This study develops a model to determine the input rate of the chemical for coagulation and flocculation process (i.e. coagulant) at industrial water treatment plant, based on real-world data. To detect outliers among the collected data, a two-phase algorithm with standardization transformation and Density-Based Spatial Clustering of Applications with Noise (DBSCAN) is applied. In addition, both of the missing data and outliers are revised with linear interpolation. To determine the coagulant rate, various kinds of machine learning models are tested as well as linear regression. Among them, the random forest model with min-max scaled data provides the best performance, whose MSE, MAPE, R2 and CVRMSE are 1.136, 0.111, 0.912, and 18.704, respectively. This study demonstrates the practical applicability of machine learning based chemical input decision model, which can lead to a smart management and response systems for clean and safe water treatment plant.

This study evaluates the potential of various coagulants to enhance the efficiency of total phosphorus removal facilities in a sewage treatment plant. After analyzing the existing water quality conditions of the sewage treatment plant, the coagulant of poly aluminium chloride was experimentally applied to measure its effectiveness. In this process, the use of poly aluminium chloride and polymers in various ratios was explored to identify the optimal combination of coagulants. The experimental results showed that the a coagulants combination demonstrated higher treatment efficiency compared to exclusive use of large amounts of poly aluminium chloride methods. Particularly, the appropriate combination of poly aluminium chloride and polymers played a significant role. The optimal coagulant combination derived from the experiments was applied in a micro flotation method of real sewage treatment plant to evaluate its effectiveness. This study presents a new methodology that can contribute to enhancing the efficiency of sewage treatment processes and reducing environmental pollution. This research is expected to make an important contribution to improving to phosphorus remove efficiency of similar wastewater treatment plant and reducing the ecological impact from using coagulants in the future.

본 연구는 노인을 대상으로 가족응집성과 생활만족도의 관계를 알아보 고, 가족응집성과 생활만족도의 관계에서 적극적 스트레스 대처의 매개 효과를 살펴보는 것을 목적으로 한다. 이를 위해 만 65세 이상의 노인 286명을 대상으로 경로분석과 부트스트래핑을 실시하였다. 분석결과 첫 째, 노인의 가족응집성은 적극적 스트레스 대처와 생활만족도에 통계적 으로 유의미한 영향을 미쳤다. 둘째, 노인의 적극적 스트레스 대처는 생 활만족도에 유의미하였다. 셋째, 노인의 가족응집성과 생활만족도의 관계 에서 적극적 스트레스 대처의 역할을 살펴본 결과 매개효과가 있음을 검 증하였다. 이상의 결과를 바탕으로 논의와 후속연구 제언을 하였다.

급변하는 경영환경에서 기업들은 생존하기 위해 다양한 전략과 실천을 위한 노력을 하고 있다. 특히, 기술과 산업이 빠르게 변화하고, 복잡성과 불확실성이 증가하는 상황에서 기업들은 중요한 혁신의 원천 으로 창의성을 중요하게 고려하고 있다. 이 가운데 조직차원의 창의성도 중요하지만 하위 단위부서인 팀 단위에서 팀 응집성, 팀 공유감과 팀 창의성(team creativity)에 대한 관심을 강조하고 있다. 팀은 팀원들의 다양한 경험과 다양한 지식을 공유하고 있기 때문에 개인보다 신속하고 효과적으로 문제를 해결할 수 있는 장점이 있어서 이에 대한 심층적 연구를 통해 개인연구나 조직연구가 제공하지 못한 다양한 결과들을 도출할 수 있다. 본 연구는 팀 연구 중, 기존 연구에서 많은 언급되었던 팀의 다양성 관점(diversity perspective)의 중요 변수인 팀 응집성과 최근 연구되고 있는 팀 교환 관계적 관점(exchange perspective)의 변수인 팀 공유감을 통해 팀 성과의 관련성을 도출하고 이때 인지된 조직지원 상황적 관계를 찾아보고자 한다. 실증적 연구의 설계는 한국기업의 팀 조사에서 팀 공유감과 팀 응집성이 팀 성과에 어떠한 영향을 주 고 있으며, 이때 인지된 조직지원이 이들 변수에 어떠한 조절효과를 보이는 지를 인과관계를 검증하고자 하였다. 가설검증을 위한 실증적 연구를 위해 팀 내 5-7명으로 구성된 84개 팀으로부터 432부의 설문지를 수거하여 이를 통계적 분석을 위한 표본으로 사용하였다. 실증적 분석결과에 의하면, 첫째, 팀 공유감과 팀 응집성은 팀 성과에 모두 정(+)의 영향을 미치는 것을 확인 할 수 있었다. 둘째, 팀 응집성의 매개효과가 존재하는지를 살펴본 결과, 팀 공유감과 팀 성과의 관계 부분매개효과를 보였는데, 이는 팀 응집성을 통해 팀 공유감이 팀 성과에 연결되어 있음을 확인할 수 있었다. 셋째, 팀 응집성과 팀 성과의 인과관계에서 인지된 조직지원이 조절효과를 보이는 지를 살펴보았는 데 도출된 결과는 팀 응집성이 높고 인지된 조직지원이 높을 때 팀 성과에 매우 유의적인 정(+)의 결과를 지지하였다.

