The remediation of contaminated groundwater, through the technology of permeable reactive barriers (PRB), involves the use of a reactive medium able to reduce the concentration of contaminants as long as remediation targets are achieved. In the present study, the use of granular mixtures composed of zero valent iron (ZVI) and lapillus for the treatment of nickel contaminated groundwater is proposed. Through short and long term column experiments, the effects of the following were analysed: i) ZVI percentage per unit volume, ii) reactive medium thickness, iii) flow velocity and iv) initial nickel concentration, on the breakthrough point occurrence (point where a rapid increase in nickel concentration in the effluent is observed). The optimal mixture composition (i.e. the optimal ZVI content per unit volume) was defined when the reactive medium was able to keep its reactivity and hydraulic conductivity for the time necessary for remediation. This capacity, as shown in this study, depends on the propagation velocity of the contamination front through the reactive medium.

Microbially induced carbonate precipitation (MICP) has been recognized as that microbial metabolism may induce a generation of calcium carbonates in the pores and/or on the surface of sand particles. However, only actual observations approach of inner structures by microscopes are difficult to understand the MICP process. In the current work, we propose a mathematical and numerical simulation model based on the reaction-diffusion system and finite difference method, respectively in order to understand dynamically calcium carbonate precipitation process and relationship between bacterial growth and precipitation. As a result, some temporal and spatial precipitation structures of calcium carbonate such as active and inactive bonds structures were obtained through some numerical examples, which are in good agreement with the existing experimental results.

Consequences of liquefaction during earthquakes can be disastrous and fatal. During the past decade, bio-mediated methods have gained researchers and engineers' attention, and have been developed to strengthen soils and mitigate liquefaction. Among these methods, a commonly used method ― the microbial induced calcite precipitation (MICP) method ― has proved to be a potential alternative technique due to its sustainability and relatively environmentally friendly character, with lower carbon emissions compared to traditional methods. In most of the existing studies on cyclic behavior of MICP-treated soils, uniformly graded fine sands like Ottawa 50-70, with a maximum diameter of 1 mm and a narrow grain size distribution, were used. As liquefaction can also occur in soils with larger grain size, it is quite important to study the applicability of MICP method to these soils and to know their behavior after treatment. In this study, we used coarser soils with a maximum grain size of 5 mm. Undrained cyclic triaxial tests were applied to MICP-treated and untreated soils. Cyclic stress ratios (CSR) and number of cycles from 0.25 (300 cycles) to 0.3 (100 cycles), 0.35 (100 cycles), 0.4 (100 cycles), up to 0.5 were applied one after another as long as liquefaction did not occur. The results obtained on one of these soils showed that the untreated soil samples liquefied at a CSR equal to 0.25 after 42 cycles, with an axial deformation around ± 4 %. For the MICP-treated samples with 8.6 % calcium carbonate content, cyclic resistance increased slightly to 63 cycles at 0.25 CSR, while the axial deformation was in one direction and relatively lower rate of increment. With around 3 % more calcium carbonate content (11.5 %), the MICP-treated soil was like cement which could withstand a much higher cyclic stress ratio (up to 0.5) with many more cycles compared to the untreated soil.

A new soil improvement method known as microbial induced calcite precipitation (MICP) has received tremendous attention of researchers in the related fields. This paper reports the results of the compatibility of compacted bio-cemented lateritic soil with municipal solid waste (MSW) leachate. Lateritic soil was treated with Sporosarcina pasteurii (S. pasteurii) suspension densities up to 2.40 x 109 cells/ml and compacted using British Standard light, BSL (or standard Proctor) energy. The permeation with leachate only yielded minimum hydraulic conductivity values of 5.02 x 10-10 m/s for the natural soil and 5.78 x 10-10 m/s for specimen treated with S. pasteurii suspension density of 2.40 x 109 cells/ml. The micrographs of specimens treated with S. pasteurii suspension density of 2.40 x 109 cells/ml and permeated with leachate only depicted the development of bio-film when compared with micrograph of the untreated soil. Test results showed significant reduction in the concentration of the MSW leachate chemical specie considered after interaction with S. pasteurii for 150 days either through bio-transformation or bio-degradation process.

