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3.3.5 Optimization of SLS and POME mixing ratio in biohydrogen production

The enriched sludge was used as inoculum in batch tested to determine its ability to
generate hydrogen from co-digestion of various mixing ratios of SLS and POME including 95:5,
90:10, 85:15, 80:20, 75:25, 70:30, 65:35, 60:40, 55:45 and 50:50 (%v/v) with initial organic
concentration of 7 g-VS added/L and 21 g-VS added/L, respectively. The assay was conducted as
batch cultivations in 120 mL serum bottles with 50 mL of working volume. In each bottle, 15
mL of inoculum was added; corresponding to 30% of working volume and the rest of the
working volume active was filled up with 35 mL of substrate/water mixture. All experiment
without supplementation of additional nutrients and no initial pH adjustment. The mixtures were
then purged with N 2 (100%) to ensure anaerobic conditions. Afterwards the bottles were closed
with butyl rubber stoppers and aluminum seal and then placed in a 55°C incubator for 5 days.
Hydrogen production in the headspace of the vials was monitored. The headspace gas was
collected for hydrogen determination daily. All experiment was done in triplicate for each
replication at each time point. At each time interval for each biogas volumes and biogas
composition were determined. Then, the optimum mixing ratio of SLS to POME with initial
organic concentration of 7 g-VS added/L was further investigated by using RSM with CCD, for
buffer and nutrients optimization. Subsequently, the effluent from H 2 potential phase with
optimal conditions was further used as substrate for the sequential methane production in the
second stage.

3.3.6 Effect of NaHCO 3, Na 2HPO 4.12H 2O and EFB ash concentrations on biohydrogen
production

A factorial central composite experimental design was used to investigate the effect of
NaHCO 3, Na 2HPO 4.12H 2O, and empty fruit brunch’s (EFB) ash concentrations on hydrogen
production. In this experiment was conducted in 16 runs and each run was performed in
triplicates. The concentration levels of the variables and the experimental design are shown in
Table 3.2 and Table 3.3. The concentrations of NaHCO 3 ranged from 3 to 9 g/L,
Na 2HPO 4.12H 2O ranged from 0 to 20 mg/L, and EFB ash ranged from 0 to 21 g/L, respectively.
A quadratic model (Sreela-or et al., 2011; Sittijunda and Reungsang, 2012) was used to evaluate
the optimization of key factors.