Ultrasound/chlorine sono-hybrid-advanced oxidation process: Impact of dissolved organic matter and mineral constituents

In this work, after exploring the first report on the synergism of combining ultrasound (US: 600 kHz) and chlorine toward the degradation of Allura Red AC (ARAC) textile dye, as a contaminant model, the impact of various mineral water constituents (Cl⁻, SO₄²⁻, NO₃⁻, HCO₃⁻ and NO₂⁻) and natural organic matter, i.e., humic acid (HA), on the performance of the US/chlorine sono-hybrid process was assessed for the first time. Additionally, the process effectiveness was evaluated in a real natural mineral water (NMW) of a known composition. Firstly, it was found that the combination of ultrasound and chlorine (0.25 mM) at pH 5.5 in cylindrical standing wave ultrasonic reactor (f = 600 kHz and P_e = 120 W, equivalent to P_A ∼ 2.3 atm) enhanced in a drastic manner the degradation rate of ARAC; the removal rate being 320% much higher than the arithmetic sum of the two separated processes. The source of the synergistic effect was attributed to the effective implication of reactive chlorine species (RCS: Cl, ClO and Cl₂⁻) in the degradation process. Radical probe technique using nitrobenzene (NB) as a specific quencher of the acoustically generated hydroxyl radical confirmed the dominant implication of RCS in the overall degradation rate of ARAC by US/chlorine system. Overall, the presence of humic acid and mineral anions decreased the efficiency of the sono-hybrid process; however, the inhibition degrees depend on the type and the concentration of the selected additives. The reaction of these additives with the generated RCS is presumably the reason for the finding results. The inhibiting effect of Cl⁻, SO₄²⁻, NO₃⁻ and NO₂⁻ was more pronounced in US/chlorine process as compared to US alone, whereas the inverse scenario was remarked for the effect of HA. These outcomes were associated to the difference in the reactivity of HA and mineral anions toward RCS and OH oxidizing species, in addition to the more selective character of RCS than hydroxyl radical. The displacement of the reaction zone with increasing the additive concentration may also be another influencing factor that favors competition reactions, which subsequently reduce the available reactive species in the reacting medium. The NMW exerted reductions of 43% and 10% in the process efficiency at pH 5.5 and 8, respectively, thereby confirming the RCS-quenching mechanism by the water matrix constituents. Hence, this work provided a precise understanding of the overall mechanism of chlorine activation by ultrasound to promote organic compounds degradation in water.     

Ultrasound for the remediation of contaminated waters with persistent organic pollutants: A short review

The rising amount of persistent organic contaminants released into water reservoirs in the last years became a cause of concern for the industry, academy, and public administration, due to their bioaccumulation, mutagenicity, and photosynthesis reduction. Therefore, the search for processes that efficiently remove such contaminants became of primary importance. In this context, ultrasound (US) is one of the most promising and economically viable alternatives to degrade organic pollutants in varied environments. Whereas the use of other advanced oxidation processes (AOPs), such as Fenton and photocatalysis, has been widely reported for this purpose, only a few papers deal with ultrasound application as a possible AOP. In this review, a general overview of ultrasound is provided, covering the last twenty years. It includes fundamental aspects of ultrasound and applications, individually or combined with other AOPs, to deplete organic pollutants from various classes in an aqueous environment. Finally, the review concludes by indicating that additional research should be conducted worldwide to explore the full potential of ultrasound as a useful AOP.     

Degradation of 2,4-dinitrophenol using a combination of hydrodynamic cavitation,chemical and advanced oxidation processes

