Enhancement of bio-S0 recovery and revealing the inhibitory effect on microorganisms under high sulfide loading.

Biodesulfurization is a mature technology, but obtaining biosulfur (S0) that can be easily settled naturally is still a challenge. Increasing the sulfide load is one of the known methods to obtain better settling of S0. However, the inhibitory effect of high levels of sulfide on microbes has also not been well studied. We constructed a high loading sulfide (1.55-10.86 kg S/m3/d) biological removal system. 100% sulfide removal and 0.56-2.53 kg S/m3/d S0 (7.0 ± 0.09-16.4 ± 0.25 µm) recovery were achieved at loads of 1.55-7.75 kg S/m3/d. Under the same load, S0 in the reflux sedimentation tank, which produced larger S0 particles (24.2 ± 0.73-53.8 ± 0.70 µm), increased the natural settling capacity and 45% recovery. For high level sulfide inhibitory effect, we used metagenomics and metatranscriptomics analyses. The increased sulfide load significantly inhibited the expression of flavin cytochrome c sulfide dehydrogenase subunit B (fccB) (Decreased from 615 ± 75 to 30 ± 5 TPM). At this time sulfide quinone reductase (SQR) (324 ± 185-1197 ± 51 TPM) was mainly responsible for sulfide oxidation and S0 production. When the sulfide load reached 2800 mg S/L, the SQR (730 ± 100 TPM) was also suppressed. This resulted in the accumulation of sulfide, causing suppression of carbon sequestration genes (Decreased from 3437 ± 842 to 665 ± 175 TPM). Other inhibitory effects included inhibition of microbial respiration, production of reactive oxygen species, and DNA damage. More sulfide-oxidizing bacteria (SOB) and newly identified potential SOB (99.1%) showed some activity (77.6%) upon sulfide accumulation. The main microorganisms in the sulfide accumulation environment were Thiomicrospiracea and Burkholderiaceae, whose sulfide oxidation capacity and respiration were not significantly inhibited. This study provides a new approach to enhance the natural sedimentation of S0 and describes new microbial mechanisms for the inhibitory effects of sulfide.

The complexation of atmospheric Brown carbon surrogates on the generation of hydroxyl radical from transition metals in simulated lung fluid.

Atmospheric particulate matter (PM) poses great adverse effects through the production of reactive oxygen species (ROS). Various components in PM are acknowledged to induce ROS formation, while the interactions among chemicals remain to be elucidated. Here, we systematically investigate the influence of Brown carbon (BrC) surrogates (e.g., imidazoles, nitrocatechols and humic acid) on hydroxyl radical (OH) generation from transition metals (TMs) in simulated lung fluid. Present results show that BrC has an antagonism (interaction factor: 20-90 %) with Cu2+ in OH generation upon the interaction with glutathione, in which the concentrations of BrC and TMs influence the extent of antagonism. Rapid OH generation in glutathione is observed for Fe2+, while OH formation is very little for Fe3+. The compositions of antioxidants (e.g., glutathione, ascorbate, urate), resembling the upper and lower respiratory tract, respond differently to BrC and TMs (Cu2+, Fe2+ and Fe3+) in OH generation and the degree of antagonism. The complexation equilibrium constants and site numbers between Cu2+ and humic acid were further analyzed using fluorescence quenching experiments. Possible complexation products among TMs, 4-nitrocatechol and glutathione were also identified using quadropule-time-of-flight mass spectrometry. The results suggest atmospheric BrC widely participate in complexation with TMs which influence OH formation in the human lung fluid, and complexation should be considered in evaluating ROS formation mediated by ambient PM.

The research on CO oxidation over Ce-Mn oxides: The preparation method effects and oxidation mechanism.

