Strategic selection of an optimal sorbent mixture for in-situ remediation of heavy metal contaminated sediments: framework and case study

Combined effect of zinc and cadmium ions on nitrification performance during the biological nitrogen removal of simulated livestock breeding wastewater

Zinc and cadmium ions are usually found in livestock breeding wastewater, and the mixed ions will have an impact on the biological nitrogen removal. Nitrification performance plays an important role in biological nitrogen removal. In order to investigate the combined effect of zinc and cadmium ions on nitrification performance and to reveal the interactions between zinc and cadmium ions, three concentration ratios of zinc and cadmium ions, as well as 18 different concentration gradients were designed with the direct equipartition ray and the dilution factor method. The effect of pollutants on the nitrification performance of biological nitrogen removal was analyzed by the nonlinear regression equation, and the concentration-addition model was conducted to probe into the relationship between the mixed pollutants and the nitrification performance. The results showed that the effect on nitrification performance increased significantly with the increase of reaction duration and pollutant concentration, which indicated that the effects are concentration-dependent and time-dependent. The concentration-addition model suggested that the interactions between zinc and cadmium ions with different concentration ratios were mainly antagonistic, and as the percentage of cadmium ions in the mixtures increased, the antagonism between the mixtures became stronger. This study will provide a relevant theoretical basis for the regulation of the ratios and concentrations of heavy metal ions during the biological treatment of livestock breeding wastewater.

Using L. minor and C. elegans to assess the ecotoxicity of real-life contaminated soil samples and their remediation by clay- and carbon-based sorbents

Toxic substances, such as polycyclic aromatic hydrocarbons (PAHs) and heavy metals, can accumulate in soil, posing a risk to human health and the environment. To reduce the risk of exposure, rapid identification and remediation of potentially hazardous soils is necessary. Adsorption of contaminants by activated carbons and clay materials is commonly utilized to decrease the bioavailability of chemicals in soil and environmental toxicity in vitro, and this study aims to determine their efficacy in real-life soil samples. Two ecotoxicological models (Lemna minor and Caenorhabditis elegans) were used to test residential soil samples, known to contain an average of 5.3, 262, and 9.6 ppm of PAHs, lead, and mercury, for potential toxicity. Toxicity testing of these soils indicated that 86% and 58% of soils caused ≤50% inhibition of growth and survival of L. minor and C. elegans, respectively. Importantly, 3 soil samples caused ≥90% inhibition of growth in both models, and the toxicity was positively correlated with levels of heavy metals. These toxic soil samples were prioritized for remediation using activated carbon and SM-Tyrosine sorbents, which have been shown to immobilize PAHs and heavy metals, respectively. The inclusion of low levels of SM-Tyrosine protected the growth and survival of L. minor and C. elegans by 83% and 78%, respectively from the polluted soil samples while activated carbon offered no significant protection. These results also indicated that heavy metals were the driver of toxicity in the samples. Results from this study demonstrate that adsorption technologies are effective strategies for remediating complex, real-life soil samples contaminated with hazardous pollutants and protecting natural soil and groundwater resources and habitats. The results highlight the applicability of these ecotoxicological models as rapid screening tools for monitoring soil quality and verifying the efficacy of remediation practices.

Optimization and mechanisms of rapid adsorptive removal of chromium (VI) from wastewater using industrial waste derived nanoparticles

