Raychoudhury, Trishikhi

The contamination of water has become a major concern, where the source of contamination could either be geogenic or anthropogenic. The contaminants discussed here are broadly grouped as inorganic contaminants, organic contaminants, and emerging contaminants. Several nanoparticles (NPs) and nanocomposites (NCs) materials are explored for removal of different types of contaminants in recent times. Numerous studies have reported on performance evaluation of those NPs and NCs in removing different contaminants. In this chapter, first, a comprehensive review of efficiency and suitability of different NPs and NCs in removing various organic pollutants such as As, Cd, Cr, Cu, Mn, Ni, Pb and Zn, organic contaminants such as dyes, halogenated hydrocarbons, PAHs, etc., and emerging contaminants are discussed. Secondly, the process involved in removing contaminants in the fixed bed column filter and the performance of NPs and NCs as the filtering material in the column filter has been discussed. The parameters affecting the performance of the fixed bed column in removing the contaminants from water are also emphasized.

Arsenic (As) contamination in groundwater is a well-established concern. Several studies have explored the possibility of immobilizing arsenite [As (III)] in-situ within the aquifer. Recent studies show a uniform distribution of ferrous sulfate (FeS) synthesized within homogenous porous media and demonstrated promising performance in immobilizing As(III). Upscaling from bench-scale to field-scale systems involves the integration of physical and chemical heterogeneities. Thus, the distribution of reducing agent (i.e., FeS), subsequent capturing of As(III) in the upscaled heterogeneous porous media system is a complex and uncertain phenomenon. Therefore, this study focuses on assessing the performance of FeS when synthesized for multiple cycles under constant flow and constant head conditions for immobilization of As(III) through a heterogeneous porous media system. A 3-D heterogenous porous media system is first simulated using a sequential indicator simulator model (SISIM). Then, the same heterogeneous media is prepared in the laboratory by packing three different-sized sand within a 3-D tank (0.67 m × 0.40 m × 0.40 m) which is subdivided into a total of 150 grids (0.096 m × 0.08 m × 0.08 m). FeS is synthesized in-situ by sequential injection of sodium sulfide (Na2S) and ferrous sulfate (FeSO4‧6H2O), as detailed in the previous study. The outcome of the study suggests that flow within the model subsurface porous media is non-uniform and follows an inter-connected preferential flow path. The progression of in-situ synthesized FeS is faster in the areas of higher hydraulic conductivity. The immobilization of As (88%) is promising by FeS synthesized within heterogeneous porous media. An overall reduction of porosity (7.7%) and hydraulic conductivity (68.3%) are observed, which is more predominant along the preferential flow path where deposition of FeS is significantly higher. To maintain constant flow rate, 60% increase in head difference is required. Whereas the flow rate decreases by 47.2% when constant head condition is adopted. Overall, the newly synthesized FeS shows promising performance in immobilizing As(III) within heterogeneous model subsurface porous media; however, there might be some possibility of pore-clogging and bypassing of flow due to deposition and subsequent retention of As, which may impact the As removal efficiency in the longer run.

The ex-situ treatment of arsenic is widely adopted; however, there are emerging concerns related to system maintenance, material replacement, and waste generation. There is a scope to explore in-situ arsenite [As (III)] remediation in the aquifers. The main objective of this study is to evaluate the performance of in-situ synthesised FeS in immobilising As (III) in the natural groundwater when transported through a three-dimensional (3-D) porous media system. In this study, a 3-D tank of 0.50 m × 0.30 m × 0.30 m (L × W × H) was packed with natural sand to represent the subsurface porous media system. The homogeneous packing and uniform flow were ensured before synthesising FeS in-situ, where a total of 1.5 pore volumes (PVs) of 20 mM sodium sulfide (Na2S) and 20 mM ferrous sulfate (FeSO4) reagent solutions were injected alternatively into the pre-saturated porous media. Finally, 300 ± 15 μg/L of As (III) spiked natural groundwater was passed through the porous media, and the samples were collected through several sampling ports for analysing for total As and Fe. The result suggests that the concentration of As (III) reaches below 11 μg/L within 644 min (4 PVs) of injection of reagents. Furthermore, almost 88.4% of As (III) get immobilised after passing 31 PVs of contaminated water. In brief, almost 406 L of As contaminated groundwater can be treated by injecting 21 L of reagents with a reagent-to-treated water ratio of 1:20.

