Removal of dinitrotoluenes and trinitrotoluene from industrial wastewater by ultrasound enhanced with titanium dioxide

Intensified degradation of tartrazine dye present in effluent using ultrasound combined with ultraviolet irradiation and oxidants

Effluent containing tartrazine can affect the environment and human health significantly prompting the current study into degradation using a sonochemical reactor operated individually and combined with advanced oxidation processes. The optimum conditions for ultrasound treatment were established as dye concentration of 10 ppm, pH of 3, temperature as 35 °C, and power as 90 W. The combination approach of H2O2/UV, H2O2/US, and H2O2/UV/US resulted in higher degradation of 25.44%, 57.4%, and 74.36% respectively. Use of ZnO/UV/US approach increased the degradation significantly to 85.31% whereas maximum degradation as 93.11% was obtained for the US/UV/Fenton combination. COD reduction was found maximum as 83.78% for the US/UV/Fenton combination. The kinetic analysis showed that tartrazine dye degradation follows pseudo first-order kinetics for all the studied processes. Combination of Fenton with UV and US was elucidated as the best approach for degradation of tartrazine.

Ultrasound for the degradation of endocrine disrupting compounds in aqueous solution: A review on mechanisms, influence of operating parameters and cost estimation

Availability of drinking water is one of the basic humanitarian goals but remains as a grand challenge that the world is facing today. Currently, water bodies are contaminated not only with conventional pollutants but also with numerous recalcitrant pollutants, such as PPCPs, endocrine disrupting compounds, etc. These emerging pollutants require special attention because of their toxicity to living organisms, bio-resistant and can sustain even after primary and secondary treatments of wastewater. Among different treatment technologies, sonolysis is found to be an innovative and promising technique for the treatment of emerging pollutants present in aqueous solution. Sonolysis is the use of ultrasound to enhance or alter chemical reactions by the formation of free radicals and shock waves which ultimately helps in degradation of pollutants. This review summarizes several studies in the sonochemical literature, including mechanisms of sonochemical process, physical and chemical effects of ultrasound, and the influence of several process variables such as ultrasound frequency, power density, temperature and pH of the medium on degradation performance for endocrine disrupting compounds. In addition, this review highlighted techno-economic perspectives focusing on the total cost required for translating the ultrasound-based processes on a large scale. Overall, the objective of this study is to exhibit a critical review of information available in the literature to encourage and promote future research on sonolysis for the degradation of Endocrine Disrupting Compounds (EDCs).

Ultrasound-Assisted Mineralization of 2,4-Dinitrotoluene in Industrial Wastewater Using Persulfate Coupled with Semiconductors

Oxidative degradation of 2,4-dinitrotoluenes in aqueous solution was executed using persulfate combined with semiconductors motivated by ultrasound (probe type, 20 kHz). Batch-mode experiments were performed to elucidate the effects of diverse operation variables on the sono-catalytic performance, including the ultrasonic power intensity, dosage of persulfate anions, and semiconductors. Owing to pronounced scavenging behaviors caused by benzene, ethanol, and methanol, the chief oxidants were presumed to be sulfate radicals which originated from persulfate anions, motivated via either the ultrasound or sono-catalysis of semiconductors. With regard to semiconductors, the increment of 2,4-dinitrotoluene removal efficiency was inversely proportional to the band gap energy of semiconductors. Based on the outcomes indicated in a gas chromatograph-mass spectrometer, it was sensibly postulated that the preliminary step for 2,4-dinitrotoluene removal was denitrated into o-mononitrotoluene or p-mononitrotoluene, followed by decarboxylation to nitrobenzene. Subsequently, nitrobenzene was decomposed to hydroxycyclohexadienyl radicals and converted into 2-nitrophenol, 3-nitrophenol, and 4-nitrophenol individually. Nitrophenol compounds with the cleavage of nitro groups synthesized phenol, which was sequentially transformed into hydroquinone and p-benzoquinone.

