Effects of Acetic Acid on the Regrowth of Heterotrophic Bacteria in the Drinking Water Distribution System

Summary Three laboratory-scale water pipe systems were set up to study the effects of adding two levels of acetic acid (10 and 50 μg acetate eq-C l⁻¹) on the bacterial regrowth in water pipes. The results of the water pipe test showed that nearly all carbon in the acetic acid could be readily utilized by bacteria and resulted in an increase in biomass concentration. The maximum heterotrophic plate counts in biofilm were equal to 3.5 × 10⁴, 8.9 × 10⁵ and 2.9 × 10⁷ c.f.u. cm⁻² while the maximum heterotrophic plate counts of free bacteria were equal to 1.2 × 10³, 5.0 × 10³ and 6.8 × 10⁴ c.f.u. ml⁻¹ for the blank and with addition of 10 and 50 μg acetate eq-C l⁻¹. These results showed that addition of acetic acid to drinking water has a positive effect on the assimilable organic carbon content of drinking water and bacterial regrowth in the distribution system. This effect is enhanced with addition of high-level acetic acid. Batch tests were also conducted using water samples collected from a Taiwanese drinking water distribution system. The bacterial regrowth potentials of the blank were equal to 4.3 × 10³, 1.5 × 10⁴, 4.9 × 10⁴ and 7.5 × 10⁴ c.f.u. ml⁻¹ for water samples collected from treatment plant effluent, commercial area, mixed area, and residential area, respectively. These results showed that the biological stability of drinking water is the highest in treatment plant effluent, followed by distributed water of the commercial area, distributed water of the mixed area, and then the distributed water of residential area.