Nowadays, the existence of metal ions in the environment like chromium (VI) is of significant worry because of its high toxicity to many life forms. Therefore, in this study, an inexpensive and eco-friendly nano-adsorbent was produced from the waste of drinking water industry for effective elimination of Cr (VI) from wastewater. The mineralogical and morphological characterization and compositions of the bulk and nano- adsorbents were performed. The adsorption capabilities of nWTRs for Cr(VI) under different experimental conditions of adsorbent dosage, time, Cr (VI) concentration, solution pH, and competitive ions were investigated. The nWTRs adsorbent exhibits very rapid adsorption potential (92%) for Cr (VI) within the first 15 min. Langmuir model showed high predictive capability for describing Cr (VI) sorption equilibrium data. The estimated maximum sorption capacity (qmax) of nWTRs and bWTRs was found to be 40.65 mg g−1 and 2.78 mg g−1 respectively. The sorption kinetics data of Cr (VI) were perfectly fitted to the model of second-order kinetics. High immobilization capability of nWTRs for sorbed Cr (VI) is evident as most of adsorbed Cr (VI) was associated with the residual fraction. The nWTRs efficiency of Cr (VI) removal from wastewater using batch and column techniques were 98.12 and 96.86% respectively. Electrostatic interactions, outer sphere complexation and pore filling are the main mechanisms suggested for binding of Cr(VI) with functional groups of nWTRs. This study demonstrates that the green low-cost nWTRs have the potential to decontaminate industrial wastewater effluents containing Cr (VI).

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.

Integrated remediation of sulfate reducing bacteria and nano zero valent iron on cadmium contaminated sediments

Integrated-remediation technologies on heavy metal polluted sediments have received much attention. In this study, Cd contaminated sediments were treated with various conditions: sulfate reducing bacteria (SRB) only and SRB combined with different dosages of nano zero valent iron (nZVI (0.5-10 mg/g)). The immobilization of Cd was found in all remediation treatments according to the decreases of mobile Cd and the increases of more stable Cd compared with control. Five typical SRBs (Desulfobulbaceae, Desulfobacteraceae, Syntrophobacteraceae, Desulfovibrionaceae and Desulfomicrobiaceae) were identified having significant influences on Cd speciation transformation and they could stabilize Cd into sulfide precipitation through dissimilatory sulfate reduction (DSR). The ANOVA results of mobilization index and Cd concentration in overlying water both demonstrated that integrated-remediation systems with 5 mg/g and 10 mg/g of nZVI (Fe5 and Fe10 systems, respectively) presented better immobilization performance than conventional SRB only system (P < 0.05). It is confirmed that nZVI could stimulate the SRB bio-immobilization possibily through providing electrons and enhancing enzyme activities during DSR. The XPS analyses and Pourbaix diagrams revealed that mackinawite may be produced in the Fe10, resulting in the possible formation of Cd-S-Fe. This study indicates that integrated-remediation of SRB and nZVI have great potential in Cd immobilization of sediments, especially with higher addition of nZVI.

Enhancing pyromorphite formation in lead-contaminated soils by improving soil physical parameters using hydroxyapatite treatment

During chemical immobilization in soil, enhancement of insoluble phases is required to prevent toxic metal from leaching into the surrounding environment. Understanding the effects of physicochemical parameters of soil on the reaction between lead and hydroxyapatite is important to enhance the formation of the insoluble pyromorphite-lead phase. However, the combined effect of soil physical parameters on pyromorphite formation and compressive strength has not been reported. This study aimed to investigate the relationship between soil texture and pyromorphite formation, as well as unconfined compressive strength in lead-contaminated soils treated with hydroxyapatite under different compaction states and moisture conditions. Our findings showed that in compacted soil, >20% of lead was formed as pyromorphite compared with 10% of lead in uncompacted soil. In particular, low porosity and a high saturation ratio of soil under the unsaturated moisture condition were favorable for pyromorphite formation. Under the saturated moisture condition, the addition of hydroxyapatite enhanced pyromorphite formation compared with that under the unsaturated moisture condition. In addition, the leaching of soluble lead into the surrounding environment could be suppressed to <0.05% of lead in soil. The addition of hydroxyapatite also increased compressive strength of the compacted soil with increased curing period despite the soil texture. Our results suggest that treatments such as compacting and seepage control with hydroxyapatite may simultaneously increase pyromorphite formation and compressive strength. Furthermore, when performing soil recycling with hydroxyapatite at sites in the groundwater zone, the soluble lead in the soil is prevented from leaching to the surrounding environment. Hydroxyapatite could be used to enable the reuse of lead-contaminated soil for lead immobilization and to increase compressive strength.

