Showing papers on "Microbial biodegradation published in 1996"

Dissipation of Polycyclic Aromatic Hydrocarbons in the Rhizosphere

Abstract: Residual contamination of soils with polycyclic aromatic hydrocarbons (PAHs) is an environmental problem for many industrial operations, including the petroleum industry. Petroleum sludges high in PAHs are often treated through landfarming in which soil is mixed with sludge, kept bare of vegetation, tilled, and fertilized to encourage microbial degradation of the contaminants. However, recent research has demonstrated that plants can enhance the dissipation of organic pollutants in the immediate environment of the root (rhizosphere). The use of vegetation to increase the degradation of two common PAH contaminants, anthracene and pyrene, was investigated in a green house experiment. Target compounds were added to a contaminated, land-farmed soil and a similar uncontaminated soil at a rate of 100 mg/kg. Four plant species were grown in each soil; after 4, 8, 16, and 24 wk of plant growth, soil and plant material were sampled and analyzed for the target PAHs. Vegetated soils have significantly lower concentrations of the PAHs than the unvegetated soils, ranging from 30 to 44% more degradation in the vegetated soils. Enchanced biological degradation in the rhizosphere appears to be a mechanism of dissipation. Leaching, plant uptake, abiotic degradation, mineralization to CO{sub 2}, and irreversible sorption were shown to bemore » insignificatnt in the averall mass balance of target compounds. The presence of plants may enhance the clean-up of PAH-contaminated soils during in situ remediation. 40 refs. 1 fig., 5 tabs.« less

Biodegradation of individual and multiple chlorinated aliphatic hydrocarbons by methane-oxidizing cultures.

Abstract: The microbial degradation of chlorinated and nonchlorinated methanes, ethanes, and ethanes by a mixed methane-oxidizing culture grown under chemostat and batch conditions is evaluated and compared with that by two pure methanotrophic strains: CAC1 (isolated from the mixed culture) and Methylosinus trichosporium OB3b. With the exception of 1,1-dichloroethylene, the transformation capacity (Tc) for each chlorinated aliphatic hydrocarbon was generally found to be in inverse proportion to its chlorine content within each aliphatic group (i.e., methanes, ethanes, and ethenes), whereas similar trends were not observed for degradation rate constants. Tc trends were similar for all methane-oxidizing cultures tested. None of the cultures were able to degrade the fully chlorinated aliphatics such as perchloroethylene and carbon tetrachloride. Of the four cultures tested, the chemostat-grown mixed culture exhibited the highest Tc for trichloroethylene, cis-1,2-dichloroethylene, tetrachloroethane, 1,1,1-trichloroethane, and 1,2-dichloroethane, whereas the pure batch-grown OB3b culture exhibited the highest Tc for all other compounds tested. The product toxicity of chlorinated aliphatic hydrocarbons in a mixture containing multiple compounds was cumulative and predictable when using parameters measured from the degradation of individual compounds. The Tc for each chlorinated aliphatic hydrocarbon in a mixture (Tcmix) and the total Tc for the mixture (sigma Tcmix) are functions of the individual Tc, the initial substrate concentration (S0), and the first-order rate constant (k/Ks) of each compound in the mixture, indicating the importance of identifying the properties and compositions of all potentially degradable compounds in a contaminant mixture.

Mineralization of free and cell-wall-bound isoproturon in soils in relation to soil microbial parameters

Abstract: Although microbial degradation into CO2 offers one of the principal means for removing organic pesticides from soils, the influence of quantitative and qualitative soil microbial properties on mineralization of pesticides is poorly understood. In a laboratory study, we examined the relationship between soil microbial biomass and activity, estimated by heat output and adenine nucleotide fractions, and the mineralization rates of 14C-ring-labelled free and plant cell-wall-bound isoproturon, a phenylurea herbicide, in four soils originating from different cropping systems. 14CO2 production of free isoproturon ranged from 14 to 23% of the initial activity over 67 d and differed significantly between soils. 14CO2 formation from cell-wall-bound isoproturon was about one-third of that of free isoproturon with only small differences in the mineralization capacities of all four soils. For free isoproturon, mineralization correlated significantly with soil microbial biomass (estimated by substrate-induced heat production) in three soils, while in a soil from a former hop plantation no correlation was found. For cell-wall-bound isoproturon, no correlation between soil microbial biomass or activity and 14CO2 production was found. High Cu concentrations in one soil, resulting from fungicide treatments during former hop cultivation, are probably the reason for an increased metabolic status of the soil microorganisms characterized by the relative quotient of heat production (rqheat) and for the higher mineralization rate of free and cell-wall-bound isoproturon per unit biomass compared to the other soils. Our results suggest that non-specific soil microbial properties are not sensitive enough to descirbe the influence of soil microbial activities on the mineralization of free and plant cell-wall-bound isoproturon.

