Showing papers on "Microbial biodegradation published in 2001"

Biodegradation and bioremediation of hydrocarbons in extreme environments

Abstract: Many hydrocarbon-contaminated environments are characterized by low or elevated temperatures, acidic or alkaline pH, high salt concentrations, or high pressure. Hydrocarbon-degrading microorganisms, adapted to grow and thrive in these environments, play an important role in the biological treatment of polluted extreme habitats. The biodegradation (transformation or mineralization) of a wide range of hydrocarbons, including aliphatic, aromatic, halogenated and nitrated compounds, has been shown to occur in various extreme habitats. The biodegradation of many components of petroleum hydrocarbons has been reported in a variety of terrestrial and marine cold ecosystems. Cold-adapted hydrocarbon degraders are also useful for wastewater treatment. The use of thermophiles for biodegradation of hydrocarbons with low water solubility is of interest, as solubility and thus bioavailability, are enhanced at elevated temperatures. Thermophiles, predominantly bacilli, possess a substantial potential for the degradation of environmental pollutants, including all major classes. Indigenous thermophilic hydrocarbon degraders are of special significance for the bioremediation of oil-polluted desert soil. Some studies have investigated composting as a bioremediation process. Hydrocarbon biodegradation in the presence of high salt concentrations is of interest for the bioremediation of oil-polluted salt marshes and industrial wastewaters, contaminated with aromatic hydrocarbons or with chlorinated hydrocarbons. Our knowledge of the biodegradation potential of acidophilic, alkaliphilic, or barophilic microorganisms is limited.

Biocatalysis and biodegradation : microbial transformation of organic compounds

Abstract: 1. General Concepts in Biodegradation and BiocatalysisDefinition of TermsScope of the Book: from Microbiology to Chemistry and Back AgainFurther Resources in Biocatalysis and Biodegradation2. A History of Concepts in Biodegradation and Microbial CatalysisThe Beginnings of Biodegradation on EarthEarly Human Observations of Biodegradation and BiocatalysisEarly Scientific Studies on Biodegradation and the Spontaneous Generation DebateMicrobial Pure Cultures from NatureEarly History of the Study of Diverse Metabolic Activities of MicrobesUnity of Metabolism in Living ThingsOxygen and OxygenasesHistory of Anaerobic BiocatalysisMolecular Genetics and Regulation Industrial Applications: Two Early Examples [box]Microbes in Organic SynthesisSummary 3. Identifying Novel Microbial Catalysis by Enrichment Culture and ScreeningWhy Use Enrichment Culture?The General Method The Pervasiveness of Enrichment Culture [box]Selection of Conditions and MediumScreening for Specific Biocatalytic ReactionsSummary4. Microbial Diversity: Catabolism of Organic Compounds Is Broadly DistributedThe Importance of Microbial (Bio)diversity Prokaryotes versus Eukaryotes: Fundamental Differences in Biodegradation [box]Fungi in Biocatalysis and BiodegradationDistribution in the Prokaryotic World of Biodegradative and Novel Biocatalytic CapabilitiesSpecialized Biodegradation by Microorganisms with Specialized MetabolismsAerobic versus Anaerobic Microorganisms in BiodegradationRepresentative Microorganisms with Broad Catabolic Abilities Pseudomonas putida F1 Sphingomonas yanoikuyae B1 Rhodococcus spp. Cunninghamella elegansMicrobial Consortia in BiodegradationGlobal Biodegradation and the "Supraorganism" ConceptSummary5. Organic Functional Group Diversity: the Unity of Biochemistry Is Dwarfed by Its DiversityMicrobial Global Cycling of the ElementsFacts and Fallacies: Natural Products versus Synthetic Chemicals and Their BiodegradationAdvocating a Discontinuation of Use of the Term 'Xenobiotic' with Respect to Biodegradation [box]An Organic Functional Group ClassificationOrganic Functional Groups Found in NatureRing Compounds Found in NatureOrganic Functional Groups: What Is Known with Respect to Biodegradation and Microbial Biocatalysis?6. Physiological Processes: Enzymes, Emulsification, Uptake, and ChemotaxisGeneral Physiological Responses to Environmental ChemicalsEnzymes Enzyme Classification [box]Enzyme Substrate SpecificityUptake: Getting Substrates to the EnzymesEmulsification: Overcoming Poor Availability of SubstrateOrganic-Solvent ResistanceChemotaxis: Getting to the SubstratesSummary7. Evolution of Catabolic Enzymes and PathwaysHistoryMajor Protein Families in Microbial BiocatalysisPrinciples of Evolution Applied to Microbial Catabolism Where Do New Catabolic Enzymes Come From? [box]Gene Transfer in the Evolution of Catabolic PathwaysCase Study: Enzyme Evolution in the Aminohydrolase Protein SuperfamilySummary8. Metabolic Logic and Pathway MapsIntroductionC1 Metabolism MetamapC2 MetamapCycloalkane MetamapBTEX Metamap: Aerobic MetabolismBTEX Metamap: Anaerobic MetabolismPAH MetamapHeterocyclic Ring MetamapTriazine Ring MetamapOrganohalogen MetamapOrganometallic MetamapSummary9. Predicting Microbial Biocatalysis and BiodegradationWhy Is It Necessary To Predict Biodegradation Pathways?Biodegradation Prediction SystemsDefining the Trunk PathwaysDefining the Organic Functional Groups Relevant to Microbial CatabolismThe Basis for Predicting Microbial Biocatalysis and BiodegradationBeyond Two Functional Groups: the Need for HeuristicsSummary10. Microbial Biotechnology: Chemical Production and BioremediationHistorical and Conceptual ProgressRecent TrendsConverting Biomass to Glucose [box]End Products of Fermentation: PharmaceuticalsMicrobial Catalysis To Produce Chiral ProductsChiral Synthesis of DichloropropBiocatalysis for Non-Medicinal, Non-Chiral Specialty ChemicalsBiotechnological Waste RecyclingCase Study of Bioremediation: Atrazine in SoilSummary11. The Impact of Genomics on Microbial CatalysisGenome Sizes and OrganizationThe Present Impact of GenomicsFunctional Genomics in the Context of Microbial BiocatalysisInadvertent Deception in Modern Biochemistry TextbooksThe Case for Reverse Functional Genomics and New Discovery in BiocatalysisSummary12. The Extent of Microbial Catalysis and Biodegradation: Are Microbes Infallible?Microbial Enzyme Diversity Evidence for Enormous Unexplored Metabolic DiversityExperiments Suggesting that Novel Biocatalytic Reactions Are UbiquitousEnzyme Plasticity and New BiocatalystsSummary13. Big Questions and Future ProspectsThe Questions and Some Thoughts on Their Ultimate AnswersSummaryAPPENDIXESA. Books and Journals Relevant to Biodegradation and BiocatalysisB. Useful Internet Resources in Biodegradation and Biocatalysis

