A novel biodegradation system for hydrophobic organic pollutants considering
pyrene as a model molecule
Saurabh Jyoti Sarma
1, Kannan Pakshirajan
2and Satinder Kaur Brar
11
Centre Eau, Terre & Environnement, INRS, Quebec (Canada)- G1K 9A9
2Department of Biotechnology, IIT Guwahati, Assam (India)-781039
Introduction
Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants.
They may be genotoxic and carcinogenic.
Low aqueous phase solubility and negligible bioavailability are major limiting factors towards their biodegradation.
However, using oil encapsulation technique bioavailability of these compounds can be enhanced.
In present study, pyrene was used as a model PAH compound.
It was dissolved in silicone oil and mixed with an aqueous phase containing sodium alginate (3% w/v)-polyvinyl alcohol (PVA) (3% w/v), at 3:7 ratio.
Mixture was emulsified using a surfactant, (Brij 30).
Using resulting emulsion alginate-PVA microspheres prepared by
emulsion gelation technique.
A chitosan coat was applied on such microspheres.
Prepared microspheres were used to deliver pyrene to
Mycobacterium frederiksbergense for degradation.
Results
Preparation of pyrene encapsulated micro-spheres
Based on emulsion stability, 3 % (w/v) PVA , 100 g/l brij 30 and 3:7 oil: aqueous phase ratio chosen for microsphere preparation.
10 % CaCl2 (w/v) and 3% (w/v) boric acid selected as gelling solution.
Characterization of the prepared beads
Microsphere prepared using 3% alginate showed sustained release of pyrene.
Chitosan coating of such microsphere further improved pyrene release behavior.
Pyrene biodegradation by M. frederiksbergense
Pyrene biodegradation experiments carried out using oil encapsulated beads contining 500mg/l, 1000 mg/l and 2000mg/l pyrene in silicone oil.
In all cases nearly complete degradation of pyrene achieved without any lag phase in degradation.
Fig.1: Photomicrograph of different emulsions prepared in the study. The scale bar represents 0.4 mm.
References
Daugulis, A.J. (2001) Two-phase partitioning bioreactors: a new technology platform for destroying xenobiotics. Trends. Biotechnol. 19: 459-464.
Sarma, S. J., Pakshirajan, K. and Mahanty, B. (2011) Chitosan coated alginate-polyvinyl alcohol beads for encapsulation of silicone oil containing pyrene: a novel method for biodegradation of polycyclic
aromatic hydrocarbons, J. Chem. Technol. Biotechnol. 86: 266–272 .
Fig.2: SEM images of chitosan coated (bottom panel) and uncoated (top panel) micro-spheres. Left-right: whole bead, bead surface, cross section (interior).
Fig.5: Degradation profiles of pyrene by M. frederiksbergense using the chitosan coated pyrene encapsulated alginate-PVA beads containing different concentrations of the PAH.
Conclusion
Silicone oil containing pyrene was successfully encapsulated
in chitosan coated alginate- PVA beads.
More than 99 % pyrene encapsulation efficiency achieved.
Chitosan coating of microsphere improved pyrene release behavior.
Employing such microspheres as delivery vehicle, nearly
complete degradation of as high as 2000 mg/l pyrene achieved.
Acknowledgement
This research work was sponsored by the Department of Biotechnology, Government of India, vide sanction no. BT/PR-8844/BCE/08/519/2007.
Fig. 4: Photograph of bioreactor vessel showing oil encapsulated bead suspended in aqueous media.
Fig.3: Effect of alginate concentration and chitosan coating on pyrene release pattern from the micro-spheres. 0 0.05 0.1 0.15 0.2 0.25 0 5 10 15 20 25 Pyr e n e c onc e n tr a tion in a qu e ou s phase (m g /l) Time (h) 1% alginate uncoated 1% alginate coated 2% alginate uncoated 2% alginate coated 3% alginate uncoated 3% alginate coated -0.20 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 -50 0 50 100 150 200 250 300 350 Py ren e c o n c en tra tio n in a q ueo us p h a se ( mg /l ) Time (h) 2000 mg/l Control 2000 mg/l 1000 mg/l Control 1000 mg/l 500 mg/l Control 500 mg/l
