Optimisation of slow-pyrolysis process conditions to maximise char yield and heavy metal adsorption of biochar produced from different feedstocks

• Taguchi design was used to optimise pyrolysis process conditions for multiple feedstocks.
• Temperature had greatest influence on char yield but not adsorption performance.
• Catalytic effect of feedstock components reduced energy input and improved adsorption.
• Grass fibre char removed 92.96% Zn from groundwater after pyrolysis for 2 h at 300 °C.

The objective of this work was to identify biomass feedstocks and optimum pyrolysis process conditions to produce a biochar capable of adsorbing metals from polluted groundwater. Taguchi experimental design was used to determine the effects of slow-pyrolysis process conditions on char yield and zinc adsorption. Treatments were repeated using six candidate feedstocks (Lolium perenne, Lolium perenne fibre, Miscanthus x giganteus, Salix viminalis, Fraxinus excelsior and Picea sitchensis) and the resultant chars were tested for metal adsorption performance. Chars produced from L. perenne and its extracted fibre displayed the greatest zinc adsorption performance and removed 83.27–92.96% respectively. Optimum process conditions in terms of both char yield and zinc adsorption performance were achieved from slow-pyrolysis at 300 °C for 2 h using a feedstock with a particle size of less than 1 mm.