Remediation of PAH-Contaminated Soils: Experimental Analysis and Modeling of Hydrodynamics and Mass Transfer in a Soil-Slurry Bioreactor

Extended Abstract Polycyclic Aromatic Hydrocarbon (PAHs)-contaminated soils are a great environmental and public health concern nowadays. Their remediation is an important field of research as several remediation techniques have been developed with the purpose of removing PAHs from soil. However, further researches are necessary to develop environmental friendly biotechnologies that allows public and private sectors to implement efficient and adaptable treatments for contaminated soils. Aerobic soil-slurry bioreactor technology has emerged as one of these technologies with high potential as an effective and feasible treatment technic for PAH-contaminated soils. For this treatment, soil is excavated, conditioned and loaded into an aerated aqueous bioreactor. Then, mechanical and/or pneumatic mixing maintains aerobic conditions and homogeneity. Furthermore, air supply and mixing represent the most energy intensive units Although, extensive research has been done on this topic, mechanisms involved in the removal of PAHs from soil are still not completely understood. In addition to the biological processes involved, important mass transfer mechanisms need to be considered (oxygen gas-liquid mass transfer, adsorption-desorption, volatilization of PAH, etc.). In general, even for volatile PAHs, volatilization is not considered in the studies whereas, in some conditions (high aeration rate), it can be a major mechanism of "PAH removal". The soil composition and concentration in the reactor should influence strongly the fluid viscosity, which is a key parameter governing the hydrodynamics and thus the mass transfer phenomena. Therefore, the aeration and mixing optimization requires a fine understanding of how different operational parameters influence the mixing and mass transfer mechanisms involved in the removal of PAHs from soil In this study, the influence of soil content (composition and concentrations) and operating conditions (air superficial velocity, stirring rate, etc.) on the mixing (rheology, etc.) and mass transfer phenomena (gas-liquid, adsorption-desorption) is addressed. Experiments are performed in a glass standard bioreactor designed to control hydrodynamic conditions and temperature. Air is injected from the bottom through a porous glass sparger. Mechanical agitation is performed by a marine propeller connected to a motor. Hydrodynamic parameters are monitored in order to study their influence on the process and, particularly on the oxygen and PAH transfer phenomena. Rheological behavior of soil/water matrix has been measured with a capillary rheometer The oxygen transfer tests showed that for a given air superficial velocity and stirring rate, the oxygen transfer coefficient in soil/water matrix is reduced in comparison with clean water results. This decrease depends on the soil composition and was more pronounced with an increase in the soil content. Moreover, the soil/water matrix could be assimilated to a non-Newtonian fluid with shear-thinning behavior (mainly pronounced for high soil content). The impact

Phytotoxicity of citric acid and Tween® 80 for potential use as soil amendments in enhanced phytoremediation

Enhanced phytoremediation adding biodegradable amendments like low molecular weight organic acids and surfactants is an interesting area of current research to overcome the limitation that represents low bioavailability of pollutants in soils. However, prior to their use in assisted phytoremediation, it is necessary to test if amendments per se exert any toxic effect to plants and to optimize their application mode. In this context, the present study assessed the effects of citric acid and Tween (R) 80 (polyethylene glycol sorbitan monooleate) on the development of alfalfa (Medicago sativa) plants, as influenced by their concentration and frequency of application, in order to evaluate the feasibility for their future use in enhanced phytoremediation of multi-contaminated soils. The results showed that citric acid negatively affected plant germination, while it did not have any significant effect on biomass or chlorophyll content. In turn, Tween (R) 80 did not affect plant germination and showed a trend to increase biomass, as well as it did not have any significant effect on chlorophyll levels. M. sativa appeared to tolerate citric acid and Tween (R) 80 at the tested concentrations, applied weekly. Consequently, citric acid and Tween (R) 80 could potentially be utilized to assist phytoremediation of contaminated soils vegetated with M. sativa

Citric acid- and Tween(®) 80-assisted phytoremediation of a co-contaminated soil: alfalfa (Medicago sativa L.) performance and remediation potential

A pot experiment was designed to assess the phytoremediation potential of alfalfa (Medicago sativa L.) in a co-contaminated (i.e., heavy metals and petroleum hydrocarbons) soil and the influence of citric acid and Tween(®) 80 (polyethylene glycol sorbitan monooleate), applied individually and combined together, for their possible use in chemically assisted phytoremediation. The results showed that alfalfa plants could tolerate and grow in a co-contaminated soil. Over a 90-day experimental time, shoot and root biomass increased and negligible plant mortality occurred. Heavy metals were uptaken by alfalfa to a limited extent, mostly by plant roots, and their concentration in plant tissues were in the following order: Zn > Cu > Pb. Microbial population (alkane-degrading microorganisms) and activity (lipase enzyme) were enhanced in the presence of alfalfa with rhizosphere effects of 9.1 and 1.5, respectively, after 90 days. Soil amendments did not significantly enhance plant metal concentration or total uptake. In contrast, the combination of citric acid and Tween(®) 80 significantly improved alkane-degrading microorganisms (2.4-fold increase) and lipase activity (5.3-fold increase) in the rhizosphere of amended plants, after 30 days of experiment. This evidence supports a favorable response of alfalfa in terms of tolerance to a co-contaminated soil and improvement of rhizosphere microbial number and activity, additionally enhanced by the joint application of citric acid and Tween(®) 80, which could be promising for future phytoremediation applications

