IN-SITU AND LABORATORY STUDIES ON THE FATE OF SPECIFIC ORGANIC-COMPOUNDS IN AN ANAEROBIC LANDFILL LEACHATE PLUME .1. EXPERIMENTAL CONDITIONS AND FATE OF PHENOLIC-COMPOUNDS

The transformation of specific organic compounds was investigated by i n situ and laboratory experiments in an anaerobic landfill leachate po llution plume at four different distances from the landfill. This pape r presents the experimental conditions in the in situ microcosm and la boratory batch microcosm experiments performed and the results on the fate of 7 phenolic compounds. Part 2 of this series of papers, also pu blished in this issue, presents the results on the fate of 8 aromatic compounds and 4 chlorinated aliphatic compounds. The redox conditions in the plume were characterized as methanogenic, Fe(III)-reducing and NO3--reducing by the redox sensitive species present in groundwater an d sediment and by bioassays. With a few exceptions the aquifer redox c onditions were maintained throughout the experiments as monitored by r edox sensitive species present in groundwater during the experiments, by redox sensitive species present in the sediment after the experimen ts and by bioassays performed after the experiments. Transformation of nitrophenol was very fast close to the landfill in strongly reducing conditions, while transformation was slower in the more oxidized part of the plume. Lag phases for the nitrophenols were short (maximum 10 d ays). Phenol was only transformed in the more distant part of the plum e in experiments where NO3-, Fe(III) and Mn(IV) reduction was dominant . Lag phases for phenol were either absent or lasted up to 2 months. D ichlorophenols were only transformed in experiments representing stron gly reducing, presumably methanogenic, redox conditions close to the l andfill after lag phases of up to 3 months. Transformation of o-cresol was not observed in any of the experiments throughout the plume. Gene rally, there was good accordance between the results obtained by in si tu and laboratory experiments, both concerning redox conditions and th e fate of the phenolic compounds. However, for phenol and 2,4-dichloro phenol, transformation was observed in same in situ experiments but no t in the corresponding laboratory experiments. In some experiments, th is could be explained by differences in the redox conditions developin g during the experiments. Nitrophenols were apparently transformed abi otically in the most reduced part of the plume, at 2 m from the landfi ll.