Biochar has received increasing attention in recent years as a potentially cost-competitive adsorbent for removing various contaminants from surface water and groundwater. However, most published studies have been conducted in the laboratory on a bench scale. Laboratory conditions do not necessarily reflect the complex, heterogeneous, and dynamic field conditions of actual contaminated surface water and groundwater environments. There is a lack of comprehensive literature review regarding the performance of biochar for contaminant removal, especially under realistic field conditions and at field scale. Here, we evaluated 31 studies on realistic applications of biochar for water remediation by searching the keywords: pilot scale, field scale, and mesocosm scale combined with biochar and water remediation. Biochar was found to be incorporated into a variety of water remediation technologies for treating both inorganic and organic contaminants, such as nutrients, heavy metals, pesticides, and pharmaceuticals in polluted waters and wastewaters. Also, biochar showed the potential to be effective on a field scale or in realistic remediation technologies, although it is not always as effective as other sorbents, such as activated carbon (AC). This is partially because AC has better physicochemical characteristics such as higher surface area and more micropores. Effectiveness for contaminant removal varies according to the targeted contaminants, the type and dosage of biochar used, and the treatment technology incorporating biochar. Finally, knowledge gaps and future research areas are identified. For example, more field scale studies are needed to test the effectiveness of biochar as an adsorbent under realistic conditions to pinpoint specific characteristics suitable for target contaminants. Physicochemical characteristics of the biochar can also change over time during the treatment process due to weathering, which may negatively affect the treatment performance. The effects of scaling up production on biochar quality should therefore also be further investigated, as physicochemical characteristics can be affected by varying the synthesis conditions. Regeneration and disposal of spent biochar is another active research area to determine the overall treatment costs.

Microbial life on plastic debris, called plastisphere, has invoked special attention on aquatic ecosystems as emerging habitats for antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB). There is scarce information concerning how properties of plastics influence ARGs and ARB, the effect of biofilms on enrichment of ARGs and ARB, and, especially, the influence of plastic transformation on ARGs and ARB. Limited research has shown that microplastic (MP) surfaces influence proliferation of antibiotic resistance (AR), aged MPs exhibit increased toxicity due to more adsorption-desorption of AR, and MP transformation is correlated with disseminating AR. Prevention measures of AR include minimizing MP releasing into aquatic environments and sewage treatment plants. The future research should aim to identify the interface mechanisms of transformed MNPs and antibiotics alone, or mixed with other contaminants, property changes of MNPs, and associated toxicity evaluation.

Achieving sustainable agricultural productivity and global food security are two of the biggest challenges of the new millennium. Addressing these challenges requires innovative technologies that can uplift global food production, while minimizing collateral environmental damage and preserving the resilience of agroecosystems against a rapidly changing climate. Nanomaterials with the ability to encapsulate and deliver pesticidal active ingredients (AIs) in a responsive (for example, controlled, targeted and synchronized) manner offer new opportunities to increase pesticidal efficacy and efficiency when compared with conventional pesticides. Here, we provide a comprehensive analysis of the key properties of nanopesticides in controlling agricultural pests for crop enhancement compared with their non-nanoscale analogues. Our analysis shows that when compared with non-nanoscale pesticides, the overall efficacy of nanopesticides against target organisms is 31.5% higher, including an 18.9% increased efficacy in field trials. Notably, the toxicity of nanopesticides toward non-target organisms is 43.1% lower, highlighting a decrease in collateral damage to the environment. The premature loss of AIs prior to reaching target organisms is reduced by 41.4%, paired with a 22.1% lower leaching potential of AIs in soils. Nanopesticides also render other benefits, including enhanced foliar adhesion, improved crop yield and quality, and a responsive nanoscale delivery platform of AIs to mitigate various pressing biotic and abiotic stresses (for example, heat, drought and salinity). Nonetheless, the uncertainties associated with the adverse effects of some nanopesticides are not well-understood, requiring further investigations. Overall, our findings show that nanopesticides are potentially more efficient, sustainable and resilient with lower adverse environmental impacts than their conventional analogues. These benefits, if harnessed appropriately, can promote higher crop yields and thus contribute towards sustainable agriculture and global food security.

