• Journal of Wetlands Research
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• v.24 no.4
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• pp.345-353
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• 2022

A wastewater treatment plant (WWTP) is a major gateway for the engineered nano-particles (ENPs) entering the water bodies. However existing studies have reported that many WWTPs exceed the No Observed Effective Concentration (NOEC) for ENPs in the effluent and thus they need to be designed or operated to more effectively control ENPs. Understanding and predicting ENPs behaviors in the unit and \the whole process of a WWTP should be the key first step to develop strategies for controlling ENPs using a WWTP. This study aims to provide a modeling tool for predicting behaviors and removal efficiencies of ENPs in a WWTP associated with process characteristics and major operating conditions. In the developed model, four unit processes for water treatment (primary clarifier, bioreactor, secondary clarifier, and tertiary treatment unit) were considered. Additionally the model simulates the sludge treatment system as a single process that integrates multiple unit processes including thickeners, digesters, and dewatering units. The simulated ENP was nano-sized TiO₂, (nano-TiO₂) assuming that its behavior in a WWTP is dominated by the attachment with suspendid solids (SS), while dissolution and transformation are insignificant. The attachment mechanism of nano-TiO₂ to SS was incorporated into the model equations using the apparent solid-liquid partition coefficient (Kd) under the equilibrium assumption between solid and liquid phase, and a steady state condition of nano-TiO₂ was assumed. Furthermore, an MS Excel-based user interface was developed to provide user-friendly environment for the nano-TiO₂ removal efficiency calculations. Using the developed model, a preliminary simulation was conducted to examine how the solid retention time (SRT), a major operating variable affects the removal efficiency of nano-TiO₂ particles in a WWTP.

• Journal of the Korean earth science society
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• v.41 no.6
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• pp.630-646
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• 2020

In rural areas, nitrate-nitrogen (NO3-N) pollution caused by agricultural activities is a major obstacle to the use of shallow groundwater as domestic water or drinking water. In this study, the water quality characteristics of shallow groundwater in Hyogyo-ri agricultural area of Yesan-gun, Chungcheongnam-do province was studied in connection with land use and chemical composition of soil layer. The average NO3-N concentration in groundwater exceeds the domestic and agricultural standard water qualities of Korea and is caused by anthropogenic sources such as fertilizer, livestock wastewater, and domestic sewage. The groundwater type mainly belongs to Ca(Na)-Cl type, unlike Ca-HCO3 type, a general type of shallow groundwater. The average NO3-N concentration (7.7 mg L-1) in groundwater in rice paddy/other (upstream, ranch, and residential) area is lower than the average concentration (22.8 mg L-1) in farm field area, due to a lower permeability in paddy area than that in farm field area. According to the trend analysis by the Mann-Kendall and Sen tests, the NO3-N concentration in the shallow groundwater shows a very weak decreasing trend with ~0.011 mg L-1yr-1 with indicating almost equilibrium state. Meanwhile, SO42- and HCO3- concentrations display annual decreasing trend by 15.48 and 13.15%, respectively. At a zone of 0 to 5 m below the surface, the average hydraulic conductivity is 1.86×10-5 cm s-1, with a greater value (1.03×10-4cm s-1) in sand layer and a smaller value (2.50×10-8 cm s-1) in silt layer.

• The Korean Journal of Nuclear Medicine
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• v.39 no.6
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• pp.413-420
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• 2005

Purpose: Neuroreceptor PET studies require 60-120 minutes to complete and head motion of the subject during the PET scan increases the uncertainty in measured activity. In this study, we investigated the effects of the data-driven head mutton correction on the evaluation of endogenous dopamine release (DAR) in the striatum during the motor task which might have caused significant head motion artifact. Materials and Methods: $[^{11}C]raclopride$ PET scans on 4 normal volunteers acquired with bolus plus constant infusion protocol were retrospectively analyzed. Following the 50 min resting period, the participants played a video game with a monetary reward for 40 min. Dynamic frames acquired during the equilibrium condition (pre-task: 30-50 min, task: 70-90 min, post-task: 110-120 min) were realigned to the first frame in pre-task condition. Intra-condition registrations between the frames were performed, and average image for each condition was created and registered to the pre-task image (inter-condition registration). Pre-task PET image was then co-registered to own MRI of each participant and transformation parameters were reapplied to the others. Volumes of interest (VOI) for dorsal putamen (PU) and caudate (CA), ventral striatum (VS), and cerebellum were defined on the MRI. Binding potential (BP) was measured and DAR was calculated as the percent change of BP during and after the task. SPM analyses on the BP parametric images were also performed to explore the regional difference in the effects of head motion on BP and DAR estimation. Results: Changes in position and orientation of the striatum during the PET scans were observed before the head motion correction. BP values at pre-task condition were not changed significantly after the intra-condition registration. However, the BP values during and after the task and DAR were significantly changed after the correction. SPM analysis also showed that the extent and significance of the BP differences were significantly changed by the head motion correction and such changes were prominent in periphery of the striatum. Conclusion: The results suggest that misalignment of MRI-based VOI and the striatum in PET images and incorrect DAR estimation due to the head motion during the PET activation study were significant, but could be remedied by the data-driven head motion correction.