Toru Inui

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.

Embodied energy as an environmental impact indicator for basement wall construction

Attempts were made to quantify the environmental impacts of the basement walls of two commercial buildings in London. Four different retaining wall options were designed based on steel and concrete systems for each of the sites. It was considered that excavation would take place with the aid of a one or two anchors system. Evaluation of embodied energy (EE) and CO2 emissions for each of the wall designs and anchoring systems were compared. Results show that there are notable differences in EE between different wall designs. Using the averaged set of Embodied Energy Intensity (EEI) values, the use of recycled steel over virgin steel would reduce the EE of the wall significantly. The difference in anchor designs is relatively insignificant, and therefore the practicality of the design for the specific site should be the deciding factor for anchor types. Generally, the scale of environmental impacts due to constructions is large compared to other aspects in life as demonstrated with the comparisons to car emissions and household energy consumption.

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.

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.

Application of grass char for Cd(II) treatment in column leaching test

Various adsorbents as well as toxicants have been investigated regarding the adsorption behaviors and mechanisms. However, most of these reports were based on batch test. The discrepancy in adsorption behaviors between batch test and column test has been recognized recently. This study was to investigate the sorption behavior of Cd(II) in a novel adsorbent made from Reed char. Batch adsorption test and column leaching test were both conducted. Various influence factors including confining pressure, pH, velocity, concentration and ionic strength were studied. The velocity was found to have negligible effect on the breakthrough of Cd(II). The adsorption affinity was observed for the first time to decrease from a high value (R(d) = 130.00) to a negligible one (R(d) = 1.20) with increasing confining pressure from 0 to 100.00 kPa. The breakthrough of acid Cd(II) solution was earlier for solutions with less pH and higher ionic strength. The Cd(II) laden adsorbent was reclaimed by flushing chelants through the column. The recycled adsorbent appeared to be applicable in the following adsorption treatment. Suggestions were provided regarding the potential engineering applications.

Large-Scale Shear Tests on Interface Shear Performance of Landfill Liner Systems

Interface shear performance of various landfill liner systems were evaluated for landfill stability by conducting large scale shear tests. Testing program covers the interfaces between (1) geosynthetics (geomembrane (GM) sheet (HDPE and PVC) and non-woven geotextile) and subsoil, (2) geosynthetics and compacted clay liner (CCL), and (3) GM and geotextile. The focus of this paper is placed on interface shear performance under both as installed condition (dry for geosynthetics and optimum moisture content for CCL or subsoil) and saturated / wet condition, since landfill liner system is often subjected to saturated / wet condition due to the higher water retention capacity of CCL as well as the contact to leachate and/or groundwater. For geotextile-GM interface, there is no significant effect on the interface shear strength. The saturated CCL-GM interface had lower shear strength compared to the interface under as installed condition, although the shear performances of CCL-geotextile interface under both conditions are similar to each other. For the interfaces between geosynthetics and subsoil, the frictional resistance of HDPE with textures surface had a significant drop from 23 to 15 degree in the saturated / wet condition.

Speciation and Mobility Assessment of Heavy Metals in the Coastal Municipal Solid Waste Incinerator Ash Landfill

In the metropolitan areas of Japan, coastal landfills have become a practical and main solution for the disposal of municipal solid waste incinerator ash (MSWIA) due to limited inland space. Leachate from the landfilled MSWIA contains many dissolved and suspended substances harmful to the surrounding environment, particularly heavy metals, such as lead, zinc, and cadmium. The mobility assessment of these heavy metals is therefore one of the important environmental issues for the coastal landfill. In this paper, modified batch tests were conducted to investigate the effects of pH and Eh changes on the mobility of heavy metals in both MSWIA and marine clay layer. Based on the speciation of heavy metals by using a sequential extraction method in the leachate-MSWIA and leachate-marine clay systems, heavy metal mobility and availability were discussed with the comparison to large-scale model test results presented by (Kamon et al. “Biochemical Effects on the Long-Term Mobility of Heavy Metals in Marine Clay at Coastal Landfill Sites,” J. ASTM Int., Vol. 3, 2006), which provides the long-term change in heavy metal concentrations and forms in the coastal MSWIA landfill site. Under the high pH (≈11) and low Eh (≈−200 mV) condition in the MSWIA-leachate system, Zn, Pb, and Cd were effectively immobilized by the formation of the reducible and oxidizable fractions of Zn and the oxidizable and residual (insoluble) fractions of Pb significantly. However, the potential mobility of Cd was relatively high since the formation of exchangeable compounds was more dominantly contributed to the immobilization. Test results on the speciation of the metals in the marine clay-leachate system accounts well for the evidence that the marine clay acts as the attenuation layer for heavy metals in leachate. These findings strongly support that heavy metal mobility is restricted in the coastal MSWIA landfill due to the formation of stable and insoluble forms under reduced-alkaline condition and the attenuation effect of the marine clay.