In the present work, degradation of 2,4-dinitrophenol (DNP), a persistent organic contaminant with high toxicity and very low biodegradability has been investigated using combination of hydrodynamic cavitation (HC) and chemical/advanced oxidation. The cavitating conditions have been generated using orifice plate as a cavitating device. Initially, the optimization of basic operating parameters have been done by performing experiments over varying inlet pressure (over the range of 3–6 bar), temperature (30 °C, 35 °C and 40 °C) and solution pH (over the range of 3–11). Subsequently, combined treatment strategies have been investigated for process intensification of the degradation process. The effect of HC combined with chemical oxidation processes such as hydrogen peroxide (HC/H₂O₂), ferrous activated persulfate (HC/Na₂S₂O₈/FeSO₄) and HC coupled with advanced oxidation processes such as conventional Fenton (HC/FeSO₄/H₂O₂), advanced Fenton (HC/Fe/H₂O₂) and Fenton-like process (HC/CuO/H₂O₂) on the extent of degradation of DNP have also been investigated at optimized conditions of pH 4, temperature of 35 °C and inlet pressure of 4 bar. Kinetic study revealed that degradation of DNP fitted first order kinetics for all the approaches under investigation. Complete degradation with maximum rate of DNP degradation has been observed for the combined HC/Fenton process. The energy consumption analysis for hydrodynamic cavitation based process has been done on the basis of cavitational yield. Degradation intermediates have also been identified and quantified in the current work. The synergistic index calculated for all the combined processes indicates HC/Fenton process is more feasible than the combination of HC with other Fenton like processes.     

Ultrasonic processes for the advanced remediation of contaminated sediments

Sediments play a fundamental role in the aquatic environment, so that the presence of contaminants poses severe concern for the possible negative effects on both environmental and human health. Sediment remediation is thus necessary to reduce pollutant concentrations and several techniques have been studied so far. A novel approach for sediment remediation is the use of Advanced Oxidation Processes, which include ultrasound (US). This paper focuses on the study of the ultrasonic effects for the simultaneous reduction of both organic and inorganic contaminants from sediments. To this end, the US technology was investigated as a stand-alone treatment as well as in combination with an electro-kinetic (EK) process, known to be effective in the removal of heavy metals from soil and sediments. The US remediation resulted in higher organic compound degradation, with an average 88% removal, but promising desorption yields (47–84%) were achieved for heavy metals as well. The combined EK/US process was found to be particularly effective for lead. Experimental outcomes highlighted the potential of the ultrasonic technology for the remediation of contaminated sediments and addressed some considerations for the possible scale-up.     

Recent trends in the applications of sonochemical reactors as an advanced oxidation process for the remediation of microbial hazards associated with water and wastewater: A critical review

Water is one of the major sources that spread human diseases through contamination with bacteria and other pathogenic microorganisms. This review focuses on microbial hazards as they are often present in water and wastewater and cause various human diseases. Among the currently used disinfection methods, sonochemical reactors (SCRs) that produce free radicals combined with advanced oxidation processes (AOPs) have received significant attention from the scientific community. Also, this review discussed various types of cavitation reactors, such as acoustic cavitation reactors (ACRs) utilizing ultrasonic energy (UE), which had been widely employed, involving AOPs for treating contaminated waters. Besides ACRs, hydrodynamic cavitation reactors (HCRs) also effectively destroy and deactivate microorganisms to varying degrees. Cavitation is the fundamental phenomenon responsible for initiating many sonochemical reactions in liquids. Bacterial degradation occurs mainly due to the thinning of microbial membranes, local warming, and the generation of free radicals due to cavitation. Over the years, although extensive investigations have focused on the antimicrobial effects of UE (ultrasonic energy), the primary mechanism underlying the cavitation effects in the disinfection process, inactivation of microbes, and chemical reactions involved are still poorly understood. Therefore, studies under different conditions often lead to inconsistent results. This review investigates and compares other mechanisms and performances from greener and environmentally friendly sonochemical techniques to the remediation of microbial hazards associated with water and wastewater. Finally, the energy aspects, challenges, and recommendations for future perspectives have been provided.     

Sonochemical synthesis,characterization, and effects of temperature,power ultrasound and reaction time on the morphological properties of two new nanostructured mercury(II) coordination supramolecule compounds

