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The usage of two-stage anaerobic digestion process is one of an approach used to reduce
sulfate containing in the SLS in formed H 2S, which is easily released from the fermentation broth
in the acidogenic stage (Kongjan et al., 2014). Furthermore, the reason for using two-stage
process was to separate hydrolysis/acidogenesis and acetogenesis/methanogenesis
microorganisms groups in separated reactor, due to there are several differences in term of
nutritional need, growth kinetics and environmental conditions, leading to a large overall
reaction rate and biogas production yield (Liu et al., 2006; Luo et al., 2010; Kongjan, 2010; Zhu
et al., 2011; Nkemka, 2012). Under the optimal environmental conditions of acidogenic and
methanogenic stages in two-stage process, there are several advantages over the single stage
process such as more process stability, higher digestion efficiency and higher methane content in
biogas. The first stage of two-stage anaerobic digestion process is acidogenic stage; the
biopolymers are broken down to soluble oligomers and monomers and are then further degraded
to organic acids, alcohols, hydrogen and carbon dioxide (Özmen and Aslanzadeh, 2009;
Kongjan, 2010; Nkemka, 2012). The second stage is methanogenic stage; end products from the
first stage are further converted to methanogenic substrates such as acetate, hydrogen and carbon
dioxide and are then further converted to methane and carbon dioxide. However, various
researches are reported about 70% of methane is originated from acetate via the aceticlastic
pathway by methanogen groups and the remaining from conversion of hydrogen and carbon
dioxide. Nevertheless, these microorganisms are more sensitive to environmental changes i.e.
composition of feedstock, feeding rate, temperature, pH, presence of oxygen as well as presence
and amount of inhibitors such as ammonia, sulfate and sulfur compounds, long-chain fatty acids,
heavy metals and other aliphatic and aromatic compounds (Boe, 2006; Özmen and Aslanzadeh,
2009; Nkemka, 2012).
In this research was carried out by using two-stage anaerobic co-digestion of skim latex
serum and palm oil mill effluent under thermophilic condition at the temperature of 55°C to
produce biogas.

1.2 Thesis objectives

The main objective of this study is to utilize skim latex serum; wastewater generated
from concentrated latex plant and palm oil mill effluent; wastewater generated from palm oil mill
plant for the purpose of anaerobic co-fermentation to produce biogas using thermophilic mixed
cultures fermentation under thermophilic temperature (55°C). In order to able to the main
objective, the experiments are constructed into 4 parts as follows:
1) To determine the optimum mixing ratio of skim latex serum and palm oil mill
effluent in order that hydrogen production.
2) To optimize nutrients and buffer concentrations for hydrogen production from the
optimum mixing ratio of skim latex serum and palm oil mill effluent was using
response surface methodology (RSM) with a central composite design (CCD).