Finding a friendly environmental technology providing effective and low-cost treatment for soils contaminated by PAHs. Part (I)

Contaminated soils show high concentrations of chemicals or other substances deriving from man’s use of the land. Soil contaminants can influence human health, surface and groundwater quality and the nature and viability of ecosystems. Therefore, government, industry, and the public now recognize the potential risks that complex chemical mixtures such as total petroleum hydrocarbons (TPH), polychloro biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), heavy metals, and pesticides pose to human health and the environment. Approximately 300 000 sites across Europe are estimated to be contaminated by past and present human activities. As a consequence, in response to a growing need to address environmental contamination, many remediation technologies have been developed to treat soil, leachate, wastewater, and groundwater.

Polycyclic Aromatic Hydrocarbons or Polynuclear Aromatic Hydrocarbons (PAHs) are chemical compounds made up of two or more fused aromatic rings in a linear or clustered arrangement (see figure below). They are produced through incomplete combustion and pyrolysis of organic matter. Both natural and anthropogenic sources such as forest fires, volcanic eruptions, vehicular emissions, residential wood burning, petroleum catalytic cracking and industrial combustion of fossil fuels contribute to the release of PAHs to the environment. However, spills of petroleum hydrocarbons were more common in the last few decades than nowadays. Their distinguishing feature is that they are highly hydrophobic. PAHs are easily adsorbed onto the organic matter of solid particles being catalogued as persistent micropollutants. Hydrocarbon spillage onto soils is a matter of concern. PAHs can be removed by natural remediation processes such as photo-oxidation, evaporation, dissolution or biodegradation. Alternatively, they can be sequestered within the soil’s mineral and organic matter structures. Significant amounts of contaminants are retained in soils. Degradation of contaminants shows an initial fast period which decreases with time. According to contaminant sequestration hypothesis, contaminants become less extractable and less bioavailable by sequestration within the soil matrix during aging. However, in general, three and four ring-PAH compounds show more bioavailability than five and six rings-PAHs. The latter compounds are strongly adsorbed into the microporous structure of particulates. Based on these hypotheses three- and four-ring PAH contaminated soils would pose a greater risk to the environment.


It is very difficult to find an efficient method of soil cleanup. Conventional remediation technologies, such as soil vapour extraction or bioventing, require years to produce concentration reductions of 50 to 90 percent, depending on soil type and volatility or biodegradability of the contaminants. Meanwhile, biodegradation is limited by low mass transfer rates in the soil matrix. In general, the time scale involved is relatively large, and the residual contaminant level achievable may not be always appropriate. Less conventional technologies such as chemical oxidation, CO2-based processes, wet air oxidation and direct oxidation processes by means of novel oxidizing agents are promising techniques to increase the degradation rate of hydrocarbons in soils. The most significant advantages are the fast treatment period and the ability to treat contaminants present at high concentrations.

Here goes a brief description about them !

Fenton’s treatment

What is Fenton reagent? Fenton’s reagent is a solution of hydrogen peroxide and an iron catalyst that is used to oxidize contaminants. It was developed in the 1890s by Henry John Horstman Fenton.

Ferrous Iron(II) is oxidized by hydrogen peroxide to ferric iron(III), a hydroxyl radical, and a hydroxyl anion. Iron(III) is then reduced back to iron(II), a superoxide radical, and a proton by the same hydrogen peroxide. The net effect is a disproportionation of hydrogen peroxide to create two different oxygen-radical species, with water (H+ + OH–) as a byproduct.

 Fe2+ + H2O2 +H+ → Fe3+ + HO + H2O

Fe3+ + H2O2 → Fe2+ + HOO+ H+

Even after over 100 years of study and use in water treatment, in-situ remediation methods were slow to use Fenton’s Reagent, owing to safety concerns. Remediation of soil and groundwater contamination is accomplished by injecting this strong chemical oxidant, and a chain reaction is initiated, forming more radicals, which are very reactive and destroy chemical bonds of organic compounds. In addition, pH adjustment using a strong acid such as sulfuric acid (H2SO4) or hydrochloric acid (HCl), is common since reactions of classic Fenton’s Reagent are more rapid and efficient under low pH conditions (pH 2 to 4 is optimal).


Ozone is defined as a triatomic molecule, consisting of three oxygen atoms, and it is formed from dioxygen by the action of ultraviolet light.

Among the technologies that can be applied “in situ” or “on site” soil ozone application is catalogued as one of the most promising systems. Molecular ozone (or its primary decomposition radical HO) steadily reacts with a high number of organic and inorganic contaminants. Injected ozone gas might directly attack target compounds, or alternatively, it can decompose over metal oxides in the surface soil to generate the non-specific hydroxyl radical which in turn can oxidise/mineralize adjacent sorbed pollutants. The efficiency of ozone in soil treatment has been assessed either at laboratory level and field scale.

