Study On The Repair Of Black Odorous Sediment And The Transformation Of Flora By Calcium Nitrate Under Low Oxygen Regulation

Over the past 40 years of economic reform and open up,China's economy has developed rapidly.A large amount of sewage discharge and waste dumping from industry,agriculture and other sources have caused the river and lake basins in the country to suffer from severe eutrophication,and even black-malodorous water have been formed.The microbial by-products caused by them pollute the surrounding air,which is likely to lead to the outbreak of individual or infectious diseases.The formation of black-malodorous water is rooted in the ecological imbalance of the water caused by excessive pollution intake.Effective technical measures and comprehensive implementation can eliminate the black and smelly phenomenon in a short period of time,but the difficulty lies in the long-term improvement and maintenance of the treated water quality to ensure that black-malodorous water does not rebound.The treatment of black-malodorous water focuses on improving the quality of sediment.Sediment is the"sink"and"source"of various pollutants,so the external emission reduction and internal control of sediment are the basis and premise.Under the guidance and control of policies,external pollution has been basically controlled.While,most of the rebound of black-malodorous water is caused by internal pollution of sediment.Therefore,the internal control of sediment pollution is the key to prevent the black and odorous water rebound.This study focused on the in-situ remediation of black-odorous sediment,combined with a variety of methods to alleviate the internal pollution of sediment.The results showed that during the 30-day experimental period,the integrated treatment group?CN/CFM/LDA?consisting of calcium nitrate?2.5 g?+composite functional microorganisms?1 g?+intermittent low dissolved oxygen aeration?0.1 m³/h,3 h/d?had the best treatment effect on 500 g black-odorous sediment.The??DO?of overlying water and sediment interstitial water in CN/CFM/LDA group increased by 0.36 and 1.5times respectively,and ORP index increased by 1.3 and 3.5 times respectively during the 30-day experimental period.In addition,the degradation rates of??TN?and??NH₃-N?in overlying water of CN/CFM/LDA are 40.1%and 67.4%,respectively.The degradation rates of??COD?and??TOC?are 92.2%and 95.6%,respectively.The removal rates of sediment w?TN?,w?NH₃-N?and w?AVS?are 53.5%,37.1%and94.14%,respectively,and the color gradually changed from dark black to khaki.The results show that low-DO regulation can obviously promote the synchronous removal of carbon and nitrogen in black-malodorous water.The results of static diffusion experiment of nitrogen in sediment showed that the release of nitrogen in sediment increased with the increase of temperature,and the lower temperature was propitious to restrain the diffusion of pollutants.In addition,because the intermediate products such asNO₂-N and NO₃-N compete with each other in the nitrification process of OH^-and sediment under different acid and alkali conditions,the diffusion degree of nitrogen to the water body is different under different acid and alkali conditions,adding calcium nitrate will inevitably transform the nitrate nitrogen into ammonia nitrogen and increase the nitrogen content of the system.According to the distribution trend of NH₄⁺-N and NO₃^--N,sediment forms NH₄⁺-N oxidation area,NH₄⁺-N accumulation area and DNRA reaction area.On the 30th day of the experiment,the average reduction rates of NH₄⁺-N in CN/CFM/LDA group were94%,86%and 88%,respectively,and anaerobic ammonium oxidation or short-range denitrification areas might be formed at the bottom of the sediment to promote the reduction or direct conversion of NO₃^--N to NH₄⁺-N and realize removal.The results of high-throughput sequencing showed that the diversity indexes of Ace,Shannon and Simpson in CN/CFM/LDA changed significantly,which indicated that low-DO regulation reduced the diversity of microbial community in sediment and promoted the transformation of dominant microbial community.A total of 53 phyla were identified in the high-throughput sequencing experiment.Dominant strains from different treatment groups were transformed into Proteobacteria.Among them,the dominant bacterial abundance of CN/CFM-5d,CN/CFM-40d,CN/CFM/LDA-5d and CN/CFM/LDA-40d were 42.40%,37.55%,65.99%and 74.17%,respectively.In addition,Spearman correlation analysis further confirmed that most bacteria are significantly related to changes in environmental factors?including DO,ORP and NH₄⁺-N?.Gradually improved dissolved oxygen conditions indirectly provide a facultative anaerobic environment for Thiobacillus and accelerate the denitrification process.16S functional prediction results show that the decrease of functional abundance of CN/CFM/LDA gene is related to the decrease of microbial community diversity.Low-DO regulation+calcium nitrate repair method can increase the number of microbial key enzymes?92360?during nitrification and denitrification,mediate the growth of denitrifying bacteria,and improve the performance of key enzymes.In addition,fluorescence RT-PCR analysis showed that the total amount of each coding gene in the experimental samples at different periods was much higher than that in the original samples.Pearson analysis pointed out that napA-nirK,nirK-nosZ,narG-nirS and napA-nosZ had significant correlation,and in the whole denitrification process,each step from NO₃^-to NO₂^-,NO and N₂ had a relatively high correlation of reductase genes involved.In general,under the control of Low-DO,calcium nitrate and composite functional microorganisms have good remediation effect on black-malodorous sediment.