Presence of Chemical Ions in Raw and Treated Water

Abstract

Dhaka water supply and sewerage authority utilizes a section of the DND canal from Sarulia to Kajla to convey raw water from the Shitalakhya river to the water treatment plant at Saidabad. Raw water quality is poor mostly in the dry season. High heavy metal concentration in the water at the intake point is found. Aluminum (Al), Cadmium (Cd), Lead (Pb), and Mercury (Hg) are detected in river water which exceed the standard limits. The treatment processes involve pre-chlorination and pH adjustment, followed by coagulation with alum, filtration and finally post-chlorination of the water. In the treated water, ammonia and aluminum exceed the drinking water standard. The existing treatment plant is not specifically designed for heavy metal removal.

Keywords – Raw water, treated water, chemical ions, heavy metals, water treatment process, chlorination.