Abstract

Sati M. Al-Rawi* and Kahtan A. Al-Najjar

This work compares the performance of four types of filters, three of them are dual media/capping filters and the fourth is a single medium sand filter. The filters were made to operate with the same effective size and the same depth. These filter were subjected to the same operating conditions of filtration rates and influent turbidity. A new locally available filter medium called ninivite (recently discovered rock) was introduced to act as an upper layer of one of the selected dual media filters. To verify the goals of this work a pilot plant similar to the classical water treatment plant was constructed. Filtration system consisted of four glass column filters, acting parallel and simultaneously. The first three columns contained 20 cm of granular ninivite rock GNR, granular activated carbon GAC, and anthracite coal respectively over 40 cm of sand. The fourth column was kept with 60 cm sand to act as a single –medium filter. The effective size of each media grains was 0.82 mm with a uniformity coefficient 1.6. A total of 18 runs for natural raw water turbidity were conducted. Run times of these experiments amounted to 12-27 h. The filters were operated at rates of 4.9, 7.3, and 9.8 m/h; which were 1, 1.5 and 2 times the current rate at treatment plants. The results were encouraging .Using filters consisting of GNR and sand operated at mentioned rates appeared to have the best performance for the studied parameters. Efficiency of turbidity removal amounted to 91.31% for sample having 9.9 NTU at filtration rate 4.9 m/h. Such performances were also recorded for other dual – media filters for the considered rates. GNR filter also showed considerable efficiency in bacterial removal.