NaClO Concentration Research Articles

Characterization of Disinfection By-Products Originating from Residual Chlorine-Based Disinfectants in Drinking Water Sources

In this study, samples from the Yangtze River, Han River, and Liangzi Lake in Wuhan City were utilized to characterize the formation of disinfection by-products (DBPs) from chlorine-based disinfection residues in drinking water sources. The results indicated that the main DBPs in drinking water sources were trichloromethane (TCM) and trichloroacetic acid (TCAA). The generation of DBPs was significantly positively correlated with oxidative substances, aromatic compounds, pH, and ammonia nitrogen (NH3-N) content in the water. The concentration of TCAA increased from 0 to 2.45 ± 0.31 mg/L when the reaction time increased to 72 h. As the NaClO concentration increased from 5 mg/L to 15 mg/L, the concentrations of TCAA, TBM, and DCAN increased from 2.03 ± 0.04 mg/L, 0 mg/L, and 0 mg/L to 2.49 ± 0.34 mg/L, 0.21 ± 0.07 mg/L, and 0.10 ± 0.04 mg/L before decreasing to 1.75 ± 0.19 mg/L, 0.17 ± 0.07 mg/L, and 0.04 ± 0.05 mg/L, respectively. The orthogonal experimental results showed that Br−, NH3-N, and pH all had significant influences on the TCM generation, whereas temperature affected the formation of TCAA in the Han River. This work reveals the factors influencing the generation of DBPs from chlorine-based disinfection residues, offering a prevention and control method for DBPs in drinking water sources from a theoretical perspective.

Degradation of norfloxacin by the synergistic effect of micro-nano bubbles and sodium hypochlorite: kinetics, influencing factors and pathways.

This study thoroughly investigated the degradation of norfloxacin (NOR) under the influence of micro-nanobubbles (MNBs) and sodium hypochlorite (NaClO), focusing on their synergistic effects. The impact of various environmental factors, including NaClO concentration, pH, inorganic anions, and surfactants, on NOR degradation efficiency within the MNBs/NaClO system was systematically assessed. The basic properties of the MNBs/NaClO system and the degradation kinetics of NOR were explored. The degradation products and pathways of NOR were explored to reveal the degradation mechanism of antibiotics in the MNBs/NaClO system by employing density functional theory (DFT) and high-performance liquid chromatography-mass spectrometry (HPLC-MS). The redox potential of the MNBs/NaClO system exhibited significantly superior properties than the single system, with bubble sizes predominantly in the nanoscale. The degradation kinetics of NOR adhered to a pseudo-first-order reaction model, with optimal degradation occurring at a 0.025% NaClO volume concentration. Acidic conditions promoted the degradation of NOR, and alkaline conditions inhibited the degradation of NOR. Inorganic anions PO43-, HCO3-, and CO32- in the water matrix led to strong inhibition of NOR degradation. Cationic surfactants accelerated the degradation process of NOR, while anionic and nonionic surfactants had a consistent inhibitory effect on the degradation of NOR. Based on the degradation behavior, three potential pathways for NOR degradation were proposed: quinolone group transformation, defluorination reaction, piperazine ring cracking and quinolone ring decomposition. This research contributes a novel technical approach for addressing antibiotic pollution and offers a theoretical framework for understanding the fate of antibiotics in the environment.

Research on smoke cleaning based on Mg(OH)2/NaClO2 seawater solution

Abstract Ship exhaust emissions contain a large amount of sulfur oxides and nitrogen oxides, which have attracted widespread attention from the international community for their pollution of the atmospheric environment. In order to reduce the emissions of these pollutants, the International Maritime Organization (IMO) and other national institutions have established strict emission standards and promoted the research and application of ship exhaust desulfurization and denitrification technology. Experimental and simulation analyses were conducted on the denitrification effect of Mg(OH)2/NaClO2 solution using a cyclic spray method. Simulation analysis was carried out using cyclic spraying. The experiment compared the reaction degree and reaction time of NO in NaClO2 seawater, NaClO2 water, and Mg(OH)2/NaClO2 marine solution. The experimental result is that in the process of cyclic spray, the removal rate of NO by these three solutions can reach 100%. The reaction time of NO is 71, 86, and 90 minutes, respectively. Under the same conditions, the simulation results showed that the reaction rate of NaClO2 water solution with NO was faster, followed by NaClO2 seawater solution. The reaction rate of Mg(OH)2/NaClO2 seawater solution with NO was the slowest of the three. When the pH value exceeds 7, it effectively inhibits the production of ClO2 gas by NaClO2. The removal rate of Mg(OH)2/NaClO2 seawater solution is directly proportional to the initial concentration of NaClO2. In addition, it could be seen from the simulation cloud diagram that the removal speed of NO in the spray reactor slows down as the concentration of NO increases.

