| | Feedstock | Pyrolysis temp (°C) | Hazard-GHGs exhibited | Risk effect | Reference |
| | MSS, slaughterhouse sludge, and paper mill sludge | 550, 750 | Cu, Cr, and Zn | Pyrolysis affected toxicity by reducing Cu and Zn in sludge.
750°C favored migration and transformation of HMs.
HM environment risks decreased.
Dewatered sludge was highly toxic before pyrolysis. | [24] | | Bagasse | 600 | Cr(VI), Crtotal | Cr(VI) and Crtotal immobilization efficiency was 100% and 92.9%.
Remediation reduced the phytotoxicity of Cr.
Leachable Fe and was favorable for plant growth. | [130] | | Broiler litter | 350, 700 | Cu(II), Cd(II), Ni(II) | High carboxyl mobilized Cu(II) retained by alkaline soil.
Base treatment of 350°C char improved the immobilization of all heavy metals.
Total sulfur released in soluble form in soil amended char. | [33] | | Residential sewage sludge and corn cob | — | As, Cd, Cu, Pb, Hg, Mo, Ni, Se, Zn, Cr | Pb, Ni, Cu, Zn, Cr largely retained in the biochar carbonization.
Hg, As, Cd, and Se fairly released during carbonization.
Carbonizer biochar never adsorbed much volatile HMs.
Biochar unsuitable for land application. | [34] | | Peanut straw (PS), soybean straw (SS) and canola straw CS) | 400 | Cu(II) | The adsorption increased with increase in pH.
The adsorption order of char: PS > SS > CS.
Cu(II) adsorption greater than commercial activated carbon. | [131] | | Dairy manure | 200, 350 | Cu, Zn, Cd | Biochar at 350°C more effective in sorbing all three metals.
Both biochars had highest affinity for Cu, then Zn and Cd. Mineral in biochar influenced biochar's high sorption capacity. | [37] | | Pine wood | 600 | As, Pb | Modified biochars sorbed higher As(V),Pb(II) than unmodified Birnessite enhanced biochar had highest sorption enhancement due to strong As(V) and Pb(II) affinity. | [132] | | Peanut shell and Chinese medicine material residue | 300–600 | Pb | Pb2+ adsorbed on biochars.
Biochars (>500°C) and Pb2+ sorption complexation reduced.
Pb2+-π interaction was enhanced. | [133] | | Pine wood and natural hematite | 600 | As | Stronger magnetic property of aqueous As by modified biochar.
Magnetized biochar can be used in As contaminant removal. | [54] | | MWTP sewage sludge | 300, 500, and 700 | Cu, Zn, Cr, Ni, Pb, and Cd | HTP and pyrolysis immobilizes HMs.
High-temperature reduced the HMs ecological risk.
Higher temperature HTP process transforms bioavailable fraction HMs to more stable fractions.
Potential environmental risk of the HMs in sludge transformed from high-risk to low-risk, or even no-risk. | [45] | | Paper mill sludge | 270 to 720 | As(V) and Cd(II) | Equilibrium uptakes of As(V) and Cd(II) were 22.8 anf 41.6 mg/g.
Decreased As(V), Cd(II), Ni(II) ions adsorption increased PO4−3 concentration.
Regeneration demonstrated through NaOH or HCl desorption. | [134] | | Pine wood sawdust | 500 | Cd, Cr, Pb, Ni | BCNs cutback health hazards of PTEs.
Reduced bioavailability and uptake of PTEs by wheat plants. The hazard indices (HIs) for PTEs in all treatments were <1. The cancer risks for Cd, Cr, and Ni higher in all treatments.
BCNs addition suppressed cancer risk compared to control. | [55] |
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