Flow-through Reactor Research Articles

Unraveling dolomite dissolution stoichiometry in circumneutral to alkaline pH environments

Abstract Examining carbonate dissolution kinetics at mineral-water interface is crucial to understand numerous environmental and geochemical processes, including global carbon cycling, CO2 sequestration in deep geological reservoirs, and trace elements release in terrestrial and aquatic environments. Here we explored the effect of circumneutral to alkaline pH solutions (pH 6–11) on dissolution kinetics of pure dolomite and Ca and Mg release stoichiometry in flow-through reactor experiments at 25 ± 1 °C. Results revealed that the dolomite dissolution rates obtained from effluent Ca and Mg concentrations (RCa and RMg in mol/cm2/s) were dependent on input solution pH and HCO3 − log activity. The pH dependence of dissolution rates showed two distinct trends, i.e., at circumneutral pH ranging between 6 and 8, the dissolution rate decreased with increasing pH, with minimum rate at pH 8. While in the highly alkaline pH range (pH 9–11), the dolomite dissolution rate increased with an increasing pH. Irrespective of the input pH, the dolomite dissolution rates indicated a reverse relationship with HCO3 − log activity, with the lowest dissolution rate (RCa = 3.80 × 10–12 mol/cm2/s) at pH 8 where HCO3 − log activity attained the highest value (− 3.957). The lower RCa and RMg obtained at pH 8 compared to all the other pH could possibly be attributed to an inhibition caused by high HCO3 − log activity in solution at this pH. Dolomite dissolution rates were non-stoichiometric at all the experimental pH values, showing higher preferential Ca over Mg release (RCa > RMg) whereas an opposite trend was observed at pH 8, with RCa < RMg at the steady state. Saturation index values calculated using geochemical speciation modelling were positive for Mg-bearing minerals (brucite, dolomite, artinite) at alkaline pH of 10–11, indicating favourable conditions for their precipitation under studied conditions. This study provides insights on the significance of log ion activities of HCO3 − and Me-OH+ under varying pH for elucidating the dissolution mechanism of dolomite in circumneutral to alkaline aqueous environments.

The Removal of Organic Pollutants and Ammonia Nitrogen from High-Salt Wastewater by the Electro-Chlorination Process and Its Mechanism

Electro-chlorination (E-Cl) is an emerging and promising electrochemical advanced oxidation technology for wastewater treatment with the advantages of high efficiency, deep mineralization, a green process, and easy operation. It was found that the mechanism of pollutant removal by electro-chlorination mainly involves an indirect oxidation process, in which pollutant removal is mainly driven by the intermediate active species, especially RCS and chlorine radicals, with a strong oxidization ability produced at the anodes. In this work, we summarized the principles and pathways of the removal/degradation of pollutants (organic pollutants and ammonia nitrogen) by E-Cl and the major affecting factors including the applied current density, voltage, electrolyte concentration, initial pH value, etc. In the E-Cl system, the DSA and BDD electrodes were the most widely used electrode materials. The flow-through electrode reactor was considered to be the most promising reactor since it had a high porosity and large pore size, which could effectively improve the mass transfer efficiency and electron transfer efficiency of the reaction. Of the many detection methods for chlorine radicals and RCS, electron paramagnetic resonance (EPR) and spectrophotometry with N, N-diethyl-1,4-phenylenediamine sulfate (DPD) as the chromogenic agent were the two most widely used methods. Overall, the E-Cl process had excellent performance and prospects in treating salt-containing wastewater.

Different dissolved organic matter sources sustain microbial life in a sandy beach subterranean estuary – an incubation study

