Abstract: A fermentation unit comprising a scoop wheel equipped with scoops on the periphery thereof, and which moves between bunker silos. The bunker silos are equipped with aeration ducts at the base thereof. Flexible scrapers located around the periphery of the scoop wheel scrape the aeration ducts. Unstacking barbs are also located on the periphery of the scoop wheel. Means are provided to adapt the unit to the type of materials to be treated.

Abstract: In a biological water purification process polluted water, including surface water to be made potable, sewage water or industrial water, is percolated through a submerged fixed bed of granular material such as activated carbon, chamottes, raw clays, etc., with an oxygenated gas being upwardly injected at an intermediate level of the bed. The water and gas delivery rates are controlled to satisfy the following relations: ##EQU1## wherein Q.sub.1 is the delivery of oxygenated gas in m.sup.3 /hr,Q.sub.2 is the delivery of water to be treated in m.sup.3 /hr,.epsilon. is the porosity of the granular material bed,.alpha. is the maximum fraction of the volume that can be occupied by the gas without affecting the effectiveness of the treatment,S is the bed section in m.sup.2,h is the height of the bed in meters,v is the vertical component of the average speed of the ascending gas bubbles in m/hr,K.sub.1 is a constant corresponding to the fraction of volume of bed occupied by immobilized gas pockets in m.sup.3,K.sub.