A series of CeO2-MnOx for highly efficient catalytical oxidation of carbon monoxide were prepared by citrate sol-gel (C), hydrothermal (H) and hydrothermal-citrate complexation (CH) methods. The outcome indicates that the catalyst generated using the CH technique (CH-1:8) demonstrated the greatest catalytic performance for CO oxidation with a T50 of 98 °C, and also good stability in 1400 min. Compared to the catalysts prepared by C and H method, CH-1:8 has the highest specific surface of 156.1 m2 g-1, and the better reducibility of CH-1:8 was also observed in CO-TPR. It is also observed the high ratio of adsorbed oxygen/lattice oxygen (1.5) in the XPS result. Moreover, characterizations by the TOF-SIMS method indicated that obtained catalyst CH-Ce/Mn = 1:8 had stronger interactions between Ce and Mn oxides, and the redox cycle of Mn3++Ce4+ ↔ Mn4++Ce3+ was a key process for CO adsorption and oxidation process. According to in-situ FTIR, the possible reaction pathway for CO was deduced in three ways. CO directly oxidize with O2 to CO2, CO adsorbed on Mn4+ and Ce3+ reacts with O to form intermediates (COO-) (T > 50 °C) and carbonates (T > 90 °C), which are further oxidized into CO2.

Harmless process of organic matter in organosilicon waste residue by fluidization-like DDBD reactor: Temperature action and mechanism.

Herein, the non-hazardous application of low-temperature plasma technology in solid waste from the silicone industry was investigated by using a fluidization-like double dielectric barrier discharge plasma (DDBD) reactor. The results show ∼92.9% TOC in the organosilicon waste residue could be removed at the conditions (Discharge power: 7.0 W, S/G: 12.5 gminL-1, SIE: 158.0 JL-1), i.e. TOC content decreases from 166.0 g/kg to 11.8 g/kg. At the same time, the energy efficiency of the TOC removal rate reach ∼732.1 gkWh-1, and the temperature of the discharge zone is below 280 °C. According to the TG-MS analysis and infrared thermal imager, it is considered that the heat energy generated in the plasma treatment process can affect the decomposition of organic matter. On the other hand, the samples were characterized before and after treatment by BET, SEM, XRD, FTIR, and GC-MS. It was proposed the organic matter was firstly gasified under the action of plasma and thermal. Then, the active group will generate and react with the C-H, C-C, or C-Si by the bombardment of sufficient energy of charged particles, leading the organic matter further to decompose into small molecules, such as CH4, H2, CO, and CO2.

Catalytic ozonation of toluene over amorphous Cu-Mn bimetallic oxide: Influencing factors, degradation mechanism and pathways.

Herein, amorphous catalysts were employed to investigate the catalytic ozonation system, revealing the degradation mechanism and influencing factors (O3 concentration, temperature, and humidity) for toluene catalytic ozonation. Cu0.2MnOx exhibited the highest toluene oxidized and excellent stability (∼85% at 60 h) based on the suitable value of Oads/Olat and potent synergy between Cu with Mn. To explore the effect of factors, the change of fresh and post-reaction samples was compared as revealed in the relevant characterization results (SEM, XRD, BET, XPS, TGA), DRIFTS and GC-MS identified the intermediates and byproducts. The results show that appropriate temperature (100 °C) and O3 concentration (2100 ppm) can effectively enhance the number of reactive oxygen species. Although H2O can increase the production of ·OH to promote degradation, it is easier to quench the active sites on the surface of amorphous catalysts. During the reaction, the main role of Cu in Cu-Mn bimetallic oxides is adsorption of toluene and O3, formation of benzoic acid, and oxidation of short-chain products. As for the adjacent Mn, it works on the cleavage of O-O in O3 and the ring-opening of benzene. Then, the mainly catalytic ozonation pathway of toluene was proposed and followed the order: toluene, benzoic acid, benzene, maleic anhydride, short-chain carbon species, CO2, and H2O.

A review of the advances in catalyst modification using nonthermal plasma: Process, Mechanism and Applications.

With the continuous development of catalytic processes in chemistry, biology, organic synthesis, energy generation and many other fields, the design of catalysts with novel properties has become a new paradigm in both science and industry. Nonthermal plasma has aroused extensive interest in the synthesis and modification of catalysts. An increasing number of researchers are using plasma for the modification of target catalysts, such as modifying the dispersion of active sites, regulating electronic properties, enhancing metal-support interactions, and changing the morphology. Plasma provides an alternative choice for catalysts in the modification process of oxidation, reduction, etching, coating, and doping and is especially helpful for unfavourable thermodynamic processes or heat-sensitive reactions. This review focuses on the following points: (i) the fundamentals behind the nonthermal plasma modification of catalysts; (ii) the latest research progress on the application of plasma modified catalysts; and (iii) main challenges in the field and a vision for future development.

