Sand Columns Research Articles

Assessment of bed clogging in surface water reservoirs under different hydrologic conditions

Physical clogging of porous media plays an important role in controlling their hydraulic conductivity. This study investigates how uniformly graded medium-to-coarse sand in a reservoir’s bed performs in response to the inflow of turbid water with fine suspended sediments. Different particle sizes, heads, and concentrations were simulated to cover a range of hydrologic conditions. A 1D sand column was used with three bed material sizes and three suspended particle sizes. Seven particle size ratios were tested under a constant head. Four heads and three suspended sediment concentrations are also evaluated. It was concluded that the decline in the relative hydraulic conductivity of the bed material is directly proportional to the ratio of sediments-to-bed particle sizes. Increasing the concentration of suspended sediments accelerated the rate of clogging, while bigger heads increased the depth of clogging. The study highlights how physical clogging affects the water balance in surface reservoirs and threatens the safety of dams.

Fates of potentially persistent and mobile organic substances in embedded outdoor columns for artificial groundwater recharge simulation

Persistent and mobile organic micropollutants (OMP) are ubiquitously found in the aquatic environment and have a high propensity to distribute in water resources and are difficult to remediate. Managed aquifer recharge systems such as artificial groundwater recharge, produce high-quality drinking water by removing numerous OMP from the source water. In this study, the fates of selected emerging and potentially persistent and mobile OMP were investigated in outdoor columns for artificial groundwater recharge simulation. Breakthrough curves of OMP were modeled to differentiate between sorption and bio-transformation. The study showed that selected OMP were persistent in the surface water and no photo-degradation was observed, except for diclofenac. The trends of dissolved organic carbon concentrations and UV light absorption at 254 nm wavelength suggest elevated biological activity in the first 0.3 m of the columns. The study revealed that the bio-transformation of cyanoguanidine, valsartan acid and diclofenac correlated with the biological activity in the sand columns. Benzyltrimethylammonium, n-(3-(dimethylamino)-propyl)methacrylamide, 1,3-di-o-tolylguanidine, 1,3-diphenylguanidine and melamine were completely eliminated within the first 0.3 m, likely due to sorption. Less mobile compounds such as carbamazepine and adamantan-1-amine also showed sorption. Sorption was also observed for diclofenac, likely due to decreased pH along the column depth. Retardation factors of several OMP were higher in the first 0.3 m of the columns, likely due to higher organic carbon contents compared to the remaining depth. Six organic substances (for example 2-acrylamido-2-methylpropane sulfonate and dimethylbenzene sulfonate) were persistent and mobile throughout the experiment. Overall, this study reveals the vital role of pH and sand organic carbon for sorption and residence time and biological activity for OMP elimination.

Impact of Pressure Waves on Water Imbibition and Flow in Unsaturated Porous Media

AbstractThe wetting front dynamics during water imbibition in dry porous media affect the ultimate water distribution pattern. In this study, we investigate the impact of pressure pulses that emit waves in the water phase on the water distribution and imbibition patterns in porous media. We present experimental results of water spatial distribution in sand columns following infiltration under abrupt pressured‐water pulses and compare them with those of continuous inflow. Applying pressure waves during infiltration increases pressure gradients behind the wetting front, which can overcome capillary and gravitational forces, leading to uniform imbibition. To simulate the process, we developed a pore‐network model incorporating an analytical solution of pressure wave attenuation to predict the imbibition pattern. Our results demonstrate that the amplitude of the pressure wave is associated with a sharp wetting front, resulting in higher water content compared to Darcy‐type continuous flow. The findings suggest that pressure waves have the potential to achieve high water content in unsaturated media and provide insights into the spatial extent of their impact on water distribution.

