This paper describes the application of the inverse fluidization technology to the anaerobic digestion of dairy wastewater. Two reactors were investigated: the inverse fluidized bed reactor and the inverse turbulent reactor. In these reactors, a granular floating solid is expanded by a down‐flow current of effluent or an up‐flow current of gas, respectively. The carrier particles (Extendospheres^(™)) were chosen for their large specific surface area (20,000 m²m⁻³) and their low energy requirements for fluidization (gas velocity of 1.5 mm s⁻¹, 5.4 m h⁻¹). Organic load was increased stepwise by reducing hydraulic retention time from more than 60 days to 3 days, while maintaining constant the feed COD concentration. Both reactors achieved more than 90% of COD removal, at an organic loading rate of 10–12 kg_COD m⁻³d⁻¹, respectively. The performances observed were similar or even higher than that of other previously tested fluidized bed technologies treating the same wastewater. 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.

Many different types of support materials are used in anaerobic fluidized bed in order to obtain high levels of biomass in the reactors. A material is usually considered the most suitable in terms of physical-chemical parameters or reactor performance, but not in terms of microbial adhesion. In this work, two commercial materials were tested as support for anaerobic biomass : peflite a.nd sepiolite. Biofilm accumulation was estimated by two methods, attached volatile solids and lipid phosphate concentration, both determined directly on attached biofilm. The biomass adhesion on sepiolite was higher than the perlite for ali the tested initial total organic carbon concentration in the reactors. We have found that biomass measurement method developed directly on attached biofilm is relevan! to the amount of living cells. We also discuss the suitability of estimating attached

The long start-up period of fluidized bed biofilm reactors is a serious obstacle for their wide installation in the anaerobic treatment of industrial wastewater. This paper presents the results of an anaerobic inverse turbulent bioreactor treating distillery wastewater during 117 days of operation at a laboratory scale. The pre-colonized bioparticles for this work were obtained from a similar reactor processing the same wastewater and which had a start-up period of 3 months. The system attained carbon removal efficiency rates between 70 and 92%, at an organic loading rate of 30.6 kg m⁺³ d⁺¹ (chemical oxygen demand) with a hydraulic retention time of 11.1 h. The results obtained showed that the start-up period of this kind of reactors can be reduced by 3 using pre-colonized bioparticles.