Solidification/stabilization of metal polluted sediment of Krivaja river

The Krivaja River is the longest natural water body (109 km) that flows completely within the borders of Serbian province of Vojvodina. In the absence of national legislation, the sediment quality was assessed in accordance with the Dutch classification methodology. It was found that the river sediment is highly contaminated with copper and zinc (192 mg kg-1 and 1218 mg kg-1 respectively), and as such is an extreme risk to the environment and human health. The solidification/stabilization (S/S) treatment with local clay, that has high capacity of cation exchange 70.2 meq/100 g and specific surface area of 630 m2 g-1, was employed for remediation of the contaminated sediment. The sequential extraction procedure showed that the copper and zinc have medium risk for the environment, with the percentage in the carbonate fraction of 18 and 22% respectively. The results of sequential extraction are not in full agreement with the results of pseudo-total metal concentration in the sediment, which only confirms that the total metal concentration is not sufficient to define the real danger to the environment. Based on the pseudo-total metals concentration, the sediment is of Class 4 (Dutch standards). However, judging from the results of sequential extraction, the metals show medium risk. Obviously, these results have to be taken into account in the assessment of the sediment quality, remediation procedures and sediment disposal in general. After the treatment, the proportion of these two metals in the first fraction is significantly reduced (Cu less than 2%, Zn 10%) in most of samples. In order to determine the long-term behavior of S/S mixtures, leaching tests were conducted in accordance with semi-dynamic ANS diffusion test for 90 days. The results indicated that clay can effectively immobilize Cu and Zn: the cumulative leached fraction of copper in mixtures with clay was in the range from 0.001% (mixture with 80% clay) to 0.15% (mixture with 10% clay), and the cumulative leached fraction of zinc in the range of 0.06% (mixture with 80% clay) to 0.10% (mixture with 10% clay). The diffusion coefficients, ranging from 1.5×10-12 cm2s-1 to 3.7×10-14 cm2s-1, showed an effective immobilization of both metals which suggests that these metals are practically immobilized in S/S mixtures even if the level of clay is low. From the point of LX values, all S/S mixtures can be used for the controlled utilization, because the leaching indices ranged from 11.8 to 13.4 for both metals. In all clay and sediment mixtures the dominant leaching mechanism is diffusion (slope values of 0.35 to 0.60), which once again confirms the effectiveness of the applied treatment and can be expected that only a very small amount of contaminants would leach into the environment over time. Future research is heading in the direction of troubleshooting the accumulation of used natural adsorbent after treatment, the possibility of permanent disposal, its regeneration or the possibility of its application as construction material

Characterisation, availability, and risk assessment of the metals in sediment after aging

The behavior of metals in sediments after their disposal to land has important implications for the environmental management. The sediment from the Carska Bara (Serbia) was polluted with adequate metal salts in order to reach severe contamination based on the pseudo-total metal content of Pb, Cd, Ni, Zn, Cu, and Cr according to the corresponding Dutch standards and Canadian guidelines. The toxicity and fate of the metal in sediment depend on its chemical form, and therefore, quantification of the different forms of a metal is more meaningful than the estimation of its total concentration. In this study, fractionation of metals in sediment has been investigated to determine its speciation and ecotoxic potential, as well as evaluation of metal potential toxicity based on the simultaneously extracted metals (SEMs) and acid volatile sulfides (AVSs) analysis at the beginning of the experiment and after 5 weeks of sediment aging. The investigations suggest that Cd, Pb, and Zn have a tendency to associate with labile fraction, the most mobile and most dangerous fraction for the environment. Risk assessment code revealed their high risk. Copper and chromium showed low to medium risk to the aquatic environment. Nickel showed no risk to the aquatic environment. This was the case at the beginning and after 5 weeks of aging. Aging yielded an increased mobility of all metals based on the increased proportion in mobile fractions. The I [SEM pound (i) ]/[AVS] ratio was found to be > 1 both at the beginning and after 5 weeks of aging, with the ratio showing an increase with time. This ratio indicates the potential availability/toxicity and, according to the US EPA criteria, the samples belong to the group with probable negative effect. If particular metals are considered, only the I [SEM pound (i) ]/[AVS] ratio for zinc was > 1 at the beginning. After 5 weeks, the ratio was > 1 for zinc, lead, and copper. Comparison of the results of sequential extraction and the results of SEM and AVS analysis showed good agreement for lead and zinc

Leachability and physical stability of solidified and stabilized pyrite cinder sludge from dye effluent treatment

