Insights into the mechanisms of mercury sorption onto aluminum based drinking water treatment residuals

Enhancing Maize Yield and Soil Health through the Residual Impact of Nanomaterials in Contaminated Soils to Sustain Food

Studying the impact of residual soil nanomaterials is a promising challenge for sustainable agricultural development to improve soil health and crop productivity. The objective of this study is to assess the long-term impacts of 50, 100, and 250 mg kg-1 soil of nanobiochar (nB) and nano-water treatment residues (nWTR) on the fertility, biological activity, and yield of maize (Zea mays L.) growing in heavy metal-contaminated soils. The results showed that when nB and nWTR were added in larger quantities, the concentrations of lead (Pb), nickel (Ni), cadmium (Cd), and cobalt (Co) extracted with DTPA decreased. With the addition of nB or nWTR, it also showed a significant increase in exchangeable cations, cation exchange capacity (CEC), soil fertility, soil organic matter (OM), microbial biomass carbon (MBC), and a decrease in soil salinity and sodicity. Catalase and dehydrogenase activities rose as nB addition increased, while they decreased when nWTR addition increased. In comparison to the control, the addition of nB and nWTR greatly boosted maize yield by 54.5-61.4% and 61.9-71.4%, respectively. These findings suggest that the researched nanomaterials' residual effect provides an eco-friendly farming method to enhance the qualities of damaged soils and boost maize production. Our research suggested that adding recycling waste in the form of nanoparticles could immobilize heavy metals, improve soil characteristics, and increase the soil's capacity for productivity.

An XAS study of Hg(II) sorption to Al-based drinking water treatment residuals

Drinking water treatment residuals (DWTRs) are produced from the coagulation and flocculation processes in conventional drinking water treatment. The abundant metal oxide content of these materials resulting from the use of coagulants, like alum and ferric chloride, has driven strong research interest into the reuse of DWTRs as sorptive materials. Using a suite of aluminum-based DWTRs, we provide new insights into Hg(II) sorption mechanisms. Experiments performed at circum-neutral pH show that sorption capacities are related to the amount of organic carbon/matter present in DWTRs. We found that carbon rich samples can scavenge about 9000 mg/kg of Hg, in contrast to 2000 mg/kg for lime based DWTRs. X-ray absorption spectroscopy (XAS) at the Hg L3 edge further characterizes mercury coordination. X-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) results point to a partial association of mercury with sulfur at low mass loadings, transitioning to a full association with oxygen/carbon at higher concentrations of sorbed Hg(II) and in DWTRs with limited sulfur content. These results suggest that sorption of Hg(II) is primarily controlled by the carbon/organic matter fraction of DWTRs, but not by the coagulants.

Properties of Recycled Nanomaterials and Their Effect on Biological Activity and Yield of Canola in Degraded Soils

Recycling waste, such as rice straw and water treatment residuals, is important to reduce harmful effects on the environment and to improve canola yield and soil quality in degraded soils. Nanotechnology for the production of nanomaterials from biochar and water treatment residues will be a future revolution for improving soil quality and increasing canola yield in degraded soil. Therefore, this study aims to identify the properties of some recycled nanomaterials, such as nanobiochar (nB) and nanowater treatment residue (nWTR), and their effect on the biological activity and productivity of canola in degraded soils. The results showed that the nWTR and nB contain many functional groups and minerals, and they also have high negative zeta potential. The addition of the studied soil amendments significantly improved microbial biomass carbon (MBC) and biological activity, which played a major role in increasing canola yield. The highest dehydrogenase (DHA) and catalase (CLA) activity was found in nWTR-treated soil at 50 mg kg−1, with increases of 32.8% and 566.7% compared to the control, respectively. The addition of nB greatly improved the growth of canola plants in the soil. This was evident from the increase in the weight of seeds, the weight of 1000 grains, the number of pods per plant, and the highest increase was for nB added at the rate of 250 mg per kg−1 soil. The addition of 50 mg kg−1 of nWTR gave the best results in seed yield by 150.64% compared to the control. These results indicate that recycled nWTR and nB are some of the best waste recycling treatments, in addition to good soil health, in increasing soil biology and canola yield in degraded soils. In the future, research on recycled nanomaterials should examine the residual effect they have on yield, soil quality, and soil fauna in the long term.

