Repurposing spent filter sand from iron and manganese removal systems as an adsorbent for treating arsenic contaminated drinking water.

Waterworks which utilise river bank filtration water sources often have to apply aeration and sand filtration to remove iron and manganese during the drinking water treatment process. After some time, the sand becomes saturated and the spent filter sand (SFS) must be disposed of and replaced. In order to valorize this waste stream, this paper investigates the reuse of SFS as an adsorbent for the treatment of arsenic contaminated drinking water. The arsenic removal performance of SFS is compared with two synthetic iron oxide coated sands (IOCS). The sorbents were first characterized by SEM, EDS, BET specific surface area, and point of zero charge (pHpzc) measurements, and then investigated under a variety of conditions. The surface of the SFS was revealed to be coated with iron manganese binary oxide. The Freundlich model best described the isotherm experiment data, indicating a non monolayer adsorption model for arsenic adsorption on the three IOCS investigated. As(III) and As(V) removals were negatively effected by the presence of PO43- and HA anions as they competed with the arsenic species for adsorption sites. However, given the status of SFS as a waste material, the results obtained in this paper suggest it may be successfully reused as a very economically and environmentally sustainable solution for small waterworks requiring both As(V) and As(III) removal during drinking water treatment.

Metal Nanoparticles in Dye Wastewater Treatment - Smart Solution for Clear Water.

BACKGROUND: In past years, nanomaterials have been actively studied and developed and successfully used in many fields. Due to water scarcity, the application of nanomaterials in water and wastewater treatment has drawn significant attention. Due to their superior features, they represent functional materials with great potential for pollution removal and environmental applications. OBJECTIVE: This literature review aims to summarize and present the metal nanoparticles used for dye wastewater treatment. The discussion subject is metallic nanoparticles for mentioned use, with a special focus on iron-based, bimetallic, and photocatalytic nanomaterials. METHODS: Reference search of "metal nanoparticles in dye wastewater treatment" was conducted in detail through the Serbian Library Consortium for Coordinated Acquisition (KoBSON). Published papers search was mainly based on Web of Science and ScienceDirect database focusing on the latest research on this topic. The corresponding literature was carefully read, analyzed, and evaluated. RESULTS: Two hundred and twenty-four scientific and review articles, thesis, and book chapters, patents were evaluated in order to summarise current trends in metal nanoparticle use in wastewater treatment. An increasing trend in scientific research regarding metal nanoparticles can be observed for the removal of different inorganic and organic pollutants. Among the most extensively tested are dye molecules, representing challenging species in terms of degradation and consequent removal. Modification, layering, combination, and green synthesis of metal nanoparticles result in materials capable of efficient and environmentally sustainable wastewater treatment. CONCLUSION: In this paper, an extensive review of metal nanoparticles in dye wastewater treatment is presented. With rapid water demand, the development of sustainable materials and technology is necessary. The use of these materials represents eco-friendly, energy-efficient, and sustainable water purification solutions. However, the matter of usage commercialization is still to be addressed.

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.

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.

Arsenic adsorption on Fe-Mn modified granular activated carbon (GAC-FeMn): batch and fixed-bed column studies.

Granular activated carbon (GAC) was modified with Fe-Mn binary oxide to produce a novel effective hybrid adsorbent (GAC-FeMn) for simultaneous removal of As(III) and As(V) from water. After characterization (including BET, SEM/EDS and XRD analyses) of the raw and modified GAC, FTIR analysis before and after As removal showed that ligand exchange was the major mechanism for As removal on GAC-FeMn. Sorption kinetics followed pseudo-second order kinetics for both As(III) and As(V) and were not controlled by intraparticle diffusion. Batch equilibrium experiments yielded adsorption capacities for As(III) and As(V) of 2.87 and 2.30 mg/g, and demonstrated that better sorption was achieved at low pH. Of the competitive anions investigated (PO43-, SiO32-, CO32-, SO42-, NO3-, Cl-), phosphate had the greatest negative effect on As(III) and As(V) adsorption. Three sorption/desorption cycles were conducted in continuous column tests with a real arsenic contaminated groundwater, with subsequent TCLP leaching tests confirming the stability of the spent sorbent. In the column tests, breakthrough curves were also obtained for phosphates, which were present at a relatively high concentration (1.33 mg/L) in the investigated groundwater. The phosphates limited the effective operational bed life of GAC-FeMn for arsenic removal. Nonetheless, the maximum arsenic adsorption capacities for GAC-FeMn obtained by the Thomas model during the three sorption cycles were high, ranging from 18.8 to 29.8 mg/g, demonstrating that even under high phosphate loads, with further process improvements, GAC-FeMn may provide an excellent solution for the economic removal of arsenic from real groundwaters.

State of the art and future challenges for polycyclic aromatic hydrocarbons is sediments: sources, fate, bioavailability and remediation techniques.

