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4.5 Conclusions

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 because of there is several problems has
occurred are: (i) overload the process; (ii) high hydrogen concentration in the liquid phase; (iii)
the growing of sulfate reducing bacteria in the H 2-CSTR reactor. At the same time, relatively
high acetate concentration produced and/or accumulated in CH 4-UASB reactor, resulting in low
methane production yield was 87±11 mL CH 4/g-VS added. Moreover, the other possible reasons
for having low methane formation are: (i) low CH 4-UASB seed; (ii) high hydrogen partial
pressure; (iii) the competition of sulfate reducing bacteria with methanogenic archaea has
occurred. Although, the energy production yield achieved in this process was still had 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.