Thermal analysis of aged chars obtained by pyrolysis and hydrothermal carbonisation of manure wastes

Biochar is being explored for the improvement of contaminated land as well as quality of soils in agricultural use. Most studies are conducted in the laboratory or involved only short-term field experiments. There remains considerable uncertainty about the long-term implications of biochar use, as a consequence of changes that arise during their ageing within soil. This work assessed the effects of chemical ageing (5% vol H2O2) on different properties of biochars and hydrochars prepared from two types of animal waste (rabbit and pig manure). Four biochars were prepared from pyrolysis of rabbit manure (pyrolysis temperature: 300 and 600 °C) and pig manure (300 and 450 °C) and two hydrochars from each manure by hydrothermal carbonisation at temperatures of 200 and 220 °C. The pristine and aged chars were compared according to the elemental composition and thermogravimetric analysis being also calculated the thermostability index and carbon stability in the ageing process. Results showed that chars prepared at lower temperatures were more sensitive to ageing. Only biochar obtained by pyrolysis at 600 °C showed a high level of resistance to ageing, reflecting the higher stability of the underlying carbon structure.