Effects of oxalic acid on the regrowth of heterotrophic bacteria in the distributed drinking water

Three laboratory-scale water pipe systems were set up to study the effects of adding oxalic acid on the bacterial regrowth and biofilm formation in the distributed drinking water. The results of water pipe experiment displayed that around 38% carbon in the oxalic acid could be converted to bacterial biomass. The maximum HPCs in biofilm were equal to 3.5 × 104, 3.38 × 105 and 2.8 × 106 CFU cm−2 while the maximum HPCs of free bacteria were equal to 1.2 × 103, 2.54 × 103 and 3.78 × 104 CFU ml−1 for the blank and with addition of 10 and 50 μg OA eq-C l−1, respectively. These results imply that the addition of oxalic acid to distributed water has positive effect on the assimilable organic carbon content of drinking water and bacterial regrowth in water pipe. This effect is enhanced with addition of high-level oxalic acid. Batch tests were also conducted using water samples collected from a Taiwanese drinking water distribution system. The bacterial regrowth potentials (BRPs) of the blank were equal to 4.25 × 103, 1.46 × 104, 4.9 × 104 and 7.54 × 104 CFU ml−1 for water samples collected from treatment plant effluent, commercial area, mixed area, and residential area, respectively. These results show that the biological stability of distributed drinking water is the highest in treatment plant effluent, the moderate in the commercial area and mixed area, and the lowest in the residential area.