Magnetic field-assisted adsorption of phosphate on biochar loading amorphous Zr-Ce (carbonate) oxide composite

For metal-based phosphate adsorbents, the dispersity and utilization of surface metal active sites are crucial factors in their adsorption performance and synthesis cost. In this study, a biochar material modified with amorphous Zr-Ce (carbonate) oxides (BZCCO-13) was synthesized for the phosphate uptake, and the adsorption process was enhanced by magnetic field. The beside-magnetic field was shown to have a better influence than under-magnetic field on adsorption, with maximum adsorption capacities (123.67 mg P/g) 1.14-fold greater than that without magnetic field. The beside-magnetic field could also accelerate the adsorption rate, and the time to reach 90% maximum adsorption capacity decreased by 83%. BZCCO-13 has a wide range of application pHs from 5.0 to 10.0, with great selectivity and reusability. The results of XPS and ELNES showed that the "magnetophoresis" of Ce3+ under the magnetic field was the main reason for the enhanced adsorption performance. In addition, increased surface roughness, pore size and oxygen vacancies, enhanced mass transfer by Lorentz force under a magnetic field, all beneficially influenced the adsorption process. The mechanism of phosphate adsorption by BZCCO-13 could be attributed to electrostatic attraction and CO32-dominated ligand exchange. This study not only provided an effective strategy for designing highly effective phosphate adsorbents, but also provides a new light on the application of rare earth metal-based adsorbent in magnetic field.

Magnetic nanoparticle loading and application of weak magnetic field to reconstruct the cake layer of coagulation-ultrafiltration process to achieve efficient antifouling: Performance and mechanism analysis

Abandoning the costly development of new membrane materials and instead directly remodeling the naturally occurring cake layer constitutes a dynamic, low-cost, long-lasting, and proactive strategy to "fight fouling with fouling". Several optimization strategies, including coagulation/modified magnetic seed loading and applying a weak magnetic force (0.01T) at the ultrafiltration end, improved the anti-fouling, retention, and sieving performances of conventional ultrafiltration process during the treatment of source water having complex natural organic matter (NOMs) and small molecule micropollutants. Two modified magnetic seeds we prepared were composite nano-seed particles (Fe3O4@SiO2-NH2 (FS) and Fe3O4@SiO2@PAMAM-NH2 (FSP)). Aim of the study was to regulate the formation of cake layer via comprehensive testing of the antifouling properties of optimized processes and related mechanistic studies. It was found to be essential to enhance the interception of xanthate and tryptophan proteins in the cake layer for improving the anti-fouling performance based on the correlation and redundancy analyses, while the use of modified magnetic seeds and magnetic field showed a significant positive impact on water production. Blockage modeling demonstrated the ability to form a mature cake layer during the initial filtration stage swiftly. This mitigated the risk of irreversible fouling caused by pore blockage during the early stage of coagulation-ultrafiltration. Morphologically, the reconstructed cake layer exhibited elevated surface porosity, an internal cavity channel structure, and enhanced roughness that can promote increased water flux and retention of water impurities. These optimized the maturity of the cake layer in both time and space. Density Functional Theory (DFT), Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, and Modified Extended Derjaguin-Landau-Verwey-Overbeek (MDLVO) calculations indicated aggregation behavior of matter on the cake layer to be enhanced effectively due to magnetic seed loading. This is mainly due to the strengthening of polar interactions, including hydrogen bonding, π-π* conjugation, etc., which can happen between the cake layer loaded with FSP and the organic matter. Under the influence of a magnetic field, magnetic force energy (VMF) significantly impacts the system by eliminating energy barriers. This research will provide innovative strategies for effectively purifying intricate source water through ultrafiltration while controlling membrane fouling.

Aerobic granulation and microbial community succession in sequencing batch reactors treating the low strength wastewater: The dual effects of weak magnetic field and exogenous signal molecule

The application of magneto-biological effects in wastewater treatment has been brought under the spotlight recently. This work explored the dual effects of magnetic field (MF) and exogenous N-hexanoyl-l-homoserine lactone (C₆-HSL) on activated sludge granulation. Results showed that exposure to MF and C₆-HSL obviously accelerated the aerobic granulation process and promoted the secretion of extracellular polymeric substances, especially polysaccharides, humic acid-like substances, aromatic proteins, and tryptophan-like substrates. Illumina MiSeq sequencing results indicated that the introduction of MF and C₆-HSL can increase the diversity and richness of microbial community without antagonism, and the biological basis for rapid granulation process in this study was the enrichment of slow-growing bacteria Candidatus_Competibacter. Besides, the overgrowth of filamentous bacteria Thiothrix could be suppressed due to the presence of MF, improving the stabilities of aerobic granular sludge. This study provides a new understanding of the MF and C₆-HSL effects on rapid aerobic granulation when treating the low-strength wastewater.

