Size Of Struvite Crystals Research Articles

Red mud as a magnesium carrier for enhanced N and P recovery from wastewater by the struvite method

The struvite method has been widely used to recover N and P from wastewater. However, the drawbacks of alkali consumption and small crystallization are not negligible. Therefore, alkaline porous carrier materials are greatly desired to enhance struvite crystalline precipitation and maintain suitable pH values. In this study, using red mud (RM) as a carrier, MgO was loaded onto RM by co-precipitation method to prepare an N and P recovery material (MgO–RM). A response surface methodology based on the Box–Behnken design was used to explore the effects of the factors on N and P recovery. The multi-objective optimization of the recovery process was carried out using the desirability function approach to achieve an economically feasible recovery. Characterizations, including SEM-EDS, BET, FTIR, XRD, and XPS, were carried out to explore the recovery mechanism. The results demonstrated that the nano-sized MgO was well deposited on the RM surface, resulting in a larger specific surface area and greater reactivity of the MgO–RM. Using RM as a carrier significantly increased the struvite crystal size, and the MgO–RM could maintain the pH value of the solution in a suitable range for struvite growth. Under optimal conditions (dosage = 3.5 g/L, N/P = 1.8, and pH value = 3.4), the maximum N and P recovery capacity by MgO–RM was 57.23 mg/g and 128.05 mg/g. The recovery process may involve coupled reactions between physical adsorption, ion exchange, coordination exchange, and chemical precipitation. Struvite produced by chemical precipitation is the main recovery mechanism.

Biochar seeding properties affect struvite crystallization for soil application

Struvite crystallization is a viable approach for recovering phosphorus from phosphorus-rich solutions such as urine and wastewater. However, designing seed materials to promote crystal growth and enhance the efficiency of struvite crystallization remains an area of active research. In this study, we investigated the seeding characteristics of biochars on struvite crystallization and the impact of biochar feedstock type and production temperature on the process. Microwave-pyrolyzed biochars produced from different feedstocks and under different temperatures were examined as seeding materials for struvite crystallization from urine and the influence of biochar properties on the overall struvite yield, nutrient recovery and struvite crystal size. Sawdust biochar (lignocellulosic biomass) produced at 500 ​°C had the highest struvite yield (7.91 ​g ​L−1), phosphate (97.9%) and ammonium recovery (87.1%), and relative crystal size (85.2%) compared to the non-seeded treatment due to its higher surface area, pore volume, and hydrophobicity of the biochar. Manure pellet biochar (non-lignocellulosic biomass) produced at 500 ​°C also exhibited performance comparable to sawdust biochar produced at 500 ​°C. Increasing pyrolysis temperature increased biochar's hydrophobicity, zeta potential, electrophoretic mobility and bulk density, irrespective of the feedstock type, thereby improving the seeding process. The ash content of biochar was negatively correlated with its surface area, pore volume, and particle size, but positively correlated with biochar's bulk density and suspension stability. In conclusion, feedstock type and pyrolysis temperature significantly affected biochar properties, which interactively influenced struvite crystallization. Therefore, biochars should be carefully selected to improve their efficiency for phosphorus recovery from phosphorus-containing solutions such as urine and wastewater, with the recovered phosphorus being used for soil applications.

Anti-uropathogenic, antioxidant and struvite crystallization inhibitory potential of fresh and fermented coconut water

Coconut water treats many health issues, including kidney stones and urinary tract infections. However, the therapeutic application of coconut water to treat urolithiasis has remained an unexplored topic. This study compares the effect of fresh coconut water (CW) and naturally fermented coconut water (FCW) on anti-uropathogenic, antioxidant, and anti-urolithiasis activities. Initial physicochemical screening established that CW is a rich source of total phenolics, protein, and minerals. Further, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay showed that CW and FCW have an antioxidant potential of 48.33 ± 2.52% and 55.12 ± 2.99%, respectively. While the FCW-treated cultures of selected uropathogens showed antimicrobial activity, the CW-treated cultures displayed negligible activity. Subsequently, anti-struvite analysis was performed using the single gel diffusion method, where different concentrations of CW and FCW were treated during struvite crystallization under in vitro conditions. The increasing concentrations of CW and FCW decreased the number and size of struvite crystals that grew in the gel medium. These results indicate that CW has antioxidant property and a marginal inhibitory effect during in vitro struvite crystallization but is not anti-uropathogenic. However, FCW shows potential antioxidant, anti-uropathogenic, and anti-struvite urolithiatic properties. Further, FTIR, SEM, and XRD techniques were used to confirm the impact of CW or FCW on struvite crystallization.

