Experimental Study On Removal Of Nitrate In Groundwater With PRB

Problems of groundwater nitrate pollution were increasingly serious, which directly affectedthe use of groundwater as a drinking water source. Permeable reactive barrier (PRB) what wasuse of biological denitrification was an effective method for removal of nitrate in groundwater,the experiment based on the carbon source problem in denitrification, comprehensive study byorthogonal test solid carbon source, temperature, pH and nitrate concentration on denitrifyingeffect of promoting denitrification and on this basis, the flow rate through the column test furtherexamine the impact of denitrification. A simulated biological wall was in series with a simulatedzeolite wall in downstream, in order to explore its influence on denitrification, especially for theabsorption of ammonia. Finally, using the actual groundwater a combination reactor was studiedon groundwater nitrate removal, providing important theoretical basis for In situ remediation ofgroundwater nitrate. The main results are as follows:In the selected factors of denitrification, permeable reactive barrier’s optimal operatingconditions is obtained by four factors and three levels orthogonal experiment, which was at theenvironment temperature of30℃, pH=7, corn stalk and sawdust mixture as the carbon source,influent nitrate concentration is30mg/L, under these conditions, the nitrate nitrogen removaleffect was best, and accumulation of nitrite nitrogen and ammonia nitrogen was at least, it can beapplied to the actual groundwater.Based on the combination it developed a series of column tests.Study on the effect of denitrification with comparing with the filling way of hybrid filler, itturned out mixed filling had obvious advantages with staged filling on the hand of reactioneffect’s last time. In addition, by column experiments of mixed filling it found that the inletvelocity has an important influence on denitrification. When the inlet velocity decreased from150mL/h to90mL/h, the concentration of effluent nitrogen nitrate decreased gradually, and theaccumulation of nitrite nitrogen in denitrification system is at the lowest level, but theaccumulation of ammonia nitrogen only in the flow rate of90mL/h was significantly decreased;when the flow rate increased from90mL/h to210mL/h, the effluent concentration of nitratenitrogen, nitrite nitrogen and ammonia nitrogen increased significantly.Combined reactor which the reaction column was in series a analog zeolite column with theremoval of nitrate nitrogen, accumulation o nitrite nitrogen and ammonia nitrogen, and pH ofreaction system were better than a single bioreactor, and the connection of zeolite column cansignificantly reduce accumulation of ammonia nitrogen, reaction system was more stable. Inaddition, by changing the inlet velocity is50mL/h,90mL/h,70mL/h, it found that in range of90mL/h on the inlet velocity, the influence on removal of nitrate nitrogen, accumulation of nitritenitrogen and effluent pH was small, but it significantly affected the accumulation of ammonia nitrogen in the reaction system, the inlet velocity was smaller, the less accumulation of ammonianitrogen.Taking groundwater in a region of Dalian as a test water reactor showed that nitrate removalof combination reactor is very high, and the effect of removal is very stable, the effluent contentof nitrite can be lower than0.02mg/L, which can reach national "Groundwater EnvironmentalQuality Standards"(GB/T14848-93) Ⅲ water quality standards required nitrite (≤0.02mg/L).Zeolite absorbed ammonia effectively, and has achieved the expected effect of combined reactor.Effluent pH of combination reactor fluctuated between6.8and7.5, which conformed to national"Groundwater Environmental Quality Standards"(GB/T14848-93) I water quality standardsrequired pH (6.5-8.5).