This paper presents reduction effect and evaluation of Cr(VI)-contaminated soil by two kinds of plants on various initial concentration on laboratory testing. In this experiment, we prepared semi-two-dimensional experimental apparatus which could evaluate movement of water and pollutant and growth of plants two-dimensionally. Simulated polluted soil mixed with K2Cr2O7 powder as pollutant homogeneously and compacted. Selected plants were komatsuna (Brassica rapa var. perviridis) and sunflower (Helianthus annuus). Effect of reduction was confirmed by checking water content, pH, standard oxidation-reduction potential Eh, water soluble Cr(VI) of soil separated in 10 cm depth and 5-7.5 cm width respectively with changing time. Cr(VI) in plant body was also investigated at the end of test. 1) The higher initial concentration of Cr(VI), the lower root length density which describes root length in unit weight of soil for both of plant. 2) For komatsuna, reduction rate of Cr(VI) in the soil was ranged between 16-48 %. For sunflower, reduction rate of Cr(VI) in the soil is ranged between 27-45 %. It differed from initial concentration of Cr(VI).

The diffusion of municipal solid waste (MSW) contaminants in compacted lateritic soil-Bacillus coagulans (B. coagulans) mixture was studied. Diffusion test for single reservoir, decreasing source was adopted. Soil samples were treated with B. coagulans at one-third (1/3) pore volume in stepped suspension density of 0, 1.5 × 108, 6 × 108, 1.2 × 109, 1.8 × 109 and 2.4 × 109 cells/ml, respectively, before compaction. Specimens were prepared at optimum moisture content (OMC) of British Standard heavy (BSH) compaction energy. Cementation reagent containing 3 g Nutrient broth, 20 g urea, 10 g NH4Cl, 2.12 g NaHCO3 and 2.8 g CaCl2 per litre of distilled water was injected by gravity in three (3) cycles of 6 hours interval into the compacted specimens. Thereafter, the specimens were sealed at the top with plastic sheets with small openings for the sequential introduction of water and leachate for 21 days and 69 days, respectively, to simulate field condition. Results obtained show that diffusion testing water content, pH and electrical conductivity within the soil column decreased with depth. Gener+B66ally, all the cations considered had diffusion coefficient (D*) and tortuosity factors (ta) values that increased with increase in B. coagulans suspension density. However, Mg2+ had value that initially decreased from 5.98 × 10-9 at 0 cells/ml to a minimum value of -4.30 × 10-8 at 1.5 × 108 cells/ml and thereafter increased to 1.64 × 10-9 at B. coagulans suspension density of 2.4 × 109 cells/ml. The apparent D* and ta values for the anions considered initially decreased to a minimum and thereafter increased. The pore fluid concentration profile for the numerous chemical classes tested showed that the compacted lateritic soil - B. coagulans mixture can attenuate K+ and Cl– ions in MSW containment application.

Chemical immobilization using a hydroxyapatite is one of the promising approach to soil with high level lead (Pb) contamination. To enhance the effectiveness of Pb immobilization by the hydroxyapatite, it is important to understand that how Pb reacts with the hydroxyapatite and forms insoluble Pb phases in the soil pore. This study conducted the up-flow-unsaturated column percolation test with the combined application of X-ray diffraction (XRD) analysis to understand the relation between the amount of Pb migrated and Pb transformed into pyromorphite in the water-unsaturated soil with regarding to the distance of Pb migration. The XRD analysis could quantify the amounts of Pb as pyromorphite formed during the water percolation test. Pb existed as water-soluble gradually migrated from the soil in the layer to the soil in the next layer with the water percolation despite the presence of hydroxyapatite. In opposite, the formation of pyromorphite was favor in the soil near the inflow side.