Molecular Docking and In Vitro Inhibitory Effect of Polyaniline (PANI)/ZnO Nanocomposite on the Growth of Struvite Crystal: a Step Towards Control of UTI.

Nowadays, nanotechnology is gaining interest on diagnostics for several chronic diseases. In the present study, the chemical oxidative method of aniline in acid medium with ammonium peroxydisulfate (APS) as an oxidant was employed to develop polyaniline (PANI)-based nanocomposite overflowing/doping on ZnO. The chemical properties, morphology, and structure of the polymer and nanocomposite were investigated using FTIR, XRD, and SEM. The characteristic FTIR peaks of PANI were reported to shift to a higher or lower wave number in PANI-doped ZnO composites due to the formation of H-bonding. Different amounts of ZnO nanoparticles were used to test this influence on the strength of the generated materials. The ability of the PANI-doped ZnO nanocomposite to inhibit struvite crystal growth was determined. The size of struvite crystals was condensed from 2.9 to 1.4cm at a concentration of 5% PANI-doped ZnO nanoparticles, and the inhibition efficiency of synthesized PANI-doped ZnO against kidney stone (struvite) was confirmed by molecular docking analyzes. The in vitro as well as in silico study revealed the potential applications of polyaniline/ZnO nanocomposite in kidney diseases.

Phosphorous recovery from septic tank liquor: Optimal conditions and effect of tapered velocity gradient

The growing recognition of the potential of recovery of products from, and recycling of, wastewater is matched by a growing interest in decentralized treatment systems. Sanitation-focused policies and interventions, undertaken by many developing countries, are dominated by septic tanks for septage management. As reserves of phosphate rock continue being depleted, recovery of phosphorus (P) from the waste stream is one of the practical strategies to deal with that depletion. Partial anaerobic digestion of septic tank liquor converts organic P to soluble orthophosphate form, allowing it to be recovered. Factors that influence such recovery, namely pH, the molar ratio of magnesium (Mg) to P, velocity gradient, and mixing duration were tested and optimized for recovering P as struvite. Interactions between the above factors and their possible influence on the efficiency of P recovery were also examined. Under optimal conditions, more than 90% of P could be recovered. The maximum size of struvite crystals was 201 μm. Among the factors that influenced P recovery, pH and the Mg/P ratio affected recovery efficiency whereas the velocity gradient and mixing duration affected the size of struvite crystals. Tapering the velocity gradient not only increased the crystal size significantly, from 280 μm to 371.9 μm, but also reduced energy requirement by 62%. The study showed that new reactors designs can be based on the concept of tapered velocity gradient to improve the properties of struvite crystals.

Recovery of phosphates(V) from wastewaters of different chemical composition

AbstractPhosphate(V) ions were recovered from wastewaters of different chemical compositions in a continuous reaction crystallization of struvite. Two real wastewaters were represented by an effluent sample from the phosphorus mineral fertilizer industry and by liquid manure derived from a cattle-breeding farm. Two other wastewaters were prepared under laboratory conditions. Impurities present in the wastewaters caused the precipitation of solid products of distinctly different quality. The mean size of struvite crystals varied from ca. 18 to ca. 40 μm. Homogeneity within their populations, quantified by the coefficient of variation CV, varied from satisfactory (CV ca. 75%) to unfavorable (CV ca. 100%), which resulted in the elongation of necessary filtration time. Calcium ions in wastewater precipitated as amorphous hydrated calcium phosphates ACP. Their content in the products varied from 33.4 up to 73.1 mass %. Also 28.32 – 32.74 mass % of P2O5, 6.35 – 14.12 mass % of MgO and 4.35 – 16.94 mass % of CaO were confirmed in the products, together with hydroxides of some metals and salts of other impurities. Based on the chemical composition of the products derived from the investigated wastewaters, their application in agriculture as valuable mineral fertilizers is recommended.

