||Consortial linuron mineralization in unsaturated sand matrix
||Owsianiak, Mikolaj (Department of Environmental Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
||Dechesne, Arnaud (Environmental Chemistry and Microbiology, Department of Environmental Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Smets, Barth F. (Residual Resource Engineering, Institute of Environment & Resources, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
||Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
||To protect groundwater resources, bioaugmentation with microorganisms immobilized in solid carriers has been considered as a remediation strategy against environmental pollutants. While laboratory studies often demonstrated promising results, failures are common.
One of the widely used herbicides of significant environmental concern is linuron, a member of athe phenylurea family. Biodegradation has been recognized to be the main route of removal of this compound from the environment, and usually occurs via toxic 3,4-dichloroaniline (3,4-DCA). Microbial consortia able to completely degrade linuron have been isolated over the last years, but a few single strains able to mineralize linuron are also available. It has often been suggested that isolated linuron-degraders or consortia would be good candidates for bioaugmentation purposes. In this study, the feasibility of using two-member microbial consortium embedded in solid carriers for soil bioaugmentation was evaluated by means of experiments and mathematical modeling.
A mathematical model was developed to simulate consortial linuron mineralization in porous media. Within a 3-D model domain that simulates a variably saturated porous matrix, linuron was supposed to be homogeneously distributed, while the consortium was distributed in hot-spots resembling alginate beads commonly used for bioaugmentation. The population of linuron-degraders was assumed to excrete stoichiometric portions of 3,4-DCA, which was subsequently taken up by the 3,4-DCA-degrading population, complementing linuron mineralization. Microbial growth in the hotspots was assumed to follow Monod kinetics, while diffusion, including air-liquid phase partitioning, was the only transport process for both solutes. With the initial hypothesis that water governs mineralization through its control of the diffusion of linuron and its metabolite, the performance of the consortium with respect to linuron mineralization as affected by the distance between hot-spots and water saturation, was investigated.
The model indicated that linuron degradation in the porous matrix was diffusion limited, regardless of the water saturation level. Mineralization time was affected by the water content, with shorter times associated with higher water saturation. The metabolic intermediate can diffuse relatively rapidly out of the hot-spots due to its volatility, potentially resulting in incomplete mineralization. However, diffusive properties of the metabolite did not affect mineralization significantly. Providing a dense distribution of hot-spots partly relieved diffusion limitations. In saturated conditions, spacing the hot-spots at a distance of 13 mm was required to obtain 90% linuron mineralization in less than 100 days. Under unsaturated conditions, the distance decreased to 5 mm. Water infiltration was an important factor affecting linuron mineralization, but did not alter considerably required hot-spot density. Possible difficulties with providing such dense bead distribution, question the value of using encapsulated cell formulations for soil bioaugmentation purposes. Possible solutions could rely on the use smaller beads, providing more dense distribution of mineralization potential.
In the experimental part of this thesis, bacterial consortia were constructed and tested for mineralization activity towards linuron. Linuron-degrading Arthrobacter globiformis D47 was combined with 3,4-DCA-degrading strains, i.e. Variovorax sp. PBD-E5, Variovorax sp. PBD-E37 or Variovorax sp. PBD-H1. None of the consortial formulations introduced into liquid medium as free or immobilized cells was more efficient than monoculture of linuron-mineralizing strain Variovorax sp. SRS16. The reasons for the apparent encapsulation failures are discussed.
The results of this study are of attention to those interested in the use of encapsulated microorganism for bioremediation purposes.
||Technical University of Denmark (DTU) : Kgs. Lyngby, Denmark
Creation date: 2011-03-15
Update date: 2011-04-13