Both an optimization statistical model and a chemical thermodynamic equilibrium computer model were proposed to develop, improve, and optimize struvite precipitation process.
The NH(4)-N in synthetically prepared wastewater was removed using struvite precipitation technology. A quadratic statistical modeling, response surface methodology (RSM), was applied to investigate the improvement availability for high-level removal of ammonium-nitrogen by struvite precipitation. Then, a chemical equilibrium model, Visual MINTEQ, was used to calculate the equilibrium speciation and saturation index in aqueous solution and solid phases. In addition, the availability of Mg(2+), NH(4)(+), and PO(4)(3-) ions as a function of pH was modeled. The predicted and experimental data indicated that the two models might describe the experiments well. The results showed that pH was an important parameter in ammonium-nitrogen removals at low initial NH(4)-N concentration. P/N molar ratio was a limiting factor on struvite precipitation at high initial NH(4)-N concentration.
Within the ranges of the investigated factors, Visual MINTEQ program can be proposed to predetermine the concentration of ammonium precipitated by struvite, and RSM can be used to predict total NH(4)-N removal by both struvite precipitation and ammonia volatilization from our investigated system operated at high pH and opened to the atmosphere.
"Several studies have used these programs to study phosphate precipitation. Wu and Zhou  used Visual Minteq to determine the ammonium precipitation as struvite from a synthetic wastewater. Çelen et al. , Ali et al.  and Lee et al.  used this program to find the conditions that maximize struvite crystallization in liquid swine wastes. "
[Show abstract][Hide abstract] ABSTRACT: Struvite precipitation represents an economical alternative to recover phosphorus from concentrated
phosphate wastewater streams. This process is not only used for removing phosphate from wastewaters
but also generates a product with commercial value as a fertiliser. Nevertheless, the economic viability of
the process depends on the availability of magnesium in the wastewaters or the use of a low cost magnesium
source. Seawater may be used as a cheap magnesium source in order to obtain efficient precipitation.
However, seawater overdosing may cause the formation of different phosphate magnesium or
calcium precipitates. The aim of this study was to determine whether thermodynamics or kinetics rule
the precipitation of multiple phosphates that were observed in a precipitation reactor. A chemical equilibrium
model, Visual Minteq, was used in order to verify which of the two indicated processes governed
phosphate precipitation in a saline wastewater. A good correspondence between the observed and predicted
multiple phosphate precipitates and phosphate concentration in the reactor was found. The nature
of the phosphate precipitates depended on the characteristics of the wastewater and the physico-chemical
reactor operational conditions. This study demonstrates that phosphorus precipitation may be predicted,
making it possible to obtain information about the conditions in which struvite precipitation
can be promoted.
[Show abstract][Hide abstract] ABSTRACT: In this study, phosphate was removed from aqueous solution and recovered as struvite (MAP, MgNH4PO4·6H2O) by fluidized-bed crystallization (FBC) process. The effects of influent pH and Mg/P molar ratio on MAP crystallization were investigated. Thermal analysis and characterization of the MAP crystals collected from the fluidized-bed reactor (FBR) were performed. The kinetics and thermodynamics of the MAP decomposition reaction were determined using the Coats–Redfern method. Experimental results show that the total concentration of phosphate in the fluidized-bed reactor (FBR) increased with influent pH and Mg/P molar ratio. Thermal analysis of MAP decomposition at different temperatures revealed two distinct stages: (1) removal of H2O from the crystal surface and (2) removal of NH3. H2O and NH3 removal were highly endothermic, non-spontaneous and thermodynamically unstable. Low pH and high Mg/P ratio favored the production of more stable MAP crystals. The FT-IR and XRD results verified the formation of magnesium hydrogen phosphate (MgHPO4) by the evolution of ammonium from MAP at temperatures between 200 and 500 °C, and its further conversion to magnesium phosphate oxide (Mg2P2O7) at temperatures greater than 800 °C.
Journal of the Taiwan Institute of Chemical Engineers 09/2014; 45(5):2395-2402. DOI:10.1016/j.jtice.2014.04.002 · 3.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The recovery of the total orthophosphate (PT) and removal of the total ammonia-nitrogen (TAN) from swine wastewater were investigated through a combined technology of using bittern as the magnesium source in struvite precipitation along with internal recycling of the chlorination product of the recovered struvite. Results revealed that the PT recovery efficiency and the struvite purity was mainly depended on the wastewater pH and the Mg:PT molar ratio. Co-precipitations of Mg3(PO4)2, MgKPO4, Ca3(PO4)2, and Mg(OH)2 (pH>9) were confirmed to be responsible for the decrease in the purity of struvite. The decomposition of recovered struvite by sodium hypochlorite (NaClO) was feasible. The TAN concentration of the swine wastewater was decreased to 63mg/L by internal recycling of the chlorination decomposition product for seven cycles. An economic evaluation showed that 37% of the treatment cost of the proposed process could be saved as compared with struvite precipitation using pure chemicals.
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