An overview of nanomaterial-based novel disinfection technologies for harmful microorganisms: Mechanism, synthesis, devices and application.

Harmful microorganism (e.g., new coronavirus) based infection is the most important security concern in life sciences and healthcare. This article aims to provide a state-of-the-art review on the development of advanced technology based on nanomaterial disinfection/sterilization techniques (NDST) for the first time including the nanomaterial types, disinfection techniques, bactericidal devices, sterilization products, and application scenarios (i.e., water, air, medical healthcare), with particular brief account of bactericidal behaviors referring to varied systems. In this emerging research area spanning the years from 1998 to 2021, total of ~200 publications selected for the type of review paper and research articles were reviewed. Four typical functional materials (namely type of metal/metal oxides, S-based, C-based, and N-based) with their development progresses in disinfection/sterilization are summarized with a list of synthesis and design. Among them, the widely used silver nanoparticles (AgNPs) are considered as the most effective bacterial agents in the type of nanomaterials at present and has been reported for inactivation of viruses, fungi, protozoa. Some methodologies against (1) disinfection by-products (DBPs) in traditional sterilization, (2) noble metal nanoparticles (NPs) agglomeration and release, (3) toxic metal leaching, (4) solar spectral response broadening, and (5) photogenerated e-/h+ pairs recombination are reviewed and discussed in this field, namely (1) alternative techniques and nanomaterials, (2) supporter anchoring effect, (3) nonmetal functional nanomaterials, (4) element doping, and (5) heterojunction constructing. The feasible strategies in the perspective of NDST are proposed to involve (1) non-noble metal disinfectors, (2) multi-functional nanomaterials, (3) multi-component nanocomposite innovation, and (4) hybrid techniques for disinfection/sterilization system. It is promising to achieve 100% bactericidal efficiency for 108 CFU/mL within a short time of less than 30 min.

Remediation for trace metals in polluted soils by turfgrass assisted with chemical reagents.

Trace metal pollution in soils is one of the universal environmental problems in the world. Phytoremediation is a green, safe, ecological, and economic method to achieve continuous reduction of soil pollutants. Turfgrass is a plant with great landscape value and has considerable biomass when used for remediation of trace metal contaminated soil. However, its remediation ability needs to be improved in future application. The combined application of turfgrass, citric acid (CA) and auxin (gibberellin, GA3) were applied in the phytoremediation of an artificial nutritive soil derived from sludge, and a field scale orthogonal experiment (L9) was conducted to understand the interaction effect and obtain the optimum phytoremediation. Experimental results showed that the types and cultural patterns of turfgrass mainly determined plant height, root length and trace metal concentration in turfgrass, however CA treatment was prone to increase the aboveground biomass and the concentrations of most trace metals in turfgrasses, especially the concentration of Ni in turfgrass. GA3 spraying significantly increased the concentration of Cd in turfgrass. The culture patterns of turfgrass played 42.4% influence on acid-extractable Cd, while CA applying had 53.8% influence on the acid-extractable Ni. The annual phytoextraction amount of trace metals based on five mowing a year were proposed to assess the remediation ability of treatments, which of the combination treatment (T3, intercropping Zoysia matrella and Lolium perenne, and applying 400 mg kg-1 CA and 30 mg kg-1 GA3) were 1.6-2.1 times higher CK group. This research provides technical reference for intercropping turfgrass for remediation of trace metals in sludge-derived nutritive soil.

Investigation of Cu-Mn catalytic ozonation of toluene: Crystal phase, intermediates and mechanism.

