Struvite precipitation thermodynamics in source-separated urine

摘要: Abstract Struvite (MgNH4PO4·6H2O) precipitation eliminates phosphate efficiently from urine, a small but highly concentrated stream in the total flux of domestic wastewater. Precipitation experiments with hydrolysed urine evaluated solubility product struvite. The stored and fully had an ionic strength between 0.33 0.56 M required estimation activity coefficients. From our data, we identified Davies approximation two constants A=0.509 B=0.3 as agreeing best laboratory results. standard Ks0=f1[NH4+]f2[Mg2+]f3[PO43−] ([ ]=concentration species; fx=corresponding coefficient) struvite was found to be 10−13.26±0.057 at 25 °C enthalpy formation ΔH 22.6(±1.1) kJ mol−1. equilibrium calculations following dissolved complexes: [MgCO3]aq, [MgHCO3]+, [MgPO4]−, [NH4HPO4]−, [NaHPO4]− lesser extent [MgSO4]aq [NH4SO4]−. Organic complexes do not seem influence substantially. For practical purposes, conditional Kscond=[Mgaq]·[NH4++NH3]·[Portho]=10−7.57 M3 derived calculate 25 °C, pH=9.0 I=0.4 M directly measured concentrations.