Integrated application of green zero-valent iron and electrokinetic remediation of metal-polluted sediment.

In recent years, more focus has been placed on integrated metal removal processes. Electrokinetic (EK) treatment is superior to other technologies because it can be applied to a variety of mediums. Green nanoparticles, on the other hand, have the potential to significantly reduce pollutant concentrations in a short period of time. In this study, we investigated the possibility of combining green zero-valent iron (nZVI) with EK on Cd and Zn-contaminated sediment. For green synthesis, extracts of dry leaves of mulberry (ML-nZVI) and oak (OL-nZVI) were used, both abundantly present in the Republic of Serbia. The results show that, despite the fact that their availability was greatly reduced, the metals were concentrated and stabilized to a significant extent in the middle of the EK cell (z/L 0.5) after all treatments. When the results were compared, OL-nZVI proved to be a more effective nanomaterial even with smaller doses of OL-nZVI, which is important in terms of achieving better economic benefits. This study identified green nano zero-valent iron as a powerful tool for metal removal when combined with electrokinetic (EK) treatment, which improves green nZVI longevity and migration. This study of the combined green nZVI-EK remediation treatment, in particular, will have an impact on future research in this field, given the achieved efficiency.

A cost effective method for immobilization of Cu and Ni polluted river sediment with nZVI synthesized from leaf extract.

This study investigates the performance of oak (OL) and mulberry (ML) leaves for synthesized of nanoscale zero-valent iron (nZVI), in immobilizing Cu and Ni in contaminated sediment. Characterization of synthesized Fe nanoparticles from oak and mulberry leaf extracts demonstrated that they are nontoxic and stabile nanomaterials for application in the sediment remediation. Effectiveness of stabilization process was performed by microwave-assisted sequential extraction procedure (MWSE) and single-step leaching tests which have been applied to evaluate the metal extraction potential. This research showed that OL-nZVI and ML-nZVI were effective in transforming available Cu and Ni to stable fraction. The maximum residual percentage of Cu increased by 76% and 73%, and for Ni 81% and 80%, respectively, with addition of 5% OL-nZVI and 5% ML-nZVI. Used single-step leaching tests (Toxicity Characteristic Leaching Procedure-TCLP and German standard test- DIN) indicated that all stabilized samples can be considered as non-hazardous waste, as all leached metal concentrations met the appropriate set criteria. Cost analysis showed that the operating cost for contaminated sediment treatment with green synthesized nZVI are 50.37 €/m3/per year. This work provides a new insight into the immobilization mechanism and environmental impact of Cu and Ni in contaminated sediment and potential way of treatment with OL-nZVI and ML-nZVI. Generally, nZVI can be an effective and versatile tool for stabilization of sediment polluted with toxic metals.

Ex situ remediation of sediment from Serbia using a combination of electrokinetic and stabilization/solidification with accelerated carbonation treatments.

The application of three simple and cost-effective technologies for ex situ remediation of the sediment of Begej River in Serbia is presented in this paper. In the first step, conventional electrokinetic treatment (EK) was carried out to reduce the amount of contaminated sediment and enhance the accumulation of metals. Subsequently, stabilization/solidification (S/S) treatment was applied to the remaining portion of polluted sediment to immobilize the accumulated metals. At the same time, the influence of accelerated carbonation on the effectiveness of the treatment was evaluated. The immobilizing agents used in this study included bio ash produced by combustion of wheat and soy straw mixture and bio ash derived from molasses incineration. After the treatments, the risk assessment was performed by using the sequential extraction procedure (SEP) and TCLP and DIN 3841-4 S4 leaching tests. The results obtained after the EK treatment revealed a reduction in the amount of polluted sediment to a half. Leaching tests and SEP performed on S/S mixtures after a 28-day maturation period indicated that accelerated carbonation decreased the mobility of critical metals, especially in wheat and soy straw mixtures. Moreover, based on the leaching tests, all prepared mixtures were categorized as non-hazardous and safe for disposal according to the relevant Serbian regulations. The newly developed method that combines EK and S/S treatments with the addition of accelerated carbonation produced reduced volumes of stabilized sediment which is safe for disposal.

Assessment of the environmental impact of sanitary and unsanitary parts of a municipal solid waste landfill.

