International Journal of Environmental Research and Public Health

Research

18 pages, 3075 KiB

Open AccessArticle

Index Properties, Hydraulic Conductivity and Contaminant-Compatibility of CMC-Treated Sodium Activated Calcium Bentonite

by Ri-Dong Fan, Krishna R. Reddy, Yu-Ling Yang and Yan-Jun Du

Int. J. Environ. Res. Public Health 2020, 17(6), 1863; https://doi.org/10.3390/ijerph17061863 - 13 Mar 2020

Cited by 16 | Viewed by 5377

Abstract

A typical sodium activated calcium bentonite (SACaB) was treated with carboxymethyl cellulose (CMC) polymer, called CMC-treated SACaB (CMC-SACaB), and it was investigated for its hydraulic conductivity and enhanced chemical compatibility. Index property and hydraulic conductivity tests were conducted on CMC-SACaB and SACaB with [...] Read more.

A typical sodium activated calcium bentonite (SACaB) was treated with carboxymethyl cellulose (CMC) polymer, called CMC-treated SACaB (CMC-SACaB), and it was investigated for its hydraulic conductivity and enhanced chemical compatibility. Index property and hydraulic conductivity tests were conducted on CMC-SACaB and SACaB with deionized water (DIW), heavy metals-laden water, and actual landfill leachate. Lead-zinc mixed (Pb-Zn) solution and hexavalent chromium (Cr(VI)) solution were selected as target heavy metals-laden water, and calcium (Ca) solution was tested for comparison purposes. The hydraulic conductivity (kMFL) was determined via the modified fluid loss (MFL) test. Liquid limit and swell index in DIW, heavy metal-laden water, and Ca solution increased with increasing CMC content. CMC treatment effectively decreased the kMFL of SACaB when exposed to Pb-Zn solutions with a metal concentration of 1 to 20 mmol/L and landfill leachate. An insignificant change in kMFL of CMC-SACaB occurred with exposure to Pb-Zn solutions with metal concentrations of 1 to 10 mmol/L, Cr(VI) and Ca solutions with metal concentration of 1 to 20 mmol/L, and landfill leachate. A slight increase in kMFL of CMC-SACaB was observed when Pb-Zn concentration increased to 20 mmol/L, and such an increment was more noticeable when the CMC content was lower than 10%. In the DIW, the measured kMFL values of CMC-SACaB and SACaB with a given range of void ratio were consistent with those obtained from the flexible-wall permeameter test. Full article

(This article belongs to the Special Issue Environmental Remediation of Soils and Groundwater)

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16 pages, 2158 KiB

Open AccessArticle

Analysis and Optimization of Mn Removal from Contaminated Solid Matrixes by Electrokinetic Remediation

by Claudio Cameselle, Susana Gouveia and Adrian Cabo

Int. J. Environ. Res. Public Health 2020, 17(6), 1820; https://doi.org/10.3390/ijerph17061820 - 11 Mar 2020

Cited by 6 | Viewed by 2219

Abstract

Electrokinetic remediation is a useful technique for the removal of ionic contaminants in soils, sediments, sludges, and other solid porous matrixes. The efficiency of metal removal and the electricity consumption in the electrokinetic treatment of soils largely depend on electric and physicochemical conditions. [...] Read more.

Electrokinetic remediation is a useful technique for the removal of ionic contaminants in soils, sediments, sludges, and other solid porous matrixes. The efficiency of metal removal and the electricity consumption in the electrokinetic treatment of soils largely depend on electric and physicochemical conditions. This study analyzes the electrokinetic treatment of Mn contaminated kaolinite clay specimen and the influence of voltage, current intensity, moisture content, pH, and facilitating agents on metal removal and energy consumption. The objective of this study is to identify the influence of the typical variables used in electrokinetic remediation. The results showed that the operation at constant voltage or constant current intensity were equivalent in terms of metal removal and energy consumption, as long as the electric field intensity was kept low to minimize the consumption in parallel electrochemical reactions, especially the electrolysis of water. The moisture content had a significant influence on the Mn removal. Moisture content higher that 50 percent resulted in very effective Mn removal as compared with kaolinite specimens with lower moisture. The control of pH in the electrolyte solutions and the addition of facilitating agents (organic acids) enhanced the removal of Mn but increased the electric energy cost. Overall, the best conditions for Mn removal involved low to moderate electric potential difference (10 to 30 V), the use of citric acid as the facilitating agent, and the pH control in the cathode at a slightly acid pH. The electrokinetic treatment of a sludge from a water treatment plant contaminated with Mn was effective when pH control on the cathode was used. Mn and various metals (66% of Mn, 30% of Cu, 56% of Zn, 21% Sr, and 21% of Fe) were removed with moderate electricity and acid consumption. Full article

