Properties of dairy-manure-derived biochar pertinent to its potential use in remediation

Conversion of waste products into biochar (BC) is being considered as one of several waste disposal and recycling options. In this study, we produced BC from dairy manures by heating at low temperatures (⩽500 °C) and under abundant air condition. The resultant BC was characterized for physical, chemical, and mineralogical properties specifically related to its potential use in remediation. The BC from all manures behaved similarly. Surface area, ash content, and pH of the BC increased as temperature increased, while yield decreased with increasing temperature. The BC was rich in mineral elements such as N, Ca, Mg, and P in addition to C, and concentrations of C and N decreased with increasing temperature as a result of combustion and volatilization; while P, Ca, and Mg increased as temperature increased. For example, C significantly decreased from 36.8% at 100 °C to 1.67% at 500 °C; whereas P increased from 0.91% to 2.66%. Water soluble P, Ca, and Mg increased when heated to 200 °C but decreased at higher temperatures likely due to increased crystallization of Ca–Mg–P, as supported by the formation of whitlockite (Ca,Mg)3(PO4)2 following 500 °C treatment. The presence of whitlockite was evidenced by X-ray diffraction analysis. Quartz and calcite were present in all BC produced. The BC showed appreciable capability of adsorption for Pb and atrazine from aqueous solution, with Pb and atrazine removal by as high as 100% and 77%, respectively. The results indicated that dairy manure can be converted into biochar as an effective adsorbent for application in environmental remediation.