2.2. Experimental setup
The upflow anaerobic contact filter (Fig. 1) had four zones
namely: bottom zone, packing zone, outlet zone and head space
for the biogas accumulation. The wastewater was pumped into
the anaerobic digester near the top of bottom zone using feed
pump, apart from feeding operation the same pump was also
used as recirculation pump. During recirculation period the
feed pump draws the digester content from just below the top
of the packing zone and transferred it to the inlet point of the
digester. While the sole recirculation pump draws the digester
content form the outlet zone and delivers it in the middle of the
packing zone. The mixing of digester content was carried out
for six cycles per day, while each mixing cycle lasted for 15 min
at an interval of 4 h. The feed pump and recirculation pump
were operated under alternating condition in order to achieve a
near homogenous mixture throughout the digester content. The
biogas from the head space entered the gas flow meter in order
to measure the volume of biogas generated, while provision
were also provided to capture biogas from the outlet of the
gas flow meter into the gas holding bags for measuring the
hydrogen content in the biogas.