BIODEGRADATION OF CHLOROPHENOLS BY MIXED AND PURE CULTURES FROM A FLUIDIZED-BED REACTOR

An aerobic, continuous-flow fluidized-bed reactor was established with inoculum from activated sludge, and fed a mixture of 2,4,6-trichlorop henol (TCP), 2,3,4,6-tetrachlorophenol (TeCP) and pentachlorophenol (P CP) as the sole sources of carbon and energy for 2 years. Experiments with the enrichment were performed with material from the reactor. Lat er, degradation experiments were completed using pure cultures of bact eria that were isolated from suspended samples of the carrier biofilm. In batch-bottle bioassays, the reactor enrichment degraded PCP, TeCP and TCP both in mineral salts (MS) and tryptone-yeast extract-glucose (TGY) media. ortho-Methoxylated chlorophenols including 4,5-dichlorogu aiacol (4,5-DCG), tetrachloroguaiacol (TeCG) and trichlorosyringol (TC S) resisted biodegradation by the enrichment both in MS and TGY media, whereas 5,6-dichlorovanillin (5,6-DCV) was readily transformed to an unidentified metabolite. Experiments with C-14 labeled chlorophe nols showed mineralization of 2,4-dichlorophenol (DCP) and 2,3,5-TCP to (CO 2)-C-14 by the enrichment. Material from the suspended biofilm after c ontinuous chlorophenol feeding for 2 years was inoculated onto TGY-aga r plates, and showed predominantly two colony types accounting for ove r 99% of the total colony counts. The two colony types, were equal in abundance. Six Gram-negative, oxidase- and catalase-positive, nonferme ntative small rods were isolated in TGY agar media supplemented with 1 0 mg/l of TeCP or PCP. All isolates formed colonies in TGY plus 150 mg /l of PCP. The isolates degraded TCP and TeCP but not PCP. In mixtures of isolated bacteria the rates of chlorophenol degradation were simil ar to those observed with individual isolates. Three isolates were ide ntified as Pseudomonas saccharophila and three were an unidentified sp ecies of Pseudomonas.