An experimental design was set up to understand the influence of five process parameters on the k... more An experimental design was set up to understand the influence of five process parameters on the kinetics of struvite precipitation in synthetic swine wastewaters. The responses studied were the kinetics of phosphorus (P) removal, the struvite precipitation rate and the dissolution rate of amorphous calcium phosphates (ACP). The kinetic study showed that the P-removal was complete in less than 1 h and was influenced positively by the added MgO. The precipitation of struvite with MgO was confirmed to follow a first-order kinetic. This study showed that ACP co-precipitated with struvite during the first 30 min. Afterwards, ACP dissolved to maintain the phosphates balance limiting the struvite growth. An initial Mg:Ca > 1.5 induced a complete dissolution of ACP in 1 h. Another experiment was conducted and it validated the results of the statistical model. This experiment also determined that 7-10 h was the best time to recover large crystals. After 10 h, the crystals were broken by stirring.
A sustainable way to recover phosphorus (P) in swine wastewater involves a preliminary step of P ... more A sustainable way to recover phosphorus (P) in swine wastewater involves a preliminary step of P dissolution followed by the separation of particulate organic matter. The next two steps are firstly the precipitation of struvite crystals done by adding a crystallization reagent (magnesia) and secondly the filtration of the crystals. A design of experiments with five process parameters was set up to optimize the size of the struvite crystals in a synthetic swine wastewater. More than 90% of P was recovered as large crystals of struvite in optimal conditions which were: low Mg:Ca ratio (2.25:1), the leading parameter, high N:P ratio (3:1), moderate stirring rate (between 45 and 90 rpm) and low temperature (below 20 °C).These results were obtained despite the presence of a large amount of calcium and using a cheap reactant (MgO). The composition of the precipitates was identified by Raman analysis and solid dissolution. Results showed that amorphous calcium phosphate (ACP) co-precipitated with struvite and that carbonates were incorporated with solid fractions.
An experimental design was set up to understand the influence of five process parameters on the k... more An experimental design was set up to understand the influence of five process parameters on the kinetics of struvite precipitation in synthetic swine wastewaters. The responses studied were the kinetics of phosphorus (P) removal, the struvite precipitation rate and the dissolution rate of amorphous calcium phosphates (ACP). The kinetic study showed that the P-removal was complete in less than 1 h and was influenced positively by the added MgO. The precipitation of struvite with MgO was confirmed to follow a first-order kinetic. This study showed that ACP co-precipitated with struvite during the first 30 min. Afterwards, ACP dissolved to maintain the phosphates balance limiting the struvite growth. An initial Mg:Ca > 1.5 induced a complete dissolution of ACP in 1 h. Another experiment was conducted and it validated the results of the statistical model. This experiment also determined that 7-10 h was the best time to recover large crystals. After 10 h, the crystals were broken by stirring.
A sustainable way to recover phosphorus (P) in swine wastewater involves a preliminary step of P ... more A sustainable way to recover phosphorus (P) in swine wastewater involves a preliminary step of P dissolution followed by the separation of particulate organic matter. The next two steps are firstly the precipitation of struvite crystals done by adding a crystallization reagent (magnesia) and secondly the filtration of the crystals. A design of experiments with five process parameters was set up to optimize the size of the struvite crystals in a synthetic swine wastewater. More than 90% of P was recovered as large crystals of struvite in optimal conditions which were: low Mg:Ca ratio (2.25:1), the leading parameter, high N:P ratio (3:1), moderate stirring rate (between 45 and 90 rpm) and low temperature (below 20 °C).These results were obtained despite the presence of a large amount of calcium and using a cheap reactant (MgO). The composition of the precipitates was identified by Raman analysis and solid dissolution. Results showed that amorphous calcium phosphate (ACP) co-precipitated with struvite and that carbonates were incorporated with solid fractions.
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