Struvite Grown in Gel, Its Crystal Structure at 90 K and Thermoanalytical Study

Interactions between Struvite and Humic Acid and Consequences on Fertilizer Efficiency in a Nonacidic Soil

The effect of humic acid extracted from peat (AHt) on improving the struvite (STR) fertilizing efficiency is explored. To this end, a soil incubation study is correlated to plant assays comparing STR, STR-AHt, and superphosphate (SSP). Characterization techniques confirm the incorporation of the AHt into the STR. The P-pool distribution of STR and SSP is similar in the soil incubation, with STR-AHt presenting a higher labile P at 90 days passing from 10 to 15% P from SSP and STR to 25% P with STR-AHt. However, when applied to barley and tomato, STR yields more shoot P content, aboveground biomass, and residual P in soil than SSP. STR-AHt does not improve the STR results. The poor correlation observed between soil incubation and plant trials highlights the role of the rhizosphere in testing the fertilizer efficiency of STR. Mechanistic assays indicate the key role of rhizosphere pH. Finally, molecular modeling reveals a higher stabilization of STR with AHt, which could reduce P release decreasing the fertilizing potential of STR-AHt, as observed in the pot trials.

Teaching Tip: Designing Three-Dimensional (3-D) Printed Struvite and Calcium Oxalate Crystals for Microscopic Examination

Accredited colleges of veterinary medicine are required by the American Veterinary Medical Association (AVMA) Council on Education (COE) to provide learners with hands-on diagnostic method training, including urinalysis. Although teaching hospitals and affiliated clinical partners offer opportunities to test and interpret urine, caseload is unpredictable. Textbook images and published case reports offer substitutes for experiential learning. However, these read-only modalities lack experiences for learners to evaluate slides microscopically for crystalluria. This teaching tip describes the development of three-dimensional (3-D) printed struvite and calcium oxalate models for skills training. Micro-precision 3-D printed models were designed using computer-aided design (CAD) software. Geometric representations in the Standard for the Exchange of Product Data (STEP) file format were exported for 3-D printing on 2 μm resolution platforms. Prints were manufactured from high temperature laminating (HTL) resin and affixed to glass slides. Although these 3-D prints are macroscopic rather than microscopic, their orientation on a fixed template side by side allows learners to differentiate between shapes, a skill that is key to urine sediment examination. These proof-of-concept prototypes will be integrated into the author's pre-clinical curriculum so that learners can gain experience identifying and differentiating between printed struvite, calcium oxalate monohydrate, and calcium oxalate dihydrate models as they would during routine inspection of urine. Formal feedback on the efficacy of these printed models will be solicited from learners and the instructional team. Future iterations will miniaturize the printed models to reflect their real-to-life microscopic dimensions more accurately.

Insights into the physical and chemical properties of struvite crystal surfaces in terms of the effectiveness of bacterial adhesion

In this paper, we present the results of research on the physicochemical properties of two selected faces of the struvite crystal, which is the main component of infectious urinary stones. Two main faces, (001) and ([Formula: see text]), ending the c-axis, were selected for the study. These faces are not related by symmetry relations, which means, among other things, that they should have a different atomic structure, which was confirmed experimentally. In addition, the studies show that the tested surfaces have hydrophilic properties, however, the ([Formula: see text]) face is more hydrophilic compared to the (001) face. The physicochemical properties of the crystal as a whole, as well as the physicochemical properties of these faces influence the magnitude of adhesion. The adhesive force in both water and artificial urine is greater for face ([Formula: see text]) compared to face (001). The assessment of the adhesion of Proteus mirabilis bacteria in artificial urine also shows that the adhesion is greater for face ([Formula: see text]) than for face (001). The adhesion of bacteria to the examined faces of the struvite crystal, and in particular the increased adhesion of bacteria to the face ([Formula: see text]), may be the first stage of biofilm formation, which may result in a high rate of recurrence of infectious urinary stones after treatment.

