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CHAPTER III

Two stages hydrogen and methane production by using thermophilic dark co-
fermentation of skim latex serum (SLS) and palm oil mill effluent (POME):

Optimization of mixing ratio and nutrients

3.1 Abstract

A batch experiment was conducted to determine the optimal mixing ratio of skim latex
serum (SLS) to palm oil mill effluent (POME), and further buffer and nutrients optimization in
the substrate which consisting of the optimal mixing ratio of SLS to POME with initial organic
concentration of 7 g-VS added/L, respectively for biohydrogen production in the first phase under
thermophilic temperature (55°C) by using thermophilic mixed cultures were studies. The
optimum mixing ratio of SLS to POME was 55:45 (%v/v) with the hydrogen content, cumulative
hydrogen, and hydrogen production yield was 27.2±1.5%, 25.1±0.6 mL H 2, and 71.8±1.7 mL
H 2/g-VS added, respectively. Then, it was optimized through employing response surface
methodology (RSM) with a central composite design (CCD). Although, the hydrogen production
yield achieved from optimization is higher than that obtained from non-optimization, approx.
22%. However, the increased yield is not uneconomical for the industrial scale when considering
cost of the external buffer and nutrients supplemented. Acetic and propionic acids were the
major soluble end-products with concentrations of 26.83±0.40 mM and 7.59±1.14 mM,
respectively under the optimum mixing ratio of SLS to POME condition. Afterwards, the
effluents achieved from H 2 production phase which consisting of SLS and POME at the mixing
ratio of 55:45 (%v/v) was further used as substrate for methane production in the second stage.
The result shows that the methane production yield obtained from co-digestion of SLS and
POME was 2 times greater than that achieved from sole fermentation of SLS.