A doctoral dissertation by a candidate at Lappeenranta University of Technology (LUT) examines the removal of harmful organic substances such as pharmaceutical residues from wastewater using only electricity. According to practical tests, pulsed corona discharge (PCD) may significantly reduce the environmental burden of pharmaceutical residues.
According to the pilot tests in the chemical technology dissertation by Petri Ajo, M.Sc. (Tech.), pharmaceutical residues, their variants and other similar compounds degrade easily from wastewater because the process is non-selective.
PCD is based on the instantaneous contact produced by an electric discharge between a plasma zone and water. In this phenomenon, water molecules and oxygen in the atmosphere create strong oxidants that degrade organic compounds into water and carbon dioxide. The study examined the formation of oxidants on the plasma-liquid-gas interface and their behaviour in the process.
Practical studies on wastewater from three locations
The study also revealed that the momentary reformation of pharmaceutical substances can be considered a normal part of the reaction chain in the purification process. It nevertheless makes the comparison of technologies more difficult and highlights the importance of a non-selective process. Pharmaceutical residues were degraded from the effluents of the wastewater treatment plants of Toikansuo in Lappeenranta and the Rinnekoti foundation in Espoo, and from the untreated sewage of the South Karelia Central Hospital.
The results gave important new information on energy-efficient oxidation, which is significant in terms of further developing the technology. The efficiency of the process depends on temperature, flow rates, delays, and the location of the process in the wastewater treatment chain.
Ajo's dissertation, titled "Hydroxyl radical behavior in water treatment with gas-phase pulsed corona discharge," underwent a public examination on 29 March 2018 at 12:00 noon in LUT's Student Union House auditorium.
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The dissertation has been published in the university's publication series Acta Universitatis Lappeenrantaensis, publication number 793. ISBN 978-952-335-212-4 and ISSN 1456-4491. The dissertation is available in the LUTPub database of Lappeenranta University of Technology at urn.fi/URN:ISBN:978-952-335-213-1