| Sediment is the main accumulation library of lake nutrients and the potential source of secondary pollution of eutrophic lake. Nutrients can be released from the sediment into overlying water when outside conditions change, which will lead to a series of major issues like water quality deterioration, algal blooms,fish deaths and ecosystems disorder. Therefore, the study of nitrogen and phosphorus release from eutrophic lake sediment can be of great theoretical and practical value.We tried to find an effective method to inhibitmicrobial proliferation in the water and carried out a research on microbial effect of phosphorus release in sediment. The main results are as follows:(1)40% formaldehyde was added into thesterilized sediments at the rate of 25 ml/kg, which could reduce the total bacterial biomass from 105 CFU/g to 102 CFU/g. The total bacterial biomass in overlying water was less than 100 CFU/m L during the first four days and could not be detectable in the remaining days after adding 40% formaldehyde into the water at the proportion of 10 ml/L. However, the mixed solution of 0.1 mol/L Cu SO4 、0.1 mol/L Cd SO4 and 1.0 mol/L K2 Cr O7 can not inhbit microbial proliferation.(2)The comparison experiment results showed thatabundant microbes could promote the phosphorus release in sediment. When total bacterial biomass was 106 CFU/m L, TP concentration in water increased by 62.1% and TP content in sediment decreased by 19.74%; however, in the sterilization group there was no detectable microbes and the TP concentration in water reduced by 12.3% and TP content in sediment raised by 18.23%.(3)121℃and 60 minutes heat sterilization of sediments could lead to water content increase and p H drop down, but it had no significant impact on organic content and TP content. Absorption of phosphorus in sediments had risen after heat sterilization. Morever the phosphorus adsorption capacity of low organic content of sediment was higher than the rich organic content one.(4)Sediment was sampled from Qingnian Lake in our university and the results showed that the phosphorus absorption and retention rate of this kind of sediment was approximately 75%,which meaned 25% phosphorus would be released after absorption. This indicated the phosphorus adsorption capacity of Qingnian Lake was not very strong, therefore the risk of phosphorus release of sediment woud be quite great. The dynamic experiment revealed that the phosphorus adsorption process of Qingnian Lake sediment could be divided into three phases. During the initial 120 minutes the absorption of phosphous was rapid and the adsorption amount was about 81%; 2 to 8 hours was intermediate phase, which about 96% phosphorus was absorded during this time; 8 to 24 hours was slow phase and phosphorus absorption of sediment was almost saturated.(5)During 35 days we ioculated two cycles of denitrification microbes into the experiment group and the results were as follows: TN was reduced from 11.68 mg/L to 3.05 mg/L; NH4+-N decreased from 9.17 mg/L to 1.35 mg/L; TP dopped from 0.33 mg/L to 0.06 mg/L and SCOD decreased from 40.54 mg/L to 15.56 mg/L.The TN removal rate of overlying water was 73.89% and the organic matter in sediment was reduced 50.9%, 3.3 times as much as the control group.TN removal rate was 3 times as that of control group, and TP increased by 62.5%, two times of control group.The innovative idea “use N to control P”was evidenced as feasible in preliminary. We can eliminate nitrogen pollutants first to reduce microbial activity, which enables phosphorus to be absorded by sediment and reduce phosphorus concentration in water. This idea is different from previous methods such as “controlling P alone” or “controlling N alone”.In conclusion, the research results can deepen our knowledge of microbes’ effect of sediment phosphorus release, and confirm the idea of “use N to control P”. All of these can help the environmental management of eutrophication. |
PDF Full Text Request