An improved computer model of struvite solution chemistry

Wrigley, T.J.; Scott, William; Webb, K.M.

doi:10.1016/0039-9140(92)80190-o

Cited by 9 publications

(10 citation statements)

References 4 publications

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“…Upon mixing salts of magnesium, ammonium and phosphate several ionic and dissolved species are formed in addition to precipitates including struvite. Various researchers have developed mathematical models for struvite precipitation [8,10,13,18,22,23,26]. These models are based on physicochemical equilibrium of the various ionic, dissolved, and solid species.…”

Section: Introductionmentioning

confidence: 99%

Validation and Applications of a Chemical Equilibrium Model for Struvite Precipitation

Gadekar

Pullammanappallil

2009

Environ Model Assess

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Removal of nutrients like nitrogen and phosphorus from wastewater can be accomplished by precipitating these as the mineral struvite (NH 4 MgPO 4 . 6H 2 O). Predicting struvite precipitation potential, yield, and purity is important for designers and operators of reactors for struvite precipitation. In this paper, a mathematical model of this precipitation process is developed using physicochemical equilibrium expressions, mass balance equations for nitrogen, phosphorous and magnesium, and charge balance. The model was simulated to explicitly solve for equilibrium concentrations of eighteen species that included dissolved (three), ionic (ten), and solid (five) species for a given set of initial concentrations of ammonium-nitrogen, magnesium and phosphate-phosphorus, and pH. The model simulations were validated against literature experimental data, which used synthetic as well as actual wastewater, and data from our experiments. The model satisfactorily predicted most data. Struvite fraction in the precipitate ranged from 27% to 100%. The purity of struvite in the precipitate and the pH that maximizes struvite fraction was dependent on the initial concentrations of ammonium, magnesium, and phosphate. Optimum pH and struvite fraction was, respectively, 8.5 and 29.3% for an equimolar mixture of ammonia, magnesium, and phosphate and 9.8 and 98.3% for 10:1.7:3.4 mM ratio. Struvite fraction in the precipitate increased as magnesium became limiting or as ammonia to phosphate ratio increased and magnesium to phosphate ratio decreased. Since the struvite component is only a fraction of the total solids, it is erroneous to report the total precipitate produced as being struvite as is conventionally done.

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Section: Introductionmentioning

confidence: 99%

Validation and Applications of a Chemical Equilibrium Model for Struvite Precipitation

Gadekar

Pullammanappallil

2009

Environ Model Assess

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“…(a) an assumption that precipitation reactions are occurring at sufficiently rapid rates to be 74 effectively at equilibrium Hanhoun et al, 2011; Loewenthal et al, 1995; 75 et al, 1998;Scott et al, 1991;Wrigley et al, 1992) The CCM experiments used a crystallizer (See schematic in Supporting Information) which 148 was a 1.0 L (working volume = 900 mL) Pyrex glass vessel with a glass heating/cooling 149 jacket and a sealed lid with crimp-sealed ports for sensors to minimize atmospheric gas- GA) and is given in Table 1. Seed crystal morphology was examined with scanning electron 207 microscopy (JEOL 2100, JEOL Ltd, Tokyo, Japan) and was found to resemble the typical 208 morphology of calcite with reasonably uniform particle size.…”

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confidence: 99%

A generalised chemical precipitation modelling approach in wastewater treatment applied to calcite

et al. 2015

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 A general kinetic-based model for precipitation has been identified and validated. The model is first order in mineral state and nth order in supersaturation. The model is tolerant to a fast kinetic coefficient, but not a slow coefficient. The kinetic effect of temperature can be corrected with Arrhenius-relationships.  This base model can be applied to multiple simultaneous precipitation reactions. 73(a) an assumption that precipitation reactions are occurring at sufficiently rapid rates to be 74 effectively at equilibrium Hanhoun et al., 2011; Loewenthal et al., 1995; 75 et al., 1998;Scott et al., 1991;Wrigley et al., 1992) The CCM experiments used a crystallizer (See schematic in Supporting Information) which 148 was a 1.0 L (working volume = 900 mL) Pyrex glass vessel with a glass heating/cooling 149 jacket and a sealed lid with crimp-sealed ports for sensors to minimize atmospheric gas- GA) and is given in Table 1. Seed crystal morphology was examined with scanning electron 207 microscopy (JEOL 2100, JEOL Ltd, Tokyo, Japan) and was found to resemble the typical 208 morphology of calcite with reasonably uniform particle size. 210The major elements (Ca, Na) in the synthetic aqueous solution were analysed with ICP-OES The species and components were also used to determine precipitation or dissolution, by Nordstrom et al., 1990;Plummer and Busenberg, 1982). For a given aqueous 289 phase, three conditions exist: 290•   0, the aqueous phase is undersaturated and a mineral solid phase can dissolve 291 into the aqueous phase; 292•   0, the aqueous phase is saturated or at equilibrium; or any time t (a dynamic state variable) (similar to the approach of (Wiechers et al., 1975)) and 308 is the order of the precipitation reaction with respect to supersaturation, , calculated as 309 follows (Nielsen, 1984): 311A non-zero initial condition of    of 1×10 -6 M (which is 0.1 mg.L -1 ) was used to model 312 the dynamic titration experiment that had no seed crystals added (self-nucleating). 314The gaseous species carbon dioxide (CO 2 ) is not considered in this model (only dissolved The only adjustable parameter in the baseline model (Eq. (7) where k cryst,25 is the reference value of k cryst at 25°C (298K), R is the ideal gas constant The objective function J (residual sum of squares) is presented in Fig. 2 and shows that the minutes (never at equilibrium). These results suggest that the precipitation was still

