BACKGROUND: The adsorption of Cr(III) ions on various pig manure biochar (BC) samples was investigated to determine the effect of operating conditions (initial pH, sorbate and sorbent concentrations) on sorptive capacity. The BC samples with higher sorption capacity showed high surface area and were rich in alkaline metals whose concentration was measured by ICP-OES. RESULTS: For BCs from anaerobically and chemically pretreated feedstock greater ΔpH changes and higher maximum capacity were noted during Cr(III) adsorption than for BC from mechanically pretreated samples, due to a higher ion exchange capacity. The maximum Cr(III) uptake of 102 mg g^-1 for the BC sample was achieved at c₀ = 300 mg dm^-3 and pH = 5. It was also observed that the high ash content effectively lowered the surface area of BCs; however all BCs investigated contained a low level of toxic metals. CONCLUSIONS: The data indicate that both the technology used for separation of the manure and pyrolysis temperature had a significant influence on the physical and chemical properties of the BC and affected its sorption capacity. In addition, compared with other sorbents pig manure BC has one of the best Cr(III) sorption capacities.