1,721,052 research outputs found
Enhanced heavy metal phytoextraction from marine dredged sediments comparing conventional chelating agents (citric acid and EDTA) with humic substances
No full textLaboratory experiments were carried out to examine the effects of chelating agents on heavy metal extraction from slightly contaminated dredged sediments from the port of Livorno (Italy). Ethylene diamine tetraacetate (EDTA), citric acid (CA) and humic substances (HS) were tested in two different concentrations each: 120 and 480, 500 and 2,000, 500 and 1,000 mg/l, respectively. Solubilisation of heavy metals (Cu and Zn) was observed for both EDTA and HS in the extraction kinetic experiments: 58% of the total Cu and 50% of the total Zn in the sediment were mobilised from the solid matrix using EDTA (480 mg/l) and 32% of the total Cu and 5% of the total Zn, using HS (1,000 mg/l). It was observed that solubilized metal levels were positively related to the chelating agent concentration. HS performance in the heavy metals mobilisation and phyto-toxicity tests was considered promising. HS represent an innovation in enhanced phytoextraction techniques: they can be considered an environmentally non-impacting bio-agronomic amendment. CA induced no significant effects on heavy metal mobilisation and it also negatively affects seed germination (Germination Index < 40%). Laboratory experiments with plants showed that none of the treatments significantly affected the biomass production and a trend could only be detected for the heavy metal uptake into shoots of Paspalum vaginatum sp. Transplantation of seashore paspalum is useful as a pre-treatment of contaminated dredged sediments, since it is a salt-tolerant species and it can be easily adaptable on a nutrient poor and fine textured medium
La fitoestrazione di metalli pesanti da sedimenti contaminati: basi di modellazione e riscontri sperimentali
No full textEfficiency assessment of a reed bed pilot plant (Phragmites australis) for sludge consolidation in Tuscany
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Phytoremediation of contaminated sediments: evaluation of agronomic properties and risk assessment
No full textThis study evaluates the possibility of reusing marine sediments in land management. The sediments, dredged from Livorno port (Italy), had previously been phytotreated, using a salt-tolerant plant cover and earthworms, with the aim of reducing the salt level and improving the texture and microbiology. In this study, sediments were investigated in order to: (1) test their capability to be used as a revitalised soil-like substrate (techno-soil), and (2) assess the human exposure risks associated with sediment management. Results obtained after 6 months of experiments performed with biological indicators composed of an association of graminae grass (Paspalum vaginatum), legumes (Trifolium alexandrinum) and earthworms (Eisenia foetida), showed that the substrate behaves like a natural soil capable of supporting biological life (total N=0.2%; total P=0.7%; EC=1.5mS center dot cm -1; -glucosidase=20 g PNP center dot g *h -1). It was also found that plants accumulate small amounts of heavy metals in shoot tissues (120mgZn center dot kg-1; 25mgCu center dot kg-1). In detail, risk analysis was performed considering: (1) sediment storage in a sealed disposal basin inside the Livorno port area, and (2) off-site phyto-remediation. The maximum hazard index was found for workers inside the port area, with values of 1.7 and 25 for dermal contact and vapour inhalation risks, respectively
Phytoremediation and Bio-physical Conditioning of Dredged Marine Sediments for Their Re-use in the Environment
No full textA meso-scale pilot plant was set up to test the efficiency of a phytoremediation technique applied to slightly contaminated marine sediments dredged from the port of Livorno (central Italy). The technique applied involved the use of plants (a grass species, Paspalum vaginatum and a shrub species, Tamarix gallica) and earthworms (Eisenia foetida sp.) in order to recreate an active ecosystem in which plants, micro- and macroorganisms could interact with each other through the rhizosphere, for the adsorption, extraction and/or degradation of pollutants. This system enables plants to grow in a fine textured and salt medium highly unsuitable for plant species, and a physical, chemical and biological amelioration of the matrix was observed at the end of the experimentation (after 9 months). The sediment was bio-physically pre-conditioned by mixing it with calcareous material from excavating activities (5:1 v/v) and applying green compost. The presence of microorganisms in the rhizosphere and the earthworms produced a reduction by about 50% of the initial total petroleum hydrocarbon content. The use of a natural chelator with phyto-hormonal properties (humic substances) showed their capability of forming stable complexes, especially with Pb, and their contribution as an agronomic fertiliser. The combined effect of the P. vaginatum and T. gallica in the extraction of heavy metals from the sediment showed promisingly high percentages of metal effectively extracted in comparison with its available fraction (e.g. available Ni = 6.2%; Ni extracted = 15.7%). The technique proposed could be promising for an operational re-use of dredged marine sediments for agricultural purposes, a suitable final destination for the great majority of these contaminated materials from rivers and harbour docks
Heavy metal distribution in a sediment phytoremediation system at pilot scale
Full text linkThe continuous stream of polluted sediments, dredged from harbors and water bodies in order to maintain the navigation, is a common practice, but the fate of these sediments is an issue recognized worldwide. This pilot case study evaluated the application of phytoremediation as sustainable management strategy for the decontamination of polluted dredged marine sediments. The synergic action of different plant species (Paspalum vaginatum; P. vaginatum + Spartium junceum and P. vaginatum + Tamarix gallica) and organic matter (compost) in removing both heavy metals (Cd, Ni, Zn, Pb and Cu) and total petroleum hydrocarbons, and in recovering the nutritive and biological sediment properties were evaluated. In addition to the detection of total metal removal efficiency, the chemical distribution of metals in the sediment phases (exchangeable, manganese and iron oxides, organic matter and residual minerals) was also measured in order to make a more realistic estimation of the phytoremediation efficiency for the sediment decontamination. Finally, a complete picture of the metal flux was obtained by investigating the metal mass-balance in the treated sediments. The results of metal content in the sediment phases showed that metal distribution was not uniform and each metal predominated in different fractions; the solubility of metals in the sediment in the decreasing order was: Cd>Zn>Cu>Pb>Ni. The higher proportion of Ni and Pb in the residual phase can be the reason of the lower translocation of these metals in the plant tissues. On the other hand, Cd, Zn and Cu were the metals most easily translocated in plant tissues, both aboveground and roots, confirming their higher availability for the plants.
The results of mass balance indicated that, at the end of the experimentation, a high content of metals were still found in the sediment. The greatest contribution in metal removal was attributed to a phytostabilization process at rhizosphere level followed by gravel and sand absorption. The capacity of rhizophere to precipitate heavy metals, could be considered as an alternative option for reducing the metal availability and, consequently, the toxicity in contaminated sediments
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