The liquid samples of total volatile fatty acids (VFAs) in the acidification
and methane phase were centrifuged at 10000 r·min−1 for 10 min,
then filtered through a 0.45 μm membrane, and finally assessed using a
capillary DB-WAX column (30 m × 0.53 mm × 1 μm) in a gas chromatograph
(GC-7820A) with nitrogen as the carrier gas. Temperatures of
injector and detector were 250 °C. The temperature of oven was 100–
220 °C, heating at a rate of 15 °C·min−1
. Sample volumes of 0.4 μl
were injected via the detector (TCD: 250 °C). An oven was used to dry
TS and VS and K2Cr2O method was applied to soluble chemical oxygen
demand (SCOD) . The biogas production was tracked with a wet
gas meter. Using a PHS-25 meter (Shanghai Leichi Instrumentation
Factory), the pH value and ORP were measured. Ammonia nitrogen
(NH4
+-N) level was determined by pay reagent luminosity law
and methanogen concentration was determined by fluoroscope TYU-
30C (Shanghai Yuguang Factory).