Preparation of N-Halamine Gelatin Sponge and Its Application in the Treatment of Skin Infection.

Nowadays, there has been an increasing research interest into N-halamine compounds due to their wide antimicrobial properties and no drug resistance. Most of the research mainly focuses on small molecular N-halamines, while few studies are on macromolecule N-halamines. In this work, antibacterial N-halamine polymer materials based on proteins (GS-Cl) were synthesized with an antibacterial component of oxidative chlorine, a support component of a gelatin sponge. After carrying out systematic characterization, the GS-Cls exhibited well-defined porous morphology and had a high efficiency in the killing of Gram-positive bacteria (E. coli) and Gram-negative bacteria (S. aureus). The loading of oxidative chlorine (Cl+%) could be controlled by changing the NaClO concentrations and chlorination times. The biocompatibility was confirmed as well. In vivo experiments suggested that the GS-Cl sample could effectively promote the healing of skin wounds in mice E. coli and S. aureus infection models. These studies show that proteins can be chlorinated and endowed with antimicrobial properties, which has great application potential in the treatment of bacteria-infected wounds.

THE EFFECTS OF NaClO2 AND H2O2 AS BLEACHING AGENTS IN THE SYNTHESIS OF CELLULOSE ACETATE FROM OIL PALM EMPTY FRUIT BUNCH

Indonesia is one of the largest palm oil-producing countries in the world. The results of palm oil processing produce a lot of waste, such as oil palm empty fruit bunches (OPEFB). The utilization of OPEFB in Indonesia is minimal, so it needs further development. OPEFB has a very high α-cellulose content, so that it can be used as raw material for manufacturing cellulose acetate. Making cellulose acetate from OPEFB consists of three main steps: delignification, bleaching, and acetylation. This study aims to compare the effects of the concentration of NaClO2 or H2O2 in the bleaching process on the physical properties of cellulose acetate from OPEFB. In the delignification process, 100 mesh-sized OPEFB powder is reacted with 5% sodium hydroxide (NaOH) at 100oC for 2 hours. The residue from deliglinfication was washed using distilled water until pH 7, filtered using filter paper, and dried using an oven at 50oC. The next step is the bleaching process using NaClO2 or H2O2 with concentration variations (1%, 2%, 3%, 4% and 5%). The bleaching process was carried out at 90oC for 1.5 hours. After filtration, the bleached residue was washed using distilled water until pH 7, filtered using filter paper, and dried using an oven at 50oC. After the bleaching process, α-cellulose powder was produced. The next step is acetylation, containing three main steps. The first step is the reaction between α-cellulose powder with acetic acid (CH3COOH) and sulfuric acid (H2SO4) at 40oC for 1.5 hours to perform activation. The second step is the addition of anhydrous cellulose in a ratio of 1:10 and mixed at 40oC for 1.5 hours. The third step is the addition of distilled water, acetic acid, and sodium acetate (CH3COONa) at 40oC for 5 minutes. Then, followed by filtration, the residue was washed using distilled water and methanol until pH 7 and dried at 50oC. The best result is using NaClO2 as a bleaching agent with a concentration of 2%, resulting in cellulose acetate yielding 98.85%, density of 1.954 g/mL, and L value of 91.897 for colorimetric test results. The density and L-value were close to commercial cellulose acetate (Sigma Aldrich). From the results of FTIR analysis, it can be concluded that the acetylation of α-cellulose into cellulose acetate has been successful, as evidenced by the formation of carbonyl groups (C=O).

Enhancing Root Canal Therapy with NIR-II Semiconducting Polymer AIEgen and Low-Concentration Sodium Hypochlorite Synergy.