The effect of different crystal phases, i.e. spinel phase (CuMn2O4) and amorphous phase (Cu0.2MnOx), was explored in Cu-Mn catalytic ozonation of toluene. The toluene removal efficiency followed the order of Cu0.2MnOx (91.2%) ˃ CuMn2O4 (74.5%) ˃ commercial catalyst Cu0.3MnOx (70.3%) in 130 min, and the higher CO2 yield (67.6%) could be also observed using Cu0.2MnOx. In order to investigate the effect of phases on the toluene degradation pathway, the intermediates and byproducts were identified by DRIFTS, GC-MS, and TOF-SIMS. No obvious difference was observed in the distribution of byproducts, except for the quantities, suggesting the discrepancy of oxidation rate. On the other hand, the catalysts were characterized before and after the ozonation process by TEM, BET, XPS, XRD, EPR, TGA, and TPR. It was proposed that for amorphous catalysts, the oxygen vacancy (Vo) helped the chemisorption of toluene, and adjacent Mn reacted as the main active site for the ozonation process. While, the redox pair of Cu+/Mn4+ and Cu2+/(Mn3+, Mn2+) in the spinel phase plays an important role in the generation of oxygen vacancies for O3 decomposition.

Application of lead oxide electrodes in wastewater treatment: A review.

Electrochemical oxidation (EO) based on hydroxyl radicals (·OH) generated on lead dioxide has become a typical advanced oxidation process (AOP). Titanium-based lead dioxide electrodes (PbO2/Ti) play an increasingly important role in EO. To further improve the efficiency, the structure and properties of the lead dioxide active surface layer can be modified by doping transition metals, rare earth metals, nonmetals, etc. Here, we compare the common preparation methods of lead dioxide. The EO performance of lead dioxide in wastewater containing dyes, pesticides, drugs, landfill leachate, coal, petrochemicals, etc., is discussed along with their suitable operating conditions. Finally, the factors influencing the contaminant removal kinetics on lead dioxide are systematically analysed.

Influence of dimethylphenol isomers on electrochemical degradation: Kinetics, intermediates, and DFT calculation.

Dimethylphenol isomers (DMP) pose a great threat to the environment, and the electrooxidation (EO) process proves to be an extraordinarily effective method to degrade DMP. However, the EO performance is affected by the molecular structure of DMP and the adopted experimental parameters. In this study, the effects of 2,4-DMP and 2,6-DMP on the working potential, limiting current density (Jlim), and pH were systematically analysed, with Ti-mesh plates used as the cathode and Ti/PbO2 as the anode. The peak potentials of 2,4-DMP and 2,6-DMP were determined to be 0.83 V and 0.77 V by cyclic voltammetry, with Jlim were 2.5 mA·cm-2 and 2.0 mA·cm-2, respectively. The whole process exhibited pseudo-first-order kinetics, and the kinetic constants (K) for the degradation of 2,4-DMP and 2,6-DMP were determined to be 0.0041 min-1 and 0.0150 min-1, respectively. Additionally, the optimal initial pH value for 2,4-DMP and 2,6-DMP was 5.0, where the highest hydroxyl (OH) radical density, as determined by the electron spin technique (ESR), was achieved at a higher current density. Comparatively, the OH radical density in the 2,6-DMP solution was lower than that in 2,4-DMP. In situ Fourier infrared (FT-IR) spectroscopy, GC-MS, and density functional theory (DFT) were employed to explore three possible degradation pathways. The main intermediates for 2,4-DMP degradation were determined to be quinone and ether, while that for 2,6-DMP degradation was quinone. According to the results of this study, the molecular structure (different methyl group positions on the benzene ring) has a great influence on the EO process.

Mechanisms of Active Substances in a Dielectric Barrier Discharge Reactor: Species Determination, Interaction Analysis, and Contribution to Chlorobenzene Removal.