Wood Ash Based Treatment of Anaerobic Digestate: State-of-the-Art and Possibilities

The problem of current agricultural practices is not limited to land management but also to the unsustainable consumption of essential nutrients for plants, such as phosphorus. This article focuses on the valorization of wood ash and anaerobic digestate for the preparation of a slow-release fertilizer. The underlying chemistry of the blend of these two materials is elucidated by analyzing the applications of the mixture. First, the feasibility of employing low doses (≤1 g total solids (TS) ash/g TS digestate) of wood ash is explained as a way to improve the composition of the feedstock of anaerobic digestion and enhance biogas production. Secondly, a detailed description concerning high doses of wood ash and their uses in the downstream processing of the anaerobic digestate to further enhance its stability is offered. Among all the physico-chemical phenomena involved, sorption processes are meticulously depicted, since they are responsible for nutrient recovery, dewatering, and self-hardening in preparing a granular fertilizer. Simple activation procedures (e.g., carbonization, carbonation, calcination, acidification, wash, milling, and sieving) are proposed to promote immobilization of the nutrients. Due to the limited information on the combined processing of wood ash and the anaerobic digestate, transformations of similar residues are additionally considered. Considering all the possible synergies in the anaerobic digestion and the downstream stages, a dose of ash of 5 g TS ash/g TS digestate is proposed for future experiments.

First experimental evidence of the piezoelectric nature of struvite

In this paper, we present the first experimental evidence of the piezoelectric nature of struvite (MgNH₄PO₄·6H₂O). Using a single diffusion gel growth technique, we have grown struvite crystals in the form of plane parallel plates. For struvite crystals of this shape, we measured the piezoelectric coefficients d₃₃ and d₃₂. We have found that at room temperature the value of piezoelectric coefficient d₃₃ is 3.5 pm/V, while that of d₃₂ is 4.7 pm/V. These values are comparable with the values for other minerals. Struvite shows stable piezoelectric properties up to the temperature slightly above 350 K, for the heating rate of 0.4 K/min. For this heating rate, and above this temperature, the thermal decomposition of struvite begins, which, consequently, leads to its transformation into dittmarite with the same non-centrosymmetric symmetry as in case of struvite. The struvite-dittmarite transformation temperature is dependent on the heating rate. The higher the heating rate, the higher the temperature of this transformation. We have also shown that dittmarite, like struvite exhibits piezoelectric properties.

Gradual Replacement of Ca2+ with Mg2+ Ions in Brushite for the Production of Ca1−xMgxHPO4·nH2O Materials

The present study investigates the gradual replacement of Ca2+ with Mg2+ ions in brushite (CaHPO4·2H2O). To date, this approach has not been systematically explored and may prove beneficial for the production of Ca1−xMgxHPO4·nH2O materials with tailored properties which are suitable for environmental and medical applications. For their production, solutions of sodium dihydrogen orthophosphate dehydrate, NaH2PO4·2H2O, calcium nitrate tetrahydrate, Ca(NO3)2·4H2O, magnesium nitrate hexahydrate, Mg(NO3)2·6H2O and ammonium hydroxide solution, NH4OH, were used. At low Mg/Ca molar ratios (up to 0.25) in the starting solution, partial replacement of Ca with Mg takes place (Mg doping) but no struvite is produced as discrete phase. When the Mg/Ca molar ratio increases gradually to 1.5, in addition to Mg-doped brushite, struvite, NH4MgPO4·6H2O, precipitates. The microstructure of the materials produced for different degrees of Ca replacement with Mg has been analyzed in depth with the use of powdered XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), thermogravimetric (TG) analysis and SEM (scanning electron microscopy). The results of this study prove that the Mg/Ca ratio in the starting solution can be monitored in such a way that materials with tailored composition are obtained.

