Advanced Oxidation Processes for Water and Wastewater Treatment

Photocatalytic degradation process of antibiotic sulfamethoxazole by ZnO in aquatic systems: a dynamic kinetic model based on contributions of OH radical, oxygenated radical intermediates and dissolved oxygen

The photocatalytic degradation process of sulfamethoxazole (SMX) using ZnO in aquatic systems has been systematically studied by varying initial SMX concentration from 0 to 15 mgL-1, ZnO dosage from 0 to 4 gL-1 and UV light intensity at the light source from 0 to 18 W(m-lamp length)-1 at natural pH. Almost complete degradations of SMX were achieved within 120 min for the initial SMX concentration ≤15 mgL-1 with ZnO dosage of 3 gL-1 and UV light intensity of 18 W(m-lamp length)-1. The photocatalytic degradation process was found to be interacted with the dissolved oxygen (DO) consumption. With oxygen supply through the gas-liquid free-surface, the DO concentration decreased significantly in the initial SMX degradation phase and increased asymptotically to the saturated DO concentration after achieving about 80% SMX degradation. The change in DO concentration was probably controlled by the oxygen consumption in the formation of oxygenated radical intermediates. A novel dynamic kinetic model based on the fundamental reactions of photocatalysis and the formation of oxygenated radical intermediates was developed. In the modeling the dynamic concentration profiles of OH radical and DO are considered. The dynamics of SMX degradation process by ZnO was simulated reasonably by the proposed model.

Preparation of Au/ZnO/Fe3O4 Composite for Degradation of Tartrazine under Visible Light

Zinc oxide has been shown to be a potential photocatalyst under UV light but its catalytic activity is limited under visible light due to its wide bandgap energy and rapid recombination of electrons and holes. Besides the catalytic recovery is a challenging issue because of its dispersion in solution. Previous work has shown that the interaction of gold nanoparticles with ZnO can reduce the band gap energy (Eg) and plasmon resonance (SPR) as well as the formation of the Schottky barrier in Au/ZnO composite can reduce the recombination of electrons and holes. In this study, Au/ZnO/Fe3O4 (AZF) composites were prepared by a simple mixing method using polyvinyl alcohol (PVA) as a binder. As-prepared composites were characterized by Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), X-ray Diffraction (XRD), UV-Vis Diffuse Reflectance (UV-Vis-DR), and Fourier Transform Infra Red (FT-IR). The catalytic efficiency of as-prepared samples was evaluated through the decomposition of tartrazine (TA), a colorant that is difficult to decompose in wastewater and has harmful effects on human health. The effects of reaction parameters such as the content of PVA, solution pH, and oxidizing agents (O2 and H2O2) on the catalytic efficiency were studied. The AZF at PVA of 0.0125 g showed the highest performance among as-prepared samples. With the presence of 12 mM H2O2 in the catalyst system, the degradation efficiency and reaction rate of TA in composite increased to 81.5% and 0.020 min−1, respectively. At this condition, photocatalysis and Fenton system catalysis occurred together. The catalytic mechanism of Tartrazine (TA) on composite was proposed and the reaction of TA was studied by the first-order kinetic model. Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Vis LED Photo-Fenton Degradation of 124-Trichlorobenzene at a Neutral pH Using Ferrioxalate as Catalyst

Chlorinated organic compounds (COCs) are among the more toxic organic compounds frequently found in soil and groundwater. Among these, toxic and low-degradable chlorobenzenes are commonly found in the environment. In this work, an innovative process using hydrogen peroxide as the oxidant, ferrioxalate as the catalyst and a visible light-emitting diode lamp (Vis LED) were applied to successfully oxidize 124-trichlorobenzene (124-TCB) in a saturated aqueous solution of 124-TCB (28 mg L^-1) at a neutral pH. The influence of a hydrogen peroxide (HP) concentration (61.5-612 mg L^-1), Fe³⁺ (Fe) dosage (3-10 mg L^-1), and irradiation level (Rad) (I = 0.12 W cm^-2 and I = 0.18 W cm^-2) on 124-TCB conversion and dechlorination was studied. A D-Optimal experimental design combined with response surface methodology (RSM) was implemented to maximize the quality of the information obtained. The ANOVA test was used to assess the significance of the model and its coefficients. The maximum pollutant conversion at 180 min (98.50%) was obtained with Fe = 7 mg L^-1, HP = 305 mg L^-1, and I = 0.12 W cm^-2. The effect of two inorganic anions usually presents in real groundwater (bicarbonate and chloride, 600 mg L^-1 each) was investigated under those optimized operating conditions. A slight reduction in the 124-TCB conversion after 180 min of reaction was noticed in the presence of bicarbonate (8.31%) and chloride (7.85%). Toxicity was studied with Microtox® (Azur Environmental, Carlsbad, CA, USA) bioassay, and a remarkable toxicity decrease was found in the treated samples, with the inhibition proportional to the remaining 124-TCB concentration. That means that nontoxic byproducts are produced in agreement with the high dechlorination degrees noticed.

