Nutrient Recovery From Human Urine By Evaporation- Crystallization And Preparation Of Soil Derived Fertilizer

Recovery of nitrogen?N?,phosphorus?P?and potassium?K?from source-separation human urine can reduce the investment and operating cost of wastewater treatment plant,save water resources,improve water eutrophication and promote resource recycling,all of which have good economical,environmental and social benefits.Aiming for complete N,P,and K recovery from human urine,the transformation law of N and P during the storage of human urine as well as the characteristics of N retention during the evaporation-concentration process were studied.Furthermore,the crystallization properties,path and products?Urine derived solid product,UDSP?during the storage and evaporation-concentration process were selective analyzed.The impact factors and optimized strategy of the soil derived fertilizer?SDF?preparation were also investigated.Finally,fertilizer value of UDSP and SDF were preliminary compared and evaluated.The main contents and results of this study were as following:1.The variation laws of pH,EC,N and P of urine collected by clean container?Urine-C?and urine collected by urinal systems?Urine-S?closed stored at 4?,25?and 37?,respectively,were compared,and the conversion principles were also analyzed.The results showed that,urine was stored at the higher temperature,and Urine-S contrasted to Urine-C at the same temperature,pH,EC,NH₄⁺-N were increased and Urea-N,PO₄^3–-P were decreased faster.Increasing of pH,EC and conversion of N in urine were the direct result of urea hydrolysis,and decreasing of PO₄^3–-P concentration was an indirect process for pH rises leading to precipitation.The conversion of N and P in urine were related to collection method and storage temperature,because of urease-producing microbe quantity was influenced at source by the former and the latter affected the activity of urease and urease-producing microbe.2.The effects of initial pH(pH_init.),pH-adjusted acid,and temperature on NH₃volatilization during hydrolysis urine?HU?evaporation process were investigated,and dynamic model of NH₃ volatilization of the above process was developed and _Sensitivity analysis based on the model was also studied.The results showed that pH_init.was the most critical factor for N retention,and the most economical pH_init.was 4 by N retention efficiency analysis of 3 pH-adjusted acids?HCl,H₂SO₄ and H₃PO₄?.The model can accurately predicte change of V_r,[TAN],pH and R'_N-loss during the above process after pH calibratation of the model,and the mean fractional bias between calculated and measured values of them were less than 1%,4%,6%and 7%,respectively.Additionally,the results of GSA and RSA of multiple input parameters revealed that effect factors of the process were ranked as follows:pH>T_liq>v>[TAN].3.Crystallization properties and products during evaporation processes of HCl-4-HU,H₂SO₄-4-HU and H₃PO₄-4-HU were investigated,and crystallization path of the above processes were analyzed by chemical simulation using PHREEQC-3.The results showed that new crystals in HCl-4-HU,H₂SO₄-4-HU and H₃PO₄-4-HU were appeared at CF_V=19.61,CF_V=9.90/19.84 and CF_V=9.90/32.89/47.62,respectively.The main composition of recovered UDSP-Cl,UDSP-S,UDSP-P were 80%NH₄Cl,41%?K,NH₄?NaSO₄·2H₂O and 30%?NH₄?₅?NO₃?₃SO₄,84%NH₄H₂PO₄,respectively.Furthermore,crystallization path during the above three evapoation processes based on PHREEQC simulation were NH₄Cl?CF_V=10.25¹00??NaCl?CF_V=71.43¹00?,NH₄NaSO₄?CF_V=10.25⁵5.56??NH₄Cl?CF_V=20¹00???NH₄?₂SO₄?CF_V=40.45¹00?and NH₄H₂PO₄?CF_V=10.25¹00??NaH₂PO₄?CF_V=38.46⁵5.5??NaCl?CF_V=45.46¹00?,respectively.4.Promotion mechanisms of soil particles?SP?on nutrient crystallization in HU were analyzed and surface adsorption process of SP on NH₄⁺and PO₄^3–were also studies.In addition,effects of temperature,pH-adjusted acid and CF_V on preparating SDF were investigated,as well as preparation strategies of SDF was optimized and fertilizer value of it was also evaluated.The results showed that main mechanisms of surface adsorption on NH₄⁺and PO₄^3–were ion exchange/molecule adsorption with the?Si?OH groups and calcium phosphate precipitation reaction/formation of inner-sphere complexes with?M?OH groups,respectively,and ion exchange between Ca²⁺and Mg²⁺on the surface of SP with NH₄⁺was also promoted the surface adsorption for PO₄^3–.Compared with the CF_V of HU,temperature and pH-adjusted acid were no significant impact on preparation process of SDF,and the higher CF_V could increase urine absorption capacity,saturated water-holding capacity and N retention of SP.Furthermore,concentrated HU was used as nutrient source not only can it promote preparation efficiency of SDF,but also can reduce N loss.The SDF preparated by SP repeatedly and alternatively absorbed H₂SO₄-4-HU and H₃PO₄-4-HU?CF_V=8?has balanced nutrient,high nutrient content,low Cl concentration and suitable pH,which was more suitable for fertilizer in agriculture compared with UDSP.