ABSTRACT:
A systematic study was conducted to demonstrate enhanced sedimentation of low-density coal particles from wastewater in a newly designed settling vessel consisting of two inclined sections, termed the Reflux Lamella Settler (RLS). The RLS is a modified settling vessel consisting of inclined sections. Inclined sections are incorporated to provide a large settling area for solid particles, thereby enhancing settling rates compared to conventional settling tanks/vessels. Two RLS were designed and fabricated: one was a small lab-scale piece of equipment, and the other was relatively large and designated the prototype RLS for experiments. The first set of experiments was performed on the lab-scale RLS and a vertical settling column, which were filled with a solution of water and coal particles. The solid particles settled at a higher rate in the RLS due to the presence of inclined sections and reached a maximum solid concentration of 0.63 (v/v) at the base. In contrast, the vertical settling column achieved a maximum solid concentration of 0.43 (v/v), indicating relatively slow settling of the solid particles. In addition, experiments were conducted on the prototype RLS to examine the settling of solid particles at a larger scale under batch process conditions and the applicability of the equipment for high flow rates. A sample comprising 1 kg of coal particles of size 0.25 mm (250 microns) and 12 kg of water was placed in the prototype RLS, and results were obtained. A maximum solid volume fraction of 0.63 (v/v) was achieved in the prototype RLS and 0.15 (v/v) in the dilute region, values that were almost identical to those in the lab-scale unit. This shows that the RLS could handle a large volume of wastewater. The coloured PVC particles were used to validate particle movement within the RLS. It showed that, after entering the RLS, these particles quickly settled on the inclined surface and slid downwards. The car wash sample was used treated in the RLS, which showed that it takes 90 minutes to settle the solid particles, resulting in a reduction in turbidity from 233 to 30 NTU during that time.

Keywords: Boycott effect, Flux, Hindered settling, Inclined channels, Total Suspended Solids,

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