Despite significant efforts to eliminate bacterial biofilm within root canals, achieving effective disinfection remains challenging due to the complex anatomy and limitations of disinfectants. In this study, a second near-infrared (NIR-II) semiconducting polymer with aggregation-induced emission (AIE) properties, named PIDT-TBT, is deliberately designed and synthesized. This proposes an AIE luminogen-based sterilization strategy in synergy with a low concentration of sodium hypochlorite (NaClO). Water-dispersible PIDT-TBT nanoparticles (NPs) are prepared, demonstrating good biocompatibility, as well as photothermal and photodynamic properties. Subsequent antibacterial tests show that PIDT-TBT NPs exhibit excellent bactericidal effects against three bacterial strains: Staphylococcus aureus, Streptococcus mutans, and Enterococcus faecalis, upon 808nm laser irradiation. In synergy with a low concentration of NaClO (0.5%) solution, PIDT-TBT NPs significantly improves the outcome of root canal treatment under 808nm laser irradiation in a human extracted tooth root canal infection model. Additionally, it is found that PIDT-TBT NPs combine with a low concentration of NaClO solution could safely dissolve dentin debris and further increase the efficiency of root canal preparation by altering the elemental composition of the inner root canal wall.

The Comparison of Catalytic Activity of Carbimazole and Methimazole on Electroreduction of Zinc (II) in Chlorates (VII): Experimental and Molecular Modelling Study.

With the help of electrochemical methods, including CV and EIS, the influence of methimazole, carbimazole, and the concentration of the supporting electrolyte on the kinetics and mechanism of zinc electroreduction on a mercury electrode was compared and analyzed. Moreover, molecular dynamics simulations of zinc/carbimazole and zinc/methimazole solutions were carried out to determine the effect of drugs on the hydration sphere of Zn2+ ions. It was shown that the electroreduction of Zn2+ in the presence of methimazole and carbimazole occurs in two steps and the first one determines the kinetics of the entire process. The presence of both drugs in the solution and the increase in the concentration of the supporting electrolyte reduce the degree of hydration of the depolarizer ions and the hydration of the electrode surface, what is a factor favoring the rate of electroreduction. Based on theoretical studies, the formation of stable complexes between Zn2+ and the molecules of both drugs in a solution was considered unlikely. However, active complexes can be formed between depolarizer ions and molecules adsorbed at the electrode surface. They constitute a bridge facilitating charge exchange during the electrode reaction, revealing the catalytic abilities of methimazole and carbimazole. In the range of cdrug ≤ 1 × 10-3 mol dm-3, carbimazole is a better catalyst, whereas in the range of cdrug ≥ 5 × 10-3 mol dm-3, it is methimazole. The effectiveness of both compounds in catalyzing the first stage of the electrode reaction increases with the increase in the NaClO4 concentration.

A Ratiometric Fast-Response Fluorescent Probe Based on Dicyanoisophorone for Monitoring HClO in Paper Test Strips and Living Mice.

A new dicyanoisophorone-based ratiometric fluorescent probe NOSA was synthesized and characterized. It showed a fast fluorescence response to HClO with the emission color change from dark green to bright red. NMR, IR, and HRMS suggested that the detection of NOSA to HClO may originate from the hydroxyl deprotection reaction by HClO on the molecule NOSA, which caused a red-shift of fluorescence. The probe NOSA displayed high selectivity and excellent anti-interference performance with a limit of detection at 3.835 × 10-7M. The convenient paper test strips were successfully obtained and applied to the detection of HClO based on fluorescence color change with the varied NaClO concentration. Moreover, spiked recovery experiments in real water samples indicated that the probe NSOA could quantitatively detect HClO, and the fluorescence bio-imagings in vivo were carried out, and HClO detection in biosystems using NOSA was realized.

Oxidation-induced starch molecular degradation: A comprehensive kinetic investigation using NaClO/NaBr/TEMPO system