In subterranean estuaries (STE), fresh and saline groundwater introduce dissolved organic matter (DOM) of different origin. This DOM serves as substrate for microorganisms that thrive in the STE. In high-energy beaches with dynamic porewater advection, microbial communities face frequent changes in groundwater composition, even at several meters depth. It is unknown how DOM from deep STE groundwater (> 5 m depth) is transformed by prevailing microbial communities. To address this question, we performed sediment incubations in flow-through reactors (FTRs) with deep (6 m depth) STE groundwater of low (1.6) and high salinity (29.1). FTR setups were sampled daily for quantification of dissolved organic carbon (DOC), and at start and end (day 13) of the incubation for analysis of DOM composition, microbial cell numbers and community composition. Solid-phase extracted DOM was molecularly characterized via ultrahigh-resolution Fourier-transform ion cyclotron resonance mass spectrometry. Both groundwater types contained mainly reworked DOM. Corroborating its presumed origin, the fresh groundwater had a more terrestrial DOM signature with a higher proportion of aromatic compounds compared to the saline groundwater. Over the course of the incubation, DOC concentrations increased primarily due to leaching of sedimentary organic matter, providing an additional source of DOM. In all setups, the DOM composition changed significantly from start to end, and similarly for fresh and saline groundwater. From the ~2700 molecular formulae (MF) detected on day 0, 34-35% were removed during the incubations, demonstrating the potential of deep STE microbial communities to degrade recalcitrant DOM that is supplied with the advective porewater flow. However, a substantial portion of MF (63-64%) was retained in both groundwater types, indicating that a fraction of deep STE-DOM is resistant to removal. Properties of MF that were newly detected on day 13 (26-28%) were indicative of labile DOM. Some of these newly detected MF were also identified in sediment-leachates, suggesting that beach sediments are a source of fresh DOM for the STE microbial communities. It is likely that due to longer groundwater residence time in the STE, continuous leaching and microbial processing shift the molecular composition of released DOM from more labile to more recalcitrant DOM.

Transformation of persistent organic micropollutants by UV and UV/H2O2 in wastewater treatment plant effluent

ABSTRACT Photochemical and advanced oxidation processes (AOPs) are promising options to simultaneously disinfect wastewater treatment plant (WWTP) effluent and degrade organic micropollutants (OMPs). In the present study, kinetic experiments with UV alone and the combination of UV and hydrogen peroxide (H2O2) as an AOP were conducted in WWTP effluent (with and without ultrafiltration) to assess the degradation of 24 OMP, 13 of which were examined for the first time, in a flow-through batch reactor setup. Four parameters were systematically varied to quantify their impacts on OMP degradation: H2O2 concentrations, UV source, water matrix, and flow rate. Most of the studied OMPs (e.g., trimethylammonium, 1,3-di-o-tolylguanidine, carbamazepine) were only significantly degraded in the presence of UV radiation and H2O2. The highest pseudo-first-order rate constants were found for diclofenac, acesulfame, diatrizoate, and sulfamethoxazole. The experiment with the highest degradation also showed the strongest abatement of UV absorbance at 254 nm. Only three of the 24 substances (cyanoguanidine, melamine, and oxipurinol) were not degraded; UV alone even increased their concentrations. Overall, upgrading a UV disinfection to an AOP using H2O2 allows the degradation of a wide range of OMP, making it an interesting process for water reuse.

Vermicomposting organic waste with Eisenia fetida using a continuous flow-through reactor: Investigating five distinct waste mixtures

In this study, the vermicomposting of source-separated organic solid waste was investigated using Eisenia fetida in a continuous flow-through reactor. This novel approach is capable of simulating the complex interactions and dynamics of a full-scale vermicomposting system, offering valuable insights into the optimization of organic waste management. The primary objective of the research was to evaluate the quality of vermicompost produced in the reactor and determine its compliance with regulatory standards. For this purpose, food waste, yard waste, and pruning waste were mixed in different proportions to create five waste mixtures, which were then subjected to an 8-week pre-composting process. Subsequently, vermicompost was produced from the pre-composted waste mixtures using a continuous flow-through reactor that allows for long-term operation without disturbing the worms. While the total Kjeldahl nitrogen (TKN) content of the vermicomposts ranged from 2.04% to 2.48%, the total organic carbon (TOC) content of the vermicomposts was between 25.68% and 32.64%. Therefore, the carbon/nitrogen (C/N) ratio was calculated to be between 12.60 and 13.66. The quality of the final compost product showed that it met the limitations suggested in the European Fertilizer Regulation for the main physico-chemical parameters and heavy metals. It is concluded that vermicomposting in a continuous flow-through system reactor would be applicable to different organic waste streams.

Photodegradation of steroid hormone micropollutants with palladium-porphyrin coated porous PTFE of varied morphological and optical properties.

