Page 73 - 048

55

lactic acid was still found as the major soluble metabolite products of all operational conditions.
Which is consistent with our previous research in batch assay that used the enriched and
acclimated hydrogen producing bacteria obtained from H 2-CSTR reactor was operated under the
volumetric mixing ratio of SLS to POME at 1:1 under HRT of 4.50 days. The result shows that
lactic acid was the main soluble metabolite products in a relatively high concentration of all
treatment. Reactions (4.1) and (4.2) shows metabolic pathway produced lactic acid by lactic acid
bacteria (LAB), which distinguished between homofermentative LAB (Reaction 4.1) and
heterofermentative LAB (Reaction 4.2) (Mariakakis et al., 2011). Although lactic acid could be
transformed to acetic, propionic (Reaction 4.3) and butyric acids (Reaction 4.4) by Clostridium
propionicum and Clostridium tyrobutyricum to generates hydrogen (Noike et al., 2002).
Nevertheless, hydrogen could be generated by secondary fermentation (Reactions 4.3 and 4.4)
which provides the biological reaction rate slower than that generated by primary reaction rate.
Moreover, a study from Noike et al. (2002) found that the hydrogen production yield gradually
decreased and ceased since high concentration of lactic acid was detected.

C 6H 12O 6 2 CH 3CH(OH)COOH (4.1)

C 6H 12O 6 CH 3CH(OH)COOH + CH 3COOH + CO 2 (4.2)

3 CH 3CH(OH)COOH 2 CH 3CH 2COOH + CH 3COOH + CO 2 + H 2O (4.3)

CH 3CH(OH)COOH + 0.4 CH 3COOH 0.7 CH 3(CH 2) 2COOH + CO 2 + 0.4 H 2O + 0.6 H 2 (4.4)

Furthermore, the other possible reason for still lower of hydrogen was generated of all
operational condition is that the growing of sulfate reducing bacteria in the H 2-CSTR reactor
which could potentially consume hydrogen generated (Reactions 4.5 and 4.6) (Schink, 1997).

2-
2-
4H 2 + SO 4 S + 4H 2O (4.5)
0
H 2 + S H 2S (4.6)