Wave generation in subsurface aeration system: a new approach to enhance mixing in aeration tank in wastewater treatment

Abstract

Energy crises in the early 1970’s created awareness of the cost of wastewater treatment and the energy required for each stage. Aeration process was the focal point of energy saving research, due to its high power consumption, which led to change the use of coarse bubble aeration system to fine bubble aeration. Until now, all commercially existing aeration systems use continuous airflow. Meanwhile, the system investigated in this paper uses pulsation flow to reduce energy consumption in aeration tank by improving oxygen transfer efficiency (OTE). In this study, a new innovative air injection method is proposed to improve OTE in the aeration basin without extra power depletion. The suggested method is simply to inject air alternatingly from two adjacent diffusers into the aeration system. It was found that OTE was improved using this method. This improvement could be attributed to water agitation caused by transient condition operation. Timing the separation between two injections is a very important aspect of the proposed system. The optimum separation time was found by varying the timing between these injections. The highest OTE was obtained at a separation time of 1.5 s and a volumetric flow rate of 42 LPM with a 57.1% enhancement in comparison to the steady state traditional aeration system.