Removal Performance Research Articles

Magnesium-modified starch cryogels for the recovery of nitrogen and phosphorus from wastewater and its potential as a fertilizer substitute: A novel nutrient recovery approach

Nitrogen (N) and phosphorus (P) are primary pollutants contributing to water quality degradation and eutrophication but are also indispensable resources for agricultural production. In this study, we synthesized porous MgO/Mg(OH)2-modified starch gels (SC-M/SC-OM) to facilitate the simultaneous removal of N and P from wastewater and address the challenges associated with separating and recycling powdered materials. By immobilizing magnesium powder within the matrix of starch gel, with the addition of 1.7 % w/w of MgO and 2.4 % w/w of Mg(OH)₂, the adsorbent can be efficiently recovered from the liquid phase, minimizing material loss. Due to their inherent pH-regulating capabilities, the modified starch gels exhibited excellent removal performance over a wide pH range. At the appropriate adsorbent dose, the maximum recovery of SC-M was 70.072 mg/g P and 25.517 mg/g N, whereas SC-OM was marginally inferior to SC-M. The pseudo-first kinetic model more accurately represented the adsorption of the two materials, showing that N and P concentrations mainly affected the adsorption efficiency, which benefits nutrient recovery at higher concentrations. Starch gels function as carriers for powdered magnesium and contribute to the synergistic removal of N and P, particularly enhancing P removal. SC-OM primarily facilitates the recovery of N and P by forming struvite. At the same time, the adsorption during the hydration process of MgO also plays a crucial role in the recovery with SC-M. Finally, the pot experiment confirmed the feasibility of using the recovered SC as a sustained release fertilizer. This study reveals the significant potential of SC-M/SC-OM for environmentally friendly nutrient removal and recovery, providing a promising approach for wastewater treatment and nutrient recycling.

Constructing ultralow-loading Cu single atoms/Fe2O3 particles on Nb2C MXenes for efficient utilization of atomic H to boost electrochemical debromination

Bromate is a commonly identified carcinogenic and genotoxic disinfection byproduct in water. Electrochemical debromination is an environmentally friendly and effective approach but it often suffers the limited reducing atomic H (H*) ability and high metal catalyst dosage. In this study, a unique composite catalyst comprised of ultra-low loading Cu single atoms (0.016 wt%) and Fe2O3 nanoparticles supported on a Nb2C MXene (denoted as Cu0.2/Fe0.1/Nb2C) was synthesized by one-step high-temperature molten salt method. The Cu0.2/Fe0.1/Nb2C significantly outperformed the Nb2C, Cu0.2/Nb2C and Fe0.1/Nb2C counterparts in the electrochemical debromination with a 94.2 % removal efficiency of bromate. It is revealed that the introducing of Cu single atoms, efficiently promotes the adsorption of H* and inhibition of competitive H2 evolution. The incorporation of Fe2O3 nanoparticles significantly increased the electronic metal-support interaction effect between the metal components and Nb2C, thereby forming a noticeable electronic cloud bridge to facilitate efficient charge transfer. Ultimately, the synergistic interplay between Cu single atoms and Fe2O3 nanoparticles plays a crucial role in achieving the remarkable removal performance of bromate. This work not only presents a significant instance of a synergistic catalyst involving metal single atoms and metal nanoparticles for effective electrochemical debromination but also advances the understanding of the electronic metal-support interaction.

Application of Immobilized Microorganism Gel Beads in Black-Odor Water with High Nitrogen and Phosphorus Removal Performance

Black-odor water, which is caused by the excessive accumulation of nitrogen and phosphorus in water, is a significant problem. Immobilized microorganisms are considered to be an effective technical solution, but there are still many key parameters to be determined, such as organic matter dissolution, insufficient stability, and insufficient phosphorus removal capacity, among other problems. In this study, the optimum raw material ratios of immobilized microorganism gel beads were determined by means of a response surface experiment. The optimal ratio of raw materials was 5% polyvinyl alcohol (PVA), 1% sodium alginate (SA), and 6% bacterial powder. In addition, the nitrogen and phosphorus removal performance of the materials was improved by loading inorganic compounds, such as 0.5 wt.% zeolite, 0.5 wt.% iron powder, and 0.2 wt.% activated carbon. Tolerance analysis determined that these gel beads could maintain a good performance in a series of harsh environments, such as during intense agitation, at high temperatures, and at low pH values, etc. The total nitrogen (TN), ammonia nitrogen (NH3-N), and phosphorus (TP) removal efficiencies were 88.9%, 90%, and 95%.