Mechanistic insight of weak magnetic field trigger transformation of amorphous Fe(III)-(oxy)hydroxide for enhanced ferrate (VI) towards selective removal of natural organic matter

It was important to regulate the formation of Fe-hydroxyl during ferrate (Fe(VI)) oxidation and hydrolysis which was beneficial for interfacial adsorption of natural organic matter (NOM). Based on the influence of weak magnetic field (WMF) on the physical and chemical characteristics of particles in chemistry. This study investigated the effect of WMF on Fe(VI) oxidation and Fe(III) flocculation performance by regulating iron species during hydrolysis, for NOM removal. Results indicated WMF efficiently accelerate the removal of NOM that the reactions rate constants in magnetization system was twice as much as the control group. With the structure and electrochemical analysis, WMF enhanced Hydrogen-bond and caused much polar hydroxyl groups combined with iron ions, further triggered Fe(III) transformed to amorphous Fe-hydroxide and ferrihydrite with large specific surface area and high surface activity which removed the pollutants by adsorption and co-precipitation, instead of crystalloid Fe₂O₃ and Fe₃O₄. In addition, the nucleation aggregation behavior and interaction energy of Fe-(oxy)hydroxide revealed that the lower free energy obtained in magnetization system, could lead to higher nucleation rate, and promoted the aggregation. WMF increased hydrophobicity of Fe-(oxy)hydroxides, further more easily adsorbed with humic acid (HA) and bovine serum albumin (BSA) with lower interaction energies than in control group. The selective removal mechanism of Fe-(oxy)hydroxide hardly to aggregate with pollutants which caused by the difference of electrostatic interaction, was illustrated that electronegativity HA and SA were liable to electrostatically attract with Fe-(oxy)hydroxide and removed while the low electronegativity BSA was difficult to remove which its attraction was weakened.

Role of weak magnetic field for enhanced oxidation of orange G by magnetic Fenton

The role of weak magnetic field (WMF) on the degradation of a common textile azo-dye, orange G (OG), by magnetic Fenton system was investigated in detail. The results showed that the presence of WMF can provide better performance of the Fe₃O₄/H₂O₂ system for OG degradation. The optimized reaction conditions were contained at 1 mM Fe₃O₄ as Fe, 20 mT of magnetic field intensity, 20 mM H₂O₂, and initial pH of 3.0. The removal efficiency of OG by Fe₃O₄/H₂O₂ coupling with WMF increased largely from 56.3 to 82.3% compared with Fe₃O₄/H₂O₂ process. Both the electron paramagnetic resonance (EPR) analysis and the quenching effect of tert-butyl alcohol (TBA) confirmed that hydroxyl radical (•OH) was the primary reactive oxygen species in WMF-Fe₃O₄/H₂O₂ system. The improving effect of WMF was explained by the magnetoconvection theory. The presence of WMF could accelerate the corrosion rate of Fe₃O₄ and thus promoted the release of Fe(II), which led to the increased production of •OH and enhanced the degradation of OG. Moreover, it was surprising to observe that the WMF induced improvement in OG degradation by heterogeneous Fenton involving the iron sludge, namely FeOOH and Fe₂O₃, as catalysts. These results indicated that WMF could be utilized as an efficient and cost-effective strategy to improve the removal of organic pollutants by iron oxide-based Fenton process.

Role of weak magnetic strength in the operation of aerobic granular reactor for wastewater treatment containing ammonia nitrogen concentration gradient

Weak magnetic field (WMF) and aerobic granular sludge (AGS) technology were both robust technologies in wastewater treatments. In this study, the AGS characteristics and nutrient removal performances were all estimated at the load of 20 to 40 mg/L ammonia nitrogen (NH₄⁺-N) and 0 to 40mT magnetic field. Results showed that 10mT was beneficial for keeping stable structure of granules when increasing NH₄⁺-N load, accompanied with increasing protein (PN) secretion in EPS. Besides, all the total nitrogen (TN) removal rate under 10mT reached above 90%, while they were all less than 80% under other WMF strength when loading with 40 mg/L NH₄⁺-N. Moreover, the simultaneous nitrification and denitrification (SND) efficiency could be enhanced by WMF of 10mT. Illumina MiSeq sequencing showed that NH₄⁺-N load changed the bacterial richness and diversity when the magnetic strength was 10mT. And Candidatus_Competibacter was identified as the main functional genes for effective operation in this system.

Weak magnetic field enables high selectivity of zerovalent iron toward metalloid oxyanions under aerobic conditions

For water treatment/remediation by zerovalent iron (ZVI), of particular concern is its selectivity toward contaminants over natural non-targets (e.g., O₂ and H₂O/H⁺). Hence, the effects of weak magnetic field (WMF) on the selectivity of ZVI toward metalloid oxyanions (i.e., As(III), As(V), Sb(III), Sb(V), Se(IV) and Se(VI)) were in-depth investigated under aerobic conditions. This study unraveled that, despite the electron utilization (EU) of ZVI with and without WMF were almost identical at reaction equilibrium, the application of a WMF could enhance the specific removal capacity (SRC) of ZVI toward metalloid oxyanions from 1.8-19.0 mg/g Fe to 12.6-85.3 mg/g Fe. Particularly, the electron efficiency (EE) of ZVI with WMF for reduction of Se(IV)/Se(VI) were 3.7- to 14.1-fold greater than that without WMF. Since the WMF-induced magnetic gradient force (F_ΔB) can derive the movement of both Fe²⁺ and metalloid oxyanions, the subsequent incorporation of metalloid oxyanions with in-situ generated iron oxides can also been mediated synchronously and thus leading to an enhanced SRC of ZVI (also EE for Se(IV) and Se(VI) reduction by ZVI). In general, our findings prove that WMF should be a promising method to promote the selectivity of ZVI for water decontamination under aerobic conditions.