In flow-through reactors, the photodegradation rate can be improved by enhancing contact and increasing the photocatalyst loading. Both can be attained with a higher surface-to-volume ratio. While previous studies focused on thin membranes (30 - 130 µm) with small pore sizes of 20 - 650 nm, this work employed poly(tetrafluoroethylene) (PTFE) supports, of which pore sizes are in the order of 10 µm, while the porosities and thicknesses are variable (22.5 - 45.3 % and 0.2 - 3 mm, respectively). These porous materials were anticipated to allow a higher loading of porphyrin photosensitisers and better light penetration for subsequent photodegradation of steroid hormone micropollutants via singlet oxygen (1O2) generation. The reactor surface refers to the surface within the PTFE pores, while the reactor volume is the total void space inside these pores. The surface-to-volume ratios between 105 and 106 m2/m3 are higher than those of typical microreactors (103 to 104 m2/m3). The weighted average light transmittance varied from 38 % with the thinnest and most porous support to 4.8 % with the thickest support. Good light penetration combined with minimal absorption by PTFE enhanced the light utilisation of the porphyrins when coated in the porous supports. Changes in the support porosity of the coated supports minimally affected steroid hormone removal, because the collision frequency in the very large pores remained relatively constant. However, varying the support thickness, porphyrin loading (0.3 - 7.7 μmol/g), and water flux (150 - 3000 L/m2.h), hence the resulting hydraulic residence time, influenced the collision frequency and steroid hormone removal. Results showed that the supports did not outperform membranes most likely because the larger pore size in the former limited contact between the hormones and 1O2. From photostability testing of the pristine supports, perfluoroalkyl substances (PFAS) released from the supports were found at 10 - 300 ng/L concentrations during accelerated ageing. While PFAS formation was detectable, the quantities during water treatment operations would be extremely low. In summary, this study elucidates the capability and limitations of porous supports coated with photosensitisers to remove waterborne micropollutants.

Simultaneous nitrification and denitrification framework for decentralized systems: Long-term study utilizing rope-type biofilm media under field conditions

This research introduces a novel approach to achieve simultaneous nitrification-denitrification (SND) under dynamic load conditions using a cost-effective rope-type biofilm technology. The approach represents a significant advancement in wastewater treatment, particularly beneficial for remote and decentralized communities. The biofilm-based SND process was developed using a pilot-scale flow-through reactor by implementing upstream carbon management with constant-timer-based aeration control versus dynamic-sensor-based aeration control strategies. The findings indicate that adding an upstream anaerobic pretreatment process to handle excess carbon plays a substantial role in achieving a sustainable SND process under a dynamic load environment using simple aeration on-off control. The most optimal nitrification performance of 0.32 g NH3-N/m2/d (89 % removal) was achieved under a 1-hour ON/30-minute OFF aeration. The process sustained an average bulk liquid DO of 5.16 mg/L and 3.80 mg/L during the aeration ON and OFF periods, respectively, facilitating a 0.13 g N/m2/d (41 %) total inorganic nitrogen (TIN) removal, notably, implementing advanced aeration strategies driven by DO, NH3, and NO3 sensors enhanced TIN removal efficiency to 72 %. The nitrification performance remained comparable (89 % removal), resulting in 3 and 10 mg N/L effluent ammonia and TIN concentration, respectively. Additionally, utilizing two multivariate approaches accounting for 82 % and 64 % of the variance, this study discerned patterns in monitored variables and performance. Additionally, the analysis underscored the difference of bulk liquid DO levels in the biofilm versus suspended systems inhibiting the SND process. Distinct bacterial communities were established in biofilms under aerobic, anaerobic, and SND conditions, with the SND reactor showing a hierarchy of functional group and enzymes, enriched sequentially from heterotrophs to denitrifiers, nitrifiers, and anammox bacteria. These innovations underline the potential of tailored control strategies to enhance a passive biofilm-based SND process efficiency under dynamic conditions, providing scalable solutions for diverse target water quality demands in remote communities and decentralized systems.