Nitrogen removal performance of bioretention cells under freeze-thaw cycles: Effects of filler structure and microbial community

Cold climates have an adverse effect on the nitrogen-removal capacity of bioretention cells, especially during freeze-thaw cycles (FTCs). To explore the effects of FTCs on the nitrogen removal performance of bioretention cells, this research compared the effects of FTCs on the pore structure and microbial community composition of the filler, and analyzed the nitrogen removal performance of the bioretention cell before (RT), during (FTC) and after (RRT) FTCs. The results demonstrated that RRT filler had a much greater number of pores with equivalent diameter <500 μm than RT filler, and that RRT had a higher pore volume and pore density than RT. Microbial community analysis revealed that the diversity and richness of the microbial community in FTC were lower than in RT, and the relative abundance of Lacunisphaera, Pseudomonas, and Dokdonella decreased significantly. There was no significant difference in microbial community richness between RRT and RT, however RRT diversity was lower. RRT has a higher relative abundance of nitrifying bacteria (Subgroup_10, Bryobacter, etc.) than RT, but a lower relative abundance of denitrifying bacteria (Pseudomonas, Dokdonella, Arenimonas, etc.). The nitrogen removal efficiency of FTC was inhibited, resulting in a decrease of 13.0 ± 4.86%, 19.7 ± 9.17%, and 26.6 ± 1.74% in the removal rates of ammonia nitrogen(NH4+-N), nitrate nitrogen(NO3−-N), and total nitrogen(TN) when compared to RT, respectively. RRT improved nitrification and increased NH4+-N removal rate by 10.3 ± 2.69% compared to RT. However, because of denitrification inhibition, the nitrogen removal performance of RRT was not able to reach RT levels, and its NO3−-N and TN removal rates decreased by 100 ± 4.70% and 58.3 ± 3.71%, respectively. This study has demonstrated that FTCs can permanently harm the bioretention cell's filler structure and microbial community, resulting in a significant decrease in the nitrogen removal performance of the bioretention cell designed according to warm climate conditions after experiencing FTCs.

Phosphorus removal in surface flow treatment wetlands for domestic wastewater treatment: Global experiences, opportunities, and challenges

Treatment Wetlands (TWs) are widely used for the treatment of domestic wastewater, with an increasing emphasis on provision of multiple co-benefits. However, concerns remain regarding achieving stringent phosphorus (P) discharge limits, system robustness and resilience, and associated guidance on system design and operation. Typically, where P removal is intended with a passive TW, surface flow (SF) systems are the chosen design type. This study analysed long-term monitoring datasets (2–30 years) from 85 full-scale SF TWs (25 m2 to 487 ha) treating domestic sewage with the influent load ranging from 2.17 to 54,779 m3/d, including secondary treatment, tertiary treatment, and combined sewer overflows treatment. The results showed median percentage removals of total P (TP) and orthophosphate (Ortho P) of 28% and 31%, respectively. Additionally, median areal mass removal rates were 5.13 and 2.87 gP/m2/yr, respectively. For tertiary SF TWs without targeted upstream P removal, 80% of the 44 systems achieved ≤3 mg/L annual average effluent total P. Tertiary SF TWs with targeted upstream P removal demonstrated high robustness, delivering stable effluent TP < 0.35 mg/L. Seasonality in removal achieved was absent from 85% of sites, with 95% of all systems demonstrating stable annual average effluent TP concentrations for up to a 30-year period. Only two out of 32 systems showed a significant increase in effluent TP concentration after the initial year and remained stable thereafter. The impact of different liner types on water infiltration, cost, and carbon footprint were analysed to quantify the impact of these commonly cited barriers to implementation of SF TW for P removal. The use of PVC enclosed between geotextile gave the lowest additional cost and carbon footprint associated with lining SF TWs. Whilst the P-k-C* model is considered the best practice for sizing SF TWs to achieve design pollutant reductions, it should be used with caution with further studies needed to more comprehensively understand the key design parameters and relationships that determine P removal performance in order to reliably predict effluent quality.

A Novel Composite Material UiO-66-Br@MBC for Mercury Removal from Flue Gas: Preparation and Mechanism.

