A saddle#x2010;shaped biocarrier, which was made of slag discharged from blast furnaces, was packed in an anaerobic fixed#x2010;bed reactor. Reactor performance was evaluated by using a synthetic wastewater composed of glucose and corn#x2010;steep#x2010;liquor. Mesophilic anaerobic bacteria from the seed sludge tank were attached to the biocarrier (which has a specific surface area of 335 m2m#x2010;3) by circulating seed sludge up through the fixed#x2010;bed reactor. During the experiment, the effluent from the top of the reactor was reintroduced into the bottom of the reactor (flow rate, 16 cm3min#x2010;1) and mixed with the influent from the feed tank (flow rate, 0.4 to 2.4 cm3min#x2010;1). The recycle ratios changed from 40: 1 to 7: 1 through the experiment, and the linear velocity in the reactor was 1.1 to 1.2 cm.min#x2010;1. When the influent COD was increased from 4 to 20 gdm#x2010;3at a hydraulic residence time (HRT) of 48 hours (corresponding to COD loading rates of 2 to 10 gdm#x2010;3day#x2010;1), the COD removal was more than 95. For variations of HRT from 48 to 12 hours, the COD removal was over 90 at a COD loading rate of 10 gdm#x2010;3day#x2010;1. The MLSS in the effluent was found to be within the range of 0.2 to 0.6 gdm#x2010;3, and the methane conversion ratio was between 0.30 to 0.33 dm3g#x2010;1COD removed (25#xB0;C). No clogging or channelling occurred in the reactor during the entire six months of the whole experiment.
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