Characteristics Of Nitrogen In Deyang City And The Study Of Degrading Nitrate

The water and industrial production of Deyang are all dependent on the groundwater,the unreasonable mining and the infiltration of the surface pollutants have resulted in the phenomenon of"three nitrogen"exceeding the standard in many groundwater.The study area is the plain area and the hilly area,based on the study of regional geological and hydrogeological data and 124 groups of groundwater samples（46 groups in plain areas and 78 groups in hilly areas）,the spatial distribution of"three nitrogen"in groundwater in the study area was analyzed by hydrogeology,Piper three line map,Kriging interpolation and Mapgis.A treatment method of Permeable Biological Reactive Geologic Body（PBRGB）is put forward for the groundwater area with high concentration of nitrate pollution in hilly area.And verify its feasibility:（1）Chemical types of groundwater in plain area are mainly HCO₃-Ca、HCO₃-Ca·Mg、HCO₃·SO₄-Ca·Mg、HCO₃·Cl-Ca·Mg,the source of pollution is mainly Petrochemicals;Chemical types of groundwater in hilly area are mainly HCO₃-Ca,the source of pollution is mainly animal husbandry and fishery（cultivation）.The main components of nitrogen in the study area are Nitrate-N.（2）Typical causes of nitrite in the plain area:Under the special groundwater chemical conditions,incomplete partial denitrification leads to nitrite accumulation in local areas;Typical causes of nitrate in hilly areas:Nitrate originates from agricultural,forestry,animal husbandry,fishery（cultivation）pollution sources.Aquifer water chemistry is not conducive to denitrification.（3）The ammonia nitrogen indicators of the study area in the study area all met the standard.The excess area of nitrate and nitrite in the plain area being about 6.56km² and 147.61 km² respectively;The excess areas of nitrate and nitrite in the hilly area were about 479.90 km² and 147.61 km² respectively,and the nitrate concentration in some areas over 100 mg/L,which requires human management.（4）In the reaction medium of PBRGB,the carbon release of solid carbon source with discarded crops is excellent and stable,the release of nitrogen is very low,the dissolved oxygen in water is consumed in a large amount,and the effluent pH and ORP were adjusted,it was an ideal solid carbon source;The reduction performance of zero valent iron is strong,the accumulation of ammonia nitrogen and nitrite in the effluent is high,and the effluent pH is alkalinity.The iron carbon microelectrodes composed of activated carbon and zero valent iron can optimize the performance of the system,which shows the increase of nitrate removal rate and the decrease of the accumulation of ammonia and nitrite.（5）It is feasible to infiltrate the bioreactor to degrade the groundwater polluted by high concentration nitrate in hilly area.Filler mass ratio zero valent iron:quartz sand:activated carbon:solid carbon source=1:1:0.1:0.05,initial nitrate concentration is about 100 mg/L,water flow rate is about 8 L/d,and the height is 40 cm along the distance,the fluctuation range of the nitrate concentration in the effluent is12.36¹8.73 mg/L.The average removal rate of the water quality standard of"groundwater quality standard"is 83.70%,and the pH and ORP in the effluent are in the theoretical optimum range.