Optimum Removal Efficiency Research Articles

Boosting BOD/COD biodegradability of automobile service stations wastewater by electrocoagulation

ABSTRACT This study investigates the application of electrocoagulation for enhancing the biodegradability of organic matter in automobile service station wastewater, notorious for its contamination with polyaromatic hydrocarbons, heavy metals, and surfactants. Optimization of key variables such as electrode material, current density, and electrical consumption is conducted, with correlation analysis assessing their impact on water quality. Experimental setups utilize a vertical configuration comprising eight monopolar steel electrode plates as cathodes and eight counter electrodes (either iron or aluminum) connected in parallel. Results indicate that employing iron as the sacrificial electrode significantly increases the biochemical oxygen demand/chemical oxygen demand (BOD/COD) ratio, highlighting the efficacy of heightened power levels in enhancing organic matter degradation. Optimal removal efficiencies, including 87.5 for COD, 96.01 for BOD, and 92.2% for total solids, are achieved at a current density of 42 A/m2 and energy consumption of 360 kWh/m3, while maintaining pH levels between 6 and 9. The findings underscore the potential of electrocoagulation with Fe, Al as anodes, and stainless-steel cathodes as an efficient wastewater treatment approach, particularly for COD, BOD, and solid particle removal, thus contributing significantly to environmental sustainability.

Appraisal of Characterization and Adsorption Isotherm in the Bioremediation of Cu and Zn Ions from Aqueous Solutions Exploiting Unmodified Corn and Coconut Husk

Environment is contaminated by heavymetals has emerged as a substantial globaly. Conventional remediation methods have proven inadequate and costly in addressing this issue. Hence, there is a pressing need to discover bio-remediation as a cost effective, effectual, and environmentally, a substitute for heavymetal removal. This work investigates the adsorption behaviour of Corn Husk (CH) and Coconut Husk (CCH), an inexpensive adsorbent, towards Cu and Zn ions for potential application in wastewater treatment. The physico-chemical variables of unmodified CH and CCH were appraised, and batch experimental methods were employed to study variables like pH, contact time, size of particle, and preliminary content of metals. The impact of solution pH on metals uptake by the adsorbent was investigated on the pH range of 3 to 8, revealing optimal removal efficiencies at pH 6 for Cu and pH 5 for Zn. Equilibrium adsorption times were determined to be 80 minutes for Cu and 60 minutes for Zn ions onto CH and CCH. adsorption volumes is conforming to mono-layer coverage, attained from the Langmuir plots were 4.792 mg/g and 4.594 mg/g respectively for Cu and Zn metals onto the CH and 4.771 mg/g and 4.400 mg/g for their adsorption onto CCH. Experimental values were confirmed to the Langmuir model and Freundlich model, with the Langmuir model providing the best fit. The CH based adsorbent was generally found to have an increased capacity of adsorption of the metal contents than Coconut husk (CCH). These findings underscore the strength of Corn husk as an active adsorbent to extract cationic heavymetal contents from industrial effluents.

Application of composite persulfate oxidation to remediate weathered lubricating oil-contaminated soils: Batch and pilot-scale studies

In this study, two novel composite persulfate (PS) oxidants [base pulverized NaOH composite persulfate (BPS) and metal (iron and manganese) composite persulfate (MPS)] were developed. The feasibility, mechanisms, and optimal conditions for remediating weathered lubricating oil (WLO)-contaminated soils using composite PS oxidants were evaluated. BPS was prepared by blending PS and NaOH powders (molar ratio = 1:0.3), while MPS was prepared by mixing PS, FeCl2, and KMnO4 at a molar ratio of 1:0.3:0.05 for PS:Fe:Mn. The oxidation of rhodamine B (RhB) dye using BPS and MPS followed second-order kinetics. MPS process was more effective in organic oxidation, likely due to its electron transfer mechanism. The generation of •SO4- in the BPS process required activation by •OH, potentially leading to more efficient and stable •SO4- generation and subsequent organic chemical oxidation. Radical analyses revealed that •SO4- was present in the pH range of 3–12, with the strongest •OH signal at pH 7–9. Employing hybrid BPS and MPS for WLO-contaminated soil remediation could achieve optimal TPH removal efficiency due to the combined generation of •OH (high reactivity) and •SO4- (stable characteristics). The addition of BPS helped neutralize acidified soils and maintained a higher soil pH (around 6.1). The multi-stage oxidation using the hybrid composite PS oxidants (MPS + BPS) at a 1:1 ratio (w/w) achieved 84 % TPH removal (initial TPH = 7721 mg/kg) after three oxidation stages (5 % w/w oxidant dosage). The composite oxidation process offers a more reactive oxidation potential with an extended oxidant life without causing a substantial pH drop.

