The dimension of the separation zone in the dissolved air flotation (DAF) process is practically determined by the rise velocity of the bubble-floc agglomerates: flocs attached to several bubbles. To improve the flotation velocity and particle removal efficiency in the DAF process, many researchers have tried to attach as many bubbles as possible to flocs. In this study, the rise velocity of bubble-floc agglomerates, considered to be the most important factor in designing the separation zone of the flotation tank in the DAF process, was investigated on the basis of comparison between theoretical and observed results. The observed rise velocity measured by a particle image analyser (PIA) and the predicted value, however, did not show similarity, in contrast to what we had expected. Furthermore, the simulated results using population balance to predict the maximum number of attached bubbles on a floc were too impractical to accept under the practical condition of the surface of the floc if there was no change of bubble size. These findings led us to suggest that there were three possible causes which could conceivably explain the observations. It was suggested that the differences between predicted and observed values could be attributed to one or more of the possible causes.
The application of magnetic ion‐exchange resin (MIEX) during chemical coagulation was investigated for the removal of organic matters responsible for fouling in membrane processes. Two different coagulants were used—polyaluminium chloride (PACl) and polyaluminium chloride silicate (PACS). The MIEX addition during coagulation with both PACl and PACS considerably enhanced removal of dissolved organic carbon. Coagulation with MIEX treatment substantially removed all portions of natural organic matter (NOM), while the MIEX treatment alone effectively removed the hydrophobic and transphilic portions of NOM. The enhanced NOM removal by PACl coagulation with the addition of MIEX had positive effects on membrane flux at moderate transmembrane pressure conditions. However, the almost identical flux patterns were reported in the experiments of coagulation with PACS and PACS with MIEX addition. The results of the specific cake resistances indicated that the MIEX addition substantially decreased the resistances. The larger size distributions of PACl with MIEX corresponded well with the flux improvement.
A DAF (Dissolved-Air-Flotation) process has been designed considering raw water quality characteristics in Korea. Although direct filtration is usually operated, DAF is operated when freshwater algae blooms occur or raw water turbidity becomes high. Pre-sedimentation is operated in case when the raw water turbidity is very high due to rainstorms. A main feature of this plant is that the operation mode can be changed (controlled) based on the characteristics of the raw water to optimize the effluent quality and the operation costs. Treatment capacity (surface loading rate) and efficiency of DAF was found to be better than the conventional sedimentation process. Moreover, low-density particles (algae and alum flocs) are easily separated while the removal of them by sedimentation is more difficult. One of the main concerns for DAF operation is a high raw water turbidity. DAF is not adequate for raw water, which is more turbid than 100 NTU. In order to avoid this problem, pre-sedimentation basins are installed in the DAF plant to decrease the turbidity of the DAF inflow. For simulation of the actual operation, bench and full-scale tests were performed for highly turbid water conditions. Consequently, it is suggested that pre-sedimentation with optimum coagulation prior to DAF is the appropriate treatment scheme.
Various kinds of micro organic pollutants have frequently been detected from a water system. Therefore, it is considered to be very important part in the drinking water treatment system. And the research about removal process and processing efficiency have been being conducted briskly. In this study, the removal efficiency was evaluated using advanced water treatment process and nanofiltration process. The removal efficiency of nanofiltration process was very different according to physical and chemical characteristics of materials. The molecular weight of cutoff was the most influential factor in the removal efficiency. And when pKa value was higher than pH of raw water or Log Kow value was below 2, the removal efficiency of material was decreased. In case of oxidation reaction, the bigger the molecular weight of material was and the more hydrophobic a material was, the less oxidation reaction occurred. And the removal efficiency was decreased. Most unoxidized materials were removed by absorption. And the more actively oxidation reaction occurred by H2O2, the more absorption reaction increased. 요약 : 수계에서 검출되는 미량유해물질의 빈도와 종류가 다양해지고 있다. 따라서 정수처리시스템에서 고려되어야 할 부분 으로 거론되고 있으며 제거공정과 처리효율에 대한 연구가 활발하게 진행되고 있다. 본 연구에서는 고도처리공정과 나노여 과공정을 이용한 제거효율을 평가하였다. 나노여과공정의 경우 물질의 물리화학적 특성에 따라 제거율이 상이하게 나타났 다. 물질의 분획분자량이 제거율이 가장 큰 영향을 미치는 것으로 확인되었다. 또한, 원수의 pH보다 높은 pKa 값을 갖거나 Log Kow 값이 2 이하인 물질의 제거효율이 감소되었다. 고도처리공정 중 산화공정에서는 대상물질의 분자량이 클수록 그리 고 소수성을 띌수록 산화반응에 의한 제거효율이 감소되었다. 흡착공정에서는 산화되지 않은 대부분의 물질이 제거되었으며 H2O2에 의하여 산화가 더 잘 진행될수록 흡착반응이 향상되었다. 주제어 : 고도처리, 나노여과, 미량유해물질, 오존, 입상활성탄 1. 서 론 급속하게 진행 중인 도시화와 산업화에 따라 상수원으로 유입되는 유해 오염물질들이 다양화되고 그 양도 증가하고 있는 추세이다. 전 세계적으로 취수원수로 사용되고 있는 지표수 중에서 내분비계교란물질(endocrine disrupting compounds, EDCs), 의약물질(pharmaceuticals and personal care products, PhACs), 신규우려물질(contaminants of emerging concerns, CECs), 개인관리용품(personal care products, PCPs) 과 같은 미량유해물질의 검출이 보고되고 있으며 물질에 대한 규제 또한 강화되는 추세이다. 미량유해물질은 ug/L, ng/L 단위의 미량으로도 인체에 위해를 가할 수 있는 물질 로 차세대 정수처리 시스템에서 반드시 고려되어야 할 부 분들이다. 응집/침전/모래여과와 같은 기존 정수처리공정, 오존/활성탄과 같은 고도처리시스템 및 막여과 공정(정밀 여과/한외여과)에서의 제거율 및 제거 메카니즘에 조사가 필 요한 실정이다. 농약류, 합성세제, 색도 유발물질, 의약물질 및 내분비계 장애물질 등의 난분해성 오염물질은 염소나 오존을 이용해 서 효과적으로 산화 제거하기에는 한계가 있으며 1,2) 산화효 율 증진을 위해 과다한 염소의 투입은 트리할로메탄과 같 은 소독부산물을 과다하게 생성시키며 과다한 오존투입의 경우도 비경제적이다. 또한, 의약물질은 특정한 생리작용을 유지하기 위해 물에 잘 용해되지만 생분해가 잘 일어나지 않고 화학적으로 안정적이기 때문에 기존의 정수처리공정 만으로는 제거하기가 힘들다. 다양한 물리화학적 성질을 가 지는 의약물질들을 원수에 주입한 후 응집과 활성탄 흡착, 오존처리를 통해서 제거를 하였을 경우, 응집과 활성탄 흡 착으로는 산성의약물질들의 제거율이 현저히 낮고 오존에 의해서도 일부 의약물질은 분해가 잘되지 않는 것으로 보 고된 바 있다. 3,4) 일반적으로 나노여과 공정에서 미량유해물질의 제거효율 은 M.W (Molecular weight), log Kow, Dipole moment, Structure 등에 따라 다르게 나타난다. 분자량이 큰 것이 일 반적으로 제거효율이 증가되지만 결합된 구조에 따라 제거 효율이 다르게 나타날 수 있다. 또한, 물질이 소수성을 띌수
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