Only seven regional MSWLF in Serbia are considered sanitary, while about 3500 landfills operate without proper pollution control. This paper presents a unique opportunity to evaluate the impact of a closed landfill, and a new sanitary landfill, which are located next to each other. The following methodologies for the landfill impact assessment were applied, based on data from 2012 to 2017: Landfill water pollution index (LWPI) and Nemerow index (PIGW) for groundwater, and the geo-accumulation (Igeo) and ecological risk (ERi) indices and several PAH ratios for soil. The performance of the leachate control system was evaluated using two adapted pollution indices: LPI and the Nemerow index (PIL). According to the obtained LWPI and PIGW values, the quality of groundwater at the new landfill is improving (LWPI = 1.05-2.62; PIGW = 0.52-1.29), while no significant changes were observed for the old landfill (LWPI = 3.06-5.13; PIGW = 2.03-4.78). High concentrations of ammonia nitrogen (1.01-22.74 mg/l), Fe (0.76-57.11 mg/l), Ni (5.80-230.09 µg/l), Pb (4.2-202.4 µg/l) and ∑PAH16 (150.93-189.55 ng/l) show the strong influence of the landfill on the groundwater quality at the old landfill, indicating the need for additional remediation action. High concentrations of Ni (21.9-133.0 mg/kg) and Cr (8.5-277.0 mg/kg) in the analyzed soil compared to other studies, as well as moderate Igeo values (IgeoNi = 0.36-1.88; IgeoCr = -1.20-1.52), raise concern and suggest the need for further monitoring. The high ERi (158.6-295.0) and Igeo values (0.91-2.30) of Hg show significant potential ecological risk. LPI and PIL values for early methanogenic phase leachate demonstrates the need to improve the leachate treatment system. The monitoring data and applied pollution indices indicate that Cr and As should be added to the EU Watch List of emerging substances, at least regarding EU potential candidate countries.

Long-term application of stabilization/solidification technique on highly contaminated sediments with environment risk assessment.

After dredging of contaminated sediment, additional remediation technique is required before its final disposal. For this purpose, this research was based on the long-term stabilization/solidification (S/S) process of highly contaminated sediment (dominantly by heavy metals) from a European environmental hot spot, the Great Backa Canal. Due to optimisation of remediation techniques, this sediment is treated with selected immobilization agents: kaolinite, quicklime and Portland cement. The use of pseudo-total metal content (selected priority substances: Cr, Ni, Cu, Cd, Zn, Pb and As) in untreated sediment, determined that sediment urgently requires remediation. Short-term (after 7 and 28 days) and long-term (after 7 years) monitoring were done in order to estimate the concentrations of metals and effect on biota from S/S mixtures during this processes. The environmental risk assessment encompassed the application of several appropriate analytical methods: the pseudo-total metal content, the German standard leaching test - DIN 3841-4 S4 and Toxicity Characteristic Leaching Procedure - TCLP test leaching tests and sequential extraction procedure (BCR) on S/S mixtures, testing the aging process and toxicity effects. After simulating real environmental conditions using all tests in all three mixtures, metals do not exceed the prescribed limit values and as such S/S mixtures are classified as non-hazardous waste. Sequential extraction procedure showed that the highest percentage of metals are in the residual phase, bound to silicates and crystalline structure. After 7 years of S/S mixture aging, kaolinite showed the highest binding capacity that was reflected in the content of metals in the residual phase (34.8% of Ni to 77.6% of Cr). DIN and TCLP leaching tests confirmed that the exchangeable phase has a minor effect on the environment. Accordingly, this remediation technology could be well applied for final disposal of this and similar extremely contaminated sediment dominantly with inorganic pollutants.

Preremedial assessment of the municipal landfill pollution impact on soil and shallow groundwater in Subotica, Serbia.

Most regional municipal solid waste landfills in Serbia are operated without control of landfill leachate and gas or with no regard for implementation of national and European legislation. For the first time in Serbia, groundwater and soil at a landfill were subject to systematic annual monitoring according to national, European legislation and adopted methodologies. Characterisation of the groundwater and soil samples from the landfill included ten metals (Fe, Mn, As, Zn, Cd, Pb, Ni, Cr, Cu and Hg), 16 EPA PAHs, nutrients and certain physicochemical parameters, in order to assess the risks such poorly controlled landfills pose to the environment. This impact assessment was performed using specially adapted pollution indices: LWPI, the Single factor pollution index and the Nemerow index for groundwater, and geo-accumulation index, ecological risk factor and selected rations of PAHs for soil. The data analysis included multivariate statistical methods (factor analysis of principal component analysis (PCA/FA)) in order to assess the extent of the contaminants detected in the groundwater and soil samples. The pollution indices (LWPI: 3.56-8.89; Nemerow index: 2.02-3.78) indicate the quality of the groundwater at the landfill is degrading over time, with PAH16, TOC, Cr, Cu, Pb and Zn as the substances of greatest concern. Heavy metals Hg (Igeo≤3.14), Pb (Igeo≤2.22), Cr (Igeo≤3.31) and Cu (Igeo≤2.16) represent the worst soil contamination. Hg has moderate (52.9) to very high (530.0) potential ecological risk, demonstrating the long-term potential effects of bioaccumulation and biomagnification. The results of this work indicate that Cr and Cu should possibly be added to the EU Watch List of emerging substances. This proposition is substantiated by relevant state and alike environmental information from nations in the region. This study demonstrates the need to develop a model for prioritization of landfill closure and remediation based on environmental risk assessment.

