Kim Broholm

Modelling TCE degradation by a mixed culture of methane-oxidizing bacteria

Abstract A model describing the growth of bacteria and the degradation of methane and trichloroethylene (TCE) based on the concept of competitive inhibition is proposed. The model has been applied to laboratory batch experiments representing different initial TCE concentrations (50–4300 μg/l) and initial methane concentrations (0.53–3.2 mg/l). The proposed model simulated successfully the data obtained for initial methane concentration (less than 1.8 mg/l), causing constant experimental growth conditions during the experiments. This indicates that the interactions between methane and TCE degradation can be explained as competitive inhibition. The model simulations of the results from the experiments with the highest initial methane concentration of 3.2 mg/l failed, supposedly because the growth conditions changed during the experiments. The proposed model is a useful engineering tool for design of treatment processes and in situ bioremediation schemes for degradation of TCE by methane-oxidizing bacteria.

Attenuation of methane and nonmethane organic compounds in landfill gas affected soils

Abstract Landfill gas (LFG) contains high concentrations of methane, which contributes to the greenhouse effect. LFG also contains aromatic hydrocarbons and chlorinated aliphatics, which, by emission to ambient air, can be a local health threat. In addition, chlorinated aliphatics may also influence the earth’s ozone layer. The objectives of the study were to investigate the degradation of LFG constituents in LFG-affected soils, and to evaluate the importance of the degradation processes to the emission. High methane oxidation potentials were found in laboratory experiments at 25 °C. The degradation seemed to follow zero order reaction kinetics, and was 3-4 times slower at 10 °C than at 25 °C. High degradation rates for benzene and toluene were also observed. In soils sampled away from the landfill, where almost no LFG contamination had been observed, longer lag phases and lower degradation rates of the two aromatic hydrocarbons were observed. Slow cometabolic degradation of trichloroethylene (TCE) and 1,...

Biodegradation of NSO-compounds under different redox-conditions

Abstract Laboratory experiments were carried out to investigate the potential of groundwater microorganisms to degrade selected heterocyclic aromatic compounds containing nitrogen, sulphur, or oxygen (NSO-compounds) under four redox-conditions over a period of 846 days. Eight compounds (pyrrole, 1-methylpyrrole, quinoline, indole, carbazole, dibenzothiophene, benzofuran, and dibenzofuran) were degraded under aerobic conditions, whereas thiophene and benzothiophene were degraded only when other compounds were degraded concomitantly. Quinoline and indole were the only two NSO-compounds degraded under anaerobic conditions, even though the microorganisms present in the anaerobic microcosms were active throughout the incubation period. A high variability in the lag period among the NSO-compounds was observed under aerobic conditions. While quinoline, indole, and carbazole were degraded with a lag period of 3–25 days, the lag periods for pyrrole, dibenzothiophene, benzofuran, and dibenzofuran were significantly longer (29–278 days). Under anaerobic conditions, lag periods of 100–300 days were observed. Differences in the degradation rate among the compounds were also observed. Indole, quinoline, carbazole, and benzofuran were quickly degraded in the aerobic microcosms, whereas a slow degradation of dibenzothiophene and dibenzofuran was observed. Pyrrole and 1-methylpyrrole were slowly degraded and 1-methylpyrrole was not completely removed within the 846 days. The anaerobic degradation rate was significantly slower than the aerobic degradation rate. The degradation rate under sulphate-reducing conditions was higher than under denitrifying and methanogenic conditions, though after re-addition of a compound a quick removal was observed. The persistence of many NSO-compounds under anaerobic conditions together with the long lag periods and the low degradation rates under aerobic conditions suggest that NSO-compounds might persist in groundwater at creosote-contaminated sites.

Sorption of heterocyclic compounds on natural clayey till

The sorption of benzofuran, dibenzofuran, benzothiophene, and dibenzothiophene from water on natural clayey till from two locations in Denmark was investigated in single solute systems for a large range of solute concentrations. The variation in sorption of a basic (quinoline) and a neutral (dibenzofuran) heterocyclic compound in samples from different depths in the natural clayey till was also investigated. The sorption isotherms for all four compounds and both clayey tills were highly non-linear, and the overall best fits were obtained with Freundlich isotherms. These observations indicate that sorption is not strictly hydrophobic or that the affinity for organic material is influenced by the sorbed solute, and that multiple components contribute to the sorption. The foc normalized linear Kd-value and Freundlich Kf-coefficient were compared with estimated Koc values. Hydrophobic sorption appears to dominate for dibenzofuran, benzothiophene and dibenzothiophene, whereas benzofuran and in particular quinoline sorption is influenced by inorganic sorption sites. This corresponds reasonably well with expectations based on estimates of critical organic carbon content. The sorption of quinoline at the uppermost sample was slightly higher (10%–20%) than for the deeper locations. This is possibly related to a slightly higher clay content at this depth. The sorption of dibenzofuran was higher at the deepest location (approximately 65%) than for the above locations. The only measured geological parameter which was significantly different in the sample from the deep location was the content of fine silt.

