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resulting in low C/N ratio about 3. O-Thong et al. (2008) investigated the effect of C/N ratio, C/P
ratio and iron concentration in POME on fermentative biohydrogen production. The results
found that the optimum C/N ratio of 74 with the hydrogen production yield of 6.33±0.14 L H 2/L
POME. On the other hand, POME contains C/N ratio about 28, which is much higher than that of
SLS. However, it was a concentrated substrate with high concentration of oil and grease of
13.70±0.12 g/L, which could potentially inhibit the process (O-Thong et al., 2012). Therefore,
adding POME into SLS could definitely have more suitable C/N ratio for hydrogen production
by using dark fermentation. Furthermore, they also high concentration of carbohydrate with
concentrations were 9.00±0.00 g/L for POME, and 0.60±0.00 g/L for SLS, respectively, which is
the real substrate for hydrogen production by dark fermentation (Abraham et al., 2009;
Prasertsan et al., 2009; Ismail et al., 2010; Mamimin et al., 2012).

Table 3.1 Physical and chemical characteristics of skim latex serum and palm oil mill effluent

Parameters Unit SLS POME
pH 4.83±0.01 4.68±0.00
TSC g/L 49.65±0.01 42.07±0.16
VSC g/L 43.46±0.39 32.24±0.89
Alkalinity mg/L CaCO 3 56±1 28±0
COD g/L 29.22±5.67 42.55±6.14
TKN g/L 5.18±0.00 1.25±0.01
Protein g/L 7.58±0.51 7.78±0.07
C/N ratio 3.27* 27.59*
Carbohydrate g/L 0.60±0.00 9.00±0.00
Oil and grease g/L 0.15±0.01 13.70±0.12
Sulfate mg/L 258±1 -
Soluble phosphorus mg/L 44±0 96±0

*C/N ratio was determined by CHN analysis using CHNS/O analyzer (Thermo Quest Flash EA
1112)

3.4.2 Optimization of SLS and POME mixing ratio in biohydrogen production

Cumulative hydrogen production under thermophilic condition obtained from individual
fermentations of SLS and POME with initial organic concentration of 7 g-VS added/L were 7.1±1.7