Electroless Production of Fertilizer (Struvite) and Hydrogen from Synthetic Agricultural Wastewaters

The drive toward sustainable phosphorus (P) recovery from agricultural and municipal wastewater streams has intensified. However, combining P recovery with energy conservation is perhaps one of the greatest challenges of this century. In this study, we report for the first time the simultaneous electroless production of struvite and dihydrogen from aqueous ammonium dihydrogen phosphate (NH₄H₂PO₄) solutions in contact with either a pure magnesium (Mg) or a Mg alloy as the anode and 316 stainless steel (SS) as the cathode placed in a bench-scale electrochemical reactor. During the electroless process (i.e., in the absence of external electrical power), the open circuit potential (OCP), the formation of struvite on the anode, and the generation of dihydrogen at the cathode were monitored. We found that struvite is formed, and that struvite crystal structure/morphology and precipitate film thickness are affected by the concentration of the H_nPO₄^n-3/NH₄⁺ in solution and the composition of the anode. The pure Mg anode produced a porous 0.6-4.1 μm thick film, while the AZ31 Mg alloy produced a more compact 1.7-9.9 μm thick struvite film. Kinetic analyses revealed that Mg dissolution to Mg²⁺ followed mostly a zero-order kinetic rate law for both Mg anode materials, and the rate constants (k) depended upon the struvite layer morphology. Fourier-transform infrared spectrometry, X-ray diffraction, and scanning electron microscopy indicated that the synthesized struvite was of high quality. The dihydrogen and Mg²⁺ in solution were detected by a gas chromatography-thermal conductivity detector and ion chromatography, respectively. Furthermore, we fully demonstrate that the reactor was able to remove ∼73% of the H_nPO₄^n-3 present in a natural poultry wastewater as mainly struvite. This study highlights the feasibility of simultaneously producing struvite and dihydrogen from wastewater effluents with no energy input in a green and sustainable approach.

Structural and Optical Properties of Struvite. Elucidating Structure of Infrared Spectrum in High Frequency Range

Study of structure and optical properties of magnesium ammonium phosphate hexahydrate crystal known as struvite is presented. Experimentally determined infrared (IR) and ultraviolet-visible (UV-vis) spectra are compared with the theoretical predictions of density functional methods. Examination of the interatomic bond lengths, Mulliken atomic charges, and binding energies of water in the magnesium hexahydrate cation, together with the analysis of the hydrogen bond pattern have allowed us to explain a special feature of the IR spectrum of struvite, a blueshift of the band corresponding to the O-H stretching mode. This mode has been assigned to a "dangling" hydroxyl group in one of the water molecules in magnesium hexahydrate. Using experimentally obtained UV-vis spectrum and performing Tauc plots analysis, optical bandgap of struvite has been narrowed to a range from 5.92 to 6.06 eV.

Time-Resolved Dynamics of Struvite Crystallization: Insights from the Macroscopic to Molecular Scale

The crystallization of magnesium ammonium phosphate hexahydrate (struvite) often occurs under conditions of fluid flow, yet the dynamics of struvite growth under these relevant environments has not been previously reported. In this study, we use a microfluidic device to evaluate the anisotropic growth of struvite crystals at variable flow rates and solution supersaturation. We show that bulk crystallization under quiescent conditions yields irreproducible data owing to the propensity of struvite to adopt defects in its crystal lattice, as well as fluctuations in pH that markedly impact crystal growth rates. Studies in microfluidic channels allow for time-resolved analysis of seeded growth along all three principle crystallographic directions and under highly controlled environments. After having first identified flow rates that differentiate diffusion and reaction limited growth regimes, we operated solely in the latter regime to extract the kinetic rates of struvite growth along the [100], [010], and [001] directions. In situ atomic force microscopy was used to obtain molecular level details of surface growth mechanisms. Our findings reveal a classical pathway of crystallization by monomer addition with the expected transition from growth by screw dislocations at low supersaturation to that of two-dimensional layer generation and spreading at high supersaturation. Collectively, these studies present a platform for assessing struvite crystallization under flow conditions and demonstrate how this approach is superior to measurements under quiescent conditions.