Experimental Study On In-situ Remediation Of Nitrate Pollution In Groundwater Well Field

Nitrate pollution in groundwater is becoming more and more serious.Drinking groundwater contaminated with nitrate may lead to methemoglobin disease,which seriously affects human health.Therefore,an in-situ horizontal well restoration system was constructed within the laboratory.This system restored groundwater nitrate contamination by means of simultaneous remediation and pumping.Firstly,a column test was constructed to study the effect of C/N on denitrification.When C/N was 2,NO₃^--N has been significantly removed and the by-products NO₂^--N and NH₄⁺-N have been controlled within a reasonable range.Secondly,on the basis of C/N=2 build a radius of100 cm,angle about 25°fan of In-situ Horizontal Well（IHW）repair system.According to different hydraulic load conditions in the experiment,there were four scenarios in the experiment.When the initial concentration of NO₃^--N was 25mg/L and the hydraulic load was 1.30³.90 m³/（m²·d）the removal rate of NO₃^--N after the stabilization of denitrification was all higher than 95%,no accumulation of NO₂^--N and NH₄⁺-N concentrations was observed,and the pH of effluent was stable at about 8.11.When the hydraulic load increased to 5.20 m³/（m²·d）,NO₃^--N continues to increase to more than16m/L without a downward trend,at which time the system lost effective denitrification.The variation range of horizontal well permeability coefficient was 35.64³3.45m/d in the test process.The microorganism particles were reasonably distributed in the whole reaction zone,and the denitrification in the horizontal well did not lead to a great change in its permeability.The analysis of water quality index in aquifer showed that denitrification in horizontal well has no obvious effect on the change of water quality in aquifer.Finally,a one-dimensional kinetic transport geochemical model considering the growth and decay of microbial units was established using PHREEQC software.After the model was calibrated and verified,the hydraulic load of the horizontal well was predicted to be about 4.88 m³/（m²·d）.This IHW repair system has stable and good biological denitrification effect,and the conclusions and parameters obtained in this experiment have certain reference significance for the actual in-situ restoration project.