(This article belongs to the Special Issue Environmental Remediation of Soils and Groundwater)

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24 pages, 7200 KiB

Open AccessArticle

Effects of Long-Term Repeated Freeze-Thaw Cycles on the Engineering Properties of Compound Solidified/Stabilized Pb-Contaminated Soil: Deterioration Characteristics and Mechanisms

by Zhongping Yang, Xuyong Li, Denghua Li, Yao Wang and Xinrong Liu

Int. J. Environ. Res. Public Health 2020, 17(5), 1798; https://doi.org/10.3390/ijerph17051798 - 10 Mar 2020

Cited by 15 | Viewed by 2987

Abstract

The effects of long-term repeated freeze-thaw cycles and pollution levels on the engineering properties (q_u, E₅₀, φ, c, and k) of Pb-contaminated soils were investigated in various laboratory tests. These soils were solidified/stabilized (S/S) with three [...] Read more.

The effects of long-term repeated freeze-thaw cycles and pollution levels on the engineering properties (q_u, E₅₀, φ, c, and k) of Pb-contaminated soils were investigated in various laboratory tests. These soils were solidified/stabilized (S/S) with three types of cement-based combined binders (C2.5S5F5, C5S2.5F2.5, and C5S5, cement, lime, and fly ash, mixed in different proportions; these materials are widely used in S/S technology). The strength and permeability coefficient of compound solidified/stabilized Pb-contaminated soils (Pb-CSCSs) were determined based on measurements of unconfined compressive strength (UCS), direct shear, and permeability. CT scanning, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) tests were employed to analyse the deterioration mechanisms under various repetitions of freeze-thaw cycles. The results showed that, under repeated freeze-thaw cycles, the engineering properties of Pb-CSCSs all degraded to varying degrees, though degradation tended to stabilise after 30 days of freeze-thaw cycles. The study also found that the pollutants obstruct hydration and other favourable reactions within the soil structure (such as ion exchanges and agglomerations and pozzolanic reactions). The activation of hydration reactions and the rearrangement of soil particles by freeze-thaw cycles thus caused the engineering properties to fluctuate, and soils exhibited different deterioration characteristics with changes in Pb²⁺ content. Full article

(This article belongs to the Special Issue Environmental Remediation of Soils and Groundwater)

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14 pages, 4009 KiB

Open AccessArticle

Analysis of Biomaterials as Green Coagulants to Control Suspended Solids for Surface Water Treatment

by Rosa Devesa-Rey, J.D. González-Aller and Santiago Urréjola

Int. J. Environ. Res. Public Health 2020, 17(5), 1777; https://doi.org/10.3390/ijerph17051777 - 09 Mar 2020

Cited by 2 | Viewed by 2320

Abstract

This study explores the use of natural, ecological coagulant-flocculants to reduce suspended particles in water. Three compounds were tested, namely: diatomaceous earth, calcium lactate and lactic acid. For this purpose, experiments in jar tests were carried out and the best compound was submitted [...] Read more.

This study explores the use of natural, ecological coagulant-flocculants to reduce suspended particles in water. Three compounds were tested, namely: diatomaceous earth, calcium lactate and lactic acid. For this purpose, experiments in jar tests were carried out and the best compound was submitted to an optimization in order to evaluate the most significant parameters affecting its use as coagulant-flocculant. First results evidenced that lactic acid remove 71% of the suspended particles during the first five minutes, and up to 83% during the first 15 min. To optimize its use, the range of suspended particles concentration, lactic acid dose and salinity gradient was tested by means of an incomplete 3³ factorial design. This technique allows reducing the number of experiments to be carried out through a response surface methodology, which enables to infer the values of the dependent variables in not studied situations, by means of predictive equations. As a result of the experiments carried out, optimal conditions to remove suspended particles were set at a lactic acid concentration of 1.75 g·L⁻¹. As lactic acid may be obtained biotechnologically from organic wastes, this use supposes a promising area by keeping products and materials in use and contributing to a circular economy. Full article

(This article belongs to the Special Issue Environmental Remediation of Soils and Groundwater)

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16 pages, 5733 KiB

Open AccessArticle

Chemical Reduction of Nitrate by Zero-Valent Iron: Shrinking-Core versus Surface Kinetics Models

by Maria Villen-Guzman, Juan Manuel Paz-Garcia, Brahim Arhoun, Maria del Mar Cerrillo-Gonzalez, Jose Miguel Rodriguez-Maroto, Carlos Vereda-Alonso and Cesar Gomez-Lahoz

Int. J. Environ. Res. Public Health 2020, 17(4), 1241; https://doi.org/10.3390/ijerph17041241 - 14 Feb 2020

Cited by 7 | Viewed by 2045

Abstract

Zero valent iron (ZVI) is being used in permeable reactive barriers (PRB) for the removal of oxidant contaminants, from nitrate to chlorinated organics. A sound design of these barriers requires a good understanding of kinetics. Here we present a study of the kinetics [...] Read more.

