Process optimization for microcystin-LR degradation by Response Surface Methodology and mechanism analysis in gas–liquid hybrid discharge system

Advanced oxidation processes for the removal of cyanobacterial toxins from drinking water

“…So far, NTPs were studied for the removal of MCs, ANTX and BMAA [108,109,[111][112][113][114][115]. Besides the type of reactive species produced in an electric discharge, other parameters also affect the treatment e cacy.…”

“…Besides the type of reactive species produced in an electric discharge, other parameters also affect the treatment e cacy. Studies on MC-LR removal in a gas-liquid surface discharge showed, that a higher operating voltage increased the degradation due to a higher energy input [111,115], and similar results were shown for the degradation of ANTX in a dielectric barrier discharge in O 2 and subsequently bubbling the gas through the sample solution [108]. Here, an increased operating voltage led to higher O 3 concentrations, which in turn also resulted in higher OH levels in water due to decomposition of dissolved O 3 [108].…”

“…Since MC-LR was expected to be unaffected in the studied pH range, the OH concentration was assumed to be reduced under alkaline pH due to reaction with OH - [109]. The concentrations of the formed reactive species can also be increased by higher gas ow rates [115].…”

“…The electrode distance also impacts the plasma chemistry, when decreasing distance between high voltage electrode and the water surface, the energy increases and intensi es the reactions induced by the plasma. For a shorter electrode distance, the transfer time into the solution is reduced especially for short-lived reactive species [111,112,115], where long transfer times can reduce the degradation effectiveness. This is why catalysts have been studied as additives in NTPs to transform long-lived species like O 3 and H 2 O 2 into the more reactive OH.…”

“…Because electric discharges also generate UV light, photocatalysts like TiO 2 have also been studied as additives to increase the formation of OH (see the chapter on photocatalysis) [114]. Due to the formation of H 2 O 2 in water, another alternative is the addition of Fe 2+ to yield the Fenton's reagent (see the chapter on Fenton oxidation) [115]. Plasma generation, intensive heat and direct electro-physical and -chemical processes at the electrode can lead to corrosion, resulting in the release of metal ions from the electrodes.…”