(Invited) One Dimensional Anodic TiO2 Nanotubes for Energy and Catalytic Applications

Self-organized TiO2 nanotube (TNT) layers, prepared by anodization of Ti have in suitable electrolytes, attracted considerable scientific and technological interest, especially due to their wide range of applications including (photo-) catalysis, hydrogen generation and biomedical uses [1,2].The advantages of anodic TNT layers compared to TiO2 nanotubes prepared by other methods (e.g. hydrothermal) are the tunability of dimensions, their directionality, the ability to absorb significant amount of incident light, and the possibility to utilize nanotube interiors and exteriors for decoration or coating with secondary materials [2].The presentation will review the recent advancements in TNT layer synthesis for their use for the photocatalytic degradation of pollutants in the liquid and in the gas phase. This will include the upscaling of TNT layers from the laboratory scale to several dozens of cm2 [3-6], with a strong focus on the anodization of 3D Ti substrates by bipolar electrochemistry, which cannot be directly connected to the potentiostat (such as Ti meshes) [5-6]. The application of these large scale TiO2 nanotube layers in flow-through photocatalytic reactors will be discussed [3-6]. Additionally, the selective etching of double wall TiO2 nanotube layers towards single wall TiO2 nanotube layers [7] and single nanotube powders [8, 9] will be presented, showing the possibility of preparing magnetically guidable single nanotube photocatalysts by a decoration with Fe3O4.The presentation will also summarize recent advancements in the utilization of TNT layers in energy conversion and energy storage applications [10], in particular Li-ion microbatteries. Experimental details and photocatalytic and battery results will be presented and discussed.

KINETICS OF ANILINE-FORMALDEHYDE INTERACTION UNDER CONDITIONS OF HOMOGENEOUS CATALYSIS

The work is devoted to the kinetic modeling of reactions for the production of 4,4-diaminodiphenylmethane (MDA) in the presence of a catalyst. FASHION is a solid substance from colorless to pale yellow in color with a faint odor. It is used on an industrial scale mainly for the manufacture of polyurethanes, which have many applications, for example, insulating materials in mail containers. MDA is also used for the manufacture of coating materials, adhesives, spandex fibers, dyes, and rubber. This product belongs to the categories of medium and low-tonnage industries, which determines its importance in the chemical industry. The importance of the process of obtaining MDA and the application of kinetic modeling of a chemical reaction is described. The paper proposes a model that allows us to predict the kinetic curves of the studied reaction for obtaining MDA. The proposed model can be used to calculate flow-through or ring-shaped chemical reactors. The type and parameters of the model were obtained by minimizing deviations of experimental and calculated values of concentrations of reagents and products, while the model showed its adequacy to the experiment. The limits of its applicability were checked using computational experiments under various conditions - the ratio "aniline:formaldehyde", reaction temperature. As a result, the kinetic curves of the reactions for obtaining MDA in the presence of a catalyst at a given temperature were predicted. Computational experiments were carried out to predict the kinetic curves of the reactions of obtaining MDA in the presence of a catalyst at a given temperature. The calculation results were compared with experimental data. It is shown that the developed model can be used to predict the kinetics of the reaction of obtaining MDA in the presence of a catalyst at a given temperature. The subsequent kinetic experiment showed the coincidence of the experimental and predicted curves. For citation: Shishanov M.V., Tsvetkov I.D., Yashunin D.V., Kuk Kh.G., Dosov K.A., Bolshakov I.A., Morozov N.V. Kinetics of aniline-formaldehyde interaction under conditions of homogeneous catalysis. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 11. P. 55-62. DOI: 10.6060/ivkkt.20246711.7030.