Zeolite and bentonite as nickel sequestrants in carbonation lime coming from the sugar industry

A laboratory trial was performed to test the sequestration capacity of two minerals (bentonite and zeolite) at three initial concentrations (2.5, 5 and 10%) in order to counter water-soluble nickel (Ni) exceeding the Italian legal limit (10 μg L^-1) in carbonation lime disposed of in a field and sampled for an 85-day lab study. The results show a noticeable reduction in water-soluble and bioavailable Ni in lime after the addition of sequestrants, especially at the dose of 5% bentonite or zeolite, thereby indicating a "ceiling effect" of the sequestrant, i.e., an increasing dose could reduce the adsorption capacity and be less effective. The alkaline pH and the presence of organic matter could be the main factors affecting the good performance of sequestrant addition, causing an increase in the negative charge of the organic and mineral colloids and the formation of unavailable Ni precipitates. The 85-day experiment seems to be sufficient to reach an adsorption equilibrium for water-soluble nickel, while for the bioavailable form a longer period appears to be necessary.

Two-way Valorization of Blast Furnace Slag: Synthesis of Precipitated Calcium Carbonate and Zeolitic Heavy Metal Adsorbent

The aim of this work is to present a zero-waste process for storing CO₂ in a stable and benign mineral form while producing zeolitic minerals with sufficient heavy metal adsorption capacity. To this end, blast furnace slag, a residue from iron-making, is utilized as the starting material. Calcium is selectively extracted from the slag by leaching with acetic acid (2 M CH₃COOH) as the extraction agent. The filtered leachate is subsequently physico-chemically purified and then carbonated to form precipitated calcium carbonate (PCC) of high purity (<2 wt% non-calcium impurities, according to ICP-MS analysis). Sodium hydroxide is added to neutralize the regenerated acetate. The morphological properties of the resulting calcitic PCC are tuned for its potential application as a filler in papermaking. In parallel, the residual solids from the extraction stage are subjected to hydrothermal conversion in a caustic solution (2 M NaOH) that leads to the predominant formation of a particular zeolitic mineral phase (detected by XRD), namely analcime (NaAlSi₂O₆∙H₂O). Based on its ability to adsorb Ni²⁺, as reported from batch adsorption experiments and ICP-OES analysis, this product can potentially be used in wastewater treatment or for environmental remediation applications.

Influence of enhancing electrolytes on the removal efficiency of heavy metals from Gabes marine sediments (Tunisia)

This study focused on the feasibility of the treatment of heavy metals-contaminated sediments from Gabes harbor (Tunisia) using enhanced electrokinetic process. It presented a laboratory short-time electrokinetic experiment. The enhancing agents, as citric, acetic acids and sodium dodecyl sulfate (SDS) were used regarding their low environmental hazard. The electrokinetic cell was specially designed in order to elaborate two experiments at the same time. This paper is composed of three parts. The first part introduces the characterization of Gabes sediments. The second part describes the design of laboratory electrokinetic cell and the followed methods. The third part is dedicated to the results analysis. Treatment efficiency revealed that more than 80% of lead was removed from Gabes marine sediments. The reduction of cooper concentration, in sediments after treatment, ranged from 74 to 87%. Despite, the high removal of cadmium that ranged from 58 to 79%, treated sediments presented Cd concentration above the threshold limit.

