Computational fluid dynamics (CFD) is a rapidly emerging field in wastewater treatment, with application to almost all unit processes. To date, it has been primarily used for evaluation of hydraulic problems at Water Resources Recovery Facilities (WRRFs). A potentially more powerful use, however, is to simulate integrated physical, chemical and/or biological processes involved in WRRF unit processes on a spatial scale and to use the gathered knowledge to accelerate improvement in plant models for everyday use, that is, design and optimized operation. In this Scientific And Technical Report (STR), the fundamentals of CFD are presented and the application of CFD for more efficient and effective design and operation of WRRFs is demonstrated. The STR's focus is on articulating the state of practice and research and development needs. Recent developments are also emphasized, including new and emerging software and computations, model calibration and verification, sources of error, etc.