Advanced oxidation processes

Advanced oxidation processes (AOPs, e.g. heterogeneous and homogeneous photocatalysis, electrochemical oxidation, ozonation, ultrasound irradiation, Fenton and alike reactions, and many more) have been investigated for the treatment of emerging pollutants over the past 20 years (Klavarioti et al., 2009). In particular, the occurrence of persistence micro-pollutants in various water matrices, such as pharmaceuticals and personal care products, raises serious environmental concerns since these xenobiotics can re-enter the water cycle, i.e.

This study focuses on the photocatalytic degradation of a pharmaceutic compound essentially employed for the treatment of hypertension using TiO2 as catalyst and UV-A irradiation. An efficient elimination yield of 99% was obtained after 10 minutes of irradiation at initial pollutant concentration of 5 mg/L and 1.2 g/L of catalyst. A higher mineralization yield of 87% was reached in 2h of reaction. Results showed that under all studied process conditions the target molecule was degraded according to a pseudo first order kinetics.

The application of non-thermal plasmas in wastewater and air purification received a lot of attention, but their potential application in drinking water treatment has scarcely been investigated. Classified as Advanced Oxidation Processes, plasmas ignited in water or at the air-water interface generate a vast range of reactive species capable of removing water contaminants.

Cavitation based advanced oxidation processes (Cav-AOPs), are a promising alternative to currently used wastewater treatment technologies. Amplified interest in this “hot” topic results in increased number of research on several aspects relating to formation of cavitation phenomena and its utilization for wastewater treatment as well as hybrid processes based of application of external oxidants effectively converted to radical species in cavitation conditions.

Ozone is commonly used in advanced oxidation processes (AOPs) in combinations with hydrogen peroxide (H2O2) and UV radiation (UV). Hydrodynamic cavitation (HC) has been experimentally proven to result in effects, typical of AOPs. Combinations of AOPs with O3, H2O2 and UV, and HC (with cavitation numbers less than 0.2, generated by various orifice plates and nozzles, with number of passes up to 12) were experimentally assessed on model water, containing organic matter.

The present study reported the decolorization by UV/H2O2 of three dyes and their binary and ternary mixtures in water, simulating colored effluents of the textile industry. The effect of the initial concentration of H2O2, the initial concentration of dyes and the reaction kinetics in the decolorization of textile dyes in water was studied. The efficiency of decolorization of three treatment processes was compared (UV, H2O2 and UV/H2O2).

Formation of toxic by-products, such as chlorinated intermediates, is one of the major drawbacks of advanced oxidation processes for saline wastewater treatment. Here a comparative analysis of electrochemical oxidation and photocatalytic degradation of 4-Ethylphenol, a non-chlorinated starting model compound of the group of alkylphenols, is presented. Main intermediates have been identified and quantified for brackish [0.03 mol*L-1] and sea water [0.6 mol*L-1] salt concentrations representative for the salt levels in various industrial effluents.

The aim of this work is to analyse the changes of dissolved oxygen ([DO], mg/L) during the oxidation of caffeine waters by photo-Fenton treatment. The concentration of dosed hydrogen peroxide would be the addition of the stoichiometric [H2O2], which reacts with organic matter ([H2O2]esteq=2.0 mM), plus the concentration in excess of [H2O2]exc that decomposes, generating O2 through radical processes, according to a ratio R=0.8164 mmol H2O2/mg O2). Operating at doses lower than the stoichiometric value [H2O2]0<2.0 mM, O2 is not emitted, as there is no excessive oxidant.