Pulsed corona discharge: the role of ozone and hydroxyl radical in aqueous pollutants oxidation

Abstract

Ozone and hydroxyl radical are the most active oxidizing species in water treated with gas-phase pulsed corona discharge (PCD). The ratio of the species dependent on the gas phase composition and treated water contact surface was the objective for the experimental research undertaken for aqueous phenol (fast reaction) and oxalic acid (slow reaction) solutions. The experiments were carried out in the reactor, where aqueous solutions showered between electrodes were treated with 100-ns pulses of 20 kV voltage and 400 A current amplitude. The role of ozone increased with increasing oxygen concentration and the oxidation reaction rate. The PCD treatment showed energy efficiency surpassing that of conventional ozonation.

Hospital Wastewater Treatment with Pilot-Scale Pulsed Corona Discharge for Removal of Pharmaceutical Residues

“…1. Further details and technical description are presented in our previous publication [25] where the gas-phase ozone concentration in the reactor was also measured, comprising around 5 mg L -1 in air atmosphere, and negligible amounts of oxidants, below 1 mg L -1 , were iodometrically measured in the treated water, which was a binary model solution with notably lower amount of oxidant consuming species than in the presently studied sewage.…”

“…Here, a maximum progesterone concentration after PCD treatment was measured as 0.072 µg L -1 at 30 W pulse power, while at 250 W the amounts remained at 0.017-0.021 µg L -1 , approximately four times lower at eight times higher pulse power. The disproportion between the rates and applied powers would suggest ozone has a notable role in the reactions [25]. The maximum value corresponds to a progesterone yield of 72 µg kWh -1 .…”

Pulsed Corona Discharge Induced Hydroxyl Radical Transfer Through the Gas-Liquid Interface

“…For water treatment purposes, the gas-liquid interface where the OH radicals are formed is a crucial environment and the plasma-liquid contact surface area thus makes an important variable 4 – 6 . In earlier work, a vertical PCD reactor in which the treated solution is allowed to shower through a perforated plate positioned above the plasma zone was employed to generate a large plasma-liquid contact surface area 6 .…”

“…In earlier work, a vertical PCD reactor in which the treated solution is allowed to shower through a perforated plate positioned above the plasma zone was employed to generate a large plasma-liquid contact surface area 6 . Increasing this contact surface improves the oxidation energy efficiency mainly due to the enhanced action of superficial OH radicals 4 , 6 . Although OH radical activity at the plasma-liquid interface is evident, it is extinguished in complete absence of O 2 4 .…”

“…Increasing this contact surface improves the oxidation energy efficiency mainly due to the enhanced action of superficial OH radicals 4 , 6 . Although OH radical activity at the plasma-liquid interface is evident, it is extinguished in complete absence of O 2 4 . So far this property, however, seems only observed with the present configuration; several other types of non-thermal plasmas applied in oxidation of aqueous organic compounds seem to have effect also in the absence of molecular O 2 7 – 11 , suggesting that these processes include various mechanisms.…”