COD (chemical oxygen demand) removal rate and efficiency of winery wastewater (WW) aerobic treatments were evaluated in an air-bubble column bioreactor using self-adapted microbial populations either free or im mobilized on polyurethane particles and in a packed-bed bioreactor immobilized oh Raschig rings. The bioreactors were fed continuously for up to 12 months using WW of different origins and with different pollution loads (COD range, 0.8-11.0 kg.m(-3)): the maximum loading rate was approx. 8.8 kg-COD m(-3).d(-1). The highest COD removal rate (6.6 kg.m(-3).d(-1)) was obtained with free activated sludge in the bubble column bioreactor; treatment efficiency and hydraulic retention time were >90% and approx. 0.8 d, respectively. The microbial populations in the three reactors were characterized.