Practical Application of an Srt Calculator Tool that Accounts for pH, do, and Temperature

Developments in process modeling, in-situ analyzers, and integrated control systems have become more robust in recent years. These developments allow more aggressive design of nitrifying activated sludge systems with low safety factor applied to the minimum aerobic solids retention time (SRTmin) needed to avoid washout. The resulting short-SRT design can be used to accommodate economy and capacity in a size-constrained reactor-settler system. Often times short-SRT designs employ an enrichment bioaugmentation scheme by continually seeding nitrifiers from another coupled (in-situ) or uncoupled (external) reactor that treats an ammonia-rich centrate stream. To better capture the intended benefit of short-SRT with low safety factor, a daily estimation of SRTmin based on temperature, dissolved oxygen and pH can be used to more accurately monitor and control the process. An SRT Calculator that employed measurement and estimation of SRTmin based on these parameters is described herein that was successful at (a) meeting consistently low effluent ammonia at short-SRT, (b) providing clear and consistent directives on process adjustments, and (c) improving the general understanding and prediction of factors that influence performance of a short-SRT system.