Within the gasifier the feedstock flowed downwards by gravity
and air as a gasifying (or oxidizing) gas was introduced into the
combustion zone of the reactor. Bottom ash samples were collected
from the ash pit at the bottom of the fixed bed downdraft
gasifier after the gasification of pure woodchip (PWG) and 20%
sludge and 80% woodchip (20SWCG). However, due to the structure
of the gasifier, some small char particles formed in the reduction
zone may fall into the ash pit and subsequently be mixed with
the bottom ash. As char can be recycled rather than landfilled in
actual gasification processes, they were removed via sieving before
the toxicity test.