The Study On The Co-transport Of EPS And Heavy Metals During The Reclaimed Water Underground Storage

Reclaimed water underground storage is an effective way to alleviate water shortages.However,some of the pollutants?such as heavy metals,dissolved organic matter,pathogenic bacteria,etc.?remain after the reclaimed water treated,resulting in potential hazards in the use of reclaimed water.Extracellular polymeric substances?EPS?is an important component of dissolved organic matter in reclaimed water,it has good adsorption effect on heavy metals.Reclaimed water in the process of underground storage will participate in groundwater circulation,EPS can facilitate the migration and transformation of heavy metals,which makes the heavy metals migration and accumulation in the aquifer,and causes pollution in the groundwater.Therefore,it is necessary to study the interaction and co-transport between EPS and Cd²⁺ that can provide important theoretical basis for the prevention of groundwater pollution and the safe storage of reclaimed water.Static adsorption experiments and Column experiments were set up to analysis the composition and content of the main structure of activated sludge EPS,studied the adsorption effect and mechanism of EPS and Cd²⁺,investigated the effect of the ionic strength and ionic composition on the migration and transformation of EPS and Cd²⁺ in aquifer media.The main research results were as follows:?1?Hot NaOH Method was used to extract EPS from aerobic activatedsludge,Chemical analysis method and 3D excitation-emission matrix spectra,FT-IR,ESEM and other instruments were used to study on the change of Cd²⁺ to EPS before and after adsorption.Results show: protein,polysaccharide and humic acid were the main component of EPS.The reaction between the hydroxyl group,amide group and carboxyl group of EPS and Cd²⁺,that made the surface of EPS produced a large number of irregular granular structure after adsorption.When the dosage of EPS was 48mg/L,the adsorption of Cd²⁺ on the EPS reached the maximum adsorption rate.?2?The zeta potential of the mixed solution of EPS and Cd²⁺ values were investigated.NaBr or CaBr2 were used as electrolyte solution,the Zeta potential value of the solution was decreased with the increase of the ionic strength of the electrolyte solution.This was mainly due to the increase of the number of positive charge with the ionic strength,which led to the decrease of the electronegativity of the solution.The ion composition of the solution was characterized by the sodium adsorption ratio?SAR?.Under the same ionic strength,the Zeta potential of the solution increased with the SAR value?The absolute value increases?,because of the decrease of Ca²⁺ concentration lead to the number of positive charges reduced,then enhanced the electronegativity of the solution.?3?Column experiments were used to research the effect of the ionic strength and ionic composition on the co-transport of EPS and Cd²⁺ in aquifer media.The results show that: in the absence of electrolyte,EPS significantlypromoted the migration of Cd²⁺ in aquifer media.Na Br and Ca Br2 were used as electrolyte,the increase of the ionic strength,led to the flow rate of Cd²⁺ was gradually increased and the initial outflow time was gradually advanced in the aquifer media,the promotion effect of Ca²⁺ on Cd²⁺ migration was stronger than that of Na+.Under the coexistence of EPS and electrolyte solution,in the initial stage,EPS inhibited the migration of Cd²⁺ by cation exchange adsorption,but with the continuous injection of EPS solution,EPS cooperated with Cd²⁺ to continue to migrate out of the sand column,and with the increase of ionic strength,the ability of EPS and Cd²⁺ co-transport in the aquifer medium were gradually increased.?4?At constant ionic strength conditions,Na Br and Ca Br2 were used as electrolyte solution,the increase of solution SAR value(the content of Ca²⁺ was decreased),led to the flow rate of Cd²⁺ was gradually reduced and the initial flow time was delayed in aquifer media.When EPS and electrolyte were coexisted,EPS inhibited the migration of Cd²⁺,the co-transport ability of EPS and Cd²⁺ in porous media was weakened when the SAR value of solution was increased.