Investigation of TNT red wastewater treatment technology using the combination of advanced oxidation processes

Different types of advanced oxidation processes and their combinations such as O₃/H₂O₂/UV, O₃/Fenton/UV, O₃/TiO₂/UV, Fenton/H₂O₂/UV, Fenton/TiO₂/UV, TiO₂/H₂O₂/UV, TiO₂/H₂O₂/O₃/UV, TiO₂/O₃/Fenton/UV, TiO₂/H₂O₂/Fenton/UV and O₃/H₂O₂/Fenton/UV were studied for the treatment of undiluted red wastewater from Z113 Factory. The treatment efficiency was evaluated by analyzing chemical oxygen demand (COD) reduction, % degradation of α-TNT, 2,4-DNT, 2,6-DNT, 2,4-DNT-3-SO₃Na and 2,4-DNT-5-SO₃Na. Among studied processes Fenton/TiO₂/O₃/UV was the most effective technology to treat red wastewater. It allows to reduce >99% of COD, α-TNT, 2,4-DNT, 2,6-DNT, 2,4-DNT-3-SO₃Na and 2,4-DNT-5-SO₃Na after 30 h of treatment with optimum operating conditions: rotation speed of 600 rpm, pH of 4 and temperature of 40 °C. According to the chromatograms obtained by gas chromatograph/mass spectrometer (GC/MS), intermediates of the decomposition of pollutants in red wastewater were identified. GC/MS, HPLC, UV-vis and Bacterial Toxicity test were used to assess effluent quality changes before and after treatment. By economic analysis, the studied process had the potential to apply in practice to treat real wastewater at the Z113 Factory.

New insights in photocatalytic removal of Alizarin Yellow using reduced Ce3+/TiO2 catalyst

The present communication aims to obtain a novel Ce³⁺/TiO₂ thin film in a single step facile method using the in situ template process. The material was characterized by the XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), TEM (transmission electron microscope), and AFM (atomic force microscope) analyses. The thin film catalyst was intended to introduce in the degradation of one of potential dye Alizarin Yellow from aqueous solutions using the UV-A radiations. The mechanisms of degradation along with the physicochemical parametric studies were conducted extensively. The mineralization of pollutant and the replicate use of catalysts further enhance the applicability of present communication. Additionally, the real matrix treatment was conducted to simulate the treatment process.

Sonocatalytic treatment of phosphonate containing industrial wastewater intensified using combined oxidation approaches

Treatment of actual industrial wastewater is a challenging task and has not been investigated using the cavitation-based approaches significantly. In the present work, sonocatalytic degradation (catalysts as CuO and TiO₂) of phosphonate based industrial wastewater, procured from a local company, has been studied in terms of COD reduction under optimized conditions (established using initial studies involving only ultrasound) of pH as 3.2, the temperature of 32 ± 2 °C and 120 min as treatment time. The combination of ultrasound with H₂O₂ and ozone in different approaches has been investigated for maximizing the COD reduction. The optimum set of operating conditions for the sonocatalytic degradation were established as power dissipation of 90 W and catalyst loading as 0.75 g/L for CuO and 0.5 g/L for TiO₂. Use of only ultrasound resulted in COD reduction of 37.2% whereas the combination of US with different approaches resulted in higher extents of COD reduction. The combined operation of US + H₂O₂ + O₃, US + O₃ + H₂O₂ + CuO, and US + O₃ + H₂O₂ + TiO₂ resulted in the extent of COD reduction as 91.5%, 93.8%, and 95.8% respectively. Overall, it has been clearly established that maximum COD reduction is obtained for the combined operation of sonocatalysis (catalyst as TiO₂) with ozone and H₂O₂.

Mineralization of dinitrotoluenes in aqueous solution by sono-activated persulfate enhanced with electrolytes

Oxidative degradation of dinitrotoluenes (DNTs) in industrial wastewater was conducted by sono-activated persulfate process assisted with electrolytes. Experiments were carried out to elucidate the influence of various operating parameters on the sonolytic behavior, such as species and concentrations of electrolytes, ultrasonic power intensity, reaction temperature, dosage of oxygen and persulfate anions. The outcomes indicate that sulfate radicals serve as main oxidants in the sono-activated persulfate process, wherein MgSO₄ electrolyte obviously inhibits microbubble coalescence, leading to enhancement of cavitation strength and DNTs removal percentage. On addition of electrolytes, the increment of DNTs removal percentages was proportional to ionic strength of electrolytes. According to the results obtained from gas chromatograph-mass spectrometer (GC-MS), it is postulated that DNTs initially undergo denitration pathway with cleavage of nitro group into o-mononitrotoluene (MNT) or oxidation of methyl group followed with decarboxylation procedure into 1,3-dinitrobenzene (DNB), respectively. Due to electrolytes observed commonly in wastewater, the sono-activated persulfate process coupled with electrolytes is potentially applied to dispose wastewater effluent from toluene nitration processes.