Two new mercury(II) coordination supramolecular compounds (CSCs) (1D and 0D), [Hg(L)(I)₂]_n (1) and [Hg₂(L′)₂(SCN)₂]·2H₂O (2) (L = 2-amino-4-methylpyridine and L′ = 2,6-pyridinedicarboxlic acid), have been synthesized under different experimental conditions. Micrometric crystals (bulk) or nano-sized materials have been obtained depending on using the branch tube method or sonochemical irradiation. All materials have been characterized by field emission scanning electron microscope (FESEM), scanning electron microscopy (SEM), powder X-ray diffraction (PXRD) and FT-IR spectroscopy. Single crystal X-ray analyses on compounds 1 and 2 show that Hg²⁺ ions are 4-coordinated and 5-coordinated, respectively. Topological analysis shows that the compound 1 and 2 have 2C1, sql net. The thermal stability of compounds 1 and 2 in bulk and nano-size has been studied by thermal gravimetric (TG), differential thermal analyses (DTA) for 1 and differential scanning calorimetry (DSC) for 2, respectively. Also, by changing counter ions were obtained various structures 1 and 2 (1D and 0D, respectively). The role of different parameters like power of ultrasound irradiation, reaction time and temperature on the growth and morphology of the nano-structures are studied. Results suggest that increasing power ultrasound irradiation and temperature together with reducing reaction time and concentration of initial reagents leads to a decrease in particle size.     

A critical review on the sonochemical degradation of organic pollutants in urine,seawater, and mineral water

Substances such as pharmaceuticals, pesticides, dyes, synthetic and natural hormones, plasticizers, and industrial chemicals enter the environment daily. Many of them are a matter of growing concern worldwide. The use of ultrasound to eliminate these compounds arises as an interesting alternative for treating mineral water, seawater, and urine. Thereby, this work presents a systematic and critical review of the literature on the elimination of organic contaminants in these particular matrices, using ultrasound-based processes. The degradation efficiency of the sonochemical systems, the influence of the nature of the pollutant (volatile, hydrophobic, or hydrophilic character), matrix effects (enhancement or detrimental ability compared to pure water), and the role of the contaminant concentration were considered. The combinations of ultrasound with other degradation processes, to overcome the intrinsic limitations of the sonochemical process, were considered. Also, energy consumptions and energy costs associated with pollutants degradation in the target matrices were estimated. Moreover, the gaps that should be developed in future works, on the sonodegradation of organic contaminants in mineral water, seawater, and urine, were discussed.     

The removal characteristics of natural organic matter in the recycling of drinking water treatment sludge: Role of solubilized organics

To clarify the role of solubilized organics derived from drinking water treatment sludge (DWTS) in the elimination of natural organic matter (NOM) in the DWTS recycling process, a probe sonoreactor at a frequency of 25 kHz was used to solubilize the organics at varied specific energies. The coagulation behavior related to NOM removal in recycling the sonicated DWTS with and without solubilized organics was evaluated, and the effect on organic fractionations in coagulated water was determined. The study results could provide useful implications in designing DWTS recycling processes that avoid the enrichment of organic matter. Our results indicate that DWTS was disrupted through a low release of soluble chemical oxygen demand (SCOD) and proteins, which could deteriorate the coagulated water quality under the specific energy of 37.87–1212.1 kW h/kg TS. The optimal coagulation behavior for NOM removal was achieved by recycling the sonicated DWTS without solubilized organics at 151.5 kW h/kg TS specific energy. Recycling the sonicated DWTS could increase the enrichment potential of weakly hydrophobic acid, hydrophilic matter, and <3 kDa fractions; the enrichment risks could be reduced by discharging the solubilized organics. Fluorescent characteristic analysis indicated that when recycling the sonicated DWTS without solubilized organics, the removal of humic-like substances was limited, whereas removal of protein-like substances was enhanced, lowering the enrichment potential of protein-like substances.     

Sonochemical synthesis of a novel nanoscale 1D lead(II) [Pb2(L)2(I)4]n coordination Polymer,survey of temperature,reaction time parameters

One new lead(II) coordination supramolecular complex (CSC) (1D), [Pb₂(L)₂(I)₄]_n, L = C₄H₆N₂ (1-methyl imidazole), has been synthesized under different experimental conditions. Micrometric crystals (bulk) or nano-sized materials have been obtained depending on using the branch tube method or sonochemical irradiation. All materials have been characterized by scanning electron microscopy (SEM), powder X-ray diffraction (PXRD) and FT-IR spectroscopy. Single crystal X-ray analyses on complex 1 showed that Pb²⁺ ion is 4-coordinated. Topological analysis shows that the complex 1 is 2,3,5C2 net. Finally, the role of reaction time and temperature on the growth and final morphology of the structures obtained by sonochemical irradiation have been studied.     