Simultaneously implement of both weak magnetic field and aeration for ciprofloxacin removal by Fenton-like reaction

This study evaluates the ability of heterogeneous Fenton-like reaction (nano zero-valent iron (NZVI)/H₂O₂) in combination with weak magnetic field (WMF) under continuous oxygen supply by air bubbling for pollutant abatement (using ciprofloxacin as a model pollutant). The considered operating variables were initial pH, catalyst dosage, reaction time and different intensities of magnetic field. Results indicated that NZVI/H₂O₂/aeration/weak magnetic field could effectively decompose ciprofloxacin at neutral condition and higher removal rates are observed at higher pH and NZVI concentrations. Superimposing a weak magnetic field leads to 20% enhancement in ciprofloxacin removal by catalytic Fenton under aeration condition. Employing simultaneously magnetic field induction and aeration exhibit excellent capability to the NZVI oxidation and significantly increased the dissolution rate of iron. Based on Fourier transform infrared spectroscopy, transformation products of NZVI are Fe₃O₄ and FeO(OH). The faster mass transport due to Lorentz and field gradient force, more oxygen diffusion to the iron surface and promoted electrochemical reactions results in more OH° production. Generation of weak magnetic field by permanent magnets and using aeration for both mixing and in situ oxygen supply significantly enhanced the Fenton reaction performance. This combination technology doesn't need any energy input and costly chemicals hence can be used easily for wastewater treatment applications.

Effects of oxygen and weak magnetic field on Fe(0)/bisulfite system: performance and mechanisms

The performance and mechanisms of 4-nitrophenol (4-NP) degradation by the Fe(0)/bisulfite system were systematically investigated for the first time. The evidences presented in this study verified that O2 was a crucial factor that affected the mechanism of Fe(0)/bisulfite-driven 4-NP degradation. In the Fe(0)/bisulfite/O2 system, Fe(0) acted as a supplier of Fe(2+) to catalyze bisulfite oxidation that induced a chain reaction to produce reactive radicals for 4-NP degradation. While under N2 purging condition, bisulfite worked as a specified reductant that facilitated the transformation of Fe(3+) to nascent Fe(2+) ions, which principally accounted for the reductive removal of 4-NP. The application of a weak magnetic field (WMF) efficiently improved the removal rate of 4-NP and did not alter the mechanisms in both Fe(0)/bisulfite/O2 and Fe(0)/bisulfite/N2 processes. The secondary radicals, HO(·), SO4 (·-), and SO5 (·-), were considered as the most possible active oxidants contributing to the oxidative removal of 4-NP and even partial mineralization under an oxic condition. Compared with anoxic conditions, the performance removal of 4-NP by the WMF-Fe(0)/bisulfite/O2 system showed less pHini dependence. To facilitate the application of WMF-Fe(0)/bisulfite/O2 technology in real practice, premagnetization of Fe(0) was employed to combine with bisulfite/O2 and proved to be an effective and applicable method for 4-NP removal.

Activating persulfate by Fe⁰ coupling with weak magnetic field: performance and mechanism

Weak magnetic field (WMF) and Fe(0) were proposed to activate PS synergistically (WMF-Fe(0)/PS) to degrade dyes and aromatic contaminants. The removal rates of orange G (OG) by WMF-Fe(0)/PS generally decreased with increasing initial pH (3.0-10.0) and increased with increasing Fe(0) (0.5-3.0 mM) or PS dosages (0.5-3.0 mM). Compared to its counterpart without WMF, the WMF-Fe(0)/PS process could induce a 5.4-28.2 fold enhancement in the removal rate of OG under different conditions. Moreover, the application of WMF significantly enhanced the decolorization rate and the mineralization of OG. The degradation rates of caffeine, 4-nitrophenol, benzotriazole and diuron by Fe(0)/PS were improved by 2.1-11.1 fold due to the superimposed WMF. Compared to many other sulfate radical-based advanced oxidation technologies under similar reaction conditions, WMF-Fe(0)/PS technology could degrade selected organic contaminants with much greater rates. Sulfate radical was identified to be the primary radical species responsible for the OG degradation at pH 7.0 in WMF-Fe(0)/PS process. This study unraveled that the presence of WMF accelerated the corrosion rate of Fe(0) and thus promoted the release of Fe(2+), which induced the increased production of sulfate radicals from PS and promoted the degradation of organic contaminants. Employing WMF to enhance oxidation capacity of Fe(0)/PS is a novel, efficient, promising and environmental-friendly method since it does not need extra energy and costly reagents.