Control of an alternating aerobic-anoxic activated sludge system - Part 2:optimization using a linearized model

Complex models, such as activated sludge model No. 1 (ASM1), have rarely be en used in practice for process control or optimization. One major reason f or this is the computational effort demanded by these models for both param eter estimation and simulation, Therefore, a linearized version of the ASM1 model is developed and applied to the control and optimization of a bench- scale alternating aerobic/anoxic activated sludge system. The model predict ion was used to optimize the aeration time by manipulating t(c) (total cycl e time) and f(a) (fraction of aeration cycle time) while meeting the permit requirement of the effluent ammonia concentration, The linear nature of th e model facilitates its use for on-line calculations, and error feedback is used to counteract problems of model inaccuracy. The model was applied to two cases in which the influent compositions were either known currently or only the previous day's information was available. The average optimized f (a) was found to be 0.30 for the first case and 0.37 for the second case, w hen the maximum effluent NH4+-N concentration was set at 1 mg/l. The effici ency of nitrogen removal was 76% for both test cases since nitrate could al most completely be removed through adequate anoxic cycle ratios resulting f rom the f(a) optimization. (C) 2000 Elsevier Science Ltd. All rights reserv ed.