Process for stimulating microbial activity in a hydrocarbon-bearing, subterranean formation

Abstract: A process is disclosed for stimulating the activity of microbial consortia in a subterranean formation to convert hydrocarbons to methane, which can be produced. Fluid and rock of the formation are analyzed. The presence of microbial consortia is determined and a characterization made (preferably genetic) of at least one microorganism of the consortia, at least one being a methanogenic microorganism. The characterization is compared with at least one known characterization derived from a known microorganism having one or more known physiological and ecological characteristics. This information, together with the information obtained from the analysis of the fluid and rock, is used to determine an ecological environment that promotes in situ microbial degradation of formation hydrocarbons and promotes microbial generation of methane by at least one methanogenic microorganism of the consortia. This information is then used as the basis for modifying the formation environment to produce methane.

Effect of Redox Conditions on MTBE Biodegradation in Surface Water Sediments

Abstract: Microbial degradation of methyl tert-butyl ether (MTBE) was observed in surface water−sediment microcosms under anaerobic conditions. The efficiency and products of anaerobic MTBE biodegradation were dependent on the predominant terminal electron-accepting conditions. In the presence of substantial methanogenic activity, MTBE biodegradation was nominal and involved reduction of MTBE to the toxic product, tert-butyl alcohol (TBA). In the absence of significant methanogenic activity, accumulation of [14C]TBA generally decreased, and mineralization of [U-14C]MTBE to 14CO2 generally increased as the oxidative potential of the predominant terminal electron acceptor increased in the order of SO4, Fe(III), Mn(IV) < NO3 < O2. Microbial mineralization of MTBE to CO2 under Mn(IV)- or SO4-reducing conditions has not been reported previously. The results of this study indicate that microorganisms inhabiting the sediments of streams and lakes can degrade MTBE effectively under a range of anaerobic terminal electron-ac...

