In China, intensive pig farming has led to serious environmental issues with the need to dispose off large quantities of pig manure. Chinese agriculture relies on high inputs of chemical fertilizers leading to gradual decreasing organic matter contents in many arable soils. We propose that hydrochars produced from pig manure could potentially replace chemical fertilizers and, at the same time, resolve the waste disposal problem. The hydrochars used in this study were produced from pig manure at five different pyrolysis temperatures ranging between 160 and 240 °C and three residence times (1, 5, and 8 h). All hydrochars were assessed for composition of major elements. Results showed that the yield and organic matter (OM) contents in hydrochars were 50-74% and 40-56%, respectively. The concentrations of total nitrogen (N), potassium (K2O), and OM in the hydrochar decreased, whereas contents of phosphorus (P2O5), copper (Cu), and zinc (Zn) increased with increasing reaction temperature and time. Hydrothermal carbonization of pig manure is a rapid method for transforming pig manure into an organic fertilizer, but it is necessary to assess the potential soil contamination risk of Cu and Zn for the pig manure hydrochar as organic fertilizer.
Keywords: Biochar; Hydrochar; Hydrothermal carbonization; Organic fertilizer; Pig manure.