Effects Of Rain And Sewage Coupled Influent On The Speciation Distribution Of Heavy Metals In Rainwater Biological Filters

With the acceleration of urbanization,the harm caused by urban rainwater runoff pollution to the water environment has gradually become well known to the public.Based on the LID(Low Impact Development)concept,my country proposes to build a "sponge city" to reduce stormwater runoff pollution.Rainwater biofilters are widely used all over the world as a typical measure of LID.However,due to global warming,the frequency of extreme weather in different regions of our country has intensified,causing damage to the system operation of the rainwater biological filter.In view of the problems of long-term drought leading to the weakening of system performance and the change of the form distribution of heavy metals in the biological filter,a new inflow mode of rainwater biological filter was proposed,that is,the rainwater and sewage coupled alternate inflow.This study compared the rain-sewage coupled alternating inflow and single-mode water inflow,the differences in environmental indicators,heavy metal species distribution and microbial communities in these two influent modes and the different soil depths in the rainwater biofilter before and after reed planting;further The differences in the removal efficiency of heavy metals Cr,Cu and Cd and the similarities and differences in the micro-environmental response mechanisms were compared.The experimental results can provide data support for the coupled-mode water inflow optimization of the rainwater biological filter,which is of great significance for improving the operation of the rainwater biological filter system,long-term use of facilities,and further understanding the internal operating characteristics of the rainwater biological filter system.The main conclusions are as follows:(1)By comparing the existing forms of heavy metals Cr,Cu,and Cd in the rainwater biofilter under the two influent modes,it can be seen that the three heavy metal elements are mainly in the residual state,and their proportion exceeds 80% under all environmental conditions.The model mainly affects the oxidizable and residual states of heavy metals in soil.After reed planting,the Cd concentration in the soil interstitial water of the coupled mode was slightly lower than that of the single mode.Regardless of whether reeds were planted or not,the difference in Cu concentration in soil interstitial water gradually increased under the two operating modes,and the Cu concentration in interstitial water in the single mode was higher than that in the coupled mode.(2)As the operating time of the device increased,the microbial abundance in the device gradually increased.When only reeds were planted at lower temperature,the microbial abundance in the soil of the coupled model was less than that of the single model.Under the condition of planting reeds at low temperature,the ACE index and Chao index of the coupledmode rainwater biofilter reached the maximum,which were 1650 and 1691,respectively.In contrast,the Shannon and Simpson indices are the smallest at 7.2689 and 0.9633,respectively.(3)Compared with the single mode,the coupled model can effectively maintain the soil moisture content in the system,increase the p H of the soil surface,and increase the organic matter content in the system,thereby affecting the oxidizable state and residue state content of heavy metals.The coupled water intake mode has a greater impact on the correlation between the microbial flora and other indicators.Different dominant bacteria genera have certain influence on the correlation of different forms and concentrations of heavy metals Cr,Cu and Cd.