Evaluation and sizing of proprietary sedimentation devices for decentralised stormwater treatment

Suspended solids removal is a key performance measure for proprietary stormwater treatment devices. Various technologies are available, with manufacturers claiming hydrodynamic separators offer performance advantages. However, it is important to assess manufacturers' claims. Accordingly, this study seeks to compare the performance of proprietary devices, by applying dimensional analysis to third-party certification data and experimental data from uncertified devices, and to determine the accuracy of a single parameter estimation (Hazen or Péclet number) of removal efficiency. Statistical analysis indicates that device performance is well described by a single parameter estimation transitioning from Hazen (Nash-Sutcliffe coefficient = 0.81 and root mean square error = 5.1%) at low surface loading rates (SLR) in all technology types (high removal efficiency) to Péclet (Nash-Sutcliffe coefficient = 0.5 to 0.61 and root mean square error = 5.9% to 4.3%) at higher SLR (low removal efficiency) for hydrodynamic separators. This indicates that performance at low SLR is well explained by gravity separation in all technology types, whilst in hydrodynamic separators removal at high SLR is better explained by gravity separation plus advection. Consequently, when high (>80%) removal efficiency is required there is no performance advantage between technology types. However, when low (<50%) removal efficiency is required hydrodynamic separators offer a 33% increase in treatment area.