The inverse turbulent bed: a novel bioreactor for anaerobic treatment

An inverse turbulent bed was investigated for anaerobic digestion. In this reactor, a granular floating solid is expanded by an up-flow current of gas. The carrier particles (Extendospheres™) were chosen for their large specific surface area (20000 m2 m−3) and their low energy requirements for fluidization (gas velocity of 1.5 mm s−1, 5.4 m h−1). It was tested with wine distillery wastewater and presented promising performances after 90 days of operation: 75–85% carbon removal with an organic loading rate of 15 kgCOD m−3 day−1. The amount of biomass (in terms of attached volatile solids) was close to 0.2 g g−1 of solid at the end of the tests. Most particles were covered with a thin biofilm of uniform thickness, which was attributed to the friction effects due to turbulence. The performance observed during the start-up was similar or even higher than that of other previously tested fluidized bed technologies treating the same wastewater.