Several typical active substances (•NO, •NO2, H2O2, O3, •OH, and O2-•), directly or indirectly play dominant roles during dielectric barrier discharge (DBD) reaction. This study measured these active substances and removed them by using radical scavengers, such as catalase, superoxide dismutase, carboxy-PTIO (c-PTIO), tert-butanol (TBA), and MnO2 in different reaction atmospheres (air, N2, and O2). The mechanism for chlorobenzene (CB) removal by plasma in air atmosphere was also investigated. The production of O═NOO-• generated by •NO took around 75% of the total production of O═NOO-•. Removing •NO increased the O3 amount by about 80% likely because of the mutual inhibition between O3 and reactive nitrogen species in or out of the discharge area. The quantitative comparison of •OH and H2O2 revealed that the formation of •OH was 3.06-4.65 times that of H2O2 in these reaction atmospheres. Calculation results showed that approximately 1.61% of H2O was used for O3 generation. Ionization patterns affected the form of solid deposits during the removal of CB in N2 and O2 atmospheres caused by Penning ionization and thermal radiation tendencies, respectively. Correlation analysis results suggested the macroscopic synergistic or inhibitory effects happened among these active substances. A zero-dimensional reaction kinetics model was adopted to analyze the reactions during the formation of active substances in DBD, and the results showed good consistency with experiments. The interactions of each active substance were clarified. Finally, a response surface method model was developed to predict CB removal by the DBD plasma process. Stepwise regression analysis results showed that CB removal was affected by the contents of different active substances in air, N2 atmosphere, and O2 atmosphere, respectively: O2-•, •OH, and O3; H2O2, O═NOO-•, and O3; •OH and O3.

Synergistic effects of glyphosate and multiwall carbon nanotubes on Arabidopsis thaliana physiology and metabolism.

Agricultural chemicals have the potential to become pollutants that adversely affect plant growth. Interactions between these compounds are likely, but potential synergies are under-researched. Multiwall carbon nanotubes are increasingly finding novel uses in agriculture, as delivery mechanisms and as slow-release fertilizers. There is potential for nanotubes to interact with other agricultural chemicals in unpredictable ways. To investigate this possibility, we examined interactions with glyphosate, a widely used herbicide that is also attracting increasing concern over its potential for non-target effects. Here we examined potential synergistic effects on hydroponically grown Arabidopsis thaliana. Single treatments did not affect plant growth significantly, or did only mildly. However, combined treatment significantly affected both plant root and shoot growth. High-level content of malondialdehyde and up-regulated of metabolic antioxidant molecules in plant indicated that combined group caused the strong oxidative damage, while the decreased of antioxidant enzyme activities indicated an imbalance between reactive oxygen species (ROS)and the antioxidant defense system due to the continuously generated ROS. Besides, several intermediate metabolites of unsaturated fatty acids synthesis pathways were up-regulated in combined treatment, which clarified that combined group changed membrane components. The increase of intermediate metabolites in combined group also reflected more energy consumption in the repairment of the disrupt of combined treatment. The synergistic effect observed was attributed to the accumulation of glyphosate resulting from permeability and transportability of the carbon nanotubes. Overall, the risk of nanotube-herbicide interaction suggests a caution use of nanotubes in agricultural applications.

A novel pilot-scale installation integrated of improved sieve-tray tower and wet electrostatic precipitator for paint mist removal.

In order to overcome the problem of decrease of the spraying exhausts purification efficiency caused by the paint mist, the installation combining of the improved sieve-tray tower and the wet electrostatic precipitator (WEP) was used for the treatment of the pilot-scale 1,000 m3 paint waste gas. The characteristics of paint mist were investigated, showing that the size distribution of oil-based paint mist located in the range of 5.4-43.4 µm with an approximate symmetrical distribution under the pressure of 0.4 MPa. The size of paint mist less than 10 µm accounted for ~50% in quantity. It was revealed that the integrated setup was able to remove the concentration of oil-based paint mist with ~98% removal efficiency, in which the improved sieve-tray tower contributed ~94% particles removal. The soluble volatile organic pollutants (VOCs) of spraying exhaust gas were also captured by sieve-tray tower, promoting VOCs removal. At last, the feasibility of integrated setup used in paint mist removal was analyzed, including the secondary pollutants treatment. The results exhibited the setup has the potential for industrial applications.Implications: Fabricating a pilot-scale installation integrated of the improved sieve-tray tower and wet electrostatic precipitator to remove spraying exhaust gas in the furniture factory efficiently. This tech meets China's VOC emission policy.

Chemical reagent-assisted phytoextraction of heavy metals by Bryophyllum laetivirens from garden soil made of sludge.

