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

Piro, Patrizia; Carbone, Marco; Penna, Nadia; Maršálek, Jiří

doi:10.1016/j.watres.2011.09.034

Cited by 25 publications

(18 citation statements)

References 10 publications

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“…As such, for cohesive particles, the settling velocity will increase as flocculation occurs, and in a depth/time diagram, the isoconcentration slopes increases with time and depth, thus resulting in a concave line (Fig. 1b) (Piro et al 2011). …”

Section: Principlementioning

confidence: 99%

“…A new approach, adapted from the work of Piro et al (2011), is developed here in order to determine the settling velocity and the propensity to flocculate for a range of sediment particles. Figure 1a provides a schematic of two particle types mixed together and settling in the free regime.…”

Section: Principlementioning

confidence: 99%

“…You (2004) proposed a method to define a settling flux based on mass budget variation over time in a similar optical array column, and to derive a settling velocity from this flux. Piro et al (2011) alternatively proposed comparing settling properties of different samples, based on model fitting of the reduction of SSC with time and depth.…”

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confidence: 99%

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Using an optical settling column to assess suspension characteristics within the free, flocculation, and hindered settling regimes

et al. 2015

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Purpose Instruments able to measure the settling velocity distribution (SVD) and investigate the flocculation behavior of suspensions for a wide range of concentrations and settling regimes are required to understand and model sediment transport in headwater catchments. Such knowledge will improve our water resource management capabilities. Materials and methods An optical settling column, equipped with a vertical array of optical sensors, was used to provide light transmission through a suspension during quiescent settling. A new method to determine the settling velocity and the propensity of suspensions to flocculate is proposed. Its reliability was evaluated based on settling tests for (1) noncohesive sediments, (2) cohesive sediments at medium (~1 g l −1 ) concentration in a natural and deflocculated state, and (3) a cohesive sediment at a very high concentration (~10 g l −1 ). This choice of sediments and concentrations allowed for the assessment of free, flocculated, and hindered settling regimes. Results and discussion The proposed data processing method provides measurements for a range of test conditions. The result showed that different populations of particles with different settling behaviors can be identified within the suspensions. In the case of noncohesive sediments, the proposed method provided SVD similar to those obtained with reference methods. The propensity to flocculate was zero as expected for inert material. The natural cohesive sediment at medium concentration exhibited a large range of SVD (10 −2 -10 −5 m s −1 ) and high propensity to flocculate. These were both reduced with the addition of a deflocculant. Identified particle behaviors were consistent with independent measurement of size distribution, microscopic, and erosion properties. In the hindered regime, a narrow SVD corresponded to the hindered front settling velocity (~10 −4 m s −1 ). Conclusions An optical settling column was able to provide reliable SVD and an evaluation of the propensity of particles to flocculate. The settling column was able to detect variations of the settling velocities with settled depth, thus highlighting that settling columns with a single measurement point may provide erroneous results by not accounting for the full spectrum of settling depth.

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Section: Principlementioning

confidence: 99%

Section: Principlementioning

confidence: 99%

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Using an optical settling column to assess suspension characteristics within the free, flocculation, and hindered settling regimes

et al. 2015

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“…The best simulation results have so far been obtained using the three empirical models below, i.e, Özer's (1994) model, San's (1989) model and lately Piro and coworkers ' (2011' ( ) model. Ozer's (1994 analytical approach was based on the observation of rainfall intensity duration frequency.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…Piro et al (2011) developed the simplest settling model presented by a power law function (Eq. (4)), where the removal of particles is expressed as a function of time at a particular distance from the top of a water column.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

A finite velocity simulation of sedimentation behaviour of flocculating particles – A real-time model evaluation

Sithebe¹,

Methula²,

Chirwa³

2014

WSA

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A mechanistic velocity model is developed to simulate the behaviour of flocculating colloidal particles in turbid water. The current model is based on one-dimensional mass transport in the vertical direction as an integrated form of the model derived by Ramatsoma and Chirwa. The percentile removal model achieved more accurate simulation of physical experimental data than known models such as the Ozer's model and San's model. In this study, an integrated velocity form was used to estimate flocculent settling velocity of fine suspended particles under near quiescent conditions. Model closeness to experimental measurements was determined as a function of the sum of squares error (SSE) between model data and experimental data. The proposed velocity model offers a distinctive advantage over the interpolated-isopercentile based models which are prone to numerical errors during interpolation. The results contribute towards the ultimate goal of achieving full automation of the design of gravitational particle separation devices for water and wastewater treatment.

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Assessment of erosion and settling properties of fine sediments stored in cobble bed rivers: the Arc and Isère alpine rivers before and after reservoir flushing

Legoût

Droppo

Coutaz

et al. 2018

Earth Surf Processes Landf

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Cohesive sediment dynamics in mountainous rivers is poorly understood even though these rivers are the main providers of fine particles to the oceans. Complex interactions exist between the coarse matrix of cobble bed rivers and fine sediments. Given that fine sediment load in such environments can be very high due to intense natural rainfall or snowmelt events and to man‐induced reservoir or dam flushing, a better understanding of the deposition and sedimentation processes is needed in order to reduce ecohydrological downstream impacts. We tested a field‐based approach on the Arc and Isère alpine rivers combining measurements of erosion and settling properties of river bed deposits before and after a dam flushing, with the U‐GEMS (Gust Erosion Microcosm System) and SCAF (System Characterizing Aggregates and Flocs), respectively. These measurements highlight that critical shears, rates of erosion, settling velocities and propensity of particles to flocculate are highly variable in time and space. This is reflective of the heterogeneity of the hydrodynamic conditions during particle settling, local bed roughness, and nature and size of particles. Generally the deposits were found to be stable relative to what is measured in lowland rivers. It was, however, not possible to make a conclusive assessment of the extent to which the dynamics of deposits after reservoir flushing were different from those settled after natural events. The absence of any relationships between erosion and deposition variables, making it impossible to predict one from another, underlined the need to measure all of them to have a full assessment of the fine sediment dynamics and to obtain representative input variables for numerical models. While the SCAF was found to be effective, an alternative to the U‐GEMS device will have to be found for the erodibility assessment in cobble bed rivers, in order to make more rapid measurements at higher shears. Copyright © 2017 John Wiley & Sons, Ltd.

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

Cited by 25 publications

References 10 publications

Using an optical settling column to assess suspension characteristics within the free, flocculation, and hindered settling regimes

Using an optical settling column to assess suspension characteristics within the free, flocculation, and hindered settling regimes

A finite velocity simulation of sedimentation behaviour of flocculating particles – A real-time model evaluation

Assessment of erosion and settling properties of fine sediments stored in cobble bed rivers: the Arc and Isère alpine rivers before and after reservoir flushing

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