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CHAPTER IV

Thermophilic dark co-digestion of skim latex serum (SLS) and palm oil mill effluent
(POME) to sequentially produce biohydrogen and biomethane

4.1 Abstract

The two-stage anaerobic process for sequential production of biohydrogen and
biomethane from thermophilic dark co-digestion of skim latex serum (SLS) with palm oil mill
effluent (POME) was investigated. The CSTR seed was treated by load shock method by using
30 g-Sucrose/L under thermophilic temperature to enrich thermophilic hydrogen-producing
seeds from anaerobic mixed culture that were collected from mesophilic wastewater treatment
pond. The production of biohydrogen in continuous process in the first stage was operated under
hydraulic retention times (HRTs) between 2.25 days and 4.50 days, corresponding to organic
loading rate of 20 g-VS/ L reactor d and 10 g-VS/ L reactor d, respectively. Hydrogen production was
achieved under HRT of 4.50 days with the hydrogen production rate and hydrogen production
yield was 341±19 mL H 2/L reactor d and 1533±88 mL H 2/L substrate, respectively, which is higher
than that achieved from HRT of 2.25 days. Under the operational conditions at 4.50-day HRT,
soluble metabolites were dominated with lactic acid (99.1-138.1 mM), acetic acid (14.7-24.1
mM), butyric acid (15.8-28.7 mM), propionic acid (12.7-26.5 mM) and ethanol (13.2-21.0 mM).
Subsequently, the homogenized effluents collected from the first stage hydrogen production
which operated under the optimal conditions was further fed into the second stage under HRT of
18 days, corresponding to the organic loading rate of 2 g-VS/L reactor d. The average methane
production rate and methane production yield was 79±12 mL CH 4/L reactor d. and 1517±199 mL
CH 4/L substrate, respectively. Further optimization for the second stage UASB is necessary due to
acetic acid accumulated in rather high concentration (63-150 mM).