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Journal of Cleaner Production 86 (2015) 24e36

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Journal of Cleaner Production

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Review

A review of approaches and techniques used in aquatic contaminatedsediments: metal removal and stabilization by chemical andbiotechnological processes

Ata Akcil a, *, Ceren Erust a, Sevda Ozdemiroglu a, Viviana Fonti b, Francesca Beolchini b

a Mineral-Metal Recovery and Recycling Research Group, Mineral Processing Division, Department of Mining Engineering, Suleyman Demirel University,TR32260 Isparta, Turkeyb Department of Life and Environmental Sciences, Universit�a Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy

a r t i c l e i n f o

Article history:Received 19 April 2014Received in revised form1 August 2014Accepted 2 August 2014Available online 16 August 2014

Keywords:BioleachingContaminated sedimentsLeachingMetalRemoval

* Corresponding author.E-mail address: ataakcil@sdu.edu.tr (A. Akcil).

http://dx.doi.org/10.1016/j.jclepro.2014.08.0090959-6526/© 2014 Elsevier Ltd. All rights reserved.

a b s t r a c t

The contamination of aquatic sediments with metals is a widespread environmental problem. Coastalaquatic ecosystems with low hydrodynamics need to be periodically dredged in order to maintain thenavigation depth and facilitate sailing; consequently large volumes of contaminated sediments need tobe managed. Conventional remediation strategies include in-place sediment remediation strategies (e.g.in situ-capping) and relocation actions; in particular, landfill disposal and dumping at sea are still widelyapplied. Both this options are becoming unsustainable, due to problems associated with contaminanttransport pathways, the uncertainties about long-term stability under various environmental conditions,the limited space capacity, costs and environmental compatibility. Alternative approaches have receivedincreased attention; treatment and reuse of contaminated sediments is politically encouraged, but itsapplication is still very limited. Because of the potential human health and environmental impacts ofcontaminated sediment, different chemical treatments are conventionally applied for contaminatedsediments before reuse in other environmental settings. Environmentally friendly techniques developedfor soils and other environmental matrices have been investigated for applications with sediments.Biotechnological approaches are gaining increasing prominence in this field and they are often consid-ered as a promising strategy for the eventual treatment of contaminated sediments. In this paper anoverview of the main treatment strategies potentially available for sediment contaminated with metals isgiven, together with a brief overview of the issue associated with the problem of the sedimentmanagement.

© 2014 Elsevier Ltd. All rights reserved.

1. Introduction

The contamination of aquatic sediments is a global scale envi-ronmental problem, that national and international authorities andregulators have faced since the last two decades (F€orstner andApitz, 2007; Apitz, 2008). Human's activities and hydrographicalcharacteristics are responsible for the accumulation of high con-centrations of contaminants in estuaries, harbours, ports andcoastal marine zones (Pellegrini et al., 1999; Tanner et al., 2000). Inall the aquatic systems, the sediment is the compartment whereparticulate and dissolved substances in the water column (as wellas contaminants) tend to accumulate, due to scavenger agents and

adsorptive components (Mulligan et al., 2001a,b; Tabak et al., 2005;Peng et al., 2009).

The problem of contaminated sediment management is closelyrelated to the need for periodical dredging activities for the main-tenance of the navigational depth in ports and waterways, but alsofor remediation and flood management (F€orstner and Apitz, 2007;Rulkens, 2005; Agius and Porebski, 2008). This implies that verylarge volumes of contaminated sediment can be produced (e.g.around 100 to 200 million cubic metres per year in Europe, ac-cording to SedNet estimations) and need to be properly managed(Bortone et al., 2004). Landfill disposal, confined aquatic disposal ordumping at sea are still themost appliedmanagement strategies allover the world, despite they also offer several disadvantages (e.g.limited space capacity, costs, low or lack in sustainability andenvironmental compatibility; Bortone et al., 2004; Adriaens et al.,2006; Agius and Porebski, 2008). Among other management

A. Akcil et al. / Journal of Cleaner Production 86 (2015) 24e36 25

strategies, the “natural attenuation” has become unsustainable, dueto political and social reasons, as well as to a difficulty in quanti-fying contaminant transport events. Contaminated sedimentremediation deals with either the removal or the control of con-taminants from polluted environmental media in or under a landsite, to protect human health and the environment (Hou et al.,2014). Conventional management/remediation strategies ofpolluted sediment involve either in-place actions or relocation ac-tions. In the first group, those strategies that do not requiredredging operations are included, like natural recovery, that con-sists in allowing that natural attenuation processes achieve reme-diation objectives without human intervention, and in-situcapping, where the sediment is isolated by the environment byinert or reactive barriers. In the other cases, dredging is followed bydisposal in submerged or partially saturated facilities, landfilldisposal or dumping at sea (Bortone et al., 2004; Adriaens et al.,2006). All these options offer several disadvantages (Bortoneet al., 2004; Rulkens, 2005) and more environmentally sustain-able alternatives (Agius and Porebski, 2008; Apitz, 2008) areneeded. The application of in-situ capping and in-situ confinedaquatic disposal are limited because of the uncertainties aboutlong-term stability under various environmental conditions (Apitz,2008; Juwarkar et al., 2010; Liu et al., 2001).

The ‘beneficial use’ of dredged materials is highly encouraged.Dredged sediment can be relocated in the same water system itcame from, e.g. for maintenance of ditches and rivers. Nevertheless,such type of operations allows the relocation of small volumes andsediments are often too contaminated to be used as received. As aconsequence, the treatment for decreasing pollutant concentrationhas become part of sediment management process (Bortone et al.,2004). Today, a particular attention is paid to identify the mosteffective treatments for dredged contaminated sediments, withpurpose of beneficial reuse either in building industries or in bea-ches nourishment (Lee, 2000; Ahlf and F€orstner, 2001; US EPA,2005). Furthermore, also because of the potential human healthimpacts of contaminated sediment, a treatment may be requiredbefore reuse in another environmental setting (Barth et al., 2001).Many treatment strategies proposed for the remediation of metalcontaminated sediments derive from techniques developed forsoils, other environmental matrices or for solid urban and indus-trial wastes (Fig. 1). Nevertheless, the differences in the sedimentproperties compared to soils and solid wastes make the applicationvery limited and often characterized by very high costs and lowfeasibility. The only technique really used is the separation of thesandy fractions (less polluted), in order to minimize the

Fig. 1. Schematic photo of the general process on contaminated sediments.

contaminated volumes that require dumping. Biotechnologicalapproaches are object of an increasing attention, but in generalclean-up procedures for the removal/recovery of metals fromcontaminated sediments refer still to laboratory- or pilot-scalestudies. On the contrary, there is an urgent need for large scale,environmentally friendly and cost-feasible techniques, in order toallow sediment beneficial reuse. Cleaner production requiresresponsible environmental management and evaluating technol-ogy options (Radonji and Tominc, 2007). Researchers often need toevaluate different alternative designs for a given chemical andbiological process and this evaluation procedure might contem-plate the environmental impacts of each alternative. Therefore,depending on the chemical and biological process, the most rele-vant environmental aspects to be taken into account should beselected and researchers should evaluate the suitable treatments toobtain a final index that will serve as the basis for the final decision(Carvalho et al., 2014). Moreover, all studies demonstrate thatfurther research is needed to assess the overall sustainability of thedeveloped approaches, so that all the three aspects of triple bottomline are considered: social, economic and environmental (Kim et al.,2014).

