A new variant of stirring mechanism for agitating contents of an anaerobic digester that makes
use of vertical and horizontal directed jets of liquid reactor content being re-circulated by and
electric pump, is reported. In order to demonstrate its working, a thermophilic pilot scale reactor
using waste water is described and various parameters analysed. As a sample run, raw
(untreated) waste water from the treatment works in Nairobi was used as the nutrient source,
while sludge from an anaerobic pond in the same treatment works was used as source of bacteria.
Measurement of various parameters like organic loading rate and characteristics of feed
wastewater (BOD, COD, pH, TS), biogas production rate in thermophilic anaerobic digester,
maximum gas yield and biogas quality were undertaken. The reactor was fed at a controlled
organic loading rate of 0.5 L/min. The reactor contained substrate to inoculums in the ratio 3:1
with the temperature was controlled using a thermostated heating coil. Digestion was carried out
in a pilot scale digester (with a capacity of 210 litres) under thermophilic (at 55 0C) anaerobic
conditions for a period of 15 days. The final average yield of biogas was 1.225 x 10-2 m3.
Average percentage composition of biogas produced by thermophilic digester was 66.6 vol. %
CH4, 30.4 vol. % CO2.