Junboum Park

Lab scale experiments for permeable reactive barriers against contaminated groundwater with ammonium and heavy metals using clinoptilolite (01-29B)

Batch tests and column tests were performed to determine the design factors for permeable reactive barriers (PRBs) against the contaminated groundwater by ammonium and heavy metals. Clinoptilolite, one of the natural zeolites having excellent cation exchange capacity (CEC), was chosen as the reactive material. In the batch tests, the reactivity of clinoptilolite to ammonium, lead, and copper was examined by varying the concentration of cations and the particle size of clinoptilolite. One gram of clinoptilolite showed removal efficiencies of more than 80% against those contaminants in all cases except in very high initial concentrations of ammonium (80 ppm) and copper (40 ppm). The effect of particle size of clinoptilolite was not noticeable. In the column tests, permeability was examined using a flexible-wall permeameter by varying particle sizes of clinoptilolite. When the washed clinoptilolite having the diameter of 0.42-0.85 mm was mixed with Jumunjin sands in 20:80 ratio (w/w), the highest permeability of 2 x 10(-3) to 7 x 10(-4)cm/s was achieved. The reactivity and the strength property of the mixed material were investigated using a fixed-wall column, having eight sampling ports on the wall, and the direct shear test, respectively. Clinoptilolite was found to be a suitable material for PRBs against the contaminated groundwater with ammonium and/or heavy metals.

Removal characteristics of As(III) and As(V) from acidic aqueous solution by steel making slag

This study focused on the environmental risk of steel making slag itself, arsenic removal mechanism and re-leaching possibility of arsenic to aqueous state after the adsorption. The purpose of the study is to promote the use of steel making slag as a low-cost adsorbent for arsenic in aqueous system. Calcium was easily dissolved out from the slag and become the dominant substance in the leachate. Some of the calcium could form amorphous calcium carbonate in alkaline condition, and arsenic in the aqueous solution would be removed by being co-precipitated with or adsorbed onto the amorphous calcium carbonate. Most of the amorphous calcium carbonate containing arsenic would be bound to amorphous iron oxide of the slag. When the slag was used as an adsorbent for arsenic removal, a little amount of toxic chemicals were leached from the slag itself under pH 0.8 to 13.6. Also, 70-80% of arsenic laden on the slag was bound to amorphous iron oxide which would not easily desorb unless given a reducing and complexing condition. Showing 95-100% removal efficiency near initial pH 2, the slag, therefore, could be used as an appropriate adsorbent for eliminating arsenic in acidic aqueous solution.

Oyster Shell as Substitute for Aggregate in Mortar

Enormous amounts of oyster shell waste have been illegally disposed of at oyster farm sites along the southern coast of Korea. In this study to evaluate the possibility of recycling this waste for use as a construction material, the mechanical characteristics of pulverized oyster shell were investigated in terms of its potential utilization as a substitute for the aggregates used in mortar. The unconfined compressive strengths of various soil mortar specimens, with varying blending ratios of cement, water and oyster shell, were evaluated by performing unconfined compression tests, and the results were compared with the strengths of normal cement mortar made with sand. In addition, the effect of organic chemicals on the hardening of concrete was evaluated by preparing ethyl-benzene-mixed mortar specimens. The long-term strength improvement resulting from the addition of fly ash was also examined by performing unconfined compression tests on specimens with fly-ash content. There was no significant reduction in the compressive strength of the mortars containing small oyster shell particles instead of sand. From these test data, the possible application of oyster shells in construction materials could be verified, and the change in the strength parameters according to the presence of organic compounds was also evaluated.

Effects of washing solution and drying condition on reactivity of nano-scale zero valent irons (nZVIs) synthesized by borohydride reduction.

Washing and drying processes are essential when synthesizing nano-scale zero valent irons (nZVIs) by borohydride reduction of iron salts in aqueous phase. However, effects of these processes on nZVI reactivity have not been investigated in detail, although different washing and drying conditions might alter surface characteristics of nZVIs and thus vary their reactivity towards reducible contaminants. In this study, effects of three washing solutions and drying conditions on the reactivity of nZVIs for nitrate were investigated. Washing with volatile solvents and drying under anaerobic condition decreased thickness of Fe-oxide layer on nZVIs and increased content of Fe(2+)-containing oxides in the layer, which enhanced nZVI reactivity toward nitrate. Volatile solvent washing could minimize the decrease in nZVI reactivity according to changing anaerobic drying condition to aerobic. Findings from this study suggest that application of washing with volatile solvents and drying under aerobic condition should be recommended as effective processes to obtain nZVIs with maximum reactivity at reasonable costs and efforts.

Adsorption and Thermal Desorption Behaviour of Asphalt-like Functionalities on Silica

The adsorption and thermal desorption behaviours of seven model compounds containing asphalt-like functionalities were studied on silica. Adsorption isotherms of the model compounds were examined at 25°C and analyzed via the Langmuir isotherm. A series of temperature-programmed desorption (TPD) experiments was also conducted on the silica samples, the activation energy for desorption (Ed) being determined by conventional TPD analysis. The adsorption and thermal desorption behaviours were correlated in terms of the activation energy (Ed tot) for complete desorption. Dimethyl sulphoxide showed the strongest adsorption and the largest value for Ed tot, implying that the high energy consumption necessary to desorb such functionalities plays a key role in the durability of asphalt–aggregate bonding.