Model for Microbial Degradation of Nonpolar Organic Contaminants in a Soil Slurry Reactor

Abstract: An extended radial pore effective diffusion model is presented, describing the (microbial) decontamination of oil contaminated soil in a slurry. The aim of the model is to estimate the biodegradati...

Microbial degradation of hydrochlorofluorocarbons (CHCl2F and CHCl2CF3) in soils and sediments.

Abstract: The ability of microorganisms to degrade trace levels of the hydrochlorofluorocarbons HCFC-21 and HCFC-123 was investigated. Methanotroph-linked oxidation of HCFC-21 was observed in aerobic soils, and anaerobic degradation of HCFC-21 occurred in freshwater and salt marsh sediments. Microbial degradation of HCFC-123 was observed in anoxic freshwater and salt marsh sediments, and the recovery of 1,1,1-trifluoro-2-chloroethane indicated the involvement of reductive dechlorination. No degradation of HCFC-123 was observed in aerobic soils. In some experiments, HCFCs were degraded at low (parts per billion) concentrations, raising the possibility that bacteria in nature remove HCFCs from the atmosphere.

Biodegradation and evaporation of polychlorinated biphenyls (PCBs) in liquid media

Abstract: During microbial degradation of PCBs in a liquid medium, two processes influence the PCB concentration in the medium simultaneously: biodegradation and evaporation. The physical loss of PCB due to evaporation frequently causes false positive results in biodegradation experiments. Therefore, if only PCBs are monitored, the determination of the PCB concentration in both liquid and gaseous phases is necessary for a correct appraisal of biodegradation. The kinetics of PCB evaporation and biodegradation were monitored and described by a simple mathematical model. The evaporation and biodegradation rate constants for individual PCB congeners were determined for PCB degradation in liquid medium byPseudomonas stutzeri andAlcaligenes xylosoxidans, both isolated from a longterm PCB-contaminated soil.

