Study On The Prevention And Control Measures Of Groundwater Nitrogen Pollution Of Reclaimed Water Reusing In River And Lake Areas

About ten billions cubic meters of reclaimed water was recharged into groundwater by river-and lake-based reuse every year.When using reclaimed water for natural recharging groundwater,nitrogen pollution might be a potential threat to underground aquifers because the migration and biotransformation of nitrogen in the natural groundwater recharge process are unclear.Therefore,nitrogen might be a potential threat to groundwater quality.The background of this research was based on the project of reclaimed water reuse in Liangshuihe River.The prevention and control measures of nitrogen pollution to groundwater during reclaimed water reusing in river and lake areas were conducted through laboratory soil column leaching experiment.Four columns was operated in the condition of sterilized soil(SS),silty clay(SC),soil with submerged plant(SSP)and biochar amendment soil(BCS).Biochar to amendment soil mixed in BCS system was filled with aquifer soil amended with 1%biochar which was produced by sawdust and straw under 400?,600? and 800? pyrolysis.The pyrolysis of sawdust biochar under 400? was chosen with the highest sorption capacity.The sorption capacity was positively correlated with surface aromaticity and pore size which have been confirmed by the analysis of biochar physical and chemical properties by elemental analysis,surface structure analysis and Fourier transform infrared spectroscopy.The results showed that the attenuation effect of the nitrogen was in the order of BCS>SSP>SC>SS,which followed first-order kinetics.The main attenuation mechanism was sorption and biodegradation.At the initial stage of the recharge,the main removal mechanism was adsorption because the microbial community structure needs to adapt to the reclaimed water quality.At later stages,Biodegradation became the key removal mechanism due to the subdued capability of adsorption and the steadiness of microbial community diversity with increasing depth and operation time.The results showed that the attenuation rate of nitrogen increased with biochar amendment because biochar improved the sorption capacity.454 pyrosequencing of 16s rRNA genes analysis showed that the dominant denitrification population of bacteria was Firmicutes at phylum level,while the main bacterial was Bacillus,Helicobacter,Halomonas,Lactobacillus,Flavisolibacter and the main archaea was Woesearchaeota_DHVEG-6 at genera level.The most important influence environment factor on denitrification is C/N.The diversity of microorganism was improved by biochar amendment which improved the biodegradation of nitrogen.These findings could facilitate the prediction of different type of nitrogen in underground aquifers.In the process of groundwater recharge with reclaimed water through river reuse,the composite bottom layer amendment with biochar might be an effective method to prevent the risk of nitrogen pollution to groundwater.