The pressurized jet aerator: A new aeration system for high-performance H2O2 electrolyzers

State-of-the-art review and bibliometric analysis on electro-Fenton process

The electro-Fenton (EF) process was first proposed in 1996 and, since then, considerable development has been achieved for its application in wastewater treatment, especially at lab and pilot scale. After more than 25 years, the high efficiency, versatility and environmental compatibility of EF process has been demonstrated. In this review, bibliometrics has been adopted as a tool that allows quantifying the development of EF as well as introducing some useful correlations. As a result, information is summarized in a more visual manner that can be easily analyzed and interpreted as compared to conventional reviewing. During the recent decades under review, 83 countries have contributed to the dramatic growth of EF publications, with China, Spain and France leading the publication output. The top 12 most cited articles, along with the top 32 most productive authors in the EF field, have been screened. Four stages have been identified as main descriptors of the development of EF throughout these years, being each stage characterized by relevant breakthroughs. To conclude, a general cognitive model for the EF process is proposed, including atomic, microscopic and macroscopic views, and future perspectives are discussed.

Synchronous removal of pharmaceutical contaminants and inactivation of pathogenic microorganisms in real hospital wastewater by electro-peroxone process

Herein, a highly efficient electro-peroxone (E-peroxone) process with graphite felt as ozone diffusion electrode (ODE) was developed for the synchronous removal of pharmaceutical contaminants and inactivation of pathogenic microorganisms in real hospital wastewater. Under optimal conditions, the total organic carbon (TOC) removal rate of real hospital wastewater could reach 93.9%. Importantly, 126 pharmaceutical compounds (antibiotics, antivirals, analgesics, antiepileptics, hormones, and others) were determined in hospital wastewater by using ultra performance liquid chromatography combined with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS/MS). 110 pharmaceutical compounds could be efficiently degraded in E-peroxone system. Concurrently, the microbial community analysis through high-throughput sequencing showed that E-peroxone process exhibited an excellent disinfection effect in real hospital wastewater. Escherichia coli as a bacterial indicator could be completely inactivated in E-peroxone process·H2O2 and hydroxyl radical (OH) were found in E-peroxone system based on the results of chemical probe experiments and electron paramagnetic resonance (EPR) analysis. The in-situ generation of H2O2 from cathodic oxygen reduction in ODE can react with ozone to produce OH, and realize high efficiencies for the elimination of pharmaceutical and sterilization. This work established a green and effective way without extra addition of chemical reagents for high-efficiency treatment of real hospital wastewater.

Degradation of antibiotics, organic matters and ammonia during secondary wastewater treatment using boron-doped diamond electro-oxidation combined with ceramic ultrafiltration

In this study, a BDD electrolytic oxidation-ceramic membrane ultrafiltration (EO-CM) system for the removals of antibiotics, organic matters and ammonia in wastewater was evaluated. Sulfamethazine (SMZ) was degraded following a pseudo first-order kinetics. The removal rate of SMZ improved with the increase of electro-oxidation time (0-60 min) and current density (5-30 mA/cm²). During the BDD electro-oxidation process, H₂O₂ and hydroxyl radicals (•OH) were generated which were detected by N, N-diethyl-p-phenylenediamine (DPD) method and electron paramagnetic resonance spectroscopy (EPR), respectively. Chemical oxygen demand (COD) was able to be removed by EO and CM processes, in which proteins and humic acids were regarded as the main removed components measured using excitation-emission matrix (EEM) technique. Moreover, BDD electro-oxidation pretreatment could make the CM process maintain a high water flux and significantly control the membrane fouling and relieve transmembrane pollution. In addition, the removal of ammonia was enhanced with the increase of chloride ions (Cl^-) in wastewater during EO process due to the generation of active chlorine (i.e., ClO^-, HClO, or Cl₂) from the oxidation of Cl^-. Chloramine and nitrogen were produced in the oxidation of ammonia by active chlorine. Overall, the results of this study suggest that BDD EO-CM system is a promising process for removing antibiotics, organic matters and ammonia.