The contamination in the sediment is often due to both organicand inorganic pollutants (mostly metals), but the latter are ofsustained and growing concern in the field of water quality man-agement: heavy metals are toxic, persistent and unlike organicpollutants they cannot be degraded (Zoumis et al., 2001; Sun et al.,2009). Very recently, development and implementation of tech-niques for metal removal from fresh water, estuarine and marinecontaminated sediments are gaining prominence not only as toolsfor the management of an environmental problem, but also as asecondary source of base valuable metals and raw materials formetallurgy and other industries. In some special cases, the sedi-ment of high priority areas can accumulate concentrations of basevaluable metals much higher than areas with high anthropogenicpressure: it has been hypothesized that the recovery of somemetals from the sediment of such sites could be economicallyfeasible (Fathollahzadeh et al., 2014). This change of perspectiveabout contaminated sediments could offer new strategies to solvethe dilemma of the management sediment with reduced environ-mental footprints. Another very important point in the debateabout dredged sediment management is the controversy betweenthe so-called “conventional” technologies (based on chemical orphysical approaches) and biotechnologies, which are based on theexploitation of microorganisms and/or their metabolic products.The former are usually considered as more efficient but also morecostly, while biological strategies would offer environmentallyfriendlymethods (especially when the contamination is mainly dueto hydrocarbons) but theywould require longer treatment time anduncertain efficiencies.

In this work, the newest findings about chemical and biologicaltechnologies for the removal/stabilization of metals from contam-inated sediments are summarized.

2. Sediment contamination with heavy metals

Heavy metals from natural and anthropogenic sources can entera natural aquatic system by a result of multiple processes: atmo-spheric deposition, erosion of the bed-rock minerals, in-stream ofindustrial effluents are just examples (Colacicco et al., 2010;Perrodin et al., 2012). As mentioned above, the sediment is thecompartment where heavy metals settle and accumulate, tillreaching concentrations very higher than in the overlying waters(Goldsmith et al., 2001; Warren and Haack, 2001). Salomons andStigliani (1995) postulated that the far less than 1% of the metalcontaminants (and other pollutants) are dissolved in the water,

A. Akcil et al. / Journal of Cleaner Production 86 (2015) 24e3626

while more than 99% are stored in the sediment. Very often,adsorbed heavy metals are not readily available for aquatic organ-isms but the variation in physical and chemical characteristics (i.e.,pH, salinity, redox potential etc.), natural resuspension phenomena,dredging activities and disposal actions may lead to the release ofthe heavy metals back to the aqueous phase, so that the sedimentmay become an important source of pollution (Singh et al., 2000;Jain, 2004; Juwarkar et al., 2010; Jain et al., 2012).

The sediment is a complex and heterogeneous matrix of manydifferent components and phases (including crystalline minerals,hydrous metal oxides, salts, biogenic calcareous particles andorganic substances (Usero et al., 1998; Brils, 2008) to which heavymetals associate by several mechanisms: particle surface absorp-tion, ion exchange, co-precipitation and complexationwith organicsubstances (Wang et al., 2010). Heavy metals deposited to thedifferent geochemical fractions in the sediment, with differentmobility. Since the composition of the sediment varies from site tosite (due to the geology, hydrography, local climate and socio-economic significance of the area (Preda and Cox, 2005; Perrodinet al., 2012), heavy metals distribute among various geochemicalphases in a site-specific way and with different grade of adsorptionand retention (Brils, 2008; Peng et al., 2008;Wang et al., 2010). As aconsequence, the determination of their concentrations does notprovide an accurate estimation of themagnitude of pollution and ofthe potential environmental impact (Chon et al., 2012; Okoro andFatoki, 2012). An indication of the potential bio-availability ofheavy metals is given indirectly by procedures of selective extrac-tions (Quevauviller, 1998; Gleyzes et al., 2002; Ure et al., 2006). Forthis reason a wide number of studies have been aimed at identi-fying the partitioning of metal contaminants in areas of interest,like ports, lakes, estuaries and marine coastal zones with highanthropogenic pressure.

Unlike organic pollutants, heavy metals cannot be degraded butare infinitely persistent and cannot be subjected to biological andchemical degradation processes. Heavy metals can just be trans-formed in more soluble/insoluble substances and/or in less toxicspecies. For this reason, many remediation strategies attempt toincrease either metal solubility (mobilization) or their stability,reducing their bioavailability (immobilization). Indeed, actionsaddresses to the speciation have consequences on solubility andtransport properties, which together determine the bio-availabilityand affect their toxicity (Tabak et al., 2005; Van Hullebusch et al.,2005).

3. Physicalechemical strategies for toxic metal removal andstabilization from the sediment

The majority of the remediation strategies aimed at movingheavy metals away from the sediment are based on phys-icalechemical strategies, often implemented in other field, likemining or soil remediation (US EPA, 2005). These technologiesattempt to transfer contaminants from the sediment particles tothe solution phase, for a beneficial use of cleaned sediment.

An analysis of the scientific literature has pointed out that thestrategies for the removal of heavymetals from the sediment can beroughly classified in 1) sediment washing techniques, aimed atsolubilizing metal contaminants by aqueous solutions of extractingchemical reagents or chelating agents; 2) electro-chemical treat-ments, where metal cations are separated by applying a electro-magnetic field; and 3) thermal treatments, in which dewatered orpartially dewatered sediment is treated by heat (Table 1). Due to thenature of water ecosystems, physicalechemical strategies can beapplied almost exclusively ex-situ/on-site.

Purely physical strategies (i.e., particle separationprocesses) findlarge application in soil remediation field (Dermont et al., 2008);

nevertheless, when applied to sediment treatment, the physicaltechniques often come down to a simple gravimetric pre-treatmentaimed at removing uncontaminated coarser fractions and atreducing the volume to be treated (Mulligan et al., 2001b). Indeed,heavy metal removal by particle separation processes is applicableonly when metal contaminants are under particulate forms(discrete particles or metal-bearing particles (Dermont et al., 2008),while in natural aquatic sediments heavymetals are mostly presentin sorbed forms (i.e., adsorbed or bound to the different geochem-ical phases) and their concentration levels are relatively low. Thecharacteristics of the sediment usually do not allow the use of thephysical approaches: usually, natural aquatic sediments have verypoor hydraulic characteristics and too high content in organicmatter or, anyway, the particle size is often too small for hydro-classifiers, gravity concentrators and centrifuges (Mulligan et al.,2001b; Bianchi et al., 2008). Flotation and ultrasonic-assistedextraction are physical techniques that appear to be feasible forex-situ treatment of sediments but their actual application is highlyaffected by the particle size, that determines the efficiency(Cauwenberg et al.,1998;Meegoda and Perera, 2001; Kyll€onen et al.,2004). However, physical properties of the sediment, like size,density, magnetism and surface hydrophobicity can be exploitedin combined physicalechemical strategies (Peng et al., 2009).