Pharmaceuticals are a group of bioactive compounds used to treat various diseases in humans and animals. Among these, diclofenac (DCF) and carbamazepine (CBZ) are most commonly used as analgesics and anticonvulsants. To fulfill the current demand, such pharmaceuticals are produced in a range of several thousand tons. Their high production causes their release in different water bodies leading to the deterioration of the water quality and causing ecotoxicity to several non-target organisms. Classical wastewater treatment plants show their lower removal efficiency. So, the development of new methods by combining older techniques is therefore required to eliminate these residues. To achieve this, the first objective of this study was to evaluates the efficacy of the non-pathogenic bacterial strain Bacillus subtilis BMT4i for removing DCF and CBZ, from an aqueous solution. For this, a series of batch experiments were conducted by keeping parameters similar to wastewater effluent to investigate the biodegradation of B. subtilis BMT4i in removing PhACs in real scenarios. Further, the viable bacteria were allowed to immobilize on activated carbons, and a comparative removal study was performed under both batch and column studies. The study showed that around 67% and 50% of DCF and CBZ were removed within 72 h when PhACs were supplied as the sole carbon source. Moreover, in co-metabolism with other carbon and nitrogen sources, the percentage removal was enhanced by 20–30%. Further, B. subtilis BMT4i were immobilized on two activated carbons i.e., ACEco, and ACDarco prepared from coconut shells and coal so that the composite could directly be used as a bioreactor. The biofilm formation over ACs was confirmed by scanning electron microscopy and Fourier-transform infrared spectroscopy. The results obtained with batch experiment showed over 85–100% removal of both PhACs in a short duration of 2 h. Moreover, the column studies revealed that around 60–77% of 1 mg/l PhACs were removed by passing over 2 L of PhACs contaminated water. Overall, the current study confirms that the B. subtilis BMT4i/ACs composite shows promising performance for removing selected PhACs from water. Hence, the synthesized composite is appropriate for extensive usage in treating wastewater containing PhACs contaminant to protect public health. Graphical Abstract: (Figure presented.) © University of Tehran 2024.

The emergence of new contaminants like engineered nanoparticles (NPs), pharmaceuticals (PhACs), etc., causes a detrimental effect on the ecosystem and the study needs to be done to understand its behavior in the natural environment. In the present study aggregation and transport behavior of zinc oxide nanoparticles (nZnO) was evaluated in the presence of one of the PhACs, carbamazepine (CBZ). At first, a series of batch experiments were performed with 50 mg/L of nZnO and 1 mg/L of CBZ at different pH (6 and 8) and electrolyte concentration (EC: 1 mmol/L and 20 mmol/L), to study the change in the hydrodynamic diameter of nZnO. The result indicates that the extent of aggregation of nZnO increases with an increase in EC from 1 mmol/L to 20 mmol/L of NaCl or CaCl2. However, in the presence of CBZ, shows greater colloidal stability at lower EC, and its effect was found to be nominal at higher EC. The transport behavior of nZnO and CBZ was assessed by column experiment, it was found that more than 97 % of nZnO and 99 % of CBZ are retained in the porous media during the injection for different test conditions. Moreover, during transport experiments of longer duration, less than 10 % of nZnO and about 72 µg/L of CBZ were released in the effluent. Therefore, the risk of the release of nZnO is reduced in the presence of CBZ.

Groundwater contamination with fluoride poses a significant global health challenge, critically affecting over one-third of the population in the north western state of Rajasthan, India. This study investigates the possibility of using magnesite, a readily available mineral in the area, as a cost-effective and locally producible option for removing fluoride. We investigated the fluoride adsorption capabilities of magnesite samples, subjected to various treatments including heat treatment at 600 °C, cold-plasma treatment, and coating with aluminium hydroxide to enhance their adsorption efficiency. The results showed that both heat-treated and cold-plasma treated magnesite had excellent abilities to remove fluoride. The cold-plasma treated samples had the highest adsorbent capacity, reaching a maximum of 9.92 mg/g at pH 9. The adsorption effectiveness of both untreated and modified magnesite was continuously high within the pH range of 5–10. It is discovered that at pH values lower than or equivalent to the point of zero charge, the capacity to remove fluoride remains mostly unchanged. This implies that the primary aspect contributing to fluoride removal is mainly due to non-specific adsorption mechanisms including columbic forces. These favorable results suggest that, while the modified magnesite demonstrates marginally improved performance, the raw magnesite powder may offer greater cost-effectiveness. © 2024 The Authors

