Study On Ammonia Nitrogenrecovery From Landfill Leachate With Electrochemical Technology

High concentration of ammonia nitrogen in landfill leachate,especially in mature landfill leachate results in difficulties in leachate treatment.At the same time,the recovery of ammonia nitrogen while removal has been attracted more interests.In this paper,the electrochemical magnesium ammonium phosphate?EMAP?technology was used to remove and recycle ammonia nitrogenn from landfill leachate.The influencing factors on ammonia nitrogenn recovery and improvement of ammonia nitrogenn removal efficiency and crystalline purity of MAP were investigated.Given that the NH₄⁺had priorities in migration in electric field,an electrochemical membrane separation system was designed and separate and recycle ammonia nitrogen efficiently.The main conclusions are drawn as follows:?1?In the EMAP treatment system,the recovery rate of ammonia nitrogen reached up to 97.39%after 2.0h reaction under the current density 50mA cm^-2,initial pH=5,n?N?:n?P?=1:1 and 2cm plate spacing.The optimum pH range with high reaction rate and high product purity was about 6⁷.A large amount of Mg²⁺at the initial solution could impact the reaction process of EMAP,but had little effect on the purity of the product.When the concentration of Ca²⁺was not high,the effect on product purity is little.?2?The split adding of dihydrogen phosphate could improve the average generation of MAP crystal,the utilization of phosphate and the purity of MAP products due to the extension of the residence time under the optimal pH.Comparing with the traditional MAP method,the EMAP method in this study had higher ammonia nitrogen removal rate,lower residual phosphorus concentration,and higher purity of products when they were adopted to to treat the practical leachate from a landfill in Chongqing.?3?A bipolar membrane electrochemical separation system was developed.Ammonia nitrogen of 2000 mg L^-1in solution could be almost completely removed and thereafter recycled in alkaline compartment.Variations of operating parameters such as current density or circulating flow rate had different effects on ammonia nitrogen migration.?4?The humic acid?HA?had a slight influence on the migration of ammonia nitrogen in electrochemical membrane separation system.With the coexistence of NH₄⁺,Mg²⁺and Ca²⁺,the average migration rates were NH₄⁺>Mg²⁺>Ca²⁺,and NH₄⁺played a dominant role.It was speculated that cations with relatively low valence or low molecular weight would have higher electromigration rate.In the process of transmembrane migration,Mg²⁺had stronger affinity to exchange groups because of its smaller ion radius which was more competitive than Ca²⁺.?5?Treating actual leachate by electrochemical membrane separation system in3.0h,the ammonia nitrogen in the raw water compartment could bo removed 86.17%and 1mol L^-1acid and base solution could be recovered in the acid and base compartment respectively;On this basis,the system of three-membranes and four-compartments was proposed,which could accelerate the desorption of ammonia nitrogen from the solution phase by using cathode gas;Calcite?CaCO₃?and amorphous Mg?OH?₂ were mainly components in the base compartment side of cation exchange membrane after treatment of actual landfill leachate.Ca²⁺contributed the most to membrane fouling,and the inhibition of Ca²⁺migration by Mg²⁺at the initial stage of system operation could slow down membrane scale.