Improving aeration efficiency

Aeration is critical to the efficiency of any activated sludge treatment process. The right amount of air at the right time and to the right organisms ensures proper pollutant degradation. In a typical treatment plant, aeration accounts for about 60% of the total power costs of the plant. Hence, failing to optimise aeration is not only detrimental to plant performance but also incurs unnecessary costs.

This paper outlines how savings can be achieved in operating costs by smarter use of aeration in typical activated sludge process. Various principles and techniques of aeration control are discussed in this paper. The main techniques being feed forward control based on influent and air on/air off method. In the latter, two classes of nitrifying organisms are made to work sequentially thus optimising the utilisation of supplied oxygen. Furthermore, real time oxygen uptake rates of the mixed liquor can be measured, which further assists in process optimisation and control.

A desktop benchmarking process was conducted to compare a number of simple aeration control regimes. It was found that approximately 15 to 20% aeration power saving can be achieved. Despite the desktop benchmarking exercise demonstrates 20% aeration saving, it has been reported that aeration saving could be around 25 to 40% at field conditions. This corresponds to a significant reduction of power consumption, greenhouse gas emission (from the power plant) and lower operational and maintenance cost.

A co-ordinated effort between the operational and maintenance staff and the equipment suppliers is vital to deliver the aeration power reduction and cost saving.