The Influence of In-Situ Oxygenator Design on Wastewater Basin Mixing

Modern biological treatment of municipal or industrial wastewaters has a high demand for oxygen due to an abundance of dissolved organics. In such processes, pure oxygen is supplied to the biomass in the wastewater to obtain a much faster destruction rate of harmful organic contaminants. The Praxair patented I-SO™ system has been successfully implemented to optimize oxygen transfer with reduced power consumption in wastewater treatment. A study of the flow structure and mixing characteristics of an in-situ oxygenation system for dissolution of gas into a large body of liquid has been performed using concurrent experimental and numerical analysis. The purpose was to improve the understanding of mixing and oxygen transfer mechanisms in wastewater treatment processes. Many factors influence the oxygen transfer rate and make each oxygenation device unique in its field application. In the present work, the impacts of impeller pumping rate, immersion depth of the aeration unit, flow rate of gas supplied to the system, geometry of the basin and type of outlet baffle on the down draft tube on the flow structure and mixing pattern are investigated. The oxygen transfer efficiency of each in-situ oxygenator can be estimated through a statistical model developed from the method of experimental design. The simulations presented here open a new area for their application as a tool fully complementary to test and measurement in a “concurrent simulation and testing” process. The opportunities and benefits offered by the process for wastewater oxygenation system design and analysis are described in detail.