The research of steady-state electrochemical kinetics of effective and selective conversion of total nitrogen to N2.

The sonoelectrochemical (SEC) oxidation of sulfamethoxazole (SMX) in simulated and actual wastewater on FTO/BaZr(0.1)Ti(0.9)O3, FTO/BaZr(0.05)Ti(0.95)O3 and FTO/BaTiO3 electrodes is hereby presented. Electrodes from piezo-polarizable BaZr(0.1)Ti(0.9)O3, BaZr(0.05)Ti(0.95)O3, and BaTiO3 materials were prepared by immobilizing these materials on fluorine-doped tin dioxide (FTO) glass. Electrochemical characterization performed on the electrodes using chronoamperometry and electrochemical impedance spectroscopy techniques revealed that the FTO/BaZr(0.1)Ti(0.9)O3 anode displayed the highest sonocurrent density response of 2.33 mA cm−2 and the lowest charge transfer resistance of 57 Ω. Compared to other electrodes, these responses signaled a superior mass transfer on the FTO/BaZr(0.1)Ti(0.9)O3 anode occasioned by an acoustic streaming effect. Moreover, a degradation efficiency of 86.16% (in simulated wastewater), and total organic carbon (TOC) removal efficiency of 63.16% (in simulated wastewater) and 41.47% (in actual wastewater) were obtained upon applying the FTO/BaZr(0.1)Ti(0.9)O3 electrode for SEC oxidation of SMX. The piezo-polarizable impact of the FTO/BaZr(0.1)Ti(0.9)O3 electrode was further established by the higher rate constant obtained for the FTO/BaZr(0.1)Ti(0.9)O3 electrode as compared to the other electrodes during SEC oxidation of SMX under optimum operational conditions. The piezo-potential effect displayed by the FTO/BaZr(0.1)Ti(0.9)O3 electrode can be said to have impacted the generation of reactive species, with hydroxyl radicals playing a predominant role in the degradation of SMX in the SEC system. Additionally, a positive synergistic index obtained for the electrode revealed that the piezo-polarization effect of the FTO/BaZr(0.1)Ti(0.9)O3 electrode activated during sonocatalysis combined with the electrochemical oxidation process during SEC oxidation can be advantageous for the decomposition of pharmaceuticals and other organic pollutants in water.

To solve the problems of deep nitrogen removal in wastewater treatment plants and the high value utilization of steel slag in the metallurgical industry, this work aims to prepare a sulfur/steel slag-based filter using the melting method. The melt granulation method and the utilization of metallurgical waste were the main innovations of this work. On this basis, the nitrogen removal performance of the filter media in simulated wastewater and actual wastewater were systematically investigated. Furthermore, the factors affecting the nitrogen removal performance of the filter media were studied, and pilot experiments were carried out. The microbial community in the reactor was also analyzed. The results showed that when the mass ratio of sulfur and steel slag was 9:1, the filter media could remove up to 90% of TN in simulated wastewater at room temperature, with a hydraulic retention time (HRT) of 5–20 h and an influent TN of 21 mg/L. In the simulated wastewater, the effluent NO3−-N was less than 2 mg/L, the SO42− was less than 200 mg/L, and the pH was between 6 and 8. The removal of TN from actual wastewater was also greater than 90% at room temperature under a hydraulic retention time (HRT) of 8–20 h and an influent TN of 8 mg/L. Influence factor experiments were conducted at room temperature, with a C/N of 2:1, a DO of 0.9–1 mg/L, and an HRT of 4 h. The results of the pilot experiment confirmed that the effluent TN was stable below 10 mg/L. The filter media was compounded for practical engineering applications. Microbial community analysis showed that the sulfur autotrophic denitrifying bacterial species Thiobacillus accounted for 3.69% and 5.55% of the simulated and actual wastewater systems, respectively. This work provides a novel strategy for the application of solid metallurgical waste in the field of nitrate-containing wastewater treatment.

