Effect of granular activated carbon particle sizes and depths in slow sand filter on water purification

Abstract

Most rural dwellers in Nigeria depend on contaminated water from ponds, streams and wells for drinking water. Every household needs simple water purification device like Slow Sand Filter (SSF) to prevent water-borne diseases. This study was conducted to determine the effect of Granular Activated Carbon (GAC) particle sizes and depths in SSF on the purification of water. Two sets of SSF were fabricated using 6 inches (15.24cm) diameter PVC pipe, fine sand (0.25 mm grain size) with 35 cm depth. GAC for the first set SSFs (particle sizes 10 mm, 14 mm with 15 cm depth) and GAC for the second set of the SSFs has 15 and 25 cm depths with particle size 10 mm. The SSF has 50 litres storage tank from which raw water flows into the filter chamber (15.25 diameter and 110 cm long PVC). The filter was kept moist for 21 days for schmutzdecke to fully develop which is effective in trapping bacteria. Raw water was poured into the SSF, water samples were collected and analyzed using standard methods. The SSF has a capacity of producing 35 litres/h clean water. Percentage reduction of Lead, Manganese, Copper, Iron, Turbidity and Total Coliform Counts of the filtered water compared with the control were 91.35-99.88%, 90.00-98.33%, 42.00-100.00%, 46.67-100.00%, 13.04-99.15% and 16.67-57.69%, respectively. The SSF increased pH and Calcium by 7.14-27.71% and 83.65-98.21%, respectively. SSF with 10 mm and 25 cm depths GAC reduced the pollutants than the other two filters and it is recommended for purifying pond water.