Study Of Removing Nitrate In Ground Water By Coated Nano Fe~0-Denitrifying Bacteria

Production lifestyles including reclaimed water for irrigation, livestock, landfill etc. pose serious threat to groundwater environment in which pollution of NO3-N have become increasingly prominent. Many studies show that there are still some shortcomings using alone chemical reduction or biological denitrification to restore nitrate in groundwater. Researchers both in and out of China have achieved good results about the nitrate removal by combination of biological and chemical approaches. But, most researchers do not consider environmental factors of groundwater in nitrate removal by biological-chemical method. Based on this, the study used argon to simulate groundwater dissolved oxygen, used cooling water to stay low temperature and coated reactor by foil to keep dark environment of groundwater. The effects of three nitrogen removal systems that are chemical reduction system supported by nano-Fe0, biological denitrification system supported by denitrifying bacteria and collaborative system supported by nano-Fe0-denitrifying bacteria were Compared using laboratory experiments. And the study made further research on nano-Fe0-denitrifying bacteria combined denitrification system through batch experiments and column experiments, the conclusions were following:(1) In the simulated groundwater temperature (15℃), dissolved oxygen (0.50mg·L-1) and dark environment, it derived that oleic acid coated nano-iron-denitrifying bacteria combined denitrification method was best by comparing of degradation of NO3-N and products of the three materials. Removal efficiency of NO3-N in groundwater can reach more than96%, conversion rate of NH4-N was about16%and the main product was gaseous nitrogen in this method.(2) It speculated that the relationship between oleic acid coated nano-iron and denitrifying bacteria was synergy in the process of nitrate removal through analyzing effect of nitrate removal and product. OH-produced by the reaction of coated nano-iron and nitrate provided a suitable pH environment for growth and reproduction of denitrifying bacteria throughout the course of the nitrate removal. H2produced by the reaction of coated nano-iron and water provided electron donor for the autotrophic denitrifying bacteria to ensure the biological denitrification in the biological denitrification stage. Meanwhile, organic acids produced in the process of the biological denitrification promoted the chemical reduction reaction supported coated nano-iron. (3) The study comparing of simulated groundwater temperature (15℃) and laboratory room temperature (25℃)obtained that the removal rate of NO3-N at25℃was18.6%higher than that of at15℃, the generation rate of NH4-N at25℃was13.7%higher than that of at15℃The conversion of NO2-N was affected by light. Convert efficiency of NO2-N under light condition was12.3%lower than that of under dark condition in the process. The initial pH had no significant effect on NO3-N removal efficiency using composite material. And the reaction system itself has a regulatory role for the pH.(4) Simulated environmental factors of groundwater, we found that the removal rate of nitrate in the reaction column packed mixing is higher than that in the reaction column packed layering. The removal rate of NO3-N in mixing column was14.3%higher than that in layering column after6d. Conversion rate of NO2-N in mixing column was12.9%lower than that in layering column, and generation rate of NH4-N in mixing column was27.1%lower than that in layering column. The longer the HRT (hydraulic retention time) was, the better the effect of nitrate removal was. The reason is that the contact time of NO3-N、nano-iron and microbial was long enough to ensure the reaction was full. The removal rate of NO3-N when the HRT was4.72h was31.4%higher than that when the HRT was0.79h after6d.