Removal of Acid Orange 7 dye using Makgeolli lees with ultrasonic assistance

AbstractThis study investigated the efficient removal of Acid Orange 7 (AO7) dye in water by using Makgeolli lees, a popular by‐product obtained during the production of traditional Makgeolli beverages in Korea. By incorporating ultrasound, the effects of contact time, Makgeolli lees dosage, initial AO7 dye concentration, and initial pH of the dye solution were investigated and comprehensively compared with the same experiment using the stirring method. The results consistently showed ultrasound not only enhances the excellent adsorption ability of Makgeolli lees but also accelerates the process compared to the stirring method. The Langmuir isotherm model best described the adsorption process for both methods, suggesting monolayer adsorption on the surface of Makgeolli lees, with maximum capacities of 25.13 mg/g for ultrasound at 40 kHz and 20.41 mg/g for stirring methods. Furthermore, the study showed that optimal dye removal efficiency can be achieved with ultrasound conditions at 28 kHz frequency, 125 W/L power density, and 100% ultrasound intensity. This research promises that the integration of low‐cost biomass coupled with ultrasound could provide a potential solution for dye wastewater treatment.

Adsorptive removal of cationic dyes from wastewater using a novel sodium alginate-based iron oxide nanocomposite hydrogel: DFT and advanced statistical physics modelling

A novel Sodium alginate-based hydrogel reinforced with varying Fe2O3 nanoparticles loading (NCH) was synthesized to remove cationic dyes methylene blue (MB) and crystal violet (CV). The NCH, with 5 % Fe2O3 loading, demonstrated optimal removal efficiency for both dyes. Detailed spectroscopic, microscopic, and spectrometric characterization techniques verified the nanocomposite structure and dye adsorption. Batch experiments revealed that at pH: 9, with a 20 mg 100 mL−1 adsorbent dose and times of 60 min for MB and 40 min for CV, with an initial concentration of 500 mg L−1, maximum adsorption capacities were achieved. MB and CV adsorption onto NCH showed distinct mechanisms: MB via physical interaction, CV via both physical and chemical interactions, including electrostatic forces and hydrogen bonding. Despite differences, the Langmuir-Freundlich model best fit the equilibrium isotherms, suggesting monolayer adsorption dominated, even with heterogeneous surface sites on NCH. A dual-site M2 statistical physics model revealed that MB and CV adsorption occurred via a multi-molecular vertical configuration on the binding sites, with heterogeneous adsorption sites contributing to dye uptake. Density functional theory demonstrated higher adsorption affinity for MB over CV, primarily due to hydrogen bonding and electrostatic interactions. NCH exhibited 80 % dye removal efficiency after five cycles, highlighting its potential for industrial effluent treatment.

Biokinetic and microbial insights into regulatory mechanisms of long-chain fatty acid degradation during food waste-lipid co-digestion within anaerobic membrane bioreactor

This study investigated the effects of varying lipid ratios on the anaerobic co-digestion of high-lipid food waste (FW) in a mesophilic anaerobic membrane bioreactor (AnMBR). At a lipid concentration of 5 %, optimal biogas production (3.84 L/L/d) and lipid removal efficiency (78 %) were achieved; however, increasing lipid concentrations resulted in significant accumulations of long-chain fatty acids (LCFAs) and volatile fatty acids (VFAs). Batch tests further demonstrated the impact of various types of LCFAs, with stearic acid showing the slowest microbial growth rate (0.033d-1), confirming its role in the accumulation of acetate-dominated VFAs, potentially limiting the methanogenesis process at elevated lipid levels. Furthermore, at 8 % lipid content, the downregulation of key LCFA degradation enzymes and dominance of hydrogenotrophic methanogens indicated adverse conditions. The importance of the intricate interplay between LCFA degradation kinetics and microbial community for the system efficiency was evidenced, offering insights for optimizing and managing high-lipidic wastes.