Zero valent iron (ZVI) is being used in permeable reactive barriers (PRB) for the removal of oxidant contaminants, from nitrate to chlorinated organics. A sound design of these barriers requires a good understanding of kinetics. Here we present a study of the kinetics of nitrate reduction under relatively low values of pH, from 2 to 4.5. We use a particle size of 0.42 mm, which is within the recommended size for PRBs (0.2 mm to 2.0 mm). In order to avoid possible mass-transfer limitations, a well-stirred reactor coupled with a fluidized bed reactor was used. The experiments were performed at constant pH values using a pH controller that allows to accurately track the amount of acid added. Since the reduction of

H^{+}

to

H_{2}

by the oxidation of ZVI will always be present for these pH values, blank experiments (without nitrate) were performed and the rate of this

H^{+}

reduction obtained. This rate of reduction was studied using three kinetic models: a regular empirical one, the Shrinking-Core Model (SCM), and the Surface Kinetics Model (SKM). The best performance was obtained from the SKM model. Therefore, this model was also used to study the results for the nitrate reduction, also with satisfactory results. In both cases, some assumptions are introduced to maintain a moderate number of fitting parameters. Full article

(This article belongs to the Special Issue Environmental Remediation of Soils and Groundwater)

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20 pages, 4864 KiB

Open AccessArticle

Influence of Freeze–Thaw Cycles and Binder Dosage on the Engineering Properties of Compound Solidified/Stabilized Lead-Contaminated Soils

by Zhongping Yang, Yao Wang, Denghua Li, Xuyong Li and Xinrong Liu

Int. J. Environ. Res. Public Health 2020, 17(3), 1077; https://doi.org/10.3390/ijerph17031077 - 08 Feb 2020

Cited by 17 | Viewed by 2605

Abstract

The solidification/stabilization (S/S) method is the usual technique for the remediation of soils polluted by heavy metal in recent years. However, freeze–thaw cycles, an important physical process producing weathering of materials, will affect the long-term stability of engineering characteristics in solidified contaminated soil. [...] Read more.

The solidification/stabilization (S/S) method is the usual technique for the remediation of soils polluted by heavy metal in recent years. However, freeze–thaw cycles, an important physical process producing weathering of materials, will affect the long-term stability of engineering characteristics in solidified contaminated soil. In addition, it is still questionable whether using large dosages of binders can enhance the engineering properties of solidified/stabilized contaminated soils. In this study, the three most commonly used binders (i.e., cement, quicklime, and fly ash), alone and mixed in different ratios, were thus added to lead-contaminated soil in various dosages, making a series of cured lead-contaminated soils with different dosages of binders. Afterward, unconfined compression strength tests, direct shear tests, and permeability tests were employed on the resulting samples to find the unconfined compressive strength (UCS), secant modulus (

E_{50}

), internal friction angle (

φ

), cohesion (

c

), and permeability coefficient (

k

) of each solidified/stabilized lead-contaminated soil after 0, 3, 7, and 14 days of freeze–thaw cycles. This procedure was aimed at evaluating the influence of freeze–thaw cycle and binder dosage on engineering properties of solidified/stabilized lead-contaminated soils. Results of our experiments showed that cement/quicklime/fly ash could remediate lead-contaminated soils. However, it did not mean that the more the dosage of binder, the better the curing effect. There was a critical dosage. Excessive cementation of contaminated soils caused by too much binder would result in loss of strength and an increase in permeability. Furthermore, it was found that UCS,

E_{50}

,

φ

,

c,

and

k

values generally decreased with the increase in freeze–thaw cycle time—a deterioration effect on the engineering characteristics of solidified lead-contaminated soils. Avoiding excessive cementation, 2.5% cement or quicklime was favorable for the value of

E_{50}

while a 2.5% fly ash additive was beneficial for the

k

value. It is also suggested that if the freeze–thaw cycle continues beyond the period supported by excessive cementation, such a cycle will rapidly destroy the original structure of the soil and create large cracks, leading to an increase in permeability. The results also showed that the contaminated soils with a larger dosage of binders exhibited more significant deterioration during freeze–thaw cycles. Full article