Optimization of sonochemical degradation of tetracycline in aqueous solution using sono-activated persulfate process

BACKGROUND

In this study, a central composite design (CCD) was used for modeling and optimizing the operation parameters such as pH, initial tetracycline and persulfate concentration and reaction time on the tetracycline degradation using sono-activated persulfate process. The effect of temperature, degradation kinetics and mineralization, were also investigated.

RESULTS

The results from CCD indicated that a quadratic model was appropriate to fit the experimental data (p < 0.0001) and maximum degradation of 95.01 % was predicted at pH = 10, persulfate concentration = 4 mM, initial tetracycline concentration = 30.05 mg/L, and reaction time = 119.99 min. Analysis of response surface plots revealed a significant positive effect of pH, persulfate concentration and reaction time, a negative effect of tetracycline concentration. The degradation process followed the pseudo-first-order kinetic. The activation energy value of 32.01 kJ/mol was obtained for US/S2O8 (2-) process. Under the optimum condition, the removal efficiency of COD and TOC reached to 72.8 % and 59.7 %, respectively. The changes of UV-Vis spectra during the process was investigated. The possible degradation pathway of tetracycline based on loses of N-methyl, hydroxyl, and amino groups was proposed.

CONCLUSIONS

This study indicated that sono-activated persulfate process was found to be a promising method for the degradation of tetracycline.

Transformations of chloro and nitro groups during the peroxymonosulfate-based oxidation of 4-chloro-2-nitrophenol

Dechlorination and denitration are known to occur during the oxidative degradation of chloronitroaromatic compounds, but the possibility of re-chlorination and re-nitration of chloro and nitro groups is not assessed despite of its importance in evaluating the applicability of advanced oxidation processes (AOPs). In this study, transformation of chloro and nitro groups in degradation of 4-chloro-2-nitrophenol (4C2NP) by sulfate radical generated via Co-mediated peroxymonosulfate activation was investigated. Both chloride and nitrate ions were found as the main inorganic products of chloro and nitro groups in 4C2NP, but their levels were much lower than that of degraded parent 4C2NP. A typical dual effect of chloride on the 4C2NP degradation kinetics was observed, whereas no measurable influence was found for addition of low level nitrate. Re-chlorination took place, but re-nitration was not verified because several polychlorophenols but none of polynitrophenols were detected. The specific degradation mechanism involved in the transformation of nitro group and chloro group was proposed.

Decomposition of nitrotoluenes in wastewater by sonoelectrochemical and sonoelectro-Fenton oxidation

Oxidative degradation of dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT) in wastewater was conducted using electrochemical and electro-Fenton processes respectively, combined with ultrasonic irradiation, wherein a synergistic effect is observed. Experiments were carried out to elucidate the influence of various operating variables on the sonoelectrolytic behavior, such as electrode potential, sonoelectrolytic temperature, acidity of wastewater, oxygen dosage, and dosage of ferrous ions. It deserves to note that the nitrotoluene contaminants could be completely decomposed by sonoelectro-Fenton method, wherein hydrogen peroxide was in situ generated from cathodic reduction of oxygen, supplied partially by anodic oxidation of water. During the sonoelectrolytic process, in spite of existence of degassing phenomenon, the high yield of hydrogen peroxide was produced due to the significantly enhanced mass transfer rate of oxygen toward the cathode, caused by ultrasonic irradiation. Because higher removal efficiency of DNTs and TNT obtained at ambient conditions, it is believed that the sonoelectrolytic method is potentially applied to dispose wastewater from toluene nitration processes.

Removal of dinitrotoluenes in wastewater by sono-activated persulfate

Oxidative degradation of dinitrotoluenes (DNTs) in wastewater was performed using persulfate anions combined with ultrasonic irradiation, wherein a synergistic effect is observed. The batch-wise experiments were carried out to elucidate the influence of various operating parameters on sono-activated persulfate oxidation, including ultrasonic power intensity, persulfate anion concentration, reaction temperature and acidity of wastewater. It is noteworthy that the nitrotoluene contaminants could be almost completely eliminated by virtue of sono-activated persulfate oxidation, wherein sulfate radicals serve as principal oxidants, of which amounts are significantly enhanced via addition of sodium sulfate. Based on the results given by gas chromatograph-mass spectrometer (GC-MS), it is postulated that the methyl group of DNTs preliminarily underwent oxidation pathway into dinitrobenzoic acid, followed by decarboxylation to form 1,3-dinitrobenzene (DNB). In sum, the sono-activated persulfate oxidation is a promising method for treatment of nitrotoluenes in wastewater.