Starch degradation often coincides with its chemical modification, and understanding how chemical modification influences starch degradation is vital for determining the properties of the resultant modified products. This work investigates the effect of oxidation on starch molecular degradation, examining factors such as oxidation degree, reaction kinetics, and degradation patterns during 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated starch oxidation under varying conditions, including reaction time, pH, temperature, and concentrations of NaBr, TEMPO, and NaClO. Results emphasize that extended reaction durations primarily lead to β-elimination, causing α-1,4 linkage cleavages. pH 8.5 favored non-selective oxidation, while pH 11 enhanced β-elimination, both slowing the reaction rate and severely damaging starch chains (Mw of 8.8 × 105 g/mol and 7.2 × 105 g/mol, respectively). Elevated temperature from 0 to 30 °C significantly expedited both selective and non-selective oxidation, dramatically reducing molecular mass to 8.1 × 105 g/mol. Increasing concentrations of NaBr and TEMPO boost the reaction rate with minimal impact on molecular mass. Meanwhile, increasing NaClO concentration from 0.2 to 2.2 mmol/g-starch not only affects the reaction rate but also reinforces β-elimination, enhancing molecular degradation. This study is insightful for starch modification to achieve desired oxidation levels and chain lengths by controlling reaction conditions, offering potential advancements in oxidized starch-based materials like nano micelles.

Intelligent dosing of sodium hypochlorite in municipal wastewater treatment plants: Experimental and modeling studies

Sodium hypochlorite (NaClO), a disinfectant extensively employed in municipal wastewater treatment plants (WWTPs), is frequently overdosed to ensure qualified effluent quality consistently. In light of the escalated disinfectant expenses and detrimental environmental impacts, it is critical to have a precise control model in place to enable intelligent dosing of NaClO. The lack of real-time disinfection evaluation indicators presents difficulties in precisely and swiftly regulating the dosage. Herein, the CT value (the product of residual chlorine concentration and contact time) was initially determined experimentally as a metric for assessing disinfection in municipal WWTPs. Fecal coliform (FC) concentrations become less than 1.0 × 103 MPN/L when the effluent CT value is regulated at 0.20 mg·min/L (calculated as Cl2). In addition, a model employing long short-term memory (LSTM) was developed to predict the dosage, utilizing simplified and suitable parameters such as COD, NH3-N concentration, flow rate, and historical dosage of NaClO as input factors, which demonstrated satisfactory performance (R2 = 0.948). Notably, dosage adjustments were made concurrently in response to CT value feedback. The intelligent dosing model under simultaneous feedforward and feedback control was applied at a full-scale WWTP for nearly two months, considerably reducing disinfectant consumption and meeting the discharge standard of FC.

Effect of NaClO4 Dopant on Chemical Bond and Electrochemical Characteristic of Benzoyl Kappa‐Carrageenan Gel Biopolymer Electrolyte

AbstractGel biopolymer electrolytes based on benzoyl kappa‐carrageenan (Bz‐κcar) as polymer host and sodium perchlorate (NaClO4) as dopants are successfully produced. The concentration of NaClO4 is varied from 0.5 to 3.0 wt% to investigate its effects on the chemical bonds and electrochemical characteristic of electrolytes. Characterizations are performed by Fourier‐transform infrared spectroscopy (FTIR) and electrochemical impedance analysis (EIS), linear sweep voltammetry, and transference number measurement. Significant changes in the FTIR spectra are detected, which indicate chemical interactions between Bz‐ƙcar and NaClO4. The ionic conductivity (σ) of the gel electrolytes increases with higher concentrations of NaClO4, suggesting that NaClO4 is an effective charge carrier in the system. The highest σ of the gel electrolyte attained at ambient temperature is 1.29 × 10−3 S cm−1. The temperature dependence of conductivity is Arrhenian in the studied temperature range and achieves an elevated σ of 7.90 × 10−3 S cm−1 at 373 K with small values in the activation energy (Ea) observed in all the prepared electrolytes. Electrochemical stability of 1.50 V achieves the highest conducting electrolyte by means of linear sweep voltammetry. Transference number measurement confirms that ions predominate the conduction of electrolyte with 0.85 ion transference number.

Artificial neural network modeling for the oxidation kinetics of divalent manganese ions during chlorination and the role of arsenite ions in the binary/ternary systems