Physicalechemical stabilization strategies have also been pro-posed as a in-situ/ex-situ remediation solution for sedimentscontaminated with metals. In this case, the aim of the treatment isto reduce the mobility rather to extract metals. Mineral-basedamendments have been reported for contaminated soils (Xenidiset al., 2010) and, more recently, for contaminated sediments(Qian et al., 2009; Peng et al., 2009; Chiang et al., 2012). Among thevarious tested amendments, iron-bearing materials (e.g. zero-valent-iron, goethite, hematite, and ferrihydrite), other adsor-bents such as alumino-silicates (clays, zeolites) and phosphateminerals (e.g. apatite) were demonstrated efficient to stabilizemetals in polluted soils and sediments (Mamindy-Pajany et al.,2013). Mamindy-Pajany et al. (2013) have also upscaled the tech-nique from the laboratory to field application, to assess the effect ofhematite, zero-valent iron and zeolite on metal/semi-metal (As, Cd,Cu, Mo, Ni, and Zn) mobility in a marine sediment sample: theresults of the pilot-scale experiment showed that Fe containingminerals at 5% amendment rate were sufficient to efficiently sta-bilize several elements in the dredged marine sediments. Owing tonano-material with higher reactivity and sorption ability than thesame material of normal size, some nano-material (e.g. nano-hydroxiapatite, nanosized metal oxides) have also been veryrecently used as amendment to metal contaminated matrices(Zhang et al., 2010; He et al., 2013; Bolan et al., 2014).

3.1. Sediment washing

Sediment washing treatments are aimed to strip off contami-nants at the surface of sediment particles and to remove solublepollutants (Rulkens and Bruning, 2005); this involves two steps:the solubilization of metals and the removal of solubilized metalsby washing the sediment with water (L€oser et al., 2006, 2007). Thephysical action of high pressure water jets is combined with thechemical action of various type of additives, which enhance theperformance of sediment washing (Dahrazma and Mulligan, 2007;Di Palma andMecozzi, 2007; Peng et al., 2009): inorganic acids (e.g.nitric acid, sulphuric acid and hydrochloric acid), organic acids andchelating agents (e.g. acetic acid, citric acid, EDTA), surfactants (e.g.rhamnolipid).

Hydrochloric acid and nitric acid, and other inorganic acids, areknown as effective in extract heavy metals from soil/sediments(Dermont et al., 2008). In particular nitric acid could be

Table 1Research and development works on chemical treatments of contaminated sediments.

Strategy Site Contaminants Operating conditions Efficiencies of treatment References

Sediment washing Penrhyn Basin and Okinawa Trough Fe, Mn Mixtures of dilute hydrochloric acids (0.1e0.3 M) and hydrogen peroxide (1.5%)

83e100% Fe, %95e100 Mn Chen et al. (1996)

Cu, Zn with 0.25% surfactin from Bacillus subtilis at37 �C and pH control at 6.7

70% Cu, 22% Zn Mulligan et al. (1999)

Cu, Zn 70% of the copper with 0.1%surfactin/1%sodiumhydrooxide, %100 of the zinc with 4%sophorolipid/0.7% hydrochloric acid

70% Cu, 100%100 Zn Mulligan et al. (2001d)

Cu, Zn at 4% sophorolipid solution with 0.7%hydrochloric acid (pH 5.4)

~100% of the Cu and Zn Mulligan et al. (2001c)

Dredged sediments from the Italianport

Cd, Cu, Pb, Zn Chelating agents: Ethylene diamine tetraacetate(EDTA), nitrilotriacetic acid (NTA), citric acidand the S,S-isomer of theethylenediaminedisuccinic acid ([S,S]-EDDS)

78e86% Pb (with 0.02e0.2 M EDTA), 76% Cu(with 0.2 M EDTA), %65 Zn (using 0.2 M citricacid) and 55e65% Cd (with 0.02 M citric acid)

Polettini et al. (2006)

Dredged sediments from the Italianport

As, Cu, Zn, Pb Chelating agents: Ethylenediaminedisuccinicacid (EDDS), EDTA, NTA, citric acidRange of pH 5e8

As 81%, Cu 85%, Zn 37%, Pb 80% Polettini et al. (2007)

Dredged sediments from an Italianharbour in the Tirrenian Sea

Cu, Zn, Pb, Fe Chelating agents: EDTA and citric acid, end of144 h

70% Cu, 65% Zn, 98% Pb and 14% Fe using EDTA;10% Cu, 82% Zn, 27% Pb and 40% Fe using citricacid

Di Palma et al. (2012)

Weisse Elster River sediments Heavy metals (sumof Zn, Ni, Cu, Cd, Crand Pb)

With 624 mmol/kg sulphuric acid at 20 �C, on arotary shaker at 130 rpm for 1 h

>70% heavy metals L€oser et al. (2007)

Lachine Canal, Canada Cu, Zn, Ni With adding 1% sodium hydrooxide to 0.5%rhamnolipid

37% Cu, 13% Zn, 27% Ni Dahrazma and Mulligan(2007)

Port of Livorno (Italy) Cu, Zn EDTA, citric acid and humic substances (HS) 58% Cu, 50% Zn using EDTA (480 mg/l) and 32%Cu, 5% Zn, using HS (1000 mg/l), no significanteffects with citric acid

Bianchi et al. (2008)

Not available Zn, Hexachlorobenzene (HCB)

Used agents:EDTATritonX100

HCB 41%Zn 30.0%

Yuan et al. (2010)

Ancona port(Italy) Zn, Cr, Ni, As Complexing agents: citric acid, oxalic acids anddiluted sulphuric acid

About 50% for all metals Beolchini et al. (2013)

Namhang (NH), Bangeojin (BE), andHaengam (HA) bay sediments, SouthKorea)

Cu, Pb, Zn Used agents: EDTA 30%, 43%, and 9% of Cu; 48%, 66%, and 8% of Pb;31%, 60%, and 14% of Zn from NH, BE, and HAsediments, respectively

Yoo et al., 2013

Electro-chemicalprocess

Port of Haakonsvern,Bergen, Norway

Cu, Zn,Pb, Cd Complexing agents: citric acid, lactic acid, in pH7.5, lasting 14 days, and current strength 50 mA

67-87% Cu, 79e98% Cd, 90e97% Zn, 91e96% Pb Nystroem et al. (2005)

Port of Haakonsvern,Bergen, Norway

Cu, Zn,Pb, Cd Complexing agents: hydrochloric acid (0.6 M),sodium chloride (0.6 M) and distilled water(DW), ammonium citrate (0.5 M), lactic acid(1 M), and citric acid (1 M), lasting 14 days, andcurrent strength 50 mA

12% Cu and Pb, 10% Zn and 18% Cd using HCl; 6%Cu and Cd, 12% Zn and 5% Pb using NaCl; 48% Cu,80% Zn, 96% Pb and 98% Cd using DW; 30% Cu,40% Zn, 13 %Pb and 18% Cd using ammoniumcitrate; 70% Cu, 78% Zn, 90% Pb and 98% Cd usinglactic acid; 25%Cu and 20% Zn using citric acid

Nystroem et al. (2006)

Port of Sisimiut (Greenland) Cu, Cd pH ¼ 2d ¼ 1.2 mA/cm2.

in 28days

Cu from 97 to 16 mg/kgCd from 0.55 to 0.03 mg/kg

Ottosen et al. (2007)

Norway Cu, Pb, Zn, Cd pH < 2in 14 daysAerobicallyd ¼ 0.6 mA/cm2, 1 mA/cm2

1.4 mA/cm2

for d ¼ 1 mA/cm2

Cu 14%, Pb 65%,Zn 78%, Cd 98%

Kirkelund et al. (2009)

Chemical-termalprocess (Novosolprocess)

