Degradation Of Nitrate In Groundwater By Rhamnolipid Modified Nano-scale Zero Valent Iron/Nano-scale Carbon Composite

Due to the excessive use of agricultural nitrogenous fertilizers,a large amount of sewage above the standards about industrial and life,landfill leachate,groundwater pollution is becoming more and more serious.In our country,more than half of the area of shallow groundwater is polluted by nitrate nitrogen.the process of agricultural production,nitrogen utilization is less than 40%,that is the main cause of nitrate pollution of ground water.In recent years,due to the advantages of wide source,large surface area,strong reducibility,Zero-valent iron nanoparticles often applied as active material in the groundwater pollution remediation.But the zero-valent iron nanoparticles have some characteristic,such as size small,nZVI in water is easy to reunite,lead to from smaller specific surface area,reactivity,mobility.Zero-valent iron nanoparticles are easy to be oxidized,which make the formation of passivation layer.therefore we need to modification of zero-valent iron nanoparticles.So as to reduce the oxidation and reunion of n ZVI,we take the rhamnolipid to modify nZVI and loaded the nano carbon(30-50 nm)on the modified zero-valent iron nanoparticles to further reduce the oxidation and reunion.Among them,the rhamnolipid belongs to the biological surfactant.Compared with chemical surfactant,the rhamnolipid has lower toxicity and good biodegradability;Compared with other load material,nano carbon can reduce the size of the active material,which can easier to migration in groundwater.We evaluate material property though material preparation,removal of pollutants,aging,microbial coupling effect,migration and so on,the concrete research content and results are as follows:(1)The preparation of rhamnolipid modified nano iron/carbon rhamnolipid and optimal dosing quantity of nanometer carbon were 0.03 g,0.28 g.After modification of the load of the nano iron carbon particle size between 120-160 nm,nano carbon load on the nanometer iron composition pattern structure,effectively reduce the phenomenon of reunion.Compared with the unmodified nanometer iron,the X-ray diffraction pattern of nanometer iron carbon materials with less impurity peak,effectively alleviate the nanometer iron oxide.(2)By removing nitrate batch experiments,the rhamnolipid and nano carbon all play significant roles in removing nitrates.Decreasing nitrate initial concentration and increase of nano iron material dosing quantity will promote the nitrate removal;Compared with nano iron,modified nano iron carbon has less effect of the above conditions change.Oxidation-reduction is the main reaction between modified nano iron carbon and nitrate.At the same time,Nanoscale zero-price iron and carbon particles all have adsorption about nitrate.The main product of reaction is ammoniumnitrogen.(3)It was significantly different passivation when the iron materials stored in different mediums.When the samples stored in the ethanol,the removal rate of nano iron,modified nano iron and modified nano iron carbon can reach more than 97%,the next was stored in the water,the worst is stored in the air,removal rate of the nitrate is less than 80%;With the increase of storage time,two kinds of material's ability to remove nitrate are dropped.The removal rate of modified nano iron carbon was more than nano iron.(4)Through the migration of column experiment contrast nano iron and modified nano iron carbon migration effect.Results show that the modified nano iron carbon has significantly higher transmittance,the migration rate was 62.17%,it was as nearly two times as nano iron(nano iron migration rate was 32.00%).(5)we take nano iron materials with denitrifying bacteria to degrade nitrate.Compare different nanometer iron material and microbial coupling effect by observing the reaction process of nitrate nitrogen,ammonia nitrogen,nitrate nitrogen,the change of total nitrogen,analysis of several system denitrification efficiency from big to small in turn for rhamnolipid modified nano iron carbon and microbial coupling system,PVP modified nano iron carbon and microbial coupling system,microorganism,polyvinylpyrrolidone modified nano iron and microbial coupling system.