Effects of creosote compounds on the aerobic bio-degradation of benzene

The inhibitory effect of creosote compounds on the aerobic degradation of benzene was studied in microcosm experiments. A total removal of benzene was observed after twelve days of incubation in microcosms where no inhibition was observed. Thiophene and benzothiophene, two heterocyclic aromatic compounds containing sulfur (S-compounds), had a significant inhibitory effect on the degradation of benzene, but also an inhibitory effect of benzofuran (an O-compound) and 1-methylpyrrole (a N-compound) could be observed, although the effect was weaker. The NSO-compounds also had an inhibitory effect on the degradation of p-xylene, o-xylene, and naphthalene, while they only had a weak influence on the degradation of 1-methylnaphthalene, o-cresol and 2,4-dimethylphenol. The phenolic compounds seemed to have a weak stimulating effect on the degradation of benzene whereas the monoaromatic hydrocarbons and the naphthalenes had no significant influence on the benzene degradation. The inhibitory effect of the NSO-compounds on the aerobic degradation of benzene could be identified as three different phenomena. The lag phase increased, the degradation rate decreased, and a residual concentration of benzene was observed in microcosms when NSO-compounds were present. The results show that NSO-compounds can have a potential inhibitory effect on the degradation of many creosote compounds, and that inhibitory effects in mixtures can be important for the degradation of different compounds.

Effect of Mineral Nutrients on the Kinetics of Methane Utilization by Methanotrophs

The effect of different mineral nutrients on the kinetics of methane biodegradation by a mixed culture of methanotrophic bacteria was studied. The substrate factors examined were ammonia, iron, copper, manganese, phosphate, and sulphide. The presence of iron in the growth medium had a strong effect on the yield coefficient. Yield coefficients up to 0.49 mg protein per mg methane were observed when iron was added at concentrations of 0.10–5.0 mg/l. Iron addition also increased the maximum methane utilization rate. The same effect was observed after addition of ammonium to a medium where nitrate was the only nitrogen source. The observed Monod constant for methane utilization increased with increasing concentration of ammonia. This shows that ammonia is a weak competitive inhibitor as observed by other researchers. Relatively high levels of both ammonia (70 mg/l) and copper (300 µg/l) inhibited the methane degradation, probably due to the toxic effect of copper-amine complexes.

Transport of creosote compounds in a large, intact, macroporous clayey till column

The transport in macroporous clayey till of bromide and 25 organic compounds typical of creosote was studied using a large intact soil column. The organic compounds represented the following groups: polycyclic aromatic hydrocarbons (PAHs), phenolic compounds, monoaromatic hydrocarbons (BTEXs), and heterocyclic compounds containing oxygen, nitrogen or sulphur in the aromatic ring structure (NSO-compounds). The clayey till column (0.5 m in height and 0.5 m in diameter) was obtained from a depth of 1–1.5 m at an experimental site located on the island of Funen, Denmark. Sodium azide was added to the influent water of the column to prevent biodegradation of the studied organic compounds. For the first 24 days of the experiment, the flow rate was 219 ml day−1 corresponding to an infiltration rate of 0.0011 m day−1. At this flow rate, the effluent concentrations of bromide and the organic compounds increased very slowly. The transport of bromide and the organic compounds were successfully increased by increasing the flow rate to 1353 ml day−1 corresponding to 0.0069 m day−1. The experiment showed that the transport of low-molecular-weight organic compounds was not retarded relative to bromide. The high-molecular-weight organic compounds were retarded significantly. The influence of sorption on the transport of the organic compounds through the column was evaluated based on the observed breakthrough curves. The observed order in the column experiment was, with increasing retardation, the following: benzene=pyrrole=toluene=o-xylene=p-xylene=ethylbenzene=phenol=benzothiophene=benzofuran<naphthalene<1-methylpyrrole<1-methylnaphthalene=indole=o-cresol=quinoline<3,5-dimethylphenol=2,4-dimethylphenol<acridine<carbazole<2-methylquinoline<fluorene<dibenzofuran<phenanthrene=dibenzothiophene. This order could not be predicted from regularly characteristics as octanol/water-distribution coefficients of the organic compounds but only from experimentally determined data. The results indicate that a thin clayey till cover of the type described in this paper does not protect groundwater against contamination by low-molecular-weight organic compounds.