Removal of hexachlorocyclohexane isomers from wastewater using activated carbon from Musa paradisiaca peel: Adsorption isotherms, kinetic, and thermodynamic studies

The potential usage of activated carbon from plantain peel (Musa paradisiaca) (TPPC) and unactivated carbon from plantain peel (UPPC) for the removal of Hexachlorocyclohexanes (HCHs) from water systems was investigated. The TPPC and UPPC were characterized using Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). Adsorption experiments were conducted as a function of adsorbent weight (2 – 10 g), temperature (30 -50 °C), and solution pH (2 - 9) under an adsorbent packed column. The Optimum removal efficiency of 98.23 % was achieved in the column studies under the following conditions: pH = 5, the dosage of adsorbent = 5 g/100 mL, temperature = 30 °C. The batch adsorption process was employed to evaluate the kinetics, equilibrium, and thermodynamics of the adsorption processes. The equilibrium study showed that Langmuir among other isotherm models applied performed better in fitting the data. Additionally, the kinetic data was best described by the pseudo-second-order model (R2 > 0.97), indicating a chemisorption mechanism. Furthermore, the thermodynamic calculations of the adsorption process suggest that HCH adsorption was exothermic (ΔH = -110.87) and spontaneous (-ΔG).

Response surface methodology optimization of sodium diclofenac adsorption using activated carbon derived from falcata tree sawdust

The presence of sodium diclofenac in water is a significant problem due to its adverse effects on terrestrial and aquatic organisms. Thus, this study investigated the Falcata tree sawdust as the precursor of activated carbon for the adsorption of diclofenac in an aqueous solution. The characterization of falcata tree sawdust-activated carbon (FTSAC) was evaluated by SEM and FTIR analysis. The activated falcata sawdust converted to activated carbon has a 30 % yield. The optimal values for the operating parameters, FTSAC dosage, initial sodium diclofenac concentration, reaction time and pH, were determined using the central composite design (CCD) of the response surface methodology (RSM). The optimal removal efficiency suggested by CCD is 93.98 % with the optimum conditions of parameters of 0.80 g FTSAC dosage, 200 ppm initial sodium diclofenac concentration, 20 min reaction time, and pH 4. These optimal values of parameters were validated by an actual experiment, and the result (average removal efficiency: 92.08 %) is within a 95 % confidence interval. On the other hand, the pseudo-second-order (R2 = 0.9991) kinetic model depicts the rate of absorption of FTSAC adsorbing SD. Moreover, the Langmuir-Freundlich isotherm or Sips isotherm model (R2 = 0.9904) is the best-fit model that describes the heterogeneous adsorption dynamics of FTSAC surfaces. This study indicates that falcata sawdust can serve as a promising and viable alternative raw material to produce activated carbon.

Refractory organic matter removal from mature leachate by bipolar electrocoagulation-electrooxidation reactor configurations

In this study, mature leachate treatment with combined electrochemical processes was investigated to benefit from the advantages of electrocoagulation (EC) and electrooxidation (EO) simultaneously. First, control experiments were conducted, the most effective anode-cathode combination for EO was selected as Ti/IrO2-Gr, the number of Al electrodes for EC was determined as 3 and the number of Fe electrodes was determined as 5. Optimization of process parameters of the combined system with Al and Fe electrodes was conducted with Box-Behnken design (BBD). With BBD, the effect of the process parameters (initial pH, current density, and reaction time) on the system responses (COD, UV254, and color removal efficiencies) was determined. The suitability of the created model in the study was analyzed statistically and the results of quadratic models were found compatible with experimental studies. The model's capacity for prediction was also confirmed by validation experiments under optimum conditions. By implementing the optimum conditions, COD, UV254, and color removal efficiencies were determined as 71.5 %, 60.2 %, and 93.2 %, respectively for the combined process with Al electrodes and 79.5 %, 68.0 %, and 97.7 %, respectively for the combined process with Fe electrodes. Correlation of actual and predicted data showed that BBD is reliable for optimizing process parameters of combined processes with Al and Fe electrodes. The obtained results showed that combined processes are more effective than hybrid processes, based on both pollutant removal efficiencies and energy consumption.

