Application Of Enhanced Denitrification Sand Filter System In Groundwater Treatment

At present,the concentration of nitrate in groundwater in large areas of China is increasing rapidly,it has up to 10 times more than 10 years ago,in many areas groundwater quality does not meet the drinking water quality requirements,local residents can only live by tap water.At the same time water plant water purification pressure is also growing due to nitrogen pollution in groundwater is increasing day by day,increasingly endangering the safety of water in the vast areas,aggravated the burden on the national economy.Nitrate nitrogen in the water is difficult to remove,in large and medium-sized cities remove nitrogen pollution is still very difficult to meet standards,in the conditions of the smaller towns people feel powerless.How to reduce nitrogen pollution and reduce the cost of water purification,is a hotspot in current research.Due to it’s low input,high efficiency advantages infiltration system was exploited by scholars of various countries,constructed rapid infiltration system is one of those treatment that designed for small towns and developed on the basis of land sewage treatment technology.inherited the advantages of traditional sewage land treatment technology having good Removal efficiency to NH₄⁺-N,COD,SS,etc,and increased hydraulic load,improved efficiency.But constructed rapid infiltration system is not so good in removing TN and TP,in the process of nitrogen transformation nitrogen and organic nitrogen were converted to nitrate nitrogen,just from one form to another,TN removal rate is very low.The experiment was carried out to improve the TN removal effect,and the possibility of its application and promotion was analyzed.After the experimental results meet certain requirements,for some areas of water pollution is serious,high quality water and far away from the area,analysis the possibility of apply improved constructed rapid infiltration system to water intake project.At the same time simulated rehydrating the well treated water into the aquifer below the contaminated water,analysis the possibility of reducing the infiltration from high-pollution water to the aquifer and reduce the degree of groundwater nitrogen pollution.In researches we established traditional constructed rapid infiltration system,aim at observing the change of removal effect under the condition of different sewage concentration and different media particle size,analyzing the relationship between removal efficiency and pollutant concentration,pore size of porous media.After that,continue to explore the effects of anaerobic environment and organic carbon source on denitrification,by way of add anaerobic section and organic carbon source to verify that the anaerobic environment and the organic carbon source are conducive to promoting denitrification.The results showed that the anaerobic environment and the organic carbon source could not act independently,only two conditions were met,denitrification could be carried out smoothly.For this reason,we change the process of sewage transport and combine with the theory of shortcut nitrification denitrification,anaerobic ammonium oxidation to increase TN removal efficiency,include the following three aspects.（1）Change the sewage treatment process,let the wastewater pre-leach the anaerobic section to Intercept the organic carbon sources in sewage,the out water will back to the anaerobic section for denitrification after nitrification.Found in the experiment that in this sewage disposal process NO3—N which produced in nitration will be removed in the anaerobic phase by denitrification.However,some ammonia nitrogen can not be removed because of the adsorption of medium prevented partial ammonia nitrogen migrate.The total nitrogen removal rate of this process is 56.61%,the removal rate of ammonia nitrogen was low,only 57.31%.After waste rubber tyre granule was used as anaerobic phase percolation media,the removal rate of ammonia nitrogen and total nitrogen was improved,total nitrogen removal rate up to 69.05%-71.84%,ammonia nitrogen removal rate up to 68.41%-72.09%.How to reduce the adsorption of ammonia nitrogen in anaerobic phase is the key to improve the removal efficiency.（2）Seal the device,and connect the upper part of the device is with a “U” shaped flume,both sides of the “U” shaped flume’s water level will flaot with sewage into and out of the diafiltration system.When one side of the water is completely discharged to the other side,the diafiltration system still has some water in and out,the air in the system will be exchanged with the air in atmosphere through “U” shaped flume,limit the oxygen entering the system during operation,and oxidation will be greatly impaired.However nitrite accumulation rate decreased with the nitrate bacteria gradually adapt to hypoxic environment and denitrification enhanced,but TN removal rate is improved at a appropriate air exchange capacity,the removal rate of total nitrogen was 50%-60% under 1/4 exchange rate,and is likely to be higher at lower exchange capacity.（3）General novel nitrogen removal technologies based on anammox reaction use the NO₂^-produced by short-range nitrification reacts with NH₄⁺ generate N2、H₂O and a small amount of NO₃^-,whether the NO₂^-produced by denitrification can also reacts with NH₄⁺ ? In the high nitrate nitrogen effluent mixed with raw water denitrification research found that there was some ammonia nitrogen in the anaerobic section removed,partial anaerobic ammonium oxidation occurred during TN removal,but the amount of occurrence is very small,accounting for 14.80%-36.63% of TN removal rate.Since NO₂^-is also reduced by nitrite-reducing bacteria during denitrification,in the anaerobic section organic carbon source is sufficient,nitrite-reducing bacteria’s activity is more active,anaerobic ammonium oxide is at an absolute disadvantage.Study how to inhibit the reduction of nitrite to nitrogen,could achieve nitrite accumulation in the process of denitrification,enhance the anaerobic ammonium oxidation,greatly simplifies the nitrogen removal process.Experiments show that,with the help of improved constructed rapid infiltration system could reduce nitrogen pollution levels in the process of taking water and reduce the production pressure of water plan in some areas where water demand is not large but nitrogen pollution is serious.