Soil heavy metal contamination caused by mining is a significant issue in China. The site of this study is located in Ganzhou of Jiangxi province in China. 102 soil samples were collected along the Yangmeijiang River. ICP-MS was used to obtain heavy metal concentrations in the soils. Significant contamination was found in the agriculture soils adjacent to the river and near mining industries. The heavy metal concentrations were high at depths of 20 cm and 40 cm. According to geo-accumulation index Igeo, the soils were extremely polluted with Cd (Igeo = 4–7), heavily polluted with As (Igeo = 2–4), moderately to heavily polluted with Pb, Zn and Cu (Igeo = 0–4) and virtually unpolluted with Ni, Cr and Hg (Igeo = -3–1). These results may be a result of large amounts of As, Cd, Pb, Cu and Zn being produced by nearby copper heap leach facilities. Based on USEPA method for health risk assessment, with ingestion being the major pathway for health risks, heavy metals pose a non-carcinogenic risk to adults (HQmax = 2.87, CRmax = 4.25 × 10-4), but pose both non-carcinogenic and carcinogenic risk to children (HQmax = 20, CRmax = 1.15×10-3). Overall, As, Pb and Cr pose the primary health risks for the soils in the study area.

Large amounts of marine sedimentary rock are excavated for the construction of modern high-speed railways and roads, and they pose environmental risk due to the release of hazardous metal(loid)s. It is therefore important understand how hazardous metal(loid)s are released from excavated rock. This study investigated the influences of alteration surface structure of excavated rock induced by atmospheric exposure with drying-wetting cycles on the release of hazardous metal(loid)s. The atmospheric exposure with the drying-wetting cycles caused the particle size reduction, but not carbonation. In addition, it induced the oxidation of framboidal pyrite, resulting in the increase in the sulfate ion release and decrease in the pH in the excavated rock. The amount of amorphous iron content decreased with the increase in the period of atmospheric exposure. The amounts of arsenic, lead, and fluoride ion release were decreased with the increase in the period of atmospheric exposure, while those of selenium was gradually increased. The amount of boron release was stable during the atmospheric exposure. On the basis of these results, this study suggests that the atmospheric exposure with the drying-wetting cycles enhances/suppresses the release of hazardous metal(loid)s from the excavated rock.

Due to the anthropogenic activity, the soil environment is deteriorated by various organic and inorganic contaminants to a greater extent in Bangalore industrial area. The movement of heavy metals in soil is driven by various physical and chemical properties of the soil. This soil contamination leads to groundwater pollution through infiltration. In this study, an attempt is made to simulate the transport of heavy metals like nickel and zinc for one of the contaminated sites of Bangalore. The existing site contamination levels are used in the model to simulate the movement of nickel and zinc in the vadose zone of the soil. The simulation is carried out for 25 years to study the changes in nickel and zinc levels in infiltrated water considering the non-linear adsorption model. The simulation results help in identifying the vulnerability of groundwater borewells to these contaminants and in arriving suitable measures to prevent groundwater pollution.

Arsenic leaching from shale rock grains was evaluated by the regulatory and modified batch leaching tests. The regulatory test was in according to the Japanese Leaching Test No. 46. The modified batch leaching tests were carried out using de-aired distilled water and eliminating headspace to simulate anaerobic conditions. The results show that dissolved oxygen (DO) in normal batch leaching tests is ~6.0 mg/L. DO can be reduced to ~2.0 mg/L by using de-aired water and eliminating the headspace and shaking step. The results suggest that a pseudo anaerobic condition can be achieved by eliminating the headspace and shaking step and conducting the tests in the vacuum deaerator since the DO was very low (~1.1 mg/L). Under the pseudo anaerobic conditions, the arsenic leaching concentrations are lowest (~0.001 mg/L), implying that arsenic leaching might be suppressed under anaerobic conditions. Furthermore, these arsenic concentrations are below the regulatory standard (As < 0.01 mg/L), suggesting that the shale rock grains are environmentally safe for utilisation in geotechnical applications.