Degradation of oxadiazon in a bioreactor integrated in the water closed circuit of a plant nursery.

Hardy ornamental nursery stock (HONS) use fertigation as a rational supply of nutrients all along the growth cycle of plants. Nevertheless, that frequency of irrigation increases the risks of nutrient and herbicide leaching and subsequent contamination of the waste water. Therefore, systems of water treatment are required in plant nurseries. Pseudomonas fluorescens strain CG5 cells were immobilized on a ceramic support (sepiolite) contained in a 150 l-bioreactor for the biodegradation of the herbicide oxadiazon in the re-circulated leachates. Percolation and inundation operating processes were assayed in the bioreactor. The levels of oxadiazon in water samples were determined by solid phase extraction on C18 columns and gas chromatography with electron capture detection system. Fifty eight percolation cycles resulted in a significant reduction of oxadiazon up to just 5 microg l(-1) at the outlet. Similar herbicide elimination was achieved after two consecutive 68-h inundation periods. In addition, it was found that the nutrient content in the waste water at the bioreactor outlet was sufficient to support an adequate plant growth.