A self‐cleaning bar screen is often used in the first filtration level of a wastewater treatment plant to screen out solid debris from sewage water. The screening process of the bar screen was numerically investigated using the arbitrary Lagrangian–Eulerian method to model the fluid–structure interaction between the sewage water and bar screen. The bar screen design is improved by installing a rotating subscreen under the bar screen to prevent solid waste from passing through. The effects of bar screen on the water flow were examined using hydrodynamic properties. The structural properties were estimated to observe the effects of water flow on the parts of the bar screen. Various inlet flow rates and positions of subscreen and rake were used to examine their effects on velocity, pressure coefficient, structural deformation and von Mises stress. The screening process decreased with the increase in sewage flow rates. The water flow significantly affected the bar screen when the subscreen and rake are not in contact.

A material density separator utilizes a high velocity channel of air with a ballistic trajectory to separate materials based on their different densities and sizes. Light materials are carried with the airflow, leaving behind the separated heavy materials. A vibrating bed is then used to collect both heavy and light plastic materials for further separation and recycling processes. The effectiveness of the separation process mainly depends on the ballistic trajectory of the air stream and the slanting position of the vibrating bed. In this study, flow characteristics inside the density separation system were investigated to optimize the ballistic trajectory of air and the slanting position of the vibrating bed to improve the separation process. Various inlet air velocities, duct shapes, and the slanting angles of the mechanical separators were used to study their effects on flow properties (velocity magnitude, pressure, shear stress, and vorticity). Results show that the ballistic trajectory of air strongly depends on the diameter and shape of the duct hole, the inclination angle of the vibrating bed, and the air inlet velocity. The selection of the suitable values of these parameters is necessary to improve the plastic separation process. separation methods utilized for the plastic recycling process. The triboelectrostatic method separates the materials based on the difference of their electrical conductivities [11,12]. This method successfully separates polyvinyl chloride (PVC) and polyethylene terephthalate (PET) but is less efficient, with low output under working conditions. The presence of labels and coating on the materials reduces the separation process, because the triboelectric probe fails to sense the material type [13,14]. The forth flotation process is another separation method that utilizes the difference in surface properties of different plastics [15,16]. This method involves two processes, i.e., the treatment of plastic materials with an alkaline solution and then the carrying out of the froth flotation process. However, the flotation method is only suitable for small PVC and PET particles (less than 10 mm). Therefore, as a preliminary step, particles size reduction and the sizing of plastic waste is required, which makes this method the most expensive and complex among all the separation processes [17,18].Density separation is the most flexible and widely used industrial separation process because of its cost-effectiveness and high capacity for recycling plastic waste. This method is used to remove dirt, stones, and metals and to separate different types of plastics based on difference in densities. The density separation is the most widely used separation process because of its ability to separate all types of industrial material [19][20][21]. Density separation can be processed with a variety of working solutions, such as dry or air-based particles (air tables or zigzag air classifiers), water-based solutions, and suspensions (separating medias) [17,19]. The plastic material sinks or floats in ...