초록
<P><B>Abstract</B></P> <P>Palm oil mill effluent (POME), an agro-industrial wastewater with high solids content, was subject to hydrolysis by 1% (w/v) nitric acid in order to increase its solubility and the fermentable sugar content from its cellulosic component. POME hydrolysate was then evaluated in an up-flow anaerobic sludge blanket (UASB) bioreactor for the production of biohydrogen gas via mixed culture under thermophilic conditions. The bioreactor was fed with pre-treated POME under varied hydraulic retention time (HRT) between 48 and 3 h at constant cycle length of 24 h to test the productivity of H<SUB>2</SUB> and the stability of UASB; no washout of biomass occurred at any cycle and the system managed to recover its H<SUB>2</SUB> production rate (HPR) after initial fluctuations. In this study, H<SUB>2</SUB>-producing granules (HPGs) were formed shortly after the start-up period, and were analysed by FESEM, FTIR, SEM-EDX, and their extracellular polymeric substances (EPS) content. The maximum HY and HPR achieved were 2.45 mol-H<SUB>2</SUB>/mol-sugar and 11.75 L<SUB>H2</SUB>/L<SUB>POME</SUB> d<SUP>−1</SUP>, respectively, at HRT 6 h. Acetic acid was found to be the major by-product at all HRTs, followed by butyric acid, while <I>Clostridium spp</I>. was found to be the most dominant H<SUB>2</SUB>-producing bacteria in the system. Results suggest that UASB has a good potential for stable H<SUB>2</SUB> production with high POME digestion rate.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Raw POME was pre-treated using dilute nitric acid. </LI> <LI> H<SUB>2</SUB>-producing granules from POME were produced in UASB. </LI> <LI> Optimum biohydrogen yield achieved was 2.45 mol<SUB>H2</SUB>/mol<SUB>sugar</SUB>. </LI> <LI> Bacterial community in H<SUB>2</SUB> producing sludge was dominated by <I>Clostridium spp.</I> </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>