Effect of the stirring speed on the struvite formation using the centrate from a WWTP

The formation of struvite (MgNH4PO4·6H2O) for nutrient recovery in wastewater treatment plants has been widely investigated; however, little attention has been paid to the effect of stirring speeds on the resulting particle size, which could affect its agronomic value as a slow-release fertilizer. In this study, struvite formation from the centrate of sewage digestate was performed under six stirring speeds (0, 100, 200, 300, 400, 500 rpm). The resulting struvite crystals were characterised using X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy. The average particle size of struvite crystals increased from 55 µm at 0 rpm to 127 µm at 100 rpm and 128 μm at 200 rpm. Further increments in stirring speeds resulted in smaller crystal sizes. These results indicated that the largest particle size can be obtained at stirring speeds ranging from 100 to 200 rpm, equivalent to a velocity gradient between 79 and 188 s-1, as there was no statistically significant difference between mean values (t-test, p<0.05). The optimum stirring speed range reported herein can be used to set operational conditions for struvite crystallisation with the benefit of producing large crystals and reducing energy consumption in stirring tanks.

Development of phosphorus recovery reactor for enlargement of struvite crystals using seawater as the magnesium source.

Struvite crystallization is an interesting method for the recovery of phosphorus (P) from wastewater. However, the struvite crystals obtained are small, which makes them difficult to separate from wastewater. A continuous reactor for enlarging struvite crystals was developed. Batch-scale experiments were conducted to investigate the optimum factors for the enlargement of struvite crystals. The results of pH experiments showed that P recovery efficiency increased with an increase of pH values (7.6 to 10), while the size of struvite crystals decreased. The results of the Mg:P ratios found that the maximum P recovery efficiency occurred at the maximum ratio of Mg:P. The sizes of struvite crystals were not significantly different. For the variation of temperature values, the results showed that P recovery efficiency and crystal sizes decreased when temperature values increased. Therefore, the optimized conditions for P recovery efficiency and enlargement of struvite crystals for the continuous reactor were pH 8.5 and an Mg:P ratio of 1.2:1 at 30 °C (room temperature). The treated swine wastewater and seawater were continuously fed in at the bottom of the reactor. After 30 days, the size of struvite crystals had increased from 125 μm to 0.83 mm (seven times).

P-recovery in a pilot-scale struvite crystallisation reactor for source separated urine systems using seawater and magnesium chloride as magnesium sources

Practical recovery of a non-renewable nutrient, such as phosphorus (P), is essential to support modern agriculture in the near future. The high P content of urine, makes it an attractive source for practicing the recovery of this crucial nutrient. This paper presents the experimental results at pilot-plant scale of struvite crystallisation from a source-separated urine stream using two different magnesium sources, namely magnesium chloride and seawater. The latter was chosen as sustainable option to perform P-recovery in coastal areas. Real seawater was used to assess in a more realistic way its efficiency to precipitate P as struvite, since its composition (with noticeable concentration of ions such as Ca2+, SO42−, Na+, …) could lead to the formation of impurities and other precipitates. 0.99 g of struvite was obtained per litre of urine irrespective of the operational conditions tested. In all tested conditions, precipitation efficiencies exceeded 90% and recovery efficiencies were higher than 87%, with an average struvite crystal size higher than 110 μm (and up to 320 μm, depending on the experimental conditions) in the harvested struvite samples. Almost pure struvite was obtained when MgCl2 was used as precipitant, while amorphous calcium phosphate and other impurities appeared in the precipitates using seawater as magnesium source. However, the lower settling velocity of the amorphous precipitates in comparison with the struvite precipitates suggests that their separation at industrial scale could be relatively straightforward.