Osmotic power is to produce electric power by using the chemical potential of two flows with the difference of salinity. Water permeates through a semipermeable membrane from a low concentration feed solution to a high concentration draw solution due to osmotic pressure. In a pressure retarded osmosis (PRO) process, river water and wastewater are commonly used as low salinity feed solution, whereas seawater and brine from the SWRO plant are employed as draw solution. During the PRO process using wastewater effluent as feed solution, PRO membrane fouling is usually caused by the convective or diffusive transport of PRO which is the most critical step of PRO membrane in order to prevent membrane fouling. The main objective of this study is to assess the PRO membrane fouling reduction by pretreatment to remove organic matter using coagulation-UF membrane process. The experimental results obtained from the pretreatment test showed that the optimum ferric chloride and PAC dosage for removal of organic matter applied for the coagulation and adsorption process was 50 mg/L as FeCl3 (optimum pH 5.5). Coagulation-UF pretreatment process was higher removal efficiency of organic matter, as also resulting in the substantial improvement of water flux of PRO membrane.

The ballasted flocculation effects of the mill scale and magnetite on activated sludge were investigated. Both ballasted flocculants (BF) could remarkably improve the sludge settleability in terms of zone settling velocity (ZSV) and sludge volume index (SVI). With the BF dosage of 0.2 to 2.0 g-BF/g-SS, the magnetite particles showed better efficiency on improving settling behavior of activated sludge than the mill scale due to higher surface area and hydrophobic property. The efficiency of SVI30 with magnetite injection was 2.5 to 11.3% higher than mill scale injection and that of the ZSV appreciated from 23.7% to 44.4% for magnetite injection. Averaged floc size of the BF sludge with magnetite dosage (0.5 g-BF/g-SS) was 2.3 times higher than that of the control sludge. Dewaterability of the sludge was also greatly improved by addition of the BF. The specific resistance to filtration (SRF) was reduced exponentially with increasing the dosage of BF. However, the BF’s particle size effect on the SRF looks to be marginal. Consequently, for improving the dewaterability, the BF played a physical role to remove the pore water of the biological flocs by intrusive attachment and a chemical role to induce aggregation of the flocs by charge neutralization.

The effects of activated carbon originated Ballasted Flocculant (BF) on the settleability of activated sludge and the recovery of BF by Hydro-cyclone (HC) were analyzed experimentally. Two kinds of BF (M-I: 125-250 μm, M-II: 250-425 μm in dia.) and three kinds of activated sludges with different SS concentration (2,300-7,100 mg/L) were applied for this study. With the dosage variation of BF from 0.14 to 1.3 g-BF/g-SS, we could obtain 24-31% improvement in SV30 (Sludge Volume after 30min sedimentation) for the lowest SS concentration sludge (2,300 mg/L). Whereas the SV30 improvement was much higher as 44-48% for the highest SS concentration sludge (7,100 mg/L). The settling characteristics of the sludge with BF followed Vesilind model the best among three models (Vesilind, Takacs and Cho model). HC could effectively separate BF with the separation efficiency of 70-90% and over 95% separation efficiency could be obtained when the HC was applied twice.

Microalgae are primary producers of aquatic ecosystems, securing biodiversity and health of the ecosystem and contributing to reducing the impact of climate change through carbon dioxide fixation. Also, they are useful biomass that can be used as biological resources for producing valuable industrial products. However, harvesting process, which is the separation of microalgal biomass from mixed liquor, is an important bottleneck in use of valorization of microalgae as a bioresource accounting for 20 to 30% of the total production cost. This study investigates the applicability of sewage sludge-derived extracellular polymeric substance (EPS) as bioflucculant for harvesting microalgae. We compared the flocculation characteristics of microalgae using EPSs extracted from sewage sludge by three methods. The flocculation efficiency of microalgae is closely related to the carbohydrate and protein concentrations of EPS. Heat-extracted EPS contains the highest carbohydrate and protein concentrations and can be a best-suited bioflocculant for microalgae recovery with 87.2% flocculation efficiency. Injection of bioflocculant improved the flocculation efficiency of all three different algal strains, Chlorella Vulgaris, Chlamydomonas Asymmetrica, Scenedesmus sp., however the improvement was more significant when it was used for flocculation of Chlamydomonas Asymmetrica with flagella.

To remove phosphorus from the effluent of public wastewater treatment facilities, hundreds of enhanced phosphorus treatment processes have been introduced nationwide. However, these processes have a few problems including excessive maintenance cost and sludge production caused by inappropriate coagulant injection. Therefore, the optimal decision of coagulant dosage and automatic control of coagulant injection are essential. To overcome the drawbacks of conventional phosphorus removal processes, the integrated sedimentation and dissolved air flotation(SeDAF) process has been developed and a demonstration plant(capacity: 100 m3/d) has also been installed. In this study, various jar-tests(sedimentation and / or sedimentation·flotation) and multiple regression analyses have been performed. Particularly, we have highlighted the decision–making algorithms of optimal coagulant dosage to improve the applicability of the SeDAF process. As a result, the sedimentation jar-test could be a simple and reliable method for the decision of appropriate coagulant dosage in field condition of the SeDAF process. And, we have found that the SeDAF process can save 30 – 40% of coagulant dosage compared with conventional sedimentation processes to achieve total phosphorus (T-P) concentration below 0.2 mg/L of treated water, and it can also reduce same portion of sludge production.