Evaluation of water consumption in rapid sand filters backwashed under varied physical conditions

Abstract

Egypt suffers from water scarcity. In water treatment plants using sand filters, a significant amount of treated water is consumed, estimated at 10%–15% of the filtered water during backwashing. The objective of this study is to determine the most effective way to reduce the amount of treated water used for backwashing. The methodology of this study was to evaluate the effects of air and water rates, treated water turbidity of 1.6 NTU or slightly higher synthetic turbidity of 4.0 NTU, and media type with single or dual media on reducing treated water consumption during rapid sand filter backwashing procedures. The experimental set up was a bench-scale filter operated at a filtration rate of 189 m3/m2/day. Backwashing with the right water and air rates reduce water usage by 18%, enhanced process performance, and reduced the ripening period. Backwashing using synthetic turbid water recovered 100% of the treated water and improved the ripening duration without affecting backwashing efficiency. This study concluded that backwashing the dual media filter with silica sand and activated carbon achieved the highest treated backwash water consumption by approximately 60%. While anthracite coal was utilized as a dual-media filter, the least reduction in treated water consumption was discovered.

Keywords

• | Filtration
• Rapid sand filter
• Backwash
• Water consumption
• Synthetic turbid water
• Dual media