Aquaculture Wastewater Treatment Based On Magnesium Tailings With Bipolar Membrane Electrodialysis Technology

Aquatic products are one of the sources of human protein and an important part of food security.China has been the world’s largest aquaculture country.Residual feed and fish metabolism produce a large amount of nitrogen（N）and phosphorus（P）in the process of aquaculture,resulting in serious water pollution.At the same time,magnesium tailings contain a large amount of magnesium resources,it will cause a waste of resources if it’s not used effectively.In this paper,bipolar membrane electrodialysis（BMED）is used to in-situ acid leach Mg²⁺from magnesium tailings to treat N and P in aquaculture wastewater,and to recover magnesium ammonium phosphate（MAP）,so as to achieve aquaculture wastewater treatment and solid waste recycling.The specific research contents are as follows:Firstly,the treatment performance of aquaculture wastewater by BMED were studied.The effects of electrolyte composition,magnesium tailings dosage,current density and quantity of wastewater on the removal of N and P were investigated.The results showed that when the initial acid concentration increased to 0.3 mol/L,the leaching rate of Mg²⁺increased 34.0%and the removal rate of P increased 111.2%.The removal rate of N and P can be significantly improved by increasing the tailings dosage.When the current density was increased to 12.5 m A/cm² and treated for 5 hours,the removal rates of N and P were increased to 51.3%and 99.2%respectively.Under the optimum treatment conditions,the P and N removal rates reach 98.9%and 53.4%respectively.Secondly,the treatment performance of BMED under multiple batch experiment was investigated.The results showed that the concentration of H⁺in the tailings chamber increased from 0.19 to 0.26 mol/L with the increase of experimental batches,which slowed down the p H rise rate of wastewater,extended the treatment time from 12 h to 20 h,and increased the energy consumption from 0.043 to 0.068 k W·h·m^-3.XRD and elemental analysis of the precipitates showed that the three batches of precipitates were of high purity MAP,with purity of 87.6%,77.8%and 95.7%,respectively.After the experiment,the leaching rate of Mg and Ca in tailings was 62.4%and 99.2%respectively.Apply the multiple treatment units of BMED to treat aquaculture wastewater.The results showed that increasing treatment units and initial p H of wastewater could significantly shorten the treatment time.When 3 tailings chambers were connected in series,the removal rates of N and P were 49.2%and 99.7%,respectively,and the treatment time was shortened from 12 hours to 8 hours.Increasing the initial p H of wastewater to 8,the treatment time continued to be shortened by 3 hours.However,multiple treatment units of BMED can increase Ca²⁺leaching and reduce struvite purity.The results of applying BMED uses magnesium tailings to treat actual aquaculture wastewater showed that the removal rate of N and P can reach 35.3%and 98.9%after 5 hours treatment.This paper provides a new way for the simultaneous treatment and recycling of magnesium tailings and aquaculture wastewater,and lays a foundation for its application in aquaculture wastewater treatment.