Two zone apparatus for biological treatment of waste water

Abstract

A biological waste water treatment carried out in a single tank. The conditions in the tank are controlled to provide a biological reaction zone containing waste water and biodegrading organisms and an overlying clarification zone from which an effluent of treated waste water flows. The recycle stream is continuously withdrawn from the biological reaction zone, supplemented with influent waste water, passed through an oxygen-dissolving device, and the supplemented stream returned to the reaction zone. The oxygen is monitored and supplied to satisfy the demands of the organisms and, at the same time, to keep the oxygen in solution. The supplemented recycle stream is continuously injected along the bottom of the biological reaction zone in a horizontal shallow inflow having a width substantially greater than its depth and a flow considerably greater than that of the influent. And, the recycle stream is withdrawn from near the bottom of the reaction zone, at a vicinity remote from the inflow, in an outflow having a substantially greater width than its depth. In this way there is created between the inflow and the outflow a horizontally relatively fast flowing undercurrent having an extensive uninterrupted interface with an overlying relatively quiescent body of mixed liquor flowing upwardly relatively slowly.