Application Of Kelp Residue Biochar Immobilized Degrading Bacteria In PAHs-contaminated Soil Remediation

Polycyclic aromatic hydrocarbons（PAHs）are a class of persistent organic pollutants widely distributed in the environment.They not only bring risks to human health,but also cause incalculable harm to the ecological environment.Among the many methods for remediating PAH-contaminated soil,biotechnology is widely used because of its environmental friendliness,high efficiency and low cost.On this basis,adding functional materials such as biochar for strengthening has a better removal effect than the degrading bacteria itself.Kelp slag is the main solid waste in kelp processing.This paper uses it as the main source and compares the other three kinds of agricultural wastes to prepare biochar and iron-modified biochar respectively,and explore their removal effect on refractory benzo[a]pyrene（BaP）in soil after immobilizing degrading bacteria.The main findings are as follows:（1）The kelp slag,corn stalk,rice husk powder,and poplar sawdust were pyrolyzed to prepare the original biochar under anaerobic conditions at 450°C,and then treated with ferric chloride solution to obtain the corresponding iron modification.bio-charcoal.Electron microscope observation found that the kelp residue biochar and the modified biochar were significantly different from the six biochars prepared from the other three materials in terms of structural properties.They are all dominated by mesoporous structures,with specific surface areas of 4.9476 m₂/g and 11.7279 m₂/g,respectively,and pore volumes of 0.021081cm₃/g and 0.048768 cm₃/g,respectively,with sufficient adsorption sites.Moreover,iron-modified kelp slag biochar had more abundant functional groups and types than unmodified biochar.（2）The adsorption process mechanism of kelp residue biochar（KBC）on BaP and its loading capacity for degrading bacteria were investigated.The results showed that the adsorption of BaP by KBC was in good agreement with the Langmuir isotherm at room temperature,and the theoretical maximum adsorption capacity was 55.14 mg/g.Their adsorption behavior conformed to the pseudo-second-order kinetic equation,and reached the adsorption equilibrium at 240 min,indicating that the adsorption method was mainly chemical adsorption.Moreover,under the action of low-concentration hydrochloric acid,KBC also has a strong desorption effect on BaP.The loading capacity of KBC to degrading bacteria is different under different conditions.When the adsorption time is 12 h,the initial p H is 7.2,and the ratio of KBC to degrading bacteria is 10:1,the unit load is the largest,which is 7.0×10¹¹cfu/g.in the subsequent degradation experiments.（3）In the inorganic salt medium of 50 mg/L BaP,the degradation rates of BaP by KBC and KMBC immobilized with degrading bacteria were 50.32%and 60.77%within 14days.Under the same conditions,the degradation rates of BaP with a concentration of 100mg/L were 35.82%and 41.24%,respectively.The degradation rate of only adding degrading bacteria was 31.88%.In the actual polluted soil（4.96 mg BaP/kg soil）,the degradation rates of KBC and KMBC immobilized with degrading bacteria within 14 days were 76.07%and86.98%,respectively,which were higher than those of corn stover 70.53%,poplar sawdust72.13%and rice shell powder 75.43%.（4）The effects of KBC/KMBC immobilized with degrading bacteria on soil ecological function were evaluated.The results showed that the bioaugmentation process increased the contents of organic matter,ammonium nitrogen,available phosphorus and available potassium in PAHs-contaminated soil,but under PAHs stress,the activities of soil dehydrogenase and polyphenol oxidase decreased,and the microbial diversity decreased.Predominant functional microorganisms with good adaptation and degradation ability increase.