Settling velocity of particulate pollutants from combined sewer wet weather discharges

Abstract

Settling velocities of TSS and of particulate pollutants (COP, PDCO, PTKN, PCu, PPb, PZn, PPAH) measured on a wide range of wet weather flow (WWF) samples collected at different levels of the Parisian combined sewer system are reported. The recorded V30 (0.01 to 0.1 mm s(-1)) and V50 (0.09 to 0.6 mm s(-1)) values exceed by a factor 10 those of dry weather sewage and also exceed the values measured for pavement runoff. These values lie however often below the 0.28 mm s(-1) reference value considered in France for the design of WWF settling facilities. A decrease in settleability is observed between a small upstream catchment and larger scaled downstream catchments. The settling behaviour of particulate pollutants varies depending on the considered parameter and can differ significantly from the TSS behaviour, due to a non homogeneous distribution of micropolluants over the different classes of particles. PZn and PTKN appear far less settleable than TSS, whereas PPAH show higher settleability.

Sediment contamination assessment in urban areas based on total suspended solids

“…In our case, it has been estimated from measurements made in streams using fine organic particles marked by a tracer (Minshall et al, 2000;Thomas et al, 2001) and on laboratory measurements. The average settling velocity suggested corresponds to measurements conducted on the River Seine after a CSO discharge (Even et al, 2004) and is in accordance with settling velocities observed using the French VICAS protocol (Gromaire-Mertz et al, 2008).…”

Sedimentation of Raw Sewage: Investigations For a Pumping Station in Northern Germany under Energy-Efficient Pump Control

“…After a thorough literature review, two methods were combined to determine the settling behavior of the collected samples. The experimental setup follows the VICPOL protocol [8]. The process itself is simple and the experimental conditions are comparable to real world conditions in stagnant pressure tubes.…”

“…For the subsequent data processing, the related VICAS protocol [23] was applied to describe the distribution of settling velocities in the sample as continuous mathematical function. Figure 1 shows a schematic view (similar to [8]) and a photo of the construction. The VICPOL protocol determines n mass fractions with their specific settling velocity v s (mm/s), by dividing the sewage sample into n sub-samples with n settling times.…”

“…For this, the cross section of the pipe is split into two segments: (i) the free cross section where water is transported (A T (m 2 )) and (ii) the cross section occupied by sediments (A s (m 2 )). Applying the geometric relationships of a circle, the area (A T ), wetted perimeter (P T (m)) (see Figure 2) and hydraulic diameter (D T (m)) of free cross section are calculated with Equations (8) to (10).…”

“…Starting with investigations on combined sewer overflow events [3], several experiments and methods have been developed to understand and describe sedimentation processes in sewer systems (e.g., [4][5][6][7]). The original driver has often been the assessment of particle bound pollution transport in combined sewer systems (e.g., [8]) or storm water systems (e.g., [9,10]). The underlying principle of those activities is to determine particle mass fractions of different settling velocity classes by laboratory experiments (ex situ), mainly performed in settling columns (also used for river sediments, e.g., by [11]).…”