Performance improvement of activated sludge wastewater treatment by nonlinear natural oscillations

The paper describes a novel operation strategy for improvement in the performance of biochemical reactors. The dynamic behavior of two coupled continuous stirred-tank reactors with recycle is studied when one of the reactors is being operated under limit cycle regimes producing self-sustained natural oscillations. The periodic output from one reactor is then used as forced input into the other reactor. The novel operation strategy is applied to wastewater treatment by the activated sludge process. It was observed and demonstrated through computation that the overall performance of the system can be enhanced in terms of time-averaged conversion by employing the above-mentioned operation strategy for a particular combination of reactor volume, recycle ratio and other operating parameters. The most significant criterion of this operation strategy lies in the fact that the performance enhancement of the overall system is achieved through natural oscillation rather than forced oscillation. In experimental studies and in eventual application to industrial processes this new concept of coupling free and forced oscillation is advantageous, as it does not require any additional external energy.