Struvite Content Research Articles

Quantification of struvite content of biosolids is necessary to avoid bias in the assessment of digester and dewaterability performance

Quantification of struvite content of biosolids is necessary to avoid bias in the assessment of digester and dewaterability performance

Quantification of struvite content of biosolids is necessary to avoid bias in the assessment of digester and dewaterability performance

Quantification of struvite content of biosolids is necessary to avoid bias in the assessment of digester and dewaterability performance

Effect of different struvite crystallization methods on gaseous emission and the comprehensive comparison during the composting

This study compared 4 different struvite crystallization process (SCP) during the composting of pig feces. Four combinations of magnesium and phosphate salts (H3PO4+MgO (PMO), KH2PO4+MgSO4 (KPM), Ca(H2PO4)2+MgSO4 (CaPM), H3PO4+MgSO4 (PMS)) were assessed and were also compared to a control group (CK) without additives. The magnesium and phosphate salts were all supplemented at a level equivalent to 15% of the initial nitrogen content on a molar basis. The SCP significantly reduced NH3 emission by 50.7–81.8%, but not the N2O. Although PMS group had the lowest NH3 emission rate, the PMO treatment had the highest struvite content in the end product. The addition of sulphate decreased CH4 emission by 60.8–74.6%. The CaPM treatment significantly decreased NH3 (59.2%) and CH4 (64.9%) emission and yielded compost that was completely matured. Due to its effective performance and low cost, the CaPM was suggested to be used in practice.

An association between kidney stone composition and urinary metabolic disturbances in children

ObjectiveTo determine kidney stone composition in children and to correlate stone fractions with urinary pH and metabolic urinary risk factors. Patients and methodsWe studied 135 pediatric patients with upper urinary tract lithiasis in whom excreted or extracted stones were available for analyses. Composition of stones was analyzed. A 24-hour urine assessment included volume, pH and daily excretions of calcium, oxalate, uric acid, cystine, creatinine, phosphate, magnesium and citrate. ResultsCalcium oxalate was the major component of 73% stones, followed by struvite (13%) and calcium phosphate (9%). Uric acid was present in almost half of stones, but in rudimentary amounts. The calcium oxalate content in calculi showed a strong relationship with calciuria, and moderate association with oxaluria, magnesuria and acidification of urine. The percent content of struvite presented reverse and lower correlations with regard to the above parameters. Calcium phosphate stone proportion had low associations with urinary risk factors. ConclusionsCalciuria, oxaluria, magnesuria and low urine pH exerted the biggest influence on calcium oxalate content in pediatric renal stones. Relationships of urinary risk factors with calculi calcium phosphate content were of unclear significance. Urinary citrate excretion did not significantly correlate with kidney stone composition in children.

Sorption of Chromium with Struvite During Phosphorus Recovery

Struvite (MgNH(4)PO(4)·6H(2)O; MAP) precipitation is a viable means of phosphorus (P) recovery from animal and human wastes. The behavior of metal contaminants such as chromium (Cr) during struvite precipitation, however, requires consideration. Here the influence of both Cr concentration and oxidation state on sorption is assessed. The Cr content of struvite precipitated in the presence of 1-100 μM Cr as Cr(III) (22.3-3030.1 mg/kg) was higher than that of solids from Cr(VI) (4.5-5.1 mg/kg) solutions. For 1-20 μM Cr(III) solids, scanning electron microscopy (SEM) revealed etch pit formation on struvite crystal surfaces, indicative of a surface interaction. The formation of an adsorbate was confirmed by X-ray absorption fine structure spectroscopy (XAFS). At initial concentrations ≥20 μM Cr(III), XAFS confirmed the formation of a Cr(OH)(3)·nH(2)O(am) precipitate. Fourier transform infrared (FT-IR) spectroscopy revealed that both Cr(III) and Cr(VI) sorption resulted in distortion of the PO(4)(3-) tetrahedra in the mineral structure. This, combined with SEM results revealed that even at low sorbed concentrations, the Cr impurity can affect the mineral surface and structure. Thus, the initial Cr concentration and oxidation state in wastes targeted for P recovery will dictate the final Cr content, the mechanism of sorption, and impact on the struvite structure.

Recovery of phosphorus as struvite from sewage sludge ash

Phosphorus (P) is an element vital for all living organisms, yet the world's reserves of phosphate rock are becoming depleted. This study investigated an effective P recovery method from sludge ash via struvite precipitation. Results showed that more than 95% of the total P content was extracted from sludge ash by applying 0.5 mol/L HCl at a liquid/solid ratio of 50 mL/g. Although heavy metal leaching also occurred during P extraction, cation exchange resin efficiently removed the heavy metals from the P-rich solution. Orthogonal tests showed that the optimal parameters for P precipitation as struvite would be a Mg:N:P molar ratio of 1.6:1.6:1 at pH 10.0. X-ray diffraction analysis validated the formation of struvite. Further investigations revealed that the harvested precipitate had a high struvite content (97%), high P bioavailability (94%), and low heavy metal content, which could be considered a high quality fertilizer.