Limestone-gypsumdesulfurization wastewater containsrecalcitrantorganic pollutants that are difficult to remove by conventional processes.This study investigates an electrochemical oxidation (EO) system foradvanced treatment after chloride and ammonia pre-removal, with afocus on elucidating the contributions of multiple reactive species,particularly reactive chlorine species, and evaluating the inhibitoryeffects of key coexisting ions, aspects that have been rarely systematicallyinvestigated. Using naphthol as a model pollutant in batch experimentswith simulated and actual wastewater, the EO system operated at 50mA cm–2 achieved high removal efficiencies: 96.3%for naphthol and 81.2% for total organic carbon in simulated wastewater,though performance was moderately lower in actual wastewater due toits complex matrix. Quenching experiments revealed the significantroles of •OH, •Cl, 1O2, and chlorine-based oxidants in the degradation process,while coexisting ions (SO42–, CO32–, NO3–, andNH4+) exhibited notable inhibition, with NH4+ and CO32– havingthe strongest effects. Electrochemical analysis indicated enhancedmass transfer and higher oxygen evolution potential in simulated wastewater,which improved current efficiency. GC-MS and ultraviolet–visible(UV–vis) analyses identified key intermediates, demonstratingthat degradation proceeds through hydroxylation, chlorination, ringcleavage, and eventual mineralization, accelerated by the synergisticaction of •OH and •Cl. This workconfirms EO as a promising technology for advanced desulfurizationwastewater treatment and provides essential insights for both theoreticalunderstanding and practical application.

Zero-valent iron (Fe0) nanoparticles (NPs) have shown excellent ability to remove contaminants hexavalent chromium (Cr(VI)) from aquatic systems. Use of support materials can help to prevent oxidation and aggregation of Fe0NPs, and thus enhance their remediation efficiency. However, most previous studies were conducted using artificially synthetic wastewater, and little is known on the remediation effects of supported Fe0NPs on actual wastewaters containing Cr(VI). Here, bentonite-supported Fe0NPs (BFe0NPs) with 1–5% of bentonite were prepared and characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. Batch experiments were performed to study Cr(VI) removal by the selected BFe0NPs from a simulated wastewater and a leachate wastewater originating from a Cr slag heap-polluted soil. The results show that Fe0NPs were uniformly dispersed on the bentonite, leading to a decreased aggregation of NPs, and the optimal mass ratio of bentonite was 4%. Batch experiment results show that lower pH values favored Cr(VI) removal by BFe0NPs. The removal percentage of Cr(VI) was higher than 90% for both wastewaters when the pH value was 2.0, but decreased significantly as pH value increased. Cr(VI) removal reaction was quite fast within the initial 10 min, and at least 85% of Cr(VI) was removed for both wastewaters. Cr(VI) removal percentage increased with increasing BFe0NPs dosages ranging from 30 to 60, but remained almost unchanged when the Fe/Cr mass ratio increased to above 60. The reaction of BFe0NPs to remove Cr(VI) followed the pseudo second-order reaction model. In most cases, the removal rates of Cr(VI) were higher in simulated wastewater than in leachate wastewater, but all approached 100% at the optimal conditions. Our present results show that BFe0NPs with 4% bentonite are efficient for treatment of Cr(VI)-containing wastewaters.

Electrocatalytic removal of nitrate by non-noble Fe3C/Cu: Property, mechanism, and practical water treatment performance.

Total nitrogen removal by Fe-activated carbon composite coupled with persulfate

Modelling of the contribution of dissolved inorganic nitrogen (DIN) from litterfall of adjacent mangrove forest to Hooghly–Matla estuary, India

Chapter 13 - Modelling nitrogen and carbon cycles in Hooghly estuary along with adjacent mangrove ecosystem

Comparison of two starch-based flocculants with polyacrylamide for the simultaneous removal of phosphorus and turbidity from simulated and actual wastewater samples in combination with FeCl3

Wastewater treatment by ozonation has the advantage of strong oxidizing ability and no secondary pollution. However, the mass-transfer resistance of the gas–liquid interface makes this process less efficient. In this work, a superaerophilic surface was introduced to solve this problem. It was confirmed that the superaerophilic surface could improve the liquid phase mass-transfer coefficient (KL) based on its super affinity to gas through the single board experiment. Moreover, aeration experiment showed that the result KL of superaerophilic packing resulted in 5.6 and 1.6 times greater values as compared to the bubbling device and the commercial aeration device. It was found that superaerophilic packing showed good performance in both simulated wastewater and actual wastewater. The decolorization time of simulated dye wastewater was shortened by 20 and 50% compared with the commercial aeration device and the bubbling device, respectively. The degradation rate of chemical oxygen demand was increased by 14% in this system. It was found that the enhancement was more obvious at a low gas flow rate and a high initial concentration of the pollutants. The stability test result showed that the prepared packing had good ozone resistance and solvent stability and can stand high temperature and hydraulic impact. This work provides a new strategy for improving gas–liquid mass-transfer efficiency and has a potential practical prospect.