太湖典型湖区水体溶解有机质的光谱学特征

应用荧光光谱、紫外光谱及多种紫外参数等光谱学手段对太湖水体溶解有机质(DOM)进行分析测定,探讨太湖典型湖区水体中DOM的来源及其影响因素。结果表明:不同湖区水体DOM组成特性呈现出一定的区域特征,位于入湖河流的T1点和T2点所代表的竺山湾湖区,结构复杂的大分子物质和腐殖质类物质含量较多,这些区域受多重来源包括生物来源、陆源及生产生活污水的影响较大;以T3为代表的梅梁湾湖区、T4为代表的贡湖湾湖区和T5所处的湖心区其DOM复杂化程度相对较低;而T6点代表的东太湖湖区,因受外界环境的影响较小,以结构简单的类蛋白物质含量居多。     

Sonoelectrochemical degradation of triclosan in water

The sonoelectrochemical degradation of triclosan in aqueous solutions with high-frequency ultrasound (850 kHz) and various electrodes was investigated. Diamond coated niobium electrode showed the best results and was used as standard electrode, leading to effective degradation and positive synergistic effect. The influence of different parameters on the degradation degree and energy efficiency were evaluated and favorable reaction conditions were found. It could be shown that 92% of triclosan (1 mg L⁻¹ aqueous solution) was degraded within 15 min, following pseudo-first order kinetics.     

Transformation of organic and inorganic sulphur in a lignite during pyrolysis: Influence of inherent and added inorganic matter

The transformation of organic and inorganic sulphur during pyrolysis of a Western Australian lignite has been studied using several complimentary techniques. The lignite contains high moisture, oxygen, volatile matter, organic sulphur and inherent inorganic matter. FTIR and solid state ¹³C TOSS NMR spectroscopic studies revealed that the high oxygen content is attributed to the oxygenated functional groups, which is saturated with organically bonded inherent inorganic matter. Sodium and chlorine are the dominant inorganic matter and present in the form of sodium chloride. TGA-MS studies of the raw lignite showed that SO₂ is the dominant sulphur-bearing gases evolved during the pyrolysis of the raw lignite. The effect of inherent and added inorganics was studied by comparing the amounts of various forms of sulphur retained in the chars of the raw lignite, the acid washed lignite and the acid washed lignite doped with sodium and kaolinite following pyrolysis in a fixed-bed reactor in nitrogen. Inherent inorganic matter was shown to reduce the decomposition of organic sulphur but has little effect on the decomposition of inorganic sulphur. Sodium helps the retention of sulphur in the chars between 400 and 500 °C while kaolinite has a better ability to retain sulphur above 600 °C.     

Effect of nitrate ions on the efficiency of sonophotochemical phenol degradation

A sonophotochemical oxidation process has been used for the treatment of an aqueous solution of phenol. The aim of this work is to evaluate the effect of nitrate ions on hydroxyl radical production and on phenol oxidation. It has been demonstrated that ultrasound can produce NOx (nitrate and nitrite), with a production rate of 2.2 μM min⁻¹. The photolysis of nitrate can significantly improve the hydroxyl radical production. The apparent rate constant for hydroxyl radical production increased from 0.0015 min⁻¹ to 0.0073 min⁻¹ while increasing initial nitrate concentration from 0 to 0.5 mM. The concentration of hydroxyl radical was directly proportional to the initial nitrate concentration. Using US/UV process, the apparent reaction rate constant of phenol degradation in the presence of nitrate reached 0.020 min⁻¹, which was relatively lower than the value obtained (0.027 min⁻¹) in the absence of nitrate. It appeared that, nitrate ions can inhibit the sonochemical degradation of organic compounds such as phenol.     

