The Key Influencing Factors On Nitrate Removal With Rice Wine Studied By Batch Experiments

Nitrogen pollution in groundwater has become one of the focus of the prevention in international water pollution currently.It will decline the quality and applicability in groundwater,and harm human health directly or indirectly.Domestic and abroad scholars generally believed that an important reason for nitrate pollution in groundwater was the excessive use and low utilization rate of nitrogen fertilizers.Centering on dissolved oxygen(DO),mass ratio of carbon to nitrogen(C/N),temperature(T)and volume ratio of water and sand(W/S)these four key influencing factors,batch experiments of the nitrate removal from groundwater was conducted in order to understand the influence of the four key factors in the denitrification process.Rice wine was selected as an external carbon source in this study.Through the experimental analysis on various factors,the main conclusions can be obtained as follows:(1)The nitrate removal ratio(NRR)reached 100% on the 5th day under the anaerobic and micro-aerobic conditions,and the NRR reached 99.8% on the 8th day under the aerobic condition.It showed that the degradation of nitrate by microorganisms can be carried out under different DO conditions,and the inhibited effect of DO on the denitrification process was no significant.The average nitrate removal rate under anaerobic,micro-aerobic and aerobic conditions were 22.76 mg/L/d,25.78 mg/L/d and 14.63 mg/L/d,respectively.It showed that the nitrate removal rate was faster and the denitrification effect was the most ideal under lower DO.A significant decrease in the nitrate concentration under the anaerobic condition requires 0.5 days(12 h),which corresponds to 0.1 mg/L of DO,while in the nitrate concentration under the micro-aerobic condition requires 1 days(24 h),which corresponds to1.5 mg/L of DO,and in the nitrate concentration under the aerobic condition requires 1.5 days(36 h),which corresponds to 3.5 mg/L of DO.The starting time of denitrification in three groups can be shown as aerobic group > micro-aerobic group > anaerobic group.It indicated that the presence of DO slightly delayed the initiation of denitrification.(2)Under the anaerobic condition,the nitrogen removal ratio was optimal(reached100%)when the carbon nitrogen ratio was 1.2(C/N=1.2),and there was no accumulation of by-products such as nitrite and acetate.Under the micro-aerobic condition,appropriate value of C/N was between 1.5~2.0,because when C/N=2.0,nitrate was completely removed and nitrite was reduced to 0,but with a small amount of acetate accumulation.However,when C/N=1.5,the nitrate removal ratio decreased,although there was few accumulation of acetate,the removal of nitrite was not thorough enough,and it was just slightly higher than the limit value.Under the aerobic condition,nitrate can be removed effectively(NRR=100%)under the condition of C/N=2.0,and there was no accumulation of by-products,while C/N was reduced to 1.5 or 1.2,nitrate removal was not complete(NRR was only 78.9%~81.0%).(3)The temperature has great influence on denitrification.The three groups of microcosms in the same conditions,running in the water temperature of 25~30?,15~20?,5~10? respectively,denitrification can be carried out in each group,but the nitrate removal rate gradually increased with the increase of temperature.The removal effect of nitrate was the best(NRR=100%)under the condition of 25~30?.The experimental results shown that25~30? was the best denitrification temperature range.(4)The degradation rate of nitrate is faster when there is more sand in the water,which means the removal ratio is higher,and the denitrification effect is more ideal.However,the appropriate W/S is the key to ensure the efficient removal of nitrate in groundwater.The denitrification effect under the condition of W/S=4:1 and W/S=5:1 were significantly better than that of W/S=10:1 and W/S=20:1.Considering the denitrification effect had no significant difference between the condition of W/S=4:1 and W/S=5:1,the application should be based on the good removal effect as the premise,and try to reduce the thickness of sand to get the maximum effective volume.Therefore,W/S=5:1 was promoted in this experiment.