Effect of residual chlorine on iron particle formation considering drinking water conditions

In drinking water, residual chlorine is very likely to coexist with iron particles. However, the understanding of the effect of residual chlorine on iron particle formation in relation to different drinking water conditions is limited. Here, we found a significant competitive relationship between residual chlorine and dissolved oxygen (DO) during iron particle formation. Composition gave a good indicator of the extent of oxidation; with DO being the sole oxidant, the most abundant iron crystal in the particles formed was FeOOH (79.12%) followed by Fe 3 O 4 (20.88%); in the presence of residual chlorine, however, the oxidation states of the iron crystals shifted upwards; the composition became as follows: FeOOH (50.64%), Fe 3 O 4 (27.96%) and Fe 2 O 3 (21.40%). The morphology of the particles formed showed interesting trends. In the presence of residual chlorine, the iron particles became denser and the specific surface area decreased. Particle size also exhibited a positive correlation with the chlorine concentration. The iron particle's specific surface areas formed with and without residual chlorine were 41.11m 2 /g and 61.30 m 2 /g, respectively. Linear regression also showed a good linear relationship between concentrations of iron ion and residual chlorine and the turbidity of the resulting water sample. Residual chlorine affects iron particle formation through different aspects, especially so when considering the interaction between residual chlorine with other oxidants and the resulting change in morphology. Runs of solutions with a high chlorine concentration through the pipe network could potentially act as a maintenance treatment. • Residual chlorine and DO were competitive during iron particle formation. • The crystals in the particles changed in the presence of residual chlorine. • Residual chlorine led to denser and lower specific surface area of particles. • Particle size exhibited a positive correlation with residual chlorine. • Residual chlorine significantly increased turbidity.