AWWA MTC57657

The effect of blending different water qualities on distribution system water quality was investigated in this field study. Waters produced from five different treatment systems; aeration (G1), NF (G4), CSF-O3-GAC (S1), IMS (CSF-NF, or S2) and high pressure reverse osmosis (RO) were blended and distributed to 18 different pilot distribution systems (PDS). G1, G4, and RO source waters were taken from the same groundwater. The RO source was augmented with salts to simulate seawater. The S1and S2 source waters were taken from the same surface water. The PDSs consist of PVC, galvanized, lined ductile iron and cast iron pipes taken from existing distribution systems and had a 5-day HRT. Chloramines were added to meet CT and residual requirements. AOC, BDOC, HPC are measures of suspended biological activity. PEPA measures attached film bioactivity. The S2 and G4 AOC are essentially equal, but the RO AOC is reduced and less than other treatments. S1 and S2 AOCs are equal. PDS biostability order is G1<G4=S1=S2<RO. During the wet season, raw surface water TOC increased significantly, and S1 AOC was also increased. BDOC was not correlated to HPCs and BDOC sensitivity was not adequate to assess biostability among treatments. PDS nitrification occurred in June and July 02 as the result of a loss of residual at 25oC to 30 oC and pH 7.8 to 8.3. During nitrification, the HPC values increased significantly, D. O. decreased; nitrification was nearly complete, which provided a carbon source for heterotrophs as the system became microaerophilic. AOC and Pepa assessment of biostability indicated HP RO increased biostability of finished water, but NF did not improve biostability relative to advanced surface water treatment at normal conditions. NF did improve biostability during the wet season. Includes 19 references, tables, figures.