Takeshi Katsumi

Performance-based design of landfill liners

Abstract Factors affecting chemical transport in geomembrane, clay and composite liners are reviewed, and a simplified performance-based method for evaluating landfill bottom liners is presented. For single geomembrane liners, mass transport of inorganic chemicals is calculated from the leakage rate from holes for an assumed frequency of hole occurrence. Transport of organic chemicals is obtained by accounting for molecular diffusion through the intact geomembrane. Migration of inorganic and organic chemicals in compacted clay liners is calculated using a solution of the 1D advection–dispersion-reaction equation. For composite liners consisting of a geomembrane and a clay liner, 3D flow and transport of inorganic chemicals is approximated using an equivalent 1D model for transport through an effective area of transport. The approximation is based on results from 3D analyses that have been conducted for a variety of cases. Migration of organic chemicals through composite liners is calculated using a 1D diffusion model. Applicability of the method is illustrated by using it to evaluate the relative performance of several different liner systems.

MSW fly ash stabilized with coal ash for geotechnical application

The solidification and stabilization of municipal solid waste (MSW) fly ash for the purpose of minimizing the geo-environmental impact caused by toxic heavy metals as well as ensuring engineering safety (strength and soaking durability) are experimentally evaluated. The mixtures of MSW fly ash stabilized with cement and fluidized bed combustion coal fly ash (FCA) were used for unconfined compressive strength tests, leachate tests, and soaking tests. The behavior of soluble salts contained in the MSW fly ash significantly affects strength development, soaking durability, and the hardening reaction of the stabilized MSW fly ash mixtures. The cement stabilization of the MSW fly ash does not have enough effect on strength development and soaking durability. The addition of cement only contributes to the containment of heavy metals due to the high level of alkalinity. When using FCA as a stabilizing agent for MSW fly ash, the mixture exhibits high strength and durability. However, the Cd leachate cannot be prevented in the early stages of curing. Using a combination of cement and FCA as a MSW fly ash stabilizer can attain high strength, high soaking durability, and the containment of heavy metals. The stabilized MSW fly ash with cement and FCA can be practically applied to embankments.

Measuring the k-S-p relations on DNAPLs migration

Abstract Migration characteristics of dense non-aqueous phase liquids (DNAPLs) in the subsurface can be expressed as a water–DNAPL two-phase system based on mainly the k – S – p relations, which describe the relations among relative permeability ( k ), degree of water saturation ( S ), and capillary pressure head ( p ). The aims of this research are to develop an experimental system with new type of probes, such as the electrical conductivity probe for measuring the degree of water saturation and the hydrophilic and hydrophobic tensiometer for measuring the pore water and DNAPL pressures, and also to estimate the results obtained from the developed experimental system. From these tests, the excellent k – S – p relations were obtained and the efficiency and validity of this developed experimental system have been confirmed in terms of the concept of the scaling coefficient calculated by interfacial tensions.

Cd(II) adsorption on various adsorbents obtained from charred biomaterials.

Cadmium could cause severe toxicant impact to living beings and is especially mobile in the environment. Biomass is abundant and effective to adsorb heavy metals, but is easy to be decomposed biologically which affects the reliability of long-run application. Several biomasses were charred with and without additives at temperatures less than 200°C in this study. The prepared adsorbents were further testified to remove Cd(II) from aqueous solution. Equilibrium and kinetic studies were performed in batch conditions. The effect of several experimental parameters on the cadmium adsorption kinetics namely: contact time, initial cadmium concentration, sorbent dose, initial pH of solution and ionic strength was evaluated. Kinetic study confirmed (1) the rapid adsorption of Cd(II) on GC within 10 min and (2) the following gradual intraparticle diffusion inwards the sorbent at neutral pH and outwards at strong acidic solution. The grass char (GC) was selected for further test according to its high adsorption capacity (115.8 mg g(-1)) and affinity (Langmuir type isotherm). The Cd(II) removal efficiency was increased with increasing solution pH while the highest achieved at sorbent dosage 10.0 g L(-1). The ionic strength affects the sorption of Cd(II) on GC to a limited extent whereas calcium resulted in larger competition to the sorption sites than potassium. Spectroscopic investigation revealed the adsorption mechanisms between Cd(II) and surface functional groups involving amine, carboxyl and iron oxide. The long-term stability of the pyrolyzed grass char and the potential application in engineering practices were discussed.

