3.1. Continuous hydrogen production
UASB reactors with a working volume of 500 ml were operated
continuously to produce hydrogen from POME wastewater using
suspended and immobilized-cells. The effects of HRTs on the
biogas production rate, composition of biogas and soluble
metabolites, and substrate utilization efficiency were examined
during the course of hydrogen production. The data for suspended
and immobilized-cell reactors are showed in Figs. 2 and 3,
respectively. The correlations between HRTs and hydrogen
generation efficiency as well as substrate utilization efficiency
were summarized in Table 2. In all cases, the biogas primarily
consisted of CO2 and H2, while CH4 was undetectable. Substrate
utilization efficiency was essentially within range of 60–91% at all
HRTs used (Table 2). Typical soluble metabolites included butyric
acid (HBu), acetic acid (HAc), propionic acid (HPr), and ethanol
(EtOH).
3. Results and discussion