###### Abstract  
In response to the finding of micromoid larvae in tap water, South Korea's water treatment system has stepped up water quality monitoring. However, due to the challenging nature of larval behavior, effective elimination remains difficult despite the use of various purification techniques such as coagulation, sedimentation, filtration, and disinfection. Based on it, the aim of this study is to evaluate the effectiveness of coagulation and chlorination in inactivating chironomid larvae and investigate their behavior. The coagulation experiment tested how the behavior of the larvae changed in water with a high turbidity level of \(\pm\)100 mg/L and 2 mg/L Al\({}^{3+}\) as a coagulant, compared to water with a lower turbidity level of \(\pm\)30 mg/L and 1 mg/L of Al\({}^{3+}\) as a coagulant. The larvae were exposed to various doses of chlorine (0.5-20 mg/L as Cl) in 500 mL beaker glasses. The behavioral activity of the larvae was observed at different time points for 5 days. It was found that chironomid larvae exhibit different responses to exposure to coagulant and chlorine, with coagulation causing the formation of flocs that cover the larval body as a protective measure. Conversely, exposure to chlorine causes a decrease in activity and growth, leading to the death of the larvae and subsequent melting. The results showed that the first instar larvae dead after 48 h of exposure to coagulation treatment, while the first instar larvae exposed to chlorination experienced mortality after a mere 5 min of exposure to 10-20 mg/L as Cl. The larvae can still grow and transform into pupae and adults, especially during the third and fourth instars, even after exposure to coagulant and chlorine with low dosage. These findings suggest that the floc generated during coagulation must be thoroughly cleaned, as it may contain larvae that can persist and develop further. Furthermore, the presence of larvae during the chlorination process highlights the need for alternative, more effective oxidants to be utilized in place of the conventional chlorine treatment. inactivity; chironomid larvae; coagulation; Al\({}^{3+}\); chlorination; water treatment Article  
W.J.M.J. to their wide distribution and rapid life cycle. As a result, these larvae may infiltrate the clean water treatment system, ultimately leading to their presence in tap water. Several significant incidents of chironomid larvae contamination in water treatment systems have been reported in various countries, including the United Kingdom, the United States, and China [3]. Recently, the detection of macroinvertebrates, specifically chironomid larvae, in tap water supplied by Korean water treatment facilities in July 2020 has prompted apprehension. A nationwide investigation that ensued following the initial discovery revealed that chironomid larvae were present in seven out of the 49 sites inspected [4]. The presence of these organisms in the water supply suggests that there may be issues with the water treatment process, as larvae can easily penetrate sand filters and end up in waterworks reservoirs [5]. Usually, the larvae are found in small numbers, visible to the naked eye, and have an aesthetic impact on tap water quality. Water treatment plants use various purification methods to remove microorganisms, including coagulation with chemical additives, sedimentation, and filtration. Additionally, some water treatment plants also use disinfection processes, such as chlorination or ultraviolet irradiation, to further ensure the safety of drinking water [6]. Currently, there is a lack of research investigating the efficacy of the coagulation process in independently inactivating chironomid larvae. However, several studies have shown that chironomid larvae are resistant to inactivation by free chlorine at standard doses. A previous study has reported that chlorine dioxide (ClO\({}_{2}\)) is used in water treatment processes as it is a potent oxidant and disinfectant at relatively low concentrations.