• Journal of Korean Society of Environmental Engineers
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• v.39 no.8
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• pp.462-469
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• 2017

Eutrophication and shortage of phosphate ore raise the necessity of phosphate removal and recovery from wastewater treatment plants. Especially, a sludge treatment system containing highly concentrated phosphate should be targeted for phosphate removal and recovery. This study thus aimed to evaluate the capability of the struvite crystallization process for phosphate removal and recovery from a sludge treatment system of a wastewater treatment plant. Analysis on phosphate concentrations and masses in the sludge treatment system revealed that digested sludge and centrate have phosphate concentrations and masses, high enough to adopt the struvite crystallization process. Chemical equilibrium modeling indicated that the struvite crystallization reaction substantially occurred with pH higher than 8 and $Mg^{2+}$ concentration 1.2 times higher than its theoretical requirement. A series of batch tests with digested sludge and centrate indicated that the phosphate removal reaction by struvite crystallization followed a first-order kinetics and reached over 80% removal efficiency at equilibrium. Aeration in the batch tests was found to purge $CO_2$ in sludge or centrate and increase pH up to 8.7, without adding NaOH. Thus, we concluded that the struvite crystallization process could be an efficient and economical process for phosphate removal and recovery from a wastewater treatment plant.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.4
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• pp.1-12
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• 2016

The Harmony Search Algorithm (HSA) is one of the recently developed metaheuristic optimization algorithms. Since the development of HSA, it has been applied by many researchers from various fields. The increasing complexity of problems has created enormous challenges for the current technique, and improved techniques of optimization algorithms are required. In this study, to improve the HSA in terms of a structural setting, a new HSA that has structural characteristics, called the Multi-layered Harmony Search Algorithm (MLHSA) was proposed. In this new method, the structural characteristics were added to HSA to improve the exploration and exploitation capability. In addition, the MLHSA was applied to optimization problems, including unconstrained benchmark functions and water distribution system pipe diameter design problems to verify the efficiency and applicability of the proposed algorithm. The results revealed the strength of MLHSA and its competitiveness.

• Journal of the Korean GEO-environmental Society
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• v.15 no.2
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• pp.17-25
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• 2014

In the present study, it were performed an unconfined compression test and a field applicability test according to a mixed ratio of SS, soil type and curing period to analyze strength and deformation characteristic in order to evaluate engineering characteristics of soil mixed pavements using the eco-friendly soil stabilizer (SS). The test results revealed that SS mixed soil shows fast strength development at the initial curing time while 28-day strength amounted for 97% of the final strength. Furthermore, coarse-grained dredged sand (DS) and weathered granitic soil (WGS) have a larger ratio of deformation coefficient with respect to unconfined compressive strength than fine-grained dredged clay (DC) and organic soil (OS). Moreover, a comparison test between natural and forced drying conditions was conducted and test result showed 54% to 67% of strength degradation while having 55% to 63% of strength degradation in the freezing and thawing test result. Finally, a repeated loading test result showed that DS experiences up to 35% of strength reduction compared to initial strength under 10,000 times loading in maximum. Thus, it was validated that an appropriate amount of fine-grained sand is necessary to secure resistance capability to repeated loading.

• The Journal of the Convergence on Culture Technology
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• v.6 no.2
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• pp.369-386
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• 2020

The purpose of this study is to examine causality closely about the mediating effect of management entity's self-checking between effects that not only mobilization for regular patrol of the relevant administrative agency, but also checking for Preventive Safety Guidance have on fire correspondence. The results of the analysis are as follows: First, not only mobilization for regular patrol of the relevant administrative agency, but also preventive safety guidance all together have been revealed to have an positive effect on management entity's self-checking. Results of these analysis have been revealed that the more not only the number of mobilization for regular patrol of the relevant administrative agency, but also the numbers of preventive safety guidance and fire fighting safety supervisor's self-checking are many, the more capability of not only management entity, but also fire fighting safety supervisor's self checking heighten. Second, not only mobilization for regular patrol of the relevant administrative agency, but also checking investigation for preventive safety guidance have been revealed to have an positive effect on fire correspondence. Results of these analysis have been revealed that the more not only the number for regular patrol of the relevant administrative agency, but also the number of fire fighting safety supervisor's checking times for preventive safety guidance are many, the more fire correspondence for the apartment house are being fulfilled much better. Finally, it has been found that both mobilization for regular patrol of the relevant administrative agency and management entity's self-checking have an effect on fire correspondence. Therefore, the effect that the relevant administrative agency's mobilization for regular patrols and preventive safety guidance, and management entity's self-checking have on fire correspondence was analyzed into what the relevant administrative agency's mobilization for regular patrols and preventive safety guidance is not only significant to do self-checking of management entity at the first stage, but also the relevant administrative agency's mobilization for regular patrols, and preventive safety guidance, and management entity's self-checking have an mediating effect in the relation between influences that have on fire correspondence.