Environ. Sci. Technol. 2005, 39, 325-330
Bioremediation of Diethylhexyl Phthalate Contaminated Soil: A Feasibility Study in Slurry- and Solid-Phase Reactors P. DI GENNARO,† E. COLLINA,† A. FRANZETTI,† M. LASAGNI,† A . L U R I D I A N A , ‡ D . P I T E A , * ,† A N D G. BESTETTI† Dipartimento di Scienze dell’Ambiente e del Territorio, Universita` di Milano-Bicocca, Piazza della Scienza 1, 20126 Milano, and Tecna Srl, via Cattaneo 9, 21013 Gallarate (Varese), Italy
The aim of the research was to verify the possibility of applying bioremediation as a treatment strategy on a poly(vinyl chloride) (PVC) manufacturing site in the north of Italy contaminated by diethylhexyl phthalate (DEHP) at a concentration of 5.51 mg/g of dry soil. Biodegradation kinetic experiments with DEHP contaminated soil samples were performed in both slurry- and solid-phase systems. The slurryphase results showed that the cultural conditions, such as N and P concentrations and the addition of a selected DEHP degrading strain, increased the natural DEHP degradation rate. On the basis of these data, experiments to simulate bioventing on contaminated soil columns were performed. The DEHP concentration reached 0.63 mg/g of dry soil in 76 days (89% of degradation). A kinetic equation was developed to fit the experimental data and to predict the concentration of contaminant after treatment. The data obtained are encouraging for a future in situ application of the bioventing technology.
Introduction Interest in bioremediation as a treatment strategy for contaminated soil has increased in recent years. It is known that the feasibility and effectiveness of bioremediation is influenced by many factors, such as the presence of suitable microorganisms, nutrient availability, temperature, and pH (1-4). Phthalic acid esters are refractory organic compounds, industrially produced in very large quantities and widely used as plasticizers. They are widespread throughout the environment, where they can be found in sediments, waste matter, and soils (5). Some are suspected of being carcinogenic (6, 7), and this has led to considerable attention being paid to their analysis, environmental fate, general toxicity, and biological degradability in the environment. Furthermore, phthalic acid esters are characterized by high hydrophobicity (5), and tend to bind strongly to the organic matter in soil. For this class of compounds it is the bioavailability of the residual contaminant fraction that determines the possibility of reaching remediation goals and that governs the treatment * Corresponding author phone: +390264482823; +390264482890; e-mail:
[email protected]. † Universita ` di Milano-Bicocca. ‡ Tecna Srl. 10.1021/es035420d CCC: $30.25 Published on Web 11/23/2004
2005 American Chemical Society
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time needed to achieve such goals. So, to design remediation operations, in-depth studies are needed. Among the phthalate esters, diethylhexyl phthalate (DEHP) is one of the most frequently used additives in the manufacture of flexible poly(vinyl chloride) (PVC). As microbial degradation is considered to be the principal sink for phthalate esters (5), several studies focused on biodegradability of DEHP have been reported in the past few years (8-20). DEHP biodegradation in aqueous or sludge samples was investigated in shake flasks (8-12). Soil where sewage sludge has been spread for fertilization purposes has low concentrations of DEHP (13-15), while concentrations up to 100 mg/g of dry soil are due to industrial contamination (spill or release from a phthalate production storage site) (16, 17). Solid-phase biodegradation studies have been performed on soil samples spiked with DEHP (18, 19). DEHP biodegradation in industrially contaminated soil has been investigated in batch soil slurry systems (16, 17), but there is little information available on the solid-phase biodegradation kinetics (20). A PVC manufacturing site in the north of Italy was found to have, as the main soil contaminant of the area, DEHP, the contamination pattern being characterized by high concentrations (from 2 to 10 mg/g of dry soil) and varying depths (from 1 to 20 m). Thus, the only reasonable approach to remediation was the use of an in situ technology. Bioremediation was chosen for its cost-effectiveness and treatment feasibility. The influence of biostimulation and bioaugmentation on DEHP biodegradation was investigated in three different systems: liquid, slurry, and solid phases. To determine the best conditions for a possible in situ application, slurry-phase and laboratory-scale pilot plant experiments were set up (1, 4, 21, 22). A mathematical model was applied to the kinetic data for an understanding of the residual DEHP concentration and to estimate the necessary treatment time.
Materials and Methods Soil Samples. The soil for the experiments was a composite sample collected at a depth of between 3 and 5 m at the DEHP contaminated site. A blank sample used for control experiments was collected in a noncontaminated area of the site at the same depth. The samples were sieved, and the fractions of