Polycyclic aromatic hydrocarbons (PAHs) are amongst the most abundant contaminants found in the aquatic environment. Due to their toxicity and carcinogenicity, their sources, fate, behaviour, and cleanup techniques have been widely investigated in the last several decades. When entering the sediment-water system, PAH fate is determined by particular PAH and sediment physico-chemical properties. Most of the PAHs will be associated with fine-grained, organic-rich, sediment material. This makes sediment an ultimate sink for these pollutants. This association results in sediment contamination, and in this manner, sediments represent a permanent source of water pollution from which benthic organisms may accumulate toxic compounds, predominantly in lipid-rich tissues. A tendency for biomagnification can result in critical body burdens in higher trophic species. In recent years, researchers have developed numerous methods for measuring bioavailable fractions (chemical methods, non-exhaustive extraction, and biomimetic methods), as valuable tools in a risk-based approach for remediation or management of contaminated sites. Contaminated sediments pose challenging cleanup and management problems, as conventional environmental dredging techniques are invasive, expensive, and sometimes ineffective or hard to apply to large and diverse sediment sites. Recent studies have shown that a combination of strategies including in situ approaches is likely to provide the most effective long-term solution for dealing with contaminated sediments. Such in situ approaches include, but are not limited to: bioaugmentation, biostimulation, phytoremediation, electrokinetic remediation, surfactant addition and application of different sorbent amendments (carbon-rich such as activated carbon and biochar) that can reduce exposure and limit the redistribution of contaminants in the environment.

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.

Potential for anaerobic treatment of polluted sediment.

Due to the anaerobic nature of aquatic sediments, the anaerobic treatment of sediments utilizing already present microflora represents an interesting treatment option. Contaminated sediment can contain a variety of organic contaminants, with easily degradable organics usually present in the higher amounts, along with traces of specific organic pollutants (total petroleum hydrocarbons and polycyclic aromatic hydrocarbons). This study applies a comprehensive approach to contaminated sediment treatment which covers all the organic contaminants present in the sediment. The aim of this study was to (1) evaluate the anaerobic treatment of aquatic sediment highly loaded with easily degradable organics via determination of potential biogas and methane production, and (2) assess possibilities of using anaerobic treatment for the degradation of specific organic pollutants in order to reduce the risks posed by the sediment. In order to promote the methanogenic conditions of the indigenous microflora in the sediment, the addition of co-substrates acetate and glucose was investigated. The results, expressed as mL biogas produced per volatile solids content in sediment (VSadded) indicate that the addition of the co-substrate has a significant impact on biogas production potential (58.7 and 55.1 mL/g VSadded for acetate and glucose co-substrate addition respectively, and 14.6 mL/g VSadded for the treatment without co-substrate addition). Theoretical biochemical methane potential was assessed by Gompertz model and Chemical oxygen demand model. The Gompertz model fit better for all the applied treatments, and was capable of predicting the final productivity of biogas and methane in the first 30 days with a relative error of less than 14%. From the aspects of specific organic pollutants, total petroleum hydrocarbon degradation was promoted by co-substrate addition (degradations of 75% and 60% achieved by acetate and glucose co-substrate addition, compared to 45% for the treatment without co-substrate addition). Polycyclic aromatic hydrocarbons were reduced by significant amounts (84-87%) in all the applied treatments, but the addition of co-substrate did not further improve their degradation.

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.

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.

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.

A chemical and microbiological characterization and toxicity assessment of the Pancevo industrial complex wastewater canal sediments, Serbia.

The wastewater canal Vojlovica of the Pancevo industrial area, Serbia, is the main collector of the effluents from the local industrial complex. The canal is directly connected to the Europe's second largest river, the Danube. Here, we present a chemical and microbiological analysis of the sediment in order to determine the fate of pollutants over the years, as well as its current condition. Dry matter, clay and organic matter content, a Kjeldahl ammonia, phosphorus, metals, and polychlorinated biphenyls as well as polycyclic aromatic hydrocarbons concentrations were measured. Microbiological analysis included heterotrophic and oil-degrading bacterial counts, isolation of the phenanthrene-degrading bacteria, and identification of cyanobacteria. Generally, in comparison to the results from previous studies, concentrations of the measured pollutants have been in a decline. Specifically, the metal and polycyclic aromatic hydrocarbon concentrations were reduced whereas microbial counts and toxicity tests did not indicate significant pollution. The obtained results are probably a consequence of an improved wastewater treatment and microbial degradation of pollutants.

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.

Response surface methodology investigation into the interactions between arsenic and humic acid in water during the coagulation process.