Solubility of NaCl in water vapor at 400–700 °C

Water significantly impacts the chemical evolution of the Earth’s crust, affecting environments from volcanic settings to hydrothermal systems. These fluids transport elements essential for geological processes, such as metal ore deposit formation. At high temperatures, as water transitions from liquid to vapor, its molecular structure changes, drastically reducing its capacity to dissolve solids and solvate ions. Here, we report experimental results of halite (NaCl(s)) solubility in water vapor at 400–700 °C and 30–300 bar using a novel U-tube flow-through reactor system. The results show that halite solubility is low (xNaCl,tot = 3.2 × 10−9 to 2.9 × 10−4 mol/mol) and increases with temperature and pressure, attributed to the dissolution of NaCl followed by its hydration according to the reaction:NaCl(s)+nH2O(g)⇋NaCl·H2On(g)Thermodynamic modeling of the experimental results indicates a preference for specific hydrated species, including NaClg, NaCl·H2O4g, NaCl·H2O6g and NaCl·H2O8g. The less hydrated gaseous NaCl species become more prevalent with increasing temperature and decreasing pressure. At temperatures below 600 °C and pressures above 50 bar, halite solubility is close to stoichiometric, whereas at higher temperatures and lower pressures, the hydrolysis of NaCl(s) to form NaOH(lq,s) or a NaClxOH(1-x)(lq,s) (x < 1) solid solution is evident, resulting in the formation of HCl(g). The logarithm of the halite equilibrium solubility constant (logKn) ranges from −10.18 to −4.19 for NaCl(g), and from −13.12 to −11.94, −15.90 to −17.28, and −19.67 to –22.73 for NaCl·H2O4(g), NaCl·H2O6(g) and NaCl·H2O8(g), respectively. Standard thermodynamic properties derived from this data reveal a temperature-independent enthalpy (ΔHn,ro), entropy (ΔSn,ro) and heat capacity (ΔCp,n,ro) of reaction for each NaCl species. While the enthalpy of reaction is nearly constant, the entropy and heat capacity decrease with an increasing degree of hydration, indicating the decreasing stability of these species with increasing temperature. Our thermodynamic model results and gas species stoichiometries are in excellent agreement with previous density functional theory (DFT) calculations (Suleimenov et al., 2006). The halite solubility data obtained here compare well with prior studies and thermodynamic models for the NaCl-H2O system.

Immobilization of laccases on mechanically ground silk fibroin nanofibers for enhanced stability

Azo dyes in textile industry effluents pose significant health and environmental risks. Laccase is an enzyme capable of degrading azo dyes, offering an environmentally friendly solution for treating textile wastewater. However, laccases need to be immobilized on specific carriers to enable effective reuse in batch reactors and continuous operation in flow-through reactors. This study employed silk fibroin nanofibers (SFNFs) obtained by mechanically grinding degummed silkworm silk as sustainable carriers to immobilize laccases through carbodiimide-mediated crosslinking. The immobilized laccases (SFNF-laccases) exhibited improved pH tolerance in the range of pH 3.0–8.0 with a smaller reduction in activity compared to free laccases (SFNF-laccases: 32.9 %, free laccases: 50.4 %). The thermal stability of immobilized laccases was also improved, showing 19, 13, and 9 % higher activities than those of free laccases at 40, 50, and 60 °C, respectively. After 8 days of storage, the activity of SFNF-laccases was 79 % of their activity immediately after immobilization, whereas free laccases retained only 29 % of their initial activity. In addition, SFNF-laccases maintained 73 % of their original operational activity in a flow-through reactor after 8 days. These results demonstrate the great potential of mechanically ground SFNFs as carriers of laccase and the resulting SFNF-laccases in industrial wastewater treatment.

Application of electro-activated persulfate oxidation enhanced with an ultraviolet process in a multi-stage flow-through filtration system for antibiotics abatement

The treatment of antibiotic wastewater from various water matrices remains challenging because of some complex pollutants in nature. Single treatment methods are often inadequate for eliminating these contaminants. The integrated technology is brilliantly effective over an individual process alone. The electro-activated persulfate oxidation enhanced with an ultraviolet process (EO/PS/UV) was established as a novel technology in antibiotic wastewater treatment. It exhibited to be highly effective with much more efficiency in degrading amoxicillin (AMX) (97.10 %) than the two couple and individual processes in a multi-stage flow-through reactor. The Box-Behnken design’s quadratic model using the response surface methodology (RSM) revealed a reasonable prediction with a suggestive correlation of R2 = 0.9986. This study shows that the AMX degradation mechanism in the EO/PS/UV process involves coordinating of SO4·-, and OH, with OH playing a more significant role. It could effectively treat the tetracycline and sulfamethoxazole within 40 min in both simulated wastewater and secondary effluent, except for tetracycline, which took only 30 min in simulated wastewater. However, AMX did not undergo sufficient removal within 100 min and required a higher EE/O compared to other pollutants. Lastly, the integrated technology has proven to be an efficient and energy-saving method for eliminating antibiotics with promising standpoints for various wastewater treatments.

