AWWA WQTC62369

When held stagnant in relatively new copper pipes, chloramine and free chlorine disinfectants decay rapidly. In the presence of soluble and insoluble cupric, species, free chlorine decay is most rapid in the presence of cupric hydroxide solid surfaces, whereas chloramine decay (as Cl₂) was slightly increased by cupric. In copper pipes, which have a virtually unlimited supply of metallic copper (Cu⁰) while in service, chloramine and free chlorine decayed almost completely during overnight stagnation even after months of exposure. The rate of this reaction was unaffected by extra ammonia, but it was slowed by the addition of phosphate or aluminum which presumably formed barriers between the water and reactive surface sites on the pipe. Experimental results are consistent with a chloramine decay path via Cu¹⁺ formed by reaction between Cu⁺² and Cu⁰. Includes 16 references, table, figures.