Acute and Chronic Toxicity Testing of Drinking Water Treatment Residuals in Freshwater Systems

The beneficial use of drinking water treatment residuals (DWTRs) faces barriers due primarily to uncertainties and concerns about their potential environmental impacts. We used total and water leachable toxic metal concentrations and 2 benthic organism-based bioassays to identify suitable DWTR substrates for introduction to freshwater systems. Using total metal contents and the consensus probable effect concentration concept, 3 DWTRs were selected and used in elutriate and toxicity studies. The concentrations of water leachable Ag, As, Cd, Cu, Cr, Ni, Pb, and Zn were below the US Environmental Protection Agency's ambient water quality criteria. Using the long-term 65-d life cycle Chironomus tentans test and 4 different endpoints (survival, adult emergence, egg case production, and number of eggs produced per female), no statistical differences were found between the DWTR treatments and the controls. Similarly, results obtained using the 10-d Hyalella azteca test showed no toxicity. However, although both survival and growth were recorded in all bioassays, the results of the 10-d C. tentans and the 28-d H. azteca tests were ambiguous. For C. tentans, 2 of the 3 DWTRs resulted in significantly lower survival rates compared to the controls. For H. azteca, no significant growth differences were observed between controls and DWTR treatments, but 2 of the 3 DWTRs resulted in significantly lower survival rates than the controls. Overall, these results suggest that certain DWTR substrates could be suitable for introduction to aquatic systems. Environ Toxicol Chem 2021;40:2005-2014. © 2021 SETAC.

Laboratory and simulation study on the Cd(Ⅱ) adsorption by lake sediment: Mechanism and influencing factors

Sediments are the major sinks for Cd(Ⅱ) in the aquatic environment. Here, the detailed binding mechanisms and effects of environmental factors on Cd(Ⅱ) adsorption onto lake sediment were tested by a batch of adsorption and characteristic experiments. Sediment samples and sediment-Cd complexes were characterized using Scanning electron microscopy, Energy dispersive spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction spectral analyses. The interactive and main effect of parameters such as pH, flow velocity, Cd(II) concentration, sediment particle size, humic acid, fulvic acid and adsorption time involved in the adsorption process were determined using two models based on response surface methodology (RSM) and a back-propagation neural network with genetic algorithm (GABP). Results showed that Cd(II) adsorption onto sediment was mainly achieved through surface complexation with O-containing groups and precipitation with carbonate and sulfide. RSM was favorable for modeling Cd(II) adsorption in lake systems because it intuitively reflected the influence of the factors and had a good fitting precision (R² = 0.8838, RSME = 2.5496) close to that of the GABP model (R² = 0.8959, RSME = 2.5410). pH, sediment particle size, and humic acid exerted strong influences on Cd(II) immobilized by the sediment. Overall, our findings facilitate a better understanding of Cd(II) mobility in lakes and provide a reference for controlling heavy metals derived from both aqueous and sediment sources.

A Screening Approach for the Selection of Drinking Water Treatment Residuals for Their Introduction to Marine Systems

Drinking water treatment residuals (DWTRs) produced in large quantities worldwide show strong sorption capacities for several contaminants including metals. These by-products of the water-treatment process are primarily discharged as wastes, to either natural or engineered systems, based on the regulations in place in the country where they are produced. To assess how DWTRs can be repurposed to limit the mobility of metals in aquatic systems, we tested their propensity to release toxic metals and their potential ecotoxicity. To account for the wide variability in their physicochemical characteristics, DWTR samples were obtained from 15 water-treatment plants across the United States. A screening procedure based on a combination of 1) the toxicity characteristics leaching procedure (TCLP), 2) total metal contents and sediment quality guidelines, and 3) acute 10-d Americamysis bahia and chronic 28-d Neanthes arenaceodentata survival and growth bioassays was used. All tested samples were found to be nonhazardous based on TCLP results. However, the concentrations of As, Cu, and Ni exceeded the sediment quality guidelines in some samples, resulting in the exclusion of 7 DWTR samples. All of the DWTRs evaluated for toxicity were nontoxic to the tested organisms. The results of the present study suggest that certain DWTRs can be introduced safely into the marine environment and, therefore, used as potential amendments or capping materials to control the mobility of certain sediment contaminants. Environ Toxicol Chem 2021;40:1194-1203. © 2020 SETAC.

