Recovery Of Nitrogen,phosphorus And Potassium From Urine By Hollow Fiber Membrane Contactor Integrated With Potassium Magnesium Phosphate Crystallization

More and more attention has been paid to energy and resource recovery in sewage treatment.Urine wastewater contains large amounts of nitrogen,phosphorus and potassium.If it can be recycled,it can not only reduce the pressure of nitrogen and phosphorus removal in sewage treatment plants,the load of nitrogen and phosphorus pollution in surface water but also supplement the demand for fertilizers to a certain extent.Based on this,this study proposed the hollow fiber membrane contactor?HFMC?integrated with potassium magnesium phosphate?Mg KPO₄,MPP?crystallization technology to recover nitrogen,phosphorus and potassium in the urine,which is of considerable significance to the construction of nutrient recovery technology for human urine.Firstly,the effects of stripping acid types?H₃PO₄,H₂SO₄ and HNO₃?on the ammonia recovery efficiency and fertilizer components of HFMC were studied.The results showed that the ammonia recovery efficiency is the best when using H₂SO₄ as the stripping solution,followed by H₃PO₄ and HNO₃.The fertilizer analysis results showed that only single-component liquid fertilizer containing N could be obtained when H₂SO₄ and HNO₃ were used as stripping solution,while N-P compound liquid fertilizer could be achieved when H₃PO₄ was used as absorption solution.To obtain N-P compound liquid fertilizer,H₃PO₄ was used as the stripping solution for further investigation.Operating parameters were optimized.The results showed that when the hydraulic residence time was 16 h,the ammonia recovery was the best and the value was 88.47±0.01%.The concentration of H₃PO₄ had little effect on the ammonia mass transfer,but it affected the fertilizer components.The contents of N and P in the liquid fertilizers obtained at different concentrations of H₃PO₄?1?4M?were 21.29?55.24 g/L and 99.41?284 g/L,respectively,both of which were mixtures of?NH₄?₂HPO₄ and NH₄H₂PO₄.Other ions were all rejected at the feed solution side.With the increase of absorption solution concentration,the proportion of?NH₄?₂HPO₄ in liquid fertilizer gradually decreased,while that of NH₄H₂PO₄gradually increased.Then,potassium magnesium phosphate?MPP?crystallization was studied concerning the effect of magnesium source and Mg:?N+K?:P molar ratio on the recovery efficiency of residual NH₄⁺,PO₄^3-and K⁺in the HFMC effluent.The results showed that when using Mg Cl₂ as the magnesium source and Mg:?N+K?:P equalling 1.3:1:1,the highest recovery efficiency of residual NH₄⁺and PO₄^3-was achieved in the crystallization process,with the recovery rates of 88.26±0.31%and 96.76±0.17%,respectively.And89.52±0.14%of additional Mg²⁺could also be recovered.High concentration of K⁺in the solution effectively inhibited the formation of sodium magnesium phosphate?Mg Na PO₄?.The XRD results of the crystallization products showed that the obtained crystal was a mixture of magnesium ammonium phosphate?Mg NH₄PO₄?and magnesium potassium phosphate?Mg KPO₄?.Mg Na PO₄was not found.Finally,the economy evaluation of nitrogen,phosphorus and potassium recovery using HFMC integrated with MPP was carried out.According to the estimation of the costs and profits,the recovery of N,P and K by HFMC+MPP technology is 1582.351 yuan/m³ urine,which has a certain economic benefit.