Struvite Solubility Research Articles

An attached microalgae platform for recycling phosphorus through biologically mediated fertilizer formation and biomass cultivation

Nutrient management is a global challenge for protecting water bodies from eutrophication and for retaining and sustainably recycling phosphorus within the biosphere. This challenge is especially important for water resource recovery facilities (WRRFs) in jurisdictions that limit nutrient loads in plant effluent. A microalgae-based biofilm platform has been designed, constructed, and tested to remove phosphorus and nitrogen from anaerobic digester (AD) effluent filtrate through cultivating biomass and inducing the precipitation of a mineral called struvite (NH₄MgPO₄ · 6H₂O) using a rotating algae biofilm reactor (RABR). RABRs function by rotating a growth substratum through nutrient rich water and then into the atmosphere, immersing microalgae in both sunlight and water. Photosynthesis is utilized in RABR operation to enhance struvite formation by increasing the pH value within the biofilm through the uptake of carbon dioxide from solution. Measurements of pH trended higher with depth through the biofilm when exposed to light confirming the function of photosynthesis in increasing pH and, as a consequence, struvite formation. In addition, reducing RPM allows more time for water to evaporate through exposure of the biofilm to the atmosphere and provides a management option to exceed struvite solubility product. Struvite precipitation was predicted based on chemical analysis and MINTEQ modeling of ADE, was confirmed using Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy, and quantified by determining ash content. Increase in pH within the biofilm was confirmed as photosynthetic photon flux density increased. While struvite precipitation and removal from wastewater is conventionally accomplished through physicochemical methods, this research is the first report of struvite enhanced formation through algae biofilm-based photosynthesis processes.

Phosphorus removal from wastewater through struvite crystallization in a continuous fluidized-bed reactor: An improved comprehensive model

Promoting a wider application of struvite precipitation for nutrient recovery from wastewaters requires more efficient reactor designs, supported by models that integrate thermodynamic, kinetic and hydrodynamic behavior. The present work addresses the modeling of phosphorus recovery by struvite crystallization in fluidized-bed reactors, revealing discrepancies and errors in the literature and proposing corrections and improvements. A reduced thermodynamic model is presented. The potential of the struvite solubility constant was estimated to be 13.12 < pK < 13.30. Furthermore, a new strategy for a simple and quick estimation of the surface-area specific rate constant ka (1.70 dm/h ≤ ka ≤ 2.19 dm/h) was implemented. The technique involves operating the reactor with liquid in the transient regime as a completely stirred tank and solid-mixed bed in the pseudosteady state. Size distribution simulation results were obtained for different operational conditions using a one-dimensional perfect size classification model for the solid phase and a plug-flow model for the liquid phase.

Fertilizer Potential of Struvite as Affected by Nitrogen Form in the Rhizosphere

Struvite is increasingly considered a promising alternative to mined phosphorus (P) fertilizer. However, its solubility is very low under neutral to alkaline pH while it increases with acidification. Here, we investigated whether supplying ammonium to stimulate rhizosphere acidification might improve struvite solubility at the vicinity of roots and, ultimately, enhance P uptake by plants. Using a RHIZOtest design, we studied changes in soil pH, P availability and P uptake by ryegrass in the rhizosphere and bulk soil supplied with either ammonium or nitrate under three P treatments: no-P, triple super phosphate and struvite. We found that supplying ammonium decreased rhizosphere pH by more than three units, which in turn increased soluble P concentrations by three times compared with nitrate treatments. However, there was no difference between P treatments, which was attributed to the increase of soluble Al concentration in the rhizosphere, which subsequently controlled P availability by precipitating it under the form of variscite-like minerals (predicted using Visual MINTEQ). Moreover, although ammonium supply increased soluble P concentration, it did not improve P uptake by plants, likely due to the absence of P deficiency. Further studies, especially in low-P soils, are thus needed to elucidate the role of nitrogen form on P uptake in the presence of struvite. More generally, our results highlight the complexity of manipulating rhizosphere processes and stress the need to consider all the components of the soil-plant system.

