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Aquatic humic substances (HS) from a bog lake water, a riverwater, and a groundwater were isolated after enrichment on XAD 8 columns and added to a Czapek-Dox nutrient broth which was used either in full strength or without glucose and/or NaNO3. The individual flasks were inoculated with natural microbial populations of corresponding water samples or with a Pseudomonas fluorescens strain isolated from groundwater. The presence of HS resulted in an increase of bacterial numbers in nearly all cultures incubated for 3 weeks at 25 degrees C on a shaker. HS reisolated from cultures without glucose or NaNO3 showed no or only minor quantitative differences as compared to those from sterile controls. In full strength nutrient broth up to 27% of HS were utilized. Data obtained by spectroscopic methods (UV/vis/FTIR) and elemental analysis indicated a decrease in particle size and a loss in aromaticity and aliphatic carbon in HS reisolated from the microbial cultures. Simultaneously an increase in the N content of HS was observed, which probably originated from some constituents of microbial biomass such as proteins and amino sugars. The NMR data also documented that significant transformations of HS occurred in the individual microbial cultures. After incubation, increased amounts of aromatic acids were detected in some liquid media and residual HS by GC/MS or capillary electrophoresis. 1H NMR spectroscopy was less effective in indicating structural differences in the HS than 13C NMR but revealed considerable detail of the microbial degradation of riverine HS, when limited sample was available. The newly developed NMR increment analysis provided substantial detail of aromatic structures in a microbially altered HS. The microbial degradation of HS strongly depended on the composition of the HS, the species selection of the microorganisms, and to a lesser extent on the culture conditions. For any series of identical inoculum and HS, full broth media initiated the most extensive alteration of HS.

On surface of PVC packing sheets in wet cooling towers thick sediment layers can often be observed (Fig. 1) which usually cause several technological troubles. Microbiological investigations were made in order to estimate whether some hygienic risk possibly based on the proliferation of hygienic relevant microorganisms in the sediment have to be considered. An abundance of bacteria actinomycetes and fungi was found in the sediments from PVC packing sheets which were exposed for 6 or 20 weeks in a wet cooling tower (Table 2). However, the microbial (colony) counts usually decreased when the exposition time increased. Pseudomonas aeruginosa was not detected at all. Coliform bacteria and Escherichia coli showed a declining development both in the sediment and in the cooling water unter test (Table 3). Total volume of plankton also decreased in cooling water incubated with small pieces of PVC packing sheets. The results indicate the sediment formation on PVC packing sheets in wet cooling towers probably not to be problem of environmental hygiene but technology. The sediment formation seems to depend mainly of the quality (i.e. pollution degree) of cooling water and also of surface properties of the packing sheets.

Biotechnological in situ measures can become a suitable mean to compete with a broad spectrum of mainly organic contaminants in soil and ground water environments. They can partly follow the spread of the contaminants, are ecologically safe and economically reasonable. Their application, however, is less effective at high concentrations of the contaminants, in the presence of toxicants and also under hydraulically unsuitable conditions. Care must be taken to avoid possible side-effects of the nutrient added, enriched microbial biomass, and some metabolical products. Long-term effects of in situ remediation techniques, and especially in connection with the possible use of added microorganisms, are not well known, yet. There is a need for further research in this complex field, in order to establish a scientific base because until now these remediation techniques were mainly based on empirical views.