In the present study

the anaerobic contact reactor (ACR) was used to produce hydrogen from diluted molasses by anaerobic fermentation

and an ethanol-type fermentation and butyric-type fermentation were established by keeping the effluent pH of the two reactors at 4.5-5.0 and 5.5-6.0

respectively. And then the comparison of the impact of influent substrate concentration on the performance of the above two reactors was investigated. For the ethanol-type fermentation system

the fermentative hydrogen-producing efficiency was enhanced when the influent chemical oxygen demanding (COD) was increased from 5000 to 12000 mg·L-1 under the HRT of 6 h

whereas

the feedback inhibition was turn to be functioned as the influent COD was increased to 15000 mg·L-1. It was found that the hydrogen production rate (HPR)

specific hydrogen rate of sludge (SHPR) and hydrogen yield (HY) was peaked at 68.8 L·d-1

744.5 ml H2·(g VSS·d)-1 and 2.3 mol H2·(mol glucose)-1

respectively

when the influent COD was 12000 mg·L-1. For the butyric-type fermentation system

the hydrogen producing efficiency was decreased on the whole as the influent COD was increased from 5000 to 20000 mg·L-1 under the HRT of 8 h. It also showed that the maximum value of SHPR and HY was 159.6 ml H2·(g VSS·d)-1 and 1.0 mol H2·(mol glucose)-1

respectively

when the influent COD was 5000 mg·L-1. It indicated that the hydrogen-producting capability of ethanol-type fermentation was better than that of butyric-type fermentation.