Sustainable Struvite Control Using Carbon Dioxide

AbstractStruvite (MgNH4PO4·6H2O) scaling in wastewater treatment plants causes significant processing issues. Struvite formation can be controlled by acid addition since struvite solubility increas...

A probabilistic approach to modeling struvite precipitation with uncertain equilibrium parameters

The precipitation and accumulation of struvite (MgNH4PO4·6H2O) within anaerobic processes has been a costly problem for wastewater facilities. To anticipate and mitigate struvite buildup, solubility models have been developed that employ equilibria software for the evaluation of equilibrium equations. Unfortunately, these programs run under the assumption that chemical equilibrium constants are single, universally accepted values when, in reality, a wide range of values have been published for these constants.In this study, a struvite solubility model was developed in which the equilibrium constants were treated as empirically distributed variables within a Monte Carlo simulation to understand the effect of uncertainty on precipitation potential over a range of pH (6–8.5), temperature (0–60°C), and ionic strength (0–1M). Using field conditions measured at a struvite-afflicted treatment plant as model input parameters, the resulting uncertainty in the struvite supersaturation ratio was found to be highly consequential, with the 90 percent confidence interval spanning well over an order of magnitude. Additionally, a sensitivity analysis was performed on the model, identifying the third orthophosphate equilibrium constant and the struvite solubility product as the most significant source of uncertainty.

Struvite Precipitation and Phosphorous Removal from Urine Synthetic Solution: Reaction Kinetic Study

Phosphorus, like oil, is a non-renewable resource that must be harvested from finite resources in the earth’s crust. An essential element for life, phosphorus is becoming increasingly scarce, contaminated, and difficult to extract. Struvite or magnesium ammonium phosphate (MgNH4PO4.6H2O) is a white, crystalline phosphate mineral that can be used as a bio-available fertilizer. The main objective of this research is to indicate the most important operating parameters affecting struvite precipitation by means of chemical reaction kinetics. The present study explores struvite precipitation by chemical method under different starting molar ratios, pH and SSR. It is shown that an increase of starting Mg: PO4: NH4 with respect to magnesium (1.6:1:1) strongly influences the growth rate of struvite and so the efficiency of the phosphate removal. This was attributed to the effect of magnesium on the struvite solubility product and on the reached supersaturation Super Saturation Ratio at optimum starting molar ratio and pH. It was also shown, by using chemical precipitation method that the determined Super Saturation Ratio (SSR) values of struvite, at 8, 8.5, 9, 9.5 and 10 are 1.314, 4.29, 8.89, 9.87 and 14.89 respectively are close to those presented in the literature for different origins of wastewater streams. The results show that SSR , pH, and starting molar ratio strongly influences the kinetics of precipitation and so phosphorous removal to reach 93% removal percent , 5.95 mg/lit as a minimum PO4 remained in solution, and 7.9 gm precipitated struvite from feed synthetic solution of 750 ml . The product was subjected to chemical analysis by means of EDIX-FTIR, SEM and XRD showing conformity with published literature. First-order kinetics was found to be sufficient to describe the rate data. The rates increased with increasing pH and so SSR and the apparent rate constants for the reaction were determined. © 2015 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Influence of tempereature on Struvite precipitation by CO2‐deagassing method

AbstractThe present study explores struvite precipitation by degassing method under different temperature (14.5‐35 °C). It is shown that an increase of temperature does not affect the nucleation kinetics but strongly influences the growth rate and the efficiency of the phosphate removal. This was attributed to the effect of temperature on the struvite solubility and then the reached supersaturation coefficient. It was also shown, by using degassing method, that the determined solubility constant (pKs) values of struvite, at 14.5, 20, 25 and 35 °C are 13.00, 12.82, 12.63 and 13.20, respectively, are close to those presented in the literature. The results show that temperature influences the kinetics of precipitation. First‐order kinetics were found to be sufficient to describe the rate data. The rates decreased with increasing temperature and the apparent rate constants for the reaction were determined. Arrhenius plots yielded a relatively apparent high activation energy Ea = 31.0 kJ·mol–1. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Growth Rate Kinetics for Struvite Crystallization

