Water Supply (Oct 2022)
Effect of hydraulic conditions on manganese accumulation by physical and chemical pathways in chlorinated water distribution system: A preliminary laboratory study
Abstract
The accumulation of manganese (Mn) in drinking water distribution systems (DWDS) is the main reason for ‘black water’ occurrences at customers' taps. Here, we focused on the impact of hydraulic conditions on Mn accumulation in well chlorinated DWDS, particularly on the physical pathway (i.e., the attachment of particulate Mn to the inner pipe surface) and the chemical pathway (i.e., the autocatalytic oxidation of Mn2+ on the surface of accumulated Mn). Mn accumulation on epoxy resin, a typical lining material for distribution pipes in Japan, was observed in laboratory-scale experiments under different water velocity conditions. The results showed that Mn accumulation was significantly enhanced under higher velocity conditions, which was then fitted with the numerical models describing Mn accumulation by the physical and chemical pathways and the detachment. The rate constants for the physical and chemical pathways had a positive relationship with the flow turbulence in the investigated range, suggesting that hydraulic conditions in DWDS play an important role in Mn accumulation. Effects of Mn speciation and water characteristics on the accumulation process were also simulated under various hydraulic conditions. Based on the obtained results, appropriate countermeasures to control manganese accumulation were then discussed. HIGHLIGHTS Effect of hydraulic condition on Mn accumulation in distribution pipes was studied.; Mn accumulated in pipes via the physical and chemical pathways in chlorinated condition.; The contribution of the chemical pathway of Mn accumulation increased with time.; The rates of both pathways were greatly affected by water velocity.; Increasing the water velocity alone may not be sufficient to reduce Mn accumulation.;
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