Study on the hydrothermal gradient extraction of hemicellulose by a flow-through reactor

The hydrothermal gradient extraction process based on the hemicellulose constituent units is important for obtaining high quality hemicellulose products. The hydrothermal extraction of sawdust hemicellulose was performed under both non-isothermal and isothermal operations using a flow-through reactor for investigating the extraction patterns. The results show that there were significant differences in the major forms of hemicellulose units at different extraction stages. For glucose, xylose, and galactose units, the selectivity of oligomeric form decreased gradually with increasing temperature, whereas it decreased and then increased under thermostatic operation. The selectivity of the mannose oligomeric form decreased and then increased in both operation modes, reaching a trough at 170 °C (96.81 %) and 60 min (55.21 %), respectively. The molecular weight of extracted hemicelluloses were mainly distributed below 70,000 Da, and gradually decreased with temperature, but increased with time. The results contribute to the quantitative and qualitative understanding of the hemicellulose gradient extraction process.

Silica solubility and molecular speciation in water vapor at 400–800 °C

Silica solubility and molecular speciation in hydrothermal water vapor have been determined through quartz solubility experiments at 400–800 °C and 50–270 bar using a novel U-tube flow-through reactor system and theoretical calculations. The results demonstrate that silica concentrations are low in water vapor (mSi,tot = 0.11–4.56 mmol/kg or xSi,tot = 8.21 × 10−5–1.98 × 10−6 mol/mol) increase with both temperature and pressure, which is attributed to the dissolution of quartz according to the reaction:SiO2(s) + (n + 2)H2O(g) ⇋ Si(OH)4·(H2O)n(g)Thermodynamic modeling and theoretical calculations employing density functional theory (B3LYP-D3), and MP2 ab initio calculations reveal the stable structures to be Si(OH)4(g), Si(OH)4·(H2O)2(g), Si(OH)4·(H2O)4(g) and Si(OH)4·(H2O)7(g) (n = 0, 2, 4, 7) under the temperature and pressure conditions of interest, with higher-order hydrated structures also present at the lowest temperatures and highest pressures. Various isomers of the gaseous silica species were identified, with the number of energetically favorable structures increasing with hydration level and the motifs shifting from silanol-water bonds to complex water-water networks. Over the temperature range of interest, the logarithm of the quartz equilibrium solubility constant (logKn) rises from −7.40 to −6.55 and −12.23 to −11.65 at 400 to 800 °C for the formation of Si(OH)4(g) and Si(OH)4·(H2O)2(g), respectively, and decreases from −16.20 to −19.15 and –22.61 to −28.74 for Si(OH)4·(H2O)4(g) and Si(OH)4·(H2O)7(g) at the same temperature range, respectively. Standard thermodynamic properties were derived based on the experimental results, revealing temperature-independent enthalpy (ΔHn,ro), entropy (ΔSn,ro) and heat capacity (ΔCp,n,ro) of reaction for each gaseous silica species. The enthalpy of the reaction is nearly constant, whereas the entropy and heat capacity decrease with increasing hydration, resulting in higher-level hydrated species becoming less important with increasing temperature. Our quartz solubility results are in good agreement with previous experimental data and thermodynamic equations, as well as the thermodynamic properties of Si(OH)4(g) at 25 °C and 1 bar.

Lignocellulose Treatment Using a Flow-Through Variant of OrganoCat Process.

This study adapts the biphasic OrganoCat system into a flow-through (FT) reactor, using a heated tubular setup where a mixture of oxalic acid and 2-methyltetrahydrofuran (2-MTHF) is pumped through beech wood biomass. This method minimizes solvent-biomass contact time, facilitating rapid product removal and reducing the risk of secondary reactions. A comparative analysis with traditional batch processes reveals that the FT system, especially under severe conditions, significantly enhances extraction efficiency, yielding higher amounts of lignin and sugars with reduced solid residue. Notably, the FT system shows partial hydrolysis of the cellulose, which increases with temperature while not producing significant amounts of furfural or 5-HMF, indicating more efficient depolymerization of polysaccharides without substantial sugar degradation. A statistical design of experiments (DOE) using a Box-Behnken design elucidates the influence of process variables (time, solvent flow rate, temperature) on the yield. Key findings highlight reactor temperature as the dominant factor affecting yields, with process time showing a significant but less pronounced impact. This study demonstrates the potential of the FT OrganoCat system for efficient lignocellulosic biomass fractionation and represents an advancement towards continuous lignocellulose processing, contributing to our knowledge of process optimization for improved biorefinery applications.

