As seen from Fig. 2, half of the carbon in poultry litter (46–
50 wt.%) was retained in the biochars. This result is not consistent
with our previous study associated with a lignocellulosic biomass
(Pala et al., 2014). In our previous study, most of the carbon in biomass
(65–73 wt.%) was retained in biochar. This difference may be
due to the high protein content in poultry litter. Based on the literature
(Yanik et al., 2007), it can be deduced that proteins can be
easily degraded in sub-critical water and do not much participate
in the char formation reactions. Above 200 C, distribution of carbon
in the gas phase increased, while the distribution of carbon
in aqueous phase decreased from 39 to 28 wt.%. This shows that
the organics in the aqueous phase were mainly degraded into gaseous
compounds by increasing the temperature. In other words,
amino acids formed from protein/manure degradation produced
low-molecular-weight carboxylic acid which might have further
produced gases by decarboxylation.