Pulsed corona discharge as an advanced oxidation process for degradation of organic compounds in water

The study focuses on a novel and advanced water/wastewater treatment technology based on principles of generation of active oxidant species in ultra-short high-voltage pulsed corona discharge (PCD) in humid air.

The PCD water treatment method is relatively new compared to other advanced oxidation methods widely used in practice, such as ozonation and catalytic wet oxidation. Conventional (mechanical, biological, chemical) water treatment methods are often insufficient for effective removal of refractory and toxic compounds that can pose a threat e.g. to aquatic life.

The quality and cost of wastewater treatment need improvements, and electric discharge technology has a potential to make a significant difference compared to other established advanced oxidation processes based on energy efficiency.

Advanced oxidation processes (AOPs) have been studied and developed to suffice the effective removal of refractory and toxic compounds in polluted water. The quality and cost of wastewater treatment need improvements, and electric discharge technology has a potential to make a significant difference compared to other established AOPs based on energy efficiency. The generation of active oxidant species such as ozone and hydroxyl radicals by high voltage discharge is a relatively new technology for water treatment. Gas-phase pulsed corona discharge (PCD), where a treated aqueous solution is dispersed between corona-producing electrodes free of the dielectric barriers, was developed as an alternative approach to the problem. The short living radicals and ozone formed in the gas phase and at the gas-liquid interface react with dissolved impurities. PCD equipment has a relatively simple configuration, and with the reactor in an enclosed compartment, it is insensitive towards gas humidity and does not need the gas transport.

In this thesis, PCD was used to study and evaluate the energy efficiency for degrading various organic compounds, as well as the chemistry of the oxidation products formed. The experiments investigate the aqueous oxidation of phenol, humic substances, pharmaceutical compounds (paracetamol, ibuprofen, indomethacin, salicylic acid), as well as lignin degradation and transformation to aldehydes. The study aims to establish the influence of initial concentration of the target pollutant, the pulsed discharge parameters, gas phase composition and the pH on the oxidation kinetics and the efficiency. Analytical methods to measure the concentrations of the target compounds and their by-products include HPLC, spectrophotometry, TOC and capillary electrophoresis.

The results of the research included in this summary are presented in the attached publications and manuscripts accepted for publication. Pulsed corona discharge proved to be highly effective in oxidizing each of the target compounds, surpassing the closest competitor, conventional ozonation. The increase in oxidation efficiencies for some compounds in oxygen media and at lower pulse repetition frequencies shows a significant role of ozone. The role of the •OH radicals was established in the surface reactions. The main oxidation products, formation of nitrates, and the lignin transformation were quantified.

A compound specific approach is suggested for optimization of the PCD parameters that have the most significant impact on the oxidation energy efficiency because of the different characteristics and responses of the target compound to the oxidants, as well as different admixtures that are present in the wastewater. Further studies in the method's safety (nitration and nitrosation of organic compounds, nitrite and nitrate formation enhancement) are needed for promoting the method.

Iris Panorel, Master of Science in Technology, will defend her doctoral dissertation at Lappeenranta University of Technology on November 8th at 12.00 noon, room 1381. Professor Santiago Esplugas, University of Barcelona, Spain, will act as the opponent. Professor Marjatta Louhi-Kultanen of Lappeenranta University of Technology will act as custos.

The dissertation has been published in the Acta Universitatis Lappeenrantaensis research series number 535. ISBN 978-952-265-477-9, ISBN 978-952-265-478-6 (PDF), ISSN 1456-4491. http://urn.fi/URN:ISBN:978-952-265-478-6 A printed version of the dissertation may be purchased from the Aalef bookstore, tel. +358 44 744 5511, or at kirjakauppa(at)aalef.fi

The doctoral candidate's personal information:
Year and place of birth: 1978, Philippines
Education: Ggraduated in 1999 from University of the Philippines, Diliman, Quezon City (BS in Chemical Engineering)
Employment: Hitachi Global Storage Technologies, Laguna, Philippines (2000-2006), Lappeenranta University of Technology (present)

More information:

Iris Panorel, tel. +358 44 01711 32, iris.panorel@lut.fi / icpanorel@gmail.com