Role of micro-size zero valence iron as particle electrodes in a three-dimensional heterogeneous electro-ozonation process for nitrobenzene degradation

A novel water treatment process (designated E-Fe⁰-O₃ process) was constructed by combining electrolysis, micro-size zero valence iron (Fe⁰) and ozone in this study. Compared with other control processes, the combined process demonstrated a remarkable synergy, and it could obtain 90.5% of NB removal within 20 min. As for the mineralization experiment, the TOC removal efficiency for NB within 120 min was higher in the E-Fe⁰-O₃ process, while the energy consumption was lower than the traditional E-O₃ and E-Fe⁰ process. Interestingly, hydroxyl radicals (OH) acted as a key role for NB removal, and the concentration of OH in different processes were compared. Further study indicated OH, direct anode oxidation, direct ozonation, and zero valence iron catalysis were all responsible for nitrobenzene removal. Besides, the durability of Fe⁰ in the E-Fe⁰-O₃ process was systematically evaluated by reusing Fe⁰ 10 times. Notably, the electric field could protect micro-size zero valence iron from passivation for catalytic ozonation after the long-term reaction. Finally, other ozone-refractory organics pollutants were also investigated in the E-Fe⁰-O₃ process, and the influence of various water matrices on NB removal was discussed. All results demonstrated that the E-Fe⁰-O₃ process was an efficient method to remove refractory organic pollutants in various natural waters.

Performance of ozone and peroxone on the removal of endocrine disrupting chemicals (EDCs) coupled with cost analysis

Micropollutants such as endocrine disruptors are one of the most important groups of chemicals polluting water resources. Conventional treatment systems may not be effective for the removal of endocrine disrupting chemicals (EDCs), and the fate of these chemicals should be carefully monitored in the effluent of wastewater treatment plants (WWTPs). Additional treatment methods such as advanced oxidation processes can be used for the removal of endocrine disruptors. This study presents the existence of endocrine disruptors in 4 different effluents: (i) municipal WWTP effluent, (ii) textile industry WWTP effluent, (iii) organized industrial zone (OIZ) WWTP effluent and (iv) pharmaceutical industry discharge and also presents their removal efficiencies by ozonation and peroxone oxidation. A broad spectrum of removal efficiencies was observed for the EDCs present in the samples since the oxidation efficiency of wastewaters containing EDCs mainly depends on the wastewater matrix and on the type of the EDCs. Ozonation was found to be a lower-cost option than peroxone oxidation at the investigated conditions.

Degradation of atrazine by catalytic ozonation in the presence of iron scraps: performance, transformation pathway, and acute toxicity

Degradation of atrazine by catalytic ozonation in the presence of iron scraps (ZVI/O₃) was carried out. The key operational parameters (i.e., initial pH, ZVI dosage, and ozone dosage) were optimized by the batch experiments, respectively. This ZVI/O₃ system exhibited much higher degradation efficiency of atrazine than the single ozonation, ZVI, and traditional ZVI/O₂ systems. The result shows that the pseudo-first-order constant (0.0927 min^-1) and TOC removal rate (86.6%) obtained by the ZVI/O₃ process were much higher than those of the three control experiments. In addition, X-ray diffraction (XRD) analysis indicates that slight of γ-FeOOH and Fe₂O₃ were formed on the surface of iron scrap after ZVI/O₃ treatment. These corrosion products exhibit high catalytic ability for ozone decomposition, which could generate more hydroxyl radical (HO^•) to degrade atrazine. Six transformation intermediates were identified by liquid chromatography-mass spectrometry (LC-MS) analysis in ZVI/O₃ system, and the degradation pathway of atrazine was proposed. Toxicity tests based on the inhibition of the luminescence emitted by Photobacterium phosphoreum and Vibrio fischeri indicate the detoxification of atrazine by ZVI/O₃ system. Finally, reused experiments indicate the approving recyclability of iron scraps. Consequently, the ZVI/O₃ system could be as an effective and promising technology for pesticide wastewater treatment.

Pretreatment of water-based seed coating wastewater by combined coagulation and sponge-iron-catalyzed ozonation technology

Coagulation-sedimentation combined with sponge iron/ozone (CS-SFe/O₃) technology was applied to pretreat water-based seed coating wastewater (WSCW) from pesticide manufacturing. Coagulation with polyferric sulfate at a dosage of 1.5 g L^-1 and a pH of 8.0 was effective, with color and chemical oxygen demand (COD) removal rates of 96.8 and 83.4%, respectively. SFe/O₃ treatment further reduced the organic content in the effluents, especially concerning the degradation of aromatic pollutants, as demonstrated via ultraviolet-visible spectrophotometry (UV-vis), excitation-emission matrix (EEM) fluorescence spectrometry, and gas chromatography-mass spectrometry (GC/MS) analyses. The residual color and COD values of the effluent were 581.0 times and 640.0 mg L^-1, respectively, under optimal conditions (ozone concentration of 0.48 mg L^-1, SFe dosage of 20.0 g L^-1, initial pH of 9.0, and reaction time of 30 min). Organic pollutants were also degraded by the high amounts of HO, which may have been generated via the transformation of ozone into HO on the SFe's surface and in the solution. Meanwhile, the biochemical oxygen demand (BOD₅)/COD ratio of the WSCW increased, which indicates that the biodegradability improved significantly. The amount of iron leached from SFe particles was 4.5 mg L^-1, which shows that the SFe catalyst has good stability. The operating cost of the combined CS-SFe/O₃ technology was estimated at approximately 2.79 USD t^-1. The results of this study suggest that the application of the combined CS-SFe/O₃ technology in WSCW pretreatment can be beneficial for removing suspended solids, degrading recalcitrant pollutants, and enhancing biodegradability for the subsequent bioprocessing treatment.