The crystallisation of struvite is one means of removing phosphate (and nitrogen) from nutrient-rich wastewater. As with all crystallisation processes, the growth rate of the crystals and its dependence on supersaturation is of considerable interest in designing processing equipment Modelling of struvite solubility using the computer package MINTEQA2 showed that struvite exhibits a minimum solubility in moderately alkaline conditions, with increasing solubility in acidic and strongly alkaline solutions, while temperature has only a minimal effect on struvite solubility. To measure the growth rate of struvite crystals, laboratory measurements were conducted in an isothermal batch I L stirred seeded crystallizer. Experiments were performed in aqueous solution at three pH levels (7.5, 8.0 and 8.5) and three temperatures (25, 35 and 40 degrees C) for similar initial ionic concentrations with phosphate being the limiting ion. These conditions were chosen to cover the pH values at which struvite readily crystallises without excessive adjustment of the wastewater pH, and at temperatures typical of many wastewaters. The increase in crystal size with time together with the decrease in the concentration of the ionic species in solution were followed. Rapid crystallisation kinetics were observed in the solution, with growth rates over 20 mu m/min at pH 8.5. A second order dependence of growth rate on supersaturation (as phosphate concentration) was observed, and the growth rate constant increased as pH increased but was insensitive to temperature over the range of conditions used. Results from a 200 L pilot-scale trial of struvite crystallisation at a local abattoir were consistent with the laboratory results.

Temperature impact assessment on struvite solubility product: A thermodynamic modeling approach

This work addresses the problem of phosphorus recovery from wastewater by struvite precipitation, which is chemically known as magnesium ammonium phosphate hexahydrate MgNH 4PO 4·6H 2O. The struvite solubility product values that are reported in the literature were found to vary significantly, from one solution to another and over the range of the experimental conditions as well. The various factors affecting the struvite solubility include pH, ionic strength and temperature. The struvite solubility product is yet a very important parameter to determine the supersaturation ratio. A thermodynamic model for phosphate precipitation is proposed to determine the phosphate conversion rate and the value of struvite solubility product for a temperature range between 15 and 35 °C. This model is based on numerical equilibrium prediction of the study system Mg–NH 4–PO 4–6H 2O. The mathematical problem is represented by a set of nonlinear equations that turns, to an ill-conditioned system mainly due to the various orders of magnitude of the involved variables. These equations have first been solved by an optimization strategy with a genetic algorithm to perform a preliminary search in the solution space. The procedure helps to identify a good initialization point for the subsequent Newton–Raphson method. A series of experiments were conducted to study the influence of pH and temperature on struvite precipitation and to validate the proposed model.

Use of magnesit as a magnesium source for ammonium removal from leachate

Using magnesit (MgCO 3) as a low cost source of magnesium ions in the struvite precipitation for the removal of high ammonium content of leachate was evaluated. Optimum molar concentration and pH conditions were analyzed to minimize the struvite solubility. Since solubility of magnesit in water is low, HCl was used to obtain soluble Mg. Maximum soluble Mg was obtained for the addition of 2 M HCl to the 1 M MgCO 3. Struvite precipitation with magnesit was effective for the removal of ammonium, suspended solid, phosphate and turbidity. Economical evaluation was made comparing the costs of two magnesium sources, MgCl 2 and MgCO 3. The economical analysis has shown that operation cost of struvite precipitation can be reduced about 18% by using MgCO 3 instead of MgCl 2. High salt concentration after struvite precipitation has no inhibitory effect on the anaerobic reactor performance.