Electrodes combined with permeable reaction barrier removes Cr (Ⅵ) from low permeability aquifers

Choosing an effective means of dealing with chromium (Cr (VI)) pollution is necessary. Electrokinetic (EK) technology is widely used in low- permeability aquifers. Zero-valent iron/activated carbon (ZVI/AC) can be used as a permeable reactive barrier (PRB) filler for the removal of Cr(Ⅵ) from in low- permeability media. However, the combined effects of these two technologies on aquifers have not been studied extensively. In this study, the ratio of zero-valent iron to activated carbon was determined through a pre-experiment. A series of batch experiment was then conducted to evaluate the effectiveness of electrokinetic (EK) combined with ZVI/AC-PRB on removal of Cr (VI). The ZVI/AC mixture before and after the reaction was analyzed by scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results of the batch experiment showed that the optimum removal efficiency of Cr (VI) was 90.38 % after 1440 min at a ZVI/AC mass ratio of 1:4. During the experiment, owing to the movement of the acid and base peaks, the pH of the anode region was generally lower than that of the other regions. The current decreased as the concentration of heavy metal ions decreased. The SEM, FTIR, and XPS results show that Cr (Ⅵ) was transformed into Cr(Ⅲ) or adsorbed on the surface under the action of ZVI/AC micro-electrolysis. In the present study, these two technologies were combined to treat Cr (VI)-contaminated aquifers. The experimental results provide a theoretical basis for the field application of the EK-PRB repair technology.

Treatment of real carwash wastewater using high-efficiency and energy-saving electrocoagulation technique

This study focused on the treatment of actual wastewater from a car wash facility using electrocoagulation. The primary objective was to decrease chemical oxygen demand (COD) and eliminate turbidity by employing various electrodes such as Stainless Steel (SS) 304, Galvanized Iron (GI), and aluminum foil (α-Al) in a batch configuration. Several factors including contact time, current density, initial pH, and electrode material were examined to optimize process efficiency. The sludge generated during electrocoagulation was analyzed using Scanning Electron Microscopy/Energy-Dispersive X-ray Spectrometry (SEM-EDS). The results indicated that COD removal efficiency initially decreased between 30 and 60 min before improving. The data for COD, turbidity, and total phosphate reduction aligned well with the pseudo-first-order kinetic model, with R2 values of 0.275, 0.898, and 0.522, respectively. Minor variations were observed in pH, Total Dissolved Solids (TDS), Electrical Conductivity (EC), and alkalinity, while the temperature increased from 12 to 18.6 °C. Optimal removal efficiency for turbidity, total phosphate, and COD was achieved at pH = 6. The study demonstrated that higher current density resulted in enhanced COD reduction and turbidity removal. Chloride levels decreased with increasing applied current. The α-Al electrode exhibited superior performance compared to SS 304 and GI electrodes, with notable pH fluctuations during the process. UV–visible absorption spectra indicated differences in treated wastewater patterns based on the electrode utilized. SEM analysis revealed distinct characteristics of sludge produced by different electrodes. Energy and electrode consumption varied among the electrodes, with SS 304 displaying the lowest values.

