SUMMARY
Large-magnitude fluid-injection induced seismic events are a potential risk for geothermal energy developments worldwide. One potential risk mitigation measure is the application of cyclic ...injection schemes. After validation at small (laboratory) and meso (mine) scale, the concept has now been applied for the first time at field scale at the Pohang Enhanced Geothermal System (EGS) site in Korea.
From 7 August until 14 August 2017 a total of 1756 m³ of surface water was injected into Pohang well PX-1 at flow rates between 1 and 10 l s–1, with a maximum wellhead pressure (WHP) of 22.8 MPa, according to a site-specific cyclic soft stimulation schedule and traffic light system. A total of 52 induced microearthquakes were detected in real-time during and shortly after the injection, the largest of Mw 1.9. After that event a total of 1771 m³ of water was produced back from the well over roughly 1 month, during which time no larger-magnitude seismic event was observed. The hydraulic data set exhibits pressure-dependent injectivity increase with fracture opening between 15 and 17 MPa WHP, but no significant permanent transmissivity increase was observed.
The maximum magnitude of the induced seismicity during the stimulation period was below the target threshold of Mw 2.0 and additional knowledge about the stimulated reservoir was gained. Additionally, the technical feasibility of cyclic injection at field scale was evaluated. The major factors that limited the maximum earthquake magnitude are believed to be: limiting the injected net fluid volume, flowback after the occurrence of the largest induced seismic event, using a cyclic injection scheme, the application of a traffic light system, and including a prioriinformation from previous investigations and operations in the treatment design.
This study was carried out to develop a process for recovering dissolved metals from acid mine drainages (AMD). AMD sludge normally consists of a heterogeneous mixture of many elements that are ...thrown out due to a lack of low purity. However, purified Fe, Al and Mn hydroxides would be potential resources. The AMD from Samma-Taejeong coal mine, Samcheok, Gangwon province in Korea was neutralized by adding neutralizing agents and oxidant, hydrogen peroxide to evaluate recovery of the metals and purity of their precipitates. The metals in AMD were recovered individually according to two process schemes: (i) only neutralization, and (ii) neutralization after addition of hydrogen peroxide. The result shows that using only neutralizing agents, both dissolved Al and Fe were concurrently precipitated around at pH4.5 so that caused the purity of each precipitate to be lowered. In the case of oxidation and then neutralization of AMD, sequence of metal removal was Fe>Al>Mn in order. Recovery ratios of dissolved Fe and Al reached 99.2–99.3% at pH4.5 and 70.4%–82.2% at pH5.5, respectively. Recovery of Mn reached 37.8–87.5% at pH8.5. Based on the results, oxidation before neutralization increased the recovery of dissolved Fe and Al in AMD with high purity of precipitates.
•Purified Fe, Al and Mn hydroxides would be potential resources.•Sequence of metal removal was Al>Fe>Mn by only neutralization.•Sequence of metal removal was Fe>Al>Mn by oxidation before neutralization.•Recovery of Fe increased from 45.8–70.3% to 99.2–99.3% at pH4.5.•Recovery of Al reached 70.4%–82.2% at pH5.5, when the purity was 94.5–99.9%.
In the Geum River, a representative altered estuary, in-situ mooring and erosion experiments were conducted to reveal the effects of human-controlled discharge on benthic sediment disturbances. The ...strong discharge through the estuarine dam increased the current velocities within the benthic boundary layer (BBL) up to 79% and 153% during spring and neap tides, respectively. During the discharge period, the suspended sediment concentration in BBL was five times higher than that during the non-discharge period. During the flood phase, a critical shear stress for erosion (τce) was in the range of 0.1278 to 0.1391 Pa. Immediately after the ebb phase with strong discharge, τce increased to 0.1848 Pa, and the erosion rate (E) decreased from 33.73 to 14.81 mg m−2 s−1. The repetition of human-controlled discharge removed the erodible sediments within BBL, exposing the underlying consolidated sediment bed with low E and high τce. The results suggest that an altered estuary is vulnerable to benthic sediment erosion under combined natural and anthropogenic forcings.
Display omitted
•Human-controlled discharge disturbed benthic sediment transport and velocity structures.•Altered estuary is vulnerable to sediment erosion under anthropogenic forcings.•Discharge removed sediments, exposing consolidated sediment with low erodibility.•Erosion experiments present direct evidence on benthic sediment resuspension.