Dunkerque (France) and Calais (France) Cd, Cr, Cu, Pb, Zn e 97% Cd, 99% Cr, 98% Cu, 99% Pb, 99% Zn forsediment from Dunkerque; 99% Cd, 91% Cr, 94%Cu, 99% Pb, 98% Zn for sediment from Calais

Zoubeir et al. (2007)

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advantageous for its oxidizing properties and could effective indestroying more metaleorganic complexes than hydrochloric acid(Kim et al., 2010, 2011). A recent study conducted by Yoo et al., 2013has investigated inorganic acids and different extracting agents(sodium citrate and sodium chloride) as additives in washingcontaminated sediment coming from marine areas. Very interest-ingly, hydrochloric acid and nitric acid washing solution main-tained an acidic pH through the washing experiments, due verylikely to the particular characteristics of the sediment sample.However, hydrochloric acid showed a similar or lower heavy metalremoval efficiency than nitric acid. Since chloride is known to be avery important ligand for metal cations and since sea water con-tains 3.5% sodium chloride, that study has also investigated thepossibility to enhance metal solubilization by sodium chloride;nevertheless, complexation with chloride was not effective.Beolchini et al. (2013) have tested the efficiency of sulphuric acid aswell as organic acids in heavy metal removal from marinecontaminated sediments. Cr and Zn showed extraction efficienciesof about 34% while the highest mobilization of Ni was about 40%with sulphuric acid. In the case of As, the performance of the sul-phuric acid were 58%.

A number of chelators have been studied and applied to increasethe solubility of heavy metals, some of which are readily biode-gradable and others that are fairly recalcitrant (NABIR 2004).Ethylene diamine disuccinate (EDDS) is relatively biodegradable,while EDTA tends to persist in the environment for long (Gorbyet al. 1998; Bohuslavek et al. 2001). Chelators are also of interestin bioremediation by phytoextraction, since chelators promote themetal uptake by plants (Meers et al. 2005). Organic acid such ascitric, oxalic, gluconic and ascorbic acids can be applied as chemicalextractants, due to their ability to chelate heavy metals in solublecomplexes. These compounds are naturally produced by bacteriaand fungi andmay offer advantages, like low environmental impactand high removal efficiency (Di Palma and Mecozzi, 2007; Penget al., 2009). In a very recent study, has pointed out the efficiencyof heavy metal removal by organic acids is strongly dependentupon the metal partitioning in the sediment (Beolchini et al., 2013)and that citric acid may mobilized higher concentrations of metalcontaminants than oxalic acid (i.e., about 50%). Furthermore, anapproach of Life Cycle Assessment (LCA) was used to investigate theenvironmental impact (potential abiotic depletion, acidification,eutrophication, global warming, ozone layer depletion and photo-chemical ozone creation) and has revealed that the use of highlydiluted sulphuric acid is also a valid alternative, both in terms ofmobilization efficiency and environmental compatibility. Polettiniet al. (2006) have tested the efficiency of four chelating agents inheavymetal removal from amarine contaminated sediment: EDTA,NTA, citric acid and the [S,S]-EDDS. This study has demonstratedthat EDTA can remove Cd, Cu, Pb and Zn with the efficienciesranging between 65 and 86%. Among the investigated heavymetals, Pb exhibited the highest removal yield (up to about 78e86%in the case of 0.02 and 0.2 M EDTA), followed by Cu (76% with 0.2 MEDTA, 57% with 0.2 M EDDS) and Zn (65% with 0.2 M citric acid, 63%using 0.2 M EDTA). Cd showed the lowest solubilization efficiencieswhen compared with the other elements. In addition, Cd removalwas highly affected by thewashing time: after 8 h of treatments thesolubilization reached 55e65% values, with a decrease to <1% in a48 h washing treatment with 0.2 M NTA. Other studies have shownsimilar results for the application of EDTA on other sedimentsamples (see Table 1), while Bianchi et al. (2008) have reported nosignificant effects on heavy metal mobilization by washing withaqueous solutions of citric acid have. In addition, the same studyhas suggested that humic substances could be also used in sedi-ment washing treatments, especially for the removal of Cu (i.e., 38%Cu removal with 1000 mg/l humic substances). In general,

EDTA was a more efficient extraction agent compared to otheragents, because EDTA can form very stable complexes with metals(Begum et al., 2012; Yoo et al., 2013), although the removal effi-ciencies are also affected by the partitioning of metals in the sedi-ment (Begum et al., 2012; Beolchini et al., 2013). Di Palma andMecozzi (2007) reported that the extraction efficiencies of Cu andPb by EDTA washing/extraction from Italian port sediments werehigher than those by citric acid washing/extraction. Li et al. (2010)showed that zinc and lead in different sediment samples can bepartly dissolved by using solutions of citric acid, tartrate acid andmalic acid, with descending efficiencies. Therefore, the use oforganic acids as chelating agents appears to be suitable to solve theproblem of dredged sediments with moderate level ofcontamination.

Surfactants are another group of compounds that can be addedto washing solutions to enhance the solubilization, dispersal, anddesorption of metal contaminants from contaminated sediments(Edwards et al., 1994, 1991; Finnerty, 1994). Due to their ability toreduce the attractive forces at the liquid's surface, surfactants havebeen investigated in the removal of organic contaminant removal atfirst (Christofi and Ivshina, 2002; Dermont et al., 2008) but they canalso be advantageous for the treatment of metal contaminatedsediments (Mulligan et al., 2001a). In the last decade, microbialoriginated macromolecules with amphipathic characteristics,namely “biosurfactants” (e.g. rhamnolipids and sophorolipids), aregaining prominence in bioremediation field. These molecules arevery interesting due to their ion complexation activity. The mech-anism for heavy metal removal by biosurfactants involves the for-mation of aggregate of biosurfactant molecules into micelles(spherical bilayers, less than 50 nm in diameter): biosurfactantmolecules are sorbed onto sediment particle surface and com-plexate with the metals (ad-)sorbed to various sediment fractions,detach of metal contaminants and transfer them in the solutionphase as micelles (Tabak et al., 2005; Meers et al., 2005). It has beendemonstrated that a solution of 0.25% surfactin (a lipopeptideproduced by Bacillus subtilis) in 1% sodium hydroxide can remove15% of Cu and 6% of Zn from freshwater sediment samples(Mulligan et al., 1999). Rhamnolipid, a glycolipid biosurfactant, canbe applied without other additives and obtain the removal of up to37% of Cu, 13% of Zn, and 27% of Ni from sediments (Dahrazma andMulligan, 2007). Mulligan et al. (2001c) tested the efficiency ofbiosurfactants in heavy metal removal from marine contaminatedsediments. A singlewashingwith 0.5% rhamnolipid removed 65% ofthe Cu and 18% of the Zn, whereas 4% sophorolipid removed 25% ofthe Cu and 60% of the Zn. At the same time, sediment washingexperiments were performed at two surfactin concentrations withand without sodium hydroxide and hydrochloric acid for thesediment: Cu 70% and Zn 40% were solubilized by using 0.1% sur-factin and 1% sodium hydroxide, while 4% sophorolipid and 0.7%hydrochloric acid removed 100% of Cu and Zn. Such results indicateclearly that anionic biosurfactants are suitable extractants eventhough metals in the exchangeable fraction were very low(Mulligan et al., 2001c). In addition, the biodegradability of bio-surfactants may offer advantages in sediment remediation, butlong-term studies of the impacts on the ecosystem should be per-formed before full-scale applications. For instance, surfactin is anon-specific cytotoxic antibiotic and a massive application on fieldcould cause the depletion of ecological functions played by thebacterial community.