Reactive migration mechanism of Fe2+ and As3+ during groundwater discharge into river water: Insight from sand column experiments

During groundwater discharge into river water, the Fe2+ and As3+ in anoxic groundwater are brought into the oxygen-bearing interaction zone. However, the reactive migration and transformation mechanism of Fe2+ and As3+ in the interaction zone are poorly understood. This study is based on sand column experiments to simulate the process of groundwater discharge into river water. Results show that the chemical oxidation and precipitation of Fe2+ in the interaction zone mediated the migration and transformation of Fe2+ and As3+. Fe2+ is oxidized by dissolved oxygen in the pore water of the interaction zone and hydrolyzed to form precipitated Fe oxides, whose 90% were poorly crystalline. The formation of Fe oxides seriously hindered the migration of Fe2+ and As3+ to river water, creating a “Fe and As enriched area” near the side edge of groundwater flow in the interaction zone. About 70% of the As3+ was converted to As(V), and it is primarily retained through adsorption on the surface of Fe oxides or coprecipitation with Fe into the poorly crystalline Fe oxides. At the same time, As3+ significantly promoted the migration of Fe2+ by inhibiting the accumulation of Fe(II) on the surface of secondary minerals and the transformation of poorly crystalline Fe oxides into iron minerals with higher crystallinity. Fe2+ and As3+ concentrations and groundwater velocity impacted the comigration of Fe2+ and As3+ in riparian sediment. This study reflects that Fe2+ controls the fate of As3+ in groundwater during groundwater discharge into river water, which is significant for water quality protection.

Laboratory studies of the temporal evolution process of the riparian groundwater flow system related to rainfall

Comprehensive investigations of the riparian groundwater flow system response to rainfall based on laboratory experiments and numerical simulation are presented and discussed. The 1D sand column experiment results showed that the capillary fringe of the sand sample was 25 cm, and the supporting capillary water height was about 65 cm. The 2D sandbox was constructed to investigate the changes of hydraulic heads and groundwater flow system in the hypothetical riparian zone under different initial water tables and rainfall intensities. When the initial water table was shallow, a small amount of rainfall infiltration resulted in a rapid and large rise of the water table due to the effect of capillary fringe. When the initial water table was equal to the riverbed elevation, groundwater flow pattern changed once after the rainfall infiltration. In the early rainfall period, a groundwater divide and two opposite local flow systems occurred; one flowed to the upslope unsaturated zone (counter directional local flow system), the other flowed to the river (codirectional local flow system). As the rain continued, the groundwater divide kept moving to the upslope and finally disappeared by forming a stable codirectional regional flow system. When the initial water table was lower than the riverbed, groundwater flow pattern was more complex and changed twice. At the beginning, all the rainfall infiltration recharged the thick unsaturated zone and there was only a counter directional regional flow system. When the water table rose to the riverbed, a groundwater divide and two opposite local flow systems were formed. The groundwater divide was moving to the upland and finally formed a steady codirectional regional flow system. More fine characterization of hydrological variation in a short-time scale in the riparian zone is necessary in the future.

Experimental study on permeability and strength characteristics of MICP-treated calcareous sand

Calcareous sand is the main fill material for island reclamation projects, but untreated calcareous sand might not be used as a reclamation fill due to its poor mechanical properties. Microbial induced calcite precipitation (MICP) was directly used to consolidate calcareous sands. One-dimensional sand column tests were conducted to identify the optimized solutions and to investigate the effects of cement solution concentration, relative density, and consolidation frequencies on the permeability and mechanical properties of MICP-treated calcareous sands. Finally, three-dimensional model tests were carried out to investigate the effective consolidation range of microbially treated calcareous sands. The results show that the MICP-treated calcareous sand shows a reduction in the permeability of the sample, while the calcium carbonate cementation and its filling effect improves the mechanical properties of the soil. The one-dimentional test results show that the effective values for cement solution concentration, relative density, and consolidation frequencies range from 0.5 mol/L to 1.5 mol/L, 30%–70%, and 5–15 times. The consolidation frequencies have the greatest influence on the permeability and strength properties of the treated calcareous sand. A quadratic polynomial regression model for permeability and strength was established through response surface analysis, and the regression model proved to be highly accurate and reliable through testing. In three-dimentional tests, the consolidation range tends to move downwards in a trapezoidal shape, showing a "big bottom and small top" pattern, with a consolidation range of approximately 34 times the diameter of the pipe. This study serves as a reference for selecting consolidation parameters for subsequent tests and applications of MICP-treated calcareous sands.