To reduce the mercury content in flue gas from coal-fired power plants and to obtain high-performance, low-cost mercury adsorbents, a novel composite material was prepared by structural design through the in situ growth method. Functionalization treatments such as the modification of functional groups and multilayer loading of polymetallic were conducted. These materials include the MOF material UiO-66 and modified biochar doped with Fe/Ce polymetallic, both of which contain unsaturated metal centrals and oxygen-containing functional groups. On the basis of obtaining the effects of adsorption temperature and composite ratio on the Hg0 removal characteristics, coupling and synergistic mechanisms between the various types of active centers included were investigated by using a variety of characterization and analysis tools. The active adsorption sites and oxidation sites were identified during this process, and the constitutive relationship between the physicochemical properties and the performance of Hg0 removal was established. The temperature-programmed desorption technique, Grand Canonical Monte Carlo simulation, and adsorption kinetic model were employed to reveal the mechanism of Hg0 removal. The results showed that the UiO-66-Br@MBC composite adsorbent possessed an excellent Hg0 removal performance at adsorption temperatures ranging from 50 to 250 °C, and targeted construction of adsorption and oxidation sites while maintaining thermal stability. The Hg0 removal by the composites is the result of both adsorption and oxidation. The micropores and small pore mesopores in the samples provide physical adsorption sites. The modified biochar acts as a carrier to facilitate the full exposure of the central metal zirconium ions, the formation of more active sites, and the process of electron transfer. The doping modification of the Br element can enhance the overall redox ability of the sample, and the introduced Fe and Ce polymetallic ions can work in concert to promote the oxidation process of Hg0. The excellent regulation of the ratio between adsorption and oxidation sites on the surface of the composite material finally led to a significant boost in the samples' capacity to remove Hg0.

Boron-doping tunes nitrogen species to abundant edge-N and B-N matrix for efficient phosphate removal in capacitive deionization: Additional accessible sites and defective centers

The elimination of eutrophication necessitates the implement of a clean and efficient phosphate removal strategy. Capacitive deionization (CDI) is recently regarded a promising approach for removing pollutants from aqueous environment with high-efficiency, facile operation, and low-energy consumption. Development of electrode materials with good properties is crucial for CDI. In this study, novel edge-N-modified boron-doped hierarchical carbon composites (MBCNs) were prepared via a hard template strategy for phosphate electrosorption. According to the pseudo-second-order kinetic, the MBCN2 electrode exhibited a dynamic capacity of 196.02 mg PO43− g−1 in 150 min with an initial concentration of 100 mg PO43− L−1 at 1.2 V. And it also demonstrated an exceptional saturation capacity of 399.70 mg PO43− g−1 under the Langmuir model. Based on theoretical analysis and experimental results, the incorporation of boron atoms in the carbon framework indicated a dual reinforcement. This included an enhanced proportion of edge-N modifications for defective centers and sufficient high-polarity B-N matrix for additional available active sites. The joint contribution of edge-N and B-N matrix revealed favorable electrical double layer capacitance, which resulted in good phosphate removal performance. This work disclosed the synergistic impact of dual nonmetallic atom doping, providing insights into the efficient phosphate removal anode for CDI.

Comparative analysis of sulfur-driven autotrophic denitrification for pilot-scale application: Pollutant removal performance and metagenomic function

Two parallel pilot-scale reactors were operated to investigate pollutant removal performance and metabolic pathways in elemental sulfur-driven autotrophic denitrification (SDAD) process under low temperature and after addition of external electron donors. The results showed that low temperature slightly inhibited SDAD (average total nitrogen removal of ∼4.7 mg L−1) while supplement of sodium thiosulfate (stage 2) and sodium acetate (stage 3) enhanced denitrification and secretion of extracellular polymeric substances (EPS), leading to the average removal rate of 0.75 and 1.01 kg N m−3 d−1, respectively with over twice higher total EPS. Correspondingly, nitrogen and sulfur related microbial metabolisms especially nitrite reductase and nitric oxide reductase encoding were promoted by genera including Thermomonas and Thiobacillus. The variations revealed that extra sodium acetate improved denitrification and enriched more SDAD-related microorganisms compared with sodium thiosulfate, which potentially catalyzed the refinement of practical strategies for optimizing denitrification in low carbon to nitrogen ratio wastewater treatment.