Sustainable removal of anodized aluminum dye by groundwater treatment waste: experimental and modeling

Groundwater treatment waste (GWTW), as an environmentally friendly renewable nanomaterial, was implemented for the removal of anodized aluminum dye Sanodure Green (SG) from aqueous solutions. The capability of the SG metal complex dye removal was assessed by measuring solution decoloration and chromium elimination degree. GWTW was characterized using FTIR, SEM, EDX, TEM, XPS and surface area measurements. Kinetic curves were obtained by changing initial dye concentration, pH, temperature and adsorbent dose. Kinetic studies showed that up to 90 % of SG dye was removed within a contact time of 20 min. The adsorption of the dye was favourable at 293 K temperature in the acidic pH region (pH 1.5-2.0) with maximum adsorption capacity 185 mg g^-1. Langmuir-Freundlich isotherm model as well as hyperbolic tangent, diffusion-chemisorption and Elovich kinetic models accurately describe the dye removal process. The calculated thermodynamic parameters confirmed that SG dye removal occurred spontaneously and exothermically. The magnitude of enthalpy change (ΔH^° = -35.80 kJ mol^-1) was in agreement with the electrostatic interaction. The adsorption potential of GWTW for SG dye removal was also evaluated using a real wastewater produced after dyeing of anodized aluminum.

Pyrolytic valorization of water treatment residuals containing powdered activated carbon as multifunctional adsorbents

This study investigated the possibility of applying pyrolysis as an alternative method to recycle powdered activated carbon-containing water treatment residuals (PAC-WTRs) discharged from the Cheongju water treatment plant as a multifunctional adsorbent. WTRs pyrolyzed for 1 h at 200-700 °C were compared with raw material. The carbon content of the PAC-WTR reaches 19.27%, with about 25% Al and 17% Si. Changes in PAC through pyrolysis imparted new adsorbent properties to WTR. As the pyrolysis temperature increased, the purity of PAC increased, and pores were regenerated to recover the Brunauer-Emmett-Teller (BET) from 6.5 m² g^-1 to 131.8 m² g^-1. In addition, the basicity increased as the carboxylic and phenolic groups on the carbon surface were decomposed, which increased the cation (methylene blue) adsorption capacity and reduced heavy metal leaching. As the coagulant regenerated with increasing pyrolysis temperature, the amount of aluminum leached and phosphate removal efficiency were increased. In the case of simultaneous removal of cations (MB⁺) and anions (PO₄^3-), the removal efficiency was higher than that for single adsorption without competition through multi-layer adsorption by Al complex and PAC complex. Therefore, the pyrolyzed PAC-WTR is capable of adsorbing and removing anions and cations simultaneously without the peril of substance leaching. The regenerated WTRs containing PAC is expected to be utilized as a multi-functional remediation material for wastewater containing various pollutants.

Remediation of mercury contaminated soil, water, and air: A review of emerging materials and innovative technologies

Mercury contamination in soil, water and air is associated with potential toxicity to humans and ecosystems. Industrial activities such as coal combustion have led to increased mercury (Hg) concentrations in different environmental media. This review critically evaluates recent developments in technological approaches for the remediation of Hg contaminated soil, water and air, with a focus on emerging materials and innovative technologies. Extensive research on various nanomaterials, such as carbon nanotubes (CNTs), nanosheets and magnetic nanocomposites, for mercury removal are investigated. This paper also examines other emerging materials and their characteristics, including graphene, biochar, metal organic frameworks (MOFs), covalent organic frameworks (COFs), layered double hydroxides (LDHs) as well as other materials such as clay minerals and manganese oxides. Based on approaches including adsorption/desorption, oxidation/reduction and stabilization/containment, the performances of innovative technologies with the aid of these materials were examined. In addition, technologies involving organisms, such as phytoremediation, algae-based mercury removal, microbial reduction and constructed wetlands, were also reviewed, and the role of organisms, especially microorganisms, in these techniques are illustrated.

Aluminum distribution heterogeneity and relationship with nitrogen, phosphorus and humic acid content in the eutrophic lake sediment

Increasing amount of aluminum (Al) gets into aquatic ecosystem through anthropogenic activity, but the knowledge about Al migration and relationships with sediments possessing different physico-chemical properties in eutrophic lakes is limited. Here, the Al migration rule and relationships with sediment nutritions in the Hangzhou West Lake, China was investigated, where a certain amount of residual Al-salts can enter because of the pre-treatment of the Qiantang River diversion project every day. Results revealed the obvious spatial distribution heterogeneity of Al in sediment vertical direction and horizontal direction following water flow. The Al content in sediment ranged 0.463-1.154 g kg^-1 in Maojiabu Lake, and ranged 9.862-40.442 g kg^-1 in Xiaonanhu Lake. Higher Al content distributed in upper layer sediment in lake with more disturbance. Total nitrogen (TN) contents were higher 0.917-3.387 mg g^-1 and 0.627-0.786 mg g^-1 in upper layer sediment than that in lower layer in Maojiabu Lake and Xiaonanhu Lake, respectively. Total phosphorus (TP) content ranged 0.779-2.580 mg g^-1, in which IP and Fe/Al-P contributed 24.9-80.8% and 17.0-51.6%, respectively. Correlations between Al content with nutrition, humic acid (HA) etc. of sediment regionally varied in Maojiabu and Xiaonanhu Lake. Spatial distribution of Al-salt in eutrophic lakes closely related with the physico-chemical characteristics of nutrients, humus, human disturbance and water division parameters. Results provides new insight into Al-salts migration and references for Al-risk evaluating in eutrophic lakes.