According to the scientific literature, sediment washing isappropriate for heavy metals weakly associated to the sedimentparticles, when hydroxides, oxides and carbonates are the mainphases involved (Ortega et al., 2008). The acid neutralizing capacityof the sediment is also a major constrain. The pH of the solutionaffects the ability of chelating agents (EDDS, EDTA, and NTA) to bind

A. Akcil et al. / Journal of Cleaner Production 86 (2015) 24e36 29

heavy metals as well the speciation of metals into soluble/insolubleforms (Bordas and Bourg, 1998). The treatment with inorganic acidmay be not appropriate for very calcareous sediments, since pro-tons would be consumed by dissolution of calcite and carbonates(Fonti et al., 2013). Additionally, sediment washing appears to bemore appropriate for sediment with coarse particles (Peng et al.,2009) and this is an important limitation for this technique:dredged materials are usually fine and, anyway, the finest particlesare more contaminated, due to the high surface available foradsorption. For these reasons, extraction tests should be conductedto determine optimal conditions (chemical type and dosage, con-tact time, agitation, temperature and extraction steps to meetregulatory requirements (Di Palma and Ferrantelli, 2005).

Techniques of sediment washing imply the potential release ofchemicals in the environment or the management of liquids con-taining contaminants and extractants. Heavy metals can be moremobile and potentially more toxic, due to their speciation as che-latoremetal complex. It follows that the development of full scalestrategies of sediment washing is based on the selection of chem-icals with characteristics of low environmental impact (lowtoxicity, high bio-degradability) and high removal efficiency.

3.2. Electro-chemical separation

Electro-chemical separation involves the application of static oralterning electro-magnetic field. A cathode and an anode areimbedded in the contaminated sediment in wet conditions and alow intensity electric current is applied. Anions move towards thepositive electrode and cations towards the negative one (Dermontet al., 2008). Heavy metals as soluble ions and bound to oxides,hydroxides and carbonates can be removed by this method butother non-ionic components can be transported due to the flow(Mulligan et al., 2001a; Ottosen et al., 2007; Kirkelund et al., 2009).The process can be used to recover ions from soils, muds, dredgedsediments and other materials. Wet high intensity magnetismseparation (WHIMS) has been successfully applied on soils toremove Cr, Cu, Ni, Pb, and Zn (Rikers et al., 1998; Sierra et al., 2014).Once the remediation process is over, the contaminants that areaccumulated at the electrodes can be extracted by electroplating,precipitation/co-precipitation, pumping water near the electrodes,complexing with ion-exchange resins or other methods (Krishnaet al., 2001). The recovery of heavy metals could improve the pro-cess economics to achieve partial cost-effectiveness.

An electro-chemical process example was applied on sedimentsamples from Haakonsvern (Norway), where different leachingagents were used (hydrochloric acid, sodium chloride, citric acid,lactic acid). The highest removal efficiencies were obtained work-ing with dry sediment (L/S 8) and with 70 mA applied current, for14 days: 67e87% Cu, 79e98% Cd, 90e97% Zn, and 91e96% Pb wereremoved (Nystroem et al., 2005). In subsequent 14 day electrodi-alytic experiment by Nystroem et al. (2006), lactic acid was used asdesorbing agent with efficiencies of 70, 78, 90 and 98% for Cd, Cu,Zn and Pb, respectively, in conditions of 50 mA constant current.

3.3. Thermal treatments

Treating contaminated sediment by heat (after a dewateringpretreatment) is an advantageous strategy since the organic pol-lutants are completely destroyed by an oxidation due to the hightemperatures useful strategy for destroying organic pollutants.During this type of treatment, many heavy metals are in immobi-lized in the sediment matrix but other metals, like Hg, As and Cd,can be volatilized or became more leachable, like As, Mo and V dueto the formation of oxyanions. Either desorption or immobilizationcan be obtained by working at different temperature range

(Rulkens, 2005). Temperature between 100 and 500 �C is used toremove pollutants by the thermal desorption. In this way, pollut-ants are not destroyed but vaporized from the sediment togetherwith water and then concentrated in a small volume. This processcan be used to remove low molecular hydrocarbons and polycyclicaromatic hydrocarbons (PAHs) to prepare the sediment for furthertreatment; nevertheless, the presence of unstable volatile pollut-ants such as chlorinated hydrocarbons special equipment andconditions can be necessary to prevent formation of dioxins andfurans; residue can be treated subsequently. At higher tempera-tures inorganic contaminant in the sediment can be immobilizedby melting (vitrification) and organic pollutants can be completelydestructed. Complete destruction of the volatilized organic com-pounds and its destruction products often requires an after-burningprocess operating at appropriate conditions. Depending on theprocess conditions and type of sediment the slag can be suitable asbuilding material.

There are several commercially available thermal chemicaltreatment processes. The X-Trax process is a heat treatment withrelatively low temperatures (400e650 �C) compared to conven-tional chemicalethermal processes. The X-Trax process has beenused in experiments for the removal of organic matter andmercuryin soils, sludges and sediments (Mulligan et al., 2001a). CementLock, developed by the Institute of Gas Technology (IGT), has beenused for dredged sediment in the New York/New Jersey Harbour(Stern et al., 1998). The sediment containedmetal contamination byAs, Cd, Cr, Pb, Hg, Se and Ag and was mixed with lime into a rotarykiln reactor smelter at 1200e1600 �C. The sediment passed thetoxicity characteristic leaching procedure (TCLP) for all metals.Volatilized heavy metals and acid gases and other combustionproducts were treated in the offgas by filtration to remove partic-ulates and activate carbon to remove heavy metals gas (Rodsandand Acar, 1995). On the contrary, the X-Trax™ process uses a rela-tively low-temperature process for removal of organics and mer-cury from soils, sludges, and sediments, which was developed byChemical Waste Management Inc. The contaminated sediment isfed into a rotary dryer (400e650 �C). Hg was then desorbed. Oxideand sulfide forms were reduced to Hg. Nitrogen carries the vapoursto the gas treatment systems. Approximately 10%e30% of the Hg isremoved by the dust scrubber (Palmer, 1996). The Novosol® processby the Solvay Company is a patented chemical-thermal treatmentin which phosphatation and calcination are combined. In the firststage, heavy metals are stabilized by mixing sediments withphosphoric acid (2e3.5%) in a tubular reactor; in the presence ofcalcite, the addition of phosphoric acid allows the formation ofcalcium phosphates minerals (e.g. hydroxyapatite). In the secondstage, the phosphated sediments is calcining at high temperature(650 C) in order to break down the organic contaminants (poly-cyclic aromatic hydrocarbons, dioxins and pesticides). With thisprocess the polluted sediment becomes inert and can be used asraw material for brick making in construction industries (Agostiniet al., 2005; Lafhaj et al., 2007).