We recently observed the emergence of fluconazole-resistant Candida parapsilosis bloodstream isolates harboring a Y132F substitution in Erg11p in South Korea. These Y132F isolates had a higher ...propensity to cause clonal transmission than other fluconazole-resistant isolates and persisted within hospitals for several years, as revealed by microsatellite typing.
The availability of groundwater is of concern. The demand for groundwater in Korea increased by more than 100% during the period 1994–2014. This problem will increase with population growth. Thus, a ...reliable groundwater analysis model for regional scale studies is needed. This study used the geographical information system (GIS) data and machine learning to map groundwater potential in Gangneung-si, South Korea. A spatial correlation performed using the frequency ratio was applied to determine the relationships between groundwater productivity (transmissivity data from 285 wells) and various factors. This study used four topography factors, four hydrological factors, and three geological factors, along with the normalized difference wetness index and land use and soil type. Support vector regression (SVR) and metaheuristic optimization algorithms—namely, grey wolf optimization (GWO), and particle swarm optimization (PSO), were used in the construction of the groundwater potential map. Model validation based on the area under the receiver operating curve (AUC) was used to determine model accuracy. The AUC values of groundwater potential maps made using the SVR, SVR_GWO, and SVR_PSO algorithms were 0.803, 0.878, and 0.814, respectively. Thus, the application of optimization algorithms increased model accuracy compared to the standard SVR algorithm. The findings of this study improve our understanding of groundwater potential in a given area and could be useful for policymakers aiming to manage water resources in the future.
The tidal flats near Sinduri beach in Taean, Korea, have been severely contaminated by heavy crude oils due to the Korea's worst oil spill accident, say the Hebei Spirit Oil Spill, in 2007. Crude oil ...compounds, including polycyclic aromatic hydrocarbons (PAHs), pose significant environmental damages due to their wide distribution, persistence, high toxicity, mutagenicity, and carcinogenicity. Microbial community of Sinduri beach sediments samples was analyzed by metagenomic data with 16S rRNA gene amplicons. Three phyla (Proteobacteria, Firmicutes, and Bacteroidetes) accounted for approximately ≥93.0% of the total phyla based on metagenomic analysis. Proteobacteria was the dominant phylum in Sinduri beach sediments. Cultivable bacteria were isolated from PAH-enriched cultures, and bacterial diversity was investigated through performing culture characterization followed by molecular biology methods. Sixty-seven isolates were obtained, comprising representatives of Actinobacteria, Firmicutes, α- and γ-Proteobacteria, and Bacteroidetes. PAH catabolism genes, such as naphthalene dioxygenase (NDO) and aromatic ring hydroxylating dioxygenase (ARHDO), were used as genetic markers to assess biodegradation of PAHs in the cultivable bacteria. The ability to degrade PAHs was demonstrated by monitoring the removal of PAHs using a gas chromatography mass spectrometer. Overall, various PAH-degrading bacteria were widely present in Sinduri beach sediments and generally reflected the restored microbial community. Among them, Cobetia marina, Rhodococcus soli, and Pseudoalteromonas agarivorans were found to be significant in degradation of PAHs. This large collection of PAH-degrading strains represents a valuable resource for studies investigating mechanisms of PAH degradation and bioremediation in oil contaminated coastal environment, elsewhere.
Display omitted
•Metagenomic analysis used to investigate for microbial community in beach sediments.•Cultivable bacteria in the 2016 samples comprised a greater variety of species.•Three bacteria were found to be significant in degradation of PAHs on beach sediments.•PAH-degrading bacteria may hold promise for the development of bioremediation strategies.
PAH-degrading bacteria are a valuable resource for studies investigating the mechanisms underlying PAH degradation and bioremediation.