Spherical sponge-inspired design of chitosan/silver cluster-loaded cellulose nanofibrils/Cu-ZIF-8 gel beads for efficient removal of Cr(VI)

Traditional photocatalysts for Cr(VI) often suffer from low catalytic activity, difficult separation and recovery, and weak stability. To address these limitations, we proposed a spherical sponge-inspired design to construct chitosan/silver cluster-loaded cellulose nanofibrils/Cu-ZIF-8 gel beads (CSCZ). This design featured a chitosan-based gel bead (the shell of the spherical sponge), silver cluster-loaded cellulose nanofibrils (the flagella of the spherical sponge), and Cu-ZIF-8 (the collar cell of the spherical sponge), which collectively endowed the CSCZ with remarkable properties. These included a high adsorption capacity (171.2 mg/g), a notable rate constant (0.2812 min−1), and enhanced stability (retaining 84.9 % of its initial removal rate after 10 cycles). In addition to the structural design, the “adsorption–reduction” synergy significantly enhanced Cr(VI) removal efficiency, as confirmed by both experimental characterizations and theoretical calculations. Furthermore, the CSCZ was utilized to treat industrial wastewater, and a custom-built flow-through reactor packed with CSCZ demonstrated the efficiency and practicability of CSCZ. This study demonstrates CSCZ’s potential to efficiently remove Cr(VI) and advances the development of photocatalytic adsorbents inspired by spherical sponge concepts.

Self-supporting three-dimensional CuNi–Sb–SnO2 anode with ultra-long service life for efficient removal of antibiotics in wastewater

Electrochemical ozone production (EOP) is a promising technology for the removal of contaminants in wastewater. However, traditional two-dimensional anodes for EOP are restricted by their reliance on substrates and limited surface area, thus exhibiting poor stability and efficiency. Herein, a novel three-dimensional Sb–SnO2 with Cu and Ni co-doped (3D CuNi-ATO) was synthesized via a facile pressing-sintering method without the Ti substrate. 3D CuNi-ATO had a specific surface area two orders of magnitude higher than conventional CuNi-ATO/Ti, as well as the significant capability of EOP that differs from intrinsic 3D ATO. This endowed 3D CuNi-ATO with the capability to remove tetracycline with a pseudo-first-order rate constant of 0.033 min−1 under a low current density of 5 mA cm−2 within 120 min, which was far more efficient than that by 3D ATO and other two-dimensional anodes reported. The 3D CuNi-ATO was confirmed stable in 100 cycles and had an accelerated service lifetime of over 1100 h versus 83 h of CuNi-ATO/Ti. The degradation of tetracycline in complex matrix and flow-through reactors further revealed the promising potential of 3D CuNi-ATO to be applied in scenarios of practical application and continuous high-rate treatment.

Removal of refractory humic acid-like components from UF filtrate of landfill leachate through pH adjustment and coupled electrochemical process

Mature landfill leachate contains large quantities of a wide range of hazardous and refractory pollutants, especially humic acid-like (HA) and fulvic acid-like (FA) substances. These have poor biodegradability and a considerable ultraviolet-light quenching capacity, severely inhibiting the performance of wastewater treatment and post ultraviolet-light disinfection, but this aspect has attracted little previous research. The Fenton reaction has proved to be a feasible method for removing ultraviolet-quenching substances (UVQSs) but in conventional systems it is unable to completely mineralize organic contaminants. In this study, a novel electro-oxidation process was developed consisting of a flow-through reactor with a Cu2O cathode to catalyze Fenton-type reactions, and oxidation at a RuO2 anode. The combination of pH adjustment and electro-oxidation was evaluated for the treatment of real ultrafiltration (UF) filtrate of mature landfill leachate. A series of analytical techniques were used to determine the performance for the removal of HA and FA. Under optimal conditions, the elimination of fluorescence characteristics of HA and FA reached 100 % and 99.3 %, respectively, according to PARAFAC results based on EEM spectra. TOC was removed by 25.5 %∼30.4 % during the pH adjustment step and 51 % by electrochemical oxidation. Changes in the molecular weight distribution and fluorescence content showed that pH adjustment played an important and significant role in removing UVQSs, and the remaining TOC after electrochemical oxidation was attributed to bioavailable amino acid-like substances. Overall, the results have demonstrated the successful development of an effective method of treating the UF filtrate from mature landfill leachate, with particular respect to the removal of the problematic HA and FA content.

