The rest two serum bottles of the quadruplet samples
were subjected to biogas composition testing by
headspace analysis. Biogas composition was
measured using a Thermo Scientific Trace GC 700
(Thermo Fisher Scientific India Pvt. Ltd, India)
fitted with Hayesep Q 80/100 mesh column with a
thermal conductivity detector. Hydrogen was used as
carrier gas at a flow rate of 15ml/min. The column
temperature was 40°C and then was raised to 140°C
with a ramp of 15°C/min. The injector and detector
temperature were 120 and 150°C. The compounds
detected were methane, carbon dioxide, nitrogen and
hydrogen sulphide.