Abstract
The aim of this study was to investigate the influence of residual
glycerine (5 and 10% w/w) from the biodiesel industry, used as a
co-substrate, on biogas production from maize silage. The experiments were
conducted in a laboratory-scale, single-stage anaerobic digester at 39ºC
and hydraulic retention time (HRT) of 60 d. Addition of 5% residual
glycerine caused organic load rate (OLR) to increase to 1.82 compared with
1.31 g organic dry matter (ODM) L-1d-1 for maize silage alone. The
specific biogas production rate and biogas yield were 1.34 L L-1d-1 and
0.71 L g ODM-1 respectively, i.e. 86% and 30% higher than for maize alone.
Increasing the residual glycerine content to 10% increased OLR (2.01 g ODM
L-1d-1), but clearly decreased the specific biogas production rate and
biogas yield to 0.50 L L-1d-1 and 0.13 L g ODM-1 respectively. This
suggested that 10% glycerine content inhibited methanogenic bacteria and
organics conversion into biogas. As a result, there was accumulation of
propionic and valeric acids throughout the experiment.
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