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4.2 Introduction

Thailand is one of the most agricultural areas in the Southeast Asia which is various
kinds of agricultural crops such as cassava, sugar cane, corn, palm oil and rubber. Among them,
rubber is the major agricultural crops cultivated in Southern Thailand, corresponding with a
mostly of located in rubber plant, whereof mostly are provided to produce concentrated latex.
There are several methods available for concentration of natural latex is comprehensive
creaming, evaporation, electro-decantation and centrifugation. Among them, centrifugation is the
most method used to produce concentrated latex in Southern Thailand. An annual production
6
capacity of concentrated latex obtained from Southern Thailand was around 1.3 x 10 metric ton
3
which is produced in 2013 (Kongjan et al., 2014). In this process about 580 m of skim latex
serum was generated and approximately of 405 ton of concentrated latex was produced. Skim
latex serum is a concentrated with a relatively high organic content in the macronutrients in
carbon, nitrogen and phosphorus which are the crucial on microbial growing. Thus, skim latex
serum generated cannot be discharged into environmental directly, thank to it could cause
seriously environmental pollutions.

There are several biological ways to treat this organic waste generated such as aerobic
and anaerobic system. Among this option, anaerobic system is a suitable approach and great
interest since there are several advantages over aerobic system such as higher organic loading
rate, lower operating cost, gave less excess biomass and produced biogas as a usable product.
Although skim latex serum contains high nutrients content as previously mentioned, but it’s also
containing in a relatively high inhibitants content such as ammonia (latex preservation) and
sulfate (latex coagulation) which is important to microbial growing as well as the efficiency of
biogas formation. Corresponds with a study from Kongjan et al. (2014) used two-stage anaerobic
digestion process found that a relatively low of hydrogen and methane production yield achieved
from sole fermentation of skim latex serum. The hydrogen generated in H 2-UASB reactor was
59.2±2.4 mL H 2/g-VS, while methane generated in CH 4-UASB reactor was 168.6±13.8 mL
CH 4/g-VS, which is just only 11 and 45% of hydrogen and methane theoretical yield (498 mL
H 2/g-VS and 373 mL CH 4/g-VS). They were reported the possible reason for having low
hydrogen formation because of the competition of hydrogen producing bacteria and sulfate
reducing bacteria to produce neither hydrogen nor hydrogen sulfide. In additional, 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 from skim latex serum fermentation, the
approach of anaerobic co-fermentation of organic wastes and two stages process was performed
in this work. Apart from rubber, palm oil is one of the most agricultural crops cultivated in
Southern Thailand. A study from O-Thong et al. (2008) found that high hydrogen production
yield was achieved from sole fermentation of palm oil mill effluent was 84.2 mL H 2/g-COD and