Combined Treatment Processes Of Yellow Water: Aiming To Recover Phosphorus And Potassium

Source separation and treatment of yellow water has been considered to bepart of sustainable sewerage system. Aiming to recover phosphorus andpotassium, this study investigated combined processes of nitrogen removal bynitritation/ANAMMOX （anaerobic ammonium oxidation） and nutrients recoveryby crystallization of magnesium potassium phosphate （MPP）.It was found that about90%removal of total nitrogen and ammonium wasachieved through nitritation/ANAMMOX using a sequence batch reactor （SBR）.To avoid the negative effect of urine organic matter on the SBR, a pretreatmentprocess was developed to remove organic matter prior to the SBR. Thepretreatment of yellow water decreased cycle time of the reactor operatingwithout affecting the nitrogen removal efficiency.Crystallization and thermodynamic characters of MPP were then studied.Solution pH and Mg:K:P molar ratio are the key factors influencing the recoveryof phosphorus and potassium. The co-crystallization of magnesium ammoniumphosphate, MPP and magnesium sodium phosphate （MSP） was confirmed viathe analysis on an X-ray diffractometer. The solubility products and standardmolar enthalpy change of reaction of MPP and MSP were calculated to be4.9×10^-13and2.2×10^-12,23.23and22.65kJ/mol, respectively. Based on thethermodynamics, the crystallization in yellow water was modeled and thesimulation was well validated through batch experiments.MPP crystallization was then investigated in a draft tube and baffle reactor（DTBR）. Mixing speed and hydraulic retention time are important operatingfactors that influence crystallization efficiency and crystal settlement. Furtherapplications of the DTBR using real urine showed that about90%K and78%Pwere recycled to multi-nutrient products, respectively.The effect of separation treatment of yellow water on existed wastewatertreatment system was studied via modeling using BioWIN. It was found that thetreatment of yellow water reduced the cost for constructing and operating anexistent wastewater treatment plant, and also decreased the emission of nitrogenand phosphorus to aquatic environment. Nutrients recovered from yellow water had a small contribution to phosphorus fertilizer production, but was valuable inimproving self-supplying of potassium fertilizer for China.