Leaching behavior of inert waste landfills.

Inert waste landfills are strictly limited to inert or non-reactive waste materials, nevertheless, due to human negligence or unavoidable circumstances, sometimes, small amounts of biodegradable or chemically reactive waste are mixed and disposed together with the inert waste. Over time, leachate generated from these biodegradable wastes may come into contact with rainfall water and percolate into groundwater and surrounding ground, degrading water quality. Additionally, the large sized industrial plastics present inside the inert waste landfill may trap and store the leachate thus enhancing the risk of contamination due to increased contact time and reducing the mechanical stability of the landfill. In this research, inert waste materials were collected from a Japanese inert waste landfill, and laboratory batch and column leaching tests were performed to determine the leaching behavior of the waste materials with variation in fibrous contents (FC) as 2% and 10% of total inert waste materials. From the batch leaching test, the inert waste was characterized as highly alkaline with a pH value of 10.3 and moderately reduced with a redox potential (Eh) value of 300 mV. The results from the column leaching test indicated that landfilling with 10% FC, comprising sizes below 10 cm, along with an installation of soil layer reduced the concentrations of heavy metals, metalloids, and total organic carbon in the leachate, thus confirming the environmental safety of the inert waste landfill.

Physical and mechanical properties of waste ground at inert waste landfills.

The physical and mechanical properties of waste ground were examined at 14 locations across 4 inert waste landfills in Japan with the goal of establishing a safe and cost-effective design methodology specific to inert waste landfills. Composition analysis, basic physical properties, angle of repose, CASPOL impact value tests, and in situ direct shear tests were conducted. Inert wastes were comprised of three main components: fibrous, granular, and soil-like content, and their compositions varied between 3.6-54%, 13-45%, and 43-74%, respectively. As the fibrous content and age after reclamation increased, the water content increased but the percentage air voids decreased. The impact value (Ia), which is an indicator of the bearing capacity, increased as the dry density increased. For all locations, the angle of repose after avalanche (αa) was found between 34 and 44°. In direct shear tests, the cohesion (c) and internal angle of friction (φ) ranged from 2 to 21 kN/m2 and 22-59°, respectively. The shear stresses obtained from these c and φ values were higher than those for the municipal solid wastes, particularly for landfills with fibrous fractions ranging 14-31% under a normal stress of 25.55 kN/m2. c increased and φ decreased as the dry density increased. The correlation calculated for c and φ with Ia for inert waste landfill were c = 4.10Ia - 21.32 and φ = -4.61Ia + 82.37. Finally, the utilization of the results obtained in this study is discussed in three design stages: planning, landfilling, and future expansion.

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.

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.

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.

Manganese removal from aqueous solution using a thermally decomposed leaf.

As a significant agricultural and industrial raw material, Mn(II) has been intensively used and widely distributed in the environment. Recent studies indicate that Mn(II) could cause acute toxicity to aqueous livings and human beings. The treatment of Mn(II) contained wastewater is stringent for environmental preservations. This paper attempts to testify the performance of Mn(II) adsorption by a novel adsorbent, natural leaf that was partially decomposed at moderate temperature. The isothermal adsorption shows high prevalence for Mn(II) with adsorption capacity determined at 61-66 mg g(-1). Various factors including adsorbent dosage, pH, temperature and equilibration time were investigated regarding the effects on Mn(II) adsorption. It was shown that a rapid equilibration within 30 min could be achieved at pH values as low as 4.0 while an endothermic and spontaneous process could be disclosed with enthalpy change ranged from 13 to 0.78 kJ mol(-1) and the entropy change ranged from -35.79 to -11.58 kJ mol(-1) from 5 to 55 degrees C, separately. Spectroscopy study revealed chemisorptions relevant to phosphate, ferrous oxide and carbonate groups, and a physisorption on carbon black, which were main components of the adsorbent. No obvious linkage was observed between Mn(II) adsorption and the amine group which is critical to heavy metal adsorption in previous studies. The proposed preparation method and the basic guidelines regarding the adsorbents' selection seem promising in the engineering practices.

Two-dimensional DNAPL migration affected by groundwater flow in unconfined aquifer.

The dense non-aqueous phase liquid (DNAPL) migration process was experimentally investigated in a laboratory-scale tank (150 cm width, 82.5 cm height, and 15 cm depth) to assess a site characterization on DNAPL contamination below a groundwater table. The heterogeneous ground of the tank model consisted of Toyoura sand (hydraulic conductivity, k = 1.5 x 10(-2) cm/s for void ratio, e = 0.62) and silica #7 sand (k = 2.3 x 10(-3) cm/s for e = 0.72). A series of experiments was carried out with or without lateral groundwater flow. Hydrofluoroether was used as a representative DNAPL. The main results obtained in this study are as follows: (1) the DNAPL plume does not invade into the less permeable soil layer with higher displacement pressure head; (2) the DNAPL plume migrates faster with lateral groundwater flow than without it; (3) lateral groundwater flow does not affect lateral DNAPL migration; rather, it promotes downward migration; and (4) pore DNAPL pressure without groundwater flow is higher than that with it. The above experimental results were compared with numerical analysis. The fundamental behaviors of DNAPL source migration observed experimentally are expected to be useful for assessing the characteristics of two-dimensional DNAPL migration in an aquifer.