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: Pilot-scale struvite crystallization tests using anaerobic effluent from potato processing industries were performed at three different plants. Two plants (P1 & P2) showed high phosphate removal efficiencies, 89+/-3% and 75+/-8%, resulting in final effluent levels of 12+/-3 mg PO(4)(3-)-PL(-1) and 11+/-3mg PO(4)(3-)-PL(-1), respectively. In contrast, poor phosphate removal (19+/-8%) was obtained at the third location (P3). Further investigations at P3 showed the negative effect of high Ca(2+)/PO(4)(3-)-P molar ratio (ca. 1.25+/-0.11) on struvite formation. A full-scale struvite plant treating anaerobic effluent from a dairy industry showed the same Ca(2+) interference. A shift in the influent Ca(2+)/PO(4)(3-)-P molar ratio from 2.69 to 1.36 resulted in average total phosphorus removal of 78+/-7%, corresponding with effluent levels of 14+/-4 mg P(total)L(-1) (9+/-3 mg PO(4)(3-)-PL(-1)). Under these conditions high quality spherical struvite crystals of 2-6mm were produced.Water Research 04/2009; 43(7):1887-92. · 4.66 Impact Factor
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ABSTRACT: Phosphate can be recovered as struvite or apatite in fluidised bed reactors. Urine has a much higher phosphate concentration than sludge reject water, allowing simpler (and less expensive) process for precipitation of phosphates. A stirred tank reactor with a special compartment for liquid solid separation was used to precipitate struvite from urine. Magnesium ammonium phosphate as well as potassium magnesium phosphate are two forms of struvite that were successfully precipitated. Liquid/solid separation was very effective, but the compaction of struvite was rather poor in the case of potassium struvite. Crystals did not form clusters and maintained the typical orthorhombic structure. Ammonium struvite had slightly lower effluent phosphate concentrations, but an average of 95% of influent phosphate was removed regardless of ammonium or potassium struvite precipitation. Fluid mechanics is believed to be important and should inform further work.Water Research 02/2007; 41(2):458-66. · 4.66 Impact Factor
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ABSTRACT: The removal of ammonium (NH(4)(+)) and phosphate (PO(4)(3-)) from supernatant of anaerobic digestion by magnesium ammonium phosphate (MAP) formation was studied. To be able to find out the loss of NH(4)(+) by its transformation to NH(3), rates of NH(4)(+) removal by aeration and by MAP formation combined with aeration were compared. NH(4)(+) removal by aeration was found to be insignificant. The kinetics of MAP formation was fast. The removal rate of NH(4)(+) and Mg(2+) was the smallest and the largest, respectively based on rate constants calculated. The removal of NH(4)(+) showed sensitivity to Mg(2+) and PO(4)(3-) concentrations and controlled the purity of MAP precipitate. The removal of PO(4)(3-) was found to be sensitive to mainly Mg(2+) ion. These results also indicated that as the supernatant solution became more saturated in terms of MAP forming ions, the effect of pH increase became insignificant in the removal of ions from the solution.Bioresource technology 08/2009; 100(13):3236-44. · 4.25 Impact Factor