Abstract
Recirculation of digestate either in the form of
liquid or solids has proven to enhance biogas production from
energy crops including lawn grass. The explanation to this is that
digestate contains suitable bacteria and trace elements (nutrients)
needed by methanogens. Influence of digestate recirculation and
recirculation percentage in biogas production from lawn grass
via anaerobic digestion was studied in laboratory scale digester
(1L plastic bottles) at mesophilic condition. Three scenarios were
used: digester without recycle digestate (control) (WRD),
digesters with recycled liquid digestate (RLD) and digesters with
recycled solid digestate (RSD). Liquid recycled digestate was
added in percentages variation ranging from 10%-60%, solid
recycle digestate was added in percentages variation ranging
from 10%-50%. The maximum biogas production with methane
content of 55% was obtained in the digester with 60% RLD on
the 8th day. During the study of recirculation of solids, highest
biogas yield with methane content of 53% was observed in a
digester with RSD of 40% on the 5th day. Retention time for both
digesters with recycled digestate was reduced and biogas
production rate was increased compared to the digester with no
recycled digestate.