In the present study the white-rot fungi BP was selected to study the degradation of nitrogen heterocyclic compounds in real and simulated coking wastewater. The study incorporated analysis of the degradation process, mechanism of action of white-rot fungi on nitrogen heterocyclic compounds, changes of enzyme activity and white-rot fungi biomass growth rate in coking wastewater (simulated and actual). The results showed that addition of ammonia nitrogen and phenol in simulated wastewater had insignificant effects on the degradation of indole. Moreover, the promoting effect of phenol on quinoline degradation was greater than the inhibition effects of ammonia nitrogen. Degradation rates of quinoline, indole and pyridine are consistent with the zero-order kinetics equation. It was also found that the addition of Mg (II) and Mn (II) promotes the degradation of quinoline by white-rot fungi in the actual wastewater, while degradation of pyridine was inhibited by three ions, out of which the inhibition of Cu (II) was the most obvious. Cu (II) was also found to have positive effects on the levels of activity of laccase enzyme secreted by the white-rot fungi as opposed to other metal ions tested. However, it was found to have inhibitory effects on the development of white-rot fungi, while Mg (II) and Mn (II) were found to promote the development of the white-rot fungi. The activity of the enzyme and the growth rate of biomass of white-rot fungi first reached the maximum levels followed by a significant decline.

Efficient degradation of inorganic nitrogen in mariculture wastewater by electrochemical methods

In recent years, the oxidation of NH4+ using Fe(Ⅲ) as an electron acceptor under anaerobic conditions (Feammox) has received significant research attention. In this study, the effect of pH and temperature on nitrogen conversion during the Feammox process was studied through activity recovery of Feammox sludge acclimated by anaerobic ammonium oxidation (ANAMMOX) sludge. Results showed that after 40 d operation, activity of Feammox sludge was recovered. There was evident ammonia nitrogen conversion and total nitrogen removal from the environment, and the products were mainly nitrate and nitrogen. The concentration of nitrite remained below 2 mg·L-1. pH value and temperature significantly influenced nitrogen transformation during the Feammox process. With pH value of 7 and temperature of 30℃ during the Feammox process, the removal rate of total nitrogen was relatively high (>50%). When the pH value was 6.5, the conversion rate of ammonia nitrogen was 80.2%. During the Feammox reaction process, precipitation of iron ion compounds and coating on the sludge surface were the main interference factors leading to continuous operation of the reactor and exploration of the reaction mechanism.