Sludge disintegration using UV assisted Sono-Fenton process

In this study, the effects of combination of ultrasonic process with UV light and both classical Fenton (CFP) and modified Fenton (MFP) processes on disintegration of waste sludge were investigated. Fe²⁺ and Fe⁰ dosage, hydrogen peroxide dosage, reaction time, pH, and different UV lamps were optimized to achieve a high degree of disintegration (DD). In addition, kinetic study and toxicity analysis were performed under optimum conditions for all processes. For CFP, the best DD 22.85% was found with optimum pH 3, reaction time 60 min, 7 g/kg TS Fe²⁺, 35 g/kg TS H₂O₂ doses, and UV-C light, while this value increased to 37.83% with ultrasound (US) application. For MFP; the best DD was achieved as 25.84% with optimum pH 3, reaction time 60 min, 5 g/kg TS Fe⁰, 25 g/kg TS H₂O₂ doses, and UV-C light; however, it rose to 42.32% in the presence of US. The use of US in all processes increased the germination percentage that expresses the sludge toxicity, up to 100%. In the kinetic study, it was found that all processes are in compliance with zeroth-order kinetics. It was concluded with this study that US has an important synergistic effect on Fenton applications and contributes to sludge disintegration.

Deactivation and Regeneration of Zeolite Catalysts Used in Pyrolysis of Plastic Wastes—A Process and Analytical Review

In catalytic industrial processes, coke deposition remains a major drawback for solid catalysts use as it causes catalyst deactivation. Extensive study of this phenomenon over the last decades has provided a better understanding of coke behavior in a great number of processes. Among them, catalytic pyrolysis of plastics, which has been identified as a promising process for waste revalorization, is given particular attention in this paper. Combined economic and environmental concerns rose the necessity to restore catalytic activity by recovering deactivated catalysts. Consequently, various regeneration processes have been investigated over the years and development of an efficient and sustainable process remains an industrial challenge. Coke removal can be achieved via several chemical processes, such as oxidation, gasification, and hydrogenation. This review focuses on oxidative treatments for catalyst regeneration, covering the current progress of oxidation treatments and presenting advantages and drawbacks for each method. Molecular oxidation with oxygen and ozone, as well as advanced oxidation processes with the formation of OH radicals, are detailed to provide a deep understanding of the mechanisms and kinetics involved (direct and indirect oxidation, reaction rates and selectivity, diffusion, and mass transfer). Finally, this paper summarizes all relevant analytical techniques that can be used to characterize deactivated and regenerated solid catalysts: XRD, N2 adsorption-desorption, SEM, NH3-TPD, elemental analysis, IR. Analytical techniques are classified according to the type of information they provide, such as structural characteristics, elemental composition, or chemical properties. In function of the investigated property, this overall tool is useful and easy-to-use to determine the adequate analysis.

Enhanced Visible-Light Driven Photocatalytic Activity of Ag@TiO2 Photocatalyst Prepared in Chitosan Matrix

Ag doped TiO2 photocatalysts (Ag@TiO2) were prepared with an aim to extend the absorption range of TiO2 into the visible region, for tentative application under solar irradiation. Photocatalyst synthesized by the novel method using chitosan for reduction of Ag+ to Ag0 nanoparticles was compared to similar catalysts previously reported. The photocatalytic activity of Ag@TiO2 obtained by a simple novel method was evaluated based on degradation of salicylic acid as a model compound. The higher activity under visible irradiation can be attributed to the surface plasmon resonance and suppression of the electron-hole recombination when deposition of Ag nanoparticles on TiO2 was achieved using chitosan. The photocatalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), high resolution TEM (HRTEM), energy dispersive X-ray spectroscopy (EDXS), selected area diffraction (SAED), and diffuse reflectance spectroscopy (DRS). The photochromism of Ag was observed and explained.