Heavy metals including Cd, Pb, and Zn are prevalent stormwater and groundwater contaminants derived from natural and human activities, and there is a lack of cost-effective treatment for their removal. Recently, biochar has been increasingly recognized as a promising low-cost sorbent that can be used to remediate heavy metal contaminated water. This study evaluates the immobilization/release performance of dairy manure-derived biochar (DM-BC) as a sustainable material for competitive removal of coexisting heavy metal ions from water and explains the underlying mechanism for regeneration/reusability of biochar. Results showed that the metal ions exhibited competitive removal in the order of Pb2+ ≫ Zn2+ > Cd2+. The pH played a decisive role in influencing metal ion speciation affecting the electrostatic attraction/repulsion and surface complexation. Higher pH led to greater removal for Pb2+ and Cd2+, whereas Zn2+ showed maximum removal at pH ≈ 7.5. Diffuse reflectance infrared spectroscopy, scanning electron microscopy, and X-ray diffraction confirmed the interactions and precipitation reactions of oxygen-containing functional groups (e.g., ─OH, CO32-, and Si─O) as key participants in metal immobilization. Langmuir, Freundlich, and Redlich-Peterson isotherm modeling data showed varied and unique results depending on the metal ion and concentration. The removal kinetics and model fitting showed that the three steps of intraparticle diffusion might be more representative for describing the immobilization processes of metal ions on the external surface and internal pores. In the flow-through columns, DM-BC effectively retained the mixed metal ions of Cd2+, Pb2+, and Zn2+ showing 100% removal for the duration of the column run over three cycles of regeneration and reuse.

Compared to individual carbon nanotubes (CNTs), the improved and newly emerging CNT-metal oxide nanocomposites (CMNCs) pose unique properties that may enable fundamentally new techniques for identifying and solving environmental issues and challenges. This chapter critically showcases the synthesis methods (ex situ and in situ) of CMNCs; reviews the state-of-the-art progress of CMNCs' environmental applications including sensors, antimicrobial agents, desalination membranes, and adsorbents for removal of contaminants; assesses the potential transport and transformation scenarios of CMNCs such as colloidal stability, aggregation, deposition, and chemical/biological transformation in the environment; and evaluates the possible impact and risk including toxicity of CMNCs to the environment, ecosystem, and human health. In particular, the interlinker molecules that are commonly used for hybridizing CNTs and metal oxides during synthesis may complicate the environmental behaviors and toxicological response of CMNCs to living organisms. Future opportunities for CMNCs' applications in environmental systems, and current knowledge gaps for evaluating their environmental behaviors, and environmental health and safety (EHS) are proposed in this chapter as well.

This study investigated the removal of fluoride from water using a calcium-modified dairy manure-derived biochar (Ca-DM500). The Ca-DM500 showed a 3.82 - 8.86 times higher removal of fluoride from water than the original (uncoated) manure-derived biochar (DM500). This is primarily attributed to strong precipitation/complexation between fluoride and calcium. The Freundlich and Redlich-Peterson sorption isotherm models better described the experimental data than the Langmuir model. Additionally, the removal kinetics were well described by the intraparticle diffusion model. The Ca-DM500 showed high reactivity per unit surface area [0.0001, 0.03, 0.16 mg F per m2 for Douglas fir-derived biochar (DF-BC), DM500. and Ca-DM500, respectively] for retention of fluoride reflecting the importance of surface complexation. The copresence of anions reduced removal by Ca-DM500 in the order SO42-≈PO43->NO3- . The sorption behavior of fluoride in a continuous fixed-bed column was consistent with the Thomas model. Column studies demonstrated that the Ca-DM500 shows a strong affinity for fluoride, a low release potential, and a stable (unreduced) removal capacity through regeneration and reuse cycles.

The effects of clay particles (montmorillonite, M) and phosphate (P) on the transport of hydrochar nanoparticles (NPs) in water-saturated porous media (uncoated and aluminum (Al) oxide-coated sands) were explored in NaCl (1–50 mM) solutions. Our results showed that the deposition behaviors of hydrochar NPs affected by M and phosphate were significantly different between pH 6.0 and pH 9.0, especially in Al oxide-coated sand. This can be attributed to their distinct surface characteristics: hydrochar agglomerates with a larger pore size distribution, more carboxylate groups, and less negative charges on the surface at pH 9.0 than those at pH 6.0. In Al oxide-coated sand, block adsorption of hydrochar was alleviated appreciably with the presence of M due to the preferential preoccupies of M on these favorable retention sites. On the contrary, M substantially increased the hydrochar retention on uncoated sand due to the formation of nanoaggregates between hydrochar and M. Differently, phosphate substantially enhanced the transport of hydrochar, even in coated sand, due to the strong phosphate adsorption onto Al oxide on the surface of sand and hydrochar. Our findings will provide useful insights into designing effective strategies for land application of hydrochar while minimizing potential environmental risks.

