Study On Nitrogen And Phosphorus Absorption And Transformation In Shallow Lakes By Immobilized Composite Microbial System

Lakes are important carriers of surface water resources and have multiple functions in global environmental change,while lake eutrophication can seriously damage lake ecosystems.Therefore,this paper is dedicated to the research of screening highly efficient nitrogen and phosphorus removal microorganisms and mixing them with multiple strains,and then using inorganic mineral carriers to adsorb and immobilize the microorganisms to remove nitrogen and phosphorus from shallow lakes through the coupling of bacteria and minerals.The heterotrophic nitrifying bacteria X-1（Acinetobacter sp.）and X-2（Pseudomonas sp.）were found to be highly effective in removing 92.82%and 84.31%of NH₄⁺-N respectively,and the strains X-1 and X-2 had aerobic denitrification ability.The strains X-1 and X-2 had the ability of aerobic denitrification,while the strains J-3 and J-5 were of the genus Comamonas sp.and the removal rates of TP were 94.73%and 90.25%respectively.The experimental strains were able to grow normally at pH 6-9 and temperature 20-30℃.The adsorption and immobilisation of mixed bacteria by mineral carriers revealed that the calcium wafers and red particles were less negatively charged,which facilitated the immobilisation of microorganisms,and the mixed bacteria were successfully immobilised on the calcium wafers and red particles by SEM and FTIR analysis.3 Among the carrier particles,the red particles had the highest biomass of 3.17×10⁹·g,followed by the calcium wafers.Therefore,the Travertine pellets and the Composite pellets were better as immobilisation carriers.In the experiments simulating the restoration of shallow lakes,the removal of COD,TP,NH₄⁺-N and TN from the overlying water column by the blank group,the bacterial suspension group,the immobilized calcium Chinese particles group and the immobilized red particles group mainly occurred in the first 6 d.The removal rates of TP and NH₄⁺-N by groups Ⅲ and Ⅳ were 91.25%and 90.13%,respectively,and 97.62%and 96.84%,respectively,resulting in sediment volume by 12.03%and 10.32%,respectively.The dominant phyla in the sediment were Amoebacteria and Bacteroides.The addition of immobilized mixed bacteria increased the abundance of Amoebacteria and Bacteroides in the sediment and enhanced the removal of nitrogen and phosphorus in the water column.The analysis of the effect of immobilized composite microbial system on sediment nitrogen and phosphorus fugitive forms showed that the concentration of each fugitive form of nitrogen in the initial sediment was SOEF-N>WAEF-N>SAEF-N>IEF-N,and at the 30th day of the experiment,IEF-N decreased,WAEF-N increased and SAEF-N increased in the sediment after immobilized microorganisms were added.The concentration of phosphorus in the initial sediment was Ca-P>OP>Fe/Al-P,with Ca-P accounting for 61.53%of the TP.In all experimental groups,Fe/Al-P and OP decreased to some extent,and the TP content did not change much.The results show that the immobilised mixed bacteria with Ca-P as a carrier transformed the nitrogen and phosphorus in the sediment into a more stable fugitive form.