Elsevier

Chemosphere

Volume 273, June 2021, 129733
Chemosphere

Evaluation of chitosan aggregates as pickering emulsifier for the remediation of marine sediments

https://doi.org/10.1016/j.chemosphere.2021.129733Get rights and content

Highlights

  • Chitosan nanoaggregates promotes the emulsification of petroleum in water.

  • Marine sediments, artificially contaminated with petroleum, were efficiently cleaned up.

  • Addition of CO2 triggered a post-treatment demulsification and the easy recovery of crude oil.

  • The washing solution may be re-utilized for successive application.

Abstract

To restore the marine environments contaminated by oil spills to an acceptable state, sediments are commonly washed with seawater, and surfactants added into the aqueous solution to increase the oil recovery. However, the resulting mixture may release toxic break-down products, and the surfactants may themselves pose an environmental risk to marine species. In this work we investigated for the first time the addition of chitosan nanoparticles to the washing solution as an alternative and greener method to ensure the cleanup of contaminated sediments.

Results showed 65.1 ± 6.4% of average removal from sand and seafloor sediments artificially contaminated at 4 wt % with crude oils displaying different specific gravity. These results were comparable to those obtained with commercial surfactant mixtures containing non-ionic and anionic surfactant (67.8 ± 5.2% removal). Moreover it was possible to recover the crude oil from the washing solution thanks to the reversible demulsification induced by the addition of CO2.

Introduction

Contamination of marine sediments by oil spill poses a potential threat to the marine ecosystems and human health, and determine losses for the economy of the coastal communities (Atlas, 1995).

Specifically, risks originate from the ingestion of contaminated fish and shellfish. Oil related compounds such as polyaromatic hydrocarbons (PAHs) display in fact both carcinogenic and sublethal effects in humans (Alden and Young, 1982). They tend to accumulate in marine organism that display a limited ability to metabolize them i.e. the bivalve mollusks, For this reason, temporary bans on fishing are applied during the period of elevated hydrocarbon concentrations in the water column with impacts on local fishery reputation and tourism activities (IMO, 2005).

Moreover, the sediment contamination may determine long term ecological effects, since the exposed organisms may face reproductive failure, growth impairment and even death (Wise et al., 2014). Not only individuals but also the entire benthic populations may be affected, with community changes underlined by the elimination of less tolerant species and in the increase in more tolerant species (Van Bernem et al., 2007).

To overcome all these issues, environmental remediation plans are carried out both by washing the sediment in situ to obtain a fast clean up and by mechanically collect the materials that are removed, treated ex situ and then relocated (National Research Council, 1989).

Especially, in the case of a heavy contamination of sensitive shorelines, the first clean-up operation, that consists in flushing the oil trapped in the marine sediments with seawater (ITOPF, 2011a, 2011b, 2011c) is decisive, because the oil becomes more difficult to treat when it is weathered (Fingas, 2012). In this context surfactants are added as an aid to liberate the oil from the substrates (IMO, 1995). They act by reducing the interfacial tension between the oil and the water, as well as decreasing the attraction between the contaminants and the sediments (Etkin, 2001). When the concentration of the surfactant reaches the critical micelle concentration, micelles are formed and the solubilization of organic contaminants is enhanced (Lessard and Demarco, 2000). The rate of mass transfer of the contaminants from the sediments to the aqueous phase thereby increases (Mulligan et al., 2001).

On the other hand, the use of surfactant is limited in practice to ex situ washing both for ecological and practical reasons. The application of surfactant in situ, is considered risky to the marine species living in intertidal (Norton and Franklin, 1980) and nearshore areas that may be sensitive to dispersed oil, (Chapman et al., 2007). In addition, some surfactants may have a detrimental effect on microbial growth and thus slow down the oxidation of crude oil (Bruheim et al., 1999), and they also may persist in the environment (Kujawinski et al., 2011). Because surfactants tend to continue to stabilize the oil in water emulsion long after the washing is performed, the separation of oil from the water may become very difficult (Fiocco and Lewis, 1999). Moreover, when the oil is dispersed, the use of sorbent materials generally becomes ineffective (ITOPF, 2011a, 2011b, 2011c). Thus surfactants are adopted as releasing agent with no concerns only in the case of sands contaminated with viscous oils that are less prone to produce dispersion and therefore easier to treat. Similarly, the addition of surfactant is common for the treatment of pebbles and cobbles inside revolving drums. Outside these cases, the use of surfactant is heavily regulated, and only few products are approved by regulatory agencies for application in situ (Atlas, 1995; Kleindienst et al., 2015; European Maritime Safety Agency (EMSA), 2006).