This study investigated the coexistence and contamination of manganese (Mn(II)) and arsenite (As(III)) in groundwater and examined their oxidation behavior under different equilibrating parameters, including varying pH, bicarbonate (HCO3−) concentrations, and sodium hypochlorite (NaClO) oxidant concentrations. Results showed that if the molar ratio of NaClO: As(III) was >1, the oxidation of As(III) could be achieved within a minute with an extremely high oxidation rate of 99.7 %. In the binary system, the removal of As(III) prevailed over Mn(II). The As(III) oxidation efficiency increased from 59.8 ± 0.6 % to 70.8 ± 1.9 % when pH rose from 5.7 to 8.0. The oxidation reaction between As(III) and NaClO releases H+ ions, decreasing the pH from 6.77 to 6.19 and reducing the removal efficiency of Mn(II). The presence of HCO3− reduced the oxidation rate of Mn(II) from 63.2 % to 13.9 % within four hours. Instead, the final oxidation rate of Mn(II) increased from 68.1 % to 87.7 %. This increase can be attributed to HCO3− ions competing with the free Mn(II) for the adsorption sites on the sediments, inhibiting the formation of H+. Moreover, kinetic studies revealed that the oxidation reaction between Mn(II) and NaClO followed first-order kinetics based on their R2 values. The significant factors affecting the Mn(II) oxidation efficiency were the initial concentration of NaClO and pH. Applying an artificial neural network (ANN) model for data analysis proved to be an effective tool for predicting Mn(II) oxidation rates under different experimental conditions. The actual Mn(II) oxidation data and the predicted values obtained from the ANN model showed significant consistency. The training and validation data sets yielded R2 values of 0.995 and 0.992, respectively. Moreover, the ANN model highlights the importance of pH and NaClO concentrations in influencing the oxidation rate of Mn(II).

Mass transfer enhancement for simultaneous desulfurization and denitrification by a venturi reactor

Interphase mass transfer is acknowledged as the rate-limiting step of simultaneous desulfurization and denitrification by wet oxidation. For this issue, this study established a venturi reactor to facilitate interphase mass transfer between flue gas and absorbent (NaClO2 solution), and to improve the efficiency of simultaneous desulfurization and denitrification. The effects of flow rate of jet, NaClO2 concentration, initial pH of solution, SO2 and NO volume concentration on the efficiency of desulfurization and denitrification were investigated. The results showed that SO2 can be completely removed at all experimental conditions. The denitrification efficiency decreased as jet flow rate increased from 8.38 L/ min to 12.87 L/min. The denitrification efficiency and overall mass transfer coefficient increased as the NaClO2 concentration increased from 0.01 wt% to 0.025 wt%. When the pH of the absorbent decreased from 9 to 3, the denitrification efficiency was improved significantly. An increasing SO2 volume concentration promoted NO removal efficiency, while SO2 and NO competed to inhibit denitrification at NaClO2 deficiency. The denitrification efficiency firstly increased and then decreased, with an increasing NO volume concentration from 500 to 1700 ppm. This study provides an important theoretical basis for the industrial application of simultaneous desulfurization and denitrification in venturi reactors.

Flexible Supercapacitor with Wide Electrochemical Stable Window Based on Hydrogel Electrolyte.

Hydrogel electrolyte can endow supercapacitors with excellent flexibility, which has developed rapidly in recent years. However, the water-rich structures of hydrogel electrolyte are easy to freeze at subfreezing and dry at high temperatures, which will affect its energy storage characteristics. The low energy density of micro supercapacitors also hinders their development. Herein, a strategy is proposed to reduce the free water activity in the hydrogel to improve the operating voltage and the energy density of the device, which is achieved through the synergistic effect of the hydrogel skeleton, N, N'-dimethylformamide (DMF), NaClO4 and water. High concentrations of DMF and NaClO4 are introduced into sodium alginate/polyacrylamide (SA/PAAM) hydrogel through solvent exchange to obtain SA/PAAM/DMF/NaClO4 hydrogel electrolyte, which exhibited a high ionic conductivity of 82.1 mS cm-1, a high breaking strength of 563.2kPa, and a wide voltage stability window of 3.5V. The supercapacitor devices are assembled by the process of direct adhesion of the hydrogel electrolyte and laser induced graphene (LIG). The micro-supercapacitor exhibited an operating voltage of 2.0V, with a specific capacitance of 2.41 mF cm-2 and a high energy density of 1.34 µWh cm-2, and it also exhibit a high cycle stability, good flexibility, and integration performance.

