Prevention of flow reversal in vertical waste treatment apparatus

Claim 1

In a modified activated sludge waste treatment method wherein an aerobic biological reaction takes place during the continuous circulation of fluid waste in a long vertical shaft treatment apparatus including a fluid waste receiving basin, a long vertical downcomer conduit connected to said receiving basin, a long vertical riser conduit surrounding said downcomer conduit with an axial fluid space therebetween, the said riser and downcomer conduits communicating with each other at their lower ends so as to permit undirectional continuous circulation of fluid waste through said conduits, and air injection means to provide oxygen to the said waste as it passes through the said dowcomer conduit, an improvement in said method whereby a potential reversal in the direction of fluid flow in the said apparatus is prevented, said improvement comprising the step of restricting the size of the internal cross-section of the said downcomer conduit at any point along its length to limit the passage of fluid therethrough by collapsing the said downcomer conduit through the application of pressure against the outside wall thereof, the said downcomer conduit being flexibly inwardly collapsible in response to excess pressure exerted by the surrounding fluid in axial space between the said riser and downcomer conduits.