Examination of Photocatalyzed Chlorophenols for Sequential Photocatalytic-Biological Treatment Optimization

Abstract

Given the known adverse effect of chlorophenols for the aquatic environments which they can reach, the development of efficient methods both technically and economically to remove them has gained increasing attention over time. The combination of photocatalytic oxidation with biological treatment can lead to high removal efficiencies of chlorophenols, while reducing the costs associated with the need to treat large volumes of aqueous solutions. Therefore, the present paper had as its main objective the identification of the minimum photocatalytic oxidation period during which the aqueous solutions of 4-chlorophenol and 2,4-dichlorophenol can be considered as readily biodegradable. Thus, the results of photocatalytic oxidation and biodegradability tests showed that, regardless of the concentration of chlorophenol and its type, the working solutions become readily biodegradable after up to 120 min of irradiation in ultraviolet light. At this irradiation time, the maximum organic content of the aqueous solution is less than 40%, and the biochemical oxygen demand and chemical oxygen demand (BOD/COD) ratio is much higher than 0.4. The maximum specific heterotrophic growth rate of activated sludge has an average value of 4.221 d−1 for 4-chlorophenol, and 3.126 d−1 for 2,4-dichlorophenol. This irradiation period represents at most half of the total irradiation period necessary for the complete mineralization of the working solutions. The results obtained were correlated with the intermediates identified during the photocatalytic oxidation. It seems that, working solutions initially containing 4-chlorophenol can more easily form readily biodegradable intermediates.

Influence of Operating Parameters on Photocatalytic Oxidation of 2,4-Dichlorofenol in Aqueous Solution by TiO2/Stainless Steel Photocatalytic Membrane

“…The second one involves a direct attack of the hydroxyl radicals which would lead to the displacement of chlorine from the para position with the formation of 2-chloro-4-hydroxyphenol. Next, there may be a successive attack of the hydroxyl radicals until the benzene ring is open, or there may be a first attack of the nascent hydrogen on the chlorine from the ortho position with the formation of hydroxyquinone followed by the successive attack of hydroxyl radicals until the opening of the benzene ring [9,32]. However, it appears that both degradation mechanisms are strongly influenced by the pH of the aqueous solution, and therefore these are in good agreement with the results found in this work.…”

Editorial: Special Issue on Photocatalytic Nanocomposite Materials (PNMs)

“…The latter appear to be capable of interacting with molecular oxygen yielding peroxo species thus providing an extended light-induced "self-cleaning" behavior. The combination of photocatalytic oxidation with biological treatment as studied by Liliana Bobirica and her colleagues was found to lead to high removal efficiencies of chlorophenols, while reducing the costs associated with the need to treat large volumes of aqueous solutions [3]. It could be shown that, regardless of the concentration of chlorophenol and its type, the working solutions become readily biodegradable following an initial irradiation by ultraviolet light with this irradiation period representing at most half of the total irradiation period necessary for the complete mineralization of the working solutions.…”