CHARACTERIZATION OF CHEMOHETEROTROPHIC BACTERIA ASSOCIATED WITH THE IN-SITU BIOREMEDIATION OF A WASTE-OIL CONTAMINATED SITE

In the course of an in situ bioremediation, different hydrologically c ontrollable test plots were installed on the ground of a waste-oil con taminated site, and continuously injected with nutrient solution and t he electron acceptors NO3-, O2, and H2O2. In a two-year period, ground water samples obtained from different recovery wells within these fiel d plots, in addition to subsoil samples, were monitored for several ch emical and microbiological parameters. The removal of hydrocarbons obs erved in the water samples could not unambiguously be attributed to bi odegradation, and was probably caused by groundwater treatment measure s. However, chemical (gaschromatographic) and microbiological data fro m the subsoil samples indicated a biological degradation of pollutants . Analysis of the groundwater samples of the different test plots reve aled only minor quantitative differences. With time, only a slight inc rease in bacterial numbers on different media, including hydrocarbon-a gar, was observed. In general, chemical and microbiological analyses o f groundwater samples cannot replace analyses of subsoil samples for a sufficient documentation of in situ remediation processes in subsoil. From the groundwater and subsoil samples, 3,446 pure cultures, obtain ed from R2A agar, were characterized morphologically and physiological ly, and identified in order to study the culturable bacterial communit ies. Several qualitative differences in composition and diversity of t he bacterial communities among the test plots were observed. More than 70 different species or taxonomic groups (most of them known as hydro carbon degrading taxa) could be identified from the groundwater sample s; these were mainly the Gram-negative genera Acinetobacter, Alcaligen es, Comamonas, Hydrogenophaga, Pseudomonas, Flavobacterium/Flexibacter /Cytophaga, and others. A high proportion of Gram-positive organisms ( 42.5%), belonging to Bacillus and the various genera of coryneform and nocardioform organisms, were isolated from the subsoil samples.