Dairy-Manure Derived Biochar Effectively Sorbs Lead and Atrazine

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Abstract
Biochar (BC) produced from agricultural crop residues has proven effective in sorbing organic contaminants. This study evaluated the ability of dairy-manure derived biochar to sorb heavy metal Pb and organic contaminant atrazine. Two biochar samples were prepared by heating dairy manure at low temperature of 200 °C (BC200) and 350 °C (BC350). The untreated manure (BC25) and a commercial activated C (AC) were included as controls. Sorption of Pb by biochar followed a dual Langmuir−Langmuir model, attributing to Pb precipitation (84−87%) and surface sorption (13−16%). Chemical speciation, X-ray diffraction, and infrared spectroscopy indicated that Pb was precipitated as β-Pb9(PO4)6 in BC25 and BC200 treatment, and as Pb3(CO3)2(OH)2 in BC350. Lead sorption by AC obeyed a single Langmuir model, attributing mainly to surface sorption probably via coordination of Pb d-electron to C═C (π-electron) and —O—Pb bonds. The biochar was 6 times more effective in Pb sorption than AC, with BC200 being the most effective (up to 680 mmol Pb kg−1). The biochar also effectively sorbed atrazine where atrazine was partitioned into its organic phase, whereas atrazine uptake by AC occurred via surface sorption. When Pb and atrazine coexisted, little competition occurred between the two for sorption on biochar, while strong competition was observed on AC. Results from this study indicated that dairy manure can be converted into value-added biochar as effective sorbent for metal and/or organic contaminants.