Channeling has already been an observed phenomenon that often occurs during settling and sedimentation processes of finer materials. However, it has been regarded as a minor factor affecting settling process, e.g. settling velocity or consolidation rate. In this study, settling behaviors of talcs, kaolins and attapulgite were reviewed by experiments with small and large settling columns with special focus on channel formation during sedimentation. The large settling column is equipped with twenty eight measuring points, which are connected to pressure transducers for measuring pore pressure changes during settling. Throughout the study, channel formation was observed and related to the experimental conditions affecting it. The excess pore pressure changes were measured during the large column tests. Channels occurred under flocculation in zone settling and also in consolidation zones; pressure drop was observed near channels in some cases. It was apparent that channels work as a facilitator to dissipate the excess pore water pressure. It is summarized that not only initial concentration but also the material properties, such as specific gravity and shape of particles, can affect the channel formation. / Master of Science

Sludge densification can be achieved through granulation/densification, migrating carriers, ballasted flocculation, or a combination of these approaches. Hydrocyclone-enabled continuous flow densification has been applied for full-scale applications; however, it requires long startup times and, in some instances, results in poor stability of the densified floc. Migrating carriers hold promise to offset these disadvantages for continuous flow processes where reasonable feast-famine or plug flow conditions cannot be achieved while drawing on the strength of hydrocyclones to retain and return the ballasting agent. This idea was tested by dosing kenaf, a plant-based renewable migrating carrier in a pilot-scale plug flow reactor equipped with a gravity selector to mimic a hydrocyclone. Results showed that kenaf could gradually reduce the sludge volume index from 170 to 50 mL/g and increase zone settling velocity from 2.5 to 7 m/h over 110 days without compromising treatment performance. Because of the selective retention of the inert plant-based carrier represented as a volatile solid in the gravity selector underflow, a traditional SRT calculation based on mixed liquor volatile suspended solids tended to overestimate daily Waste Activated Sludge (WAS) requirements and resulted in active sludge inventory loss. An oxygen utilization rate-based method was developed and verified for easy SRT correction to avoid kenaf interference with the sludge wasting protocol. Denser kenaf incorporated into the sludge matrix during flocculant settling contributed to the settleability improvements. However, a lack of biofilm formation on the kenaf surface was observed even after 110 days of treatment is intriguing and different from other studies. Challenges with initial kenaf floating and interference with conventional SRT calculations were two significant lessons learned from this study, and countermeasures were provided accordingly. It was concluded that kenaf could work in synergy with gravimetric ballast separation, such as with a hydrocylone, for quick and sustainable sludge settleability improvements. / Master of Science / Improving wastewater treatment involves making the sludge (the solid part of the waste) settle faster and more efficiently. This can be done in two main ways, i.e. forming dense, compact sludge particles or using materials to make the particles heavier so they settle quicker. A trendy method, known as "aerobic granulation," uses special equipment but has drawbacks, i.e., it takes a long time to get started, and the particles aren't very stable. Another method, "ballasted flocculation," shows promise because it can address these issues while still using the same equipment for reusing the added material. To test this hypothesis, we investigated using a natural material called kenaf, a plant-based product, to help improve sludge settling. We ran the experiment in a small-scale treatment system designed to mimic large-scale operations. Adding kenaf reduced the volume of sludge by over two-thirds and made it settle three times faster, and all these were achieved without affecting the wastewater treatment performance. However, using kenaf introduced some challenges. It made it harder to accurately measure how much sludge was being wasted daily, leading to an unexpected loss of sludge in the system. To fix this, we developed a novel, simple method to calculate sludge levels more accurately. We also found that kenaf worked well because it became part of the sludge, helping it settle faster, though it didn't let bacteria grow on its surface. Two key lessons emerged, and we suggested ways to deal with these problems. Overall, kenaf worked effectively with existing equipment to make sludge settle faster and more sustainably, offering a promising solution for wastewater treatment systems.

Each year in the United States, large volumes of material are dredged out of lakes and waterways and are dumped in confined disposal facilities so that they can consolidate. A mathematical model is proposed to predict the settling of the dredged material by predicting the ?primary? self-weight consolidation curve of silt particles under zone settling conditions. Using a relatively ?pure? specimen of silt, self-weight consolidation tests were performed at concentrations ranging from 10 to 200 grams per liter. To generate the predicted curve, the model requires the location of the zone interface at 180, 600, and 720 seconds and the assumed A-value. The A-value is used to ?fine-tune? the predicted curve so that it will fit the experimental curve. When values of ?A? from 0.85 to 0.95 are used, the predicted curve will fit the experimental curve for all concentrations considered. Thus, to predict the ?primary? self-weight consolidation of the dredged material, a sedimentation test using a sample of the dredged material must first be performed.

Ce travail porte sur l’étude expérimentale et la modélisation de la sédimentation des boues activées. Un pilote expérimental associant une colonne de sédimentation et un transducteur ultrasonore est proposé. Des profils de vitesse de sédimentation et de concentration en particules sont obtenus grâce à ce dispositif, ce qui permet de mieux comprendre les mécanismes de décantation des boues. Ces résultats sont utilisés afin de développer une approche numérique. Un modèle de sédimentation est construit en intégrant des fonctions expérimentales. Une méthodologie mettant en œuvre la différentiation automatique du modèle est ensuite élaborée et appliquée, d'une part, à l'analyse de sensibilité du modèle aux paramètres des fonctions utilisées et, d'autre part, à l'identification des valeurs de ces paramètres à l'aide des résultats expérimentaux. La conjonction des approches expérimentale et numérique proposées constitue un processus efficace pour le développement des modèles de sédimentation. / This work deals with the experimental investigation and modelling of activated sludge settling. An experimental setup combining a settling column and an ultrasonic transducer is proposed. Settling velocity and concentration profiles are obtained using this setup, allowing for a better understanding of the mechanisms of activated sludge settling. These results are applied to the development of a numerical approach. A settling model using experimental functions is built. A methodology based on the automatic differentiation of the model is developed. This methodology is used, on the one hand, to analyse the sensitivity of the results to the model parameters and, on the other hand, to identify the parameter values on the basis of experimental data. The combination of the proposed experimental and numerical methods yields an efficient process for the development of sedimentation models.