Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe Modeling and simulation of an optimal unified tank model for aeration- sedimentation processes in wastewater treatment plants Bayram Arda Kuş*, Tolgay Kara Department of Electrical and Electronics Engineering, Gaziantep University, 27310, Gaziantep, Turkey ARTICLE INFO Keywords: Process modeling Process simulation Wastewater treatment Optimization Whale optimization algorithm ABSTRACT The operation of Wastewater Treatment Plants (WWTPs) depend not only on the influent characteristics and air blown into the tank, but also the design of the tank structure. In this paper, the mathematical model of the aeration tank is derived by the dynamic equations of physical and biological processes. It is aimed to obtain an effective alternative model for secondary treatment. In the conventional approach, two separate tanks are used for aeration and sedimentation processes. A Unified Tank Model (UTM) for both phases is proposed and in- vestigated in this research. To reach the desired optimized solution, a recently introduced metaheuristic method based on whale feeding behavior, named as Whale Optimization Algorithm (WOA) is used. The dynamic model of real system behavior in the proposed conditions is observed by computer simulation. The results are examined and discussed in the cases of the conventional approach and proposed alternative model. The optimization problems based on aeration system and dissolved oxygen (DO) concentration are defined to find optimal location of the diffusers in tank which is solved using whale optimization method. The optimal design shows better DO performance compared to the conventional approach. The aeration duration and accuracy of DO variation in the proposed UTM design with WOA optimization are shown to be significantly improved. The results of optimal WOA solution in UTM design present a useful alternative with good accuracy in following the desired DO value. 1. Introduction Wastewater treatment (WWT) is a very complex and detailed pro- cess. In a full scaled WWT process operation, mathematical relations between the chemical, physical and biological processes are not easy to model [1]. Recently, many researchers in interdisciplinary areas carried out studies for the treatment of wastewater and its removal without harming the nature. The design and the specific application of an ac- tivated sludge WWT plant (WWTP) is mainly focused on removal of biological nitrogen, biological phosphorus, and organic carbon sub- stances [2]. A WWTP is a combination of complicated processes and it requires execution of several steps for efficacy of WWT process in- cluding establishment, operation and maintenance. Existing studies focus more on decentralized systems in order to decrease the initial cost despite the fact that decentralized plants may have drawbacks re- garding both operation and maintenance steps in WWTP. For efficient operation and maintenance, qualified labor and proper control systems are needed [3]. There has to be an equilibrium between operation and energy consumptions, as well as safety and environmental concerns. The activated sludge mainly consists of a mixture of wastewater and bacteria population, which is kept moving in water by stirring or aeration [4]. Aeration process is the biggest cause of energy con- sumption, which constitutes approximately 60 % of the total consumed energy in a WWTP [5]. The role of aeration is important for two as- pects. First, oxygen is a main component for bacteria and other types of microorganisms to live, grow, and multiply. Second, it supports mixing sludge with the sewage where air is bubbled into the aeration tanks through wastewater that contains dissolved organic substances [6,7]. The living bacteria consume the dissolved organic materials, which are the pollutants in the waste [6,8,9]. During nitrification, the amount of DO concentration has a crucial role in the reduction of ammonium and ammonia nitrogen (SNH) and nitrate (SNO 3 ) concentrations which are more difficult to keep below the legally determined limits [10]. For that reason, DO control and optimization has been a target of a various researches recently [11–13]. The aim of the secondary clarifier is to obtain the purified water (effluent) from the activated sludge through sedimentation. The secondary clarifier and the aeration tank together can be considered as a single process from a process control viewpoint [14]. Different types of reactors such as; Batch Reactor, Complete mix Reactor, Plug flow Reactor, Suspended Reactor, the Moving Bed Biofilm Reactor (MBBR) and Membrane Bioreactor (MBR) are used in https://doi.org/10.1016/j.jwpe.2020.101487 Received 13 May 2020; Received in revised form 24 June 2020; Accepted 28 June 2020 ⁎ Corresponding author. E-mail addresses: akus@ilbank.gov.tr (B.A. Kuş), kara@gantep.edu.tr (T. Kara). Journal of Water Process Engineering 37 (2020) 101487 2214-7144/ © 2020 Elsevier Ltd. All rights reserved. T