TiO2-loaded phosphogypsum-modified biochar for the removal of ofloxacin and Cu2+: Performance, mechanisms, and toxicity assessment

The combined contamination of antibiotics and heavy metals usually occurs in aquaculture wastewater and has high ecological toxicity. Currently, most research only focuses on the removal of a single heavy metal or antibiotics, and there is little research on the simultaneous removal of both. Therefore, to effectively treat them, this study prepared TiO2-loaded phosphogypsum-modified biochar (TYBC450) for adsorption and photocatalytic removal of ofloxacin (OFL) and copper (Cu2+). The removal performance and mechanisms of OFL and Cu2+ were explored, and their ecological toxicity was assessed through zebrafish acute toxicity experiments. The results suggested a synergistic effect between OFL and Cu2+. The adsorption efficiencies of TYBC450 for OFL and Cu2+ were 88.16% and 90.87% (the adsorption capacities were 1.75 and 3.65 mg/g, respectively). Bridging, precipitation, and complexation effects were the main co-adsorption mechanisms. The photocatalytic efficiencies of OFL and Cu2+ were 91.23% and 72.09% (the rate constants were 0.0101 and 0.0045 min-1, respectively). OFL acted as a hole-trapping agent, while Cu2+ acted as an electron acceptor, hindering the combination of e- and h+. There were 12 intermediates in the OFL degradation process, which had lower toxicity than the mother organism. Both the cyclic regeneration and actual aquaculture wastewater application tests indicated that TYBC450 had potential application prospects.

SO2 removal performance and breakthrough prediction of activated carbon-based chemical filters for electronics cleanroom air purification

Electronic cleanrooms have strict control requirements for SO2 concentration due its significant influence on product yield, and application of chemical filters is the main measure of SO2 control. In this study, 8 activated carbon (AC)-based chemical filters were collected and tested for their SO2 purification performance and resistance. These filters had very similar initial efficiencies (all >95 %) but large differences in 20 % breakthrough adsorption capacity (49–294 g at 9 ppm and 0.35 m/s). The adsorption capacity is found to be positively correlated with pleat density, which is a main structural parameter of pleated chemical filter. Meanwhile, the filter resistance (9.3–34 Pa at 0.35 m/s) demonstrates a decreasing and then increasing trend with increasing pleat density. This indicated the existence of an optimal range of pleat numbers that can be used to achieve a balance between resistance and adsorption capacity. A comprehensive performance evaluation index (Z′-index) is proposed for assessing the integrated resistant and adsorption capacity performance of chemical filters (19–210 g/W for 8 samples). A lumped parameter model was proposed for predicting the breakthrough curves at low concentration based on the traditional semi-empirical breakthrough models. The prediction deviation of the breakthrough curve at real cleanroom scenario (2 ppb) is less than 15 %. In addition, a rapid filter life prediction method based on filter design parameters is developed from the lumped parameter model. This work helps the understanding of the impact of filter structure parameters on performance and facilitate the development of high-performance chemical filters for SO2 contaminant control in electronic cleanrooms.

Mixed superoleophilic/superoleophobic hard granular media for coalescence of oil-in-water-emulsion

To enhance the coalescence separation efficiency of oil/water emulsions, the coalescence mechanism of oil droplets between two media of opposite wettability was investigated. A coalescent-bed comprising a mix of superhydrophobic and superoleophilic quartz sand, along with superhydrophilic and underwater superoleophobic quartz sand, was constructed in a coalescer. Single-factor and response surface experiments were used to study the effects of oleophilic/oleophobic sand mixing ratio, apparent velocity, initial oil concentration, bed thickness, sand particle size on coalescence-separation performance, and to determine the optimal experimental conditions. Employing the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the agglomeration mechanism of oil droplets within the mixed particle bed was analyzed based on interfacial energy dynamics. Results indicate that the mixing ratio of the two sands significantly influences coalescence separation performance. An optimal oleophilic/oleophobic sand mixing ratio of 1:1 yielded a mass factor of 0.69 kPa−1, showcasing superior coalescence separation efficiency and an optimal balance of separation efficiency and pressure drop. Under the optimal conditions of apparent velocity of 2.7 m/h, initial oil concentration of 471.9 mg/L, bed thickness of 12.6 cm and mixed sand particle size of 0.5 mm, the oil/water separation efficiency reached 98.08 % ± 0.87 %, with effluent oil droplet size being 2.5 to 3 times larger than at the inlet. Analysis of the oil droplet coalescence mechanism revealed a synergistic effect between the two quartz sands, enhancing oil removal performance. The strong affinity of oil to the superhydrophobic and superoleophilic sand surface increases oil droplet wetting and coalescence efficiency, while the water attraction on the superhydrophilic and underwater superoleophobic sand surface forms a stable water film, improving the flux of the continuous water phase and reducing pressure drop across the bed. This study demonstrates that combining quartz sands of opposite wettability not only overcomes the limitations of single-wettability surfaces in coalescing oil removal but also achieves high efficiency and low energy consumption in oil removal.