This work is concerned with exploring the possibilities of using solidification/stabilization (S/S) treatment for toxic sludge generated in dye effluent treatment, when pyrite cinder is used as catalytic iron source in the modified heterogeneous Fenton process. S/S treatment was performed by using different clay materials (kaolin, bentonite and native clay from the territory of Vojvodina) and fly ash in order to immobilize toxic metals and arsenic presented in sludge. For the evaluation of the extraction potential of toxic metals and the effectiveness of the S/S treatment applied, four single-step leaching tests were performed. Leaching test results indicated that all applied S/S treatments were effective in immobilizing toxic metals and arsenic presented in sludge. X-ray diffraction analysis confirmed the formation of pozzolanic products, and compressive strength measurement proved the treatment efficacy. It can be concluded that the S/S technique has significant potential for solving the problem of hazardous industrial waste and its safe disposal. [Projekat Ministarstva nauke Republike Srbije, br. III43005 i br. TR37004

Removal of As(III) and Cr(VI) from aqueous solutions using “green” zero-valent iron nanoparticles produced by oak, mulberry and cherry leaf extracts

Abstract The production of nano zero-valent iron nanoparticles, using the extract from natural products, increased in recent years as it represents green and environmentally friendly method. Synthesis of green zero-valent iron nanoparticles (nZVI) using oak, mulberry and cherry leaf extracts (OL-nZVI, ML-nZVI and CH-nZVI) proved to be a promising approach for As(III) and Cr(VI) removal from aqueous solutions. The oak, mulberry and cherry leaves were chosen because of their high oxidant capacity as an important property for the production of the nZVIs. Also, oak, mulberry and cherry trees are widely distributed and easy to find in Vojvodina, the north province of Serbia. Characterization of produced green nZVI materials confirmed the formation of nanosize zero-valent iron particles within the size of 10–30 nm. Nanoparticles were spherical in shape and represented stable material with minimum agglomeration observed by TEM and SEM morphology measurements. Batch experiments revealed that the adsorption kinetics followed pseudo-second order rate equation. The obtained adsorption isotherm data could be well described by the Freundlich model. In addition, investigated pH effect showed that varying the initial pH value had a great effect on As(III) and Cr(VI) removal. This study indicated that nZVI could be produced by low cost and non toxic method with oak, mulberry and cherry leaf extracts and potentially be used as a new green material for remediation of water matrices contaminated with As(III) and Cr(VI)

Three different clay-supported nanoscale zero-valent iron materials for industrial azo dye degradation: A comparative study

In video streaming it is important that the video stream reaches the users in time, and without errors. To retransmit lost packets in a largescale multimedia video transmission is often unfeasible because of the retransmission delay. Because of that errors require either costly retransmissions or causes a downgrade of performance for the receiving user, an important goal is to minimize the number of errors that occurs when transmitting data during video streaming through a wireless channel. In this paper an adaptation-algorithm is proposed, which adapts itself in such away that the receivers of e.g. the broadcast will receive enough packets in order to be able to FEC-decode the received data in low- as well as high loss-scenarios. The algorithm adapts itself by changing the rate of FEC-encoded redundant packets based on the current packet-loss-rate of the channel, with the aim of optimizing the bandwidth-usage and providing the receiver with playable data meeting deadlines. It adds an additional self-adaptive amount of FEC-encoded redundant packets for each FEC-encoded-session in order to guarantee the ability of the receiver to FEC-decode the data and play the media, even under the conditions in which the inteference-level of the channel increases during the transmission of each such session. Simulations demonstrate that in a wireless channel with a packet loss rate of 10%, using 1000 source packets per FEC-encoded unit, 12.6% redundant packets are required in order to ensure a FEC-decoding-failure probability < 1/1000 .När man streamar video är det viktigt att videostreamen når användarna i tid och utan fel. Att återsända förlorade paket i en storskalig överföring av video är ofta olämpligt p.g.a. den fördröjning som återsändning av paket orsakar. Eftersom att fel kräver antingen kostsamma återsändningar eller orsakar en försämring av prestandan för den mottagande användaren, är det ett viktigt mål att minimera antalet fel som uppstår när man överför data genom en trådlös nätverkskanal. I denna thesis presenteras en anpassningsalgoritm, som anpassar sig själv på sådant sätt att mottagarna av t.ex. broadcast kommer att motta tillräckligt många paket för att kunna utföra en FEC-dekodning av datan i scenarion med både små och stora paketförluster. Algoritmen anpassar sig själv genom att ändra andelen av FEC-kodade redundanta paket baserat på kanalens nuvarande andel av paketförluster, med målet att optimera användandet av bandbredd och att förse mottagaren med uppspelbar data inom deadlines. Andelen FEC-kodade redundanta paket är beräknade så att datan ska kunna dekodas och spelas upp även under de förhållanden där störningsnivån i kanalen ökar under överföringen av datan. Simuleringar, gjorda i en trådlös kanal i vilken 10% av paketen förloras, visar att det med 1000 paket av den ursprungliga datan krävs ytterligare 12.6% redundanta paket per FEC-kodad enhet för att uppnå en sannolikhet för ett misslyckande av FEC-dekodningen < 1/1000