Removal of Heavy Metals and Metalloids from Water Using Drinking Water Treatment Residuals as Adsorbents: A Review

Heavy metal contamination is one of the most important environmental issues. Therefore, appropriate steps need to be taken to reduce heavy metals and metalloids in water to acceptable levels. Several treatment methods have been developed recently to adsorb these pollutants. This paper reviews the ability of residuals generated as a by-product from the water treatment plants to adsorb heavy metals and metalloids from water. Water treatment residuals have great sorption capacities due to their large specific surface area and chemical composition. Sorption capacity is also affected by sorption conditions. A survey of the literature shows that water treatment residuals may be a suitable material for developing an efficient adsorbent for the removal of heavy metals and metalloids from water.

Remediation of chromium and mercury polluted calcareous soils using nanoparticles: Sorption -desorption kinetics, speciation and fractionation

Stabilization is an emerging technology for the cost-effective remediation of heavy metals polluted soils. To evaluate the potential of water treatment residual nanoparticles (nWTR) in reducing Hg and Cr mobility in contaminated calcareous soil, sorption-desorption kinetics; speciation and fractionation experiments were performed. Application of nWTR strongly enhanced Cr and Hg sorbed in the calcareous soil, whereas the released amount of both metals through 6 successive desorption steps dramatically decreased. The power function model best described the desorption kinetic data of Cr and Hg from nWTR amended and non-amended calcareous soil. Fractionation experiment data demonstrated that nWTR amendment significantly increased metals concentration in the residual fraction (RS) and simultaneously decreased the more accessible forms of Hg and Cr. Addition of nWTR at a rate of 0.3% to the contaminated calcareous soil significantly increased Hg and Cr in the RS fraction from 69.27% and52.62% to 93.89% and 90.05% respectively. Additionally, the formation of stable Hg and Cr species such as Hg(OH)₂ amor, CrSO₄. xH₂O and Cr(OH)₂) were increased as a result of nWTR application. These findings jointly indicate the enhancement of Hg and Cr immobilization in the nWTR amended calcareous soil. FTIR spectroscopy analysis indicated the contribution of OH group and Al-O-Si of nWTR in Hg and Cr sorption process and suggests chemo-sorption reaction between both metals and the nWTR surface functional groups. Overall, the final results confirm the strong capability of nWTR application in reducing Hg and Cr risks in highly contaminated sites of the calcareous soil.

Insights into the mercury(II) adsorption and binding mechanism onto several typical soils in China

To better understand the Hg(II) adsorption by some typical soils and explore the insights about the binding between Hg(II) and soils, a batch of adsorption and characteristic experiments was conducted. Results showed that Hg(II) adsorption was well fitted by the Langmuir and Freundlich. The maximum adsorption amount of cinnamon soil (2094.73 mg kg^-1) was nearly tenfold as much as that of saline soil (229.49 mg kg^-1). The specific adsorption of Hg(II) on four soil surface was confirmed by X-ray photoelectron spectroscopy (XPS) owing to the change of elemental bonding energy after adsorption. However, the specific adsorption is mainly derived from some substances in the soil. Fourier transform infrared spectroscopy (FTIR) demonstrated that multiple oxygen-containing functional groups (O-H, C=O, and C-O) were involved in the Hg(II) adsorption, and the content of oxygen functional groups determined the adsorption capacity of the soil. Meanwhile, scanning electron microscopy combined with X-ray energy dispersive spectrometer (SEM-EDS) more intuitive revealed the binding of mercury to organic matter, metal oxides, and clay minerals in the soil and fundamentally confirmed the results of XPS and FTIR to further elucidate adsorptive phenomena. The complexation with oxygen-containing functional groups and the precipitation with minerals were likely the primary mechanisms for Hg(II) adsorption on several typical soils. This study is critical in understanding the transportation of Hg(II) in different soils and discovering potential preventative measures.