Pyrene biodegradation with layer-by-layer assembly bio-microcapsules

- The pollutant-degrading bacteria could be encapsulated into the bio-microcapsules.
- Pyrene degradation rate by the cells was significantly increased by encapsulation.
- Cells in the bio-microcapsules could endure high initial pyrene concentrations.
- Cells in the bio-microcapsules could endure wider pH and temperature conditions.

Biotechnology is considered as a promising technology for the removal of polycyclic aromatic hydrocarbons from the environment. Free bacteria are often sensitive to some biotic and abiotic factors in the environment to the extent that their ability to effect biodegradation of organic pollutants, such as polycyclic aromatic hydrocarbons, is hampered. Consequently, it is imperative to carry out investigations into biological systems that will obviate or aid tolerance of bacteria to harsh environmental conditions. Chitosan/alginate bio-microcapsules produced using layer-by-layer (LBL) assembly method were tested for pyrene (PYR) biodegradation under harsh environmental conditions. Morphology observation indicated that the flake bio-microcapsules could be successfully prepared through LBL assembly method. Surface analysis showed that the bio-microcapsules had large fractions of mesopores. The results of the biodegradation experiments revealed that the 95% of 10 mg L−1 PYR could be removed by the bacteria encapsulated chitosan/alginate bio-microcapsules in 3 days, which was higher than that of the free bacteria (59%). Compared to the free cells, the bacteria encapsulated chitosan/alginate bio-microcapsules produced 1-6 times higher PYR biodegradation rates at a high initial PYR concentration (50 mg L−1) and extremely low pH values (pH =3) or temperatures (10 °C or 40 °C), as well as high salt stress. The results indicated that bacteria in microcapsules treatment gained a much higher tolerance to environmental stress and LBL bio-microcapsule could be promising candidate for remediating the organic pollutants.

Layer-by-layer assembly chitosan/alginate bio-microcapsules were prepared, and pyrene-degrading bacteria were successfully encapsulated into them. The microcapsule- encapsulated bacteria demonstrated immense environmental adaptability and excellent ability of pyrene degradation in high initial pyrene concentration, acidic, low temperature or high salt stress conditions.165