Laboratory Observation of the Response of a Buried Pipeline to Freezing Rubber-Sand Backfill

This paper addresses the potential use of granulated rubber as backfill material for buried pipelines in cold regions. An experiment on a laboratory scale buried pipe was conducted to evaluate the pipe-backfill interaction upon freezing. Two backfill materials were employed. In Case 1, sand was used as backfill material. In Case 2, granulated rubber was mixed with sand. Induced circumferential and longitudinal strains along the pipe were measured with movement of the freezing front into the backfill and an estimate of the freezing soil pressure was obtained based on the measured pipe strain. Experimental results showed that the behavior of the buried pipe was influenced by the progression of the freezing front and type of backfill material. Cold temperatures advanced faster into the sand backfill compared to the rubber-sand backfill due to the good thermal characteristics of rubber. Circumferential strains increased in both backfills indicating the development of freezing soil pressure in the backfill. Dominant vertical compressive strains were observed at 0° and 180° in both backfills. A significant reduction in strain and pressure exerted on the pipe upon freezing in the rubber-sand backfill was confirmed and the application of rubber mixed with sand as backfill material is possible.

Removal of arsenate and arsenite from aqueous solution by waste cast iron

The removal of As(III) and As(V) from aqueous solution was investigated using waste cast iron, which is a byproduct of the iron casting process in foundries. Two types of waste cast iron were used in the experiment: grind precipitate dust (GPD) and cast iron shot (CIS). The X-ray diffraction analysis indicated the presence of Feo on GPD and CIS. Batch experiments were performed under different concentrations of As(III) and As(V) and at various initial pH levels. Results showed that waste cast iron was effective in the removal of arsenic. The adsorption isotherm study indicated that the Langmuir isotherm was better than the Freundlich isotherm at describing the experimental result. In the adsorption of both As(IH) and As(V), the adsorption capacity of GPD was greater than CIS, mainly due to the fact that GPD had higher surface area and weight percent of Fe than CIS. Results also indicated the removal of As(III) and As(V) by GPD and CIS was influenced by the initial solution pH, generally decreasing with increasing pH from 3.0 to 10.5. In addition, both GPD and CIS were more effective at the removal of As(III) than As(V) under given experimental conditions. This study demonstrates that waste cast iron has potential as a reactive material to treat wastewater and groundwater containing arsenic.

Laboratory study on the dielectric properties of contaminated soil using CPT deployed probe

Over the past decade, direct-push geotechnical sensors or penetration probes have earned widespread acceptance in the geoenvironmental fields of study as a more viable and cost-effective solution for the assessment of soil and groundwater contamination. Of these, resistance cone penetrometer (RCPT) devices equipped with electrical sensors have been successful in qualitatively locating contaminated areas. While the RCPT method has proved to be successful for delineating inorganic contaminants in the saturated zone, its applicability in the vadose zone and soils contaminated by hydrocarbon compounds have been doubtful. The objective of this research is therefore focused on verifying the applicability of capacitance measurements on an existing RCPT module to provide information on the moisture content and presence of various kinds of contaminants. Laboratory experiments were performed on carefully prepared soil layers to investigate the sensitivity of the measured capacitance on the soil moisture content and different types of contaminants. Results confirmed that the measured capacitance of soils reflected the volumetric amount of water present in both un-contaminated and contaminated soils. In addition, capacitance measurement showed potentials for applicability in detecting plumes of non-aqueous phase contaminants above the groundwater table. Consequently, recommendations were made on the basis to which capacitance measurements can support interpretations of the electrical resistivity data.

Modified Cyclic Shear Test for Evaluating Disturbance Function and Numerical Formulation of Geosynthetic–Soil Interface Considering Chemical Effect

Geosynthetics have been broadly used in waste landfill sites for filtration, drainage, and separation. Geosynthetics contact soil directly, creating a geosynthetic–soil interface corresponding to the external forces and conditions. The differences in the intrinsic material characteristics at the interface induce complicated stress–strain behaviors and strain-softening processes. Recent studies have presented the behaviors of geosynthetic–soil systems as depending on the interface shear strength degradation, which is affected by ambient factors such as the water content, chemical condition, etc. In this study, the disturbed state concept (DSC) and a disturbance function are introduced to explain the cyclic shear stress behavior of the interface. The degree of interface damage can be expressed by the disturbance function, and the shape of the disturbance function curve represents the intrinsic characteristics of the material. Massive sets of cyclic shear tests have been performed to investigate the effects of the pH values of leachates on the shear behavior of the geosynthetic–soil interface. Both geosynthetics and Jumunjin sand have been submerged in acid, neutral, and basic solutions for 200 days. A multi-purpose interface apparatus that can simulate the cyclic shear conditions of a geosynthetic–soil interface has been newly manufactured and modified for better performance. Test results display remarkable distinction in chemical degradation trends according to the pH values. New disturbance function parameters that determine the characteristics of the shear strength of the interface were estimated according to the chemical conditions as well. Furthermore, it was discovered via focused ion beam electronic microscopy that the different patterns of damage on the surface of soil particles with different pH values induce variation in the disturbance phase at the geosynthetic–soil interface. For the numerical formulation of the disturbance function, the constitutive equations of the DSC were modified using the Mohr–Coulomb model. Based on the modified DSC equations, verification and numerical implementation shall be performed for further study.

Microplastics pollution in different aquatic environments and biota: A review of recent studies

Microplastics (MPs) are generated from plastic and have negative impact to our environment due to high level of fragmentation. They can be originated from various sources in different forms such as fragment, fiber, foam and so on. For detection of MPs, many techniques have been developed with different functions such as microscopic observation, density separation, Raman and FTIR analysis. Besides, due to ingestion of MPs by wide range of marine species, research on the effect of this pollution on biota as well as human is vital. Therefore, we comprehensively reviewed the occurrence and distribution of MPs pollution in both marine and freshwater environments, including rivers, lakes and wastewater treatment plants (WWTPs). For future studies, we propose the development of new techniques for sampling MPs in aquatic environments and biota and recommend more research regarding MPs release by WWTPs.