An improved understanding of in situ mineralization in the presence of dissolved arsenic and both ferrous and ferric iron is necessary because it is an important geochemical process in the fate and transformation of arsenic and iron in groundwater systems. This work aimed at evaluating mineral phases that could form and the related transformation of arsenic species during coprecipitation. We conducted batch tests to precipitate ferrous (133 mM) and ferric (133 mM) ions in sulfate (533 mM) solutions spiked with As (0–100 mM As(V) or As(III)) and titrated with solid NaOH (400 mM). Goethite and lepidocrocite were formed at 0.5–5 mM As(V) or As(III). Only lepidocrocite formed at 10 mM As(III). Only goethite formed in the absence of added As(V) or As(III). Iron (II, III) hydroxysulfate green rust (sulfate green rust or SGR) was formed at 50 mM As(III) at an equilibrium pH of 6.34. X-ray analysis indicated that amorphous solid products were formed at 10–100 mM As(V) or 100 mM As(III). The batch tests showed that As removal ranged from 98.65–100%. Total arsenic concentrations in the formed solid phases increased with the initial solution arsenic concentrations ranging from 1.85–20.7 g kg−1. Substantial oxidation of initially added As(III) to As(V) occurred, whereas As(V) reduction did not occur. This study demonstrates that concentrations and species of arsenic in the parent solution influence the mineralogy of coprecipitated solid phases, which in turn affects As redox transformations.

The soil major component of clay plays an important role in governing the fate and transport of engineered nanomaterials (e.g., the most commonly used titanium dioxide nanoparticles; nTiO2) in the subsurface environments via forming nTiO2-clay aggregates. This research is designed to unravel the interplay of naturally-occurring bacteria (Escherichia coli) and phosphate on the transport and retention of nTiO2-kaolin aggregates in water-saturated porous media. Our results showed that nTiO2-nTiO2 homoaggregates and nTiO2-kaolin heteroaggregates dominated in the nTiO2-kaolin nanoaggregate suspension. Transport of nTiO2-kaolin aggregates was enhanced with the copresence of E. coli and phosphate, particularly at the low pH of 6.0. This effect is due to the greater adsorption of phosphate and thus the greater enhancement in repulsive interaction energies between aggregates and sand grains at pH 6.0 (vs. pH 9.0). The charged “soft layer” of E. coli cell surfaces changed the aggregation state and the heterogeneous distribution of nTiO2-kaolin aggregates, and subsequently stabilized the nTiO2-nTiO2 homoaggregates and nTiO2-kaolin heteroaggregates via TEM-EDX measurements and promoted the physical segregation between the aggregates (separation distance = 0.486 vs. 0.614 μm without vs. with the presence of E. coli) via 2D/3D AFM identifications, both of which caused greater mobility of nTiO2-kaolin aggregates with the presence of E. coli. Nonetheless, transport of nTiO2-kaolin aggregates was lower with the copresence of E. coli and phosphate vs. the singular presence of phosphate due to the competitive adsorption of less negatively charged E. coli (vs. phosphate) onto the aggregates. Taken altogether, our findings furnish new insights into better understanding the fate, transport, and potential risks of nTiO2 in real environmental settings (soil and sediment aquifer) where clay, bacteria, and phosphate ubiquitously cooccur.

