This paper describes the application of the inverse fluidization technology to the anaerobic digestion of wine distillery wastewater. In this reactor, a granular floating solid is expanded by a current of gas. The carrier particles (Extendospheres (TM)) were chosen for their large specific surface area and their low energy requirements for fluidization. The experimental procedure was defined to examine the effect of transient changes in organic load on the performance of an anaerobic inverse turbulent bed (ITB) reactor. Moreover, in order to evaluate treatment efficiency, the active biomass concentration was estimated using the phospholipids analysis. The ITB bed reactor appeared to be a good option for anaerobic treatment of high strength wastewater, particularly for the treatment of wine distillery wastewater. The system attained high organic loading rate (OLR) with good chemical oxygen demand (COD) removal rates and it exhibited a good stability to the variations in OLR and HRT. It was found that the main advantages of this system are: low energy requirement because of the low fluidization velocities required; there is no need of a settling device, because solids accumulate at the bottom of the reactor, so they can be easily drawn out and particles with high-biomass content can be easily recovered. Lipid-phosphate concentration has been revealed as a good method for biomass estimation in biofilms since it only includes living biomass. The comparison of the measured concentration of volatile attached solids with the estimated active biomass concentration by means of phospholipids analysis indicated that extremely high active biomass concentrations can be maintained in the system. (c) 2006 Elsevier B.V. All rights reserved.