4. Biological strategies for heavy metal removal fromcontaminated sediments

Bioremediation strategies have been recently considered as apromising answer to the problem of contaminated sediment(Guevara-Riba et al., 2004; Tabak et al., 2005). As explained above,metal contaminants are not absolutely fixed in the sediment; un-like organic pollutants, they cannot be degraded since they are notsubjected to biological and chemical degradation processes occur-ring in the sediment but can be mobilized by changing theirspeciation (Van Hullebusch et al., 2005; Peng et al., 2009). Biore-mediation strategies for heavy metal removal from sediments

Fig. 2. Schematic comparison of the thiosulfate (A) and polysulfide (B) mechanisms in(bio)leaching of metal sulfides. MS: metal sulfides, M2þ: metal cations, Af: Acid-ithiobacillus ferrooxidans, At: Acidithiobacillus thiooxidans and Lf: Leptospirillum fer-rooxidans (Schippers and Sand, 1999; Schippers et al., 1996; Rohwerder et al., 2003).

A. Akcil et al. / Journal of Cleaner Production 86 (2015) 24e3630

attempt to exploit natural biological processes leading to bio-immobilization of metals that are components of natural biogeo-chemical cycles (White et al., 1997). In this group of remediationtechniques, the metabolic products of key microorganisms are thedriving force in dissolving metal species into aqueous solutions(Erust et al., 2013). Indeed, metal mobilization can bemediated by arange of microorganisms and processes, including autotrophic andheterotrophic leaching, chelation by microbial metabolites andmethylation.

Microorganisms applied in bioremediation may be endogenousin the contaminated area or they may be isolated from differentsystems and brought to the contaminated site. In the first case,microorganisms are already adapted at the environmental condi-tions and bioremediation strategies consist basically into stimulateand exploit the microbial function leading to the bioremediationobjectives (Biostimulation). In the second one, microorganisms arechosen on the basis of their metabolic properties, including theirtolerance of high concentration of metals and other contaminants,and added to contaminated sediments to enhance bio-transformation (Bioaugmentation). This could require changes inthe natural environmental conditions (e.g. concentration of oxygen,pH, etc.) to favour microbial activity. Bioremediation strategies canbe applied directly in the contaminated site, without movingsediment (“in-situ”), in the contaminated area but with small scalemovimentation of the sediment to treat (“on site” or “in-place”), orin areas or reactors designed on purpose for sediment treatment,that require removal and transportation.

Leaching of metals mediated by microorganisms (i.e., Bio-leaching) is a well-established technology in mining; in particular,non-phylogenetic group of acidophilic, aerobic and chemo-lithotrophic strains, known as Fe/S oxidizing bacteria are exploitedfor large-scale operations of metal recovery from ores. In biore-mediation process in which elemental sulphur (S0) is used as asubstrate, the rate of microbial sulphur oxidation is a limiting stepgoverning the efficiency of the process (Seidel et al., 2002, 2006;Ilyas et al., 2014).

The main products of the metabolism of such strains are sul-phuric acid (and a list of sulphur oxidation intermediates) and ferricions. The most known and studied strains in this group are Acid-ithiobacillus ferrooxidans, At. thiooxidans and Leptospirillum fer-rooxidans, but many other species are known, today (Dopson andJohnson, 2012; Johnson, 2012) In addition, iron-oxidizing andsulphur oxidizing strains among Archaea have been identified, sothe microbial diversity in bioleaching and bio-oxidation processesis much wider than previously hypothesized (Brierley and Brierley,2013; Vera et al., 2013). The solubilization of metal sulfides by Fe/Soxidizing bacteria has long been described as a process based ontwo independent mechanisms: a ‘direct mechanism’ (i.e., the directenzymatic oxidation of the sulphurmoiety of themetal sulfide) andan ‘indirect mechanism’ (i.e., the non-enzymatic metal sulfideoxidation by Fe(III) ions combined with enzymatic (re)-oxidation ofthe resulting Fe(II) ions; Sand et al., 2001). However, it is nowgenerally accepted that the ‘direct mechanism’ of biological metalsulfide oxidation does not exist. Conversely, the true effectors formetal solubilization from ores are the products of bacterial meta-bolism, previously known as the ‘indirect mechanism’ (Rohwerderet al., 2003). According to Rohwerder and Sand (2007), the Fe/Soxidizing bacteria approach the mineral surface by creating a bio-film, in a contact sub-mechanism), while some planktonic bacteriacells remain floating in the bulk solution (non-contact sub-mechanism). In either case, the dissolution of metal-bearing min-erals can follow two different reaction pathways, which depend onthe acid-solubility of the sulfides involved: acid-insoluble metalsulfides (e.g. pyrite, molybdenite, tungstenite) are exclusivelyoxidized via electron extraction (the thiosulfate pathway), while

acid-soluble metal sulfides (e.g. sphalerite, galena, arsenopyrite,chalcopyrite, hauerite) are dissolved by the combined actions ofFe(III) oxidative attack and proton attack (the ‘polysulfide pathway’,Schippers and Sand, 1999). These two pathways are simplified inFig. 2.

Inorganic source of reduced sulphur or elemental sulphur and/or ferrous iron, can be used as energy source to favour the microbialactivity. The use of pyrite as an energy source in bioleachingexperiment for heavy metal solubilization form marine sedimentshas also been reported (Wong et al., 2004).

As bioleaching consists of a combination of proton attack andoxidation processes, sediments with high contents of metal sul-phides and other reduced forms of metals should be particularlysuitable for clean-up strategies based on bacterial leaching.Nevertheless, a very recent study have demonstrated that metalsin the other geochemical fractions can be solubilized by bio-leaching, too (Fonti et al., 2013). On the contrary, the concentrationof the sediment to be treated and its content in carbonate andparticulate organic matter are among the main constraints to beconsidered.

Table 2 reports some of the main scientific papers about bio-logical strategies for metal removal from contaminated sediments.The majority of the studies were performed at laboratory scale andno feasibility assessment was carried out, with few exceptions. Intheir works on river sediment samples, Seidel et al. (1998) andL€oser et al. (2007) were among the first scientists to show that S-oxidizing bacteria can be applied for sediment remediation, withmetal removal efficiencies higher than those obtained by chemicalleaching with H2SO4. Further studies have investigated factorsaffecting bioleaching efficiencies: sediment concentration in theprocess, microorganisms involved, type and concentrations ofgrowth substrata for Fe/S oxidizing bacteria, initial pH, T and so on.Some studies have used synthetic sediment samples, spiked withmetal sulfides. For instance, in their study Kim et al. (2005) havereported solubilization efficiencies of 80% and 60% for Cd and Ni,respectively, on artificially contaminated sediment. Control testsshowed that their results were significantly affected by the pres-ence of Acidithiobacillus ferrooxidans. Studies have also pointed outthat a bacterial adaptation to the sediment is needed (Beolchiniet al., 2012).

Table 2Research and development works on biohydrometallurgical treatments of contaminated sediments.

