Characterization of the settling process for wastewater from a combined sewer system

Among the methods used for determining the parameters necessary for design of wastewater settling tanks, settling column tests are used most commonly, because of their simplicity and low costs. These tests partly mimic the actual settling processes and allow the evaluation of total suspended solids (TSS) removal by settling. Wastewater samples collected from the Liguori Channel (LC) catchment in Cosenza (Italy) were subject to settling column tests, which yielded iso-removal curves for both dry and wet-weather flow conditions. Such curves were approximated well by the newly proposed power law function containing two empirical parameters, a and b, the first of which is the particle settling velocity and the second one is a flocculation factor accounting for deviations from discrete particle settling. This power law function was tested for both the LC catchment and literature data and yielded a very good fit, with correlation coefficient values (R2) ranging from 0.93 to 0.99. Finally, variations in the settling tank TSS removal efficiencies with parameters a and b were also analyzed and provided insight for settling tank design.

► The determination of the mathematical function, describing TSS iso-removal curves.
► The analysis was based on experimental data and was validated on literature data.
► The physical description of the parameters of the relationship was obtained.
► It is possible to use this methodology to estimate quantitatively the flocculation.
► It will be possible to use this methodology as a tool in the wastewater treatability analysis.