Abstract
Phosphate (V) ions were continuously removed from synthetic wastewater containing inorganic impurities using magnesium and ammonium ions. The product was magnesium ammonium phosphate (V) hexahydrate, struvite, MgNH4PO4 × 6H2O. Research ran in stoichiometric conditions in DT MSMPR type crystallizer with internal circulation of suspension. Increase in process environment pH from 9 to 11 resulted in 3-time decrease of mean struvite crystals size (from 40.1 to12.6mm). Elongation of mean residence time of suspension in a crystallizer up to 3600 s resulted in improvement of the product quality. Mean size of struvite crystals enlarged up to50.2mm. Based on kinetic calculations results (SIG MSMPR model) it was concluded, that linear struvite crystal growth rate varied within 5.04 × 10–9 – 1.69 × 10–8 m/s range, whereas nucleation rate within 1.4 × 107 – 1.7 × 1010 1/(s m3) limits. In solid product, besides struvite, also all impurities present in wastewater were identified analytically as hydroxides, phosphates and other salts.
Highlights
Inexpensive and available, secondary phosphorus sources can be industrial, municipal liquid wastes, liquid manure, urine and other waste solutions containing phosphate (V) ions [1]
Based on kinetic calculations results (SIG MSMPR model) it was concluded, that linear struvite crystal growth rate varied within 5.04 × 10–9 – 1.69 × 10–8 m/s range, whereas nucleation rate within 1.4 × 107 – 1.7 × 1010 1/(s m3) limits
Process ran in DT MSMPR type crystallizer of working volume Vw 0.6 dm3
Summary
Inexpensive and available, secondary phosphorus sources can be industrial, municipal liquid wastes, liquid manure, urine and other waste solutions containing phosphate (V) ions [1]. Its course and final results are strongly affected by temperature, concentrations of main reacting substances (phosphate(V), magnesium and ammonium ions), process environment’s pH, reaction crystallization of expected product, and co-precipitating sparingly soluble salts or/and hydroxides of some metals present in wastewaters [1, 4,5,6]. The solution contained, besides phosphate (V) ions, : magnesium, ammonium, aluminium, calcium, copper, iron, potassium, zinc and nitrate (V) ions In this environment sodium and chloride ions were present from dissolved in water crystalline salts from which synthetic wastewater was made. One can compare the presented results with the data concerning struvite production process from solutions containing phosphate (V) ions only, of concentration 1.0 mass % [10]. Influence of pH (from 9 to 11) and mean residence time of suspension in a crystallizer (from 900 to 3600 s) on product crystal size distri-
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