Both pH and volatile fatty acid (VFA) inhibit the hydrolysis of particulate organic waste. It is not clear yet whether VFA or pH is the dominant factor in hydrolysis inhibition. The effects of pH and acetate on the enzymatic hydrolysis of potato samples containing mainly carbohydrate were studied at fixed pH values (5-9) and with/without 20 g L(-1) acetate. The leaching liquors were refreshed at prescribed intervals. Experimental results showed that both pH and acetate influenced the hydrolysis of carbohydrate, but that pH was more influential than acetate. Numerous kinetic models could fit the hydrolysis data during the first 40 h of hydrolysis when inhibitive effects were not significant. The simplified Chen-Hashimoto model, -dS/dt = K(H)S/(K(s)(S(0) - S) + S), closely fit all of the experimental data. Also, the fitting achieved by applying the non-competitive inhibition model (K(H) = K(H)(0)/(1 + I/K(1))) on three inhibitors (H(+), OH(-), total/undissociated/dissociated acetate) was excellent for carbohydrate hydrolysis. (0 2007 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.