Entwicklung von Labormethoden zur Prognose des mikrobiellen Selbstreinigungspotentials kontaminierter Grundwässer und Böden

摘要

This work has been part of the DFG priority program 546 “Geochemical processes with long-term effects in anthropogenically-affected seepage- and groundwater”. The investigations aimed at developing a practice-orientated method which allows to predict the microbial effects on long-term behaviour of xenobiotics and the capability for natural attenuation at a contaminated site. Samples of soil and groundwater from a former gaswork site highly contaminated with BTEX and PAH were insert in short- and long-term experiments to investigate their microbial potential. In the short-term experiments a nutrient limitation as well as toxic effects were determined limiting a microbial degradation of xenobiotics. BTEX-contaminated soil samples showed an enhanced O2-consumption, however the microbial respiration of with PAH contaminated soil samples was inhibited. This effect could partly be avoided by adding nutrients like ammonium and phosphate. Microbial degradation activity was assessed in the long-term experiments by monitoring the CO2-production and in the aerobic experiments additionally the O2-consumption as well as by determination of the decrease of contaminants, electron acceptors and increase of organic acids as metabolits. In batch-culture with groundwater a decrease of contaminants was proved, in the soil suspension however the fate of the xenobiotica after an incubation over 400 days could not be determined. The comparison with batch-cultures as soil suspension or with a water content of 50 % of the maximum water holding capacity of the soil sample showed that different conditions during the incubation have been apeared depending from the various matrix of the gravelly and loamy soil samples. In a batch-culture with gravelly soil all in the soil avaiable nutrients as well as contaminants dissolve and a nearly homogenous medium is obtained. However, with loamy soil samples it comes into a two-phase-system without a complete mixture of the liquid and solid phase. Because of these circumstances microbial acitivity preferably took place at the interface soil-water and in the first layer of the solid phase. The measured parameters of the liquid phase did not reflect the processes in the solid phase. Another problem was that producted CO2 dissolve in the water phase and was just partly released in the gasphase, thus a quantifying of respiration rate was difficult. The approach aimed in the beginning to determine the microbial acitivity by measuring CO2 and O2 could not be reached contentedly. The qaulifying and quantitying of the sulphate reducing processes in the soil suspensions have been difficult because of the partly high origin sulphate content of same soil samples. Soil samples showed significant higher activities than ground water samples. The activity of the different samples both soil and groundwater differed widely and was lower under anaerobic than under aerobic conditions. Due to the heterogeneity of the soil samples the results of the experiments with groundwater were not comparable to the microbial activity in the soil suspensions. The described strategy of investigations seems to be suitable in connection with hydrogeological data to estimate the potential of natural attenuation and enhanced natural attenuation, but optimizing is imperative. The soil suspension as test design can not be recommended.