Selenium is an essential element for flora and fauna in trace amounts. It plays a crucial role in bolstering photosynthesis and facilitating thyroid hormone metabolism. However, excessive consumption of selenium can result in health concerns such as reproductive complications and cancer. Selenium usually coexists with minerals such as copper and coal in the natural environment. The associated activities, such as copper mining and coal combustion, have greatly accelerated the mobilization of selenium. The selenium released through coal combustion is mostly captured in the flue gas desulfurization (FGD) wastewater as inorganic selenite and selenate.Our lab previously validated the viability of direct electrochemical reduction (SeDER) to remove dissolved selenite from a simplified FGD water matrix using planar gold and graphite cathodes, where more than 94% of the aqueous selenite can be converted to elemental Se(0) deposited on the cathode surface. Graphite is eventually selected for its low material cost, decent removal performance, and minimum secondary pollution as compared to gold and other non-noble metal cathodes. This direct electrochemical deposition process provides many benefits that existing biological and indirect electrochemical methods lack, such as zero chemical addition and low to zero solid generation. However, this method is only suitable for wastewater with elevated temperatures necessary to generate conductive Se(0) for continuous reduction. The inclusion of a heating process adds complexity to the design, impeding the scalability of the SeDER system. Furthermore, the application of SeDER is constrained to Se-impacted wastewater with an elevated temperature.In this study, we propose a novel reactor design utilizing electrochemical reduction to treat Se-impacted wastewater at ambient temperature. The electrodes we used are made of graphite for the reasoning stated above. The reactor consists of a pair of planar graphite anode and cathode, and the inner chamber is filled with cylindrical graphite particle electrodes (PEs) separated by a nylon spacer to create an anodic chamber and a cathodic chamber. The PEs act as an extension of the planar electrodes, which offers numerous reaction sites and minimizes the travel distance for selenite ions to reach the electrode surface. In our 120-mL batch test with 0.1-mM selenite in 100-mM phosphate buffer, the exact system without filler removed 0% selenite at room temperature, while the filled 3D system removed on average 50% of the selenite in 3 hours. Using the same 3D system, we then investigated performance enhancement with a recirculating operation. The total working volume is fixed at 200 mL, while the flow rate and the applied voltage vary. The flow rate is set at the values with hydraulic retention time (HRT) fixed at 15 min, 30 min, and 60 min. The system-applied voltage is set at -1.9V (just enough for selenite reduction), -2.1V, and -2.3V. We found that the shortest HRT combined with -2.1V system applied voltage yielded the highest selenite removal performance in all tests, with an average of 47% removal in 3 hours. We hypothesized that the shorter HRT provides a faster flow rate that refreshes the PE’s surface from insulative Se(0) deposition, which provides sustainable reaction sites for the incoming selenite. At -2.1V, the potential is negative enough to allow selenite reduction while fewer parasitic reactions (e.g., hydrogen evolution reaction) occur compared to that under -2.3V.With the selected system voltage and flow rate, we eventually explored competing ion behavior and switched from a simplified water matrix to simulated Se-impacted wastewater. We found that of all the commonly found competing ions (i.e., sulfate, nitrate, and chloride), chloride significantly impacts selenite removal, with performance dropping to 10% removal in 3 hours. Nitrate slightly decreased the selenite removal, with an average Se removal performance of 23%. Sulfate, on the other hand, resulted in an increase in selenite removal after addition. We hypothesize that a high sulfate concentration in simulated wastewater could help alleviate the repulsing force from the cathode surface for the selenite ions. The double layer of the PEs could also be compressed by the high ionic strength, which decreases the capacitance and promotes selenite reduction. To confirm this hypothesis, we conducted an electrochemical impedance study to analyze the effect of competing ions on reaction kinetics and capacitance. We also performed surface analysis for the wasted planar electrodes and PEs to investigate the change in morphology and observed possible chemical residue. These characterizations will help us develop a regeneration protocol in long-term operation and help us scale up our prototype to manage actual Se-impacted wastewater.

In this study, three kinds of monocarboxylic acids, formic, acetic, and propionic acids, are first applied to modified microalgae residuals (M1-RD, M2-RD, and M3-RD, respectively) after lipid extraction, aiming to enhance the adsorption capacity and selective binding ability for Hg(II) ions in simulated wastewater. The effect of pH, temperature, and initial Hg(II) concentration was investigated to identify the optimum adsorption conditions. Batch adsorption tests showed that the maximum adsorption efficiency obtained was 96.7% for M1-RD, 91.1% for M2-RD, and 84.4% for M3-RD at pH 4.05 compared to 48.5 and 57.6% for raw and residual microalgae at pH 5.01, respectively. The adsorption capacity of raw, residual, and modified microalgae increased with the increase of the temperature. Langmuir and Freundlich isotherm model tests showed that the maximum equilibrium adsorption capacity among three modified adsorbents reached 63 ± 3 mg/g for M1-RD, in contrast to 17 ± 1 and 25 ± 2 mg/g for raw and residual microalgae, respectively. The characterization of the modified sample by Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller, and scanning electron microscopy showed that the fibrous structure of the algae was decomposed by carboxyl groups in organic acids involved in microalgae, resulting in a larger surface area and more binding sites. In consideration of ion interference in the actual process, a kind of actual desulfurization wastewater from a 1000 MW coal-fired power plant (Guangdong, China) was introduced in the simulated adsorption system. Verification tests in desulfurization wastewater showed that up to 96% of Hg(II) ions were removed, probably as a result of co-precipitation of mercury and other co-existing ions.