Simultaneous ammonium and phosphate removal with Mg-loaded chitosan carbonized microsphere: Influencing factors and removal mechanism

A sustainable approach for efficient ammonium recovery, and simultaneous TOC removal from aqueous solutions by vesicle-like iron phosphate-based carbon nanomaterials

NH4+ is an ion with versatile potential; however, the release of wastewater containing this component, regardless of its high or low concentration, causes severe eutrophication in aquatic systems and contaminates numerous manufacturing processes. Thus, this study developed a sustainable method that can simultaneously remove, recover NH4+, polish water, oxidize organic matter, and yet release a material that can still be used as fertilizer. Regarding NH4+ removal, FeP400 rapidly exhibited an exceptional NH4+ uptake capacity (343.5 mg g-1) within 8 min, even in dairy processing wastewater with high NH4+ concentrations and diverse co-existing components. FeP400 could oxidize organic compounds spontaneously to remove TOC, indirectly enhancing its NH4+ uptake up to 33.5 % through charge balance mechanisms. The adsorption process involved both chemical (i.e., double-salt precipitation) and physical mechanisms (i.e., H-bonding and electrostatic interaction), as confirmed by thermodynamics, FT-IR, and XPS analyses. Regarding recovery, FeP400 can be reused for over 10 cycles with high removal (81 %) and NH4+ recovery (88 %), a significant improvement over conventional options. FeP400 also performed efficiently under flowing conditions using low-range NH4+ and TOC samples over 10 cycles, polishing not only 34.1 L of water with undetected NH4+, neutral pH, and extremely low TOC but also effectively recovering the NH4+ uptake at an economical cost. Lastly, its environmentally friendly nature, which contains essential nutrients for plant growth, further enhances its recyclability after release. Thus, FeP400 is believed to offer a transformative, sustainable, and highly efficacious solution to the NH4+contamination and critical ultrapure water issues that industries urgently address.

Directional Freeze-Drying-Mediated Chitosan Aerogel with Ordered Structure Allowing High-Efficient Removal of Se(IV) from Wastewater

The progress of industrialization has led to a notable elevation in selenium (Se) levels within aquatic environments, surpassing established thresholds and posing significant risks to both human health and ecological equilibrium. Chitosan (CS) exhibits considerable potential in mitigating waterborne pollutants owing to its nontoxic nature, cost-effectiveness, and the presence of abundant hydroxyl and amino functional groups along its backbone. However, its subpar mechanical and thermal stability, susceptibility to acidic dissolution, and challenges in recycling impede its widespread use in water pollution mitigation. To address the aforementioned issues, this study employs a liquid nitrogen-directed freezing process to synthesize chitosan aerogel, aiming to enhance the adsorption efficiency of Se(IV). Morphological and adsorption tests demonstrate that the compact and closely interconnected porous structure facilitates diffusion of Se(IV) into the aerogel, thereby enhancing its adsorption efficiency. The theoretical adsorption capacity of the CS aerogel for Se(IV) is 56.45 mg/g, surpassing that of numerous natural and composite adsorbents, with adsorption equilibrium achieved within 2.5 h. Moreover, the CS aerogel demonstrates substantial potential in remediating Se(IV)-contaminated wastewater and improving circulation stability. A series of characterization results demonstrate that the primary adsorption mechanism of the CS aerogel onto Se(IV) involves electrostatic interactions, complemented by hydrogen bonding between the amino and hydroxyl groups of the CS aerogel and Se(IV), thereby augmenting the adsorption efficacy. This study introduces innovative avenues for tailoring the functionality of 3D macroscopic materials to address the remediation of heavy metals in aquatic environments.

Metal-doped biochar for selective recovery and reuse of phosphate from water: Modification design, removal mechanism, and reutilization strategy

Phosphorus (P) plays a crucial role in plant growth, which can provide nutrients for plants. Nonetheless, excessive phosphate can cause eutrophication of water, deterioration of aquatic environment, and even harm for human health. Therefore, adopting feasible adsorption technology to remove phosphate from water is necessary. Biochar (BC) has received wide attention for its low cost and environment-friendly properties. However, undeveloped pore structure and limited surface groups of primary BC result in poor uptake performance. Consequently, this work introduced the synthesis of pristine BC, parameters influencing phosphate removal, and corresponding mechanisms. Moreover, multifarious metal-doped BCs were summarized with related design principles. Meanwhile, mechanisms of selective phosphate adsorption by metal-doped BC were investigated deeply, and the recovery of phosphate from water, and the utilization of phosphate-loaded adsorbents in soil were critically presented. Finally, challenges and prospects for widespread applications of selective phosphate adsorption were proposed in the future.

