Microwave-assisted hydrothermal carbonization of pig feces for the production of hydrochar

Abstract

In this study, microwave-assisted hydrothermal carbonization of pig feces is investigated. The yield of hydrochar decreases with increasing reaction temperature/time, while it increases with rising solid-liquid ratio. The addition of CaO raises the yield of hydrochar, while the use of H2SO4 reduces the yield of hydrochar. Under non-catalytic conditions or with CaO as catalyst, most of P and heavy metals (Zn, Cr, Cu, Cd, Pb, and Ni) are retained in hydrochar, while large amounts of K/N are migrated into process water. In the presence of H2SO4, the migration of P and heavy metals (except Cu) into process water is significantly enhanced. Compared to raw pig feces, hydrochars exhibit higher thermal stability and porosity, and contain lower contents of soluble N/P/K nutrients. Direct use/discharge of process water is restricted by its high COD and its high content of nutrients, Zn and Cr.