Optimal Mixing of Gas and Chemicals in WRRFs Using Computational Fluid Dynamics (CFD): Case Examples for Coagulant Dosing and Pure Oxygen Mixing

Computational Fluid Dynamics has recently gained significant ground in the water industry due to the increased awareness about the tool, process requirements becoming more stringent and maturity of both software and hardware (computational power). Virtual design testing using computational fluid dynamics (CFD) (Nopens et al., 2018), what we like to call ‘virtual piloting’ or ‘virtual experimenting’, extends testing freedom drastically, does not require real-life system modifications and provides much more system understanding (Rehman et al., 2017). Optimal mixing is important for many wastewater treatments processes. If mixing is accounted for properly, preferably in the design stage, it reduces process footprint, lowers OPEX and increases process reliability and performance.
This paper describes two full-scale examples in which advanced 2-phase CFD (liquid/gas) was used to evaluate different design scenarios prior to real-life implementation. The first case relates to the optimal dosing and mixing of coagulant in a primary treatment at a Water Resource Recovery Facility (WRRF) in New Zealand. The second case relates to optimal oxygen transfer and mixing in an industrial WWTP in the Netherlands. CFD was used to optimise a) the influent mixing (avoid short-circuiting) and b) the mixing of the oxygen or coagulant dosed. Based on the simulation outcomes, informed and optimal design decisions were taken.