Changes in Cd forms and Cd resistance genes in municipal sludge during coupled earthworm and biochar composting

• Published in: Ecotoxicology and environmental safety 2024-11, Vol.286, p.117179, Article 117179
• Main Authors: Yu, Zhimin, Zhou, Meng, Zhang, Hongwei, Yuan, Lei, Lv, Pin, Wang, Limin, Zhang, Jizhou
• Format: Article
• Language: English
• Subjects: Animals; Biogeochemical cycle; Biomass; Cadmium - toxicity; Cd resistance genes; Charcoal; Composting; Eisenia foetida; Heavy metal gene chips; Oligochaeta - genetics; Sewage; Soil Pollutants - toxicity; Vermicomposting
• ISSN: 0147-6513; 1090-2414; 1090-2414
• DOI: 10.1016/j.ecoenv.2024.117179

There is a close relationship between microbial activity and the bioavailability of heavy metals, and heavy metal resistance genes can affect the activity of heavy metals. To evaluate the effects of coupled earthworm and biochar composting on Cd forms and Cd resistance genes in sludge, the BCR continuous extraction method was applied to classify the Cd forms, and Cd resistance genes were quantitatively determined with heavy metal gene chip technology. The results showed that the changes in earthworm biomass during composting were sufficiently fitted by logistic models and that adding biochar effectively increased earthworm biomass. The coupled treatment of earthworms and biochar promoted the degradation of sludge. The coupled treatment of earthworms and biochar reduced the proportion of acid-extractable and reducible Cd relative to total Cd, increased the proportion of oxidized and residual Cd relative to total Cd, transformed Cd forms from active to inert, and reduced the gene copy number of Cd resistance genes (czcA, czcB, czcC, czcD, czcS, czrA, czrR, cadA, and zntA). czcB was identified as a key gene that affected acid-extractable Cd and residual Cd contents; czcA, czcB, czcD, and czcS were identified as key genes that affected the reducible Cd content; czrR and cadA were identified as key genes that affected the oxidized Cd content; and czcC was identified as a key gene that affected the total Cd content. Cd resistance genes could directly affect the Cd form or indirectly affect Cd form through their interactions with each other. [Display omitted] •Adding biochar effectively increased earthworm biomass.•The Cd forms in the sludge were transformed from active to inert by coupled earthworm and biochar composting.•Coupled earthworm and biochar composting reduced the copy number of Cd resistance genes in the sludge.•Cd resistance genes can directly affect Cd forms or indirectly affect Cd forms through gene interactions.