2.3. Analytical methods
Composition and volume of the biogas produced from all digesters were measured daily for the first 10 or 20 days and every 2 or 3 days afterwards, depending on biogas production. Biogas volume was measured by water displacement. Methane content was analyzed using gas chromatography (GC122, China) equipped with a thermal conductivity detector and a 2 m stainless-steel column (TDX-01). The injector, detector and oven temperatures were 140, 140 and 100 C, respectively. Nitrogen served as the carrier gas. The biogas yield was expressed as the volume of biogas produced
based on the initial total VS in the feedstock. The methane and biogas production in each bioreactor are reported in normalized micro liters, i.e., the biogas and methane volume produced was corrected to standard temperature and pressure (273 K, 1 atm).