Adsorpiton of Heavy Metals Onto Biochars From Anaerobically Digested Residues.

Useing biochars from anaerobically digested residues to adsorb heavy metals from water is a novel approach to environmental remediation. This study examined the ability of two digested residue derived biochars, digested animal waste char (DAWC) and digested sugarbeet pulp char (DSBPC), to remove lead from water. The biochars were made from slow pyrolysis of the anaerobically digested residues at 600 ^oC in a nitrogen environment. While both DSBPC and DAWC were effective adsorbents of lead, DAWC had a higher sorption capacity than DSBPC. The maximum lead sorption capacity of DSBPC was about 287 mmol kg^-1, while the sorption capacity of DAWC was about 246 mmol kg^-1. Post-sorption characterizations using energy dispersive x-ray diffraction (EDS) and scanning electron microscopy (SEM) indicated that the sorption of lead by DSBPC and DAWC was mainly related to the precipitation mechanism, with the precipitation of lead carbonate (PbCO₃) predominant in both biochars. This was further confirmed by an increase in pH of the aqueous lead solution from 4 – 5 before adsorption, to a pH of 9 – 10 at the end of the experiment. These results suggest that biochars derived from anaerobically digested residues may be effective, low-cost adsorbents of lead or other metals.