Effects of Pyrolysis Temperature and Holding Time on Physicochemical Properties of Swine-Manure-Derived Biochar

Biochars were slowly pyrolyzed from dried swine manure waste by slow pyrolysis at different temperatures (300–750 °C) and heating times (0–120 min). The influence of pyrolysis temperature and heating time on the physicochemical properties of the biochars were studied. It was found that the ash content, pH, mineral nutrients, total heavy metals (except Zn), and pore properties of all swine-manure-derived biochars increased with increasing temperature and time. The yield and N, O, and H contents decreased with increasing temperature and time. The manure-derived biochar was rich in soil macronutrients and micronutrients, such as N, P, K, Ca, Mg, Na, Fe, Mn, Cu, and Zn. Excessive pyrolysis temperature (i.e., 750 °C) significantly increased the electrical conductivities of the biochars, i.e., the amount of soluble salts, and was also associated with the risk of volatilization of heavy metals (e.g., Zn) with low melting point. Linear correlation analyses showed that there were significant correlations between physical and chemical characteristics of the biochars, and the P values of correlation coefficients were often