Bioavailability and biodegradation of polycyclic aromatic hydrocarbons

Abstract: One of the main problems in biological soil remediation is the slow or incomplete degradation of hydrophobic organic pollutants. The principal reason for this problem is the fact that these compounds bind strongly to the soil matrix or occur as a separate non- aqueous phase in the soil. As most microbiological processes take place in the water phase, transport of the polluting compound to this phase is essential for biodegradation to occur. When this transport is the limiting factor in the biodegradation process, this is termed limiting bioavailbility. This thesis deals with the effect of bioavailability on the biodegradation of polycyclic aromatic hydrocarbons (PAHs). PAHs are hydrophobic organic pollutancs that are abundantly present in contaminated soils and give raise to ervironmental concern because of their toxicity and mutagenicity. Most PAHs are degradable by microorganisms and the important biochemical aspects of the PAH-degradation hav been revealed. PAHs are nevertheless considered persistent pollutants in soil, a fac that is attributed to their limited bioavailability. The first part of the research consisted of the isolation of bacteria capable of degrading the PAHs, naphthalene, phenanthrene, and anthracene. Subsequently a number of isolated bacterial strains were grown in batch and continuous cultures to determine the most important microbial growth parameters, such as the maximum growth rate, the Monod saturation constant, and the bacterial growth yield. The effect of bioavailability on the biodegradation of PAHs was studied in two model systems: (i) crystalline PAHs and (ii) PAHs bound to a matrix. For studying the bioavailability of crystalline PAHs the results of dissolution and biodegradation experiments were compared. In the degradation experiments it was found that two phases could be observed during batch growth: an exponential growth phase, followed by a linear growth phase, in which biomass formation was limited by the availability of the PAHs. By using a model in which Monod kinetics for bacterial growth were coupled to dissolution kinetics for substrate availability, it was shown that the observed degradation rates were matched by the rates of dissolution of the PAHs to the aqueous phase. Therefore it was concluded that in this system only aqueous phase PAHs were available for bacterial uptake and that the bioavailability of the PAHs was not directly stimulated by the presence of the microorganisms. With matrix-bound PAHs desorption and biodegradation experiments were conducted. The first matrices studied were the synthetic porous resins XAD4 and XAD-7. The desorption of naphthalene from these materials was studied in batch and continuous desorption experiments. The results from these experiments could be described using a two-compartment model in which the matrix is divided in a fraction with shallow pores and one with deep pores. In biodegradation experiments with naphthalene- loaded resins the same type of batch-growth kinetics was observed as described above for crystalline substrates: exponential growth, followed by a phase in which substrate availability limits the degradation rate. By comparing the results of the desorption experiments and the biodegradation experiments it was shown that the biodegradation proceeded faster than could be explained by desorption alone. Therefore it was concluded that the bacteria had a positive effect on the bioavailability of naphthalene that was adsorbed onto the resins. This effect was not caused by the presence of bacterial excretion products. In contrast to this it was found that the biodegradation of soil-bound naphthalene and phenanthrene could be explained by degradation of PAHs present in the aqueous bulk phase only. Thus, the bioavailability of sorbed PAHs depends on the type of matrix the PAHs are sorbed onto. The second part of this thesis deals with the most widely applied solution for the problem of limited bioavailability: the application of surface-active agents or surfactants. Surfactants are molecules that usually consist of a hydrophillic and a hydrophobic part. Due to this they have a tendency to concentrate at surfaces and interfaces and to form new interfaces. There are several different ways by which surfactants may increase the bioavailability of hydrophobic compounds in soil: - solubilization in the aqueous phase by the presence of micelles, aggregates of 20-200 surfactant molecules with a hydrophobic interior; - emulsification of liquid hydrocarbons in the waterphase; - facilitated transport, a term that covers several processes, such as mobilisation of pollutant present in soil pores or interaction pollutant with single surfactant molecules; Surfactants may also have a negative effect on pollutant bioavailability, for instance by the toxic effect or preferential degradation of the surfactant, or by interference with the natural interactions among microorganisms and pollutant. The effect of several nonionic surfactants on the bioavailability of PAHs was studied in the same model systems as described above: crystalline PAHs and PAHs sorbed onto a matrix. Dissolution experiments with crystalline naphthalene and phenanthrene showed that the presence of surfactants caused an increase in the apparent solubility and in the maximum dissolution rate of these PAHs. Both phenomena have an effect on the bioavailability of PAHs. Although it was found that micellar PAHs were not readily available for uptake by the bacteria, the transport of PAHs from the micelles is sufficiently fast to allow almost complete exponential growth on solubilized PAHs. The effect on the maximum dissolution rate is probably more important because this is the most relevant factor under bioavailability-limiting conditions. Addition of surfactant to cultures growing on PAH in the dissolution-limited phase resulted in an increase in the linear growth rate. This shows that for crystalline PAHs surfactants can be used to increase the bioavailabilty For sorbed naphthalene similar results were found. In desorption experiments it was shown that in the presence of surfactant, the partitioning of naphthalene to the waterphase as well as the maximum desorption rate was increased. Addition of surfactants to cultures growing on sorbed naphthalene in the desorption-limited phase resulted in an increase in the degradation rate. This shows that surfactants can be used for enhancing the bioavailability of sorbed PAHs. The first general conclusion from this thesis is that the bioavailability of hydrophobic pollutants in soil is a complex matter and therefore difficult to quantify. In model systems under laboratory conditions, however, it was possible to simulate the essential processes. This experimental work revealed the most important mechanisms that play a role in bioavailability limtations. Because of the large impact of bioavailability on both the performance of biological soil remediation and on the risks posed by soil contamination, it is essential that standard methods be developed which provide criteria for bioavailability. These criteria may be used to predict the results of biological soil remediation processes and may form a basis for soil quality limits in which the bioavailability of the pollutant is considered. Secondly, the application of surfactants can be concluded to be a promising option for enhancing the bioavailability of hydrophobic pollutants. In two model sytems it was shown that addition of surfactants speeded up the biological degradation of PAHs markedly and some explanations for this phenomenon have been found. However, to allow the use of surfactants as a standard technique in biological soil remediation, more insight into the complex interactions involved in the introduction of surfactants into soil is necessary.