Hydraulic Barrier Performance of SBM Cut-off Wall constructed by the Trench Cutting and Re-mixing Deep Wall Method

Containment using a soil-bentonite mixture (SBM) cut-off wall is a valid method to prevent the contaminants in soil from migrating in the aquifer. A new construction technique for the SBM vertical cut-off wall has been developed by employing the trench cutting and re-mixing deep wall method to achieve excellent homogeneity of the wall. This paper addresses this construction method and the laboratory testing results on the hydraulic barrier performance of SBM focusing on its chemical compatibility. Hydraulic conductivity values were measured for SBM specimens, which were processed from various types of soil with different concentrations of divalent cation (Ca 2+ ) in the permeant or in the pore water of original soil. For the Ca 2+ concentrations lower than 0.01 M in soil pore water, there is no significant effect on the hydraulic conductivity of SBM. For the higher Ca 2+ concentrations, more than one order of magnitude higher hydraulic conductivity values were observed. The correlation between the hydraulic conductivity and the void ratio change in SBM specimen implies that the void ratio change could be a good indicator of the hydraulic conductivity for different types of soil.

Soil excavation and reclamation in civil engineering: Environmental aspects

Abstract Three topics on the excavation and utilization of soils in Japan are presented in this paper. First, the current status of the generation and reuse of excavated soils is presented. Since natural contamination has been a concern in recent years, several efforts including experimental studies to evaluate the environmental suitability of these materials have been conducted. Second, traceability in environmental geotechnics is becoming an important consideration. One joint project, in which the excavated soils generated from shield tunnel excavation are utilized as a soil material for reclamation, utilizes the electronic toll collection (ETC) system to track the soil materials. Third, the utilization of recovered soils obtained from disaster debris mixtures generated by the 2011 East Japan earthquake and tsunami is required. Several issues on the proper treatment to obtain the soils from waste mixture and to utilize these soils in geotechnical applications are discussed.

Biochemical Effects on the Long-Term Mobility of Heavy Metals in Marine Clay at Coastal Landfill Sites

In coastal landfill facilities that are constructed to contain municipal and industrial wastes in Japan, natural marine clay layers serve as bottom liners to prevent pollutant migration. Leachates from landfills are rich in dissolved organic carbon (DOC) that can be used by micro-organisms. Biological processes could lead to redox reactions that change the pH and Eh. These biochemical factors may strongly influence the behavior of pollutants leached from landfills, particularly heavy metals. In this paper, modified batch tests were conducted to investigate the effects of pH and Eh and to simulate both chemical and biochemical reactions on zinc mobility in a marine clay layer. To examine the effects of pH and Eh, the pH and Eh were controlled by adding acid or base, respectively, and a reducing agent. To study the zinc mobility, biochemical reactions were enhanced by cultivating native micro-organisms, which gradually changed the pH and Eh conditions. Batch tests with different DOC concentrations were also conducted to evaluate the effect of DOC on zinc mobility. In addition, biochemical processes in the bottom clay liners at coastal landfill sites that receive municipal solid waste (MSW) incinerator ash were simulated by batch tests using a solution of MSW incinerator ash mixed with seawater along with cultivating native micro-organisms found in marine clay. The experimental results indicated that microbial activities in closed soil-water systems result in strongly reduced conditions compared to that controlled by a strong reducing agent, and that the zinc mobility is lowered through the formation of sulfides. Although microbial activity was initially limited under highly alkaline conditions due to MSW incinerator ash, the pH gradually decreased mainly due to the formation of organic acids from microbial activity. Under the oxidized conditions, the solubility of zinc was controlled by pH and the Eh had a negligible effect on the zinc concentration. DOC in the leachate served as a bioavailable carbon source for microbial activities, which promoted anaerobic conditions in the soil-water system and the immobilization of zinc. However, DOC also formed soluble complexes with heavy metals, which increased the zinc concentration. These observations confirmed that heavy metals in the leachates became immobilized under the conditions found at landfill bottom liners when estimated in terms of pH, Eh, and DOC.