Microbial degradation of phenanthrene and pyrene in a two-liquid phase-partitioning bioreactor.

Abstract: A study was conducted to determine the potential of two-liquid phase-bioreactors for the treatment of (polycyclic aromatic hydrocarbons) PAHs. Phenanthrene and pyrene were supplied two times at a concentration of 100 mg/l of reactor broth, either as crystals or dissolved in silicone oil. Complete phenanthrene biodegradation was achieved within 3 days after each addition to the biphasic-inoculated reactor. Its concentration in the monophasic reactors dropped by 93% within 4 days, but remained incomplete for the duration of the experiment. Pyrene removal occurred to a limited extent only in the presence of phenanthrene. Significant pollutant losses were recorded in the monophasic reactors, most likely caused by volatilization. Pollutant degradation was improved upon repeated phenanthrene amendment to the biphasic system. Biphasic reactors allow the fast and complete degradation of PAHs and prevent their hazardous disappearance. The use of biphasic reactors for the degradation of poorly soluble pollutants should become more beneficial when the substrate-interface uptake mechanism is operating. Thus, biphasic reactors should be integrated into the microbial enrichment procedure.

Anaerobic cometabolic conversion of benzothiophene by a sulfate-reducing enrichment culture and in a tar-oil-contaminated aquifer.

Abstract: Heterocyclic aromatic compounds constitute an important fraction of petroleum- and coal-derived tar oils and account for approximately 5% of creosote (32) Among the sulfur heterocyclic compounds, benzothiophene and dibenzothiophene usually dominate and are the major sulfur-containing compounds in crude oil Investigations of microbial degradation of benzothiophene and dibenzothiophene have focused on (i) the characterization of biochemical degradation reactions and microbial desulfurization processes to remove sulfur from petroleum and (ii) the inhibitory effects of thiophenes on the degradation of other compounds So far, only cometabolic degradation in the presence of an additional primary substrate has been reported for the microbial degradation of benzothiophene (6) Two primary aerobic transformation reactions have been described: dioxygenase-catalyzed diol formation followed by extradiol cleavage, analogous to aerobic naphthalene degradation by pseudomonads (11, 14, 15), and the oxidation of the sulfur atom, resulting in a sulfone (16, 18, 33) Several environmental studies reported heterocyclic compounds to inhibit the aerobic and anaerobic degradation of other aromatic compounds, indicating their significance in mixed contaminations such as oil-tar (3, 12, 13, 24, 27, 30) On the other hand, effective degradation of benzothiophene in a mixture with other aromatic compounds was observed in a contaminated aquifer (7) Fewer data are available on the anaerobic degradation of benzothiophene, although aquifers polluted with aromatic hydrocarbons usually become anoxic as a consequence of the high oxygen demand for the degradation of organic compounds Some investigations gave evidence for the anaerobic degradation of benzothiophene and dibenzothiophene leading to the production of hydrogen sulfide (22, 26) Biphenyl was the major product of dibenzothiophene degradation by the sulfate-reducing bacterium Desulfovibrio desulfuricans strain M6 (21) In that study, dibenzothiophene probably served as an electron acceptor for anaerobic respiration, a process which has been described as well for other organosulfur compounds (23) In an aquifer-derived methanogenic microcosm, mononuclear aromatic and alicyclic transformation products of benzothiophene, such as p-hydroxybenzene sulfonic acid, phenylacetic acid, benzoic acid, phenol, cyclohexane carboxylic acid, 2-hydroxythiophene, and others, have been observed (17) The present study focused on the cometabolic anaerobic conversion of benzothiophene with naphthalene as a primary substrate The formation of metabolites by a sulfate-reducing enrichment culture is discussed, and laboratory results are compared with the fate of benzothiophene in a tar-oil-contaminated aquifer

