Coupling Ultrasound to the Electro‐Oxidation of Methyl Paraben Synthetic Wastewater: Effect of Frequency and Supporting Electrolyte

Exploring the progress and challenges of ultrasonic technology in environmental remediation

Amidst escalating environmental pollution due to accelerated industrialization and urbanization, there is an acute demand for effective and sustainable environmental remediation strategies. Ultrasonic technology, recognized for its green and efficient characteristics, has gained significant prominence in mitigating environmental pollution in aquatic, soil, and atmospheric ecosystems. The review provides a comprehensive analysis of the role of ultrasonic treatment in wastewater treatment, air quality improvement, and soil remediation. We systematically evaluate existing research to assess the effectiveness of ultrasonic technology in degrading pollutants and its potential for large-scale deployment. The review also examines the challenges associated with ultrasonic remediation, including optimizing operational parameters, enhancing energy transfer efficiency, and understanding the unique degradation mechanisms for various pollutants. Furthermore, we discuss environmental and safety considerations, along with the economic implications related to equipment costs and energy consumption. This review aims to contribute to the advancement of ultrasonic technology in environmental remediation by presenting a forward-looking perspective, aligning with the goals of environmental protection and sustainable development.

A review on reactive oxygen species generation, anode materials and operating parameters in sonoelectrochemical oxidation for wastewater remediation

The application of sonoelectrochemical (SEC) oxidation technique involving the incorporation of ultrasound irradiation into an electrochemical oxidation system has found enormous success for various purposes, especially for organic synthesis and water treatment. Although its industrial application towards the removal of organic contaminants in water is not popular, its success on the laboratory scale is often attributed to the physical and chemical effects. These effects arise from the influence of ultrasound irradiation, thus eliminating electrode passivation or fouling, improving mass transfer and enhancing reactive oxygen species (ROS) generation. The continuous activation of the electrode surface, improved reaction kinetics and other associated advantages are equally occasioned by acoustic streaming and cavitation. This review hereby outlines common ROS generated in SEC oxidation and pathways to their generation. Furthermore, classes of materials commonly employed as anodes and the influence of prominent operational parameters on the performance of the technique for the degradation of organic pollutants in water are extensively discussed. Hence, this study seeks to broaden the significant promises offered by SEC oxidation to environmentally sustainable technology advances in water treatment and pollution remediation.

Remediation of soils contaminated with methomyl using electrochemically produced gaseous oxidants

This prospective work focuses on the use of two different gaseous oxidants (chlorine dioxide and ozone) to remediate soil polluted with methomyl in two different applications: ex-situ and in-situ. In the first, the soil washing is integrated with the bubbling of the oxidant, while in the second, the gas was introduced by a perforated pipe located sub-superficially. Regarding the soil washing treatment, results demonstrate that direct use of ozone is not very efficient, although an important improvement is obtained following activation with hydrogen peroxide or UV light. In contrast, chlorine dioxide exhibited complete methomyl depletion from the soil, although with higher energy consumption and technical complexity compared to ozone. The direct dosing of the gaseous oxidants in perforated pipes is effective, achieving methomyl removals of 7.8 % and 9.2 % using ozone and chlorine dioxide, respectively. In these cases, soil conditions are not significantly modified, which becomes an important advantage of the technology as compared with other electrochemically assisted soil remediation process, in which large regions of the treated soil are affected by important changes in the pH or by depletion of ions. This lower impact makes these novel technologies more promising for further evaluations.

On the performance of distinct electrochemical and solar-based advanced oxidation processes to mineralize the insecticide imidacloprid

Water contamination by contaminants of emerging concern is one of the main challenges to be solved by our desired sustainable society. In the same time, different technologies for water treatment are becoming enough mature to be implemented. In this work, two different advanced oxidation processes (AOP) were investigated: i) electrochemical processes (electrochemical, photoassisted electrochemical, electro Fered-Fenton, and photo-electro Fered-Fenton - PEF-Fered) using a BDD and DSA® electrodes under UVA and UVC irradiation (9 W) and ii) solar-based AOP using four distinct oxidants (HOCl, H₂O₂, S₂O₈^2-, HSO₅^-) in the presence or absence of Fe²⁺ ions to oxidize and mineralize imidacloprid (IMD: 50 mg L^-1) containing solutions. The PEF-Fered (1.0 mM Fe²⁺ and 50 mg L^-1 h^-1 H₂O₂) under UVA or UVC irradiation and HOCl/UVC (NaCl 17 mM) processes using a BDD and DSA® electrodes (10 mA cm ^-2), respectively, performed equally well to completely oxidize and mineralize (∼90%) IMD at the expense of only ∼0.3 kWh g^-1. Low amounts and highly oxidized byproducts identified through liquid chromatography tandem mass spectrometry were observed for the HOCl/UVC process using a DSA® electrode. Concerning the solar-based AOP, all assessed oxidants (4 mM h^-1) successfully oxidized IMD within 3 h of treatment, whereas only H₂O₂ and HOCl led to significant (∼60%) TOC abatement after 6 h treatment. The use of Fe²⁺ (0.5 or 1.0 mM) had no significant improvement in the oxidation and mineralization of IMD.

Improving biotreatability of hazardous effluents combining ZVI, electrolysis and photolysis

In this work, nine types of combination advanced oxidation processes/zero-valent iron (AOP-ZVI) were tested, in order to determine if any of these combinations demonstrate good chances as pretreatment for the biological degradation processes of organochlorinated pollutants. To do this, the changes undergone in the respirometric behavior, toxicity and short-term biodegradability were compared. The three AOPs studied were anodic oxidation with mixed metal oxides anodes (AO-MMO), with boron doped diamond anodes (AO-BDD) and photolysis and they were evaluated in three different modes: without any addition of ZVI, with ZVI-dehalogenation as pre-treatment and with ZVI-dehalogenation simultaneous to the AOP treatment. Clopyralid has been used as a model of chlorinated hydrocarbon pollutant. Results show that technologies proposed can successfully treat wastes polluted with clopyralid and the biological characteristics of the waste are significantly modified by dehalogenating the waste with ZVI, either previously to the treatment or simultaneously to the treatment, being the information provided by the three techniques very important in order to evaluate later combinations of the advanced oxidation technologies with biological treatments.

Sonoelectrochemical Degradation of Propyl Paraben: An Examination of the Synergy in Different Water Matrices

The synergistic action of anodic oxidation using boron-doped diamond and low-frequency ultrasound in different water matrices and operating conditions for the decomposition of the emerging contaminant propyl paraben was investigated. The degree of synergy was found to decrease with an increase in current in the range 1.25–6.25 mA/cm² or the ultrasound power until 36 W/L, where a further decrease was observed. Despite the fact that the increased propyl paraben concentration decreased the observed kinetic constant for both the separated and the hybrid process, the degree of synergy was increased from 37.3 to 43.4% for 0.5 and 2 mg/L propyl paraben, respectively. Bicarbonates (100–250 mg/L) or humic acid (10–20 mg/L) enhanced the synergy significantly by up to 55.8%, due to the higher demand for reactive oxygen species. The presence of chloride ions decreased the observed synergistic action in comparison with ultrapure water, possibly due to the electro-generation of active chlorine that diffuses to the bulk solution. The same behavior was observed with the secondary effluent that contained almost 68 mg/L of chlorides. The efficiency was favored in a neutral medium, while the hybrid process was delayed in alkaline conditions.