(This article belongs to the Special Issue Environmental Remediation of Soils and Groundwater)

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9 pages, 888 KiB

Open AccessArticle

Use of Nanoscale Zero-Valent Iron for Remediation of Clayey Soil Contaminated with Hexavalent Chromium: Batch and Column Tests

by Cleomar Reginatto, Iziquiel Cecchin, Karla Salvagni Heineck, Antonio Thomé and Krishna R. Reddy

Int. J. Environ. Res. Public Health 2020, 17(3), 1001; https://doi.org/10.3390/ijerph17031001 - 05 Feb 2020

Cited by 21 | Viewed by 3445

Abstract

This study investigated the reduction of hexavalent chromium (Cr(VI)) in a clayey residual soil using nanoscale zero-valent iron (nZVI). Five different ratios between nZVI and Cr(VI) were tested in batch tests (1000/11; 1000/23; 1000/35; 1000/70, and 1000/140 mg/mg) with the soil. With the [...] Read more.

This study investigated the reduction of hexavalent chromium (Cr(VI)) in a clayey residual soil using nanoscale zero-valent iron (nZVI). Five different ratios between nZVI and Cr(VI) were tested in batch tests (1000/11; 1000/23; 1000/35; 1000/70, and 1000/140 mg/mg) with the soil. With the selected proportion resulting best efficiency, the column tests were conducted, with molded specimens of 5 cm in diameter and 5 cm in height, with different nZVI injection pressures (10, 30, and 100 kPa). The soil was contaminated with 800 mg/kg of Cr(VI). The Cr(VI) and Cr(III) analyses were performed following the USEPA 3060A and USEPA 7196A standards. The results show that the reduction of Cr(VI) is dependent on the ratio between nZVI and Cr(VI), reaching 98% of efficiency. In column tests, the pressure of 30 kPa was the most efficient. As pressure increased, contaminant leaching increased. The permeability decreased over time due to the gradual increase in filtration and formation of oxyhydroxides, limiting nZVI mobility. Overall, nZVI is efficient for soil remediation with Cr(VI), but the injection process can spread the contaminated if not properly controlled during in situ application. Full article

(This article belongs to the Special Issue Environmental Remediation of Soils and Groundwater)

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14 pages, 3207 KiB

Open AccessArticle

SHMP-Amended Ca-Bentonite/Sand Backfill Barrier for Containment of Lead Contamination in Groundwater

by Yu-Ling Yang, Krishna R. Reddy, Wen-Jie Zhang, Ri-Dong Fan and Yan-Jun Du

Int. J. Environ. Res. Public Health 2020, 17(1), 370; https://doi.org/10.3390/ijerph17010370 - 06 Jan 2020

Cited by 15 | Viewed by 3765

Abstract

This study investigated the feasibility of using sodium hexametaphosphate (SHMP)- amended calcium (Ca) bentonite in backfills for slurry trench cutoff walls for the containment of lead (Pb) contamination in groundwater. Backfills composed of 80 wt% sand and 20 wt% either Ca-bentonite or SHMP-amended [...] Read more.

This study investigated the feasibility of using sodium hexametaphosphate (SHMP)- amended calcium (Ca) bentonite in backfills for slurry trench cutoff walls for the containment of lead (Pb) contamination in groundwater. Backfills composed of 80 wt% sand and 20 wt% either Ca-bentonite or SHMP-amended Ca-bentonite were tested for hydraulic conductivity and sorption properties by conducting laboratory flexible-wall hydraulic conductivity tests and batch isothermal sorption experiments, respectively. The results showed that the SHMP amendment causes a one order of magnitude decrease in hydraulic conductivity of the backfill using tap water (1.9 to 3.0 × 10⁻¹⁰ m/s). Testing using 1000 mg/L Pb solution resulted insignificant variation in hydraulic conductivity of the amended backfill. Moreover, SHMP-amendment induced favorable conditions for increased sorption capacity of the backfill, with 1.5 times higher retardation factor relative to the unamended backfill. The Pb transport modeling through an hypothetical 1-m-thick slurry wall composed of amended backfill revealed 12 to 24 times of longer breakthrough time for Pb migration as compared to results obtained for the same thickness slurry wall with unamended backfill, which is attributed to decrease in seepage velocity combined with increase in retardation factor of the backfill with SHMP amendment. Overall, SHMP is shown to be a promising Ca-bentontie modifier for use in backfill for slurry trench cutoff wall for effective containment of Pb-contaminated groundwater. Full article

(This article belongs to the Special Issue Environmental Remediation of Soils and Groundwater)

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