Larvae Found in Filters at 3 of 435 Water Purification Plants Nationwide... None in Tap Water

Ministry of Environment Announces Comprehensive Survey Results of General Water Purification Plants
Comprehensive Measures to Be Prepared by the End of Next Month

Sedimentation basin of the Gongchon Water Purification Plant in Incheon, where chironomid larvae were first discovered. (Photo by Yonhap News)

[Asia Economy Reporter Moon Chaeseok] The Ministry of Environment announced on the 28th that, following a comprehensive survey conducted from the 17th to the 26th of last month at 435 general water purification plants nationwide, no larvae were found in the reservoirs and consumer endpoints of all general water purification plants.

However, a small amount of larvae was detected in the filtration basins of three purification plants located in Hapcheon, Gyeongnam; Yeongok, Gangneung, Gangwon; and Mupung, Muju, Jeonbuk.

The fact that larvae were not found in the reservoirs and consumer endpoints means that the filtration basins filtered out the larvae, preventing them from flowing into the tap water supplied to households.

Generally, tap water passes through multiple stages such as the intake, mixing basin, sedimentation basin, and filtration basin, followed by chlorine injection, then through the purification reservoir, pump room, and reservoir before being supplied to homes.

The Ministry of Environment estimated that larvae were found in the filtration basins of the Hapcheon and Muju purification plants because the backwash cycle, which involves inverting and cleaning the filtration basin, was operated on a longer 7-day cycle instead of the usual 2 to 3 days.

The valley water used at the Hapcheon and Muju purification plants is of very high quality, so the backwash cycle was operated relatively longer, which led to the occurrence of larvae.

At the Gangneung purification plant, larvae were found to have entered because the filtration basin was exposed to the outside.

The Ministry of Environment plans to replace the sand in the filtration basins of the three purification plants and shorten the backwash cycle by the 31st of this month as corrective measures.

Earlier, in a comprehensive survey of 49 advanced water treatment plants announced on the 21st, larvae were found on the surface of activated carbon filtration basins (activated carbon beds) at seven purification plants, including Gongchon and Bupyeong purification plants in Incheon. Activated carbon beds refer to water purification facilities made from porous carbon materials similar to charcoal.

In Incheon, the activated carbon beds where larvae were found were isolated, and after flushing water through the reservoirs and pipelines, no larvae were detected at any of the 266 observation points along the pipelines after the 22nd.

The Ministry of Environment reported that although some larvae remaining in the tap water at the end of the pipelines have been found in households, the number of cases has decreased. The number of larvae found in Incheon households was 24 on the 21st, 18 on the 23rd, 2 on the 25th, and 4 on the 26th.

Furthermore, no insects have been found in the tap water supply system so far.

The Ministry of Environment plans to establish a comprehensive countermeasure plan related to the larvae issue by the end of next month.

Prior to this, source-blocking measures will be implemented to prevent larvae from entering water purification facilities.

Fine insect screens, double doors, and insect traps will be installed in purification plant buildings, and additional openable blocking facilities will be added to activated carbon beds to triple-block the access of organisms.

The surrounding environment of purification plants and insect prevention facilities will be inspected daily for abnormalities.

During the summer, the backwash cycle of activated carbon beds will be shortened as much as possible.

From this month through next month, water storage tanks and reservoirs will be cleaned simultaneously to prevent the breeding of midges and other insects.

To allow citizens to check the status of larvae occurrence by residential area, the "Our Neighborhood Tap Water Status" will be posted on the Ministry of Environment’s website.

Shin Jinsoo, Director of the Water Integration Policy Bureau at the Ministry of Environment, stated, "We will promptly and accurately disclose all processes related to the tap water larvae incident, thoroughly analyze the causes, and take measures to prevent similar cases from recurring."

This content was produced with the assistance of AI translation services.