Phosphorus Removal and Recovery from Hog Lagoon Supernatant Using a Gravity-Settled Batch Reactor and Increased pH

In Canada, the majority of swine waste is stored in open lagoons and land applied according to crop nitrogen requirements. This practice over-applies phosphorus (P) two- to five-fold, leading to potential runoff or leaching loss of P to the environment. Removing P from liquid hog waste is an important step in correcting the N:P ratio of manure applied to cropland. Reclaiming this P as struvite (MgNH4PO4) would ease environmental concerns of eutrophication, provide a saleable fertilizer, and help address the limited global supply of phosphate. Most struvite reactors are capital and operationally intensive, making the process too expensive to be implemented by the average farmer. In addition, high calcium levels found in some supernatants compete with magnesium (Mg), and struvite formation is impaired. The objective of our study is to test the effective P removal and settled solids quality from using a low energy, low capital, pilot-scale gravity-settled batch reactor. Lagoon supernatant with total phosphate (TP) concentration from 58 to 216 mg L-1 and pH of 6.7 was adjusted to pH 8.5 and allowed to settle with no addition of magnesium chloride. Results show that TP was reduced by 76.5%, total suspended solids were reduced by half, soluble P was reduced by approximately 90% (94.5 to 10.3 mg L-1), and particulate mineral forms of P were reduced by 69% (83 to 26 mg L-1), perhaps by flocculation. The dried solids had a TP concentration of 5.6%, total nitrogen of 6.3%, and potassium of 3.8%. Struvite content in the solids was estimated at 30%, and calcium phosphates comprised the remainder of the mineral P compounds. Half of the dried solids were estimated to be organic. The presence of calcium did not impede good P removal, perhaps due to long settling times (24 h). These results indicate that nutrient-rich supernatants with high suspended solids are good targets for P recovery, but product purity is a challenge.

Analysis of mixed stones is prone to error: a study with US laboratories using micro CT for verification of sample content

This project sought to test the ability of commercial stone analysis laboratories to correctly analyze urinary stones. Human stone specimens were cleaved into pieces, and the pieces of each specimen were verified as being similar using micro-computed tomography (micro CT), a non-destructive method. Thus, similar specimens from 25 stones were sent to five laboratories, and a sixth piece was kept for analysis in our laboratory using Fourier-transform infrared spectroscopy (FT-IR). The results showed that laboratories were very good at analyzing pure specimens, but with mixed specimens the accuracy and consistency varied. In six stones containing apatite, a mineral easily identified using micro CT, apatite was missed 20% of the time. Struvite content in the specimens was inconsistently reported, with laboratories differing in their reports of the presence of struvite in six of the 25 stones (24%). A mixed stone containing atazanavir was not reported by any of the laboratories as containing that drug. Nomenclature differed among the laboratories, especially with regard to apatite, which was variously reported as hydroxyapatite, carbonate apatite, or as apatite with calcium carbonate. One laboratory reported protein in every stone, while for all others protein was reported in only one stone. We conclude that physicians need to be aware that reports on mixed stones, which represent >90% of all calculi, can be erroneous. It is likely that supplying a greater amount of stone material will assist a laboratory in making a correct analysis of mixed stones. Also, standardization of nomenclature could assist in analysis reproducibility, but this remains to be tested.

Favorable Operating Conditions for Obtaining High-Value Struvite Product from Sludge Dewatering Filtrate

Abstract Struvite (MgNH4PO4) is emerging as a potential fertilization product for agriculture. As other phosphate minerals that can be precipitated from wastewater are known to have lower value as fertilizers, the overall fertilization quality of the solids precipitated in struvite recovery systems depends largely on the percentage of struvite in the mixture of precipitated solids. This work focused on determining the most appropriate operating conditions (with a focus on pH and hydraulic retention time [HRT]) for removing >90% of the dissolved phosphate and, at the same time, attaining a precipitate with the highest possible struvite content from typical filtrates of sludge dewatering belt press systems. To this end, a continuous laboratory-scale completely mixed reactor was operated at different pH values and HRTs and the precipitant composition was determined. Theoretical calculations showed that the most cost-effective MgCl2 dosage to typical Israeli belt press filtrate is ∼10 mM. Using this dosage, ∼...

Phosphorus recovery by struvite crystallization in WWTPs: Influence of the sludge treatment line operation

Phosphorus recovery by struvite (MgNH(4)PO(4).6H(2)O) crystallization is one of the most widely recommended technologies for treating sludge digester liquors especially in wastewater treatments plants (WWTP) with enhanced biological phosphorus removal (EBPR). In this paper, phosphorus recovery by struvite crystallization is assessed using the rejected liquors resulting from four different operational strategies of the sludge treatment line. Phosphorus precipitation and recovery efficiencies of between 80-90% and 70-85%, respectively, were achieved in the four experiments. The precipitates formed were mainly struvite, followed by amorphous calcium phosphate and, in some experiments, by calcite. The highest global phosphorus recovery taking into account both the sludge line and the crystallizer was achieved when mixed thickening and high elutriation were carried out (8.4 gP/kg treated sludge). However, low struvite content was obtained in the crystallizer with this operation scheme due to the high calcium content in the elutriation stream. Therefore, if the final purpose is to obtain struvite, the reduction of the elutriation flowrate is widely recommended in the case of high water hardness.

