The Experiment Research On The Problem Of Secondary Pollution Of Biological Denitrification In Groundwater

With the rapid development of industry and agriculture, different degrees of groundwater contamination appear. Among all those contaminations, nitrogen pollution is the most serious. Many techniques and methods of pollution control of the nitrate in groundwater have been reported at home and abroad. Biological denitrification has been the focus due to its high efficiency and low energy consumption. Yet there are still problems of traditional bioremediation such as secondary pollution of water, easy to plug of the aqueous medium, N2 O gas pollution.There are sereral secondary pollution problems in the known groundwater nitrate bioremediation process, such as the accumulation of nitrite, carbon source surplus, ammonia formation. Secondary pollution causes and means of prevention and control of bio-remediation of nitrate have been studied in this paper, whose solid-phase organic carbon carrier is walnut shell. The aim is solve the secondary pollution problems during the process.Firstly, to control the nitrite accumulation appeared in the bioremediation,shake flask test has been used. So as to analyze the nitrate nitrogen and nitrite nitrogen removal rate and phosphorus source effect in the system in which nitrate and nitrite are the main electron acceptors. And then nitrite accumulation influencing factors during the denitrification can be probed. The results show that: both carbon and phosphorus sources are the key factors affecting the nitrite accumulation in the denitrification process. Competitiveness of the nitrate-reducing bacteria on the carbon source is strong than that of nitrite-reducing bacteria when carbon source is not enough. And nitrites accumulation can be seen. Ceteris paribus the denitrification rate when phosphorus is added is 1.16 and 1.23 times than when it is not in the system whose main electron acceptors are nitrate and nitrite.Secondly. nitrate pollution bioremediation stage and water attenuation stage are simulated separately via two plexiglass columns in series. Secondary pollution causes in the repair process and natural attenuation law of secondary pollutants in water has been analyzed while walnut shell is used as solid-phase carbon sourcecarrier. Thus we can analyze the migration and transformation of nitrogen during the whole process. Study shows that, it is the best when water CODMn value is 15-30mg/L. While ensuring nitrate nitrogen removal rate, the subsequent nitrite nitrogen naturally decays to a safe concentration. Ammonia appears a downward trend although it is not up to standard.Finally, Comprehensive analyzing of the shake flask test and column test data,secondary pollution prediction and control means of nitrate pollution bioremediation are explored while walnut shell is used as solid-phase organic carbon carrier. From discussions, we can predict secondary pollution generation and its pollution level via permanganate index and nitrate nitrogen concentration of the periodic testing denitrification segment water. When effluent nitrite concentration is too high, natural attenuation should be made when the effluent nitrogen ratio of the denitrification is 1,whereas suitable carbon source control should be considered when it is less than 0.5.