxidising potential of 2,8 V. Phenols and the related compounds quite easily undergo oxidation, especially with Fenton and photo-Fenton reactions
Both sorption and oxidation of organic compounds (including phenols) with AOP methods have advantages (high output and efficiency) and disadvantages (treatment of used sorbents, significant use of oxidants and increased sewage volume). In order to focus on the advantages of sorption and advanced oxidation while limiting their disadvantageous effect a combination of these two processes is considered. In this case the removal of contaminants is arranged as a two- or one-stage process. In the first one the removal of organic compounds covers sorption and then oxidation of the adsorbed substances with the use of AOP, which leads to a simultaneous regeneration of activated carbon. While in the latter case simultaneous sorption and oxidation of organic compounds is considered. In these both cases activated carbon acts as a sorbent of organic compounds and catalyst in the production of hydroxyl radicals OH* which are responsible for oxidation of organic compounds both in the solution and adsorbed on the activated carbon. It has been proven that in the presence of activated carbon in the environment of hydrogen peroxide, oxidation occurs of such organic compounds that do not undergo oxidation with the same oxidant in the aqueous solution. The applicability of activated carbon for the simultaneous removal of organic compounds is dependent on both their sorption and catalytic properties. Activated carbon should be alkaline, have high specific volume, pores’ volume, iodine number and significant dechlorination ability.
The applicability of oxidation of organic compounds with the use of hydroxyl radicals created on the surface of activated carbon for regeneration of the used sorbents has also been proven.
Słowa kluczowe:
fenol, chlorofenol, węgiel aktywny, utlenianie, rodnik hydroksylowy
038. Application of Sorption and Advanced Oxidation Processes for Removal of Phenols from Aqueous Solutions
Keywords:
phenol, chlorophenol, activated carbon, oxidation, hydroxyl radicals
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Zadanie Czasopismo, Annual Set The Environment Protection Volume 17. Year 2015 (wersja elektroniczna) dofinansowane ze środków Ministerstwa Nauki i Szkolnictwa Wyższego