Risk level and removal performance of antibiotic resistance genes and bacterial pathogens in static composting with different temperatures

The effect of different levels of temperature on resistance genes is not clear in mesophilic static composting (<50 °C). This study conducted livestock manure composting with different temperature gradients from 20 to 50 °C, it was found that the reduction rates of risk rank-I antibiotic resistance genes (from 3 % to 66 %), metal resistance genes (from −50 % to 76 %) and bacterial pathogens (from 72 % to 91 %) all increased significantly with increasing temperature from 20 to 50°C. The vulnerability of bacterial communities increased significantly, and the assembly process of bacterial communities changed from deterministic to stochastic with the increase of composting temperature. Higher temperature could accelerate the removal of thermolabile resistance genes hosts or pathogenic hosts carrying mobile genetic elements by directly or indirectly affecting organic acids content. Therefore, for soil safety, the temperature of the manure recycling process should be increased as much as possible.

Baffled flow constructed wetland-microbial fuel cell coupling systems for combined secondary and tertiary wastewater treatment with simultaneous bioelectricity generation

Baffled flow constructed wetland-microbial fuel cell (BFCW-MFC) coupling systems were constructed with baffles embedded in cathode chamber. The performance of BFCW-MFCs operated at different hydraulic retention times (HRTs) was evaluated. At the representative HRT of 48 h, embedding 1 or 2 baffles (i.e., BFCW-MFC1 and BFCW-MFC2) produced 32.9 % (29.5 mW/m3) and 53.2 % (34.0 mW/m3) more power density than control system (22.2 mW/m3), respectively. Comparable organics biodegradation efficiencies were observed in BFCW-MFCs at the same HRTs. BFCW-MFC1 and BFCW-MFC2 had higher ammonium and total nitrogen removal efficiency. All systems had decreased nitrogen removal performance as shortening HRT from 72 to 12 h. Multiple nitrogen removal processes were involved, including ammonium oxidation, anammox, and heterotrophic and autotrophic denitrification. The predominant bacteria on electrodes were identified for analyzing bioelectricity generation and wastewater treatment processes. Generally, simultaneous wastewater treatment and bioelectricity generation were obtained in BFCW-MFCs, and embedding 1 or 2 baffles was preferable.

Influence of Mechanical Factors on the Cutting Performance of an Ultrasonic Bone Scalpel

Abstract The ultrasonic bone scalpel is a cutting-edge surgical instrument that leverages ultrasonic mechanical effects to remove bone tissue with precision, safety, and efficacy. While the adoption of the instrument has surged, the intricate relationship between its mechanical effects and the efficiency of bone removal remains ambiguous. This study aimed to elucidate the quantitative interplay between the mechanical parameters of the instrument and its bone removal performance. To achieve this, we engineered a testing apparatus capable of consistently regulating the scalpel’s cutting force, traversal speed, and depth of cut. The bone removal proficiency of the instrument was then assessed under varying conditions: cutting forces, ultrasonic power outputs, tip traversal speeds, and bone densities. Comprehensive data analysis unveiled a distinct quantitative correlation between the aforementioned parameters and bone removal rates. Furthermore, we identified optimal parameter combinations that maximize cutting efficiency. These insights are pivotal for the design, fabrication, evaluation, and clinical application of ultrasonic bone scalpels, offering a robust reference for future advancements in the field.

