Corrosion control strategies for the Halifax regional distribution system

Corrosion in drinking water distribution systems is an important issue for many water utilities because it can lead to water losses, increased headlos s, and deterioration in water quality. The objective of this investigation was to evaluate the effectiveness of different corrosion control strategies for maintaining water quality in the Halifax regional distribution system. The corrosion control methods investigated at the pilot scale were lime ad dition, polyphosphate addition, and pH adjustment with NaOH. The strategies were evaluated with both pilot- and full-scale distribution systems. The p ilot-scale system used in the investigation consisted of four 1.5-m section s of 100-year-old cast-iron pipe. Water flowed continuously through the pip e section for the first phase of the pilot-scale investigation. For the sec ond phase of the pilot study, water was allowed to stand in the pipe for 1, 3, 6, and 12 h, which was intended to represent a no-flow or dead zone in the distribution system. Eight sampling points were used in the full-scale portion of the investigation. The hydraulic retention times of the sampling point ranged from 1.5 to 55 h. Both the lime and polyphosphate treatments provided similar performance during the pilot-scale continuous flow and sta nding periods. However, lime addition significantly increased post-filtered turbidity levels, which resulted in excessive deposition of insoluble mate rial during the standing periods. At full scale, polyphosphates provided be tter corrosion protection than pH adjustment with NaOH. Based on both pilot - and full-scale data collection, polyphosphate was considered as the prefe rred corrosion control strategy for the Halifax regional distribution syste m.