Microbiological inoculation with and without biochar reduces the bioavailability of heavy metals by microbial correlation in pig manure composting.

Biochar provides a suitable microenvironment for the growth of microorganisms. It may directly or indirectly affect changes in the population of microorganisms, thus affecting heavy metal bioavailability. This study aims to explore the effects of microbiological inoculation with and without biochar on microorganisms and on the bioavailability of heavy metals during pig manure composting. Three composting experiments were conducted under various conditions including no treatment (CK), only microbiological inoculation (TA), and integration with biochar (TB). Compared with raw materials before compost, TA reduced the bioavailability of Cu by 25.1%, Zn by 25.64%, and both Pb and Cr by 1.75%. TB reduced the bioavailability of Cu by 35.38%, Zn by 19.34%, Pb by 0.81%, and Cr by 3.9%. Furthermore, correlation analysis demonstrated that Debaryomyces were the primary fungi, possibly controlling the passivation of Cr. Bacillus, Fusarium, Pseudogracilibacillus, Sinibacillus, and Botryotrichum were the primary bacteria and fungi potentially governing the passivation of Zn, Lastly, Debaryomyces and Penicillium were the primary bacteria and fungi potentially controlling the passivation of Pb and Cu, respectively. Overall, we demonstrated that pig manure added to the microbial inoculum and biochar effectively reduced the bioavailability of heavy metals, thereby offering an applicable technology for reducing heavy metal contamination during pig manure composting.