Biosurfactant-affected mobility of oxytetracycline and its variations with surface chemical heterogeneity in saturated porous media

Herein, the influences of rhamnolipid (a typical biosurfactant) on oxytetracycline (OTC) transport in the porous media and their variations with the surface heterogeneities of the media (uncoated sand, goethite (Goe)-, and humic acid (HA)-coated sands) were explored. Compared to uncoated sand, goethite and HA coatings suppressed OTC mobility by increasing deposition sites. Interestingly, rhamnolipid-affected OTC transport strongly depended on the chemical heterogeneities of aquifers and biosurfactant concentrations. Concretely, adding rhamnolipid (1–3 mg/L) inhibited OTC mobility through sand columns because of the bridging effect of biosurfactant between sand and OTC. Unexpectedly, rhamnolipid of 10 mg/L did not further improve the inhibition of OTC transport owing to the fact that the deposition capacity of rhamnolipid reached its maximum. OTC mobility in Goe-coated sand columns was inhibited by 1 mg/L rhamnolipid. However, the inhibitory effect decreased with the increasing rhamnolipid concentration (3 mg/L) and exhibited a promoted effect at 10 mg/L rhamnolipid. This surprising observation was that the increased rhamnolipid molecules gradually occupied the favorable deposition sites (i.e., the positively charged sites). In comparison, rhamnolipid facilitated OTC transport in the HA-coated sand column. The promotion effects positively correlated with rhamnolipid concentrations because of the high electrostatic repulsion and deposition site competition induced by the deposited rhamnolipid. Another interesting phenomenon was that rhamnolipid's enhanced or inhibitory effects on OTC transport declined with the increasing solution pH because of the decreased rhamnolipid deposition on porous media surfaces. These findings benefit our understanding of the environmental behaviors of antibiotics in complex soil-water systems containing biosurfactants.

Combined settlement and clogging in drainage sand layer for suspended solids, colloids and inorganic salts

Blockage of leachate drainage facilities is a common engineering problem in landfill operation. The key factors that cause blockage of drainage facilities in landfill leachate are the deposition of suspended solids (SS) with colloids and the precipitation of inorganic salts. To determine the combined sedimentation law of SS, colloids and inorganic salts, a combined sedimentation test of suspended solids, colloids and inorganic salts was conducted. To further clarify the resulting clogging characteristics of the water-conducting sand layers, a sand column blocking test were conducted, and mineral composition and grain characteristics of sediments were determined. The experimental results shown that the colloids (silver iodide) and inorganic salts (calcium chloride or aluminum sulfate) increased the sedimentation rate of SS by 8 to18 times. Among them, the effect of AgI colloid was the most significant, followed by effect of calcium chloride, while effect of aluminum sulfate was the weakest. Compared with sand column clogging caused by SS, this combined migration shortened the sand column clogging time by more than half and reduced hydraulic conductivity by nearly two to three orders of magnitude. This study contributes to the accurate assessment of the service performance of landfill leachate drainage systems.

A numerical approach for simulation of stress-controlled cyclic shear loading in a soil column considering partial drainage

Liquefaction strength curves (LSCs) are commonly generated based on undrained stress-controlled cyclic testing to define the liquefaction potential of sands. However, these LSCs do not consider the effect of partial drainage on liquefaction potential. This is mainly because there are very limited experimental techniques to run stress-controlled tests for partially drained sands. This manuscript proposes a procedure to numerically simulate a saturated sand column with a free drainage boundary at the top (or top and bottom), accelerated horizontally at the bottom with constant acceleration cycles of duration designed to generate constant cyclic shear stress histories in the column. This is done for columns subjected to low and high overburden pressures. The paper starts with numerical simulations of a typical undrained cyclic direct simple shear, CDSS tests by applying a stepped velocity wave to a single soil element, an already established approach. This approach only works for a single element in undrained condition which is fixed at the base. Then, the proposed procedure is implemented by applying stepped acceleration time histories at the base of soil columns having one or two drainage boundaries. In these stepped acceleration runs, the durations of the acceleration cycles are controlled to achieve a partially drained stress-controlled CDSS kind-of-loading at specific elevations within the soil columns. The technique is used to show the effect of partial drainage on sand liquefaction behavior at both low and high overburden pressures. The results show that the effect of drainage is much more significant at higher overburden. The existence of both top and bottom drainage boundaries resulted in less liquefaction vulnerability, as compared to having only one drainage boundary at the top of the sand column. The results show that liquefiable sand layers in the field may be less prone to liquefaction under high overburden pressure than predicted by the current state-of-practice, which relies mainly on undrained small-scale cyclic tests.

