Enhanced control of activated sludge process using predetermined set-points

Abstract

The performance of activated sludge process (ASP) is evaluated by the effluent quality which is determined by five different variables of the treated wastewater such as ammonia, total nitrogen, COD, BOD₅ and TSS. To keep these five variables within the limits as per environmental regulations, nitrate and nitrite concentration (S _NO) in the second anoxic reactor and the dissolved oxygen concentration (S _O) in the last aerobic reactor of the ASP should be maintained at prescribed levels. To do that, a closed-loop control configuration is required and proper set-points for these closed-loop control configurations are needed. In this paper, the optimal values of controller set-points are determined for nitrogen removal in the activated sludge process. Effluent quality limits have been considered to evaluate the optimal set-points for the Indian climatic conditions. Once the optimal set-points are determined, PI controllers are used to control S _NO in the second anoxic reactor and S _O in the last aerobic reactor of the ASP. Further, feed-forward control is incorporated to minimize the effect of disturbances, which enters along with the influent. No case studies of BSM1 model have been reported in the literature for the Indian wastewater. In this work, the dynamic simulation of an activated sludge process is performed using the data collected from the sewage treatment plant, located in India. The results of the simulation showed that feed-forward with PI control strategy, ASP can be efficiently controlled without any effluent violations, when compared to BSM1.