Improving the prediction of ammonium nitrogen removal through struvite precipitation.
ABSTRACT 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.
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ABSTRACT: In the present study, struvite decomposition was performed by air stripping for ammonia release and a novel integrated reactor was designed for the simultaneous removal and recovery of total ammonia-nitrogen (TAN) and total orthophosphate (PT) from swine wastewater by internal struvite recycling. Decomposition of struvite by air stripping was found to be feasible. Without supplementation with additional magnesium and phosphate sources, the removal ratio of TAN from synthetic wastewater was maintained at >80% by recycling of the struvite decomposition product formed under optimal conditions, six times. Continuous operation of the integrated reactor indicated that approximately 91% TAN and 97% PT in the swine wastewater could be removed and recovered by the proposed recycling process with the supplementation of bittern. Economic evaluation of the proposed system showed that struvite precipitation cost can be saved by approximately 54% by adopting the proposed recycling process in comparison with no recycling method.Scientific Reports 05/2015; 5:10183. DOI:10.1038/srep10183 · 5.08 Impact Factor
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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 · 2.64 Impact Factor
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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.Bioresource Technology 09/2014; 172C:253-259. DOI:10.1016/j.biortech.2014.09.024 · 5.04 Impact Factor