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3.5 Conclusions

The generating of biohydrogen and biomethane from two-stage dark co-digestion of SLS
and POME was successfully achieved. The highest hydrogen production yield achieved from
SLS: POME mixing ratio of 50:50 (%v/v) with the hydrogen production yield was 85.7±4.9 mL
H 2/g-VS added. 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 (run 14) with the hydrogen
production yield was 91.7±3.9 mL H 2/g-VS added. Nevertheless, it is increased just only 22%
which is still not uneconomic for applying in the industrial scale when considered the economic
cost of the external buffer and nutrients supplemented. This experiment is still having low of
hydrogen production yield was obtained, the possible cause is that due to they are not initial pH
suitable for biohydrogen production. Moreover, the other reasons is that using of anaerobic
mixed cultures, its able to produce lactate resulted lead to not hydrogen production from lactate
formation pathway. Meanwhile, higher of methane production yield achieved from co-digestion
of SLS and POME of 418±10 mL CH 4/g-VS added was obtained. Which are correlates to the lower
of VFA concentration at the end of the 27 days of methane fermentation, indicated that VFA
produced in the H 2 potential stage was converted to CH 4 in the second stage of the sequential
processes.