AEROBIC MINERALIZATION OF 2,6-DICHLOROPHENOL BY RALSTONIA SP. STRAIN RK1

A new aerobic bacterium was isolated from the sediment of a freshwater pond close to a contaminated site at Amponville (France), It was enri ched in a fixed-bed reactor fed with 2,6-dichlorophenol (2,6-DCP) as t he sole carbon and energy source at pH 7.5 and room temperature. The d egradation of 2,6-DCP followed Monod kinetics at low initial concentra tions. At concentrations above 300 mu M (50 mg . liter(-1)), 2,6-DCP i ncreasingly inhibited its own degradation. The base sequence of the 16 S ribosomal DNA allowed us to assign the bacterium to the genus Ralsto nia (formerly Alcaligenes). The substrate spectrum of the bacterium in cludes toluene, benzene, chlorobenzene, phenol, and all four ortho- an d para-substituted mono- and dichlorophenol isomers. Substituents othe r than chlorine prevented degradation. The capacity to degrade 2,6-DCP was examined in two fixed-bed reactors. The microbial population grew on and completely mineralized 2,6-DCP at 2,6-DCP concentrations up to 740 mu M in continuous reactor culture supplied with H2O2 as an oxyge n source. Lack of peroxide completely stopped further degradation of 2 ,6-DCP. Lowering the acid-neutralizing capacity of the medium to 1/10t h the original capacity led to a decrease in the pH of the effluent fr om 7 to 6 and to a significant reduction in the degradation activity. A second fixed-bed reactor successfully removed low chlorophenol conce ntrations (20 to 26 mu M) with hydraulic residence times of 8 to 30 mi n.