Evaluation of Floc Characteristics Induced by Heavy Metals in an Estuarine Environment

Abstract

AbstractExperimental investigations were carried out to understand the role of metal fraction and turbulence on the flocculation of kaolin flocs. Mixing experiments were done in a flocculatorand themicro-scale investigations were carried out using an image-capturing system followed by an image-processing technique. The floc characteristics were analyzed for different meal concentrations (0, 0.1, 0.5, 1, 5, 10, 20 mg/l), salinities (0, 15 and 30 g/L), turbulent conditions (0, 5, 10, 20, 30 and 40 s−1) and time intervals (0, 10, 20 and 30 min). The work was followed by an analysis of floc size, fractal dimension, floc density, and floc volume fraction in three size classes: 0–50 µm, 50–100 µm, and >100 µm. The maximum floc size was observed at a salinity of 30 g/L and turbulence shear of 10 s−1for the highest heavy metal concentration of 20 mg/l. An increase in heavy metal concentration enhanced the aggregation process at high salinity conditions and low turbulence shear rates. The rise in turbulence shear initially increased floc size, which further decreased at high turbulence shears. Resistance of flocs to breakage was analyzed using the parameter breakage coefficient. The breakage coefficient is the ratio of the number of flocs before breakage to the number of flocs after breakage.The breakage coefficient of macro-flocs was determined from the experimental results and a relationship in terms of metal concentration is proposed. The study suggests that the binary breakage model finds application at intermediate turbulence ranges of 20 s−1 with the highest metal concentration of 20 mg/l. Thus, a relation for the breakage coefficient in terms of metal concentration was generated through the detailed analysis of the breakage coefficient from the experimental outcomes. Therefore, the developed model can be applied to quantify the breakage coefficient under all ranges of turbulence shear encountered in estuaries with mixed sediments.KeywordsFloc characteristicsMetal concentrationSalinityTurbulenceBreakage coefficient