###### Abstract  
Wastewater invariably accumulates soluble and insoluble waste and requires treatment at a wastewater treatment plant (WTP) to become reusable. The preliminary screening of insoluble waste occurs through a wastewater screening mechanism (WSM) before entering the WTP. The present study computationally investigates the impact of a WSM, comprising a main screen, sliding sub-screen, and rake, on channel flow distribution, deformation, and stresses. Various sub-screen configurations, fully and partially lowered, are examined. The fluid-structure interaction between sewage water and the WSM was solved using the arbitrary Lagrangian-Eulerian approach. Unlike similar studies in the past which have been conducted in 2D, the present study considers the 3D design and thus captures a greater complexity of the WSM assembly. The velocity distribution inside the channel, structural deformation, and von Mises stresses of WSM components were analyzed for a range of inlet velocities at different stages of the screening process. The results reveal that a fully lowered sub-screen with an inactive rake ensures a uniform flow through the WSM, while a partially lowered sub-screen induces persistent flow separation. Structural analysis reveals significant deformation in the upper mid-region of the sub-screen and fluctuating deformations in the rake, accompanied by elevated von Mises stresses. The study serves as a design guideline for manufacturing and operating a WSM, ensuring the prevention of unfavorable stress and deformation in the WSM and the WTP. wastewater screening mechanism; flow separation; fluid-structure interaction; deformation; von Mises stress 2020  
remove the insoluble waste [3]. A mechanical wastewater screening mechanism (WSM) is typically installed at the inlet of a WTP and is used in the screening process to filter the heavy slug of debris. One screen type is a bar screen, which comprises a series of parallel steel bars that are typically spaced approximately 0.25 m to 0.75 m apart. Such solid waste may be discarded or submitted to a sedimentation process at the beginning of the WTP [4; 5; 6]. A rake system may also be used to remove the solid waste that has accumulated on the bar screen [7]. A front screen, which is commonly known as sub-screen, is occasionally designed to catch large chunks of debris to avoid overloading the main screen. The position or orientation of the sub-screen can be changed to regulate the flow of the heavy solid waste. The structure of the screen may vary depending on factors such as the desired size of openings (aperture) between the bars [8]. The strength of the bar screen, particularly the rake system, may be considerably compromised by the passage of sewage water. A substantial increase in the flow velocity causes the solid debris to bypass the bar screen without being retained, hence resulting in potential harm to the components of the WTP [9]. The interaction between water flow and the bar screen, and its reciprocal influence, may be characterized as a fluid-structure interaction (FSI) problem. The experimental modelling and investigation of the FSI associated with the bar screen pose significant challenges due to the substantial costs associated with its fabrication and operation. The modelling of the FSI problem on a large scale is possible due to developments in computational fluid dynamics, such as the bar screen. The arbitrary Lagrangian-Eulerian (ALE) method is a well-known numerical technique that is used to model and solve the effects of fluid flow on the deformation of structures [10; 11; 12; 13; 14]. Numerous studies have been conducted to examine the impact of accumulated garbage on the overall flow dynamics. [PERSON] and [PERSON] conducted a study to investigate the factors influencing the performance of the bar screen. Their findings indicated that the sewage water flow rate, spacing between the screen bars, and frequency of the raking system are the primary determinants of the bar screen's performance [9; 15].