Analysis of ultrasonic pre-treatment for the ozonation of humic acids

Pello Alfonso-Muniozguren; Cristian Ferreiro; Elodie Richard; Madeleine Bussemaker; José Ignacio Lombraña; Judy Lee

doi:10.1016/j.ultsonch.2020.105359

Analysis of ultrasonic pre-treatment for the ozonation of humic acids

Ultrason Sonochem. 2021 Mar:71:105359. doi: 10.1016/j.ultsonch.2020.105359. Epub 2020 Oct 7.

Authors

Pello Alfonso-Muniozguren¹, Cristian Ferreiro², Elodie Richard³, Madeleine Bussemaker⁴, José Ignacio Lombraña⁵, Judy Lee⁶

Affiliations

¹ Chemical and Process Engineering, University of Surrey, Guildford GU27XH, United Kingdom; Department of Chemical Engineering, Faculty of Science and Technology, University of the Basque Country UPV/EHU, 48940 Leioa, Spain.
² Department of Chemical Engineering, Faculty of Science and Technology, University of the Basque Country UPV/EHU, 48940 Leioa, Spain.
³ Chemical and Process Engineering, University of Surrey, Guildford GU27XH, United Kingdom; Department of Chemistry, IUT Besançon-Vesoul, University of Franche-Comté, 25000 Besançon, France.
⁴ Chemical and Process Engineering, University of Surrey, Guildford GU27XH, United Kingdom.
⁵ Department of Chemical Engineering, Faculty of Science and Technology, University of the Basque Country UPV/EHU, 48940 Leioa, Spain. Electronic address: ji.lombrana@ehu.eus.
⁶ Chemical and Process Engineering, University of Surrey, Guildford GU27XH, United Kingdom. Electronic address: j.y.lee@surrey.ac.uk.

Abstract

This paper presents an intensification study of an ozonation process through an ultrasonic pre-treatment for the elimination of humic substances in water and thus, improve the quality of water treatment systems for human consumption. Humic acids were used as representative of natural organic matter in real waters which present low biodegradability and a high potential for trihalomethane formation. Ultrasonic frequency (98 kHz, 300 kHz and 1 MHz), power (10-40 W) and sonicated volume (150-400 mL) was varied to assess the efficiency of the ultrasonic pre-treatment in the subsequent ozonation process. A direct link between hydroxyl radical (HO) formation and fluorescence reduction was observed during sonication pre-treatment, peaking at 300 kHz and maximum power density. Ultrasound, however, did not reduce total organic carbon (TOC). Injected ozone (O₃) dose and reaction time were also evaluated during the ozonation treatment. With 300 kHz and 40 W ultrasonic pre-treatment and the subsequent ozonation step (7.4 mg O₃/L_gas), TOC was reduced from 21 mg/L to 13.5 mg/L (36% reduction). HO attack seems to be the main degradation mechanism during ozonation. A strong reduction in colour (85%) and SUVA₂₅₄ (70%) was also measured. Moreover, changes in the chemical structure of the macromolecule were observed that led to the formation of oxidation by-products of lower molecular weight.

Keywords: Advanced oxidation processes; Fluorescence; Humic subtances; Sonication; Water treatment.

MeSH terms

Heterocyclic Compounds / chemistry*
Humic Substances / analysis*
Hydroxyl Radical / chemistry
Ultrasonic Waves*

Substances

1,2,4-trioxane
Heterocyclic Compounds
Humic Substances
Hydroxyl Radical