MICROBIAL-DEGRADATION OF PHENOLS AND AROMATIC-HYDROCARBONS IN CREOSOTE-CONTAMINATED GROUNDWATER UNDER NITRATE-REDUCING CONDITIONS

Batch experiments were carried out to investigate the biodegradation of phenols and aromatic hydrocarbons under anaerobic, nitrate-reducing conditions in groundwater from a creosote-contaminated site at Fredensborg, Denmark. The bacteria in the creosote-contaminated groundwater degraded a mixture of toluene, phenol, the cresols (o-, m- and p-cresol) and the dimethylphenols 2,4-DMP and 3,4-DMP at both 10-degrees and 20-degrees-C. Benzene, the xylenes, naphthalene, 2,3-DMP, 2,5-DMP, 2,6-DMP and 3,5-DMP were resistant to biodegradation during 7-12 months of incubation. It was demonstrated that the degradation of toluene, 2,4-DMP, 3,4-DMP and p-cresol depended on nitrate or nitrite as electron acceptors. 40-80% of the nitrate consumed during degradation of the aromatic compounds was recovered as nitrite, and the consumption of nitrate was accompanied by a production of ATP. Stoichiometric calculations indicate that in addition to the phenols and toluene other carbon sources present in the groundwater contributed to the consumption of nitrate. If the groundwater was incubated under anaerobic conditions without nitrate, sulphate-reducing conditions evolved after approximately 1 month at 20-degrees-C and approximately 2 months at 10-degrees-C. In the sulphate-reducing batches disappearance of toluene, phenol, o-cresol and m-cresol was observed, whereas no removal of benzene, the xylenes, naphthalene, 2,3-DMP, 2,4-DMP, 2,5-DMP and 3,5-DMP was detected during 7 months of incubation.