Volatile fatty acids (i.e., acetic and butyric acids) and biosolvents
(i.e., ethanol and butanol) were measured by a gas chromatography
(GC, model 7890A; Agilent Technologies, U.S.A.) on a
Durabond (DB)-WAXetr column (30 m 0.25 mm 0.25 lm;
J&W, U.S.A.) equipped with a flame ionization detector (FID). The
oven temperature was initially held at 60 C for 2 min, increased
at 15 C/min to 230 C, and held for 1.7 min. Helium was used as
the carrier gas, with a column flow of 1.5 mL/min. Five-point standard
curves were obtained by running standard solutions containing
acetone, butanol, ethanol, acetic acid, and butyric acid.