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Table 3.3 Central composite experimental design matrix defining NaHCO 3, Na 2HPO 4.12H 2O,

and EFB ash concentrations on hydrogen production yield.

Run Parameter
X 1: NaHCO 3 (g/L) X 2: Na 2HPO 4.12H 2O (mg/L) X 3: EFB ash (g/L)
1 6 10 0
2 3 0 0
3 9 10 15
4 9 20 30
5 3 0 0
6 6 20 15
7 9 0 0
8 9 20 0
9 6 0 15
10 3 20 0
11 6 10 30
12 9 0 30
13 6 10 15
14 3 10 15
15 3 20 30
16 6 10 15

3.3.7 Methane potential from co-digestion of SLS with POME

The enriched methanogenic inoculum was used to determine methane potential from co-
digestion of SLS and POME. The batch assay was carried out in 500 mL serum bottles with 300
mL working volume and was conducted in triplicates. Each bottle contained 250 mL enriched
methanogenic inoculum and 50 mL substrate/water mixture achieved from H 2 batch production
stage of our previous studied with the optimal mixing ratio of SLS to POME of 55:45 (%v/v) and
without supplementation of additional nutrients and no initial pH adjustment. Each bottle was
then flushed with nitrogen gas to ensure anaerobic conditions and was then closed with butyl
stoppers, sealed with aluminum cap and subsequently was placed in a 55°C incubator for 27
days. The headspace gases were collected at time intervals for biogas determination until biogas
production ceased. The biohydrogen and biomethane produced was followed the method
described by Zheng and Yu (2005).