Research On Removal And Enrichment Of Low-Concentration Ammonia Using Ion-Exchange And Capacitive Deionization

According to the theory and practice of sustainable development,it is increasingly recognized that wastewater treatment plant will be a resource factory.Although there are lots of nutrient and enenrgy in municipal wastewater,an economic and efficient recovery method isn't proposed because of high flow and low concentration in wastewater.The explorations of carbon pre-concentrition technology make it possible to recover energy and resource.Based on the new wastewater treatment of membrane coagulation reactor pre-concentrate wastewater for resource recovery,this paper proposes a way to remove and enrich low-concentration ammonia in membrane filtered water using ion exchange?IE?and membrane capacitive deionization?MCDI?.This paper studies on the feasibility of three techniques to remove and concentrate ammonia including IE,MCDI and MCDI+IE.First,NZ and SAC are selected as ion adsorbent from Natural zeolite?NZ?,modified zeolite?MZ?,strong acid cation exchange resin?SAC?,weak acid cation exchange resin?WAC?.In the dynamic ion exchange colume experiments of NZ and SAC,SAC is easier to desorb and regenerate than NZ,whose regenetatent volume respectively 8 BV and 24 BV,resulting in a higher ammonia concentration.But Ca²⁺and Mg²⁺in wastewater reduce the ammonia absorb capacity of SAC,leading its breakthrough volume decreased from 352 BV to 180 BV.Secondly,this paper studies on the ion selectivity in MCDI deionization process to diminish Ca²⁺and Mg²⁺interference in SAC ion-exchange ammonia enrichment.Calcium and magnesium ion are preferably adsorbed by MCDI in cycle batch experiment.After the pretreatment of 3 MCDI cycles,inflow conductivity reduces from1450 us/cm to 800 us/cm,ammonia removal rate reaches 35%while that of Ca²⁺and Mg²⁺are 65%,leading to ratio of ammonia to total cation increasing which is beneficial to enrichment in IE process.Comparing with IE,MCDI+IE process treats over twice wastewater using same resin and recover 163%ammonia in a regeneration period.At last,the feasibility of MCDI process alone to remove and enrich ammonia is discussed.Ammonia is enriched in electrode desorption solution and avoids high NaCl concentration in enrichment which will reduce difficulty of subsequent recycle treatment.It would be a simple and efficient way to remove and enrich ammonia with better ion selectivity and high er adsorbing capacity in future.From the point of large-scale application in ammonia removal and enrichment in wasterwater,economic cost of MCDI is high result from its low absorption capacity.MCDI+IE process combines advantages of MCDI ion selectivity and IE technology maturity,but with complex system.Although with low ion selectivity,unit equipment investment cost of IE is acceptable.