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VII

Thesis Title Optimization of Hydrogen and Methane Production with a Two-Stage
Anaerobic Co-digestion of Skim Latex Serum (SLS) and Palm Oil Mill
Effluents (POME) under Thermophilic Condition
Author Mr. Kullachat Sama
Major Program Applied Chemistry
Academic Year 2014

ABSTRACT

Determination of biohydrogen production potential (BHP) at various mixing ratios of
skim latex serum (SLS) to palm oil mill effluent (POME) at initial concentration of 7 g-VS added/L
and 21 g-VS added/L was conducted in batch dark fermentation at thermophilic conditions. At the
organic concentration of 7 g-VS added/L and SLS: POME mixing ratio of 55:45 (%v/v), high
hydrogen production yield of 71.8±1.7 mL H 2/g-VS added was achieved. 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. Furthermore, buffer and nutrients optimization were then investigated through
response surface methodology (RSM) with a central composite design (CCD) at initial organic
concentration of 7 g-VS added/L, and 55:45 (%v/v) SLS:POME mixing ratio. 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. Afterwards, the
effluents achieved from H 2 production phase, consisting of SLS and POME at the mixing ratio of
55:45 (%v/v) and 7 g-VS added/L was further used as substrate for biomethane potential (BMP) in
the second anaerobic stage. The methane production yield of 418±10 mL CH 4/g-VS added, which
was 2 times greater than that achieved from sole anaerobic digestion of SLS was obtained.
The two-stage anaerobic process for sequential production of hydrogen and methane
from thermophilic dark co-digestion of SLS with POME at a mixing ratio of 55:45 (%V/V) was
investigated. The first stage was operated in a continuously stirred tank reactor (CSTR) for
producing at the hydraulic retention times (HRTs) of 2.25 days and 4.50 days, corresponding to
organic loading rate of 20 g-VS/ L reactor d and 10 g-VS/ L reactor d, respectively. Hydrogen
production was achieved at the HRT of 4.50 days with the hydrogen production rate and
hydrogen production yield was 341±19 mL H 2/L reactor d and 1533±88 mL H 2/L substrate,
respectively, which is higher than that obtained from the HRT of 2.25 days. Under the
operational conditions at the 4.50-day HRT, soluble metabolites were dominated with acetic acid
(14.7-24.1 mM), butyric acid (15.8-28.7 mM), propionic acid (12.7-26.5 mM), ethanol (13.2-
21.0 mM), and lactic acid (99.1-138.1 mM). Subsequently, the homogenized effluents collected
the first stage hydrogen production operated at 4.50-day HRT was further fed into the second
stage at the HRT of 18 days, corresponding to the organic loading rate of 2 g-VS/L reactor d. The
average methane production rate and methane production yield was 79±12 mL CH 4/L reactor d and
1517±199 mL CH 4/L substrate, respectively. Further optimization for the second stage UASB is
necessary due to acetic acid accumulated in rather high concentration (63-150 mM).