Experimental study of the impact of Reynolds number and chlorine concentration on manganese concentration in pilot-scaled water distribution system

Discoloration of the water is one of the major customer complaints in drinking-water-distribution systems (DWDSs). Manganese is one of the main sources of discoloration because once it oxidizes and accumulates on the pipe wall of distribution systems, the aesthetic water quality of DWDSs is affected. Therefore, understanding the potential conditions for manganese issues in DWDSs is important for proper management of drinking water. We performed an experiment to explore the effect of the Reynolds number and residual-chlorine concentration on the manganese concentration. A pilot-scaled water-distribution system was designed and fabricated, and 12 different system conditions having various residual-chlorine concentrations and the Reynolds numbers were analyzed. The result demonstrated that the decay rate of the total manganese concentration was increased with the increase both in the Reynolds number and the residual-chlorine concentration. However, the total manganese concentration did not exhaust under the condition of Cl-2/Mn(II) < 1.