The bio-cathode of microbial fuel cells systems: Performance analysis under different microbial community conditions

This study aims to investigate the conversion of different microbial community compositions in the cathode chamber in a dual-chamber bioelectrochemical system. A denitrifying bacterial community, or sludge, was enriched for denitrification by microbial consortia and subsequently acclimatized within the cathodic chamber of microbial fuel cells, either within a mixed microbial community sludge microbial fuel cell (M-MFC) or a pure culture of microorganisms in a microbial fuel cell (P-MFC). The bioelectrochemical systems were treated with different nitrate concentrations in the cathodic chamber: the MFC with low concentration nitrate (MFC1, 25 mg/L nitrate; MFC2 50 mg/L nitrate), the MFC with medium concentration nitrate(MFC3, 75 mg/L nitrate; MFC4 100 mg/L nitrate), and MFC with high concentration nitrate (MFC5, 125 mg/L nitrate; MFC6 150 mg/L nitrate; MFC7 175 mg/L nitrate), and the initial COD in the anodic chamber was based on demand(C to N ratio is 5). M-MFC exhibited better-electrogenerated capability than P-MFC. However, P-MFC exhibited better nitrogen removal performance compared to M-MFC. The best performance was attained by both types of MFCs when the nitrate content was 100 mg/L. The maximum output voltages in M-MFC4 and P-MFC4 were 449 mV and 171 mV, respectively. The average conversion rate of M-MFC4 and P-MFC4 were 2.9 mg*L−1 *h−1 and 10.5 mg*L−1 *h−1, respectively. The analysis of the microbial community of two treated MFCs in the cathode chamber in the optimal state indicated that non-electrode denitrification predominantly occurs in P-MFC. The cathode chambers were mostly populated by denitrifying microorganisms. The dominant species in M-MFC were Azonexus, Zoogloea, Ignavibacterium, and Pirellula, and the dominant species in P-MFC were Comamonas, Aeromonas, and Acidovorax. The species was assessed by qPCR analysis, and the results validated the use of a bacterial consortium for domestication as a more suitable method to improve the stability and performance of the MFCs.

Effect of carbaryl contamination on bioretention system nitrogen removal performance.

Stormwater runoff is the main source of carbaryl in natural waters; bioretention cells can effectively retain and remove carbaryl from stormwater runoff. However, the accumulation of carbaryl in the bioretention cell impacts its stormwater purification ability, especially nitrogen removal performance. To investigate the mechanisms behind the influence of carbaryl in stormwater runoff on the nitrogen removal performance of bioretention cells, the purification of carbaryl in bioretention facilities was compared under four carbaryl concentrations (0, 0.5, 1.0, and 2.0 mg/L); the effects of carbaryl input on nitrogen removal and the microbial community structure inside the filler were analyzed. After entering the bioretention cell, carbaryl was mainly adsorbed within the filler at a depth of 10-30 cm, and the desorption-adsorption process continued during subsequent rainfall. Carbaryl input negatively affected the denitrification performance of the bioretention cell. The removal rate of nitrate nitrogen (NO3--N) decreased by 61.13-100.09%, and that of total nitrogen (TN) was reduced by 24.82-38.95%. Carbaryl accumulation reduced the abundance and diversity of microorganisms in the bioretention cell. The relative abundance of some denitrifying bacteria genera (Terrimonas, Bdellovibrio, Aquabacterium, Ohtaekwangia, Sphingomonas, and SWB02) also decreased, which was the main reason for the decrease in the nitrogen removal performance.

Effect of chromophore type on efficiency of reactive dye removal using polyamidoamine dendrimer

AbstractIn this study, by selecting a sample of dyes from a wide variety of chromophores used in the production of reactive dyes (monoazo, bisazo, metal azo, phthalocyanine, anthraquinone, copper formazan and triphendioxazine), the colour removal performance of polyamidoamine (PAMAM) dendrimer in reactive dyes was statistically evaluated depending on the dye chromophore groups (and accordingly molecular weight and number of sulfo groups of the dye), dendrimer concentration and centrifugation time. When all the results were examined, it was observed that the colour removal efficiency was significantly lower in metalazo and copper formazan‐based reactive dyes, whereas colour removals ranging from 93% to 98% could be obtained in bisazo, triphendioxazine, monoazo, anthraquinone and phthalocyanine dyes. With the use of dendrimer, the best colour removal efficiencies occurred at pH 3. However, it was found that the centrifugation time of 15 min is sufficient for all dyes, and a longer centrifugation does not provide any additional benefit in terms of colour removal.