Nutrient recovery from anaerobically digested chicken slurry via struvite: Performance optimization and interactions with heavy metals and pathogens

The aim of this study was to assess the potential of struvite precipitation to recover nutrients from anaerobically-processed poultry slurry and struvite's interactions with heavy metals (Zn, Cu, Pb, Cr, and Ni) and pathogens (total coliforms and Escherichia coli). The impacts of pH, Mg, N, and P molar proportion, reaction time, and mixing rate and duration were explored to determine the optimal conditions for nutrient recovery through struvite precipitation. A pH range of 9.5 to 10.5, was ideal for P and N removal and recovery, with a molar ratio of 1:1:1 for Mg:N:P. A mixing rate of 150rpm for 10min could allow nutrient recovery with little loss (3.32%) of NH₃ through volatilization, and also achieve an optimal struvite crystal size (50–60μm). The results of X-ray diffractometry and scanning electron microscopy confirmed that the precipitates generated at pH9 and 10 were orthorhombic struvite. Moreover, along with the recovery of nutrients, 40, 45, 66, 30, and 20% of Zn, Cu, Pb, Cr, and Ni, respectively, and 70% total coliforms and E. coli were removed by struvite precipitation from poultry slurry. This was observed despite that the levels of contaminants (heavy metals) detected in struvite were well below the permissible limits and free of pathogens. Consequently, it was inferred that the struvite quality was reasonable by virtue of its heavy metal and pathogen content, and therefore appropriate for application in the field. Similarly, struvite precipitation has multiple benefits as it can effectively recover nutrients as well as reducing pathogenic populations.

EFFECT OF CONTINUOUS CRYSTALLIZER PERFORMANCE ON STRUVITE CRYSTALS PRODUCED IN REACTION CRYSTALLIZATION FROM SOLUTIONS CONTAINING PHOSPHATE(V) AND ZINC(II) IONS

Continuous reaction crystallization of struvite from aqueous solutions containing phosphate(V) (1.0 mass %) and zinc(II) ions (from 0.1 to 2.0 mg kg-1) in a continuous DT MSMPR crystallizer was investigated. The influence of pH (9 - 11) and mean residence time (900 - 3600 s) on the product characteristics and its chemical composition was tested. Struvite crystals of mean size 22-41 µm were produced. An increase in Zn2+ concentration decreased the mean crystal size and homogeneity. An elevation of the pH also decreased the struvite crystal size. Augmenting the mean residence time influenced product quality advantageously. Coexistence of struvite and Zn(OH)2 in the product was confirmed analytically.

Synthesis of struvite (MgNH4PO4·6H2O) and its use for sorption of nickel ions

The influence of the conditions of the struvite synthesis on its ability to form crystals with developed faces of different forms (hkl) and on the possibility of the subsequent transition to more stable forms was examined. The correlation between the ζ-potential of the struvite particle surface, struvite crystal size, and tendency to form agglomerates was demonstrated. The sorption rate in the system consisting of struvite, nickel ions, ammonium ions, and water can be increased by combining the internal diffusion and recrystallization of the solid interaction products. The possibility of enhancing the sorption performance by properly choosing the anionic composition of solutions of nickel salts for the sorption was revealed. The conditions for preparing struvite for its use as agent for improvement of contaminated soils to immobilize heavy metal ions were substantiated.

Effects of organic matter on crystallization of struvite in biologically treated swine wastewater

ABSTRACTA sustainable way to recover phosphorus (P) in swine wastewater involves a preliminary step of P dissolution followed by the separation of particulate organic matter (OM). The next two steps are firstly the precipitation of struvite crystals done by adding a crystallization reagent (magnesia) and secondly the filtration of the crystals. To develop the process successfully at an industrial scale, the control of the mechanisms of precipitation is the key point in order to obtain high value-added products, that is, big struvite crystals easy to harvest and handle. Experiments with process parameters optimized previously in a synthetic swine wastewater were performed on real swine wastewater to assess the role of the OM on struvite crystallization. After 24 h, with a pH increase to 6.8 only, 90% of the initial P was precipitated and 60% was precipitated as struvite. 80% of the solid recovered was in the fraction > 100 µm. The other forms recovered were brushite, amorphous calcium phosphate, NaCl, KCl and OM. The influence of OM on struvite precipitation in acidified swine wastewater was negative on the reaction kinetics but positive on the size of the struvite crystals. The presence of colloidal particles increased the size of the struvite crystals but slowed down the kinetics due to the viscosity induced by the repulsive force of the colloids. The maximum size of single struvite crystals (200 µm) was observed with the presence of particulate OM.

