Surface-Modified Waste Scallop Shell as a Flocculant and an Optical Method for Evaluating Flocculation Performance

Surface-modified waste scallop shells were investigated as a solid flocculant for removing suspended particles, and a light transmission method was examined as a simple approach for evaluating flocculation behavior. Kaolin suspensions (3, 5, 10 g/L, pH 6.95–7.05) were used as model wastewater. Temporal changes in transmitted light intensity were monitored using a white LED–sensor optical system after agitation of the suspension was stopped. The transmitted light intensity, I, was normalized by the intensity measured for particle-free water (I0), and an optical extinction index, A = −log10(I/I0), was used to describe the attenuation of light in the suspension. An apparent clarification rate (rate of change in optical extinction), v, was defined from the initial decrease in the optical extinction index and used as an operational kinetic parameter for comparing flocculation behavior under identical conditions. The results showed that the surface-modified scallop shell particles exhibited measurable flocculation activity toward kaolin suspensions, although the performance was lower than that of commercial polymer flocculants. The optical transmission method enabled continuous monitoring of the flocculation process and provided a practical index for comparing the flocculation performance of different materials.