A SOLUBILITY AND THERMODYNAMIC STUDY OF STRUVITE

Accumulation of magnesium ammonium phosphate hexahydrate (struvite) on surfaces in contact with wastewater, especially in anaerobic sludge digestion and post-digestion processes, is a widely reported problem in the wastewater treatment industry. The solubility and thermodynamic properties of struvite at different temperatures was studied. Struvite thermodynamic solubility products at temperatures between 10 and 60 °C were determined by variation of solution ionic strength and extrapolation to zero ionic strength, using an appropriate activity coefficient model. The pKsp value of struvite at 25°C was found to be 13.36(±0.07). The pKsp value for a temperature range of 10-60 °C varies from 14.36(±0.05) to 14.01(±0.03) with the minimum value of 13.17(±0.05) at 30°C. The effect of ionic strength, pH and temperature on struvite solubility was also studied. The solubility of struvite determined in deionized water was found to be 169.2 (±4.3) mg l-1 at 25°C, with the maximum value of 212.7 (±3.8) mg l-1 at 35°C. Standard enthalpy of reaction, ΔHγ °, calculated from the average Ksp values for the temperature range of 10-30 °C, was 23.62 Kcal mol-1. An analytical expression for the Ksp as a function of temperature has been developed by fitting experimental data.

Struvite precipitation thermodynamics in source-separated urine

Struvite (MgNH 4PO 4·6H 2O) precipitation eliminates phosphate efficiently from urine, a small but highly concentrated stream in the total flux of domestic wastewater. Precipitation experiments with hydrolysed urine evaluated the solubility product of struvite. The stored and fully hydrolysed urine had an ionic strength of between 0.33 and 0.56 M and required the estimation of activity coefficients. From our data, we identified the Davies approximation with the two constants A=0.509 and B=0.3 as agreeing best with our laboratory results. The standard solubility product K s 0= f 1[NH 4 +] f 2[Mg 2+] f 3[PO 4 3−] ([ ]=concentration of the species; f x =corresponding activity coefficient) of struvite in urine was found to be 10 −13.26±0.057 at 25 °C and the enthalpy of struvite formation Δ H was 22.6(±1.1) kJ mol −1. The equilibrium calculations required the following dissolved complexes: [MgCO 3] aq, [MgHCO 3] +, [MgPO 4] −, [NH 4HPO 4] −, and [NaHPO 4] − and to a lesser extent [MgSO 4] aq and [NH 4SO 4] −. Organic complexes do not seem to influence the solubility product substantially. For practical purposes, a conditional solubility product K s cond=[Mg aq]·[NH 4 ++NH 3]·[P ortho]=10 −7.57 M 3 was derived to calculate struvite solubility in urine at 25 °C, pH=9.0 and ionic strength I=0.4 M directly from measured concentrations.

Exploring the Determination of Struvite Solubility Product from Analytical Results

The solubility of magnesium ammonium phosphate hexahydrate (struvite) was determined in different water and wastewater solutions, by using the analytical results of the solubility tests conducted in the Environmental Engineering Lab at the University of British Columbia. The various factors affecting the struvite solubility such as pH, ionic strength and the temperature of the solutions were also studied in this project. The struvite solubility product values were found to vary significantly from one solution to another and over the range of the experimental conditions as well. For instance, the solubility product (Ksp ) determined at 20°C for anaerobic digester supernatant from the Penticton, B.C. Advanced Wastewater Treatment Plant, was found to vary from 8.46 × 10−15 (pKsp =14.07) to 1.3x10−13 (pKsp =12.89), over a pH range of 6.45 to 8.97; while in the case of distilled water, with the same struvite crystals and at the identical temperature, it was found to vary from 5.21 × 10−15 (pKsp =14.28) to 2.12 × 10−13 (pKsp =12.67) over a pH range of 7.01 to 9.62. These results explore the possible reasons for widely varying struvite solubility reported in the literature. A possible correlation was also developed to correlate struvite solubility product with varying temperature. Furthermore, an attempt was made to establish a correlation between conductivity and calculated ionic strength of the solutions. A significant gap, between the values predicted by the correlation developed in this study and those predicted by the existing correlation, was also observed.