Efficient removal of U(VI) by graphene-based electrode modified with amidoxime: Performance and mechanism

The burgeoning interest in nuclear energy as a sustainable power source brings to the fore significant environmental and human health concerns associated with wastewater from uranium mining. This study presented the successful synthesis of amidoxime modified graphene-based electrode materials (PAO-N-rGO/CF) designed for treating uranium containing wastewater. The influencing factors of PAO-N-rGO/CF during the electrokinetic restoration process were systematically investigated, exploring the mechanisms of adsorption and electrochemical reduction from the perspectives of establishing adsorption theoretical models, evaluating electrochemical performance, and characterizing reduction products. According to the results, the optimal removal efficiency for U(VI) by PAO-N-rGO/CF reached 99.93 % under conditions of an applied voltage of 5 V, an electrification duration of 20 min, and a pH of 7. Compared to Ca2+, K+, and Mg2+, PAO-N-rGO/CF exhibited strong selectivity for UO22+. Whether dissolved oxygen was present or not, PAO-N-rGO/CF maintained its excellent electrochemical performance. After undergoing 10 cycles of reuse, the removal efficiency for U(VI) only decreased by 8.75 %. The establishment of the adsorption model demonstrated the presence of a chemical bond between uranium and amidoxime groups. The electrochemical performance tests evidenced that PAO-N-rGO/CF exhibited superior electron transfer capability. The reduction of (UO2)3(OH+)5 to UO2 in wastewater at a pH = 7 was verified by analysis of the reduction products. The successful development and mechanistic study of the novel and efficient electrode material provide theoretical support for the control of radioactive nuclide pollution and possess practical value for engineering applications in treating uranium containing wastewater.

Adsorptive and oxidative removal of phenolphthalein by sono-assisted synthesized FeAcC in advanced oxidation-integrated fluidized bed reactor

ABSTRACT Environmental water sources are under increasing threat due to the addition of harmful chemicals not addressed by conventional water treatment processes. To work on this concern, the current study aimed to synthesize sono-assisted Fe-modified activated carbon-chitosan (FeAcC) composite and construct a laboratory-scale ozone-integrated fluidized bed reactor (FBR) to eliminate phenolphthalein (php). Following 120 min of incubation, the adsorbent demonstrated a 27.28 mg g−1 of php adsorption capacity at pH 4 with 0.5 g L−1 of adsorbent dosage. The adsorption efficacy and mechanism were defined using isotherm and kinetic models. The study investigated the impact of different factors including, initial concentration, reuse of FeAcC, recirculation flow rate, and hydraulic retention time (HRT), on the efficiency of php removal. The optimum removal efficiency was observed at approximately 95% after 20 min of operation at 1.5 L min−1 recirculation flow rate (batch FBR) and 70 min of HRT (continuous FBR) under 400 mg h−1 ozonation rate. Experimental parameters were optimized using response surface methodology (RSM) with central composite design (CCD) to improve php removal. The large-scale implementation of the findings in the future can be a step for adding new technology for clean water treatment processes for emerging toxic pollutants.

Novel multineedle-to-cylinder plasma coupled with bimetallic catalysts for efficient removal of sulfides and ammonia in odor gases

Dielectric barrier discharge (DBD) plasma is a promising technology for treating odor gases. This study developed an innovative multineedle-to-cylinder (MC) configuration DBD plasma reactor and investigated its synergistic effect with bimetallic catalysts. The results demonstrated that MC-DBD plasma achieved complete elimination of ammonia and organic sulfides, while the removal efficiencies of inorganic H2S and CS2 reached 44.0 % and 53.0 % respectively. Compared with conventional plasma, the specific energy input (SEI) of MC-DBD was significantly reduced to 4.44 J/L. Furthermore, with the incorporation of Mn-Ce/ZSM-5 catalyst, optimal removal efficiencies of H2S and CS2 were significantly improved to 82.6 % and 90.7 %, and the SEI was reduced by 18 %. The electrical performance revealed that the low energy consumption was mainly attributed to stable fast-pulse micro-discharge channels and significantly enhanced inhomogeneous electric fields achieved by the filament discharge mode. Catalyst characterization (X-ray photoelectron spectroscopy and O2-temperature programming desorption) confirmed that surface catalytic reaction mainly follows the Mars-van Krevelen mechanism, where increased lattice oxygen content and the electron transfer between Mn and Ce play crucial roles in enhancing malodor degradation performance. This work proposes an efficient solution for degrading mixed malodors and provides an experimental and theoretical basis for optimizing plasma structure as well as researching treatment of mixed pollutants.

