Increase of biogas production through co-digestion of lipids and sewage sludge

The aim of this study was to assess the feasibility of co-digesting lipids originated from domestic
wastewater along with sewage sludge. Three lab-scale single stage mesophilic anaerobic digesters
were operated under a constant hydraulic retention time (15 days). One system (C) was fed on a
daily basis with sewage sludge and served as the control system and its operation was compared
with two experimental systems (E1 and E2). Both experimental systems received mixtures of sludge
and lipids with different lipids content (20 % for system E1 and 60 % for system E2 on a VS basis),
whereas organic loadings were 2 KgVS m-3 d-1 and 3,5 KgVS m-3 d-1 for systems E1 and E2,
respectively.
According to the results it can be stated that the addition of lipids to sewage sludge up to 60 % on a
VS basis resulted in a significant increase of biogas production without producing any severe effects
on the properties of the digested sludge. More specifically biogas production of reactor E1 was 18 %
greater than that of reactor C, whereas biogas produced in reactor E2 was even greater (50 %
higher than that of reactor C). Finally it is interesting that during start-up a lag phase was recorded at
reactor E2 before biogas production initiated, which should be attributed to the time required for
growth of acetogenic bacteria capable to degrade LCFA.