Its key benefits as an oxidant in soil and groundwater remediation are: destruction of targeted pollutants; rapid reaction – process allows for a quick turnaround; contaminants are destroyed rather than transferred from one phase to another; clean reaction – no hazardous by-products produced; and micro-bubbles act to extract pollutants from both groundwater and soil pores, so acting across the total soil body.

 Supercritical CO2, green solvent for the 21st century

Supercritical fluids (SCFs), in particular supercritical carbon dioxide, are progressively deserving the epithet of “green solvents for the 21st century”. SCFs offer properties that are intermediate between liquids and gases.

Carbon dioxide usually behaves as a gas in air at standard temperature and pressure (STP), or as a solid called dry ice when frozen. If the temperature and pressure are both increased from STP to be at or above the critical point for carbon dioxide, it can adopt properties midway between a gas and a liquid. More specifically, it behaves as a supercritical fluid above its critical temperature (304.25 K) and critical pressure (72.9 atm or 7.39 MPa). Its properties can be summarized in lower viscosity and thermal conductivity than in liquids and better diffusion characteristics.  Carbon dioxide does not require an excessive amount of energy to get supercritical conditions. As well, other advantages include the low cost of the carbon dioxide, high chemical stability and lack of toxicity.

All of these properties make supercritical CO2 an important commercial and industrial solvent due to its role in chemical extraction in addition to its low toxicity and environmental impact. The relatively low temperature of the process and the stability of CO2 also allow most compounds to be extracted with little damage or denaturing. So, the use of supercritical CO2 in soil remediation processes is recently being considered. The advantages of using CO2 include the affinity for non-polar contaminants that are tightly adsorbed into solid particulates.

Rivas FJ, García R, García-Araya JF, & Gimeno O (2008). Promoted wet air oxidation of polynuclear aromatic hydrocarbons. Journal of hazardous materials, 153 (1-2), 792-8 PMID: 17945415

The installation of the Vadose Monitoring System (VMS) was carried out successfully in Belgium last June

The installation of the Vadose Monitoring System (VMS) was carried out successfully in Belgium last June

I am pleased to announce that Natalia Fernandez together with her research group, HGeo³-Hydrogéologie et Géologie de l’Environnement, proceeded with the installation of the Vadose Monitoring System (VMS) in Belgium in June. The objective is to develop a methodology that is able to quantify contaminant fluxes, identify their sources and pathways and understand the various reactive processes in soil and groundwater.

The combined experiment consisted of a tracer test performed directly in the vadose zone via infiltration rings, located within an infiltration pond. To do this, a flexible sleeve was installed in a slanted borehole with the aim of capturing a tracer infiltrated throughout undisturbed material above the borehole. To measure water content, Flexible Time Domain Reflectometry probes (FTDR), which contain stainless steel waveguides, were installed in the outer wall of the flexible sleeve. As well, Vadose Sampling Ports (VSP) were placed in the inner wall of the flexible sleeve for sampling pore water in the vadose zone. Finally, additional boreholes were installed in the unsaturated zone to conduct cross-hole geophysics with the aim of monitoring contaminants and tracers as they move into the saturated zone (see it in the pictures).

The outlook of this experiment is to use the advantages of the combination of the Vadose Monitoring System and geophysical techniques with the aim of developing a conceptual model that better characterizes the transport of pollutants in the vadose zone of industrial sites. The objective is to use such a methodology as an approach to improve risk assessment and remediation measures for the vadose zone.

Natalia experiment 0 Natalia experiment 1Natalia experiment 2  Natalia experiment 2b Natalia experiment 3aNatalia experiment 3bNatalia experiment 4aNatalia experiment 4b   Natalia experiment 5

Happy World Environment Day 2013

2013 marks the 40th Anniversary of World Environment Day, every year on June 5th for forty years, people across the planet celebrate the United Nations World Environment Day. It is a day for action. Hundreds of thousands of activities take place in virtually every country in the world to improve the environment now and for the future. Not to be outdone, the ADVOCATE project wishes to help in this day to promote the importance of developing innovative in situ remediation concepts for the sustainable management of contaminated land and groundwater for improving the Environment for us and our future.

Over the past several decades, increasing human population, economic development, and emergence of global markets, have resulted in immense pressures on natural resources, and these pressures are expected to intensify further over the next few decades. Throughout this project, we are seeking to address a solution to the four critical technical and socio-economic issues facing the sustainable use and development of groundwater resources in Europe (i) existing and future requirements to protect, improve and increase the quality and quantity of groundwater resources; (ii) cost-effective and sustainable re mediation strategies for land and groundwater contamination; (iii) huge legacy of contaminated sites impacting groundwater across Europe which compromises the socio-economic well being and sustainable development of Member States, and (iv) the chronic shortage of skilled professionals in this area to deal with such problems.

