| In recent years,urban stormwater management and non-point source pollution control have become research hotspots.As an important low-impact development technology,biological retention systems have considerable application prospects in runoff stormwater control.In order to solve the problems of unstable rainwater purification effect and poor storage performance of traditional biological retention systems,this study uses straw biochar and bamboo biochar as modified fillers to construct biological retention systems ER1 and ER2,and compare them with the traditional biological retention system CR,focused on the infiltration and storage performance of ER1 and ER2 and their rainwater purification effects under different rain-dry-wet alternate periods,influent hydraulic load,and rainfall duration.At the same time,in order to further explore the purification mechanism of the biological retention system,the composition of the microbial community,nitrogen cycle genes and microbial activity were tested.The main research results are as follows:(1)The rain-dry-wet cycle has a significant impact on the nitrate nitrogen removal effect of ER1,ER2,and CR.ER1 has a better rainwater purification effect during the dry-wet cycle.Compared with CR,the average effluent concentration of nitrate nitrogen,ammonia nitrogen,nitrite nitrogen and phosphate of ER1 decreased by 54.75%,45.71%,74.83% and 29.63%.(2)Influent hydraulic load has a significant impact on the effluent concentration of nitrate nitrogen and nitrite nitrogen in the biological retention system.With the increase of hydraulic load,the nitrate nitrogen and nitrite nitrogen effluent concentration of the system will increase,but Influent hydraulic load has little effect on the effluent concentration of ammonia nitrogen and phosphate in the biological retention system.The ER1 with straw biochar as the modified filler has the best rainwater purification effect under different influent hydraulic loads.When the influent hydraulic load is0.3m3/(m2·d),the average nitrate nitrogen,ammonia nitrogen and phosphate The removal rates were 56.7%,92.5% and 88.15%.(3)The results of three-dimensional fluorescence analysis showed that the content of aromatic proteins in ER1 and ER2 increased significantly.The peak fluorescence intensity of tyrosine protein was increased by 72.02% and 42.97% compared with CR,and the peak fluorescence intensity of tryptophan protein was similar to that of CR.Compared with CR,it is increased by 194.24% and 89.95% respectively.As an organic carbon source and aromatic proteins,the biochar is easily degraded and utilized by microorganisms,which promotes the denitrification of the biological retention system.In addition,the peak fluorescence intensity of microbial metabolites in ER1 and ER2 is compared The CR increased by 21.77% and 2.97%,respectively,which indicates that the use of biochar as an external carbon source and loading matrix promotes the growth and reproduction of microorganisms and enhances the microbial activity in the biological retention system.(4)Through high-throughput sequencing analysis,it was found that Pseudomonas,Arthrobacter,Pseudogulbenkiania,Novosphingobium,Comamonas,Hydrogenophaga and other bacteria with denitrification function.As an external carbon source,the biochar promoted the colonization and growth of denitrification bacteria in the system.Compared with CR,the abundance of denitrifying bacteria was significantly increased.(5)Three genes related to the denitrification process,NXRB,NARG,and NIRS,were found in the biological retention system by real-time fluorescent quantitative PCR.Compared with CR,the copy numbers of the three genes in ER1 increased by 7.97 times,1.91 times and 6.62 times.(6)Based on the Hydrus2D/3D platform,the soil water infiltration model of ER1,ER2,and CR is constructed.The simulation results show that the biochar has a significant improvement effect on the infiltration performance of the biological retention system.When the constant head boundary is 10 cm,the average infiltration rate of ER1 and ER2 in the unsaturated infiltration stage are increased by 87.7% and76.23% compared with CR,and the saturated water storage capacity of ER1 and ER2 is increased by 41.94% and 19.35% compared with CR. |
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