Microbe used Efficiencies of treatment (%) Temperature(�C)

Time Scale/Type of reactor Adjusted pH References

Sulphur-oxidizing bacteria Zn, Cd, Mn, Co and Ni 61e81%, Cu 21%

35 21d Batch reactor 2.8 Seidel et al. (1998)

Acidithiobacillus thiooxidans andAcidithiobacillus thioparus

Cu 95e96%, Zn 72e81%, Pb16e60%, Ni 10e47%

30 5h Completely mixedbatch (CMB) reactor

2e4 (Acidithiobacillusthiooxidans)5e7 (Acidithiobacillusthioparus)

Chen et al. (2003)

Acidithiobacillus thiooxidans andAcidithiobacillus ferrooxidans

Ni, Zn, Cu and Cr >90%, Pb60.4%

37 18d Continuous reactor <2.0 Tsai et al. (2003)

Acidithiobacillus thiooxidans andAcidithiobacillus ferrooxidans

Cu 97e99%, Zn 96e98%,Mn 62e68%, Ni 73e87% andPb 31e50%

30 8d Air-lift bioreactor <4.0 Chen and Lin (2004)

Acidithiobacillus ferrooxidans Cd 80%, Ni 60% 22 ± 2 5d Batch reactor 2.5 Kim et al. (2005)Acidithiobacillus ferrooxidans Zn, Cd, Ni 70e90%, Me 67% 30 28d Fixed-bed bioreactor 4 Seidel et al. (2006)Fungal versus bacterial,

Acidithiobacillus and LeptospirillumMn 77%, Zn 44%, Cu 12%, Cd1.6%, Pb <2%

43d Air-lift bioreactors 2.7 Sabra et al. (2011)

Acidithiobacillus thiooxidans andAcidithiobacillus ferrooxidans

Cr, Cu and Zn >80%, Pb 63% 30 48d Bioreactor 2e3.5 Akinci and Guven(2011)

Autotrophic Fe/S-oxidising bacteria(Acidithiobacillus ferrooxidans,Acidithiobacillus thiooxidans,Leptospirillum ferrooxidans) andheterotrophic Fe-reducing bacteria(Acidiphilium cryptum)

Cr >88%, Zn and Ni >40% 25 14d Bioreactor 2.0 Beolchini et al.(2013)

Table 3Descriptions of sediment remediation technologies (Reis et al., 2007).

In situ technologiesPhysical/Chemical Treatments Capping

Containment BarriersSolidification/StabilizationConfined Disposal Facility

Ex Situ TechnologiesBiological Treatments Bioslurry

Containment LandComposting

Physical/Chemical Treatments ChelationOxidationDechlorinationSolidification/StabilizationBasic Extractive SludgeSolvent ExtractionCarver-Greenfield ProcessSoil WashingContainment Barriers

Thermal Treatments Thermal DestructionTechnologies

IncinerationPyrolysisHigh-Pressure OxidationVitrification

Thermal DesorptionTechnologies

X*TRAX SystemDesorption and VaporizationExtractionHigh-Temperature Thermal SystemLow-Temperature Thermal SystemLow-Temperature Thermal AerationAnaerobic Thermal Processor

A. Akcil et al. / Journal of Cleaner Production 86 (2015) 24e36 31

The real application of biological strategies for metal removalfrom sediment is complicated by various problems, which are stillunsolved. The required time for pilot scale studies, research,development and technology commercialization is estimated to be10 years at least, or even more (Brierley, 2010). Anyway, researchand development time is not the sole problem and other aspectsneed to be faced by the scientific community and authorities. Ouranalysis of the scientific literature suggests that sediment biore-mediation technologies have very site-specific effects. Therefore,nearly every process that is developed it does require on-sitepiloting and, perhaps, even large-scale demonstrations, which arevery costly and time-consuming. Furthermore, competitivenesswith consolidated chemical and thermal processes make biotech-nological processes not always preferable. In addition, the coststhat may occur during the commercialization of new bio-technologies should be examined in detail, because they probablyrequire a high capital investment (Brierley, 2010; Gahan et al.,2012). Notwithstanding, biohydrometallurgical strategies areconsidered as environmentally friendly and it is thought that theywill make significant contributions to research and development inthe future (Watling, 2006; Gahan et al., 2012).

Biosorption and bioaccumulation processes could provide analternative solution for the remediation of sediments contaminatedwith metals. Biosorption is a physicalechemical and metabolically-independent process based on a variety of interactions amongbiological material and metal, including adsorption, ion exchange,surface complexation and precipitation (Veglio’ and Beolchini,1997; Vegli�o et al., 1997, 2000). More recently, a wider definitionof the term “biosorption” is used, including both passive and activeprocesses in case of living biomass and often referred to as bio-accumulation (Valls and de Lorenzo, 2002; Fomina and Gadd,2014). A wide variety of active and inactive organisms have beenemployed as biosorbents to sequester metal ions from aqueousenvironments. Over the past two decades, much effort has beendevoted into identifying readily available non-living biomasscapable of effectively removing toxic metals/semimetals. Thesebiosorbents typically include algae (Pennesi et al., 2012; He andChen, 2014), fungi (Gadd, 2008), bacteria (Vijayaraghavan andYun, 2008), and agricultural waste (Vegli�o et al., 2003).

However, most of the available research papers and patents(Fomina and Gadd, 2014) deal with biosorption applied to watersystems (e.g. industrial wastewater, groundwater), while literaturelacks of studies addressing biosorption as a bioremediation strategyfor sediments. Indeed, few examples are available were fungalstrains are reported to successfully stabilize metals in soils (e.g.copper and cadmium) (Li et al., 2014) and biosorption is ratherreported as one of the processes responsible for metal stabilizationwithin phytoremediation strategies (Mani and Kumar, 2014).

Also organic amendments (e.g. compost), that are low in metal/semi-metal can be used as a sink for reducing the bioavailability of

Table 4Main advantages and disadvantages of in situ treatment (Renholds, 1998).

Advantages Disadvantages

Relatively inexpensive Lack of process controlUsually results in less resuspension

of contaminated sediments thanremoval technologies

Poor environmental conditionsfor treatment

Treats, does not contain, contaminants Lower treatment efficiency thanex situ treatment

Reduces handling and exposureof sediments

Limited experience with insitu treatments

A. Akcil et al. / Journal of Cleaner Production 86 (2015) 24e3632

metal semi-metals in contaminated soils and sediments throughtheir effect on the adsorption, complexation, reduction and vola-tilization (Kumpiene et al., 2008; Park et al., 2011). Most of theresearch work has been performed on soils contaminated withcopper (Farrel et al., 2010; Soler-Rovira et al., 2010; Beesley et al.,2014) arsenic (Farrel et al., 2010; Beesley et al., 2014) cadmium(Beesley et al., 2014), lead (Farrel et al., 2010; Beesley et al., 2014),zinc (Farrel et al., 2010) and it has been poorly addressed to sedi-ment remediation. Nevertheless, taking into account both the highpotential of this approach in reducing metal toxicity and possibledifferences in the responses of soils and sediments, it is consideredas strategic to address further research work to assess the effect ofcompost on the remediation of sediments contaminated withmetals.

5. Technological application and patent analysis

Potentially available remediation options for contaminatedsediments have been summarized by Reis et al. (2007) and they areshown in Table 3. Themajority of the techniques reported in Table 3are based on the ex-situ/on-site approaches. Indeed, periodicaldredging activities are requested for the preservation of navigationdepths in ports. Consequently huge amounts of contaminatedsediments need an ex-situ/on site treatment and cannot be left inplace, either for their high contamination or for the port mainte-nance activities. Nevertheless, in the case of moderate contami-nation and out of port sites, in-situ strategies would be preferable,since they could decrease sediment handling and, consequently,the exposure of contaminants caused by resuspension/volatiliza-tion processes (Table 4).

