Using flow simulation to inform the design and placement of remediation units in rivers

Nitrogen pollution of surface water systems is becoming a global problem, especially within river networks that receive run-off from agricultural land. Methods such as riparian buffering and the construction of artificial wetlands have proven effective when the conversion of land is achievable. An alternate approach is to consider in-stream remediation methods that capture and process incoming river flow. Their design must consider a number of factors, such as effective remediation capacity within the system, and the delivery of water to the treatment region. Computational modelling can be an efficient means for exploring these large design spaces. The results from our models show that unit performance is influenced by flow penetration into the unit, which typically improves with increasing void fraction until through-flow is achieved, after which removal performance decreases, due to decreasing functional surface area. Splitting units into smaller sub-units placed in tandem parallel to the stream-wise flow also results in a performance increase, although only if sufficient spacing is given between the upstream and downstream units to prevent wake interactions, and allow freestream flow to mix into the wake of the upstream unit. Unit efficiency is also observed to improve with increased occlusion of the channel cross section.

Automated summary

Nitrogen pollution of surface water systems is a global problem, and methods such as riparian buffering and the construction of artificial wetlands have proven effective. Computational modelling shows that unit performance is influenced by various factors, and splitting units into smaller sub-units can increase efficiency.