Search

The Campine region in Flanders is well-known for its highly cadmium (Cd)-contaminated soils due to past anthropogenic activities. Enhanced Cd exposure can cause cellular damage in plants, and consequently reduces crop growth and plant quality (Jozefczak et al., 2014). Currently, few cost-effective and non-destructive remediation techniques exist (Tang and Ni, 2021). Therefore, alternative soil remediation techniques should be assessed. Biochar is a solid material that is produced by pyrolysis of biomass. Because of its functional surface, it can be used as a cost-effective adsorbent for various (in)organic pollutants in soils and waste waters (Sizmur et al., 2017). However, differences in biochar properties will affect their adsorption performance. Therefore, suitable biomass streams and biochar production conditions should be selected to increase adsorption efficiency. Biochars from eight biomass feedstocks (spent peat, green waste, chicken manure, coffee grounds, flax shives, insect frass, tree bark and apple wood) were subjected to pyrolysis at 450 and 600 °C (pilot-scale rotary kiln reactor) and evaluated for their Cd removal efficiency (CRE) in a buffered 2-(N-morpholino)ethanesulfonic acid (MES) solution (0.025 M Cd; pH = 6; 1:20 solid:liquid ratio) for ten days. The results show that CRE varied from 4 to 96 wt.% with the highest CRE by chicken manure biochars (94-96 wt.%). Insect frass biochar (produced at 450 °C) also had a high CRE (77 ± 4 wt.%). All the other biochars exhibited a CRE below 50 wt.%. A 10-day kinetic adsorption study in the MES solution was executed on four biochars (450 °C) (tree bark, spent peat, insect frass and chicken manure) due to their divergent adsorption performance. A 24-hr desorption step with 0.01 M Ca(NO3)2 was executed to investigate the leachability of the adsorbed Cd. Chicken manure biochar showed the fastest Cd removal rate with a removal of 93 ± 1 wt.% within one day, while the Cd removal of insect frass biochar started at 41 ± 2 wt.% and gradually increased to 77 ± 4 wt.%. Cd Leaching from the loaded biochar was limited (< 10 wt.%) but spent peat biochar leached approx. two times more Cd compared to chicken manure biochar. Future pot and large-scale plant growth experiments with these biochars will provide more insight on their performance in real-life scenarios. This will open new possibilities for the remediation of Cd-contaminated soils.