A novel Electro-Fenton process characterized by aeration from inside a graphite felt electrode with enhanced electrogeneration of H2O2 and cycle of Fe3+/Fe2

A novel Electro-Fenton process characterized by aeration from inside a graphite felt electrode with enhanced generation of H₂O₂ and cycle of Fe³⁺/Fe²⁺ was proposed. The new type of Electro-Fenton process was used to degrade organic pollutants via graphite felt electrode aeration (GF-EA). The H₂O₂ concentration by GF-EA could reach 152-169 mg/L in a wide pH range (3-10), which was much higher than that achieved by graphite felt using solution aeration (GF-SA, 37-113 mg/L). For the degradation of nitrobenzene (NB), benzoic acid (BA), bisphenol A (BPA), and sulfamethoxazole (SMX) at pH 5.5, the percentage degradation by GF-EA could reach 55%, 56%, 80%, and 60% higher than those obtained by GF-SA, respectively. The solution TOC removal by GF-EA were enhanced by 29-51% relative to GF-SA. Mechanism analysis showed both OH and ferryl species were involved in the reaction system, and the amounts of OH and dissolved iron species in GF-EA group were 7.7 times and 4-8 times higher than those in GF-SA group, respectively. Besides, the mass transfer rate of GF-EA system was 5.4 times higher than that of GF-SA system. High amounts of H₂O₂, dissolved iron species and OH were attributed to the enhanced mass transfer of O₂ and the solution.

Clopyralid degradation by AOPs enhanced with zero valent iron

Four different technologies have been compared (photolysis, ZVI + photolysis, electrolysis and ZVI + electrolysis) regarding the: (1) degradation of clopyralid, (2) extent of its mineralization, (3) formation of by-products and main reaction pathways. Results show that photolysis is the less efficient treatment and it only attains 5 % removal of the pollutant, much less than ZVI, which reaches 45 % removal and that electrolysis, which attains complete removal and 78 % mineralization within 4 h. When ZVI is used as pre-treatment of electrolysis, it was obtained the most efficient technology. The identification of transformation products was carried out for each treatment by LCMS. In total, ten products were identified. Tentative pathways for preferential clopyralid degradation for all processes were proposed. This work draws attention of the synergisms caused by the coupling of techniques involving the treatment of chlorinated compound and sheds light on how the preferential mechanisms of each treatment evaluated occurred.

Electro-Absorbers: A Comparison on Their Performance with Jet-Absorbers and Absorption Columns

This work focuses on the removal of perchloroethylene (PCE) from gaseous streams using absorbers connected with electrolyzers. Two types of absorption devices (jet absorber and absorption column) were compared. In addition, it has been evaluated the different by-products generated when a simultaneous electrolysis with diamond anodes is carried out. PCE was not mineralized, but it was transformed into phosgene that mainly derivates into carbon tetrachloride. Trichloroacetic acid was also formed, but in much lower amounts. Results showed a more efficient absorption of PCE in the packed column, which it is associated to the higher gas–liquid contact surface. Jet absorber seems to favor the production of carbon tetrachloride in gaseous phase, whereas the packed column promotes a higher concentration of trichloroacetic acid in liquid. It was also evaluated the scale up of the electrolytic stage of these electro-absorption devices by using a stack with five perforated electrode packages instead of a single cell. Clarification of the effect of the applied current density on the speciation attained after the electrolysis of the absorbent has been attempted. Experiments reveal similar results in terms of PCE removal and a reduced generation of gaseous intermediates at lower current densities.

A comparison between flow-through cathode and mixed tank cells for the electro-Fenton process with conductive diamond anode

This work focusses on the production of hydrogen peroxide and in the removal of bromacil by the electro-Fenton process using two different electrochemical cells: mixed tank cell (MTC) and flow-through cell (FTC). Both cells use boron doped diamond (BDD) as anode and carbon felt as cathode to promote the formation of hydrogen peroxide. In the case of the MTC, two surface area ratios, A_cathode/A_anode, have been used. Results show that the H₂O₂ produced by MTC and FTCPSC increases with the time until a stabilization state. For the FTCPSC, the average hydrogen peroxide concentration produced increases progressively with the current, while for MTC the maximum values are found in applying very low current densities. In addition, the FTCPSC provides higher concentrations of hydrogen peroxide for the same current density applied. Regarding the MTC, it can be stated that the higher the area of the cathode, the higher is the amount of H₂O₂ produced and the lower is the cell voltage (because of a more efficient current lines distribution). The initial oxidation of bromacil is very efficiently attained being rapidly depleted from wastewater. However, the higher production of hydrogen peroxide obtained by the FTCPSC cell does not reflect on a better performance of the electro-Fenton process. Thus, bromacil is better mineralized using the MTC cell with the lowest cathode area. This observation has been explained because larger concentrations of produced hydrogen peroxide seems to benefit the oxidation of intermediates and not the mineralization.