Enhancing the efficiency of zero valent iron by electrolysis: Performance and reaction mechanism

Electrolysis was applied to enhance the efficiency of micron-size zero valent iron (mFe⁰) and thereby promote p-nitrophenol (PNP) removal. The rate of PNP removal by mFe⁰ with electrolysis was determined in cylindrical electrolysis reactor that employed annular aluminum plate cathode as a function of experimental factors, including initial pH, mFe⁰ dosage and current density. The rate constants of PNP removal by Ele-mFe⁰ were 1.72-144.50-fold greater than those by pristine mFe⁰ under various tested conditions. The electrolysis-induced improvement could be primarily ascribed to stimulated mFe⁰ corrosion, as evidenced by Fe²⁺ release. The application of electrolysis could extend the working pH range of mFe⁰ from 3.0 to 6.0 to 3.0-10.0 for PNP removal. Additionally, intermediates analysis and scavengers experiments unraveled the reduction capacity of mFe⁰ was accelerated in the presence of electrolysis instead of oxidation. Moreover, the electrolysis effect could also delay passivation of mFe⁰ under acidic condition, as evidenced by SEM-EDS, XRD, and XPS analysis after long-term operation. This is mainly due to increased electromigration meaning that iron corrosion products (iron hydroxides and oxides) are not primarily formed in the vicinity of the mFe⁰ or at its surface. In the presence of electrolysis, the effect of electric field significantly promoted the efficiency of electromigration, thereby enhanced mFe⁰ corrosion and eventually accelerated the PNP removal rates.

Industrial wastewater advanced treatment via catalytic ozonation with an Fe-based catalyst

An Fe-based catalyst was used as a heterogeneous catalyst for the ozonation of industrial wastewater, and key operational parameters (pH and catalyst dosage) were studied. The results indicated that the Fe-based catalyst significantly improved the mineralization of organic pollutants in wastewater. TOC (total organic carbon) removal was high, at 78.7%, with a catalyst concentration of 200 g/L, but only 31.6% with ozonation alone. The Fe-based catalyst significantly promoted ozone decomposition by 70% in aqueous solution. Hydroxyl radicals (·OH) were confirmed to be existed directly via EPR (electron paramagnetic resonance) experiments, and ·OH were verified to account for about 34.4% of TOC removal with NaHCO₃ as a radical scavenger. Through characterization by SEM-EDS (field emission scanning electron microscope with energy-dispersive spectrometer), XRD (X-ray powder diffraction) and XPS (X-ray photoelectron spectroscopy), it was deduced that FeOOH on the surface of the catalyst was the dominant contributor to the catalytic efficiency. The catalyst was certified as having good stability and excellent reusability based on 50 successive operations and could be used as a filler simultaneously. Thereby, it is a promising catalyst for practical industrial wastewater advanced treatment.

Coagulation-flocculation as pre-treatment for micro-scale Fe/Cu/O3 process (CF-mFe/Cu/O3) treatment of the coating wastewater from automobile manufacturing

A coagulation-flocculation as pre-treatment combined with mFe/Cu/O₃ (CF-mFe/Cu/O₃) process was developed to degrade the pollutants in automobile coating wastewater (ACW). In coagulation-flocculation (CF) process, high turbidity removal efficiency (97.1%) and low COD removal efficiency (10.5%) were obtained under the optimal conditions using Al₂(SO₄)₃·18H₂O and CaO. The effluent of CF process (ECF) was further disposed by mFe/Cu/O₃ process, and its key operating parameters were optimized by batch experiments. Optimally, COD removal efficiency of ECF obtained by the mFe/Cu/O₃ process (i.e., 87.6% after 30 min treatment) was much higher than those of mFe/Cu alone (8.3%), ozone alone (46.6%), and mFe/Cu/air (6.1%), which confirms the superiority of the mFe/Cu/O₃ process. In addition, the analysis results of UV-vis, excitation-emission matrix (EEM) fluorescence spectra and GC/MS further confirm that the phenol pollutants of ECF had been effectively decomposed or transformed after CF-mFe/Cu/O₃ process treatment. Meanwhile, B/C ratio of ACW increased from 0.19 to 0.56, which suggests the biodegradability was improved significantly. Finally, the operating cost of CF-mFe/Cu/O₃ process was about 1.83 USD t^-1 for ACW treatment. Therefore, the combined process is a promising treatment technology for the coating wastewater from automobile manufacturing.