Insights into the effects of natural pyrite-activated sodium percarbonate on tetracycline removal from groundwater: Mechanism, pathways, and column studies

In-situ chemical oxidation based on sodium percarbonate (SPC) has received much attention for remediation of groundwater contaminated with organic pollutants due to the high efficiency, stable reaction, and sustainability of SPC. Currently, metal ions and their composite materials, are mainly employed for the activation of SPC. However, due to its narrow pH range, slow Fe3+/Fe2+ circulation, and generation of refractory sludge, its application in groundwater is limited. In this study, SPC was activated with natural pyrite (FeS2) to remove tetracycline, which was selected as the target pollutant. FeS2 exhibited excellent catalytic activity and stability towards the degradation of tetracycline. The tetracycline degradation efficiency of SPC/FeS2 system reached 70 % within 10 min, and nearly half of the tetracycline was degraded in the first 5 min of the reaction. The optimum SPC dosage for the tetracycline removal was 8 mM, with FeS2 dosage of 0.5 g/L. The tetracycline removal efficiency remained above 60 % after 4 cycles, indicating its good recycling efficiency of the system. SPC/FeS2 system was not significantly affected by the initial pH or the presence of Cl−, SO42−, NO3− while, HCO3−, Ca2+, Mg2+, and humid acid suppressed the reaction. The electron paramagnetic resonance spectroscopy and quenching experiments demonstrated that OH and O2− played a dominant role in tetracycline removal by the system. S22−, as an electron donor, was able to participate in the Fe3+/Fe2+ cycle. In addition, the 13 transformation products were determined by liquid chromatography-mass spectrometry predicted that the degradation pathway of tetracycline consisted of hydroxylation, demethylation, and decarbonylation reactions. Finally, the dynamic simulation experiments of SPC/FeS2 sand column showed that FeS2 effectively activated SPC and significantly reduced the toxicity in groundwater after the packed column treatment. This study reveals that FeS2 can efficiently activate SPC and has good prospects for tetracycline-contaminated groundwater remediation applications.

Rhamnolipid-induced alleviation of bioclogging in Managed Aquifer Recharge (MAR): Interactions with bacteria and porous media

The prevention and treatment of bioclogging is of great significance to the application of Managed Aquifer Recharge (MAR). This study investigated the alleviating effect of biosurfactant rhamnolipid (RL) on bioclogging by laboratory-scale percolation experiments. The results show that the addition of RL greatly reduced bioclogging. Compared with the group without RL, the relative hydraulic conductivity (K′) of the 100 mg/L RL group increased 5 times at the end of the experiment (23 h), while the bacterial cell amount and extracellular polymeric substances (EPS) content on the sand column surface (0–2 cm) decreased by 60.8% and 85.7%, respectively. In addition, the richness and diversity of the microbial communities within the clogging matter decreased after the addition of RL. A variety of bacterial phyla were found, among which Proteobacteria were predominant in all groups. At the genus level, RL reduced the relative abundance of Acinetobacter, Bacillus, Klebsiella, and Pseudomonas. These microbes are known as strong adhesion, large size, and easy to form biofilms, therefore playing a critical role during MAR bioclogging. Moreover, RL changed the surface properties of bacteria and porous media, which results in the increase of electrostatic repulsion and decrease of hydrophobic interaction between them. Therefore, RL mediated the bacteria-porous media interaction to reduce biomass in porous media, thereby alleviating bioclogging. This study implies that RL's addition is an environmentally friendly and effective method to alleviate the bioclogging in MAR.