In this framework, Jessop and coauthors recently introduced the use of switchable surfactants for sediment washing, not only as an alternative solution to clean up the sediments, but also for the recovery of crude oil (Ceschia et al., 2014). According to the described process, after the completion of the washing step and the separation of the sediments, the crude oil is reclaimed by introducing the washing solution into a separator, where the surfactant is “turned off” thanks to the addition of CO2 (that reacts with the anionic moiety of the “switchable” surfactant). In summary, when the crude oil is reclaimed, by applying a decarbonation step, the water is recycled for a further soil washing application. However, the switchable surfactants tested by the Jessop group were mainly designed for ex situ application, and due to their poor biodegradability and high affinity to seawater and sediments cannot be applied in situ.

In our view, chitosan is a very promising candidate to be applied on field following the switchable surfactant approach. Chitosan is in fact a biobased and biodegradable material (Hu et al., 2015; Athas et al., 2014) obtained by the alkaline deacetylation of chitin, the second most abundant polymer in nature after cellulose (Elsabee et al., 2009). It has recently been demonstrated that chitosan may form aggregates that are capable of inducing the formation of oil in water Pickering emulsion (Payet and Terentjev, 2008; Liu et al., 2012). This emulsion may be switched off by addition of CO2 (Ren et al., 2018), following a reversible mechanism that looks very similar to the mechanism pioneered by the Jessop group with carbamates and carboxylates salts (Darabi et al., 2016) and differs by the fact that it doesn’t involve either anionic or cationic interactions as with conventional surfactants, but the colloidal stabilization of the emulsion caused by solid particles, as described by Pickering (Prince, 2015).

Here, the hydrophobicity, structure, size and concentration of the solid particles may play an important role on emulsion stability (Ho et al., 2016). In addition, since crude oil is a very complex mixture of different compounds from several different classes i.e. hydrocarbons (paraffins, naphthenes, aromatics), nitrogen and sulfur compounds, waxes, asphaltenes, inorganics i.e. vanadium and nickel (Kharisov et al., 2014; Kilpatrick, 2012) very complex interactions may take place.

As described for paraffins (Liu et al., 2012), smaller particles are more easily adsorbed onto the droplet interface and therefore lead to a more homogenous layer around the droplet. It was indicated that at least the particle size should be one order of magnitude smaller than the size of the emulsion droplets. Studies have also shown that the size of the self-aggregated chitosan particles depends on the molecular weight of the chitosan (Janes and Alonso, 2003), and that pronounced breakup of chitosan leads to the formation of smaller and monodisperse self-aggregated particles (Ho et al., 2016). However, it was also observed that this favors higher exposition of protonated amino group residues, which end up in a lower Pickering emulsion (Rodrigues Costa et al., 2018).

Starting from this basis, we evaluated the performance of chitosan aggregates as switchable emulsifier for the remediation of marine sediments contaminated by crude oil for the first time. Tests were carried out with marine sediments artificially contaminated with known amounts of petroleum crude oils having different grades (American Petroleum Institute, 1980). The mass of oil recovered was determined gravimetrically. A commercially available surfactant mixture was used as reference to compare the performances. Microscopical observation and advanced analytical techniques were employed to understand the mechanism of interaction between the crude oil, the sediments and the chitosan aggregates.

Section snippets

Sample

Extra pure sea-sand purchased from Sigma Aldrich (1.07711 Supelco) and marine sediments from the Mediterranean Sea were employed for running the preliminary oil recovery experiments. Specifically, the sea-sand was constituted by nonporous silica in the particle size range of 0.1–0.315 mm, the marine sediments were sampled from the Gulf of Salerno at 56 m of water depth. The Gulf of Salerno (South-eastern Tyrrhenian Sea) hosts a relatively wide continental shelf that extends for about 70 km from

Chitosan aggregates

DLS analysis of the chitosan aggregates solution (Supplementary, Fig. S14) displayed a bi-modal size distribution with an average size of approximately 138 nm and a polydispersity index of 0.326. These results are close to those previously reported by Ren and coauthors (Ren et al., 2018). Detail from SEM imagines of the dried particles confirmed the size distribution and the aggregation state (Fig. 2).

