Invited PaperModelling Of Settling Tanks - A Critical Review

Modelling of settling tanks started in 1905, when Hazen presented his simple one-dimensional laminar flow model with single-sized solid particles. In the period 1904-1967 simple theoretical models were developed, which assumed a simplified (e.g. a uniform) flow pattern. Between 1967 and 1977 empirical models followed, which correlated removal efficiency with important design parameters. Since 1976 advanced, two-dimensional, numerical models have been developed. These model have been applied to settling tanks with increasing geometrical and process complexity, ranging from simple rectangular tanks without density effects to tanks with complicated geometries with inlet deflectors, inlet vanes, sludge hoppers and density effects. Future models for settling tanks are expected to be three-dimensional, computationally more efficient and including biological parameters as process variables. These models would be capable to handle complicated tank geometries and deal with problems encountered in settling tanks, such as sludge rising and bulking.