纳米Fe_(3)O_(4)/生物炭促进红壤性水稻土中六氯苯厌氧脱氯作用研究

Study on the Anaerobic Dechlorination of Hexachlorobenzene in Hydragric Acrisols Promoted by Nano-Fe_(3)O_(4)/Biochar

为明确磁铁矿(Fe_(3)O_(4))与生物炭对厌氧土壤中六氯苯(HCB)还原脱氯降解的影响及其机理,首先制备并表征了纳米Fe_(3)O_(4)、生物炭及纳米Fe_(3)O_(4)/生物炭复合材料,采用红壤性水稻土的泥浆进行厌氧培养试验,分析反应体系的pH、Eh、吸附态和溶解态Fe(Ⅱ)与HCB脱氯降解过程之间的内在关系。结果发现,灭菌对照处理的HCB脱氯降解作用很弱,表明HCB还原脱氯主要在微生物的作用下进行;添加生物炭可通过降低土壤的酸性、增强反应体系的还原性且促进生成吸附态Fe(Ⅱ)而加速HCB还原脱氯降解;纳米Fe_(3)O_(4)促进HCB还原脱氯的效果较生物炭更强,主要归因于添加纳米Fe_(3)O_(4)使反应体系中生成更多的吸附态Fe(Ⅱ);纳米Fe_(3)O_(4)/生物炭复合材料促进HCB还原脱氯的效果较纳米Fe_(3)O_(4)更强,是因为Fe_(3)O_(4)/生物炭复合材料的比表面积更大且纳米Fe_(3)O_(4)的分散性更好,更有利于反应体系中的电子传递过程。因此,与纳米Fe_(3)O_(4)和生物炭相比,纳米Fe_(3)O_(4)/生物炭复合材料是一种更加理想的HCB污染土壤的修复剂。

【Objective】Reductive dechlorination is a key pathway for the degradation of hexachlorobenzene(HCB)which is a persistent organic pollutant.In anaerobic paddy soils,magnetite(Fe_(3)O_(4))can enhance the direct dechlorination under the action of iron-reducing bacteria and their interacting microorganisms which have a dechlorination function.The process is characterized by an increased electron transfer rate and enhanced chemical reductive dechlorination of organic chlorinated pollutants by an acceleration in the production of adsorbed Fe(Ⅱ),which is an effective electron donor.To improve the dispersity of Fe_(3)O_(4),this study attempted to load nano-Fe_(3)O_(4)onto biochar and then clarified the effect of nano-Fe_(3)O_(4)/biochar composite material on the reductive dechlorination of HCB in anaerobic paddy soil and their possible mechanisms.【Method】First,nano-Fe_(3)O_(4),biochar and nano-Fe_(3)O_(4)/biochar composite materials were prepared,and their surface morphologies,crystal structures,and characteristic functional groups were characterized.Then,the anaerobic incubation experiment was conducted in slurry systems with Hydragric Acrisols as the tested soil.The internal relationships between pH,Eh,adsorbed or dissolved Fe(Ⅱ),and the HCB dechlorination process in the reaction systems were analyzed.【Result】Results showed that the dechlorination degradation of HCB was negligible for the sterilized control treatment,indicating that the reductive dechlorination of HCB was mainly completed by microorganisms.The addition of single biochar accelerated the reductive dechlorination of HCB by increasing soil pH,enhancing the reducibility of the reaction system,and promoting the formation of adsorbed Fe(Ⅱ).The addition of exclusive nano-Fe_(3)O_(4)presented a stronger effect on promoting the reductive dechlorination of HCB than the addition of biochar alone.This was mainly because nano-Fe_(3)O_(4)could significantly enhance the production of adsorbed Fe(Ⅱ)through dissimilatory Fe reduction and adsorbed Fe(Ⅱ)as an effective electron donor to accelerate the chemical reductive dechlorination of HCB.Also,the application of nano-Fe_(3)O_(4)/biochar composite material presented a stronger effect on promoting the reductive dechlorination of HCB than the single nano-Fe_(3)O_(4).This was attributed to the larger specific surface area of nano-Fe_(3)O_(4)/biochar composite material and better dispersity of nano-Fe_(3)O_(4)on the biochar surface.This was more beneficial for the electron transfer process in the reaction system relative to the exclusive nano-Fe_(3)O_(4)application.【Conclusion】In conclusion,the nano-Fe_(3)O_(4)/biochar composite material was a more efficient remediation additive for HCB-contaminated soil compared with single nano-Fe_(3)O_(4)and biochar.In the future,the nano-Fe_(3)O_(4)/biochar composite material can be promoted and applied in the remediation and treatment of polychlorinated organic pollutants.