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This paper compares the operation of a traditional single-stage system with a two-stage, reversible flow biodenitrification system for removing nitrates from drinking water. The purpose of this study was to investigate the ability of these two-stage systems to remove nitrate and residual organics from treated water as compared to single-stage units. In the reversible flow system, the second-stage (i.e. follow) reactor is operated in series with the first-stage (i.e. lead) reactor. After a given period of operation, the flow regime is reversed so that the follow reactor becomes the lead one and vice versa. The active solids remaining in the follow reactor (previously the lead one) are capable of removing residual soluble organics and nitrates to levels below the concentrations provided by single-stage units particularly at HRTs as low as 0.5 h. Nitrate-nitrogen removal efficiency improved slightly from 98 to 99.5% for the single- and two-stage systems, respectively. Most notably, reversible flow reactors were found to reduce long-term effluent residual organics concentrations with an average of approximately 1/3 that of the single-stage system. Also the reversible flow system, with its design redundancy, demonstrated the ability to receive extreme shock loads with no sustained loss of treatment efficiency.