Crude oil in water emulsion

As first, we carried tests to verify the emulsification process induced by chitosan

Conclusions

In conclusion, chitosan aggregates may be used to replace synthetic surfactant in the cleanup of oil contaminated sediment. Because the successive addition of CO2 into the washing mixture promotes the dissolution of the aggregates and induces a tunable demulsification, it is possible to recover the crude oil from the washing mixture at the end of the cleanup operation. Overall, the method presented appears to be suited for in situ application, because the water can be recirculated and the

Credit author statement saras

Francesco SaliuConceptualization, Methodology, Writing – original draft, Edoardo Maucci recovery experiments, nanoparticle preparation, Claudio Allevi, Supervision, Funding acquisition, Iikpoemugh Elo: Nanoparticle characterization, Roberto della Pergola Revision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The work was supported by University of Milano Bicocca - FAR 2017. We gratefully thanks Anthony Visconti from SARAS for the help in proofreading the paper.

References (43)

  • M.Z. Elsabee et al.

    Surface active properties of chitosan and its derivatives

    Colloids Surf. B Biointerfaces

    (2009)
  • K.W. Ho et al.

    Comparison of self-aggregated chitosan particles prepared with and without ultrasonication pretreatment as Pickering emulsifier

    Food Hydrocolloids

    (2016)
  • A.M. Al-Sabagh et al.

    Petroleum oil dispersion efficiency and stability using eco-friendly chitosan-based surfactant and nanoparticles

    J. Dispersion Sci. Technol.

    (2012)
  • R.W. Alden et al.

    Open ocean disposal of materials dredged from a highly industrialized estuary: an evaluation of potential lethal effects

    Arch. Environ. Contam. Toxicol.

    (1982)
  • API Manual of Petroleum Measurement Standards, (Chapter 11).1 – 1980, Volume XI/XII, Adjunct to: ASTM D1250-80 and IP...
  • J.C. Athas et al.

    An effective dispersant for oil spills based on food-grade amphiphiles

    Langmuir

    (2014)
  • R.M. Atlas

    Petroleum biodegradation and oil spill bioremediation

    Mar. Pollut. Bull.

    (1995)
  • P. Bruheim et al.

    Effects of surfactant mixtures, including Corexit 9527, on bacterial oxidation of acetate and alkanes in crude oil

    Appl. Environ. Microbiol.

    (1999)
  • E. Ceschia et al.

    Switchable anionic surfactants for the remediation of oil-contaminated sand by soil washing

    RSC Adv.

    (2014)
  • H. Chapman et al.

    The use of chemical dispersants to combat oil spills at sea: a review of practice and research needs in Europe

    Mar. Pollut. Bull.

    (2007)
  • A. Darabi et al.

    CO2-responsive polymeric materials: synthesis, self-assembly, and functional applications

    Chem. Soc. Rev.

    (2016)
  • S. Deshpande et al.

    Water Res.

    (1999)
  • D.S. Etkin

    Analysis of oil spill trends in the United States and worldwide

  • Manual on the applicability of oil spill dispersants Part I: overview

  • M. Fingas

    The Basics of Oil Spill Cleanup

    (2012)
  • R.J. Fiocco et al.

    Oil spill dispersants

    Pure Appl. Chem.

    (1999)
  • Z. Hu et al.

    Synergistic stabilization of emulsions and emulsion gels with water-soluble polymers and cellulose nanocrystals

    ACS Sustain. Chem. Eng.

    (2015)
  • IMO/UNEP Guidelines on Oil Spill Dispersant Application Environmental Considerations

    (1995)
  • Manual on Oil Pollution – Section IV Combating Oil Spills

    (2005)
  • Effects of oil pollution on the environment – technical information paper number 13

  • Fate of marine oil spills– technical information paper number 2

  • Cited by (0)

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