The anaerobic digesters having a total volume of 1,100 ml. and a working volume of 1,000 ml. was used in all
experiments. There was no initial pH adjustment except for the wastewater: sludge 1:1 which was adjusted to pH 7. The
temperature was controlled at the 35C by temperature-controlled water circulator. Biogas production was measured daily by
water displacement method as used by other authors [3-6]. The methane content was measured using Gas Chromatograph
(GC-8A Shimadzu) and the average value was 56 % methane.
Chemical analysis
All analytical procedures are performed in accordance with standard methods for examination of water and
wastewater[7].
Kinetic model of biogas production
Semi-empirical model (Gompertz model)
It is customary to use some form of kinetic or empirical models to describe the data and estimate the BMP from model’s
parameters. Recently, Gompertz equation has been used very often which has the following forms