Improvement of subgrade soil with sand columns for construction railway embankment: A case study

AbstractA railway on 4 m height embankment is being built in the south of Iraq. The railway alignment is extending on a compressible soil experienced impermissible settlement according to the results of soil investigation of the soil at the project site. A trial for reducing the settlement was done adopting sand piles. Nonlinear analysis was conducted to evaluate the settlement of soil before and after using the proposed technique.The results indicated that without any improvement, the expected total settlement of the railway embankment on the compressible clay layer is 170.2 mm. By inserting granular piles of diameter 0.3 m, it was obtained settlement decreases to 88.7 mm with reduction being in range of ∼48%.

Clay-induced permeability decline in sandstone reservoirs: Insights from a coupled NMR-SEM experimental approach

The blockage induced by solid particles transport and deposition is one of the main causes of injectivity decline in geothermal sandstone reservoirs during reinjection. This paper investigates clay-induced clogging mechanisms to provide a better understanding to formation damage problems encountered in geothermal fields. In-depth NMR measurements were carried out during core-flooding experiments where illite clay particles (120 nm) were injected in sand-packed columns. SEM imaging was performed to compare the porous space before and after damage and study the morphology and distribution of the deposited particles in the sand column. Pressure drop measurements and NMR T2 relaxation time distributions revealed that clogging occurs in two stages: surface deposition and pore bridging. This was further confirmed by SEM images showing that pore-blocking illite ribbons were formed in the porous space.

Biochar and zero-valent iron sand filtration simultaneously removes contaminants of emerging concern and Escherichia coli from wastewater effluent

Advanced treated municipal wastewater is an important alternative water source for agricultural irrigation. However, the possible persistence of chemical and microbiological contaminants in these waters raise potential safety concerns with regard to reusing treated wastewater for food crop irrigation. Two low-cost and environmentally-friendly filter media, biochar (BC) and zero-valent iron (ZVI), have attracted great interest in terms of treating reused water. Here, we evaluated the efficacy of BC-, nanosilver-amended biochar- (Ag-BC) and ZVI-sand filters, in reducing contaminants of emerging concern (CECs), Escherichia coli (E. coli) and total bacterial diversity from wastewater effluent. Six experiments were conducted with control quartz sand and sand columns containing BC, Ag-BC, ZVI, BC with ZVI, or Ag-BC with ZVI. After filtration, Ag-BC, ZVI, BC with ZVI and Ag-BC with ZVI demonstrated more than 90% (> 1 log) removal of E. coli from wastewater samples, while BC, Ag-BC, BC with ZVI and Ag-BC with ZVI also demonstrated efficient removal of tested CECs. Lower bacterial diversity was also observed after filtration; however, differences were marginally significant. In addition, significantly (p < 0.05) higher bacterial diversity was observed in wastewater samples collected during warmer versus colder months. Leaching of silver ions occurred from Ag-BC columns; however, this was prevented through the addition of ZVI. In conclusion, our data suggest that the BC with ZVI and Ag-BC with ZVI sand filters, which demonstrated more than 99% removal of both CECs and E. coli without silver ion release, may be effective, low-cost options for decentralized treatment of reused wastewater.Graphical

Application of electric fields to improve cementation homogeneity of biogrouted sands