Struvite formation, analytical methods and effects of pH and Ca2 +

Struvite formation is mainly controlled by concentrations of Mg2+, NH4+ and PO4 3+, pH, temperature, and other ions like Ca2+. Experiments evaluating the effects of pH and Ca2+ on struvite formation indicated that XRD is only a qualitative method to analyze the struvite content in precipitating compounds, which was also reflected in microscopic images. The element analyses preceded by a dissolution method were introduced to quantitatively determine the struvite content and were shown to be an efficient enough method. Based on element analyses, the struvite content could be calculated according to the N content in the precipitations, based on the molar ratios (1:1:1) of Mg, N and P in pure struvite (MgNH4PO4 x 6H2O). It was found that the optimal pH ranges for the struvite content >90% were respectively at 7.5 approximately 9.0 with ultra pure water as solute and at 7.0 approximately 7.5 with tap water (mainly consisting of ground water) as solute. Applying a pH > 8.0 in real wastewater containing Ca2+ might result in impure struvite contents in the precipitate due to the effect of Ca2+.

Kinetics of struvite to newberyite transformation in the precipitation system MgCl 2–NH 4H 2PO 4–NaOH–H 2O

The influence of the initial reactant concentrations on the composition of the solid phases formed in the precipitation system MgCl 2–NH 4H 2PO 4–NaOH–H 2O was investigated. The precipitation diagram constructed shows the approximate concentration regions within which struvite, newberyite, and their mixtures exist at 25 °C and an aging time of 60 min. It was found that immediately after mixing the reactant solutions, struvite (MgNH 4PO 4·6H 2O) precipitated in nearly the whole concentration area, while newberyite (MgHPO 4·3H 2O) appeared mostly within the region of the excess of magnesium concentration. It was also found that after aging time of 60 min the precipitation domain of struvite alone is much broader than that of newberyite or the domain of their coexistence, and shows that struvite is more abundant in the systems in which the initial concentration of ammonium phosphate is higher than that of magnesium. The kinetics of struvite to newberyite transformation (conversion) was systematically studied under the conditions of different initial reactant concentrations and different initial pH in the systems in which a mixture of both phases precipitated spontaneously. The struvite to newberyite conversion period was found to be strongly related to the ratio of initial supersaturations, S N/ S S, rather than to the any particular physical quantity that can describe and predict the behavior of the precipitation system. Experimental data suggest a solution-mediated process as a most possible transformation mechanism. Along with a continuous monitoring of the changes in the liquid phase, the content of struvite in the solid phase was estimated by means of a Fourier transform infrared (FT-IR) method, developed for this particular precipitation system.

Formation and transformation of struvite and newberyite in aqueous solutions under conditions similar to physiological.

The precipitation of magnesium phosphates in the system MgCl(2)-NH(4)H(2)PO(4)-NaOH-H(2)O was studied at a wide range of reactant concentrations at 37 degrees C and an initial pH(i) of 7.4. Precipitates were aged for 24 h and characterized by means of optical and scanning electron microscopy, x-ray diffractometry, FT-IR spectroscopy and thermogravimetry. Struvite was found to precipitate in nearly the whole concentration region investigated. Pure newberyite and a mixture of struvite and newberyite were obtained in a narrow range only with a pH(24 h)<6.4. The transformation of struvite into newberyite was studied by following changes in the liquid and solid phases. Thus, the changes of pH and the content of struvite in the precipitate as a function of time were recorded. The influence of the initial pH(i) and temperature on the transformation process is discussed. Analysis of the experimental data suggests a solution mediated transformation process as a possible mechanism of struvite transformation.

Recurrence rates and severity of urinary calculi.

During the last ten years, data of urinary calculi was received in 4094 cases on the criterion of "recurrence", whereby the answer was "yes" in 1446 cases. The overall "adjusted relative recurrence rate" (ARRR) is therefore 35.3%. The importance of an exact physical analysis of urinary stones, involving a differentiation of the various Ca oxalates and Ca phosphates, becomes clear looking at the high recurrence rates for the monomineralic stones of the Ca stone class like brushite and weddellite (ARRR = 66.7% and 50.0%, respectively) compared to apatite and whewellite (ARRR = 36.5% and 29.2%, respectively). Dramatic changes in the composition of the recurrent stone were observed only in 12.7% of all cases. The highest ARRR was found in infection stones with a large content of struvite (about 75%), whereas the total recurrence rate of the infection stone class was about 38%. An assessment of the "danger" of a urinary stone taking into account the criteria of "composition" and "prevalence to recur" is given.