R. Mecozzi

Use of different chelating agents for heavy metal extraction from contaminated harbour sediment

This study presents the results of laboratory-scale experimental tests of contaminant extraction from marine sediment slurries. The sediment was collected in a harbour situated in a high-density industrial area, characterised by a high pollution level of heavy metals. The objective of this study was to investigate the effectiveness of selected chelating agents (rhamnolipids, EDDS, EDTA and citric acid) in heavy metal removal from contaminated sediments. To this aim, contamination of the sediment used in this experiment was artificially increased to reach final values of 1250 mg·kg−1 Cu and 2026 mg·kg−1 Pb. The investigated parameters during the washing tests were chelant concentration and overall washing time. To evaluate the sediment characteristics, COD and acid digestion were performed, whereas total organic carbon and heavy metal concentration were determined on the solutions extracted. The results show that the use of EDDS and EDTA gave good extraction efficiencies (up to 95%), unlike the lower removal rates achieved by using citric acid and rhamnolipids. In addition, major cations, mainly Fe and Ca, were found to be strong competitors with the target metals for metal–ligand complex formation.

Effect of modified Fenton treatment on the thermal behavior of contaminated harbor sediments

This study presents the results of experimental Fenton-like treatments conducted on marine sediment slurries (2g sediment vs. 20 ml liquid). The sediment was collected in a harbor situated in a high density industrial area, characterized by a great hydrocarbon C>12 and PAHs contamination. The investigated parameters were: the H(2)O(2) dose, the reagents pH and the effect of a phosphate salt and ferrous iron addition. To evaluate sediments characteristics COD, particle size, thermogravimetric and differential thermal analyses were performed under N(2) and O(2) atmosphere while dissolved organic carbon and COD analyses were performed on the filtrate. Results indicate that the treatment was able to change the organic matter to a less hydrophobic state, to destroy part of the organic carbon (up to 78% decrease of the 200-400 degrees C labile organic matter), to lower the COD of the sediment (60% COD removal maximum) and to increase the cumulated distribution undersize. In addition as the treated sediment showed easier-to-handle characteristics, reduced caking and lower aggregation capacity, the modified Fenton treatment could also be considered a pre-treatment of a successive thermal treatment.

Batch and column tests of metal mobilization in soil impacted by landfill leachate

The percolation of landfill leachate, even in the absence of a high concentration of specific pollutant, may induce a strong modification of soil chemical and physical characteristics, due to the alteration of the natural equilibrium between the aqueous phase and the soil matrix. As a result, a huge amount of cations can be solubilized, thus inducing groundwater pollution. In this work batch and column experiments of metal mobilization from a soil sampled down gradient of a municipal waste landfill in Northern Italy are presented. The experiments were initially performed in batch scale on soil slurries at different pH and Eh. Distilled water was used first and then a groundwater sampled down-gradient in the same site. Subsequently, to better simulate the aquifer conditions, 50 d column tests were performed on 15 kg of saturated soil. The concentrations of Fe, Mn, and Ni were evaluated when these selected environmental parameters were altered. Results indicated a greater release when acidic conditions were achieved, a positive effect in this case of the addition of an oxidant and a great Mn mobilization when negative redox potentials were established.

Effect of acidification and modified Fenton treatment on a contaminated harbour sediment

This study presents the results of laboratory experimental oxidation treatments conducted on marine sediments highly polluted with hydrocarbons. The purpose of the study was to compare the effect of a modified Fenton treatment conducted with acidified stabilised H2O2 with one of simple acidification with H2SO4 used as control to evaluate the potential of heavy metal mobilisation. The H2O2 initial concentration was 0.62 M and KH2PO4=1.15 g·L−1. To evaluate changes in the solid and liquid phase, chemical oxygen demand (COD), thermogravimetric analysis (TGA) and differential thermal analysis (DTA) under O2 atmosphere analyses were performed on the solid, while total organic carbon (TOC), COD, pH and Eh were measured on the liquid. Evaluation of the heavy metal mobilisation was performed using sequential extraction procedures. Results indicate that the treatment was able to change the organic matter to a less hydrophobic state, to destroy part of the carbon and to lower the COD of the sediment. In addition, the treated sediment showed easier-to handle characteristics, reduced caking and lower aggregation capacity. However some mobilisation of Cu occurred while the concentration of Fe lowered.

A comparison between different advanced oxidation processes for the remediation of PCP contaminated wastewaters

In this paper a comparison between different advanced oxidation processes (AOP), for the remediation of a wastewater contaminated with 100 mg/l of pentachlorophenol (PCP), is proposed. The AOP chosen were: Fenton or Fentonlike reactions in which the soluble iron catalyst salt was added as Fe(II) or Fe(III) or a mixture of Fe(II) and Fe(III), and ozonation. In the latter case the effects of the presence of a solid iron oxide (hematite) were also evaluated. For the Fenton’s reactions, the investigated parameters were: pH (from pH=1.5 to pH=5), reaction time, H2O2/PCP ratio (from 5/1 to 20/1), Fe/H2O2 ratio (from 0 to 2/1) and the effect of a H2O2 stabilizer: KH2PO4. The highest TOC removal (75%) was reached, using stabilized H2O2 and Fe(II), when H2O2/PCP=5/1 and Fe/H2O2=1/1; in this case, dechlorination was 96% and KH2PO4 increased H2O2 lifetime significantly. Fe(III) or the mixture of Fe(II) and Fe(III), proved to be more efficient than Fe(II) when H2O2/PCP<15/1 and Fe/H2O2<1/1. For ozonation the effects of pH and of the ratio between airflow and the solution’s volume, were investigated. The highest efficiencies (TOC removal=35%, Cl release=80%) were reached when O3=0.24 mg/l at pH=11; however diminishing the volume of treated solution, 47% TOC removal and stoichiometric Cl release were observed. The addition of hematite resulted in a slight increase of TOC removal and Cl release. By comparing the experimental results, among the tested AOP systems, Fenton’s reaction proved to be the most effective for PCP remediation.