Petra Hedbavna, from the University of Sheffield and fellow of the ADVOCATE project, is using bacterial batteries to generate electricity from groundwater pollution. Basically, the bacteria can remove toxic compounds from aqueous solutions and generating electricity at the same time that the pollutants are being removed. In this connection, Petra explains that groundwater can be contaminated by organic compounds which compromise the water quality (Figure 1). As well, it is known that bacteria present in groundwater are able to biodegrade this pollution but they require oxygen for respiration, which can be supplied with the traditional technology, pumping oxygen, against, it is consumed electricity.

Figure 1

However, a new technology is being carried out where the electricity is produced while contamination is biodegraded by means of what is called – microbial fuel cells. This microbial fuel cell technology used for biodegradation enhancement is potentially highly sustainable because electricity is not consumed but produced. Microbial fuel cells used for enhanced biodegradation are still in development, only tested under laboratory conditions (Figure 2). The amount of electricity produced by this technology is not significant and it is not going to solve the world energy crisis. The main advantages are increasing the biodegradation rate of contamination and electricity savings.

Figure 2

It is also important to note that not only scientists developing new technologies for electricity production that can make a difference to the environment. Saving energy at work and at home on daily basis can decrease the world electricity consumption significantly. The University of Sheffield promotes electricity saving by a programme called Energy Matters. Money saved on electricity bills is used for student scholarships (you can find more information on the university webpage Energy_Matters).

Another possibility for removing the pollutants from groundwater is using permeable reactive multi-barrier (PRmB) systems as a sustainable in situ technology for the remediation of groundwater contaminated with mixed organic/inorganic contaminants. Franklin Obiri-Nyarko, from Hydrogeotechnika Ltd in Poland and fellow of the ADVOCATE project, is investigating new and potentially suitable reactive materials for treating these contaminants, as well as evaluating and enhancing the long-term performance of the PRmB system. The focus of his experiments are on the assessment of the removal efficiencies of these materials, understanding the contaminant removal processes, and deducing the key barrier parameters to develop the pilot-scale PRmB system. The performance of the pilot installation coupled with modelling studies will be used to assess the longevity of the system. The results will play a major role in improving the generic understanding and in advancing knowledge of both the scientific and technical aspects of this technology.

This vision of our project is just a small part upon which the entire project is consisted. 14 fellows are involved coming from 20 academic and industry partners throughout five different countries providing to the project a close integration of various scientific, technical, environmental and socio-economic aspect.

We, also, won’t fail on this occasion to remind you, this year’s theme focuses on food waste and food loss. Think.Eat.Save. Reduce Your Foodprint is the new campaign of UNEP and the Food and Agricultural Organization of the UN. It draws attention both to the issue and the absurdity that high volumes of perfectly edible produce are never making it from the farm to the fork.

Indeed, at least one third of everything we grow on this planet is lost between the field and the consumer. It is an ethical, economic and environmental issue given the enormous waste of energy, water, fertilizers and other inputs as a result of food that is produced but never eaten. Each one of us can do something about this, from this post we invite people across the world to make an effort to both raise awareness and to take practical actions whether in your home, when you are buying in the supermarket or well anywhere. Because by reducing food waste, we can save money, minimize environmental impacts and make food production more sustainable and resilient. Most importantly, we can move towards a world where everyone has enough to eat.



Do you know all about the ADVOCATE project ?

Our research topics encompass both socio-economic and sustainability aspects and different remediation processes depending on several factors. Issues as important as the quantification of contaminant transport, biogeochemical processes and degradation at field scale are being developed at the Université de Liége in Belgium. Natalia Fernandez is one of the early-stage researchers that make up the ADVOCATE team and is working at the Université of Liége. Natalia’s research is exploring links between soil and vadose zone processes for in situ remediation of groundwater. Although risk analysis and mitigation programmes for polluted soil and groundwater are used to understand pollutant fate and transport, certain shortcomings have been identified. Consequently, Natalia is developing an efficient and robust procedure for assessing pollutant transport from the pollution site to the groundwater body.

As well, the groundwater-surface water interface is an important factor when a remediation soil treatment is being developed, that is why Vidhya Viswanathan from EAWAG in Switzerland and Uwe Schneidewind from Flemish Institute for Technological Research in Belgium have to focus their efforts on the studies about the influence of surface water-groundwater interaction and the subsurfaces heterogeneities respectively. In view of that, Vidhya’s project examines the impact of restoration on the function of the river Thur in Switzerland. This is done by looking at diurnal and seasonal changes in flow and water quality. The search will identify and measure different parameters to see how these influence each other, as a descriptor of this interaction between the two environmental systems. In related work, Uwe is investigating which parameters are of importance and how they are related to each other in the context that the groundwater-surface water interface of lowland rivers often shows increased contaminant attenuation potential compared with the adjacent aquifer. For this he is conducting modelling studies to determine reaction rates and hydraulic parameters, and their interdependence across different spatial and temporal scales. The results of both will allow up-scaling of attenuation and identify how variation in these due to heterogeneity affects prediction of attenuation.

