Behavior of chemical contaminants under controlled redox conditions in an artificial sequential soil column system...

A leachate pollution plume was simulated in a sequential soil column system (SSCS), defined by a longitudinal redox cascade from methanogenic, sulfate-, nitrate-reducing to aerobic conditions. A mixture of contaminants, including compounds such as perchloroethene (PER), 1,1-dichloroethene (DCE), 1,4-dichlorobenzene (DCB), 2-nitrophenol (NP), and benzene (BEN) was supplied to the methanogenic column; their conversion was followed during passage through the SSCS. After establishment of a steady state, parameters were changed to simulate changes in the environment and to follow the reactions of the system. Acetate, initially introduced as an anaerobically easy degradable carbon source, was first omitted and later added again to the system. Furthermore, the medium flow rate and by that the load of the test compounds was increased 4 fold. Changes transiently increased the residual concentrations of most of the xenobiotics. Within seven months after acetate omission, turnover of contaminants had almost returned to the original steady state. Flow and load increase resulted in increased transformation of compounds such as PER, NP, and BEN. After readdition of acetate, the turnover of most of the xenobiotics increased within the next five weeks. Microbial populations for the anaerobic batch cultures, obtained from the specific columns, were used to investigate metabolites formed and conversion kinetics of the xenobiotics. Almost the same conversion pattern was found in batches and columns, except no transformation of DCE and DCB was detected in the SSCS, though both compounds were converted in batch cultures.