Crystallization of struvite from metastable region with different types of seed crystal

The main feature of this paper was to recognize struvite crystallization in the metastable region of supersaturation. Thermodynamic equilibria of struvite were simulated to identify the minimum struvite solubility limit, thereafter validated by existing thermodynamic modelling packages such as PHREEQC and the derived data from existing struvite solubility curve. Using laser light scattering detection, spontaneous nucleation was identified by the slow increase of pH in a supersaturated solution of struvite. The crystallization experiment, conducted close to the saturation region in metastable zone, initiated struvite growth. The conducted experiment showed that mother crystal (struvite) was more effective as seeds for struvite crystallization.

Predicting struvite formation in digestion

The solubility constant for struvite (MgNH 4PO 4·6H 2O) was measured in formation and dissolution equilibrium experiments. The proposed solubility constant (p K SO=13.26) accurately predicted struvite precipitation in sludge handling facilities at the Sacramento Regional Wastewater Treatment Plant, whereas the solubility constant in common use did not. An improved method was developed for predicting struvite precipitation potential in anaerobic digestion and post-digestion processes. Method improvements include consideration of ionic strength effects on ion activities, magnesium phosphate complexation effects on ion speciation, and an experimentally derived struvite solubility constant. The improved method accurately predicted struvite to be less soluble than predicted by earlier methods.

Effects of choreito and takushya consumption on in vitro and in vivo struvite solubility in cat urine

Abstract Objective To determine the effects of the takushya portion of choreito, a traditional Chinese treatment for urolithiasis, on urine and struvite crystal variables in cats fed diets containing takushya. Sample Population 6 male and 6 female adult cats, all considered to be clinically normal on the basis of physical examination findings, results of CBC, serum biochemical analyses, urinalyses, and urine cultures; and freedom from urolithiasis on the basis of urethrocystoscopic (females) or urethrocystographic (males) findings. Procedure Cats were fed a commercial canned diet supplemented with 0.1-mg of takushya/kg of body weight, or with 0.5 mg of choreito/kg. Diets were fed, using a Latin-square design, to 3 groups of 4 cats (2 male, 2 female) each for 2 weeks, followed by blood and 24-hour urine sample collections. Results Consumption of takushya, which comprises 20% by weight of choreito, was not associated with adverse effects in cats at the amounts provided during the period of study. Moreover, takushya was responsible for most of the effect of choreito consumption on reduction of urine pH, and approximately half its ability to reduce struvite crystal formation in cat urine. Clinical Relevance Alternative treatments for struvite urolithiasis in cats may be feasible. (Am J Vet Res 1997;58:150–152)

POTENTIAL REDUCTION OF STRUVITE FORMATION FROM ANAEROBIC SWINE LAGOON EFFLUENT BY TREATMENT IN CONSTRUCTED WETLANDS

Effluents from both cells of a two-cell anaerobic lagoon system treating flushed swine waste from theUniversity of Missouri Swine Farm were treated in parallel constructed wetlands submerged flow (SF) and free watersurface (FWS). Reductions in magnesium, ammonium, and total phosphorus ion concentrations in the wetlands weremeasured and used to calculate ion activity products (IAP) for struvite and compared to struvite solubility products (Ksp).Comparison of IAPs with Ksps indicated that the wetlands reduced the potential for struvite formation by 54 to 70%. Thereductions were largely due to ammonium losses from the wetlands.

Struvite deposits in pipes and aerators

Struvite created maintenance and operational problems in the Ponggol Pigwaste Plant (PPP) in Singapore a few months after the commissioning of the plant. Struvite growth was studied in the laboratory and in pipes and aerators at the PPP. Struvite solubility and removal with addition of chemicals and physical cleaning have been studied. Sulfuric acid removes struvite cheaper and faster than acetic acid. The struvite crystals are MgNH 4PO 4.6H 2O. A general formula for the prediction of the growth rate and control of deposition of struvite crystals in the shaft section of floating aerators in the aerated anaerobic lagoon (AAL) in the PPP was developed from experimental data.