This study investigated the adsorptive removal of fluoride from simulated water pollution using various (hydro)oxide nanomaterials, which have the potential to be used as sorbents for surface water and groundwater remediation. Tested nanomaterials include hematite, magnetite, ferrihydrite, goethite, hematite-alpha, hydroxyapatite (HAP), brucite, and four titanium dioxides (TiO2-A [anatase], TiO2-B [rutile], TiO2-C [rutile], and TiO2-D [anatase]). Among 11 (hydro)oxide nanomaterials tested in this study, ferrihydrite, HAP, and brucite showed two to five times higher removal of fluoride than other nanomaterials from synthetic fluoride solutions. Freundlich and Redlich-Peterson adsorption isotherms better described the adsorptive capacity and mechanism than the Langmuir isotherm based on higher R 2 values, indicating better fit of the regression predictions. In addition, the adsorption kinetics were well described by the intraparticle diffusion model. Column studies in a fixed bed continuous flow through system were conducted to illustrate the adsorption and desorption behavior of fluoride on ferrihydrite, HAP, or brucite. Experimental results fitted well with the Thomas model because of the R 2 values at least 0.885 or higher. By comparisons of the adsorption capacity and the rate constant, columns packed with ferrihydrite exhibited not only faster rates but also higher sorption capacity than those packed with HAP or brucite. Desorption tests in deionized water showed that the adsorbed fluoride could be desorbed at a lower efficiency, ranging from 4.0% to 8.9%. The study implicated that (hydro)oxide nanomaterials of iron calcium and magnesium could be effective sorptive materials incorporated into filtration systems for the remediation of fluoride polluted water.

Chemical oxidation is a promising pretreatment step coupled with bioremediation for removal of polycyclic aromatic hydrocarbons (PAHs). The effectiveness of Fenton, modified Fenton, potassium permanganate and activated persulfate oxidation treatments on the real contaminated soils collected from a coal gas plant (263.6 +/- 73.3 mg kg(-1) of the Sigma 16 PAHs) and a coking plant (385.2 +/- 39.6 mg kg(-1) of the Sigma 16 PAHs) were evaluated. Microbial analyses showed only a slight impact on indigenous microbial diversity by Fenton treatment, but showed the inhibition of microbial diversity and delayed population recovery by potassium permanganate reagent. After potassium permanganate treatment, the microorganism mainly existed in the soil was Pseudomonas or Pseudomonadaceae. The results showed that total organic carbon (TOC) content in soil was significantly increased by adding modified Fenton reagent (1.4%-2.3%), while decreased by adding potassium permanganate (0.2%-1%), owing to the nonspecific and different oxidative properties of chemical oxidant. The results also demonstrated that the removal efficiency of total PAHs was ordered: permanganate (90.0%-92.4%)> activated persulfate (81.5%-86.54%)> modified Fenton (81.5%-85.4%)> Fenton (54.1%-60.0%). Furthermore, the PAHs removal efficiency was slightly increased on the 7th day after Fenton and modified Fenton treatments, about 14.6%, and 14.4% respectively, and the PAHs removal efficiency only enhanced 4.1% and 1.3% respectively from 1st to 15th day after potassium permanganate and activated persulfate treatments. The oxidants greatly affect the growth of soil indigenous microbes, which cause further influence for PAHs degradation by bioremediation. (C) 2019 Elsevier Ltd. All rights reserved.

Toxic substances such as heavy metals or persistent organic pollutants raise global environmental concerns. Thus, diverse water decontamination approaches using nano-adsorbents and/or photocatalysts based on nanotechnology are being developed. Particularly, many studies have examined the removal of organic and inorganic contaminants with novel graphene-based nano spinel ferrites (GNSFs) as potential cost-effective alternatives to traditionally used materials, owing to their enhanced physical and chemical properties. The introduction of magnetic spinel ferrites into 2-D graphene-family nanomaterials to form GNSFs brings various benefits such as inhibited particle agglomeration, enhanced active surface area, and easier magnetic separation for reuse, making the GNSFs highly efficient and eco-friendly materials. Here, we present a short review on the state-of-the-art progresses on developments of GNSFs, as well as their potential application for removing several recalcitrant contaminants including organic dyes, antibiotics, and heavy metal ions. Particularly, the mechanisms involved in the adsorptive and photocatalytic degradation are thoroughly reviewed, and the reusability of the GNSFs is also highlighted. This review concludes that the GNSFs hold great potential in remediating contaminated aquatic environments. Further studies are needed for their practical and large-scale applications.

