Process control system of granular media filter considering daily flow-rate fluctuation

Abstract

In this study, to investigate the influence of fluctuation in hydraulic loads on both the operation of filtration process and the quality of filtered water for a domestic water treatment plant, two different control methods were analyzed and compared with each other: (1) constant-rate filtration using a flow meter and a flow modulation valve (rate control method; RC method), (2) constant-level filtration using equal-flow splitting inlet weirs, water level sensors, and a flow modulator valve (level control method; LC method). From the results of experiments, it could be showed that a sudden flow surge may cause significant particle detachment in terms of particle count in filtered water under conditions of LC method. In addition, this method can lead to difficulty in maintaining residual chlorine at the outlet of clear well. On the other hand, the RC method, in two aspects - the process operation and the quality, is evaluated to be more appropriate than the LC method with seriously large fluctuation in inlet flow.