Distribution and ecological risk assessment of organic and inorganic pollutants in the sediments of the transnational Begej canal (Serbia-Romania).

This research is designed to determine the level and types of pollution in the highly contaminated sediments of the international Begej canal in Timis district, Romania and north-eastern Serbia. The cross-border canal stretch investigated is currently not navigable, but represents an important waterway between the Danube River in Serbia and the city of Timisoara. Surface sediments were monitored annually from 2008 to 2016 at 36 representative sampling locations, with a wide range of analyses, including eight heavy metals of long-term monitoring concern (Ni, Zn, Cd, Cr, Cu, Pb, As and Hg) and the 16 USEPA PAHs. The purpose of this study was to determine the diversity and impact of anthropogenic and natural sources of pollution at the pollution hot spots on the canal: at the Itebej lock (near the border with Romania) and downstream at the Klek lock. Sediment quality and ecological risk were assessed in order to determine pollutants of concern. Several multi-proxies were applied (e.g. geo-accumulation index (Igeo), ecological risk index (RI) and total benzo[a]pyrene equivalent (B[a]Peq)). To determine and predict trends, multivariate statistical methods (factor analysis of principal component analysis (PCA/FA)) were carried out on the organic and inorganic parameters analysed. In the near-border region, acute and significant ecological impacts were observed. The heavy metals Hg, Cr, Pb, Cu and Zn, and the carcinogenic PAH dibenzo[a,h]anthracene, were historically the most frequently detected harmful substances to biota in this and the wider Pannonia region. This is the first long-term study to quantify and derivate the most frequently detected harmful substances of concern for this and similar sites in the wider region, and is additionally supported by significant national and similar environmental data from previous studies in the region.

The role of organic matter and clay content in sediments for bioavailability of pyrene.

Evaluation of the bioavailable fractions of organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) is extremely important for assessing their risk to the environment. This available fraction, which can be solubilised and/or easily extracted, is believed to be the most accessible for bioaccumulation, biosorption and/or transformation. Sediment organic matter (OM) and clay play an important role in the biodegradation and bioavailability of PAHs. The strong association of PAHs with OM and clay in sediments has a great influence not only on their distribution but also on their long-term environmental impact. This paper investigates correlations between bioavailability and the clay and OM contents in sediments. The results show that OM is a better sorbent for pyrene (chosen as a model PAH) and that increasing the OM content reduces the bioavailable fraction. A mathematical model was used to predict the kinetic desorption, and these results showed that the sediment with the lowest content of OM had an Ffast value of 24%, whereas sediment with 20% OM gave a value of 9%. In the experiments with sediments with different clay contents, no clear dependence between clay and rate constants of the fast desorbing fractions was observed, which can be explained by the numerous possible interactions at the molecular level.

Distribution of organic and inorganic substances in the sediments of the "Great Backa Canal", a European environmental hotspot.

The Great Backa Canal in Serbia is one of the most polluted waterways in Europe. Surface sediments from the canal were subject to systematic annual monitoring between 2007 and 2014 at 33 representative sampling sites. Eight heavy metals (Ni, Zn, Cd, Cr, Cu, Pb, As and Hg), mineral oils, 16 EPA PAHs and selected pesticides and polychlorinated biphenyls (PCB) were monitored. This study aims to evaluate the quality of the sediments and determine the potential ecological risks in order to establish pollutants of interest. The spatial and temporal influence of different and intense sources of pollution are investigated. The analysis includes multivariate statistical methods (factor analysis of principal component analysis (PCA/FA)) in order to assess the extent and origin (anthropogenic or natural, geogenic sources) of the contaminants detected in the sediment samples and the risks the present to the environment. Various sources, predominantly the food industry, were found to be responsible for most of the contamination by Cd, Cu, Cr and Zn, the mineral oils and PAHs (dibenzo[a,h]anthracene and benzo[a]pyrene contributed 86.0% of the total between 2007 and 2014). In contrast, the As was convincingly of geogenic origin, and the Hg, Pb and Ni present exhibit dual origins. Cd and Cu significantly raise the levels of potential ecological risk at all sampling locations, demonstrating the long-term effects of bioaccumulation and biomagnification. Significantly, the results of this work indicate that Cu, As and dibenzo[a,h]anthracene should be added to the EU watch list of emerging contaminants. This is supported by significant national and similar environmental data from countries in the region.