Table 5The main patents related to in situ treatment of sediments contaminated with metals (E

Year Code Title

2011 WO2011061300 Method for the cleanup of contaminated site/sediments2013 US20131930662009 JP2009074301 Noxious chemical substance diffusion prevention mat2009 WO2009038476 Product and method for creating an active capping layer

surfaces of contaminate sediments2008 WO2008070293 Low-impact delivery system for in-situ treatment of con

sediment2009 US20091039832008 KR20080099092 Non-dredging reactive in-situ sediment treatment facilit

process, and clean-up remediation of river, lake, and resthis

2006 US2006051162 Rotating containment tool for contaminated sediment rein an aqueous environment

2003 KR20030097120 Sediment remediation agent and in situ remediation metsediment using the same

2002 CA2441259 Environmental remediation method and apparatus2005 US20050460552002 US2002151241 Reactive geocomposite for remediating contaminated se2000 FR2781702 Rehabilitation of polluted soils, sludges and sediments b

introducing hydrolysate of marine algae1993 US5256001 Cylindrical system for in-situ treatment of underwater

contaminated material1993 WO9301899 System for in-situ treatment of underwater contaminate

There are currently several patents existing at internationallevel related to technologies of contaminated soils which, with thenecessary precautions, can also be applied to sedimentary matrix.As reported above, since the efficiency of the treatment changes asa function of the characteristics of the contaminated matrix, pro-cesses developed for the remediation of soils are not alwayseffective to achieve adequate quality standards when applied todredging sediment (US EPA, 1993; Rulkens and Bruning, 2005).Consequently, a number of processes specific for management/remediation of contaminated sediment have been patented. Thesepatents deal with both in-situ (Table 5) and ex-situ application(Table 6), in the case of contaminationwith metals. The aim of suchpatents is to offer sustainable alternatives to landfill and dumpingat sea. For the in situ application, most of patents deal with activecapping of the contaminated site, with stabilization through spe-cific sorbents, with solidification/stabilization by injection ofcementitious materials and, more recently, with biotechnologicalapproaches addressed at stimulating microbial communities. In thecase of the ex situ/on site application, targeted technologies arebased on thermal treatments, on sediment washing, eventuallyintegrated with advanced oxidation in the case of mixed contami-nation, again on stabilization with sorbents, and, last, but not least,on biotechnological approaches (bioaugmented slurry bioreactorsand phytoremediation). As a whole, the temporal evolution ofpatents suggest that a shift is in progress, from the high impactthermal processes and cement solidification towards the moreenvironmentally friendly approaches (chemical and biologicaltreatments).

6. Strategies and future recommendations

The management of contaminated sediment and dredged ma-terials is an environmental problem of major concern. A widenumber of studies have addressed such problem, with various ap-proaches (physical, chemical, biological) and application (in situ, exsitu/on site). As a whole, the present work reviews the most recentapproaches based on chemical and biotechnological processes tar-geted at the treatment of sediments contaminated with metals.Chemical and biological processes should focus on understandinghow the characteristics of the sediment and of the metal contami-nation affect the efficiency of remediation strategies; furthermore,

uropean Patent Office, 2014).

Description

Anaerobic mesophilic bacteria for the remediation of sitescontaminated with metals and polychlorinated biphenylsActive capping layer

across Active capping layer

taminate Mix of sorbent material, bentonite and sand

y andervoir by

Injection apparatus for solutions targeted at decontamination

mediation Cylindrical rotating equipment that contains the contaminatedsediments and allows the treatment through specific reagents

hod of Sorbent material enriched with electron acceptors

Coating by a thin layer of gas microbubbles

diments Active capping layery Sorbent material, consisting of a hydrolysate of marine algae

Cylindrical equipment that contains the contaminated sedimentsand allows the injection of cementitious materials

d material Injection of cementitious materials

Table 6The main patents related to ex situ treatment of sediments contaminated with metals (European Patent Office, 2014).

Year Code Title Description

2014 CN103496833 Bottom sediment heavy metal pollution modularized ex situtreatment method

Stabilization/solidification with cement and lime

2011 KR20110008515 Stabilization method of heavy metal contaminated dredgedsediments

Sorption onto apatite

2008 EP1914017 Method for treatment of contaminated soils and sediment Stabilization/solidification followed by thermal desorption, formixed contamination

2007 SI22156 Cleaning of soil and sediments by using advanced oxidation Sediment washing that integrates advanced oxidation withchelating agents, for mixed contamination2007 EP1787734 The use of advanced oxidation processes for remediation of heavy

metals and radionuclides contaminated soils and sediments in aclosed process loop

2004 KR20040087861 Sediment treatment method using constructed wetland and systemthereof

Phytoremediation

2004 JP2004276019 Treatment method for contaminated mud and other contaminateobject to be treated

Sorption onto stone dust and bentonite

2003 KR20030062988 Remediation and dewatering of dredged slurry and mine tailingwith vacuum method and electrokinetic phenomenon

Electrokinetic remediation

2002 KR20020013016 Biological remediation method of contaminated sediment/soil andequipment thereof

Aerobic slurry bioreactor, inoculated with microbial consortia(Bacillus sp., Pseudomonas sp. and Acinetobacter sp) and a chemicalsurfactant

2002 CA2353225 Process for extraction of metals Sediment washing2001 WO0115823 Apparatus and method for removing contaminants from fine

grained soil, clay and siltSediment washing

2001 US6010624 Contaminated sediment treatment process Stabilization/solidification with cement and sorbents2001 KR20010054440 Contaminant sediment treatment method using low temperature

heat treatment and calcium compoundThermal treatment at 600 �C after addition of calcium carbonate

1999 US5868940 Method for on-site remediation of contaminated natural resourcesand fabrication of construction products

Thermal treatment and production of building materials

1994 US5292456 Waste site reclamation with recovery of radionuclides and metals Sediment washing followed by photolysis

A. Akcil et al. / Journal of Cleaner Production 86 (2015) 24e36 33

the analysis of the environmental impact should not be overlooked,also for the strategies widely considered as environmentallyfriendly by the scientific community. Literature and patent analysishas evidenced that an evolution is in progress towards environ-mentally sustainable solutions: from high impact (thermal treat-ment and cementification) to low impact (chemical and biological)processes. In the future, full scale applications for sedimentdecontamination are expected to be found; nevertheless, a newthinking is necessary for a really sustainable management ofdredged sediments, in order to consider such solid matrix as aresource rather than an environmental problem, taking into accountits richness in oligoelements, microelements and organic nutrients.

The cost of remediation application will depends on severalfactors including the needs for mixing the mineral with thecontaminated sediment, and whether the application and mixturescan be accomplished on the wet contaminated sediment or need tobe performed after pre-treatments. The high activity of the heavymetals and the competitive price of this techniques (in comparisonwith others available disposal and remediation technologies) makethe proposed technology a sustainable solution for in shore man-agement of contaminated sediments. A large-scale study will pro-vide valuable information to address concerns about the full cost ofremediation application and long-term accumulation of heavymetals.

Acknowledgements

This collaborative research was based on the results of bilateralcontacts of Suleyman Demirel University, Engineering Faculty,Dept. of Mining Eng., Mineral Processing Division Mineral - MetalRecovery and Recycling (MMR&R) Research Group, Isparta, Turkeyand Department of Life and Environmental Sciences, Universit�aPolitecnica delle Marche, Ancona, Italy, The authors (AA and SO)express their sincere gratitude to the Research Projects Coordina-tion Unit of the Suleyman Demirel University (project no: BAP3711-YL2-13).

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