The biological hydrogen (bio-H(2)) production from apple pomace (AP) by fermentation using natural mixed microorganisms in batch process was studied under various experimental conditions. The river sludge was used as a seed after being boiled for 15 mm. The results show that the optimal pretreatment for AP was to soak it in the ammonia liquor of 6% for 24 h at room temperature. An optimal fermentation condition for bio-H(2) production was proposed that the pretreated AP at 37 degrees C, the initial pH of 7.0 and the fermentation concentration of 15 g/1 could produce a maximum cumulative H(2) yield (CHYm) of 101.08 ml/g total solid (TS) with an average H(2) production rate (AHPR) of 8.08 ml/g TS/h. During the conversion of AP into H(2), acetic acid, ethanol, propionic acid and butyric acid were main liquid end-products. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.