Submerged fixed film biological treatment system

In an aerobic process for treating an aqueous liquor containing a biodegradable waste product wherein the liquor is introduced into a container and the waste product biologically digested as it is passed through the container from an inlet to an exit, said biological digesting being accomplished by contacting the liquor with an oxygenating gas in the presence of a submerged porous mass supporting aerobic microorganisms;

• the improvement for effecting efficient oxygen transfer and utilization which comprises:
• establishing and maintaining at least a first and second vertically extending chamber within said tank, said chambers being in fluid communication with each other at the upper and lower ends;
• establishing and maintaining a corrugated packing within said first and second chambers, said corrugated packing having channels defining a serpentine pathway in the vertical direction;
• passing liquor and oxygenating gas upwardly through said corrugated packing in at least one of said first vertically extending chambers generating an oxygen rich liquor whereby a portion of the waste product is biologically digested by microorganisms supported on said corrugated packing, and;
• returning a portion of oxygen rich undigested liquor from said first chamber downwardly through said second vertically extending chamber and in contact with microorganisms supported by the packing and then returning a portion of the liquor into a first chamber.