Propagación in vitro de Annona deceptrix (westra) H. Rainer (Annonaceae) una especie en peligro de extinción en Ecuador

This work aims to develop a protocol for the in vitro propagation of Annona deceptrix (westra) H. Rainer. In addition, it measures survival in ex-vitro conditions. Nodal shoot segments were used as explants, disinfected with different NaClO concentrations and exposure times, and then precultured in the Murashige and Skoog (MS) basal culture medium. Woody Plant Medium (WPM) was used for the multiplication and rooting phase, with different types and concentrations of phytoregulators. In the establishment phase, the explants responded better with the 1% NaClO treatment for 15 minutes, where the highest survival percentage was observed at 72.04%. For the variable number of shoots and stem diameter, the treatment with BAP (1 mgL-1) + (GA3 0.25 gL-1) + (WPM) reached the best average with a value of 2.00 and 2.35, respectively. Mm, respectively. For root induction, the best response was obtained when 3mgL-1 IBA (T3) was added to the culture medium, reaching an average root length of 5.75 cm after 60 days of culture in the medium. The rooted Vitro plants of an approximate height of 5 cm were brought to the mesh house for their acclimatization; in this phase, the survival rate was evaluated during the first week of acclimatization, and the plant's growth fifteen days after sowing in trays containing a peat-based substrate, where T3 had an average survival of 70% and higher plant height at 60 days, indicating that this treatment promoted faster seedling development under conditions exvitro. Keywords: Annona deceptrix, propagation, in vitro rooting, ex-vitro acclimatization, growth regulators.

Optimizing the Antimicrobial Activity of Sodium Hypochlorite (NaClO) over Exposure Time for the Control of Salmonella spp. In Vitro.

Fish is a nutritionally rich product; however, it is easily contaminated by pathogenic microorganisms, such as Salmonella spp. Therefore, this study aimed to identify the best concentration of sodium hypochlorite (NaClO), exposure time, and water temperature that allow the most effective antimicrobial effect on the viable population of Salmonella spp. Thus, Salmonella Enteritidis ATCC 13076 and Salmonella Schwarzengrund were exposed to different time frames, ranging from 5 min to 38.5 min, temperatures between 5 and 38.5 °C, and NaClO concentrations ranging from 0.36 to 6.36 ppm, through a central composite rotational design experiment (CCRD). The results demonstrated that the ATCC strain exhibited a quadratic response to sodium hypochlorite when combined with exposure time, indicating that initial contact would already be sufficient for the compound's action to inhibit the growth of the mentioned bacteria. However, for S. Schwarzengrund (isolated directly from fish cultivated in aquaculture), both NaClO concentration and exposure time significantly influenced inactivation, following a linear pattern. This suggests that increasing the exposure time of NaClO could be an alternative to enhance Salmonella elimination rates in fish slaughterhouses. Thus, the analysis indicates that the Salmonella spp. strains used in in vitro experiments were sensitive to concentrations equal to or greater than the recommended ones, requiring a longer exposure time combined with the recommended NaClO concentration in the case of isolates from aquaculture.

Construction and Application of Fluorescent Probes with Imine Protective Groups for Hypochlorite Detection.

Several fluorescent probes have been designed to detect ClO- in biological systems based on the isomerization mechanism of C = N bonds. Particularly, fluorescein has emerged as an important fluorophore for detecting ClO- because of its unique properties. Previously, we introduced the fluorescein analog F-1 with an active aldehyde group. In this study, two ClO- fluorescent sensors (F-2 and F-3) with imine groups were designed and synthesized using diaminomaleonitrile and 2-hydrazylbenzothiazole as amines. The electron cloud distribution of F-2 and F-3 in ground and excited states was explored via Gaussian calculations, reasonably explaining their photophysical properties. The fluorescence detection of ClO- in solution using the two probes (F-2 and F-3) was realized based on the mechanism of imine deprotection with ClO-. NaClO concentration titration demonstrated that the colorimetric detection of ClO- with the naked eye could be achieved using both F-2 and F-3. However, after adding ClO-, the fluorescence intensity of probe F-2 increased, whereas that of probe F-3 first decreased and then increased. Probes F-2 and F-3 exhibited good selectivity, anti-interference capability, and sensitivity, with the detection limits of 169.95 and 37.30 µM, respectively. Owing to their low cell toxicity, probes F-2 and F-3 can be applied to detect ClO- in vivo. The design approach adopted in this study will further advance the future development of ClO- chemical probes through the removal of C = N bond isomerization.

