Water treatment system for a city in the dry zone of Sri Lanka consists of an aerator and slow sand filters. Raw water comes from a large irrigation tank. Predominant algae in this tank isSynedra sp. This algae causes frequent blocking of the filters and bad odor in filtered water. Prefiltration is a simple technique and chemical free process which improves not only physical properties of water but also the microbiological quality. In this study, two horizontal flow roughing filters (HRF) were investigated with pilot-scale and field-scale plants. A series of experiment at the pilot-scale plant show that algae count and turbidity are below 20 and 15 FTU respectively, the results of which are within the safe limits for proper operation of slow sand filters in Sri Lanka. There is a considerable reduction inSynedra population (80–87% in thrms of cell count) as well as color and turbidity (50–60%). Highest percentage removal was obtained for the filtration velocities below 1.5 m/h for color and turbidity, and below 2 m/h for algae removal. Field-scale experiments show that filter length does not provide a significant effect on the percentage reduction of algae count, color and turbidity. Horizontal flow velocity was maintained at 1.0–2.5 m/h. As the flow velocity increased upto 4.5 m/h, algae removal reduced to 70% while color and turbidity to 40%.
Performance evaluation of horizontal flow roughing filter as a pretreatment system
KSCE J Civ Eng
KSCE Journal of Civil Engineering ; 2 , 2 ; 187-193
1998-06-01
7 pages
Article (Journal)
Electronic Resource
English
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