Preface

International audienc

Impact of pyrometallurgical slags on sunflower growth, metal accumulation and rhizosphere microbial communities

Metallurgical exploitation originates metal-rich by-products termed slags, which are often disposed in the environment being a source of heavy metal pollution. Despite the environmental risk that this may pose for living organisms, little is known about the impact of slags on biotic components of the ecosystem like plants and rhizosphere microbial communities. In this study, metal-rich (Cu, Pb, Zn) granulated slags (GS) derived from Cu production process, were used for a leaching test in the presence of the soil pore solution, showing that soil solution enhanced the release of Cu from GS. A pot experiment was conducted using as growing substrate for sunflower (Helianthus annuus) a 50% w/w mix of an agricultural soil and GS. Bioavailability of metals in soil was, in increasing order: Pb < Zn < Cu. Sunflower was able to grow in the presence of GS and accumulated metals preferentially in above-ground tissues. Microbial diversity was assessed in rhizosphere and bulk soil using community level physiological profiling (CLPP) and 16S rRNA gene based denaturing gradient gel electrophoresis (DGGE) analyses, which demonstrated a shift in the diversity of microbial communities induced by GS. Overall, these results suggest that metallurgical wastes should not be considered inert when dumped in the soil. Implications from this study are expected to contribute to the development of sustainable practices for the management of pyrometallurgical slags, possibly involving a phytomanagement approach.Fil: Agnello, Ana Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Fermentaciones Industriales. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Fermentaciones Industriales; Argentina. Université Paris-Est. Laboratoire Géomatériaux et Environnement; FranciaFil: Potysz, A.. University of Wrocław.Institute of Geological Sciences; PoloniaFil: Fourdrin, C.. Université Paris-Est. Laboratoire Géomatériaux et Environnement; FranciaFil: Huguenot, D.. Université Paris-Est. Laboratoire Géomatériaux et Environnement; FranciaFil: Chauhan, P.S.. Council of Scientific and Industrial Research. National Botanical Research Institute; Indi

Combination of surfactant enhanced soil washing and electro-Fenton process for the treatment of soils contaminated by petroleum hydrocarbons

International audienceIn order to improve the efficiency of soil washing treatment of hydrocarbon contaminated soils, an innovative combination of this soil treatment technique with an electrochemical advanced oxidation experiment was enriched with surfactant Tween® 80 at different concentrations, higher than the critical micellar concentration (CMC). The impact of soil washing was evaluated on the hydrocarbons concentration in the leachates collected at the treatment. Results showed that a concentration of 5% of Tween® 80 was required to enhance hydrocarbons extraction from the soil. Even with this Tween® 80 concentration, the efficiency of the treatment remained very low (only 1% after 24 h of washing). Electrochemical treatments performed thereafter with EF on the collected eluates revealed that the quasi-complete mineralization (>99.5%) of the hydrocarbons was achieved within 32 h according to a linear kinetic trend. Toxicity was higher than in the initial solution and reached 95% of inhibition of Vibrio fischeri bacteria measured by Microtox® method, demonstrating the presence of remaining toxic compounds even after the complete degradation. Finally, the biodegradability (BOD5/COD ratio) reached a maximum of 20% after 20 h of EF treatment, which is not enough to implement a combined treatment with a biological treatment process

Preface. Contaminated Soils : From Monitoring to Remediation

International audienceThis special issue is devoted to soil pollution man-agement occurring in Europe and all over the world. The first step consists in the characterization of the site and the soil contamination followed by the selection of the best treatment methods. Among those methods, physico-chemically-and biologically-based tech-niques are particularly of interest. Generally, higher concentrations of an organic or metallic compound in the soil of the site of interest compared to the local background result in the decision to start a remediation process. The choice of the appropriate technique relies on a cost-benefit analysis together with the intrinsic characteristics of the site. Among the most used, physico-chemically-based techniques mainly consist in the use of chemical compounds able to extract, or complex, and solubilize the pollutant from the solid matrix to a liquid phase. The choice of the extractant or chelant depends on the intrinsic physicochemical characteristics of the pollu-tants. Surfactants are required to extract hydrophobic molecules as well as the complexation abilities of chelants are used for the clean-up of metal-polluted soils. Both in situ (i.e. soil flushing) and ex situ (i.e. soil washing) methods can be implemented. These two different remediation approaches are reviewed in this special issue. Biological treatments are more and more consid-ered based on their low cost and low maintenance. Remediation techniques based on living organisms such as bacteria, fungi or plants, can be easy to handle but they require a perfect, or at least a good, knowledge of the soil characteristics. Considering their high resilience, these techniques are able to deal with a wide range of organic molecules, from pesti-cides to crude oil, and trace elements as well as radionuclides. In order to deal with heavy metals, the use of plants appears to be mandatory as phytoextrac-tion is the only biological in situ technique. The implementation of remediation processes based on the combination of both bacteria and plants is a key point of these biological techniques as reviewed in this special issue. This special issue is mainly based on invited contributions presented at the International ''Summer school on contaminated soils: from characterization to remediation'', held from 18th to 22nd June 2012, in Champs-sur-Marne, France. This Summer School was financially supported by the Education, Audiovisual and Culture Executive Agency (EACEA) of the European Commission in the framework of the Erasmus Mundus Programme (FPA 2010–0009) and by the Université Paris-Est Marne-la-Vallée