Biogeochemical Behavior Of Cr In Riverbed Sediment

Sediment is an important part of the river's ecological environment and plays an important role in the process of nutrient supply and migration and transformation of heavy metals in rivers.However,as the final concentration of pollutants,the secondary release of pollutants is harmful to water environment.With the rapid development of industry in Xi'an,Xianyang and weinan of Shaanxi section of Weihe River,the pollution of heavy metals in rivers is obvious,especially in the Xianyang-Xi'an section,where the pollution of heavy metals Cr is serious and the water quality is inferior.Based on the sediments in Weinan and Xianyang sections of the Weihe River,the vertical distribution of Cr in the Weihe River sediments was studied by field investigation,sampling,environmental microbial technology and soil column simulation.The migration and transformation of Cr in the river-sediment system and the main influencing factors were revealed.The results are as follows:(1)Through field investigation,sampling,testing and comprehensive research,it is found that the percentage of TOC,microbial biomass,particle size d < 45 um and clay content in sediments of Xianyang section are slightly higher than those of Weinan section.In addition to the sediments of 5-15 cm in Weinan section,5-15 cm in Xianyang section and 15-25 cm in other layers,Cr in the sediments exceeded the environmental background value.The sediments are weak alkaline and oxidizable,and the pH,Eh,EC,TOC and microbial quantity decrease with the increase of sediment burial depth.Heavy metal Cr migrates and accumulates downward with the increase of vertical burial depth of sediments.There is a significant correlation between Cr and pH,Eh,EC,TOC,microbial biomass,Fe and Mn in sediments.(2)The adsorption and reduction process of Cr(?)in sediments mainly depends on the physical and chemical properties of sediments and microbial action.In batch experiments,when the Cr(?)solution is 8mg/L and the pH is between 7-9,the adsorption and reduction ability of the sediments to Cr(?)increases with the increase of pH.The sediments in 5-15 cm and 15-25 cm layers have good adsorption and reduction ability to Cr(?).In the experiment of microbial acclimation,the optimum concentration of microorganism and Cr(?)is 120 mg/L.The reduction amount of Cr(?)is up to 60 mg/L,and the microbial growth activity is good at this concentration.The microbial tolerance of the sediments in Xianyang 5-15 cm,15-25 cm and Weinan 15-25 cm sediments is good.The reducing bacteria of Cr in sediments are Bacillus cereus,Bacillus subtilis,Bacillus pallidum and Bacillus thuringiensis respectively.The microorganisms in sediments of Weinan are more abundant than those in Xianyang section.(3)In the soil column experiment,the migration behavior of Cr(?)in the sediment-water interface of Weinan and Xianyang is basically the same.The content of Cr(?)and Cr(?)in the sediment-water interface increases rapidly 10 days before the experiment;After 10 days,the contents of Cr(?)and Cr(?)stabilized.After the 24 th day,both the Xianyang and Weinan soil columns release Cr into the water environment,Cr accumulates significantly in the sediments.The release of Cr in Xianyang section was in the form of Cr(?),while that in the sediments in Weinan section was in the form of Cr(?).The adsorption and reduction of Cr(?)by sediments in Xianyang section is stronger than that of sediments in Weinan section.The adsorption of Cr(?)decreases with the increase of burial depth.The adsorption of Cr(?)by sediments in Weinan section is better than that of sediments in other layers except sediments in 5-15 cm layer.(4)The adsorption of Cr(?)in sediments of Weinan section relies on the physical and chemical properties of sediments and microbial action,but the biological action has little influence;there are more microorganisms in sediments of Xianyang section,which have strong migration and transformation effect on Cr(?),but with the prolongation of soil Cr experiment time,the restraining effect of Cr in sediments and water environment reduces the number of microorganisms,and the biological action of chromium(?)is weakened,At this time,the physicochemical action of sediments was mainly relied on.During the adsorption and reduction process of sediment Cr,the deeper the sediment depth,the weaker the physicochemical and microbial effects,the smaller the migration and transformation of Cr,the stronger the migration and transformation effect of Cr(?)by microorganisms than the physicochemical effect.