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“…Physicochemical modelling of wastewater has therefore become an important field of research and development during recent times , Lizarralde et al 2015, Maurer et al 1999, Musvoto et al 2000b, Wrigley et al 1992. Currently, there are significant worldwide efforts being invested in addressing shortfalls in physicochemical descriptions in industrystandard models.…”

Section: Figure 11 -Major Physicochemical Processes Occurring In a Tmentioning

confidence: 99%

“…The majority of existing models of chemical precipitation are equilibrium-based (Allison et al 1991, Loewenthal et al 1995, Ohlinger et al 1998, Parkhurst 1995, Scott et al 1991, Wrigley et al 1992). …”

Section: Equilibrium Approach To Precipitation Modellingmentioning

confidence: 99%

“…an assumption that precipitation reactions are occurring at sufficiently rapid rates to be effectively at equilibrium (Hanhoun et al 2011, Loewenthal et al 1995, Ohlinger et al 1998, Scott et al 1991, Wrigley et al 1992 or instead treating them as kinetic reactions in the dynamic state equation set (Maurer et al 1999, Musvoto et al 2000a, van Rensburg et al 2003);…”

Section: Introductionmentioning

confidence: 99%

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Dynamic modelling of minerals precipitation in wastewater treatment

Mbamba¹

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In wastewater treatment, there is an increasing focus on nutrient and energy recovery and a reduction in energy consumption to counter climate change. Because of this, integrated mathematical modelling platforms are required to support plant-wide developments making use of emerging, resilient and environmental-friendly technologies. A reliable model description of a wastewater treatment plant should include both biology and physico-chemistry. However, existing standard models used across the wastewater sector have a biological focus with over-simplified descriptions of important physicochemistry, especially with minerals precipitation which is a very important class of physicochemical reactions.As part of development of a more widely applicable physicochemical framework, this thesis sought to identify a suitable minerals precipitation modelling approach that could give reasonable results in mainstream use with wastewater treatment. This research aim was approached in three steps. Firstly a review of available modelling approaches suggested a simple equilibrium kinetic-based modelling approach could be feasible. This approach was then validated in a simple system of calcite in synthetic solutions using pH titration experiments with the reliable Constant Composition Method (CCM).Further statistical analysis focused on clarifying key environmental factors that influence calcite precipitation to determine whether these are necessary to include in a model. Secondly, the proposed model approach was further tested on different types of wastewater and for multiple parallel precipitation reactions. Experiments included dynamic titration or aeration with synthetic wastewater and real wastewater. Thirdly, the general physicochemical modelling approach was implemented in a plant-wide platform together with standard biological models, namely activated sludge model No 2 (ASM2d) and Anaerobic Digestion Model No. 1 (ADM1). The plant-wide model evaluation compared simulations with real data from a full-scale wastewater treatment plant, and used steadystate, dynamic and scenario analyses to test the model performance.Experimental evidence for calcite precipitating in synthetic aqueous solutions, suggested that minerals precipitation kinetics could be reliably described with a 1 st order dependency on mineral Further testing for multi-species systems in real wastewater indicated that precipitation was dominated by the mineral struvite, forming together with varied and minor amounts of calcium phosphate and some calcium carbonate. Kinetic rate coefficients (kcryst), which were statistically fitted, were generally in the range 0.35-11.6 h -1 with 95% confidence intervals of 10-80% relative.The results confirmed that the baseline model approach provided a statistically good fit of measured pH, dissolved calcium, magnesium, total inorganic carbon and phosphate. With this application, the precipitation modelling approach offered the advantage of only requiring a minimal number of empirical fitted parameters (kcryst values), res...

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An improved computer model of struvite solution chemistry

Cited by 9 publications

References 4 publications

Validation and Applications of a Chemical Equilibrium Model for Struvite Precipitation

Validation and Applications of a Chemical Equilibrium Model for Struvite Precipitation

A generalised chemical precipitation modelling approach in wastewater treatment applied to calcite

Dynamic modelling of minerals precipitation in wastewater treatment

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