Sodium hypochlorite-assisted osmotic backwashing for mitigating forward osmosis membrane fouling during pre-concentrating wastewater

Forward osmosis (FO) membrane has drawn substantial attention to pre-concentrating organic matter in wastewater for biogas production. However, membrane fouling control is an ongoing challenge for the feasibility of the FO system. Although chemical cleaning using a caustic solution (e.g., solution pH = 11) can remove organic foulants on the polyamide-based membranes, it can damage cellulose triacetate (CTA)-based FO membrane due to hydrolysis. This study assessed the efficacy of sodium hypochlorite (NaClO)-assisted osmotic backwashing to mitigate CTA-based FO membrane fouling during pre-concentrating primary wastewater effluent. The cleaning strategy employing a low concentration of NaClO achieved a higher restoration of water flux than conventional hydraulic flushing and sole osmotic backwashing. The water flux after NaClO-assisted osmotic backwashing (NaClO concentrations = 10–80 mg/L) reached 97–102%. Irreversible foulants on the membrane surface were fully removed by NaClO concentration from 20 to 80 mg/L. During four filtration cycles using a 40 mg-NaClO/L cleaning solution, the reverse salt flux increased from 4.3 to 6.3 g/m2h. This indicates that for a long-term operation, applying lower concentrations of NaClO (e.g., 20 mg/L) may be needed to avoid the changes in reverse salt flux. This study suggests that FO membranes during pre-concentrating primary wastewater effluent can be stably operated with NaClO-assisted osmotic backwashing.

Study on DeNOx of NaClO2 in simulated seawater solution enhanced by hydrodynamic cavitation

Ship exhaust causes significant air pollution, and NOx is one of the most challenging pollutants to remove. In this study, we propose a novel method for denitrification (DeNOx) using NaClO2-simulated seawater solution enhanced by hydrodynamic cavitation. We investigate the impact of initial solution pH, temperature, NaClO2 concentration, and the inlet pressure of the hydrodynamic cavitation reactor on DeNOx efficiency. The results indicate that under optimal conditions, a 100 % DeNOx efficiency can be achieved with a NaClO2 concentration of 0.1 mmol/L. Cavitation enhances mass transfer by generating microjets and increasing the gas–liquid contact area. The oxidation of NO and NO2 by hydroxyl radicals and chlorine oxygen radicals produced through cavitation could potentially enhance NOx removal efficiency. The presence of dissolved salts in simulated seawater might boost cavitation activity by reducing vapour pressure and increasing interfacial tension, leading to the more robust collapse of cavitation bubbles and thereby reinforcing cavitation effects. In addition, the multiple reactive inorganic chlorinated radicals (Cl, HClO / ClOH·-, Cl2·-) formed in simulated seawater due to the presence of Cl- might also play an essential role in DeNOx. This study demonstrated that the DeNOx by NaClO2 in simulated seawater enhanced by hydrodynamic cavitation was a promising option for NOx removal, especially for ocean-going vessels.

Effects of multi-frequency ultrasonic assisted sodium hypochlorite on the cleaning effect and quality of fresh-cut scallion stems

This study aimed to evaluate the feasibility of multi-frequency ultrasound-assisted sodium hypochlorite (NaClO) on fresh-cut scallion stem (FCS) cleaning. Ultrasonic cleaning parameters (frequency mode, frequency amplitude, and the sample to water ratios) were optimized against cleanliness and microbial biomass as evaluation indexes. Under the optimum conditions, the free chlorine residues and quality attributes of FCS were also investigated. The results showed that the cleanliness of FCS improved significantly (p < 0.05) and the total number of microorganisms, especially Escherichia coli, decreased dramatically under the optimized cleaning condition with the simultaneous ultrasound (US) at the sweep frequency (SF) combination of 20 + 28 kHz, the ultrasonic density of 60 W/L, pulse time of 10 s, which indicated that the shelf life of FCS would be extended. Compared to FCS after the 250 ppm NaClO cleaning, the retention of ascorbic acid (AA), color, and texture structure of FCS had no significant difference after ultrasound-assisted NaClO treatment. Meanwhile, the content of allicin increased by 52.5% under ultrasound-assisted cleaning. The integration of US into the cleaning process resulted in a notably reduction of 68% in NaClO concentration, as well as the weight loss and respiration rate (RR) of the scallion stems. Therefore, ultrasound-assisted NaClO cleaning was regarded as a promising and effective approach for cleaning fresh-cut vegetables.