Effect of sawdust addition and composting of feedstock on renewable energy and biochar production from pyrolysis of anaerobically digested pig manure

Pyrolysis experiments were conducted on the separated solid fraction of anaerobically digested pig manure (SADPM). The aim of these experiments was to investigate the influence of (1) sawdust addition and (2) composting the feedstock, on the products of pyrolysis and on the net energy yield from the pyrolysis process. Mixtures of SADPM and sawdust were made to give the following treatments; manure only, 4:1(w/w) and 3:2(w/w). These mixtures were pyrolized at 600 °C both before and after aerobic composting. The yields of the biochar, bio-liquid and gas were influenced by the addition of sawdust to the SADPM and by composting of the feedstock. With the addition of sawdust, biochar and gas higher heating values (HHV) increased, while bio-liquid HHV decreased. More than 70% of the original energy in the feedstock remained in the biochar, bio-liquid and gas after pyrolysis, increasing as the proportion of sawdust increased. The HHV of the biochar decreased, while the HHV of the bio-liquid increased, after the feedstocks were composted. The energy balance showed that increasing the rate of sawdust addition to SADPM resulted in an increased net energy yield. The addition of a composting stage increased the net energy yield for the manure only feedstock only. However, with increasing sawdust addition, composting of the feedstock reduced the net energy yield.