Investigating the Turbidity Removal Performances in Low-Cost Granular Media Filtration

Abstract

Demand of fresh water resources is increasing rapidly due to increased population growth, rapid urbanization, lowering of ground water table and involvement of high cost in water treatment. The slow sand filtration (SSF) and rapid sand filtration (RSF) are simple and comparatively low-cost granular media filtration technology commonly used for water purification. However, the performance of granular media filtration influence by the media types, sizes, depth and modifying agent such as coagulants used in the media. In this study, the performance of three different sizes filter media (e. g. small: 0.56-0.70 mm; medium: 0.80-1.8 mm; large: 1.5-3.0 mm) were carried out for three state of experiments including clean water filtration, backwashing and dirty water filtration using 52 mm diameter and 1 metre height filter columns (named as column 1, 2 and 3 respectively). The head loss linearly varies with flow velocity for three filter columns and the increment rate of clean water head loss was found higher for smaller size media compared to medium and large size for clean water filtration due to occupying large pore spaces. Bed expansion was fund higher for column 3 compared to column 1 and 2 due to the larger grain size of filter media for backwashing filtration. From backwashing plot, clear exponential growth was observed for column 3 filter media and was found significant after flow velocity 20 m/h. The outflow turbidity line slope is comparatively steeper for high turbid water (200 mg/l) than the low turbid water (25 mg/l) based on dirty water experiment. The filter media with smaller grain sizes are very effective for removing turbidity up to 51% from highly dirty water (200 mg/l) and varies from 25% - 50% for comparatively less turbid water (50 and 25 mg/l). These findings confirm the capability of medium category granular media filtration unit for removing turbidly from wastewater. This further enables us for proper selection of suitable filtration media and related optimization parameters for enhancing the low cost SSF and RSF filtration.