Karakterisasi Performa Adsorben Cangkang Telur Pada Proses Penyerapan Logam Merkuri (Hg)

Mercury (Hg) is a highly toxic heavy metal with no biological benefits, posing significant environmental and health risks upon exposure. This study investigates the adsorption characteristics of chicken eggshell-derived adsorbents for the removal of Hg from aqueous solutions. The adsorbent preparation involved washing, drying, calcination, and KOH activation. Results indicated that the 170-mesh size adsorbent exhibited the highest adsorption efficiency, achieving a 99.70% removal rate of Hg. adsorption capacity tests revealed values ranging from 79,90 to 88,90 mg/g, conforming to the Indonesian National Standard (SNI) for activated carbon. Functional group analysis using Fourier-Transform Infrared Spectroscopy (FT-IR) identified a significant increase in aldehyde and ketone groups post-activation. The adsorption process reached equilibrium within 90 minutes, with optimal removal efficiency observed at an initial Hg concentration of 3,0 mg/L. These findings suggest that chicken eggshell-based adsorbents are a cost-effective and efficient solution for mitigating Hg contamination in wastewater, offering a sustainable alternative to conventional methods.

Employing a magnetic chitosan/molybdenum disulfide nanocomposite for efficiently removing polycyclic aromatic hydrocarbons from milk samples

This study aimed to develop a highly efficient nanocomposite composed of magnetic chitosan/molybdenum disulfide (CS/MoS2/Fe3O4) for the removal of three polycyclic aromatic hydrocarbons (PAHs)—pyrene, anthracene, and phenanthrene. Novelty was introduced through the innovative synthesis procedure and the utilization of magnetic properties for enhanced adsorption capabilities. Additionally, the greenness of chitosan as a sorbent component was emphasized, highlighting its biodegradability and low environmental impact compared to traditional sorbents. Factors influencing PAH adsorption, such as nanocomposite dosage, initial PAH concentration, pH, and contact time, were systematically investigated and optimized. The results revealed that optimal removal efficiencies were attained at an initial PAH concentration of 150 mg/L, a sorbent dose of 0.045 g, pH 6.0, and a contact time of 150 min. The pseudo-second-order kinetic model exhibited superior fitting to the experimental data, indicating an equilibrium time of approximately 150 min. Moreover, the equilibrium adsorption process followed the Freundlich isotherm model, with kf and n values exceeding 7.91 mg/g and 1.20, respectively. Remarkably, the maximum absorption capacities for phenanthrene, anthracene, and pyrene on the sorbent were determined as 217 mg/g, 204 mg/g, and 222 mg/g, respectively. These findings underscore the significant potential of the CS/MoS2/Fe3O4 nanocomposite for efficiently removing PAHs from milk and other dairy products, thereby contributing to improved food safety and public health.

Dynamic wetting characteristics of two droplets impacting a spherical dust particle

The removal of dust based on water misting is one of the most effective measures for dust control, and the basis of this method lies in the liquid–solid impact behavior. To further improve the dust removal efficiency, in this work, the removal mechanism was studied at the microscopic level, and the dynamic impact between two water droplets and a spherical dust particle was simulated using the coupled level-set/volume-of-fluid (CLSVOF) method. The optimal parameter ranges for micron-level dust removal were determined through the method of variable control, and the reliability of the obtained results was experimentally verified. When two droplets continuously or simultaneously impact a spherical particle, the liquid film formed undergoes deformation phenomena such as fusion, rupture, stretching, contraction, and fragmentation. The liquid film is more likely to break at higher droplet velocities, leading to the filling of the gas film and hindering the wetting process. The optimum contact angle and velocity range of the liquid droplets to completely encapsulate the dust particles were found to be θ = 2 and V = 10–20 m/s, respectively. The experimental results also showed that for the same dust particle size, the dust removal efficiency initially increased but then decreased with increasing dust concentration. The optimum dust removal efficiency of 98.1 % was achieved for θ = 2 and V = 10 m/s. This study sheds new light on the dust removal mechanism of water mist-based dust removal technologies and can aid in the design and parameter optimization of more effective dust suppression systems.