Degradation of endocrine disruptor bisphenol A by ultrasound-assisted electrochemical oxidation in water

Micropollutants are becoming an increasing problem for the environment and wastewater treatment. One example is Bisphenol A (BPA), an endocrinic disruptor, which is widely used in plastic production. Due to its endocrine disrupting effects on aquatic (micro-)organisms and its ubiquity, in surface- and wastewater alike, adequate treatment techniques are necessary.In this study, the degradation of BPA by a sonoelectrochemical hybrid system was investigated, using a low frequency (24 kHz) ultrasound horn and two boron doped diamond electrodes. It was found that by the combination of the individual processes, i.e. ultrasound and electrochemical oxidation, more than 90% of BPA could be removed within 30 min at an initial concentration of 1 mg L⁻¹. Moreover, synergistic effects were discovered and a considerable improvement compared to the individual processes could be achieved by using a potential of 5 V, whereas synergistic effects were absent at a potential of 10 V. This study provides investigation of ultrasound amplitude, potential and electrode positioning on BPA degradation. The reaction was found to follow pseudo first order kinetics with a rate constant of 0.089 min⁻¹. Samples were analysed by high pressure liquid chromatography (HPLC) using a diode array detector. Moreover, the presence and distribution of hydroxyl radicals within the reactor was visualized by using sonochemiluminescence.     

Sonochemical synthesis of PdO@silica as a nanocatalyst for selective aerobic alcohol oxidation

A sonochemical method has been employed for the synthesis of palladium oxide (PdO) nanoparticles deposited on silica nanoparticle. By sonochemical process, the PdO nanoparticles were doped on the surface of silica at room temperature and atmospheric pressure with short reaction time. Silica nanoparticles were used as a supporting material to suppress aggregation and thereby to increase surface area of PdO nanoparticles. Fabricated PdO-doped silica nanoparticle (PdO@SNP) was applied as a nanocatalyst for selective alcohol oxidation reaction in the presence of molecular oxygen. The PdO@SNP composite showed higher catalytic activity and selectivity than unsupported PdO nanoparticle for aerobic alcohol oxidation reaction.     

Mechanistic investigations in sono-hybrid (ultrasound/Fe2+/UVC) techniques of persulfate activation for degradation of Azorubine

Persulfate-based oxidation of recalcitrant pollutants has been investigated as an alternative to OH radical based advanced oxidation processes due to distinct merits such as greater stability and non-selective persistent reactivity of ${\text{SO}}_4^{\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}-}$ oxidant species. The present study has attempted to highlight mechanistic features of persulfate-based decolorization of textile dye (Azorubine) using sono-hybrid techniques of activation. Three activation techniques, viz. sonolysis, Fe²⁺ ions and UVC light and combinations thereof, have been examined. UVC is revealed to be the most efficient decolorization technique. The mechanism of sonolysis (i.e. thermal activation of persulfate in the bubble-bulk interfacial region) is revealed to be almost independent of the mechanism of UVC. Fe²⁺ activation is revealed to have an adverse interaction with UVC due to scavenging of sulfate radicals by Fe²⁺ ions. The best hybrid activation technique for persulfate-based degradation and mineralization of Azorubine is UVC + ultrasound. Due to independent mechanisms, degradation and mineralization of the dye obtained with simultaneous application of UVC and ultrasound is nearly equal to the sum of degradation and mineralization obtained using individual techniques.     

Performance and energetic analysis of hydrodynamic cavitation and potential integration with existing advanced oxidation processes: A case study for real life greywater treatment

The current work is a “first of a kind” report on the feasibility and efficacy of hydrodynamic cavitation integrated Advanced Oxidation Processes (AOP’s) towards treatment of a real life greywater stream in form of kitchen wastewater. The work has been carried out in a sequential manner starting with geometry optimization of orifice plate (cavitating device) followed by studying the effects of inlet pressure, pH, effluent dilution ratio on degradation of TOC and COD. Under optimized conditions of pH 3, 4 bar pressure, TOC and COD reduction of 18.23 and 25% were obtained using HC for a period of 120 min. To improve the performance of HC, further studies were carried out by integrating H₂O₂ and O₃ with HC. Using 5 g/h optimum dosage of H₂O₂, 87.5% reduction in COD was obtained beyond which it started decreasing. Moreover, integrating O₃ (57.5% reduction in COD) increased the treatment cost. However, a hybrid process (HC + H₂O₂ + O₃) yielded 76.26 and 98.25% reductions in TOC and COD within 60 min. The energetics of all the processes and the treatment costs were studied in detail and it was concluded that combined process of HC + H₂O₂ + O₃ surpassed by far the performances of HC + H₂O₂ and HC + O₃.     