Analytical characterization of the persistent residues after microbial degradation of mineral oils

Abstract: The residual fractions remaining after microbial degradation of diesel fuel, different deparaffinized raffinates and extracts from long-term contaminated soils were analyzed by liquid chromatography, gas chromatography, infrared spectrometry and mass spectrometry. The quantity of saturated hydrocarbons decreased after the microbial treatment, whereas the portion of polar compounds increased. The total content of aromatics changed only insignificantly. n-Paraffins < C26 were found to be no longer present in mineral oils degraded to exhaustion. Infrared spectrometry revealed oxygen compounds in the residues, mainly ketones, fatty acids and esters. Elementary analysis confirms the presence of nitrogen, oxygen and sulphur compounds in the degraded products. The gas chromatograms of high boiling oils, as well as of residues and extracts, consist mainly of a large base "envelope" (about 95% of the total area); thus gc/ms coupling reaches the limits of its applicability. However, mass spectrometry with direct inlet gives valuable information regarding hydrocarbon type analysis. The results revealed the preferable degradation of alkanes, 1-ring aliphatics and benzenes and an enrichment of condensed cycloaliphatics and aromatics. The latter compounds are known to be resistant to microbial attack.

Effect of oxygen amendments and soil pH on bioremediation of industrially contaminated soils

Abstract: Polynuclear aromatic hydrocarbons (PAHs), by-products of coal conversion processes, have contaminated soils near coal plant sites either through accidental spills or systematic discharge. Because these compounds are carcinogenic, mutagenic, and teratogenic, remediation of such sites is a legitimate concern. For this study, contaminated soil samples were obtained from the Alberta Research Council (ARC) primary clean-up facility. Preliminary analysis of the soil was done for contaminant characterization and determination of initial contamination levels. Acinetobacter sp. was used for aerobic treatment of soil over a five-week period under optimum conditions. Because the rate of biodegradation is influenced by the pH, it is of interest to study the effect of pH on remediation efficiency in the physiological pH range of 5.0 to 9.0. Also, oxygen amendment via hydrogen peroxide solution was used to improve remediation in a packed bed, and the results were compared with those obtained under completely mixed conditions.

Influence of Different Redox Conditions on the Biodegradation of the Pesticide Metabolites Phenol and Chlorophenols

Abstract: The fate and behaviour of phenol and monochlorophenols during bankfiltration and underground passage with variable redox conditions were investigated. A model ecosystem was used consisting in laboratory filter columns filled with natural underground material and operated with natural aerobic and anaerobic groundwater to create different redox situations. The test substances (phenol, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol) were added continuously to the infiltrating water and their concentration in the filter effluents determined. Beside the redox conditions other factors known to affect microbial degradation processes like the substrate concentration and the underground material were varied stepwise. Phenol was degraded under both, aerobic and anaerobic conditions. The presence of oxygen is more favourable to degradation; no lag phase was observed under aerobic conditions. In a sulfate reducing environment, phenol could only be degraded after microbial adaptation. The length of the lag ph...

An investigation of the aerobic microbial degradation of sulfur, nitrogen, and oxygen heterocycles by three local marine bacterial consortia

