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Microplastic pollution has been widely studied as a global issue due to increased plastic usage and its effect on human and aquatic life. Microplastics originate from domestic and industrial activities. Wastewater treatment plants (WWTPs) play an important role in removing a significant amount of microplastics; otherwise, they end up in bioaccumulation. This study provides knowledge about the characteristics of microplastics, removal efficiency, and the correlation between wastewater quality and microplastic concentrations from three different WWTPs that differ in the type of biological and advanced wastewater treatment techniques that are believed to play an important role in microplastic removal. Microplastics of different types, such as fragments, fibers, and beads, are identified by using an optical microscope before and after the treatment process at each stage to assess the effect of different treatment techniques. In the screening unit and primary clarifier unit, WWTP-B shows the highest removal efficiency with 74.76% due to a distribution flow system installed before the primary clarifier to ensure a constant flow of wastewater. WWTP-B uses a bioreactor consisting of a filter plate coated with activated carbon (BSTS II) that can enhance the adaptability and adhesion of microorganisms and showed that 91.04% of the microplastic was removed. Furthermore, only WWTP-A and WWTP-B were applied coagulation, followed by the disc filter; they showed significant results in microplastic removal, compared to WWTP-C, which only used a disc filter. In conclusion, from all WWTP, WWTP-B shows good treatment series for removing microplastic in wastewater; however, WWTP-B showed a high rate of microplastic removal; unfortunately, large amounts of microplastics are still released into rivers.

In response to the finding of chironomid 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 ±100 mg/L and 2 mg/L Al3+ as a coagulant, compared to water with a lower turbidity level of ±30 mg/L and 1 mg/L of Al3+ 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.

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