Apparatus for the anaerobic filtration of waste water

In an apparatus for the anaerobic filtration of waste water, said apparatus being of the type including an enclosure having therein a submerged filter of filling material, means for introducing waste water to be treated into a lower portion of said enclosure such that said waste water passes through said filter from bottom to top and submerges said filter, during which biogas is produced, means for removing filtered water from an upper portion of said enclosure above said filter, and means for collecting said biogas above said filter, the improvement wherein said filter comprises:

• a lower layer comprising an ordered arrangement of vertically extending members defining vertical channels through which passes the water being treated and having a large specific surface of up to 200 m.sup.2 /m.sup.3 ;
• an upper layer positioned above said lower layer and comprising a loosely packed arrangement of members having a specific surface greater than 200 m.sup.2 /m.sup.3 ;
• and
• means for supporting said upper layer and for separating said upper layer from said lower layer and comprising an intermediate layer of loosely packed hollow cylindrical bodies dimensioned or shaped to rest on said members of said lower layer without blocking said vertical channels and to prevent said members of said upper layer from penetrating downwardly into said members of said lower layer, each said cylindrical body having a diameter of at least four times larger than the height thereof, said diameter of each said cylindrical body being at least 1.5 times the widths of said channels defined by said members of said lower layer.