Oily Wastewater Treatment by Using Fe3O4/Bentonite in Fixed-Bed Adsorption Column

Oily wastewater is a major environmental issue resulting from different industrial and manufacturing activities. Contaminated water with oil represents a significant environmental hazard that can harm numerous life forms. Several methodologies have been tested for the removal of oily wastewater from aqueous solutions, and adsorption in a flow-through reactor is an effective mechanism to reduce these effluents. This study focuses on evaluating the ability of Fe3O4/Bent material to adsorb gasoline emulsion from a solution using a fixed-bed column, and it involves analyzing the resulting breakthrough curves. The FT-IR, SEM, EDX, and XRD techniques were used to characterize Fe3O4/Bent. Various ranges of variables were examined, including bed height (2–4 cm), flow rate (3–3.8 mL/min), and initial concentration (200–1000 mg/L), to determine their impacts on the mass transfer zone (MTZ) length and the adsorption capacity (qe). It was shown that a higher bed height and a lower flow rate contributed to a longer time of breakthrough and exhaustion. At the same time, it was noted that under high initial gasoline concentrations, the fixed-bed system rapidly reached breakthrough and exhaustion. Models like the Yoon–Nelson and Thomas kinetic column models were employed to predict the breakthrough curves. Thomas and Yoon–Nelson’s breakthrough models provided a good fit for the breakthrough curves with a correlation coefficient of R2 &gt; 0.95. Furthermore, with a fixed-bed system, the Thomas and Yoon–Nelson models best describe the breakthrough curves for gasoline removal.

Using flow-through reactor to enhance ferric ions electrochemical regeneration in electro-fenton for wastewater treatment

Electrochemical regeneration of ferric ions catches more and more attention since it could decrease iron sludge to avoid the sludge problem while it could simultaneously obtain similar robust removal efficiency to refractory organic contaminants in wastewater treatment as the normal Fenton agent method. However, the electrochemical regeneration of ferric ions in aqueous solution was very slow. In this paper, the mass transfer limit of ferric ions in electro-Fenton reaction was evaluated. Koutecky-Levich equation reveals an extremely low diffusion coefficient (D0) value of ferric ions since its complex coordination of [Fe(HO)x(H2O)6-x]3-x. The D0 value was only 2.70 × 10−6 cm2·s−1. Flow-through reactor was therefore introduced in which the ferric ions was designed to penetrate through the 73.1 μm porous holes in the graphite fiber electrode. The μm-scaled confinement of ferric ions diffusion inside the holes was proved to successfully enhance the reduction current of ferric ions by more than 200 % since the diffusion distance of the ferric ions was significantly decreased in the flow-through reactor. However, besides the benefit of the flow-through reactor, the ferric ions reduction electro-Fenton (FeRR electro-Fenton) in flow-through still faces both the pH limit and H2O2 decomposition problems. Hydrogen evolution reaction (HER) could also cause the decrease of pH which exceeded the optimal pH window for Fenton and therefore destroyed the electro-Fenton reaction consequently although the electrochemical reaction of FeRR was 770 mV prior to HER reaction. The regeneration of Fe (II) process simultaneous destruction of H2O2 since H2O2 e-reduction was 120 mV prior to FeRR reaction, which resulted in only very low H2O2 concentration suitable for FeRR electro-Fenton. Even using stepwise addition of H2O2 in electro-Fenton, the decomposition of H2O2 still could not be avoided. Although the decomposition of H2O2 quite limited the application of FeRR electro-Fenton in real application, FeRR electro-Fenton still supports the enhancement removal efficiency of the refractory organic contaminants under low organic contaminants application.