The influence of creosote compounds on the aerobic degradation of toluene

The inhibiting effect of 14 typical creosote compounds on the aerobic degradation of toluene was studied in batch experiments. Four NSO-compounds (pyrrole, 1-methylpyrrole, thiophene, and benzofuran) strongly inhibited the degradation of toluene. When the NSO-compounds were present together with toluene, little or no degradation of toluene was observed during 16 days of incubation, compared with a total removal of toluene within 4 days when the four compounds were absent. Indole (an N-compound) and three phenolic compounds (phenol, o-cresol, and 2,4-dimethylphenol) also inhibited the degradation of toluene, though the effect was much weaker that of the four NSO-compounds. O-xylene, p-xylene, naphthalene and 1-methylnaphthalene seemed to stimulate the degradation even though the influence was very weak. No effects of benzothiophene (an S-compound) and quinoline (an N-compound) were observed. Benzofuran (an O-compound) was identified as the compound that most inhibited the degradation of toluene. An effect could be detected even at low concentrations (40 μg/l).

Transport and biodegradation of creosote compounds in clayey till, a field experiment

The transport and biodegradation of 12 organic compounds (toluene, phenol, o-cresol, 2,6-, 3,5-dimethylphenol, naphthalene, 1-methylnaphthalene, benzothiophene, dibenzofuran, indole, acridine, and quinoline) were studied at a field site located on the island of Funen, Denmark, where a clayey till 10–15 m deep overlies a sandy aquifer. The upper 4.8 m of till is highly fractured and the upper 2.5 m contains numerous root and worm holes. A 1.5–2 m thick sand lens is encountered within the till at a depth of 4.8 m. Sampling points were installed at depths of 2.5 m, 4 m, and in the sand lens (5.5 m) to monitor the downward migration of a chloride tracer and the organic compounds. Water containing organic compounds and chloride was infiltrated into a 4 m×4.8 m basin at a rate of 8.8 m3 day−1 for 7 days. The mass of naphthalene relative to chloride was 0.39–0.98 for the sampling points located at a depth of 2.5 m, 0.11–0.61 for the sampling points located at a depth of 4 m, and 0–0.02 for the sampling points located in the sand lens. A similar pattern was observed for eight organic compounds for which reliable results were obtained (toluene, phenol, o-cresol, 2,6-, 3,5-dimethylphenol, 1-methylnaphthalene, benzothiophene, and quinoline). This shows that the organic compounds were attenuated during the downward migration through the till despite the high infiltration rate. The attenuation process may be attributed to biodegradation.

Transport and biodegradation of creosote compounds in a large, intact, fractured clayey till column

An experiment was conducted using a large, intact column of fractured clayey till to study the transport and biodegradation of 25 organic compounds typical of creosote. The column (0.5 m in height and 0.5 m in diameter) was collected from a depth of 2.5–3 m at an experimental site on the island of Funen, Denmark. For the first 82 days of the experiment, the column was infiltrated with water containing nitrate, but no organic compounds. During this period, significant nitrate removal and nitrite production were observed indicating that denitrification occurred in the clayey till. After 82 days, a mixture of 25 organic compounds with a total concentration of approximately 70 mg l−1 was added to the influent water together with a conservative tracer (92 mg bromide l−1). Most of the organic compounds were transported as rapidly as bromide, and only carbazole, dibenzofuran, fluorene, dibenzothiophene, and phenanthrene were significantly retarded. No extensive loss of organic compounds was observed during this period, which was attributed to the high concentration of applicated organic compounds. After 40 days, the influent concentration of organic compounds was lowered by a factor of 5; subsequently, significant biodegradation of phenol, ethylbenzene, toluene, quinoline, indole, p-xylene, and o-cresol was observed. Additionally, o-xylene, naphthalene, 1-methylnaphthalene, phenanthrene, fluorene, 2-methylquinoline, carbazole, acridine, benzothiophene, dibenzothiophene, benzofuran, dibenzofuran, pyrrole, 1-methylpyrrole, and benzene were biodegraded to some degree when oxygen was added concomitantly with nitrate (92 days after the addition of organic compounds). Pyrrole, 1-methylpyrrole, and benzene were only slightly biodegraded. The biodegradation of benzene was likely inhibited by the presence of pyrrole and/or 1-methylpyrrole. The study has shown that the transport of low-molecular-weight organic compounds through fractured clayey till may occur as rapid as the transport of bromide. Consequently, there is a high risk of groundwater contamination if aquifers are overlain with fractured clayey till with properties similar to the till used in this column study. The study has also shown that the till provides an environment where biodegradation of some organic compounds may occur when oxygen is provided. However, the concentration of oxygen present in water will often not be sufficient for complete biodegradation of the organic compounds at the concentrations known to be typical for creosote sites.