Bioremediation of petroleum hydrocarbons in soil

Abstract: A review of the literature on the biodegradability of representative hydrocarbons in petroleum (PHCs) indicates that microbes (bacteria and fungi) isolated from soil, sediments, and biosolids can readily metabolize compounds of chain lengths up to C 30 -C 44 including n -alkanes, branched alkanes with few alkyl groups, and 1-to 3-ring alkylated or nonalkylated aromatics. In general,highly branched alkanes, cycloalkanes, 4-to 6-ring condensed aromatics, and alkylated thiophenes and dibenzothiophenes are partially metabolized or are completely recalcitrant. The extent of microbial degradation of crude oils, oily wastes, and fuels in soils depends on the distribution of PHC structures, concentration, presence of a nonaqueous phase liquid (NAPL), degree of evaporative loss (weathering), and sequestration (nonbioavailability). Declines in bulk PHC in laboratory and field experiments with crude oil or refined oil products in soils are the result of volatilization and biodegradation. Studies on vapor losses of PHC from oily soils indicate that previously reported rates of decline attributed primarily to biodegradation have been overestimated. Bioremediated soils, however, are characterized by low leaching (aqueous) potential, reduced toxicity (soil species bioassays), and the persistence of a readily extractable, nonbioavailable residual phase PHC fraction. Additional research is needed to determine the (1) extent and actual biodegradation rates of PHC classes in crude oils and fuels using reference radiolabeled hydrocarbons, (2) biodegradability of PHCs in NAPL phases of soils, and (3) chronic toxicity of sequestered PHC to microbes and higher soil species. This information will be useful for assessing the long-term bioavailability and impact of oily wastes on soil ecosystem diversity and function.

Microbial Degradation of Polycyclic Aromatic Hydrocarbons

Abstract: The review summarizes the current knowledge of different metabolic pathways of polycyclic aromatic hydrocarbons degraded by bacteria and fungi; several pathways for their bacterial degradation are elucidated. Attention is also paid to a special group of ligninolytic fungi which are very promising organisms for remediation of contaminated soils.

Biodegradation of Natural and Synthetic Rubbers

Abstract: Introduction Historical Outline General Considerations Early Investigations on the Biodegradation of Natural Rubber Biodegradation of Rubber Pipe Joint Rings Degradation by Fungi Recent Developments Investigations in the Authors' Laboratory Conclusions Microorganisms Capable of Rubber Biodegradation Actinomycetes Microorganisms Other than Actinomycetes Optimization of Rubber Biodegradation Previous Experiences Recent Efforts Enzymatic Mechanisms and Genetic Basis Primary Degradation Reaction for cis-1,4-Polyisoprene Analogous Degradation Known from Other Isoprenoids Catabolism of Rubber Degradation Products Recent Investigations in the Authors' Laboratory Biodegradation of Synthetic Rubbers Biodegradation of trans-1,4-Polyisoprene Anaerobic Biodegradation of cis-1,4-Polyisoprene Perspectives and Biotechnological Applications Acknowledgements Keywords: Actinomycetes; bacteria; biodegradation; biodeterioration; cis-1,4-polyisoprene; carotenoids; classification; dioxygenase; fungi; isoprene rubber; isoprenoids; latex; latex gloves; lignostilbene; microbial degradation; microorganisms; natural rubber; optimization; oxidative cleavage; oxygenase; pipe-joint rings; polyisoprene; rubber degradation; rubber hydrocarbon; rubber polymer; rubber recycling; synthetic rubbers; taxonomy; Actinomyces; Aspergillus; Cladosporium; Fusarium; Gordonia; Micromonospora; Mycobacterium; Nocardia; Penicillium; Proactinomyces; Pseudomonas; Streptomyces; Xanthomonas

Biodegradation of dibenzothiophene by thermophilic bacteria

Abstract: Anaerobic microbial biodegradation of dibenzothiophene (DBT) was studied using thermophilic bacteria obtained from crude oil. A mixed culture was obtained that degraded 98% of DBT at 0.5 mg ml−1 at 65 °C over 15 days both in the presence and in the absence of Methyl Viologen.

Basic examinations on chemical pre-oxidation by ozone for enhancing bioremediation of phenanthrene contaminated soils.

