The role of chloride ions in plasma-activated water treatment processes

The effect of chloride ions (Cl^-) on the efficiency of hydroxyl-based (OH) water treatment processes, especially plasma treatment systems, remains controversial with conflicting reports of enhanced and deteriorating roles. In this study, we show that during the plasma treatment stage, the scavenging nature of Cl^- towards OH decreases the percentage of contaminant removal. On the other hand, the percentage of contaminant removal increases during the post-treatment phase due to the formation of singlet oxygen (¹O₂) from the reaction of hypochlorous acid (HOCl) and hydrogen peroxide (H₂O₂). Our results show that there exists an optimum Cl^- concentration at which the removal percentage is at its maximum. We also investigated the effect of pH on the role of Cl^-. We present possible solution characteristic-dependent reaction pathways and their effect on the treatment process.