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.

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.

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.

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.