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

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.

SUBMITTER: Alfonso-Muniozguren P

PROVIDER: S-EPMC7786617 | biostudies-literature | 2021 Mar

REPOSITORIES: biostudies-literature

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

Alfonso-Muniozguren Pello P Ferreiro Cristian C Richard Elodie E Bussemaker Madeleine M Lombraña José Ignacio JI Lee Judy J

Ultrasonics sonochemistry 20201007

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) ...[more]

PMID: 33291062

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Project description:We report the results of a structure-activity relationship study that was undertaken to identify humic substance chemistries that drive the plant biostimulant response. The effects of seven extensively chemically characterized, ore-derived humic acids (HA) on corn seedling biomass and root and shoot morphological parameters were investigated. Chemometric analyses were then conducted to identify correlations between HA chemical features and plant biomass and morphological characteristics. The primary chemical driver of plant biomass and morphology was the ratio between HA electron accepting capacity (EAC) and electron donating capacity (EDC). The HA electron accepting capacity is found in quinones and semiquinone free radicals, while the HA electron donating capacity is found in polyphenolics and glycosylated polyphenolics. Based on our results, we propose a mechanism of action for ore-derived HA plant biostimulation that involves the interplay of pro-oxidants, in the form of quinones and semiquinone radicals, and antioxidants, in the form of polyphenols and possibly glycones and carbohydrates. The quinones/semiquinones initiate an oxidative stress response via the stimulation of transmembrane electron flow that results in both reactive oxygen species (ROS) production (i.e., an oxidative burst) and membrane depolarization, the latter of which allows Ca2+ flux from the apoplast into the cytoplasm. Based on the magnitude of depolarization, a specific cytoplasmic Ca2+ signature is produced. As a secondary messenger Ca2+, via binding to Ca2+- sensor proteins, transmits the signature signal, resulting in specific intracellular responses that include changes to plant morphology. The greater the EAC, the greater the ROS production and magnitude of plasma membrane depolarization and resulting stress response. The HA antioxidants are able to scavenge and quench the ROS and thus modulate the intensity and extent of the stress response to greater or lesser degrees, based on their concentrations and radical scavenging efficiencies, and thus modify the Ca2+ signature and ultimately the intracellular molecular responses.

Project description:The main aim of this study was the analysis of the interaction between humic acids (HAs) from different soils and Zn(II) ions at wide concentration ranges and at two different pHs, 5 and 7, by using fluorescence and FTIR spectroscopy, as well as potentiometric measurements. The presence of a few areas of HAs structures responsible for Zn(II) complexing was revealed. Complexation at ?-sites (low humified structures of low-molecular weight and aromatic polycondensation) and ?-sites (weakly humified structures) was stronger at pH 7 than 5. This trend was not observed for ?-sites (structures with linearly-condensed aromatic rings, unsaturated bonds and large molecular weight). The amount of metal complexed at pH5 and 7 by ? and ?-structures increased with a decrease in humification and aromaticity of HAs, contrary to ?-areas where complexation increased with increasing content of carboxylic groups. The stability of complexes was higher at pH 7 and was the highest for ?-structures. At pH 5, stability decreased with C/N increase for ?-areas and -COOH content increase for ?-sites; stability increased with humification decrease for ?-structures. The stability of complexes at ? and ?-areas at pH 7 decreased with a drop in HAs humification. FTIR spectra at pH 5 revealed that the most-humified HAs tended to cause bidentate bridging coordination, while in the case of the least-humified HAs, Zn caused bidentate bridging coordination at low Zn additions and bidentate chelation at the highest Zn concentrations. Low Zn doses at pH 7 caused formation of unidentate complexes while higher Zn doses caused bidentate bridging. Such processes were noticed for HAs characterized by high oxidation degree and high oxygen functional group content; where these were low, HAs displayed bidentate bridging or even bidentate chelation. To summarize, the above studies have showed significant impact of Zn concentration, pH and some properties of HAs on complexation reactions of humic acids with zinc.

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

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

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