MgO-laden biochar enhances the immobilization of Cd/Pb in aqueous solution and contaminated soil

Great progress has been made in recent years to alleviate the heavy metal pollution,but the development of low-cost and eco-friendly adsorbents is still challenging.In this work,MgO-loaded biochar,as a potential adsorbent,was successfully synthesized via copyrolysis of corn straw and MgCl2∙6H2O at 600℃and used for heavy metal immobilization in aqueous solution and contaminated soil.Nemerow pollution index and potential ecological risk index methods were also used to assess the potential ecological risk of the metals in soil after remediation.The results showed MgO-laden biochar exhibited a much higher Cd2+adsorption capacity than the pristine biochar.Pseudo-second-order and Langmuir/Langmuir-Freundlich equations could describe the adsorption kinetics and isotherm of Cd2+well.The maximum adsorption capacity of Cd2+could reach to 1058.8 mg g−1 estimated by Langmuir-Freundlich equation.Cd2+adsorption on MgO-laden biochar composite mainly involved the hydrolyzation of MgO,ionization of Mg(OH)2 and precipitation of Cd2+and OH−.In addition,complexes with oxygen-containing groups and adsorption by Mg(OH)2 also enhanced Cd immobilization.The result of soil-leaching test showed that the concentrations of TCLP-leaching(Toxicity Characteristic Leaching Procedure)Cd and Pb reduced by 22.4%and 29.0%,respectively,after 4%of MgO-laden biochar amendment,and the integrated pollution index and potential ecological risk decreased by 28.9%and 28.5%,respectively.These results suggest that MgO-laden corn straw biochar may be promising for application as a low-cost adsorbent for wastewater treatment and soil remediation.

Responses of soil microbial communities to manure and biochar in wheat cultivation of a rice-wheat rotation agroecosystem in East China

Soil contamination in agroecosystems remains a global environmental problem. Biochar has been suggested as an organic amendment to alleviate soil pollution, sequester carbon(C), and improve soil fertility. However, information on how bacterial and fungal communities in acidic bulk and rhizosphere soils respond to swine manure and its biochar is still lacking. In this study, biochar and swine manure were applied at two rates of 1.5 and 3 t ha-1in a rice-wheat rotation field to assess how soil characteristics, especially p H and chemical element availability, correlate to compositional variations of bacteria and fungi in bulk and rhizosphere soils. Our results showed that high rates of biochar and manure promoted the bacterial richness in bulk and rhizosphere soils by increasing soil pH and reducing soil arsenic(As) and copper(Cu) availability. Compared with soil As and Cu availability, soil p H had opposite effects on beta diversity of both the bacterial and fungal communities. Specifically, biochar and swine manure applications stimulated the bacterial classes Gemmatimonadetes, Deltaproteobacteria, and Gammaproteobacteria by increasing soil pH and decreasing soil available chemical elements. Opposite trends were observed in fungal communities responding to biochar and manure. For example, biochar restrained the fungal class Eurotiomycetes by decreasing soil As and Cu availability, but manure inhibited Leotiomycetes mainly because of an increase in soil pH and a decrease in soil dissolved organic C. These suggest that both bacterial and fungal communities respond significantly to biochar and manure amendments in both bulk and rhizosphere soils, possibly because of their sensitive adaptation to variations in soil environmental factors, such as pH level and chemical element availability.