Qualitative and quantitative factors affecting treatment chemical costs in a multiple reservoir‐single treatment plant system

Abstract

A Multiple Reservoir‐Single Treatment Plant (MRSTP) system involves the conveying of raw water from different reservoirs to a common collection chamber and then directing the blended mix to a sole water treatment plant. In a case study, water from three sources having different qualities was mixed in various proportions in laboratory conditions and subjected to standard jar tests. Aluminium sulphate was used as the primary coagulant and lime was added for pH adjustment. Activated silica and two different types of cationic polyelectrolytes were used as coagulant aids. The treatability parameters chosen were turbidity, colour, pH and TOC. The concentrations obtained by simulated mixing in the lab proved to be identical to the actual field blends and also the computed values. The jar tests confirmed that for different blends, the use of activated silica resulted in the highest treatment chemical costs but when the polyelectrolytes were substituted a saving of 35.8% to 53.5% in treatment chemical costs was effected.

Key words:

• Multiple reservoirs
• single treatment plant
• mixing proportions
• jar tests
• coagulant aids
• optimal chemical costs