Modelling the Effects of Multiple Fractal Dimensions on the Flocculation and Resuspension Processes of Cohesive Sediment

The flocculation of cohesive sediments represents a critical process in coastal sediment transport, with its appropriate representation in numerical models crucial for the prediction of contaminant transport, coastal morphodynamics and engineering problems. In this study, a flocculation model considering the effects of multiple fractal dimensions is incorporated into a two-phase numerical modelling framework and used to investigate the effects of spatio-temporal variations in sediment concentrations on the temporal evolution of local floc sizes. Initially, the model is applied to simulate the aggregation of clay suspensions in a vertical grid-stirred settling column, with results confirming the importance of multiple fractal dimensions when predicting the time evolution of floc sizes. The adoption of multiple fractal dimensions, in particular, allows the two-phase numerical model to better match the measured settling column data with improved overall correlation. This is especially the case when predicting initial floc size growth during the early period of settling when the flocs tend to adjust more rapidly to their equilibrium sizes. The two-phase model is then applied to simulate field measurements of mud resuspension process in a tidally driven channel. Again, by considering multiple fractal dimensions within the flocculation model, better agreement is obtained between observed and modelled suspended sediment concentrations, while predicted floc sizes are also in general accord with previous field measurements made within the same estuary.

Automated batch settling column with vibrated rods and evaluation protocol for living waters mud thickening

Gravity solid-liquid phase separation is applied in minerals industries, waste water treatment, filtration, sewage, drinking water, ocean (water) engineering, dredging, environment and biotechnology. The healthy nation of freshwaters like Lake Balaton and River Bodrog can be maintained by regular mud dredging. The on-water pure mechanical mud thickening would be a really beneficial technology. A new automated batch settling column with vibrated rods had been developed and fundamental tests had been carried out with model materials (glass sand) and muds (Siofok, Tihany, Tokaj). A numerical evaluation protocol with spline interpolation and derivation had been developed by with simple key parameters were determined. Results can be used for the design of a new type of thickener called the rod-lamella thickener.

Flocculation of Clay Suspensions by Anionic and Cationic Polyelectrolytes: A Systematic Analysis

The characteristics of clayey suspensions, majorly composed of quartz microparticles, in the presence of anionic and cationic polyelectrolytes were investigated using different techniques. A wide range of clay concentrations was used, i.e., from 0.07 to 1000 g/L for different experimental techniques, based on the fact that the clay concentration possible to analyze with selected experimental methods was significantly different. The optimum flocculant to clay ratio was defined as the ratio that gives the fastest initial floc growth by static light scattering or fastest initial settling velocity by settling column experiments. In case of anionic polyelectrolyte, it was observed that the optimum flocculant dose depends on the amount of cations present in the system. For suspensions made with demi-water, a lower optimum flocculant dose (<1 mg/g) than for suspensions prepared in tap water (2.28 mg/g) was observed. At these lower salinities, the supernatant remained turbid in all the experiments and was, therefore, not a good measure for optimal anionic based flocculation. The equilibrium floc size at a given shear rate was found to be independent on the shear history of the floc and only dependent on the current applied shear. This was confirmed by both light scattering and rheological analysis. In case of cationic polyelectrolyte, the optimum flocculant ratio (5–6 mg/g) corresponded to the ratio that gives the lowest electrophoretic mobility for each clay concentration and to the ratio that gives the fastest settling velocity for the highest clay concentrations (12–15 g/L), where static light scattering measurements were not possible. All investigation techniques, therefore, proved to be good indicators for predicting the optimum flocculant to clay ratio. For the lowest concentrations (1.75–8.7 g/L) studied by settling column measurements, the optimum flocculant ratio was observed to increase with decreasing clay concentration, for fixed mixing conditions. The optimum flocculant to clay ratio was not always corresponding to the clearest supernatant and the size of flocs at optimum dosage was dependent on the mixing efficiency. The equilibrium floc size at a given shear rate was found to be dependent on the shear history of the floc and the current applied shear. This was confirmed by both light scattering and rheological analysis.

Settling of Road-Deposited Sediment: Influence of Particle Density, Shape, Low Temperatures, and Deicing Salt

Separation of particulate matter (PM) is the most important process to achieve a reduction of contaminants present in road runoff. To further improve knowledge about influencing factors on the settling of road-deposited sediment (RDS), samples from three sites were collected. Since particle size distribution (PSD) has the strongest effect on settling, the samples were sieved to achieve comparable PSDs so that the effects of particle density, shape, fluid temperature, and deicing salt concentration on settling could be assessed using settling experiments. Based on the experimental data, a previously proposed model that describes the settling of PM was further developed and validated. In addition, RDS samples were compared to a standard mineral material, which is currently in use to evaluate treatment efficiency of stormwater quality improvement devices. The main finding was that besides PSD, particle density is the most important influencing factor. Particle shape was thoroughly described but showed no significant improvement of the prediction of the settled mass. Temperature showed an effect on PM settling; deicing salts were negligible. The proposed models can sufficiently predict the settling of RDS in settling column experiments under varying boundary conditions and are easily applicable.

The Study of Discrete Settling Velocity for Raw Water of Tigris River in Kut by Settling Column

The objective of this research is to make settling column for measuring the suspended solids (SS) and dissolved solid (DS) in water by doing discrete and flocculate on it. This device is manufactured in the laboratories at University of Wasit, college of engineering. This device consists of plastic pipe with a diameter and height of 20 cm and 2 m respectively and it has four ports which are located at different depths. Also, it contains moto-diver to rotate the water inside the plastic tube (simulated reality from the river, mix water to prevent sedimentation). This design also involves water tank for storing the sample and moto to transfer water from the tank to the plastic tube. Samples are taken from the Tigris River in the governorate of Waist, Kut City. Samples are taken at depth of 5 meters and the results are accurate with several analyses have been done on it. This project is done by Stokes law in which particles have settled with detention time as a requirement and the depth of the settling tank. The optimum alum ratio is also obtained by jar test which is equal to 450mg/l. The results showed that the best ratio of removing (X˚ /˳) which is equal to 48% and thus finding the detention time in the tank and depth of tank as a purpose of design sedimentation tank with these requirements.