Evaluation Of Long-term Operation Of PRB For Remediation Of Ammonia Nitrogen In Riverside Groundwater

Groundwater in riverside areas is an important source of drinking water in northern China,and its quality is strongly affected by surface water.The problem of ammonia nitrogen pollution in surface water caused by human activities has become increasingly prominent,which has gained attention from the public to ammonia nitrogen pollution in groundwater.Aiming at solving the problem of ammonia nitrogen pollution in riverside groundwater in Liguanbao,Shenyang,a remediation demonstration project was taken as an example.According to the monitoring data of PRB operation for many years,this study evaluated the long-term operation effect of PRB from the aspects of reactivity and permeability,and established the corresponding evaluation method.The main results obtained are as follows:(1)The PRB technology demonstration project in the study area has been in operation for 8years.In the early stage of operation,the removal efficiency was maintained at a high level.However,the removal efficiency of ammonia nitrogen in groundwater decreased during the later stage of operation.Due to the operation of PRB,the low DO concentration of the system weakened the nitrification process.And the removal of ammonia nitrogen mainly depend on the adsorption of the zeolite medium,and the reduction of adsorption reaction sites caused media inactivation with the extention of running time,on the other hand.The decrease of PRB permeability coefficient indicates to a certain extend that the accumulation of microorganisms and their metabolites decreased the porosity of PRB media,causing a decrease in the permeability of PRB.(2)Indoor experiments research showed the removal of ammonia nitrogen by natural zeolite mainly relies on adsorption and ion exchange.So it cannot fundamentally remove ammonia nitrogen,while the removal of ammonia nitrogen by biological zeolite mainly relies on ion exchange adsorption coupled with the nitrification of microorganisms.In the process of using PRB to solve the problem of ammonia nitrogen pollution.It can be seen that the removal of ammonia nitrogen in the long-term operation of the PRB was mainly nitrification,followed by adsorption,which can ensure the long-term operation of the PRB.Using the way of continuous dosing of Oxygen-Releasing Compounds(ORC)can enhance the activity of microorganisms,provide a better oxygen supply environment for nitrification.Monitoring results showed that without the addition of oxygen-releasing compounds,the nitrification of PRB is relatively limited.(3)Based on the pollutant removal effect and mechanism,hydraulic performance and microbialactivity,the evaluation methods of long-term operation of PRB have been established.The theoretical operating life of the PRB technology demonstration project is designed to be 10 years,the premise is that oxygen-releasing materials must be added to the oxygen-releasing wells.Since no oxygen-releasing compounds have been added during the current 8 years of operation,while the actual operating life of the PRB was 4 to 5 years.The reason is that oxygen was continuously supplied to the system in column and tank experiment.The main reason for the difference is that the original engineering design parameters must ensure that 75% of ammonia nitrogen is converted into nitrate nitrogen through nitrification.On the contrary,when no oxygen-releasing compounds is added,aerobic ammonia oxidizing microorganisms are not developed,so that only 50% ammonia nitrogen can be effectively converted into nitrate nitrogen in the later operating stage.