AbstractThe inhomogeneity of cementation is a common problem in soil improvement with microbially induced carbonate precipitation process (MICP), which is caused by uneven spatial distribution of bio‐induced calcium carbonate precipitation. Electric field adjustment method was developed and adopted for improving cementation homogeneity of bio‐grouted sands in this research. Horizontal one‐dimensional biogrouting experiments were conducted in sand columns under 0.1 V/cm of direct current (DC) electric field. The column treated with DC electric field showed a significant improvement in homogeneity of calcium carbonate precipitation as compared to the control (without DC electric field). Spatial distribution of calcium carbonate in columns were affected by the properties of bacteria, whether suspended or attached. In general, the attached bacteria with uneven spatial distribution played an important role in the calcium carbonate precipitation when flow rate was regulated at 0.54 cm/min, while the suspended bacteria could also be attached upon times with consumption of cations during biogrouting. With the influence of electric field, suspended bacterial transport in porous media occurred in one direction to the target locations because of the electrophoresis at an average speed of 0.14 cm/h, while sodium ion was found to be moved from anode to cathode by electromigration approach. Electrolysis of water, on the other hand, resulted a slight fluctuation in pH, even though this variation did not show any significant effect on the metabolic activity of bacteria and microbial‐induced carbonate precipitation process. The redistribution of suspended bacteria and sodium ion in porous media provided a possible for attached bacteria to distribute uniformly, which could be considered as the key factor to influence spatial distribution of the bio‐induced calcium carbonate in application of electric field adjustment method.

Transport and Retention of Fecal Indicator Bacteria in Unsaturated Porous Media: Effect of Transient Water Flow.

For production of clean drinking water, the processes governing bacterial remobilization in the unsaturated zone at transient water flow are critical. Although managed aquifer recharge is an effective way to dispose of pathogens, there are concerns about recontamination after heavy precipitation. To better understand how bacteria that were initially retained in porous media can be released to groundwater due to transient water content, transport experiments and modeling for Escherichia coli and Enterococcus moraviensis were conducted at the soil column scale. After inoculating dune sand columns with a bacteria suspension for 4 h, three rainfall events were performed at 24-h intervals. The effluent from sand columns was collected to analyze bacteria breakthrough curves (BTCs). After the rainfall experiments, the bacteria distribution in the sand column was determined. The collected BTCs and profile retentions were modeled with HYDRUS-1D, using different model concepts, including one-site kinetic attachment/detachment (M1), Langmuirian (M2), Langmuirian and blocking (M3), and two-site attachment/detachment (M4). After inoculation, almost 99% of the bacteria remained in the soil. The M1 and M2 bacteria models had a high agreement between observed and modeled concentrations, and attachment and detachment were two significant mechanisms for regulating bacteria movement in a porous medium with fluctuations in water flow. At the end of the experiment, the majority of bacteria were still found within the depth range of 5 cm to 15 cm. Our experiments show that E. coli is more mobile in sandy soils than E. moraviensis. The results of this study also suggest that the unsaturated zone is an important barrier between microbial contamination at the soil surface and groundwater. Follow-up studies are needed to completely understand the variables that regulate bacteria remobilization in the unsaturated zone of dune sands. IMPORTANCE At managed artificial recharge sites in the Netherlands, recontamination of infiltrated water with fecal indicator bacteria has been observed. The results of this study suggest that the unsaturated zone is an important barrier between microbial contamination at the soil surface and groundwater. Bacteria that accumulate in the unsaturated zone, on the other hand, can multiply to such an extent that they can be released into the saturated zone when saturation increases due to major rain events or a rise in groundwater level.

A novel numerical strategy to analyse the installation and set-up effects of sand compaction piling

Sand compaction piling has been long recognized to exert considerable influence on the treated soils in various aspects. One noteworthy regard is the strength set-up or the set-up effect in soil due to the sand compaction pile installation. However, due to its complex nature, it is extremely difficult to numerically model the actual piling process, which is characterised mainly by the repeated withdrawal and re-driving of the casing tube and by the gradual expansion of the sand column. Crude simplifications of various forms had thus to be adopted in the past. This paper reports the development of an innovative approach that can replicate not only the actual sand compaction pile installation process but also the post-installation soil consolidation phenomenon. With that, the set-up effect can be realistically reflected by numerical means.