Transport behavior of zinc oxide nanoparticles (nZnO) has been investigated widely; however, not many studies have identified the transport mechanisms through mathematical modeling by simulating both breakthrough curve (BTC) and retention profile (RP) under varying environmental conditions. Thus, this study focuses on investigating the transport behavior of nZnO in the subsurface under a wide range of environmental conditions through mathematical modeling. A mathematical model is developed to simulate nZnO transport in porous media and the values of the associated parameters are estimated by fitting the model to the experimental data under a broad range of physicochemical conditions reported in the literature. The model performance is assessed by evaluating its ability to simulate both the nZnO BTC and RP, and it demonstrates promising performance. It is found that nZnO retention in the soil is mainly governed by reversible deposition on grain surfaces and straining. Moreover, nZnO transport through coarse-grained soil at high velocity and low ionic strength (IS) in the presence of a dissolved form of natural organic matter (NOM) may lead to an increased risk of groundwater contamination. The nZnO transport behavior can be simulated better by incorporating size-dependent dispersivity in the developed model.

The objective of this study is to investigate the removal of selected pharmaceuticals such as ibuprofen (IBP), diclofenac (DCF), and carbamazepine (CBZ) by activated carbon (AC) when they are present in the aqueous solution as an individual entity or as a mixture. The coconut (AC(Eco)) and lignite (AC(Darco)) derived ACs after and before the impregnation of cerium were used as the adsorbent. Batch experiments were carried out for assessing the removal efficiency under varying conditions. The removal efficiencies of those pharmaceuticals were in the range of 66.2-99.8%. In the case of IBP and DCF, the removal was found to decrease slightly by AC(Eco) and AC(Eco)-Ce when the mixture of pharmaceuticals was used as compared to individual pharmaceuticals. The sorption kinetics results indicated that IBP (for both AC(Eco) and AC(Darco)) and CBZ (AC(Eco)) were best fitted to the pseudo-first-order kinetics model, whereas the DCF (both for AC(Eco) and AC(Darco)) and CBZ (AC(Darco)) fits better to pseudo-second-order model. The outcome of the study indicates that selected ACs were found effective in removing IBP, DCF, and CBZ when they are present as an individual entity or as a mixture in the aqueous solution.

Fluoride (F−) contamination in drinking water is a major problem in many parts of the world. In India, millions of people are exposed to F− contamination. Thus, it is important to assess the regional groundwater quality and the performance of potential nanoparticles (NPs) in removing F− under those natural groundwater conditions. The objectives of this study were (i) to assess the regional groundwater quality of F− contaminated zones, (ii) to evaluate the performance of different metallic NPs in removing F− and identify the promising NPs under natural groundwater conditions, and (iii) to identify the groundwater quality parameters impacting the performance of NPs. To achieve the objective, the groundwater samples are first collected from a few districts within Rajasthan, India, and then the water quality parameters are assessed. A series of experiments are conducted to evaluate the F− removal efficiencies by a wide range of NPs under both de-ionized (DI) water and natural groundwater conditions. The outcome of this study indicates that the groundwater in most of the water samples in the region is unfit for consumption as it exceeds the permissible limits (Bureau of Indian Standards, BIS) for total dissolved solids (TDS, 2035 mg/L), hardness (699 mg/L), alkalinity (504 mg/L) and F− (3.56 mg/L) concentration. The performance of NPs in removing F− (as sorption capacity, mg/g) follows the order of nAl2O3 ∼ nZnFe2O4 > nZnO ∼ nMgO.Al2O3> nMgO > nCeO2 > nLa2O3> nAlCeO3> nFe2O3 ∼ nAl2TiO5 > n(CeO2).(ZrO2) under DI water conditions. However, under F− contaminated natural groundwater, nLa2O3 nanoparticle shows promising performance with reasonable sorption capacity (11.12 ± 2.0 mg/g). Amongst the water quality parameters, Ca2+, Mg2+, hardness and TDS have the most adverse effect on F− sorption. The lower value of F− concentration in the groundwater is another factor limiting the F− sorption capacities. In summary, it could be inferred that nLa2O3 is a promising NP, which could be applied in different forms in water filters for F− removal from natural conditions. Moreover, pre-treatment of raw water for TDS and hardness reduction might be necessary. Overall, the study aims to control drinking water quality by targeting F− contamination, especially under water-stressed semi-arid regions, which is aligned with the SDGs of Clean Water and Sanitation (SDG 6) and Good Health and Well–Being (SDG 3). © 2025 Elsevier B.V., All rights reserved.