Study on hydrogen production with hysteresis in UASB

This paper uses a 10-1 UASB (upflow anaerobic sludge blanket) bench-scale reactor to treat the esterification wastewater of a polyethylene terephthalate manufacturing plant. Two organic loading rates are used to evaluate the effect on H-2 production of temperature gradually step-down and step-up in the range of 11-25 degreesC. Experimental results show that H-2 production is positively related to temperature. H-2 production increases with temperature at the higher organic loading rate (4.5 kg COD m(-3) d(-1)). However, the H-2 produced does not go back to its original concentration but rather follows a hysteresis curve. This hysteresis also occurs in the corresponding concentrations of COD, acetate, propionate and butyrate. As in the H-2 profiles, these parameter curves return clockwise during the temperature step-up. At the lower organic loading rate (2.2 kg COD m(-3) d(-1)), no obvious hysteresis is observed for H-2 curve. The pattern of other parameters, except for the propionate, returns counterclockwise resulting in the hysteresis phenomena. (C) 2003 Elsevier Ltd. All rights reserved.