Experimental measurements and numerical simulations of the transport and retention of nanocrystal CdSe/ZnS quantum dots in saturated porous media: Effects of electrolytes, organic ligand, and natural organic matter

This study explores the transport and retention of CdSe/ZnS quantum dot (QD) nanoparticles in water-saturated sand columns as a function of electrolytes (Na+ and Ca2+), ionic strength, organic ligand citrate, and Suwannee River natural organic matter (SRNOM). Numerical simulations were carried out to understand the mechanisms that govern the transport and interactions of QDs in porous media and to assess how environmental parameters impact these mechanisms. An increase in the ionic strength of NaCl and CaCl2 increased QDs retention in porous media. The reduction of the electrostatic interactions screened by dissolved electrolyte ions and the increase of divalent bridging effect are the causes for this enhanced retention behavior. Citrate or SRNOM enhanced QDs transport in NaCl and CaCl2 systems by either increasing the repulsion energy barrier or inducing the steric interactions between QDs and the quartz sand collectors. A non-exponential decay characterized the retention profiles of QDs along the distance to the inlet. The modeling results indicated the four models containing the attachment, detachment, and straining terms – Model 1: M1-attachment, Model 2: M2-attachment and detachment, Model 3: M3-straining, and Model 4: M4-attachment, detachment, and straining – closely simulated the observed breakthrough curves (BTCs) but inadequately described the retention profiles.

Stabilization of Iron (0) in plasma treated semi porous polylactic acid based particles for in situ groundwater remediation

This study aims at incorporating reactive zero valent iron (ZVI) nanoparticles into water dispersible, biodegradable polymeric particles acting as a slow release reservoir of ZVI for targeting groundwater contaminants in situ. In order to accomplish the goal, three simple steps were adopted such as: 1) electrojetting of PLA (polylactic acid) with FeCl3 (∼17 wt%) to yield ∼700 nm sized monodisperse spherical particles (PLA_FeCl3) 2) surface modification of PLA_FeCl3 particles using oxygen plasma to enhance surface hydrophilicity and porosity (∼ 75%) 3) reduction of plasma treated PLA_FeCl3 particles in presence of NaBH4 to produce ZVI (size: 20–50 nm) entrapped PLA particles (PLA_ZVI) with high encapsulation efficiency of iron (∼85%). The plasma treated semi-porous PLA_ZVI particles exhibited slow and sustain release of iron (∼90% in ∼100 hrs) that were further employed to completely decontaminate both methyl orange (hydrophilic dye) and trichloroethylene (hydrophobic waste). Interestingly, the plasma treated particles were recyclable up to fourth batch, whereas the non-plasma treated one hardly show any recyclability due to burst release of surface entrapped iron from the latter. Moreover, the plasma treated hydrophilic particles provided stable dispersion (96 hrs) and prolonged reactivity (∼10 days in sand column) in water as opposed to non-plasma treated particles displaying 1 min dispersion stability in water. As a result, the plasma treated particles displayed smooth transportability through sand column (>80%) with negligible attachment efficiency (α = 1.1) onto sand particles. These attributes make them a potential alternative to bare ZVI (transportability <20%) for targeting hazardous pollutants by injecting them in groundwater.

Transport and interaction of cadmium and active sludge extracellular polymeric substances in saturated sand influenced by ionic strength and composition.

Artificial groundwater recharge with reclaimed water (secondary effluent from wastewater treatment plants) has become an important approach to solving water scarcity worldwide. Microorganisms in activated sludge can secrete many extracellular polymeric substances (EPS). However, information on the impact of EPS on the movement of heavy metals in porous media and their environmental effects on underground networks is limited. To assess this risk, we extracted EPS from the aerobic section of a wastewater treatment plant using hot sodium hydroxide and conducted experiments using one-dimensional sand columns to investigate how ion composition and strength affect the movement and interaction of cadmium (Cd) and EPS in porous media. The results showed that EPS facilitated Cd migration in porous media. Sodium (Na) and calcium (Ca) ions promoted the migration of Cd in porous media and EPS-Cd complexation. The effect of Ca was more significant than that of Na. As the Na adsorption ratio increased, the migration ability of Cd in porous media and the complexation ability of EPS with Cd decreased. Therefore, when estimating the migration of EPS and Cd in subsurface environments, careful consideration should be given to prevent the risk of groundwater pollution.