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CHAPTER V

CONCLUSIONS

5.1 Summary

This thesis has focus on mixing ratio and nutrients optimizations for biohydrogen
potential (BHP) from batch thermophilic anaerobic dark co-fermentation of skim latex serum
(SLS) and palm oil mill effluent (POME) using thermophilic anaerobic mixed cultures.
Therefore, the biomethane potential (BMP) using effluents achieved from hydrogen stage under
the optimal conditions was also investigated. Moreover, in this thesis has also investigated the
effect of hydraulic retention times (HRTs) on the sequential productivity of biohydrogen and
biomethane from the optimal mixing ratio of SLS and POME in a lab-scale reactor for a period
longer than 90 days and 70 days, respectively for hydrogen and methane stages operation. The
main outputs of this thesis work can be summarized as follow.

 The generating of biohydrogen and biomethane from batch two-stage dark co-digestion
of SLS and POME was successfully achieved. Satisfactory hydrogen and methane
production yields of 85.7±4.9 mL H 2/g-VS added and 418±10 mL CH 4/g-VS added,
respectively were achieved from the mixing ratio of SLS to POME at 50:50 (%v/v) with
7 g-VS added/L. The response surface methodology (RSM) results indicated that only
NaHCO 3 concentration had significant individual effect on hydrogen production yield.
The maximal hydrogen production yield achieved from moderate condition with the
hydrogen production yield was 91.7±3.9 mL H 2/g-VS added.

 In this research, the hydrogen generated in H 2-CSTR reactor is still low with the
hydrogen production yield was 34±2 mL H 2/g-VS added due to overload the process has
occurred, leading to metabolic pathway shift to lactate formation pathway. At the same
time, relatively high acetate concentration produced and accumulated in CH 4-UASB
reactor, resulting in low methane production yield was 87±11 mL CH 4/g-VS added.
Although, the energy production yield achieved in this process was still low of 3917.30
kJ/kg-VS, this study provides valuable information in order to further define the optimal
conditions for acidogenic and methanogenic stages operation.