Development and Field Testing of a New Intelligent Sequencing Batch Reactor (iSBR) Control System

The Daniel Island WWTP serves an area that is experiencing phenomenal growth. The Sequencing Batch Reactors (SBR) that provide secondary treatment at the plant are rapidly approaching their design capacity and so the Charleston Water System commissioned Black & Veatch to investigate options to optimize the treatment capacity of the SBRs beyond their existing design capacity.The plant optimization used an intelligent control approach termed the “intelligent” SBR or “iSBR”. The iSBR control approach measures the oxygen uptake rate (OUR) of the mixed liquor to determine when the SBR has completed treatment, indicated by a sudden decrease in the OUR as the activated sludge reaches an endogenous state. The iSBR control was tested in two steps. Firstly, a dynamic process model of the plant was used to prove iSBR control approaches based on OUR, dissolved oxygen (DO) and rate of change of DO (“dO/dt”). Secondly, a 5-day full-scale trial was carried out on one of the SBRs at Daniel Island. The fullscale trial was successful and so the control was left in operation after the trial period was over. This is the first time the iSBR control approach has been used successfully in a full-scale application.The iSBR control system in conjunction with the addition of extra aeration capacity enabled the plant to increase its design rating by 50%. Addition of an influent equalization tank will enable the plant to increase its design still further to effectively double the plant capacity.