Selective removal of thallium from water by MnO2-doped magnetic beads: Performance and mechanism study

Aqueous thallium has posed an increasing threat to environment as human's intensified activities in mining, refining, process and discharge. Remediation on thallium pollution has been of up-most importance to water treatment. In present work, MnO2 and magnetic Fe3O4 have been implanted to sodium alginate (SA) in presence of carboxyl methyl cellulose (CMC), and the resultant beads consisted of SA/CMC/MnO2/Fe3O4 were characterized. The materials were applied to treatment of Tl-contaminated water as adsorbent in lab. The removal results revealed that the adsorption capacity reached 38.8 mg (Tl)·g (beads)-1 and almost 100 % removal efficiency was achieved. The residual Tl was below 0.1 μg·L-1, meeting the discharge standard regulated in China. The kinetic adsorption was better described as a pseudo-second-order and three-step intra-particle diffusion model. Freundlich isotherm was well fitted the experimental data. The absorbent shown an excellent competitive specificity (KTl/M: ∼104!) over common hazardous ions Cu2+, Cd2+, Co2+, Pb2+ and Cr3+, as well as naturally abundant K+ and Na+ (KTl/M: 10-102) in mimic environmental conditions. Regeneration and reusability of the absorbent was also verified by five absorption-desorpotion cycles. XPS results revealed that a redox reaction between Mn4+ with Tl+, and an ion exchange of H+ (-O-Fe) and Tl+ were assumed to be main process for the specific capturing. This study provided an efficient SA/CMC/MnO2/Fe3O4 composite beads that could be a promising adsorbent for Tl-polluted water treatment.

Enhanced simultaneous removal of phosphate and ammonium from swine wastewater using magnetic magnesium-loaded Chinese herbal medicine residues: Performance, mechanism, and resource utilization

Magnetic magnesium (Mg)-loaded Chinese herbal medicine residues (MM-TCMRs) were fabricated to simultaneously remove and recover phosphate and ammonium from wastewater. The MM-TCMRs exhibited larger specific surfaces and rougher structures with massive spherical particles than those of original residues. They could be separated by adjusting the magnetic field. The phosphate and ammonium adsorption by MM-TCMRs were matched with the pseudo-second-order model, while the Langmuir model yielded the maximum adsorption capacities of 635.35 and 615.57 mg g-1, respectively. Struvite precipitation on the MM-TCMRs surface was the primary removal mechanism with electrostatic attraction, ligand exchange, intra-particle diffusion, and ion exchange also involved. The recyclability of MM-TCMRs confirmed their good structural stability. More importantly, the nutrient-loaded MM-TCMRs enhanced alfalfa growth and improved soil fertility in planting experiments. Collectively, the MM-TCMRs are promising candidates for nutrient removal and recovery from wastewater.

Sustainable phosphorus adsorption and recovery from aqueous solution by a novel recyclable Ca-PAC-CTS

Phosphorus removal has been explored for a long time, however sustainable phosphorus adsorption and recovery with adsorbents recycling is rarely reported. This work proposes a sustainable phosphorus recycling route with calcium-modified powdered activated carbon with chitosan (Ca-PAC-CTS). The morphology, functional groups and crystal structure of Ca-PAC-CTS were characterized. The maximum phosphorus adsorption capacity was 16.73 mg/g Ca-PAC-CTS with Langmuir model at 298 K. Stable phosphorus sorption on Ca-PAC-CTS could be observed at the large range of pH (4- 10) when coexisting with NO3-, SO42-, Cl- and F-, except HCO3-. 98.95 % The recovery of adsorbed phosphorus could get to 98.95 % using 0.05 M sulfuric acid solution, and the phosphate adsorption efficiency through Ca-PAC-CTS remained to be more than 80 % after five adsorption-desorption cycles, suggesting that Ca-PAC-CTS was one of the promising adsorbents for sustainable removal and recovery of phosphorus in aqueous solution.