Facile preparation of oxygen vacancy-rich magnesium oxide for advanced removal of phosphate from aqueous solutions

In this study, oxygen vacancy-rich magnesium oxides (SH-MgO and SC-MgO) were successfully prepared by the combination of chemical precipitation with high-temperature calcination. Effects of alkaline reagents (NaOH and Na2CO3) on surface morphology, pore structure and particle size distribution of SH-MgO and SC-MgO were analyzed. Besides, the phosphate removal performance and mechanisms were also investigated. The specific surface area of SH-MgO and SC-MgO was 98.03 and 62.35 m2 g−1, respectively. The corresponding average particle sizes were 211.98 and 19.56 μm. The phosphate adsorption followed the Vermeulen model and thus the rate of adsorption was limited by the intraparticle diffusion. The high affinity and selectivity of SH-MgO and SC-MgO for phosphate implied their great potentials in practical application. The EPR results demonstrated the presence of large numbers of oxygen vacancies in SH-MgO and SC-MgO. The phosphate removal mechanisms mainly included oxygen vacancy capture, electrostatic attraction, surface precipitation and inner-sphere complexation. This study provided a new strategy for facile preparation of oxygen vacancy-rich magnesium oxide, which was extremely significant for advanced removal of phosphate to reduce eutrophication.

Singlet oxygen dominant-activation by hollow structural cobalt-based MOF/peroxymonosulfate system for micropollutant removal

Despite the keen interest in potentially using the metal-organic framework (MOF) in advanced oxidation processes (AOPs), their application for environmental abatement and the corresponding degradation mechanisms have remained largely elusive. This study explores the use of cobalt-based MOF (CoMOF) for peroxymonosulfate (PMS) activation to remove tetracycline (TC) from water resources. Under optimal conditions, the given catalytic system could achieve a TC removal of 83.3%. Radical quenching tests and EPR analysis revealed that SO4•–, HO•, •O2−, and 1O2 could participate in the catalytic degradation, but the discernible removal mechanism was mainly ascribed to the nonradical pathway induced by 1O2. At only 5 mg/L of CoMOF, the performance of the catalytic system was superior to that of PMS alone for different types of micropollutants. The CoMOF/PMS system could also reliably deal with typical anions in water, such as Cl−, SO42−, HCO3−, and PO43−. The MOF catalyst could last for four cycles with a minor decrease in reactivity of ∼30%. However, the removal performance decreased markedly when aromatic natural organic matter (NOM) were present in the water bodies, and the effectiveness was lower in alkaline or acidic environments. Our work offers insights into the catalytic degradation of CoMOF/PMS applied in contaminated water remediation and serves as a baseline for fabricating an efficient MOF with enhanced catalytic performance and stability.

Investigation of the Deionization Rate of Asymmetric Capacitive Deionization Technology for the Treatment of Short-Chain Perfluoroalkyl Substances (PFAS)

Objectives : This study aims to introduce and evaluate the effectiveness of asymmetric membrane capacitive deionization (ACDI) in removing short-chain perfluoroalkyl substances (PFAS), specifically perfluorobutane sulfonic acid (PFBS), from aqueous solutions. This study offers important insights for the advancement of CDI technology in the sustainable treatment of industrial wastewater containing PFAS.Methods : ACDI was employed by removing the anion exchange membrane from conventional membrane capacitive deionization system. The effect of key operational parameters such as voltage (0.5~1.2 V), initial concentration (50~500 mg/L), and flow rate (1~5 ml/min) on PFBS removal efficiency was systematically investigated. Additionally, PFBS removal performance in the presence of chloride ions was also investigated to determine competing ion effects.Results and Discussion : The ACDI system significantly outperformed both CDI and MCDI, achieving a maximum deionization rate of 0.032 mg/g/s, compared to 0.012 mg/g/s for CDI and 0.01 mg/g/s for MCDI. Increasing the applied voltage from 0.5 V to 1.2 V enhanced the deionization rate, with the highest rate observed at 1.2 V. Higher initial PFBS concentrations also improved the deionization rate, increasing from 0.0009 mg/g/s at 50 mg/L to 0.032 mg/g/s at 500 mg/L. The optimal flow rate was found to be 2 ml/min, balancing ion contact time and throughput, resulting in the highest deionization rate. The presence of competing ions, such as chloride, reduced PFBS removal efficiency, as shown by the decrease in deionization rate when NaCl was added to the feed solution.Conclusion : Overall, the ACDI system demonstrated superior deionization capacity and energy efficiency for PFBS removal, highlighting its potential as a sustainable and efficient technology for treating water contaminated with short-chain PFAS. Future research should address the challenges posed by competing ions in real-world wastewater to further optimize the ACDI system’s performance.