Physicochemical Treatment Processes Of Yellow Water:Aiming To Recover Nitrogen,Phosphorus And Potassium

Aiming to meet the demand of the implementation of source separation drainage system and recover nitrogen,phosphorus and potassium,this study investigated in situ urine stabilization-evaporation process for non-diluted yellow water treatment in rural areas,and optimized magnesium potassium phosphate hexahydrate crystallization for diluted yellow water treatment in urban areas.The effect of Ca?OH?₂ on urea hydrolysis in non-diluted yellow water was investigated.Ca?OH?₂ could increase the pH of non-diluted yellow water to above12,which could effectively inhibit urea hydrolysis.Thermodynamic model was used to study the stabilization reaction under different conditions.The results showed that Ca?OH?₂ could effectively inhibit urea hydrolysis under all the conditions.The optimal operating parameters were determed as normal temperature and Ca?OH?₂ dosage of 10 g·L^-1.In situ urine stabilization-evaporation reactor was operated.The final solids of the evaporation process were mainly consisted of urea and potassium.The yellow water were quit stable during and the pH maintained above 12 the evaporation process.The decomposition rate of urea would be only 5%if the operating period is one month.When 10 g·L^-1 Ca?OH?₂ was dosed,24.8 g final product of the combined process was yealded from 1 L yellow water,and the recovery effeciencies of N,P and K were 90%,92%,and 98%,respectively.The crystallization process of magnesium potassium phosphate hexahydrate in a stirred reactor was investigated.The crystallization kinetics of magnesium potassium phosphate hexahydrate was measured and the mechanism of feeding and stirring on the crystallization process was analyzed.The maximum crystal size could only reach 63?m.The parameter optimization of stirred reactor had limitations increasing the size of crystals.The crystallization of potassium magnesium phosphate hexahydrate in a fluidized bed crystallizer was investigated.Using the optimized FBR operational parameters,as pH of 10.5,Mg:P molar ratio of 1:1,supersaturation ratio of 3.0,and superficial velocity of 350 cm·min^-1,pellets of high purity?86±2%?with a maximum size of 4 mm were achieved.The removal efficiencies of K and P reached 20³5%and 80⁹0%,respectively.Furthermore,we proposed a kinetic model to describe the pellet growth.The pellet growth rate was determined as G=5.046×10^-9SV^0.88S^1.96.The model combined with mass balance approach could predict P and K removal efficiencies of the FBR well.