Also, when a site is contaminated by heavy metals, those can not be degraded, the only existing risk reduction measures are removal or immobilization using different technologies such as In Situ Bioprecipitation (ISBR). The permeable reactive multi-barrier (PRmB) system is a relatively new technology that Franklin Obiri Nyarko from Hydrogeotechnika in Poland is using for treating specific contaminants, as well as evaluating and enhancing the long term performance of the PRmB systems. The results will play a major role in improving the general understanding and advancing knowledge of both the scientific and tecnical aspects of this technolgy. Whereas Franklin is working with mixed organic contaminants (BTEX) and some heavy metals and is also collaborating with Johana Grajales from AGH University of Science and Technology in Poland too, who is using the same system in her laboratory studies, field work and numerical modelling for removing tetrachloroethylene (PCE) and trichloroethylene (TCE) from Nowa Deba field site. Her first results show that the feasibility studies indicated that the installation of a PRmB system may be effective to reduce TCE and PCE concentration under the site specific conditions.

Based on the results of Franklin, Okasana Voloschenko from The Helmholtz Centre for Environmental Research in Germany will conduct field studies at sites with existing barriers and diffuse pollution to examine up-scaling of design parameters determined previously by Franklin. Moreover, her research explores the role of aerobic and anaerobic microbial processes in the removal of ammonium from contaminated groundwater in constructed wetlands (Cws), using a study site located downstream of the Leuna industrial chemical area in Germany. As well, Ben Doulatyari from EAWAG in Switzerland will interpret the results with multi-scale modelling tools and statistical methods to develop performance-based criteria for the design, monitoring and assessment of sequenced reactive barriers. Also, Ben is studying in the river Thur the dynamics of the vegetartion biomass at different points of the stream, as well as catchment hydraulics, managed aquifer recharge and natural attenuation processes.

To cover all points of view regarding the remediation processes within the project it is necessary to study both the bioremediation processes and the framework, methods and tools which advance the use of these sustainable systems. That is why, on the one hand, Alice Badin from University of Neuchatel in Switzerland is focusing her project on sites contaminated with chlorinated solvents using a useful method of measuring the isotopic signature of solvents that could be a great help in providing a rigorous basis to identify the source and timing of chemicals released to groundwater. And on the other hand, Petra Hesbavna from University of Sheffield in United Kingdom is developing a microbial fuel cells for enhancement of in situ bioremediation of soil and groundwater because the microbial fuel cells are believed to be one of the future sources of sustainable energy. Organic compounds are degraded by microbial metabolism and electrons released during this process are transferred to the electrode of the microbial fuel cell . The Petra’s results show that this groundwater composition will be an ideal inoculum for a microbial fuel cell system, to test the concept as a method for the enhanced bioremediation of contaminated groundwater.

Using geostatistical, probabilistic and numerical modelling methods is possible to evaluate the technologies and approaches used throughout the project. The goal is to develop a unified framework for ISR. In this connection, Juan Pena from Université de Liége in Belgium is focused his research on characterization of the subsurfaces medium, which will lead to new conceptual ways of the modelling that account for the properties of, and interactions between, selected reactive tracers and soil aquifer materials, and on developing optimized single and multiple-well tracer techniques. Likewise, Lukasz Cieslak from University of Sheffield in United Kingdom is exploring interactions between microorganisms in aquifers, which use a range of oxidants to biodegrade organic contaminants. This creates a sequences of zones in contaminated groundwater, which represent different terminal electron accepting processes (TEAP). Lukasz has completed an initial sampling programme to characterise the hydrochemistry and microbiology of an organic contaminant plume fringe at the site, using a series of high-resolution multilevel samplers.

Because the economic aspect is the most important factor for the stakeholders, without being cost-effective the technology will not be introduced within the foreseeable future. Consequently, Alistair Beames from The Flemish Institute for Technological Research is developing a decision-support framework to assist stakeholders in choosing between brownfield revitalization alternatives. Brownfield revitalization planning entails the careful consideration of remediation alternatives capable of reducing contamination level to the required target values, as well as determining the optimal land-use scenario for the remediated site. Also, Alistair is developing the Social Impact Assessment component of the eventual decision-support framework, the focus of the review is on whether the social aspect of sustainability is adequately accounted for in these existing tools.

Finally, my name is Ruth García de la Calle and I am the person that will try to promote the network and bring closer to the public everything relating to the remediation of soil and groundwater to give you an easy scientific understanding about this topic.