Making municipal sludge into garden soil is a challenging issue in land using due to the high content of heavy metals, however phytoremediation can reduce the heavy metal pollution in the soil. Three artificial regulators were used in combination to improve phytoremediation of heavy metals by Bryophyllum laetivirens from municipal sludge made garden (MSMG) soil. Results showed that B. laetivirens grew well in MSMG soil and bioaccumulated Cu, Pb, Zn, Cd, and Ni by 2.16-11.0 times higher than those grew in local common garden soil. The application of ethylenediaminetetraacetic acid (EDTA), indole-3-acetic acid (IAA) and microbial liquid (BL) promoted the bioaccumulation of heavy metals of plants in MSMG soil, with 2.1-6.8 times than the control group. The optimum dose for the phytoremediation of B. laetivirens was the combining treatment of 3 mmol kg-1 EDTA, 10-10 M IAA, and 5 ml kg-1 BL, which has been successfully applied in MSMG soil. EDTA treatment is more direct and effective in facilitating HM uptake of root, while the other two treatments play important roles in promoting the transport of HMs in plants.

EDTA-enhanced phytoremediation of heavy metals from sludge soil by Italian ryegrass (Lolium perenne L.).

Landscaping of sludge is a kind of recycling disposal, but the potential heavy metal risks limit its application. In this paper, the sludge soil was remediated by ryegrass, and the effect of ethylene diamine tetraacetic acid (EDTA) was studied through pot experiments. Italian ryegrass was planted in the sludge soil treated with six gradients concentrations of 0, 1, 2, 3, 4, 5 mmol kg-1 of EDTA, and the planting conditions were kept the same. After 45 days of planting, compared with the control group (without EDTA treated), the application of 1-5 mmol kg-1 EDTA decreased ryegrass biomass by 2-43%, reduced soil pH value by 0.21-0.34 unit, and reduced 4.1-9.7% capacity of exchange cation, but increased 1.4-8.6% soil organic matter. After growing ryegrass, the contents of heavy metals decreased by 10% for Cu, 15% for Zn, 6% for Ni, 14% for Cd and 44% for Pb; and after spraying EDTA decreased again by 33% for Cu, 31% for Zn, 56% for Ni, 24% for Cd, and 68% for Pb. In ryegrass, the uptake heavy metals were enhanced, and bio-concentration factor of Cu, Zn, Ni, Cd, and Pb of EDTA treated groups were 1.9, 1.6, 4.1, 2.7, and 4.8 times of the control group, respectively. However, EDTA only significantly increased transfer factor values of Cu and Zn, and made bio-extraction factor value of Cu greater than 1. The remediation factor values were used to comprehensive assess accumulation capacity of heavy metals by ryegrass under EDTA treating, and they ordered in Zn > Cu > Ni > Cd > Pb, and the best dose was 2 mmol kg-1 EDTA. Prediction models for bio-concentration factor were established by using stepwise multiple linear regression, explaining 94.9-99.3% of the corresponding elements with soil organic matter, EDTA dosage, and/or pH value (p < 0.005). This paper provided effective heavy metals remediation data for municipal sludge landscape and the prediction models.

Tackling environmental challenges in pollution controls using artificial intelligence: A review.

This review presents the developments in artificial intelligence technologies for environmental pollution controls. A number of AI approaches, which start with the reliable mapping of nonlinear behavior between inputs and outputs in chemical and biological processes in terms of prediction models to the emerging optimization and control algorithms that study the pollutants removal processes and intelligent control systems, have been developed for environmental clean-ups. The characteristics, advantages and limitations of AI methods, including single and hybrid AI methods, were overviewed. Hybrid AI methods exhibited synergistic effects, but with computational heaviness. The up-to-date review summarizes i) Various artificial neural networks employed in wastewater degradation process for the prediction of removal efficiency of pollutants and the search of optimizing experimental conditions; ii) Evaluation of fuzzy logic used for intelligent control of aerobic stage of wastewater treatment process; iii) AI-aided soft-sensors for precisely on-line/off-line estimation of hard-to-measure parameters in wastewater treatment plants; iv) Single and hybrid AI methods applied to estimate pollutants concentrations and design monitoring and early-warning systems for both aquatic and atmospheric environments; v) AI modelings of short-term, mid-term and long-term solid waste generations, and various ANNs for solid waste recycling and reduction. Finally, the future challenges of AI-based models employed in the environmental fields are discussed and proposed.