Interactions between arsenic and natural organic matter (NOM) are key limiting factors during the optimisation of drinking water treatment when significant amounts of both must be removed. This work uses Response Surface Methodology (RSM) to investigate how they interact during their simultaneous removal by iron chloride coagulation, using humic acid (HA) as a model NOM substance. Using a three factor Box-Behnken experimental design, As and HA removals were modelled, as well as a combined removal response. ANOVA results showed the significance of the coagulant dose for all three responses. At high initial arsenic concentrations (200µg/l), As removal was significantly hindered by the presence of HA. In contrast, the HA removal response was found to be largely independent of the initial As concentration, with the optimum coagulant dose increasing at increasing HA concentrations. The combined response was similar to the HA removal response, and the interactions evident are most interesting in terms of optimising treatment processes during the preparation of drinking water, highlighting the importance of utilizing RSM for such investigations. The combined response model was successfully validated with two different groundwaters used for drinking water supply in the Republic of Serbia, showing excellent agreement under similar experimental conditions.

Assessment of the bioavailability and phytotoxicity of sediment spiked with polycyclic aromatic hydrocarbons.

Large amounts of sediment are dredged globally every year. This sediment is often contaminated with low concentrations of metals, polycyclic aromatic hydrocarbons, pesticides and other organic pollutants. Some of this sediment is disposed of on land, creating a need for risk assessment of the sediment disposal method, to minimize the degradation of environmental quality and prevent risks to human health. Evaluating the available fractions of certain polycyclic aromatic hydrocarbons is very important, as in the presence of various organisms, they are believed to be easily subject to the processes of bioaccumulation, biosorption and transformation. In order to determine the applicability of applying these methods for the evaluation of pollutant bioavailability in sediments, the desorption kinetics from the sediment of various polycyclic aromatic hydrocarbons in the presence of Tenax and XAD4 were examined over the course of 216 h. Changes in the PAH concentrations in dredged sediments using five different seed plants during a short time of period (10 days) were also followed. Using chemical extraction techniques with Tenax and XAD4, a time of around 24 h is enough to achieve equilibrium for all four PAHs. Results showed good agreement between the seed accumulation and PAH extraction methods with both agents. If we compare the two extraction techniques, XAD4 gave better results for phenanthrene, pyrene and benzo(a)pyrene, and Tenax gave better results for chrysene.

Trace level voltammetric determination of lead and cadmium in sediment pore water by a bismuth-oxychloride particle-multiwalled carbon nanotube composite modified glassy carbon electrode.

Two multiwalled carbon nanotubes-based composites modified with bismuth and bismuth-oxychloride particles were synthesized and attached to the glassy carbon electrode substrate. The resultant configurations, Bi/MWCNT-GCE and BiOCl/MWNT-GCE, were then characterized with respect to their physicochemical properties and electroanalytical performance in combination with square-wave anodic stripping voltammetry (SWASV). Further, some key experimental conditions and instrumental parameters were optimized; namely: the supporting electrolyte composition, accumulation potential and time, together with the parameters of the SWV-ramp. The respective method with both electrode configurations has then been examined for the trace level determination of Pb(2+) and Cd(2+) ions and the results compared to those obtained with classical bismuth-film modified GCE. The different intensities of analytical signals obtained at the three electrodes for Pb(2+) and Cd(2+) vs. the saturated calomel reference electrode had indicated that the nature of the modifiers and the choice of the supporting electrolyte influenced significantly the corresponding stripping signals. The most promising procedure involved the BiOCl/MWCNT-GCE and the acetate buffer (pH 4.0) offering limits of determination of 4.0 µg L(-1) Cd(2+) and 1.9 µg L(-1) Pb(2+) when accumulating for 120 s at a potential of -1.20 V vs. ref. The BiOCl/MWCNT electrode was tested for the determination of target ions in the pore water of a selected sediment sample and the results agreed well with those obtained by graphite furnace atomic absorption spectrometry.

Hydrodynamic chronoamperometric method for the determination of H2O2 using MnO2-based carbon paste electrodes in groundwater treated by Fenton and Fenton-like reagents for natural organic matter removal.

A simple hydrodynamic chronoamperometric method based on the application of an unmodified carbon paste electrode (CPE) and bulk-modified with different contents of MnO2 was investigated for the determination of H2O2. The optimized method involving the CPE with 5% of MnO2 was applied for the determination of the H2O2 consumption in samples of groundwater from the Central Banat region (Province of Vojvodina, Serbia) treated by the Fenton (Fe(2+) and H2O2) and Fenton-like (Fe(3+) and H2O2) reagents to remove natural organic matter at different initial concentrations of iron species, and of their ratios to the initial concentration of H2O2. Under optimized conditions, with a working potential of 0.40V vs. the saturated calomel electrode and a phosphate buffer solution (pH 7.5) as supporting electrolyte, the method enabled the quantitation of H2O2 in the concentration interval from 1.4 to 65 µg mL(-1) with a relative standard deviation of less than 10%. The results obtained for the H2O2 consumption are in good agreement with those obtained by parallel measurements related to the efficiency of organic matter removal.