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백영애(Youngae Baek),이광제(Kwangje Lee),양윤선(Yunsun Yang) 대한환경공학회 2022 대한환경공학회지 Vol.44 No.11
최근 물환경에서의 오염지표인 깔따구의 유충이 일부 지역 수돗물에서 검출되어 논란이 일고 있다. 이에 국내 정수장에서 대부분 운영되고 있는 모래, 활성탄/모래, 활성탄 공정에서의 깔따구 유충의 거동특성을 분석하고 유충제어를 위한 효율적 운영방법을 제시하고자 한다. 본 연구에서는 여과실험을 위해 파이롯 규모의 사각컬럼 (W300×L300×H3500~5000 mm)을 사용하였으며, 현장과 동일하게 2.5 m의 여재층고로 운영하였다. 처리대상 유입수는 G정수장의 모래여과수로 한강에서 채집한 깔따구 유충을 주기적으로 투입하여 약 40~50일간 운영하였다. 그 결과, 모래여과지와 활성탄지에서는 운영초기 5일, 활성탄/모래의 경우 15일간 유충은 검출되지 않았으나 역세척 이후 모래 및 활성탄지에서는 운영 9일째부터, 활성탄/모래는 15일 이후부터 유충이 검출되기 시작하였다. 활성탄 하부에 모래포설한 경우 활성탄지 단독운영에 비해 유충검출이 약 6일정도 지연되었으나 유입수에 유충이 지속적으로 유입되고 역세척이 주기적으로 이루어지게 되면 유충이 여층전체에 이동하여 분포하므로 유충 누출은 불가피한 것으로 나타났다. 실제 약 50일간 운영후 활성탄 층고별 유충분포를 조사한 결과, 상층 30%, 중층 12%, 하층 35%, 하부집수장치 0.2% 정도로 여층 전체에 유충이 분포하는 것을 알 수 있었다. 따라서 유충유입 초기부터 역세척 주기를 단축하고 역세척시 활성탄 팽창률을 높여 유충의 신속한 배출이 필요하다. 본 연구결과에서도 역세척 속도를 0.57 m/min이상으로 할 경우 활성탄 팽창률은 30%이상으로 역세척 속도를 0.45 m/min으로 할 경우에 비해 유충 배출이 약 2배 증가하는 것을 확인하였다. 따라서 유충제어를 위한 여과공정의 효율적 운영방안으로는 모래여과의 경우 여재팽창이 어려운 경우는 린스시간을 늘리고, 활성탄의 경우는 역세척 속도를 높이고 역세척 주기를 단축시켜 유충을 신속히 배출해 낼 필요가 있다. Recently, midge larvae, which are indicators of aquatic environmental pollution, have been detected in tap water in some areas, resulting in controversy. Therefore, the objective of this study is to analyze the behavioural features of midge larvae in sand, GAC (granular activated carbon) and GAC/sand processes, which are mainly operated in domestic water purification plants, and suggest effective operating methods for larval control. In this study, a pilot-scale square column (W300×L300×H3500~5000 mm) was used for the filtration experiment and was used with a filter height of 2.5 m as well as in the field. The water to be treated was the sand filtered from the water purification plant G, and midge larvae from the Han River were injected periodically and operated for an estimated 40 to 50 days. As a result, no larvae were detected during the first five operational days in the sand filter and GAC and 14 days in the case of GAC/sand. However, after backwashing, larvae were detected from the 9th day of operation for sand and GAC, and from the 15th day for GAC/sand. In the case of sand laying under the GAC, larvae detection was delayed by approximately 6 days compared to the operation of the GAC alone. Following examination of larval distribution in relation to the height of the activated carbon layer after approximately 50 days of operation, it was found that the larvae were distributed on 17% in the upper layer, 7% in the middle layer, 19% in the lower layer and 0.2% in the lower water collection device. Therefore, it is necessary to shorten the backwashing cycle from the initial stage of larval introduction and to increase the rate of expansion of GAC during the backwashing to quickly flush out the larvae. The results of this study also confirmed that when the backwash speed was 0.57 m/min or more, the rate of expansion of GAC was 30% or more, and larval rejection increased approximately twice when compared with a washing rate of 0.45 m/min. Consequently, as a method of effective functioning of the filtration process for larval control, in the case of sand filtration, when it is difficult to expand the filter media, it is necessary to increase the rinsing time, and in the case of GAC, it is necessary to quickly discard the larvae by increasing the backwashing rate and shortening the backwashing cycle.
Deep bed로 구성된 활성탄/모래 공정에서의 입자성 물질 저감연구
백영애 ( Baek Youngae ),조우현 ( Joe Woohyun ),이광제 ( Lee Kwangjae ),홍숭희 ( Hong Seounghee ),박현 ( Park Hyeon ) 한국수처리학회 2020 한국수처리학회지 Vol.28 No.6
A water purification plant does not have a filter-to-waste valve, and the lack of free space makes the installation of such a valve difficult. In this study, we tried to reduce particulate matter by laying sand under the activated carbon without installing additional facilities. As a result of laying the lower sand to reduce the leakage of granular activated carbon, it was possible to reduce the particulate matter by about 15-20 % compared to the granular activated carbon process alone. The operating head rose about 10-20 cm when sand was laid, but there was no sharp rise and it was considered to be acceptable on site. In addition, the bacterial activity in the granular activated carbon column immediately after backwashing was detected at a maximum of about 120 per 100 mL. Despite the low water temperature (below 15℃), bacteria that are uncommon in the sand-filtered water proliferate and act as biological activated carbon in the granular activated carbon process, but it was found that it decreased by about 20% when sand was laid under the activated carbon. Regarding backwashing, it was confirmed that the activated carbon and sand layers were well mixed during air washing and then well separated again during rinsing due to the difference in specific gravity between the activated carbon and sand. A result of this study is that, in order to reduce leakage particles from granular activated carbon, it is recommended to use sand with a commercially available sand size of 0.55-0.6 mm (uniformity coefficient of 1.4 or less) when laying sand under granular activated carbon with an effective size of 0.65 mm.