Struvite precipitation as a technology to be integrated in a manure anaerobic digestion treatment plant – removal efficiency, crystal characterization and agricultural assessment

AbstractBACKGROUNDThe formation of struvite (MgNH4PO4 · 6H2O) from digested slurry is an opportunity to recover nutrients as a slow‐release fertilizer. A series of batch and continuous experiments were conducted to assay the influence of operational parameters, total solids and organic matter content on the quality and size of struvite crystals formed. Finally, the agronomic bioavailability of struvite was assessed in a greenhouse experiment.RESULTSIn terms of process conditions an optimum pH of 9 was found, while changes in temperature (from 25 °C to 36 °C) showed to exert no influence whatsoever. On the other hand, though the presence of Na+ didn't affect the efficiency, high amounts of Ca2+ decreased the percentage of Mg2+ and NH4+ removed. CO2 stripping presented a reduction in the reagents required (NaOH) to raise the pH, with a similar removal efficiency and good quality of the struvite obtained. Nevertheless, the presence of organic matter resulted in a reduction on the size of struvite crystals. Agronomic assays showed that struvite P availability is similar to that of synthesis ammonium phosphate fertilizers.CONCLUSIONSThe results point to struvite precipitation as a good strategy to recover nutrients from digested manure and to improve nutrient management. © 2014 Society of Chemical Industry

Morphology of struvite crystals as an evidence of bacteria mediated growth

Influence of Proteus mirabilis on the growth, morphology and size of struvite crystals in artificial urine has been studied. The growth in the presence of Proteus mirabilis shows formation of struvite crystals of more regular habits compared with that in the absence of bacteria. This implies that in the presence of Proteus mirabilis, struvite crystals grow with relative growth rates within smaller range of variability compared to the absence of bacteria. The results show that bacteria affect size and struvite morphology while the habit remains almost unchanged. It is suggested that the changes in struvite crystal morphology are induced by the presence of Proteus mirabilis. Microorganism's negatively charged residues interact electrostatically with positive ions which outcrop given surfaces and lead to an enhanced expression of these surfaces. This means that microorganisms actively mediate in growth processes. Therefore, the investigations provide evidence for the importance of biological regulation in crystallization process.

Comparative in vitro studies on disodium EDTA effect with and without Proteus mirabilis on the crystallization of carbonate apatite and struvite

Effect of disodium EDTA (salt of ethylenediamine tetraacetic acid) on the crystallization of struvite and carbonate apatite was studied. To evaluate such an effect we performed an experiment of struvite and carbonate apatite growth from artificial urine. The crystallization process was induced by Proteus mirabilis to mimic the real urinary tract infection, which usually leads to urinary stone formation. The results demonstrate that disodium EDTA exhibits the effect against P. mirabilis retarding the activity of urease – an enzyme produced by these microorganisms. The spectrophotometric results demonstrate that, with and without P. mirabilis, the addition of disodium EDTA increases the induction time and decreases the growth efficiency compared to the baseline (without disodium EDTA). These results are discussed from the standpoint of speciation of complexes formed in the solution of artificial urine in the presence of disodium EDTA. The size of struvite crystals was found to decrease in the presence of disodium EDTA. However, struvite crystals are larger in the presence of bacteria while the crystal morphology and habit remain unchanged.

