2.3. Fabrication of Digesters
Each digester (Fig. 1) was made of 60 L of metal drum
as the digester vessel. On the vessel, there were: (i)
substrate inlet pipe with the diameter of 8 cm installed
with the angle of 30° toward vertical wall on the height of
15 cm from the bottom of vessel; (ii) residue output pipe
with the diameter of 8 cm with the angle of 45° toward
vertical wall on the height of 25 cm from the bottom of
vessel; (iii) gas sealed stirrer shaft on the center of
cylinder with two stirrer installed at 13 and 40 cm from
the bottom of vessel and (iv) biogas output pipe with the
diameter of 0.8 cm connected with the gas volume meter
installation. All the connection were conducted with metal
welding to avoid the gas leak.
2.4. Monitoring Parameters
Response variables due to the treatments were daily
biogas production, total biogas production in 20 days,
fluctuation of substrate pH and the quality of biogas
combustion. The digester was connected with the
reversed measuring flask (1.000 cm3) with the
assumption that the moved water was equal with the
volume of biogas. The volume of produced biogas on the
each digester was separately recorded. The pH was
determined using pH-meter. The water boiling test was
performed using Bunsen lamp, where the glass was filled
with the distilled water, statif and hand thermometer.