After the BMP tests were performed; analyses of the glycerol
co-digestion systems were moved to 4 L continuously stirred tank
reactors (CSTRs). Co-digestion in the CSTRs was done using primary
sewage sludge as the substrate material. The CSTRs allowed
for continuous gas output monitoring using wet test meters and
gas composition analysis by collecting samples in Tedlar bags
weekly and performing GC analysis of the biogas. The CSTR also
allows for variation of glycerol and primary sludge loading. This
data along with digestate and co-digestate monitoring, determined
the range of maximum benefit for addition of glycerol to the
system. The addition of increasing amounts of glycerol resulted
in a corresponding increase in gas production (Fig. 2). The specific
gas production increased from 0.35 to 0.92 m3/kg VS d. Fig. 2