The Application of Solar Cells in the Electrokinetic Remediation of Metal Contaminated Sediments.

In this study, solar cells were used to generate an electric field for the electrokinetic remediation of metal contaminated sediment (Nickel, Cadmium, Zinc). For determination of metals mobility, bioavailability and potential toxicity, sequential extraction procedure, simultaneously extracted metals (SEM) and acid-volatile sulphide ratios (AVS) were performed before, during and after treatment.After 21 days of treatment, 63% Ni, 82% Cd and 58% Zn was removed from the anode region. The application of the electric field changed the chemical composition of the sediments. The risk assessment analysis based on pseudo total metals content, the risk assessment code and the relationship between SEM and AVS, indicates that a simple singular approach for risk assessment analysis and evaluation of the quality of sediments is not enough.

Organic and inorganic priority substances in sediments of Ludas Lake, a cross-border natural resource on the Ramsar list.

For the first time, long-term monitoring (from 2002 to 2014) was carried out of surface sediments in Ludas Lake, a Ramsar site in northern Serbia. Organic (16 EPA PAHs, mineral oils, selected pesticides and polychlorinated biphenyls (PCBs)) and inorganic substances (eight heavy metals: Ni, Zn, Cd, Cr, Cu, Pb, As and Hg) were continually investigated. Dibenzo[a,h]anthracene (DahA) and fluorene (Flo) were found at levels indicative of causing adverse effects to biota. Diagnostic ratios of specific PAHs were dominated by high molecular weight components, particularly DahA, which contributed 81.78 % of the total high carcinogens, benzo[b]fluoranthene (BbF) and Flo. Potential ecological risk factors (ERi) and the high relative standard deviations (RSD) obtained (up to 245 %) for the parameters monitored confirm the high periodical anthropogenic impact from industry, municipal wastewater and agriculture. The highest concentration of inorganic pollution found was for Cd (440-831 mg/kg) at all sites, Cu (439 mg/kg) in the eastern part of the lake and Cu (388 mg/kg) and Hg (771 mg/kg) in the northern part of the lake. Based on factor analysis of principal component analysis (PCA/FA), As and phenanthrene (Phe) had significant loadings (0.808 and 0.907, respectively). This association of As with organic anthropogenic sources was also confirmed with the sum of PAHs, pyrene (Pyr) and mineral oil by 3D factor plot, corroborating the theory of As mobilization from metal-reducing microbes as organic (methylated) forms, accelerated by phenanthrene. According to EU national and regional data results, this research suggests that Cu, As, dibenzo[a,h]anthracene and Flo should be added to the list of priority pollutants within the context of applying the European Water Framework Directive (WFD).

Priority substances in sediments of the "Carska Bara" special nature reserve, a natural scientific research area on the UNESCO list.

Surface sediments were subject to systematic long-term monitoring (2002-2014) in the Republic of Serbia (Province of Vojvodina). Eight heavy metals (Ni, Zn, Cd, Cr, Cu, Pb, As and Hg), mineral oils (total petroleum hydrocarbons), 16 EPA PAHs, selected pesticides and polychlorinated biphenyls (PCB) were monitored. As part of this research, this paper presents a sediment contamination spatial and temporal trend study of diverse pollution sources and the ecological risk status of the alluvial sediments of Carska Bara at three representative sampling sites (S1S3), in order to establish the status of contamination and recommend substances of interest for more widespread future monitoring. Multivariate statistical methods including factor analysis of principal component analysis (PCA/FA), Pearson correlation and several synthetic indicators were used to evaluate the extent and origin of contamination (anthropogenic or natural, geogenic sources) and potential ecological risks. Hg, Cd, As, mineral oils and PAHs (dominated by dibenzo(a,h)anthracene and benzo(a)pyrene, contributing 85.7% of the total) are derived from several anthropogenic sources, whereas Ni, Cu, Cr and Zn are convincingly of geogenic origin, and exhibit dual origins. Cd and Hg significantly raise the levels of potential ecological risk for all sampling locations, demonstrating the effect of long-term bioaccumulation and biomagnification. Pb is isolated from the other parameters, implying unique sources. This research suggests four heavy metals (Zn, Cr, Cu and As) and dibenzo(a,h)anthracene be added to the list of priority pollutants within the context of the application of the European Water Framework Directive (WFD), in accordance with significant national and similar environmental data from countries in the region.

