Page 21 - 048

3

reducing bacteria to produce either hydrogen or hydrogen sulfide. Hydrogen sulfide (H 2S) has
inhibitory effect on methanogenic archaea at even low concentration of 20 – 30 mM (Boe, 2006).
Thus, to enhance the biogas production potential, there are several methods such as using various
biological and chemical additives under different operating condition, pretreatment of both
substrate and seed sludge, co-digestion of organic substrates and two-stage process (Liu et al.,
2006; O-Thong et al., 2008; Luo et al., 2010; Alrawi et al., 2011; O-Thong et al., 2012). Among
various options, in this research was focused on two methods to enhance the biohydrogen
production, including co-digestion of organic substrates and two-stage anaerobic process.
Anaerobic co-digestion of organic wastes has been extensively researched due to this
method has several advantages compared to single substrate digestion such as increased process
stability, improves the biogas production yield, synergistic effect and easier handling of mixed
waste steams (Mata-Alvarez et al., 2000; Nayono et al., 2010; O-Thong et al., 2012). This
research was carried out by using anaerobic co-digestion of skim latex serum (SLS); wastewater
generated from concentrated latex plant and palm oil mill effluent (POME); wastewater
generated from palm oil mill plant as substrate to produce biogas. POME was used as co-
substrate due to it contains large quantities of nutrients, including carbohydrates ranged 8.3 –
24.7 g/L, total phosphorus ranged 0.47 – 1.25 mg/L and oil content ranged 2.3 – 10.6 g/L (Badiei
et al., 2011; Fang et al., 2011; Khemkhao et al., 2012). POME has been widely used as substrate
to produce biogas. Mamimin et al. (2012) used thermoanaerobacterium-rich sludge as inoculum
to produce biohydrogen in a continuously stirred tank reactor (CSTR) with the highest hydrogen
production yield of 4.2 L H 2/L POME was obtained under hydraulic retention time (HRT) of 2
days. Badiei et al. (2011) used anaerobic sequencing batch reactor (ASBR), the maximum
hydrogen production yield was 0.34 L H 2/g-COD feeding achieved under the HRT of 72 h. At the
same time, methane potential achieved from batch sole fermentation of POME and deoiled
POME was 503 and 610 mL CH 4/g-COD added, respectively. Meanwhile, biomethane production
potential in continuously fed reactor was 436 and 438 mL CH 4/g-VS added achieved from POME,
while 600 and 555 mL CH 4/g-VS added achieved from deoiled POME which was operated in
upflow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors
(Fang et al., 2011). Although satisfactory of biohydrogen and biomethane production from
individual fermentation of POME was observed. There are, however, several researches was
carried out by using co-digestion of POME such as co-digestion with rumen fluid take from the
first compartment of cow’s stomach (Alrawi et al., 2008), oil palm empty fruit bunches (O-
Thong et al., 2012) and skim latex serum (Sama et al., 2014). Our previous study used anaerobic
co-digestion of SLS and POME, the result shows that the optimal mixing ratio of SLS and
POME was 75:25 (%v/v) with the highest hydrogen production yield was 35.0±1.2 mL H 2/g-
COD which was 1 and 5 times greater than that achieved from sole fermentation of SLS and
POME, respectively. One of the benefits of using POME as co-substrate is that to adjust C/N
ratio in the mixture as it contains high C/N ratio ranged 37 – 68. Moreover, POME was also used
to dilute several inhibitants in the SLS to enhance the efficiency of biogas production.