To design an appropriate remediation plan at polluted sites, the spatial distribution of soil contaminants should be accurately assessed using geostatistical approaches such as co-kriging. In this ...study, we evaluated whether portable X-ray fluorescence (PXRF) spectroscopy can provide a reliable dataset to improve the spatial assessment of contaminated soils. For this purpose, soil samples were collected at a high density in a former smelting area (70 m by 65 m) that was highly polluted with arsenic (As) and lead (Pb). The samples were analyzed using inductively coupled plasma atomic emission spectroscopy (ICP-AES; n = 153). In addition, at the sampling locations, As and Pb levels were scanned in the field using PXRF spectroscopy (n = 156). As a result, PXRF measurements were highly correlated with ICP-AES data and seemed appropriate as a secondary variable for spatial evaluation with co-kriging. Thus, we conducted ordinary co-kriging (OCK) using a part of ICP-AES data (primary variable) and all PXRF data (auxiliary variable), and compared the interpolation result with that by ordinary kriging (OK) using the same number of ICP-AES data. We assumed that the ICP-AES data represented true values but were less effective in cost and analytical time. A best spatial map of As and Pb levels was constructed by OK using all the training ICP-AES data (n = 123) for performance comparison and the prediction errors were calculated using the test ICP-AES data (n = 30). Comparison results indicated that the spatial distribution of contamination levels estimated by OCK was more similar to the best spatial map than that by OK when the same number of ICP-AES data was used; OCK addressed the spatial heterogeneity despite the small number of training data, while OK lost the heterogeneity. OCK using PXRF data also improved the prediction of spatial distribution even with the cutting of the sample size of ICP-AES data; the number of samples that minimized errors was reduced by 40 and 50% for As and Pb, respectively, in OCK. As a last step, the uncertainty of the spatial extent of soil contamination for remedial action or additional investigation was addressed using sequential Gaussian co-simulation algorithms, which incorporated PXRF measurements as a secondary variable and provided the probability of exceeding the regulatory limits of a soil contaminant. The probability map can help risk-based decision making in contaminated sites within budget and time constraints. The results of this study demonstrate that PXRF provides a reliable auxiliary dataset to improve the spatial assessment of contaminated soils, with reducing the time and cost of investigations.
•PXRF analysis of soil was effective for spatial assessment of metals contamination.•OCK was better to examine spatial distributions of soil contaminants than OK.•OCK using PXRF data could decrease the sample density by 40–50% with maintaining the accuracy.•Uncertainties of site evaluation for remedial action could be quantified by SGCS.
Although the widths of fault damage zones commonly show a positive correlation with displacements, these relationships also show a somewhat scattered distribution. We believe that one of the ...fundamental reasons for this problem is strongly related to subjective definitions and inconsistent uses of the term ‘damage zone’. Thus, firstly we classify damage zones into along-fault, around-tip and cross-fault damage zones based on descriptive views of an arbitrary fault exposure as well as their tridimensional locations around a segmented fault system. Secondly, we propose an advanced field technique and data acquisition method to more accurately define a damage zone using the distribution of cumulative fracture frequency. We tested this method on new field and borehole observations as well as previously published data to identify damage zone boundaries, and express them as a change in slope gradients of the cumulative distribution of deformation structures. The results show how this slope change can be a useful criterion in accurately defining the width of damage zones and some internal properties of fault zones. We argue that this damage zone classification and definition method should be adopted and used to prevent discrepancies in field data. This will help us to gain a better understanding of fault damage zone properties and their scaling with fault displacement.
The demand for hydrogen in South Korea is projected to reach 3.9 Mt by 2030, of which 2.96 Mt clean hydrogen is aimed by 2030. As such, we conduct an economic analysis of a low greenhouse gas ...emission hydrogen supply chain in South Korea using several H2 transportation methods in this study. The types of supply chains considered are green and blue ammonia; green and blue liquid hydrogen (LH2) imported from the Gulf Cooperation Council (GCC) region; and blue hydrogen produced in South Korea. A base-case analysis shows that the imported blue ammonia scenario is the most cost-effective option with 3.40 USD/kgH2, followed by the domestic blue hydrogen with 4.33 USD/kgH2, and imported green ammonia with 4.56 USD/kgH2. In environmental analysis, imported green ammonia shows the lowest CO2 footprint with 4.20 kgCO2/kgH2, followed by imported green LH2 with 6.26 kgCO2/kgH2, and domestic blue hydrogen with 7.34 kgCO2/kgH2.
•Imported blue ammonia scenario is the most cost-effective option at 3.40 USD/kgH2•Cost reduces further when ammonia is used for power generation or as a marine fuel•Imported blue and green LH2 show a far higher hydrogen supply cost than the others•Electrolysis has largest portion of hydrogen supply cost•Imported green ammonia shows the lowest CO2 footprint with 4.20 kgCO2/kgH2
PDF