Effect of hydraulic retention time and seed material on phosphorus recovery and crystal size from urine in an air-agitated reactor

Phosphorus (P) recovery from urine is affected by various parameters. This study evaluates the effects of hydraulic retention time (HRT) and seed material on P recovery and crystal size in an air-agitated reactor. Results show that ortho-phosphate removal and struvite recovery efficiencies were 96.3% and 89.5%, and 97.1% and 93.0%, after five runs of HRTs of 1 and 2 h, respectively. Low loss of crystals from effluent urine solutions indicates high struvite recovery efficiency and is correlated with the structure and design of the reactor. The average particle size decreased from 40.0 to 31.7 μm as the HRT increased from 1 to 2 h. The two types of seed materials (zeolite and molecular sieve) did not affect the ortho-phosphate removal efficiency but affected the struvite crystal size. In particular, multi-stage addition of zeolites increased the average crystal size from 33.7 to 57.0 μm.

Precipitation and Crystallization of Struvite from Synthetic Wastewater under Stoichiometric Conditions

Phosphate (V) ions were continuously removed from synthetic wastewater containing inorganic impurities using magnesium and ammonium ions. The product was magnesium ammonium phosphate (V) hexahydrate, struvite, MgNH4PO4 × 6H2O. Research ran in stoichiometric conditions in DT MSMPR type crystallizer with internal circulation of suspension. Increase in process environment pH from 9 to 11 resulted in 3-time decrease of mean struvite crystals size (from 40.1 to12.6mm). Elongation of mean residence time of suspension in a crystallizer up to 3600 s resulted in improvement of the product quality. Mean size of struvite crystals enlarged up to50.2mm. Based on kinetic calculations results (SIG MSMPR model) it was concluded, that linear struvite crystal growth rate varied within 5.04 × 10–9 – 1.69 × 10–8 m/s range, whereas nucleation rate within 1.4 × 107 – 1.7 × 1010 1/(s m3) limits. In solid product, besides struvite, also all impurities present in wastewater were identified analytically as hydroxides, phosphates and other salts.

Effect of Copper (II) Ions on Quality of Struvite Produced in Continuous Reaction Crystallization Process at the Magnesium Ions Excess

The research results concerning continuous removal of phosphate (V) ions from solutions containing 1.0 or 0.20 mass % of phosphate (V) ions and 0.2 or 0.5 mg/kg of copper (II) ions using magnesium and ammonium ions addition are presented. Continuous reaction crystallization of struvite MgNH4PO4 × 6H2O ran both under stoichiometric conditions and at 20% excess of magnesium ions (pH 9, t 900 s). It was concluded, that presence of copper (II) ions in a process system influenced product quality moderately advantageously. Mean size of struvite crystals enlarged by ca. 6% only. Lower concentration of phosphate (V) ions and excess of magnesium ions caused, that products of ca. 9% - 13% larger crystal mean size (up to ca.40mm) were removed from the crystallizer. Presence of struvite crystals and copper (II) hydroxide were detected analytically in the products (Cu in a product varied from 6 to 90 mg/kg). Presence of copper (II) ions favored crystallization of struvite in the form of tubular crystals.

Impact of calcium on struvite crystal size, shape and purity

Struvite precipitation occurs spontaneously in wastewater treatment plants under conditions that are influenced by many factors including concentration of Mg 2+, NH 4 +, and PO 4 3− ions, pH, temperature, and mixing energy. These parameters are often difficult to control and as a result struvite generates problems of scale deposits in areas such as pipes and recirculation pumps. At the same time, struvite is considered as a potentially marketable product as an alternative fertiliser. For those two reasons, it has become important to study the principles of struvite precipitation, and to assess the parameters controlling struvite crystallisation. In the present work, the influence of Ca 2+ ions on the precipitation of struvite was investigated in aqueous solutions containing Mg 2+, NH 4 +, and PO 4 3− ions in a molar ratio 1:2:2 at room temperature and constant pH. Different laboratory experiments have been used to assess the effects of Ca 2+ ions on size, shape, and purity of the crystals formed. Tools used include particle size analysis, X-ray diffraction (XRD), and scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDS). The experimental results showed that the presence of calcium in the media can affect significantly struvite crystal growth and the characteristics of the crystal produced.