Abstract: Bacterial samples were collected from three marine beaches in coastal Newfoundland and enriched by growth on 1-methylnaphthalene. The most prominent bacterial cell type for each consortium was isolated in a serial dilutions test, and a substrate utilization profile was obtained for each using the Biolog Microstation System. Each bacterial community was tested for its ability to degrade sulfur heterocycles (benzothiophene: BT, 3-methyl-benzothiophene: 3-MBT, and dibenzothiophene: DBT), a nitrogen heterocycle (carbazole: CARB), and an oxygen heterocycle (dibenzofuran: DBF). Incubations were carried out at an optimum temperature for culture (25°C) and at a temperature more typical of a northern environment (4°C). Degradation of the compounds was determined using gas chromatography-mass spectroscopy (GC-MS) and degradation products were identified using GC-MS and Fourier transform infrared spectroscopy (FTIR). Bacterial growth was monitored using optical density measurements to determine the dry weight (μg) of cells/mL and the number of colony forming units/mL (CFU/mL). The 2-ringed heterocycles were degraded faster and to a greater extent than the 3-ringed compounds. Degradation of BT was not statistically different from that for 3-MBT and, likewise, a comparison of the 3-ringed heterocycles showed no significant differences in degradability at either incubation temperature. There was a significant difference in degradation of the compounds at the two incubation temperatures as biodegradation was 3 to 5 times greater at 25°C than at 4°C. Statistical examination revealed that no one culture demonstrated a significantly greater ability to degrade the 5 heterocycles studied which means that the bacterial consortium isolated from a beach in Bonne Bay, NF., where the sediments exhibited no visible signs of hydrocarbon contamination, demonstrated the ability to degrade the heterocyles as efficiently as bacterial communities from visibly contaminated soils at Come by Chance and Port aux Basques, NF. This study represents the first comprehensive investigation of the ability of local bacteria to biodegrade a range of aromatic compounds. It provides a preliminary understanding of the fate of aromatic compounds in sediments, in terms of their half-life versus environmental temperature.

Untersuchungen an Modellökosystemen zum Verhalten von Bromoxynil bei der Grundwasseranreichung

Abstract: The behaviour of the herbicide bromoxynil (3,5-dibromo-4,hydroxybenzonitrile) during artificial groundwater recharge and underground passage of water was investigated. The investigations included the determination and identification of metabolites. In the experiments model ecosystems were used, simulating the field conditions during slow sand filtation and underground passage. A commercial product of bromoxynil was applicated continuously to the systems with an concentration of 1 mg bromoxynil per litre. The investigation time was 4 weeks. Biodegradation of bromoxynil could be observed during slow sand filtration as well as under aerobic and anaerobic groundwater conditions. The degradation rate was 93 to 99 % in the slow sand filter and 78 to 83 % in different groundwater systems. Microbial adaptation increased the degradation rates in pretreated systems. Under anaerobic groundwater conditions no lag-phase could be observed. Under aerobic conditions an adaptation time of more than 3 weeks was necessary, to induce the biodegradation of bromoxynil. The identified metabolites (3-bromo-4-hydroxybenzonitrile, 3-chloro-5-bromo-hydroxy-benzonitrile, 3-bromo-4-hydroxybenzamide, 3,5-dibromo-4-hydroxybenzoic acid) indicated an incomplete metabolism, even after 3 weeks in the slow sand filter. A transport of these metabolites into the groundwater is possible. Additional investigations of the bioactivities (esterase activity) showed an inhibition of microbial activities up to 55 % in model ecosystems treated with bromoxynil. These results indicated, that high concentrations of bromoxynil can influence the microbial degradation processes during groundwater recharge.

Critical Experiments to Determine Feasibility of Organic Contaminant Biodegradation in Cationic Surfactant Treated Media.

Abstract: : A soil column with 20 sampling ports was designed to assess the binding and potential microbial degradation of naphthalene in Columbus Air Force Base aquifer soil treated with the surfactant, hexadecyltrimethylammonium bromide (HDTMA). HDTMA was found to be toxic to most aerobic soil microorganisms when applied to the soil. However, when the HDTMA was bound to soil, the toxicity decreased and the microbial populations readily recovered to normal levels. Naphthalene was used as a test substrate and was found to readily bind to HDTMA treated soil under anaerobic conditions. When aeration was applied, microbial populations adapted to HDTMA at a faster rate than to the test substrate, naphthalene. This phenomenon caused naphthalene to be desorbed from the soil and naphthalene began to migrate behind metabolized surfactant. Naphthalene metabolism was not observed as assessed by chromatographic analysis of soil sample extracts collected along the column length. Metabolized surfactant was found to leach from the soil column. Under the conditions of this study, it appears that the surfactant technology may have limited utility in soils where pollutant-adapted microbial populations do not recover at sufficient speed to compete with surfactant utilization.