Abstract The kinetics of anaerobic treatment of wastewater (consisting of whey plus wash water with a COD of 30 g/1) from a cheese factory was investigated using bioreactors which contained suspension of micronized clays (Sepiolite, Saponite and Bentonite), to which the anaerobic microorganisms adhered. On the assumption that the overall process conforms to first-order kinetics, experimental data pairs (namely the methane volume yielded (G) and time (t)) fitted the equation: G m = G m · [ I − exp(- K 0 · t)]. The apparent kinetic constants, K 0, were determined under various conditions. The mean values were 2.5 days −1 (Sepiolite), 1.9 days −1 (Saponite), 0.8 days −1 (Bentonite) and 0.5 days −1 (Control). The yield coefficients of methane, Y p, were around 350 ml CH 4 STP/g COD. The elimination of COD exceeded 82% in all cases.