Correlation of different pollution criteria in the assessment of metal sediment pollution.

In this article an assessment of the sediment metal pollution (cadmium, copper, chromium, lead, nickel, zinc) in the Veliki Backi canal (Serbia) was carried out using pseudo-total metal content, contamination factor (CF), pollution load index (PLI) and enrichment factor (EF). The study also encompassed pore-water metal concentrations and an assessment of sediment pollution based on the analysis of simultaneously extracted metals (SEM), acid volatile sulphides (AVS) and the sequential extraction procedure. The concentrations of metals are likely to result in harmful effects based on the comparison with sediment quality guidelines (Dutch, Canadian, US EPA - United States Environmental Protection Agency). The ratio of simultaneously extracted metals and volatile acid sulphides was found to be greater than 1 in only one location, which is already recognized as a place of high risk based on the criteria applied. Other samples had Σ[SEM]/[AVS] < 1, despite their high risk classification based on the applied criteria. According to the sequential extraction procedure, zinc and nickel exhibit high risk in most samples, whereas other metals show low and medium risk. The CF values for Cr, Cu and Zn were > 6 in most samples, which denotes very high contamination by these metals. The PLI values indicated moderate and high pollution. The EF values for all metals studied except for Cd in some cases were >1.5, suggesting anthropogenic impact. The obtained results will be invaluable for future activities regarding sediment monitoring and will facilitate the selection of appropriate criteria when evaluating sediment quality.

Electrokinetic Treatment of Cr-, Cu-, and Zn-Contaminated Sediment: Cathode Modification.

Enhanced electrokinetic (EK) removal of Cr, Cu, and Zn from sediment by using original and modified integrated ion exchange (IIX™) cathodes was investigated. IIX cathode design and EK device process modifications were made to improve performance: separation of IIX cathode components (IIXS), combination of modified IIX cathode with pulsed electric field (IIXSP), and separation of IIX cathode components with addition of an anion exchange resin compartment (IIXA). After using the IIXSP, overall Cr, Cu, and Zn removal efficacies were significantly improved compared with the other treatments investigated. No improvements in overall Cr, Cu, and Zn removal efficacies were achieved by utilization of IIXA. Nevertheless, significant removal efficacies occurred at the anode region since distribution of the alkaline front was prevented. However, metal accumulation in the cathode region occurred. This was a consequence of metal cation complexation with Cl- released from the anion exchange resin that changed the direction of metal migration. Enhancing EK remediation of Cr-, Cu-, and Zn-contaminated sediment can be achieved by using a modified IIX cathode.

Behavior of zinc, nickel, copper and cadmium during the electrokinetic remediation of sediment from the Great Backa Canal (Serbia).

This paper describes a bench-scale study dealing with the removal of heavy metals by electrokinetic (EK) remediation from sediment of the Great Backa Canal (Vojvodina, Republic of Serbia), with an emphasis on the dependence of removal efficacies on the physicochemical states of the heavy metals and sediment chemistry. Sediment samples were spiked with the following heavy metals (mg kg(-1)): Zn 4400, Ni 900, Cu 1140 and Cd 57. In addition to determining the pseudo-total metal content in the contaminated sediment before and after EK treatment, BCR sequential extraction was also performed to examine the distribution of the contaminants in the sediment. Conventional EK remediation (EXP I) was ineffective in removing the heavy metals investigated, so two enhanced processes were developed. In both these processes, the mass of treated sediment was reduced to avoid the presence of inactive electric field areas in the sediment and increase current density. The first enhanced experiment (EXP II) used acetic acid (HAc) solution (pH 2.9) as an anolyte. Combined with the smaller sediment mass, this resulted in an increase in overall removal efficacies (9% for Zn, 15% for Ni, 10% for Cu and 15% for Cd). The second enhanced experiment (EXP III), as well as using HAc solution as an anolyte, made use of a cation exchange membrane in the cathodic chamber to minimize pH changes in the region adjacent to the cathode, which negatively influenced the removal of some heavy metals. However, no improvement in removal efficacy was achieved in EXP III. Since the redox potential of the sediment drops during the EK process, metals removal is limited by the formation of their sulfides. In conclusion, the removal of heavy metals by EK remediation is governed by a complex interplay of the complexation, precipitation and reduction processes, and the difficulties encountered in their optimization can explain the unsatisfactory effectiveness achieved by the described remediation procedure. Improved understanding of the behavior of metal ions during EK treatment can be useful in predicting and enhancing the efficacy of the process.