Simultaneous lead and antimony immobilization in shooting range soil by a combined application of hydroxyapatite and ferrihydrite

This study investigated whether a combined application of hydroxyapatite and ferrihydrite could immobilize lead and antimony in shooting range soil in which the level of lead contamination is markedly higher than that of antimony. In addition, we evaluated the stability of lead and antimony immobilized by the combined application with varying soil pH. The levels of water-soluble lead and antimony for the combined application were lower than those of single applications of hydroxyapatite or ferrihydrite, indicating that the combined application could suppress the levels of water-soluble lead and antimony by 99.9% and 95.5%, respectively, as compared with the levels in shooting range soil without immobilization material. The amounts of residual lead and amorphous Fe/Al oxide-bound antimony fractions in sequential extraction increased with a decrease in the exchangeable and carbonate lead fractions as well as in non-specifically bound and specifically bound antimony fractions. The alteration of lead and antimony phases to chemically more stable ones as a result of the combined application would result in the suppression of their mobility. The stability of immobilized lead and antimony in the combined application was equal to that of lead with a single application of hydroxyapatite and that of antimony with a single application of ferrihydrite within neutral to alkaline pH conditions, respectively. Therefore, this study suggests that the combined application of hydroxyapatite and ferrihydrite can simultaneously immobilize lead and antimony in shooting range soil with neutral to alkaline pH.

Combined toxic effects of heavy metals and antibiotics on a Pseudomonas fluorescens strain ZY2 isolated from swine wastewater

A Pseudomonas fluorescens strain ZY2, isolated from swine wastewater, was used to investigate the synergistic effects of five heavy metals (Pb, Cu, Zn, Cr(VI) and Hg) on bacterial resistance to antibiotics. Results indicate that the combined effects of antibiotic type, heavy metal type and concentration were significant (p < 0.01). Cross-resistance to Hg and antibiotics was the most noticeable. Moreover, the resistance to Hg and cefradine or amoxicillin, and Cr and amoxicillin were synergistic for low heavy metal concentrations, and turned antagonistic with increasing concentrations, while the resistances to Cr or Cu and cefradine, Pb or Cu and amoxicillin, Cu and norfloxacin showed reverse effects. In addition, resistance to Zn and amoxicillin were always synergetic, while resistance to Pb and cefradine or norfloxacin, Cr or Hg and norfloxacin as well as all the heavy metals and tetracycline were antagonistic. These results indicate that bacterial resistance to antibiotics can be affected by the type and concentration of co-exposed heavy metals and may further threaten people’s health and ecological security severely via horizontal gene transfer.

Atom-efficient route for converting incineration ashes into heavy metal sorbents

Bottom ashes produced from municipal solid-waste incineration are suitable for sorbent synthesis because of their inherent composition, high alkalinity, metastable mineralogy, and residual heat. This work shows that bottom ashes can be atom-efficiently converted into valuable sorbents without the need for costly and hazardous chemicals. The ashes were hydrothermally treated in rotary autoclaves at autogenic pH conditions to promote the conversion of precursor mineral phases into zeolites and layered silicate hydrates. Two main mineral phases were formed: katoite and sodium aluminum phosphate silicate hydrate. These mineral alterations are accompanied by a tenfold increase in specific surface area and a twofold reduction in average particle size. Performance evaluation of the new sorbents for Cd(2+), Zn(2+), and Pb(2+) adsorption at pH5 indicates sorption capacities of 0.06, 0.08, and 0.22 mmol g(-1), respectively, which are similar to those of natural adsorbents and synthetic materials obtained from more demanding synthesis conditions.

Comparison of mineral-based amendments for ex-situ stabilization of trace elements (As, Cd, Cu, Mo, Ni, Zn) in marine dredged sediments: a pilot-scale experiment

Trace element pollution of marine dredged sediments is an emerging problem all over the world. Comparing to other wastes, trace elements stabilization is more difficult both due to the wide range of contaminants present in the marine sediments and their inherent physicochemical properties. In this study, a pilot-scale experiment was performed to stabilize As, Cd, Cu, Mo, Ni, and Zn in a multi-contaminated sediment sample using hematite, zero-valent iron and zeolite. Results showed that iron-based amendments were able to reduce the leaching and the bioavailability of trace elements in the sediment sample, while zeolite was unsuitable. Chemical stabilization through iron-based amendments seems to be a promising approach as a low-cost alternative to traditional stabilization methods involving chemical reagents.