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The impact of changes in physical-chemical conditions and selected treatments on the mobility of metals in sediment / water systems

By Dejan Krčmar

Abstract

U radu je ispitana distribucija metala u sistemu sediment/voda na najugroženijim vodotocima u AP Vojvodini. Na osnovu dobivenih podataka urađena je procena rizika na osnovu analize porne vode, kiselog volatilnog sulfida i simultano ekstrahovanih metala i sekvencijalne ekstrakcione procedure. Procena mobilnosti metala u sistemu sediment/voda određena je promenom fizičko-hemijskih uslova u realnom sistemu (vodotok) i u laboratorijskim uslovima. Ispitana je efikasnost in-situ (aeracijom sistema sediment/voda) i ex-situ remedijacije sedimenta metodama termičkog tretmana i solidifikacije/stabilizacije. Rezultati su ukazali da u svakom vodotoku i zaštićenoj zoni postoji lokacija u kojoj je sediment barem po jednom metalu klasifikovan (holandski sistem klasifikacije sedimenata) kao zagađen (klasa 3) ili izuzetno zagađen sediment (klasa 4). Generalno, kvalitet sedimenta manjih vodotoka (Krivaja, Nadela, Kudoš, Veliki Bački kanal i Begej) je lošiji u odnosu na ostale ispitivane vodotoke. Procena dostupnosti metala u sedimentu Velikog Bačkog kanala ukazala je da na svakom ispitivanom profilu postoji minimum jedan metal i jedna metoda koja definiše sediment kao visoko rizičan. Takođe je zaključeno da je sediment na delu od 2+000 do 4+900 km zagađeniji, jer postoji veći broj metala i metoda koji ga definišu kao visoko rizičnim. Ovako dobijeni rezultati ukazuju da nije dovoljan jednostavan i samo jedan pristup u oceni kvaliteta sedimenta i proceni rizika koji metali mogu da ispolje u akvatičnom ekosistemu. Ukazano je da pomeranje sedimenta (npr. otvaranja ustave), dovodi do promene fizičkohemijskih uslova u sistemu sediment/voda, resuspenzije i transporta sedimenta. Usled ovih promena povećava se dostupnost metala i dolazi do povećanja njihove koncentracije u vodenoj fazi čime se znatno povećava rizik i mogućnost ispoljavanja negativnih efekata na akvatični ekosistem. U slučaju resuspenzije sedimenta u sistemu sediment/voda pronađena je zavisnost između koncentracije metala u suspendovanim materijama i vodi od sadržaja određenih frakcija u suspendovanim materijama (sadržaj organskih materija i frakcije do 63 μm). Remedijacione tehnike često su ekonomski neprihvatljive zbog velike zapremine zagađenog sedimenta. Ukazano je da primena in-situ aeracije, omogućava smanjenje količine sedimenta (čime se smanjuju troškovi eventualno naknadnog tretmana sedimenta), a da je tretman solidifikacije/stabilizacije sedimenta sa glinom i termičke remedijacije zadovoljavjući sa aspekta izluživanja metala. Dobijeni rezultati izvedenih testova izluživanja ukazali su na moguću primenu ovih tretmana u pogledu rešavanja problema sedimenta koji je zagađen metalima, bilo u pogledu sigurnog odlaganja na deponiju ili u smislu njegove upotrebe kao dodatka pri proizvodnji građevinskog materijala (opeke), osnove za puteve, uređenje obale (nasipa) itd. Na taj način mogu se znatno umanjiti troškovi izmuljivanja i manipulacije kontaminiranog sedimenta, a sama remedijacija učiniti mnogo prihvatljivijomThis work investigates the distribution of metals in the sediment / water systems of the most endangered rivers in Vojvodina. Utilizing the data obtained, risk assessments are carried out based on analysis of pore water, acidic volatile sulphides and simultaneously extracted metals and sequential extraction procedure. The assessment of metal mobility in the sediment / water system is determined by the changing physical and chemical conditions in real systems (waterways) and under laboratory conditions. The effectiveness of in-situ (aeration of sediment / water) and ex-situ remediation of sediment by thermal treatment methods and solidification / stabilization are investigated. The results show that in each waterbody and protected area, certain locations have sediment which for at least one metal, is classified (by the Dutch system of sediment classification ) as polluted (class 3) or highly polluted (class 4). In general, the quality of sediment in smaller rivers (Krivaja, Nadela, Kudoš, Veliki Bački canal and Begej) is inferior to the other rivers studied. Assessment of the metals availability in the sediments of the Veliki Bački canal indicates that in each profile examined, at least one metal and one method defines the sediment as very hazardous. It is also shown that the sediment at the section from 2 +000 to 4 +900 km is the most polluted, with a number of metals and methods that define it as a high risk. The results indicate that it is inadequate to have a simple singular approach to sediment quality assessment and the assessment of the risks posed by metals detected in aquatic ecosystems. This work shows that sediment movement (e.g. from opening a sluice gate) leads to changes in the physical-chemical conditions of the sediment / water system, with resuspension and sediment transport. These changes increase metals availability and increase their concentrations in the aqueous phase, significantly increasing the posed risk and the possibility of adverse effects on aquatic ecosystems. In the case of sediment resuspension in the sediment / water system, a relationship was found between the concentration of metals in suspended matter and the concentration in the water for certain fractions of suspended matter (organic matter content and the fraction up to 63 μm). Remediation techniques are often not economically viable due to the large volume of contaminated sediments involved. It is shown that the implementation of in-situ aeration reduces the amount of sediment (which reduces the costs of subsequent sediment treatment), and that solidification / stabilization treatment with clay and thermal remediation results in satisfactory remediation with respect to metals leaching. Leaching test results show the potential of these treatments to solve the problem of sediments which are contaminated with metals, either in terms of safe disposal in landfill or in terms of its use as a supplement in the production of building materials (brick), as road foundation, or for river bank reinforcement (dams), etc.. Thus, the costs of dredging and manipulating contaminated sediments can be significantly reduced, making remediation itself much more applicable

Topics: sediment, metali, mobilnost, remedijacija sedimenta, solidifikacija/stabilizacija, aeracija, sediment, metals, mobility, sediment remediation, metal immobilization, solidification/stabilization, aeration
Publisher: Универзитет у Новом Саду, Природно-математички факултет
Year: 2010
OAI identifier: oai:nardus.mpn.gov.rs:123456789/5400
Provided by: Nardus
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