Scaled-up development of magnetically recyclable Fe3O4/La(OH)3 composite for river water phosphate removal: From bench-scale to pilot-scale study

Comparative assessment of formation pathways and adsorption behavior reveals the role of NaOH of MgO-modified diatomite on phosphate recovery

The phosphate adsorption behavior on MgO-modified diatomite has been routinely investigated. Batch experiments tend to show that the addition of NaOH during preparation largely promoted adsorption performance, but comparative studies of MgO-modified diatomite with and without NaOH (MODH and MOD) based on morphology, composition, functional groups, isoelectric points and adsorption behavior have not been reported. We demonstrated that NaOH can etch the structure of MODH and promote the migration of phosphate to active sites, which allowed MODH to have a faster adsorption rate, superior environmental adaptability, adsorption selectivity and regeneration performance. The phosphate adsorption ability was enhanced from 96.73 (MOD) to 197.4 mg P/g (MODH) under optimum conditions. Furthermore, the partially hydrolyzed Si-OH group reacted with Mg-OH via a hydrolytic condensation reaction to form a new Si-O-Mg bond. Intraparticle diffusion, electrostatic attraction and surface complexation may be the main modes of phosphate adsorption by MOD, while the MODH surface mainly relied on the synergy of chemical precipitation and electrostatic attraction due to the abundant MgO adsorptive sites. Indeed, the present study provides a new understanding of the microscopic analysis of sample differences.

In-situ modified biosynthetic crystals with lanthanum for fluoride removal based on microbially induced calcium precipitation: Characterization, kinetics, and mechanism

In this research, in-situ modified biosynthetic crystals with lanthanum (BC-La) were synthesized based on anaerobic microbially induced calcium precipitation (MICP) and investigated its capacity for groundwater defluoridation under various operational conditions. The kinetic and thermodynamic models were simulated to explore the effect of the material on the removal of fluoride ion (F^-) under various parameters (pH, initial concentration of F^-, and temperature). BC-La had the maximum F^- adsorption capacity of 10.92 mg g^-1 and 96.66% removal efficiency. The pseudo-second-order kinetic model and Langmuir isotherm model were the best kinetic and isotherm models for F^- removal from BC-La, which indicated that F^- were mainly spontaneously removed through chemisorption and adsorption processes. The specific surface area was 54.26 m² g^-1 and the average pore size was 9.0670 nm. BC-La mainly contained LaCO₃OH, LaPO₄, CaCO₃, Ca₅ (PO₄)₃OH, and F^- was mainly removed through ion exchange with the material surface. Moreover, OH^-, PO₄^3-, and CO₃^2- significantly influenced the F^- removal. This work suggested a novel method for in-situ modification of anaerobic biosynthetic crystals, which improved the defluoridation effect of traditional biosynthetic crystals, increased the stability of the BC-La and allowed to remove F^- from groundwater consistently.

Pilot-scale phosphate recovery from wastewater to create a fertiliser product: An integrated assessment of adsorbent performance and quality

Eutrophication and the predicted limited future availability of rock phosphate has triggered the increased development of phosphorus (P) recovery technologies, however, for remote regions, recovery solutions are still limited. Here, we report on a novel pilot-scale technology (FILTRAFLO^TM-P reactor) to recover phosphate (PO₄^3-) from wastewater effluent through a filtration/adsorption process in a rural setting. This unit employs enhanced gravitational filtration through adsorption media (here, a novel KOH deacetylated crab carapace based chitosan-calcite material (CCM)) with continuous self-backwashing. Trials were designed to assess how the FILTRAFLO^TM-P unit would operate under 'real' conditions (both at low and high PO₄^3- levels), and to ascertain the effectiveness of the adsorbent to recover phosphate from final effluent. High removal was achieved at low phosphate concentrations, bringing the residual effluent PO₄^3- level below 1 mg/L (EU limit for sensitive water bodies), while phosphate was efficiently harvested (at more than 50%) at higher PO₄^3- levels. Surface microprecipitation and inner-sphere complexation were postulated as the main PO₄^3- adsorption mechanisms through XRD, XPS and EDX elemental mapping. Further, a quality assessment of the P-enriched CCM (which could be used as a potential soil amendment) was undertaken to consider elemental composition, microbiological assessment and quantification of organic micropollutants. Quality analysis indicated ∼2.5% P₂O₅ present, trace levels (well below legislative limits) of heavy metals and extremely low levels of organic pollutants (e.g., PCBs, pharmaceuticals). No detectable levels of target bacterial pathogens were observed. Pot trials showed that ryegrass cultivated with the addition of the CCM adsorbent achieved higher plant dry matter and P concentration when compared to unfertilised controls, with a slow-release kinetic pattern. This study showed that CCM used with the FILTRAFLO^TM-P pilot reactor has high potential to recover phosphate from effluents and encourage resource recovery via bio-based management of waste.