Treatment of Vegetable Oil Industry Wastewaters with Coagulation-flocculation Methods

This study was conducted to investigate potential use of environment-friendly treatment technologies in treatment of vegetable oil industry wastewaters containing various pollutants at high concentrations and compounds resistant to biodegradation. Within the scope of the study, coagulation-flocculation processes were experimented. Various configurations were tried to achieve optimum removal efficiencies. In coagulation-flocculation experiments with Al2(SO4)3.18H2O coagulant, the highest COD (92%) and Oil-Grease (89%) removal efficiencies were achieved at 800 mg Al+3/L coagulant dose. In experiments with FeCl3.6H2O coagulant, the highest COD (88%) and Oil-Grease (89%) removal efficiencies were achieved at 600 mg Fe+3/L coagulant dose.

Ultrasound-improved removal of chloride ions from coking circulating water by Friedel’s salt precipitation: Efficiency enhancement and mechanisms

The concentration of chloride ions should keep appropriate in the coking circulating water to prevent multiple detrimental effects on the environment. Even though Friedel’s salt precipitation is a practical and economically beneficial method to remove chloride, the chloride removal of traditional method is insufficient. A modified ultrasonic method for the removal of chloride by Friedel’s salt precipitation was proposed. A number of influential elements including the ratio of reagents, reaction time, pH, temperature, stirring speed, sulfate, and fluoride, were fully investigated. The results showed that sulfate and fluoride could inhibit the chloride removal through a competitive effect with chloride. With ultrasonic enhancement, the optimal removal efficiency of chloride ions was 87.20 %, compared to 82.17 % without ultrasonic enhancement. Additionally, the reaction time was shortened by 15 minutes utilizing ultrasonic. The cavitation and mechanical disruption effects of ultrasound conjunction with precipitation can improve the efficiency of chloride removal. This study provided a theoretical foundation of ultrasonic synergistic Friedel’s salt precipitation method for chloride removal, and offered guidance for the use of Friedel’s salt with enhanced techniques in other fields.

Enhanced Orange II Removal Using Fe/Mn/Mg2-LDH Activated Peroxymonosulfate: Synergistic Radical Oxidation and Adsorption

In this study, Fe/Mn/Mg2-LDH was utilized for the first time as a catalyst for peroxymonosulfate (PMS) activation to facilitate the removal of Orange II. This composite was characterized using various techniques, such as XRD, FTIR, SEM-EDS, BET, and XPS. The results revealed a well-defined lamellar structure of Fe/Mn/Mg2-LDH with a metal molar ratio of Fe/Mn/Mg at 1:1:2. Moreover, the structural stability of Fe/Mn/Mg2-LDH was confirmed through the XRD, FTIR, and SEM. Fe/Mn/Mg2-LDH exhibited a good adsorption capacity towards Orange II and highly efficient PMS activation. The optimal removal efficiency of Orange II (98%) was achieved under the conditions of pH 7.0, [PMS] = 1.0 mmol L−1, [Fe/Mn/Mg₂-LDH] = 1.6 g L−1, and [Orange II] = 50 μM. Additionally, this system demonstrated good adaptability across a wide pH range. The presence of Cl− and humic acids (HA) did not significantly inhibit Orange II removal, whereas inhibitory effects were observed in the presence of CO32− and PO43−. The removal mechanism of Orange II was attributed to a synergy of adsorption and oxidation processes, wherein the generated surface radicals (SO4•−ads and HO•ads) on the surface of the Fe/Mn/Mg2-LDH played a predominant role. Furthermore, the Fe/Mn/Mg2-LDH exhibited good reusability, maintaining a removal rate of 90% over five cycles of recycling. The Fe/Mn/Mg2-LDH/PMS system shows promising potential for the treatment of wastewater contaminated with refractory organic pollutants.