| With the progress of society and the development of humans,more and more heavy metals are disorderly discharged into rivers with waste water.These heavy metals are gradually attached on minerals and organic matters and eventually accumulated in the sediments of rivers,causing serious heavy metal pollution of sediments.Chlorapatite(ClAP)has been widely concerned by researchers since it can form stable compounds with lead(Pb),but it has been limited in practical application due to its low solubility,mineral structure and low mobility in sediments.In this regard,the stabilized nano-chlorapatites(PNPs)were successfully synthesized by using various surfactants as stabilizers for Pb immobilization in sediments,and we have also explored the mechanisms about their strengthening behaviors in Pb stabilization.Moreover,in order to investigate the Pb-immobilization-affiliated effect of PNPs on the sediments microenvironment and provide a theoretical guidance for the extensive application of PNPs,we have also researched the impacts of PNPs on physicochemical properties,microbial enzyme activity and microbial community structure in sediment.The specific research works and achievements in this paper include five parts as below:The first part synthesized a new class of nano-chlorapatite(SDS-nClAP)using sodium dodecyl sulfate as a stabilizer for Pb immobilization in contaminated sediment and investigated the effects of SDS-nClAP on Pb speciation and TCLP-leachable(toxicity characteristic leaching procedure)Pb in the sediment.Results showed that the product SDS-nClAP was dispersed uniformly in the solution and the nanoparticles were in a spherical or spheroidal shape with the average diameter ranging from 5 to 10 nm.The stabilization experiment showed that both SDS-nClAP and ClAP could transform the Pb from labile fraction into stable fraction and at the same time decrease the TCLP-leachable Pb in contaminated sediment,which eventually reduce the ecological risk of Pb.In addition,SDS-nClAP could not only effectively promote the transformation of Pb to stable fraction,but also performed better in removing TCLP-leachable Pb in the sediment as compared with ClAP.The change of available phosphorus in the sediment verified the dissolution-precipitation mechanism involved in Pb immobilization,and the change of organic matter suggested that the micro-organisms may play an important role in it.In second part the rhamnolipid stabilized nano-chlorapatites(Rha-nClAP)was successfully synthesized for Pb immobilization in polluted sediment in consideration of the algicidal activity ability of rhamnolipid(Rha).It was found that Rha-nClAP was in an average size of 5-8 nm with smooth spherical shape.Remediation experiment showed that Rha-nClAP was remarkable in promoting the Pb immobilization as compared with SDS-nClAP and ClAP.Furthermore,results demonstrated that the Rha concentration in synthesized Rha-nClAP could greatly influence the remediation efficiency and the highest stabilization efficiency of Pb appeared when the concentration of Rha was close to its critical micelle concentration(25 mg/L).On the other hand,the analysis about the change of available phosphorus revealed that the ClAP could be used more efficiently by the metal after being modified by Rha,which could also decrease the potential risk of eutrophication.The change of organic matter showed that the Rha may have some inner relationships with the behaviors of microbes.The third part investigated the effects of PNPs on physicochemi cal properties of sediment during the Pb remediation.Three kinds of PNPs,including CMC-nClAP(sodium carboxymethyl cellulose),SDS-nClAP and Rha-nClAP,were used for detecting their impacts on pH value,cation exchange capacity,organic matter and total phosphorus.Amendment experiments showed that all the PNPs could effectively reduce the TCLP-leachable Pb in sediment while their effects on physicochemical properties were different from each other.Changes of cation exchange capacity and organic matter in CMC-nClAP and SDS-nClAP treated sediment were highly similar while they were opposite in Rha-nClAP treated sediment,indicating that the different results may mostly related to the properties of the stabilizer since the former were chemical-surfactant and the later was biosurfactant.The influence of PNPs on pH value and total phosphorus showed similar tendency.Correlation analysis showed that PNPs may induce the interactions between TCLP-leachable Pb and physicochemical properties.The fourth part described the effects of PNPs on microbial enzyme activities in sediment.The impacts of PNPs on microbial enzyme activity,including dehydrogenase,phosphatase,catalase,sucrase,urease and protease,were investigated respectively.Results showed that addition of PNPs could rapidly affect the enzyme activities in treated sediment and the activities of dehydrogenase,phosphatase,and sucrase could be significantly enhanced after 45-d treatment while the other three enzymes exhibited no consistent trends.Moreover,there were significant differences in enzyme activities among different PNPs treated sediments.And this may be probably caused by the nano properties of PNPs,the changes of Pb bioavailability and the physicochemical properties of surfactants involved in PNPs.The fifth part studied the impacts of PNPs on microbial community structure in sediments.High-throughput sequencing technology was used to analyze the microbial community diversity,species abundance and structural composition after PNPs amendment in sediments.It was found that PNPs coud increase the abundance of microbial species,change community diversity,and affect the community composition.Moreover,SDS-nClAP could not only enhance the microbial abundance but also improve the species diversity in sediments.Hot maps and relative abundance plots showed that the predominant species(Proteobacteria,Firmicutes and Bacteroides)in the sediment have not been changed after the addition of PNPs while the relative abundance of these dominant species has been affected.Especially for SDS-nClAP and Rha-nClAP treated sediments,in which the relative abundance of Proteobacteria changed obviously.Besides,according to the results of Venn diagram,microbial community structure in the PNPs treated sediments maintained a good homology with the blank group,indicating that PNPs did not completely change the microbial community structure of sediments.For the results of principal component analysis,the microbial community structure of the sediment was slightly affected by CMC-nClAP but greatly affected by Rha-nClAP and SDS-nClAP.In general,those results showed that the influence of PNPs on the microbial community structure was closely related to their stabilization effect on Pb and the properties of surfactants involved in the materials.In this paper,PNPs were synthesized and their immobilization effects on Pb were confirmed.Besides,the mechanism about their strengthening behaviors in Pb stabilization has been explored,presenting a new idea for the treatment of Pb pollution in sediment.In addition,the impacts of PNPs on physicochemical properties,microbial enzyme activity and microbial community structure in sediment were verified,which provide the theoretical guidance for the applications of PNPs. |
PDF Full Text Request