Plant Performance Using Dissolved Oxygen Control

The Renton Sewage Treatment Plant offered a unique opportunity to obtain unbiased, comparative performance evaluation data for both automatic and manual dissolved oxygen control. The data were ranked in ascending order and plotted on logarithmic probability paper to obtain a frequency distribution. The parameters that were considered were BOD in the effluent, BOD and COD removals, sludge volume index, and settleability. All the parameters showed in improvement when the operation was changed to automatic dissolved oxygen control with the exception of COD values, which reflected little change. A rate constant that considered BOD removals, hydraulic flow, and the concentration of mixed liquor suspended solids was used to determine the overall efficiency of process. In changing from manual to automatic dissolved oxygen control, the rate constant changed from 0.0260 to 0.1018, which reflects an improvement of 391%.