Process Optimization of Electrochemical Oxidation of Ammonia to Nitrogen for Actual Dyeing Wastewater Treatment.

To mitigate the potential environmental risks caused by nitrogen compounds from industrial wastewater, residual ammonia after conventional wastewater treatment should be further eliminated. In this work, an electrochemical oxidation process for converting ammonia to nitrogen in actual dyeing wastewater was investigated. The effects of the main operating parameters, including initial pH value, applied current density, NaCl concentration, and flow, were investigated on ammonia removal and products distribution. Experimental results indicated that, under optimal conditions of an initial pH value of 8.3, applied current density of 20 mA cm-2, NaCl concentration of 1.0 g L-1, and flow of 300 mL min-1, the ammonia could be completely removed with N2 selectivity of 88.3% in 60 min electrolysis. A kinetics investigation using a pseudo-first-order model provided a precise description of ammonia removal during the electro-oxidation process. Experimental functions for describing the relationships between kinetic constants of ammonia removal and main operating parameters were also discussed. Additionally, the mechanisms and economic evaluation of ammonia oxidation were conducted. All these results clearly proved that this electro-oxidation process could efficiently remove ammonia and achieve high N2 selectivity.

BP-ANN Model Coupled with Particle Swarm Optimization for the Efficient Prediction of 2-Chlorophenol Removal in an Electro-Oxidation System.

Electro-oxidation is an effective approach for the removal of 2-chlorophenol from wastewater. The modeling of the electrochemical process plays an important role in improving the efficiency of electrochemical treatment and increasing our understanding of electrochemical treatment without increasing the cost. The backpropagation artificial neural network (BP-ANN) model was applied to predict chemical oxygen demand (COD) removal efficiency and total energy consumption (TEC). Current density, pH, supporting electrolyte concentration, and oxidation-reduction potential (ORP) were used as input parameters in the 2-chlorophenol synthetic wastewater model. Prediction accuracy was increased by using particle swarm optimization coupled with BP-ANN to optimize weight and threshold values. The particle swarm optimization BP-ANN (PSO-BP-ANN) for the efficient prediction of COD removal efficiency and TEC for testing data showed high correlation coefficient of 0.99 and 0.9944 and a mean square error of 0.0015526 and 0.0023456. The weight matrix analysis indicated that the correlation of the five input parameters was a current density of 18.85%, an initial pH 21.11%, an electrolyte concentration 19.69%, an oxidation time of 21.30%, and an ORP of 19.05%. The analysis of removal kinetics indicated that oxidation-reduction potential (ORP) is closely correlated with the chemical oxygen demand (COD) and total energy consumption (TEC) of the electro-oxidation degradation of 2-chlorophenol in wastewater.

Differential control of anode/cathode potentials of paired electrolysis for simultaneous removal of chemical oxygen demand and total nitrogen.

Paired electrolysis can take advantage of both anodic oxidation and cathodic reduction, and thus improve current efficiency for electrochemical wastewater treatment. In this work, differential control of anode/cathode potentials of paired electrolysis for simultaneous removal of chemical oxygen demand (COD) and total nitrogen (TN, including ammonia, nitrate, and nitrite) was studied. We first determined the optimal potentials for anodic oxidation of COD/NH4+ or cathodic reduction of NO3-/NO2- (minimization of over-oxidation or over-reduction) by preliminary cyclic voltammetry and constant-potential electrolysis experiments, i.e., 1.6 V for anodic oxidation and -1.26 V for cathodic reduction in this case. The optimal working potential of the cathode was achieved at appropriate current density in the paired electrolysis system, the working potential of the anode was independently controlled by adjusting the ratio of its surface area to that of the cathode. In this way, both the cathode and anode could work under optimal potentials. At an optimized cathodic current density of 5.0 mA cm-2 and cathode/anode surface area ratio of 2:1, the removal efficiencies of COD and TN from simulated wastewater reached 91.9% and 86.2%, respectively. Additionally, the developed paired electrolysis system was validated by treating an actual pharmaceutical wastewater, results for which showed that a total current efficiency of 84.8% was achieved, which was at least twice as high as that of traditional electrochemical processes.