Journal of Ecology and Rural Environment ›› 2022, Vol. 38 ›› Issue (6): 802-809.doi: 10.19741/j.issn.1673-4831.2021.0372

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Risk Assessment of Heavy Metals in Sludge Biochar and Its Effects on Ryegrass Growth

MA Ruo-jun, JIA Hong-yu, DU Yi, YU Jun-long, ZHAO Xiao-dong, ZHANG Xiu-xia   

  1. College of Chemical and Chemical Engineering, China University of Petroleum, Qingdao 266580, China
  • Received:2021-06-08 Online:2022-06-25 Published:2022-06-24

Abstract: To investigate both the potential ecological risks of heavy metals in sludge biochar and effects of sludge biochar on plant growth as well as microbial diversity in soil, sludge biochar was prepared by pyrolysis of municipal sludge. The potential ecological risks of sludge and its biochar were evaluated by the risk assessment code (RAC), Muller geo-accumulation index (Igeo) and potential ecological risk index (RI). The effects of sludge biochar application on the growth of ryegrass were then discussed through pot experiments. The changes of microbial diversity in ryegrass root-soil were analyzed by 16S rRNA sequencing technology and bioinformatics. The results indicate that the RAC and RI indexes in the sludge decreased significantly after pyrolysis, and the bioavailability of heavy metals decreased, but the Igeo of each heavy metal increased, and the geological cumulative risk increased. According to the pot experiment, when adding 5% sludge biochar, the germination rate, average leaf weight per plant and average leaf length of ryegrass were promoted to reach 94%, 0.179 8 g and 13.74 cm, increased by 16.0%, 62.12% and 29.15%, respectively in contrast with pots without adding biochar. There was no significant influence in the abundance of bacterial community of ryegrass root soil by adding biochar, but the bacterial community diversity of the soil slightly decreased. The results of this study show that sludge-based biochar has a significant stabilizing effect on heavy metals, and its heavy metal content is lower than the standard of farmland risk screening value in China (GB 15618-2018), and the level of potential ecological risk is relatively low. At the same time, by the application of carbon, the growth of ryegrass could be promoted at a certain ratio.

Key words: sludge biochar, ecological risk of heavy metals, ryegrass growth, sludge recycling

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