Reduced graphene oxide (rGO) hybridized with magnetite and/or elemental silver (rGO/magnetite, rGO/silver, and rGO/magnetite/silver) nanoparticles were evaluated as potential adsorbents for toxic heavy metal ions (Cd (II), Ni(II), Zn(II), Co(II), Pb(II), and Cu(II)). Although the deposition of iron oxide and silver nanoparticles on the rGO nanosheets played an inhibitory role in metal ion adsorption, the metal adsorption efficiency by the nanohybrids (NHs) was still higher than that reported for many other sorbents (e.g., activated biochar, commercial resins, and nanosized hydrated Zr(IV) oxide particles). X-ray photoelectron spectroscopy analyses revealed that complexation with deprotonated adsorbents and cation exchange was an important mechanism for Cd(II) ion removal by the rGO and NHs. Competitive adsorption tests using multi metals showed that the adsorption affinity of metal ions on the rGO and its NHs follows the order (Cu(II), Zn(II)) > Ni(II) > Co (II) > (Pb(II), Cd(II)), which is similar to the order observed for single-metal adsorption experiments. These results can be explained by the destabilization abilities of the rGO and NHs, as well as the ionic radii of the considered metal ions. Our findings demonstrate the feasibility of using rGO-based NHs as highly efficient adsorbents for heavy metal removal from water.

Nanotechnology has unprecedentedly revolutionized human societies over the past decades and will continue to advance our broad societal goals in the coming decades. The research, development, and particularly the application of engineered nanomaterials have shifted the focus from "less efficient" single-component nanomaterials toward "superior-performance", next-generation multifunctional nanohybrids. Carbon nanomaterials (e.g., carbon nanotubes, graphene family nanomaterials, carbon dots, and graphitic carbon nitride) and metal/metal oxide nanoparticles (e.g., Ag, Au, CdS, Cu2O, MoS2, TiO2, and ZnO) combinations are the most commonly pursued nanohybrids (carbon-metal nano- CNTs Env on Water hybrids; CMNHs), which exhibit appealing properties and promising multifunctionalities for addressing multiple complex challenges faced by humanity at the critical energy-water- environment (EWE) nexus. In this frontier review, we first highlight the altered and newly emerging properties (e.g., electronic and optical attributes, particle size, shape, morphology, crystallinity, dimensionality, carbon/metal ratio, and hybridization mode) of CMNHs that are distinct from those of their parent component materials. We then illustrate how these important newly emerging properties and functions of CMNHs direct their performances at the EWE nexus including energy harvesting (e.g., H2O splitting and CO2 conversion), water treatment (e.g., contaminant removal and membrane technology), and environmental sensing and in situ nanoremediation. This review concludes with identifications of critical knowledge gaps and future research directions for maximizing the benefits of next-generation multifunctional CMNHs at the EWE nexus and beyond.

Increasing consumption of metal-oxide nanoparticles (NPs) and carbon-based nanomaterials has caused significant concern about their potential hazards in aquatic environments. The release of NPs into aquatic environments could result in adsorption of NPs on microorganisms. While metal-oxide NP-conjugated carbon-based nanohybrids (NHs) may exhibit enhanced toxicity toward microorganisms due to their large surface area and the generation of reactive oxygen species (ROS), there is a lack of information regarding the ecotoxicological effects of NHs on marine diatom algae, which are an indicator of marine pollution. Moreover, there is scant information on toxicity mechanisms of NHs on aquatic organisms. In this study, four NHs (ie, ZnO-conjugated graphene oxide [GO], ZnO-conjugated carbon nanotubes [CNTs], TiO2 -conjugated GO, and TiO2 -conjugated CNT) that were synthesized by a hydrothermal method were investigated for their toxicity effects on a Thalassiosira pseudonana marine diatom. The in vitro cellular viability and ROS formation employed at the concentration ranges of 50 and 100 mg/L of NHs over 72 hours revealed that ZnO-GO had the most negative effect on T. pseudonana. The primary mechanism identified was the generation of ROS and GO-induced dispersion that caused electrostatic repulsion, preventing aggregation, and an increase in surface areas of NHs. In contrast to GO-induced dispersion, large aggregates were observed in ZnO/TiO2 -conjugated CNT-based NHs. The scanning electron microscopy images suggest that NHs covered algae cells and interacted with them (shading effects); this reduced light availability for photosynthesis. Detailed in vitro toxicity effects and mechanisms that cause high adverse acute toxicity on T. pseudonana were unveiled; this implied concerns about potential hazards of these mechanisms in aquatic ecosystems.