Sonochemical Degradation of Benzothiophene (BT) in Deionized Water, Natural Water and Sea Water

This paper deals with the sonochemical water treatment of polycyclic aromatic sulfur hydrocarbons (PASHs), one of the most common impurities found in waste water coming from petroleum industry. The best fit of the experimental data appears to be the kinetic parameters determined using the Michaelis-Mentonmodel in the concentrations range of the study. For the initial increase in the degradation rates, it is simply considered that the more the bulk concentration increases, the more the concentration in the interfacial region increases. This will be explained by Michaelis-Menton kinetics. The influence of organic compounds in the water matrix as a mixture with Benzothiophene (BT) was also evaluated. The results indicated that BT degradation is unaffected by the presence of bisphenol A (BPA). Finally, the results indicated that ultrasonic action is involved in oxidation rather than pyrolitic processing in the BT sonochemical degradation.

Aqueous OH Radical Reaction Rate Constants for Organophosphorus Flame Retardants and Plasticizers: Experimental and Modeling Studies

Aqueous ·OH reaction rate constants ( k_OH) for organophosphate esters (OPEs) are essential for assessing their environmental fate and removal potential in advanced oxidation processes (AOPs). Herein experimental and in silico approaches were adopted to obtain k_OH values for a variety of OPEs. The determined k_OH for 18 OPEs varies from 4.0 × 10⁸ M^-1 s^-1 to 1.6 × 10¹⁰ M^-1 s^-1. Based on the experimental k_OH values, a quantitative structure-activity relationship model that involves molecular structural information on the number of heavy atoms, content index, and the most negative charge of C atoms was developed for predicting k_OH of other OPEs. Furthermore, appropriate density functional theory (DFT) and solvation models were selected, which together with transition state theory were employed to predict k_OH of three representative OPEs. The deviation between the DFT calculated and the experimental k_OH values ( k_cal/ k_exp) is within 2. Half-lives of the OPEs were estimated to be 0.5-22791.3 days in natural waters and 0.044-19.7 s in AOPs, indicating the OPEs are potentially persistent in natural waters and can be quickly eliminated by AOPs. The determined k_OH values and the in silico methods offer a scientific base for assessing OPEs fate in aquatic environments.

Benchmarking the scientific research on wastewater-energy nexus by using bibliometric analysis

With an exponential increase in urbanization and industrialization, water pollution is an inevitable consequence of relatively lagging wastewater treatment facilities. The conventional activated sludge process for wastewater treatment primarily emphasizes the removal of harmful substances to maintain increasingly stringent effluent discharged standards, which is considered an energy-intensive technique. Therefore, innovative and sustainable wastewater treatment should pay more attention to energy and resource recovery in dealing with fossil fuel depletion, global-scale energy security, and climate change. A bibliometric analysis was applied to trace wastewater-energy nexus-related research during the period 1991 to 2015, with respect to the Science Citation Index EXPANDED (SCI-EXPANDED) database. Journal of Hazardous Materials, ranking 1st in h-index (79), was the most productive journal (431, 4.5%) during the same time, followed by International Journal of Hydrogen Energy (422, 4.4%) and Water Research (393, 4.1%) journal, the latter owning a topmost journal impact factor. Though, China (2154, 22.5%) was the most productive country, while the USA with highest h-index (88) was the favorest collaborative country. The Chinese Academy of Sciences, China (241, 2.5%) produced the maximum publications. A novel method called "word cluster analysis" showed that the emerging sustainable processes and novel renewable energy application are applied in response to the desire for a net wastewater-energy nexus system. Based on different wastewater types, the emerging energy and sources recovery treatment processes of Anammox, anaerobic digestion, and microbial fuel cells gained extensive innovation. Evaluation indicators including sustainability, life cycle assessment, and environmental impact were appropriately used to dissert feasibility of the novel treatment methods in regard of renewable energy utilization, energy savings, and energy recovery. The transformation of the new concept of "broaden income source, economize on expenditures and exploit inner potential" should be generalized in order to achieve an environmentally sustainable development of wastewater-energy nexus system.