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3.3.8 Analytical methods

The volume of biogas produced was measured using water displacement method. The
hydrogen content was measured by gas chromatography (Shimadzu GC 14A equipped with
thermal conductivity detector, TCD) fitted with a 1.5 m stainless steel column paced with
molecular sieve 58 (80/100 mesh). Argon was used as a carrier gas at a flow rate of 15 mL/min.
The temperature of the injection port, oven and detector were 100, 50, and 100°C, respectively.
0.5 mL of sampling gas was injected in triplicate (Akutsu et al., 2009; O-Thong et al., 2008).

Volatile fatty acids (VFAs) including acetic acid, propionic acid, butyric acid, and
alcohols such as ethanol (EtOH) were analyzed by a gas chromatography (Shimadzu, GC 8A)
equipped with a flame ionization detector (FID). A column capillary packed with
nitroterephthalic acid-modified polyethleneglycol (DB-FFAP) and with a length of 30 m was
used. The chromatography was performed using the following program: 100°C for 5 min, 100-
250°C with a ramping of 10°C/min, 250°C for 12 min. The detector temperature was set at
300°C (O-Thong et al., 2008; Prasertsan et al., 2009). Lactic acid (HLa) was analyzed by a high
performance liquid chromatography (HP1100, Hewlett-Packard GMGH) with the following
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operating conditions; Pinnacle II C18 Columns, ultraviolet (UV) detector at 210 nm, 2.5 mM of
H 2SO 4 was used as a mobile phase with a flow rate of 0.8 mL/min, and an oven temperature of
45°C (Castelló et al., 2009). The liquor samples were first centrifuged at 10,000 rpm for 10 min,
and were then filtered through 0.45 µm nylon membrane. Calculation of chemical oxygen
demand (COD) balance was followed the method described by Sittijunda and Reungsang (2012).

Chemical oxygen demand (COD), pH, total solid content (TSC), Volatile solid content
(VSC), alkalinity, total Kjeldahl nitrogen (TKN), protein content, total organic nitrogen (TON),
carbohydrate content, sulfate content, oil and grease and soluble phosphorus were determined in
accordance with the procedures described in the standard methods (APHA, 1999).

3.4 Results and discussion

3.4.1 Characteristics of substrates used

Physical and chemical characteristics of raw SLS and raw POME were summarized in
Table 3.1. The result shows that SLS was a concentrated substrate with high concentration of
total Kjeldahl nitrogen (TKN) and low concentration of chemical oxygen demand (COD),