Sonochemical degradation of 3-methylpyridine (3MP) intensified using combination with various oxidants

3-Methyl pyridine (3MP) is a toxic and hazardous organic compound having considerable negative impact on environment and living organisms. The objective of this work to report a novel treatment strategy based on sonochemical degradation of 3MP, in combination with oxidants such as hydrogen peroxide, Fenton’s reagent, peroxymonosulphate (PMS), and potassium persulphate (KPS) as well as solar irradiations. A bath sonicator operating at 25 kHz frequency and rated power dissipation of 100 W was applied in the work to study different approaches with an objective to enhance the removal of 3MP in lesser time. Effect of operating parameters such as pH (over the range of 2–10), treatment time, temperature (25–55 °C) and ultrasonic power (25 W to 150 W) on the degradation has been studied and the best conditions were used in subsequent combination approaches. It was demonstrated that ultrasound in combination with PMS, ferrous sulphate (FeSO₄) and solar irradiations (approach of US/PMS/FeSO₄/solar irradiation) is the best treatment strategy yielding maximum degradation as 97.4% with highest cavitational yield as 1.920 × 10⁻⁴ mg/J and highest synergetic Index as 2.70. Kinetic analysis revealed that first order mechanism fitted well to all the approaches involving different combinations of ultrasound, oxidising agents and solar irradiation. Degradation products were also analysed that established the degradation mechanism as C₂ and C₃ ring cleavages forming 1, 4-dihydro3-methylpyridine followed by Levulinic acid as non -toxic main by-product. Overall the work clearly demonstrated an effective treatment approach involving combined sonication with oxidants for remediation of 3MP also providing insights on kinetics and mechanism of degradation.     

Impact of ultrasound treatment on lipid oxidation of Cheddar cheese whey

Ultrasound (US) has been suggested for many whey processing applications. This study examined the effects of ultrasound treatment on the oxidation of lipids in Cheddar cheese whey. Freshly pasteurized whey (0.86 L) was ultrasonicated in a contained environment at the same range of frequencies and energies for 10 and 30 min at 37 °C. The US reactor used was characterized by measuring the generation of free radicals in deionized water at different frequencies (20–2000 kHz) and specific energies (8.0–390 kJ/kg). Polar lipid (PL), free and bound fatty acids and lipid oxidation derived compounds were identified and quantified before and after US processing using high performance liquid chromatography equipped with an evaporative light scattering detector (HPLC–ELSD), methylation followed by gas chromatography flame ionized detector (GC-FID) and solid phase micro-extraction gas chromatography mass spectrometry (SPME-GCMS), respectively. The highest concentration of hydroxyl radical formation in the sonicated whey was found between 400 and 1000 kHz. There were no changes in phospholipid composition after US processing at 20, 400, 1000 and 2000 kHz compared to non-sonicated samples. Lipid oxidation volatile compounds were detected in both non-sonicated and sonicated whey. Lipid oxidation was not promoted at any tested frequency or specific energy. Free fatty acid concentration was not affected by US treatment per se. Results revealed that US can be utilized in whey processing applications with no negative impact on whey lipid chemistry.     

Preparation of cube micrometer potassium niobate (KNbO3) by hydrothermal method and sonocatalytic degradation of organic dye

Cube micrometer potassium niobate (KNbO₃) powder, as a high effective sonocatalyst, was prepared using hydrothermal method, and then, was characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). In order to evaluate the sonocatalytic activity of prepared KNbO₃ powder, the sonocatalytic degradation of some organic dyes was studied. In addition, some influencing factors such as heat-treatment temperature and heat-treatment time on the sonocatalytic activity of prepared KNbO₃ powder and catalyst added amount and ultrasonic irradiation time on the sonocatalytic degradation efficiency were examined by using UV–visible spectrophotometer and Total Organic Carbon (TOC) determination. The experimental results showed that the best sonocatalytic degradation ratio (69.23%) of organic dyes could be obtained when the conditions of 5.00 mg/L initial concentration, 1.00 g/L prepared KNbO₃ powder (heat-treated at 400 °C for 60 min) added amount, 5.00 h ultrasonic irradiation (40 kHz frequency and 300 W output power), 100 mL total volume and 25–28 °C temperature were adopted. Therefore, the micrometer KNbO₃ powder could be considered as an effective sonocatalyst for treating non- or low-transparent organic wastewaters.