Denitrification Of Eutrophic Water By In Situ Immobilized Nitrobacteria-Denitrifying Bacteria

At present, eutrophication has been serious day by day, so an economic and effective remediation technology is critically needed to solve this problem. This paper tries to make an improvement in this field. Co-immobilized microorganism denitrification and its application of in situ remediation in an entrophic waterbody were studied. The results are as followed:Nitrobacteria and denitrifying bacteria were activated and enriched firstly. During this process, nitrobacteria removed ammonia nitrogen efficiently and the removal rate kept steadily and was above 90% after 23 day cultivation in a given culture medium and conditions. As for denitrifying bacteria, nitrate removal rate was steady-going and up to 90% after 8 week cultivation. Nitrite regressed after a short-lived accumulation in the process, and this is probably related to pH and carbon source. Therefore, more attention should be paid to the experimental conditions of pH and carbon source.Entrapping methods with polyvinyl alcohol (PVA) carrier and sodium alginate (SA) carrier were studied. The results showed that the optimization of immobilization with PVA carrier appeared when concentrations of PVA, SA and active carbon were 7.5%, 0.5% and 1% respectively with 24h crosslink time. And that the optimal conditions of immobilization with SA carrier occurred when the concentrations of SA, active carbon and CaCl2 were 4%, 1% and 4% respectively. Considering the capability of immobilized beads, entrapment with PVA carrier is superior to that with SA carrier as was shown in the experiment.Three kinds of immobilization beads with PVA carrier were made of nitrifying bacteria and denitrifying bacteria at the ratio of 1:1, 2:1 and 3:1 respectively. Then the feasibility of nitrate removal by the three different immobilization beads was studied. The results showed that total nitrogen and ammonia nitrogen removal rates of immobilization beads with ratio of 2:1 were higher than the other two markedly.The denitrification of in situ bioremediation in a eutrophic waterbody by co-immobilized microorganism was studied. The results of field monitoring showed that concentrations of TN and TP ranged from 4.1 to 6.2 mg/L, and 0.12 to 0.18 mg/L respectively, and pH ranged from 8.5 to 9.2, which indicated the water was eutrophic seriously. Three monitoring systems were set up to study the change trend of nitrogen. The control system consisted of surface sediments and the overlying water, and the other two environments made by adding cultivated bacteria and co-immobilized microorganism in the mixture, respectively. The results showed that TN concentration in the control system decreased by 34% (from 14.0 mg/L to 9.2 mg/L), indicating that the waterbody has the self-repairing capability and can keep balance to a degree. As for the other two systems, 5 days later, TN removal efficiency of immobilized beads was 59% whereas that of the cultivated bacteria was 31% merely. 7 days later, NH4+-N removal efficiency of immobilized beads was 98%, while that of cultivated bacteria was a little lower (94%). There was no accumulation of NO3--N and NO2--N in the system of immobilized microorganism, while there was a long-time accumulation of NO3--N and NO2--N in the system with cultivated bacteria.