Study On The Combined Remediation Of Pb Contamination In Aquatic Environments By Pb-tolerant Microorganisms And Hydrocotyle Vulgaris

Microbial-phytoremediation is currently one of the main methods for remediating environmental heavy metal pollution at home and abroad.Microorganisms play an important role in improving the cumulative effect of plants on heavy metals,promoting plant growth and reducing the content of heavy metals in the environment.In this study,a Pb-resistant strain was screened,its genus identification,growth and adsorption characteristics and adsorption mechanism were investigated,and a combined remediation strain was identified.The Pb enrichment effect of plants was selected to investigate their physiological and accumulation characteristics under different Pb²⁺concentration stress,to establish a Pb-tolerant microbial-phytoremediation system,to study the effects of Pb-tolerant strains on the physiological and accumulation characteristics of plants under different Pb concentration stress,and to provide theoretical support for the study of combined microbial-phytoremediation of Pb pollution in the water environment.The main findings of this thesis are as follows:（1）A Pb-resistant strain K was isolated from the residual sludge of a secondary sedimentation tank of a wastewater treatment factory in Hefei,and was identified as Klebsiella sp.Strain K achieved 80.01%removal in a medium with 200 mg/L Pb²⁺concentration.The growth adjustment period of K bacteria was 0-15 h,the logarithmic growth period was 15-42 h,the stable period was 42-60 h,and after 60 h it entered the decay period.The optimum growth and adsorption conditions for K bacteria were p H=5,10%of inoculum,30℃and 130 r/min;SEM,EDS and Mapping analysis of K bacteria showed that the morphology of K bacteria strains changed after adsorption of Pb²⁺,the folds disappeared,polymers appeared between the bacterial bodies,the content and distribution position of bacterial constituent elements changed significantly,and the way of Pb²⁺adsorption by strain K bacteria was surface adsorption.（2）After preliminary experiments,it was screened that the enrichment coefficients for Pb in the upper and lower parts of the Hydrocotyle vulgaris were 2.50 and 39.52respectively,and that Hydrocotyle vulgaris was highly enriched for the heavy metal Pb.Hydrocotyle vulgaris grew rapidly under low Pb concentration stress,its relative conductivity and malondialdehyde content increased with increasing Pb concentration,and its pigment,glutathione and antioxidant enzyme activities showed an overall trend of first increasing and then decreasing,indicating that the low Pb environment produced adverse stimuli to plant cells,enhancing tolerance to Pb stress in Hydrocotyle vulgaris by scavenging active oxygen radicals in plants through the initiation of a series of defense mechanisms;as the Pb concentration increased,the peroxidation of plant cells deepened,membrane permeability increased,reactive oxygen radicals accumulated faster than they could be scavenged,and the resistance to Pb stress in Hydrocotyle vulgaris was weakened.（3）With the prolongation of Pb stress time and the increase of stress concentration,the Pb content in the body of Hydrocotyle vulgaris kept increasing while the enrichment coefficient first increased and then decreased,indicating that Hydrocotyle vulgaris has a strong ability to enrich in low Pb environment within a short period of time,but the high Pb concentration led to the accumulation of too much Pb²⁺in the body of Hydrocotyle vulgaris,which inhibited the normal growth and metabolism of the plant,thus affecting its tolerance to Pb and its enrichment ability;the enrichment coefficient of Pb in the underground part of Hydrocotyle vulgaris was much larger than that in the aboveground,indicating that the roots of Hydrocotyle vulgaris have the ability to accumulate Pb efficiently,and the accumulation of Pb in the roots can effectively reduce the Pb content in the environment.（4）In the combined restoration system of Hydrocotyle vulgaris and microorganisms,inoculation with Klebsiella sp.showed little change in leaf water content compared to the uninoculated strain,but the relative conductivity decreased,especially in the high concentration range.As the concentration of Pb stress increased,the chlorophyll content of Hydrocotyle vulgaris leaves increased and then decreased after inoculation with the strain,carotenoid content,antioxidant enzymes and GSH content increased,and MDA content decreased.The enrichment of Pb in the above-and below-ground parts of Hydrocotyle vulgaris increased in the low Pb concentration environment,and the enrichment and translocation capacity was significantly enhanced.The Pb enrichment capacity of the above-ground part of Hydrocotyle vulgaris increased on average by207.47%and that of the below-ground part by 184.27%at Pb²⁺concentrations of 20-40mg/L.The synergistic treatment of Hydrocotyle vulgaris with the K strain improved the enrichment capacity of Hydrocotyle vulgaris in the low Pb²⁺Pb enrichment capacity and Pb²⁺translocation from roots to aboveground parts.Fig[30]Table[15]References[84]...