The effects of porphyritic andesite on the hydrolysis and acidogenesis of solid organic wastes were investigated by batch and continuous experiments using a rotational drum fermentation system. The results of the batch experiment show that if porphyritic andesite (1%, 3%, and 5% reactants) is added initially, the pH level increases and hydrolysis and acidogenesis are accelerated. The highest surface based hydrolysis constant (26.4 x 10(-3) kg m(-2) d(-1)) and volatile solid degradation ratio (43.3%) were obtained at a 1% porphyritic andesite addition. In the continuous experiment, porphyritic andesite elevated the first order hydrolysis constant from 13.10 x 10(-3) d(-1) to 18.82 x 10(-3) d(-1). A particle mean diameter reduction rate of 33.05 mu m/d and a volatile solid degradation rate of 3.53 g/L d(-1) were obtained under the hydraulic retention time of 4, 8, 12 and 16 d. (C) 2009 Elsevier Ltd. All rights reserved.