Woods Charred at Low Temperatures and Their Modification for the Adsorption of Cr(VI) Ions from Aqueous Solution

Despite being prepared at higher temperatures and involving greater energy consumption, activated carbons always show a smaller capacity and affinity towards the adsorption of Cr(VI) ions. After a brief review regarding Cr(VI) ion contamination and treatment, the preparation of a novel biosorbent from pyrolyzed wood char for Cr(VI) ion adsorption is described. Pyrolysis was conducted at temperatures within the range 200–350 °C, thereby helping to protect beneficial functional groups, saving energy and hence reducing costs. The influence of pH, concentration, adsorbent dosage, ionic strength and equilibration time on Cr(VI) ion adsorption by this biosorbent was investigated. It was shown that the char obtained at 200 °C possessed the highest Cr(VI) ion retention capacity (31.96 mg/g) but required the longest equilibration time (> 47 d). Coating the char with nano-scale iron oxide greatly improved its adsorption affinity towards Cr(VI) ions, with a higher adsorption affinity (Henrys law Kd = 2.988 ℓ/mg) and an enhanced Cr(VI) ion adsorption capacity (53.45 mg/g) being accomplished within a much shorter equilibration time (24 h). Spectroscopic studies confirmed that complexation of Cr(VI) ions occurred via surface hydroxy groups. The methods proposed for preparing and modifying wood char are likely to be applicable in industrial wastewater treatment.

Column percolation test for contaminated soils: Key factors for standardization

Column percolation tests may be suitable for prediction of chemical leaching from soil and soil materials. However, compared with batch leaching tests, they are time-consuming. It is therefore important to investigate ways to shorten the tests without affecting the quality of results. In this study, we evaluate the feasibility of decreasing testing time by increasing flow rate and decreasing equilibration time compared to the conditions specified in ISO/TS 21268-3, with equilibration periods of 48h and flow rate of 12mL/h. We tested three equilibration periods (0, 12-16, and 48h) and two flow rates (12 and 36mL/h) on four different soils and compared the inorganic constituent releases. For soils A and D, we observed similar values for all conditions except for the 0h-36mL/h case. For soil B, we observed no appreciable differences between the tested conditions, while for soil C there were no consistent trends probably due to the difference in ongoing oxidation reactions between soil samples. These results suggest that column percolation tests can be shortened from 20 to 30days to 7-9days by decreasing the equilibration time to 12-16h and increasing the flow rate to 36mL/h for inorganic substances.

Speciation and mobility assessment of zinc in coastal landfill sites with MSW incinerator ash.

The mobility of zinc in coastal landfill sites reclaimed by municipal solid waste incinerator ash (MSWIA) was modeled and investigated by conducting a large column test. Temporal and spatial variations in the pH, redox potential (Eh), total organic carbon, and microbial activity were measured in pore water to observe their influences on the mobility of heavy metals throughout the test. After 502 days, permeation was terminated. Then to determine the content and forms of Zn along the column, MSWIA and marine clay samples were analyzed by the community bureau of reference modified sequential extraction procedure. Zn was partitioned into four defined chemical fractions: exchangeable, reducible, oxidizable, and residual. The results showed that attenuation processes occurred within the ash layer, Zn mobility was minor, and coastal landfill conditions promoted the immobilization of heavy metals. Both pH and Eh were the main factors for controlling the solubility of Zn. Moreover, under reduced-alkaline conditions, the reducible fraction was affected, but the oxidizable fraction was slightly favored. The formation of zinc sulphides might be another attenuation mechanism for Zn.