Researchers studied how heating sewage sludge turns it into biochar, affecting heavy metal content. They found that higher temperatures during pyrolysis process led to stronger carbonization and increased surface area of biochar. Heavy metals like Zn, Cu, Cr, and Ni were concentrated in biochar at higher temperatures, while Pb and Cd decreased. The process also transformed bioavailable heavy metals into more stable forms, reducing their toxicity by about four times. Pyrolyzing sewage sludge at around 600°C resulted in biochar with low ecological toxicity.