Lamella modules are the principal components of sedimentation tanks applied to water purification systems. The design of lamella modules determines the efficacy of the sedimentation process. This paper examines the efficacy of sedimentation tanks in the removal of solids suspended in wastewater within the pulp and paper industry. A comprehensive three-dimensional computational fluid dynamics (CFD) analysis was conducted to examine the influence of design parameters on the flow field and settleability of suspended particles in four distinct lamella module designs. The calculations were performed using the discrete phase model, which was supported by Ansys Fluent. Therefore, it can be concluded that the high sedimentation efficiency of the Lamella module, which is designed with two layers, makes it a suitable treatment for the wastewater produced by the pulp and paper industry in particular, at high flow rates and with small particles. Based on these results, there are significant practical implications for the advancement of wastewater treatment technologies.