Dual-function hydrogel composite for post-electroplating cationic and anionic metal removal: A practicality study

Metals produced as by-products of the electroplating process pose threats to both human and environmental health, so it is important that they are removed from electroplating effluents. In this study, a dual-function hydrogel composite, prepared from a pair of cationic and anionic hydrogel composites via a facile method, was tested in batch and in a fluidized-bed column to treat a simulated electroplating effluent. For the batch treatment, both adsorption and desorption reached equilibrium within 30 min, showing the dual-function composite's fast adsorption capacity. Additionally, the removal efficiency was found to be pH-independent, and insignificant effect was found in the co-presence of monovalent ions (up to 10 meq L^-1). Reusability of the dual-function composite was tested for six cycles, where the treated effluent consistently met discharge standards, and the reused adsorbent was confirmed by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy to be highly stable. The fast settling by gravity of the dual-function composite in batch motivated further studies of the material in a fluidized-bed column. Process variables such as feed flow, airflow, and adsorbent's bed depth were optimized using response surface methodology (RSM). Using an optimal solution, the model predicted a treatable cationic volume of 1045 mL and an anionic volume of 1695 mL; their corresponding experimental values were 1028 and 1680 mL. Therefore, in terms of practicality (fast removal, pH-independence, high stability, and gravity-driven settling), the application of the dual-function composite in a fluidized-bed reactor has shown much promise for the simultaneous removal of post-electroplating cationic and anionic metals.

Magnetic Adsorbents for Wastewater Treatment: Advancements in Their Synthesis Methods

The remediation of water streams, polluted by various substances, is important for realizing a sustainable future. Magnetic adsorbents are promising materials for wastewater treatment. Although numerous techniques have been developed for the preparation of magnetic adsorbents, with effective adsorption performance, reviews that focus on the synthesis methods of magnetic adsorbents for wastewater treatment and their material structures have not been reported. In this review, advancements in the synthesis methods of magnetic adsorbents for the removal of substances from water streams has been comprehensively summarized and discussed. Generally, the synthesis methods are categorized into five groups, as follows: direct use of magnetic particles as adsorbents, attachment of pre-prepared adsorbents and pre-prepared magnetic particles, synthesis of magnetic particles on pre-prepared adsorbents, synthesis of adsorbents on preprepared magnetic particles, and co-synthesis of adsorbents and magnetic particles. The main improvements in the advanced methods involved making the conventional synthesis a less energy intensive, more efficient, and simpler process, while maintaining or increasing the adsorption performance. The key challenges, such as the enhancement of the adsorption performance of materials and the design of sophisticated material structures, are discussed as well.

Phosphate Removal from Wastewater by Magnetic Amorphous Lanthanum Silicate Alginate Hydrogel Beads

It is of both fundamental and practical importance to develop effective adsorbents for removing phosphate from aqueous solutions continuously. In this study, magnetic amorphous lanthanum silicate alginate hydrogel beads (MALS-B) were prepared and used for phosphate removal. Mesoporous silica materials with highly ordered and hexagonal channel structures were synthesized from natural mineral rectorite (REC) at room temperature. On this basis, amorphous lanthanum silicate (ALS) was synthesized by theone-pot method using a silicon source from REC and a commercial lanthanum source. Further, MALS-B were synthesized from sodium alginate (SA) with ALS and Fe3O4 as the incorporated adsorbable and magnetic nanoparticles via a simple cross-linking method in CaCl2 solution. The synthesized hydrogel beads were characterized by various techniques. ALS and Fe3O4 existed relatively independently in MALS-B, where ALS provided adsorption sites and Fe3O4 provided magnetism. They played a synergistic role in phosphate removal. The saturation magnetization value of MALS-B was 17.38 emu/g, enabling theirfacile separation from aqueous solutions after phosphate adsorption. MALS-B exhibited a preferable adsorption capacity of 40.14 mg P/g for phosphorus compared to other hydrogel beads based on adsorption experiments. More significantly, MALS-B exhibited excellent selectivity for phosphate in aqueous solutions with various interfering ions and possessed a high affinity to phosphate in a wide pH range. MALS-B showed the treatment volume of 480 BV when effluent phosphate concentration was below 0.5 mg/L in fixed-bed column adsorption. The adsorption mechanism was also revealed. Our work demonstrates that MALS-B can serve as a promising adsorbent for continuous phosphate adsorption.

Synthesis of MgAl-LDH@ZIF-8 composites by in situ growth method for highly efficient phosphate removal

Removal of phosphate from wastewater by adsorption has become one of the effective ways to mitigate the negative effects of eutrophication in water bodies, and efficient adsorbent is the key....