Biochar prepared from Fe-rich sludge as suitable microbial carriers for facilitating biodegradation of phenanthrene in soil

BACKGROUND: Converting waste biomass to biochar by pyrolysis is increasingly recognized as an effective waste regeneration method and could be applied in contaminated soil bioremediation. In this work, we compared the properties of three biochars (FB300, FB500 and FB700) derived from iron (Fe)-rich sludge (FS) at 300, 500 and 700 °C, and selected FB500 as microbial carrier to evaluate its function in facilitating phenanthrene (PHE) biodegradation in soil. RESULTS: Increasing pyrolysis temperature induced a positive relationship with the ash content, pH and pore size of biochars, but a negative relationship with the yield and surface area of the biochars. FB300 and FB500 maintained more organic matter than FB700, whereas, FB500 and FB700 had greater aromatic constituents and more crystal structures than FB300. Besides, FB500 showed the strongest stability and unique magnetic properties. Thus, FB500 was selected as microbial carrier in facilitating PHE biodegradation in soil. The degradation results indicated that FB500 with bacteria immobilization played a significant role in PHE degradation; its PHE removal rate of 58.15 ± 4.90% was much higher than that of 38.73 ± 3.98% for free bacteria treatment on the first day of degradation. CONCLUSION: Fe-rich sludge can be efficiently converted into biochar that in turn can serve as microbial carrier for PHE biodegradation in contaminated soil. FB500 with bacteria immobilization was proven to promote PHE degradation. Pyrolyzing Fe-rich sludge to biochar is a promising method for remediation of PAH-contaminated soil.