| Heavy metal pollution widely comes from industrial production,agricultural activities,and municipal sewage.The heavy metal remediation has become a technical problem.Biochar(BC),as one kind of porous carbon materials formed by biomass pyrolysis,can stabilize heavy metals through adsorption,precipitation and other physicochemical effects.However,biochar released a large number of dissolved biochar(DBC),which the composition is more complex,including dissolved organic matter(DOM),anion and cations,nanoparticles and so on.At present,the study about DBC is limited,and its environmental impact is still not clear.In this paper,the physical and chemical properties of BC,washed biochar(WBC),and DBC,along with the interaction and mechanisms of Pb(II)sorption were studied.Moreover,the effect on microbial community structure in Pb(II)contaminated soil was further studied deeply.Pyrolysis temperatures and releasing processes can significantly affect the physicochemical properties of BCs.The low-temperature BC and WBC contain abundant hydroxyl groups,carboxyl groups,methylene groups,aromatic structures,etc.,while H/C value(BC:0.07~0.018,WBC:0.061~0.015)decreased as the improvement of pyrolysis temperature.The decrease of the infrared characteristic peaks further indicates the number of functional groups is rapidly decreased and the aromaticity is improved.The increase of pyrolysis temperature also increases the release o dissolution of Al,Ca,Mg,Mn,Na and Si ions from BCs,and improves the alkalinity of BC.BC,differing from WBC,owned more functional groups and higher carbon layer defects(ID/IG values)at the same pyrolysis temperature,while WBC has a larger specific surface area and aromaticity.Compared to BC,the WBC adsorption rate,capacity and pH were all reduced at the same preparation temperature.The differences between BC and WBC was ascribed to DBC,which strongly affected the sorption of Pb(II).Moreover,the increase of sorption performance was found as the increase of pyrolysis temperature.Three-dimensional fluorescence spectroscopy indicated DOM of Typha-derived BC350 was composed of fulvic acid(including 43.36%)and humic acid(including 56.64%),while the binding ability of Pb(II)to fulvic acid is stronger.By adding Pb(II)the DOM concentration of BC350 solution decreased by 51.33%,while the BC800 solution contained almost no DOM,but its pH value rapidly decreased from 10.49 to 8.04 within 7h.The phenomenon indicated that interaction of DBC with heavy metals was resulted from the complexation of DOM at low-temperature,and precipitation due to high pH as high-temperature DBC.Sorption of Pb(II)by BC conformed to the Langmuir isotherm adsorption model and the second-order kinetic model,including physical and chemical adsorption,such as pore adsorption of insoluble carbon skeleton,chelation and complexation between organic matter and heavy metal Pb(II),precipitation of alkaline substances,gravitational interaction caused by surface charge,cation-π bond,and correlation interaction between BC-DBC-Pb.The significantly distinct properties and sorption performance of BC and WBC were found due to the existence of DBC.Thus,the impact of BC,WBC,and DBC on the soil was further identified.The variation and succession of bacterial community in BC,WBC,and DBC-soil containing Pb(II),were studied by high throughput technique.1055 OUT,12 doors,19 classes,60 orders,103 families,19 families and 261 species were affirmed,while the Shannon,Ace,and Chao index of the BC-soil was higher than that of other samples,Simpson index is smaller than the rest of the sample,indicating that the addition of BC is beneficial to the increase of microbial diversity,thus changing the bacterial community in the soil.There were different in the gate level of bacteria among soil samples,among which the abundance of Proteobacteria was the highest,followed by Bacteroidetes and Firmicutes.There are also differences in the genus of the genus,among which Macellibacteroides,Bacillus,Comamonas and Petrimonas are abundant. |
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