Some nanomaterials including Fe-0, Ag-0, and ZnO are well known for their antibacterial effects. However, very few studies have examined antibacterial effects of nanohybrids. Given that metal oxides, mainly ZnO and TiO2, are known to increase mobility, surface area, and photocatalysis when combined with carbon-based nanomaterials, ZnO- and TiO2-conjugated carbon nanotube and graphene oxide nanohybrids were investigated for their antibacterial effects on Escherichia colt (DH5a, a multidrug-resistant coliform bacterium). Graphene-oxide (GO) based nanohybrids (ZnO-GO and TiO2-GO) induced increased dispersion compared to carbon-nanotube (CNT)based nanohybrids (ZnO-CNT and TiO2-CNT). Among the four types of nanohybrids, ZnO-conjugated nano hybrids exhibited a higher antibacterial property, resulting in the antibacterial effect (measured with growth inhibition of cells) in the order ZnO-GO > ZnO-CNT > TiO2-GO > TiO2-CNT. Among four possible antibacterial mechanisms (generation of reactive oxygen species (ROS), physicochemical characteristics, the steric effect, and release of metal ions), a primary mechanism ROS generation was identified; whereas, physicochemical characteristics and the steric effect were part of contributing mechanisms. The increasing dispersion of TiO2/ZnO on GO may have contributed to the antibacterial effects due to increasing surface areas. Similarly, significant damages to E. colt cell membranes were found by the GO sheet with its sharp edges. Our results suggest that applying GO-based ZnO or TiO2 could be an effective antibacterial method, especially for the treatment of multidrug-resistant bacteria in the water.

In this study, the removal efficiency PAHs by chemical oxidation combined with microbe remediation was evaluated in two contaminated soils. The number of indigenous soil microbes decreased after the addition of chemical oxidants and then increased by nutrients addition. The total removal efficiencies of PAHs by chemical oxidation and nutrient addition followed the order: activated persulfate > potassium permanganate > modified Fenton reagent > Fenton reagent. There are 24.29-27.97%, 22.00-23.67%, 10.24-13.74% and 1.9-2.5% contributions separately due to nutrient treatment in Fenton, modified Fenton, activated persulfate and potassium permanganate treatment, which show significantly difference. The different chemical oxidants exhibited 78-90% removal efficiency for 5-6 rings PAHs, while 52-85% removal efficiency for 2-4 rings PAHs. With the addition of nutrients, the growth of indigenous microbes was enhanced significantly, and the contents of 2-4 rings PAHs in the soil were further decreased. Furthermore, the removal efficiencies of NAP and ANY were increased by more than 45%, while the removal efficiencies of ANE, FLE and PHE were about 30% at Fenton system. There was a complementary enhancing effect of microbial remediation for PAHs degradation after chemical oxidation.

The aggregation and long-term (25 days) sedimentation behaviors of reduced graphene oxide (RGO) and its three successively self-assembled nanohybrids with magnetite (Fe 3 O 4 ) and zerovalent silver (Ag 0 ) nanoparticles have been investigated. The aggregation behaviors of the nanomaterials in NaCl and CaCl 2 were found to be in good agreement with the Derjaguin–Landau–Verwey–Overbeek (DLVO)-type interactions and the Schulze–Hardy rule. The colloidal stability decreased with the increasing ratios of the edge-based functional groups (COO − and C=O) to the total oxygen-containing functional groups decorated on the basal planes (C–O) and edges of RGO, as quantified by x-ray photoelectron spectroscopy analysis. In the presence of natural organic matter (NOM), the aggregation of RGO and its nanohybrids was greatly inhibited as a result of the enhanced electrosteric repulsions arising from the adsorbed NOM macromolecules. The long-term sedimentation kinetics results showed that the RGO nanohybrids were less stable in synthetic groundwater containing higher electrolyte concentrations, which was likely because of the greater charge screening or neutralization effect imparted by higher monovalent and divalent electrolyte concentrations. Our findings have important implications for evaluating the environmental impact and toxicity of the emerging class of multifunctional nanohybrids whose environmental behaviors are currently largely unknown.