Extensive research efforts have been concentrated on the development and validation of computational fluid dynamics (CFD) models for Up-flow Anaerobic Sludge Blanket (UASB) reactors, a key technology in anaerobic wastewater treatment. This study evaluates the effectiveness of different CFD modeling approaches, single-phase, two-phase, and three-phase, in simulating UASB reactors used in wastewater treatment. By conducting a thorough literature review, the research compares how each modeling approach addresses key factors such as reactor geometry, meshing techniques, governing equations (continuity, momentum, and turbulence models), and their validation against experimental data. The study places particular emphasis on how well each phase model captures the interactions among solid, liquid, and gas phases within UASB reactors. The findings aim to identify which modeling approach provides the most accurate predictions of velocity distribution, volume fraction, and turbulence. This analysis will help pinpoint gaps in current research and suggest improvements in CFD modeling, ultimately contributing to better water quality management and enhanced bioenergy production through optimized UASB reactor designs.