Abstract: Biological treatment of polycyclic aromatic hydrocarbons (PAH) has been demonstrated to be a feasible and common remediation technology which has been successfully applied to the clean-up of contaminated soils. Because bioavailability of the contaminants is of great importance for a successful bioremediation, a chemical pre-oxidation step by ozone was tested to enhance the subsequent biodegradation steps. Oxidation of PAH by ozone should result in reaction products that have a better solubility in water and thus a better bioavailability. A major part of this work was done by examinations of the model substance phenanthrene as a typical compound of PAH. After initial ozonation of phenanthrene, analysis by GC-MS showed at least seven identified conversion-products of phenanthrene. In comparison with phenanthrene these conversion products were more efficiently biodegraded by Sphingomonas yanoikuyae or mixed cultures when the ozonation process resulted in monoaromatic compounds. Primary ozonation products with biphenylic structures were found not to be biodegradable. Investigations into the toxicity of contaminated and ozonated soils were carried out by well-established toxicity assays using Bacillus subtilis and garden cress. The ozonated soils surprisingly showed higher toxic or inhibitory effects towards different organisms than the phenanthrene or PAH itself. The microbial degradation of phenanthrene in slurry reactors by S. yanoikuyae was not enhanced significantly by preozonation of the contaminated soil.

Effects of alkylphosphates and nitrous oxide on microbial degradation of polycyclic aromatic hydrocarbons

Abstract: We conducted a series of liquid-culture experiments to begin to evaluate the abilities of gaseous sources of nitrogen and phosphorus to support biodegradation of polycyclic aromatic hydrocarbons (PAHs). Nutrients examined included nitrous oxide, as well as triethylphosphate (TEP) and tributylphosphate (TBP). Cultures were established using the indigenous microbial populations from one manufactured gas plant (MGP) site and one crude oil-contaminated drilling field site. Mineralization of phenanthrene was measured under alternative nutrient regimes and was compared to that seen with ammoniacal nitrogen and PO4. Parallel cultures were used to assess removal of a suite of three- to five-ring PAHs. In summary, the abilities of the different communities to degrade PAH when supplemented with N2O, TEP, and TBP were highly variable. For example, in the MGP soil, organic P sources, especially TBP, supported a considerably higher degree of removal of low-molecular-weight PAHs than did PO4; however, loss of high-molecular-weight compounds was impaired under these conditions. The disappearance of most PAHs was significantly less in the oil field soil when organophosphates were used. These results indicate that the utility of gaseous nutrients for PAH bioremediation in situ may be limited and will very likely have to be assessed on a case-by-case basis.

Characterisation of the microbial biomass in lignite-containing mine soils by radiocarbon measurements

Abstract: A method of sample preparation is presented which allows for the characterisation of the soil microbial biomass by 14 C activity measurements at natural abundance of 14 C. By the use of freeze-drying instead of chloroform for the disruption of microbial cells, the possible contamination of the sample by 14 C is avoided. Our data show a close relationship between the two methods. After extraction by CaCl 2 the 14 C activity of the freeze-dried labile carbon was recorded by accelerator mass spectrometry. Our data for lignite-containing mine soils indicate that lignite carbon which does not show 14 C activity is incorporated in the soil microbial biomass. The method can thus be used to follow microbial degradation of fossil carbon (e.g. lignite) in soil.

Analytical determination of the microbial utilization and transformation of humic acids extracted from municipal refuse.

Abstract: Humic substances are usually the refractory part of natural organic matter, and in a landfill they can retain inorganic and organic micropollutants. This study has investigated analytically whether humic acids (HA) extracted by use of alkali from either fresh municipal refuse or from refuse disposed of in a landfill for up to 12 months can resist microbial degradation under aerobic conditions. When added as a supplementary nutrient source, up to 63.6% of HA was utilized and this percentage was enhanced to a mean value of 88.5% when different HA preparations were used as the sole source of carbon. In cultures of a soil microbial community containing the same preparations as sole sources of nitrogen, HA was usually completely utilized. The remaining HA re-isolated from some microbial cultures were highly depleted in carbon and, simultaneously, the nitrogen content was enhanced. The FTIR spectra were indicative of strong participation of aliphatic structural units in the refuse-related HA preparations. Because of the microbial activity, different carbonaceous substances were primarily removed from the HA structure, and an increase in nitrogenous molecular groups became apparent. The structural transformations brought about by soil microorganisms "in vitro" corresponded to those occurring naturally in HA obtained from refuse aged for 12 months in a landfill.

Effects of Potassium Permanganate Oxidation on Subsurface Microbial Activity

Abstract: In situ chemical oxidation has the potential for degrading large quantities of organic contaminants and can be more effective and timely than traditional ex situ treatment methods. However, there is a need to better characterize the potential effects of this treatment on natural processes. This study focuses on potential inhibition to anaerobic dechlorination of trichloroethene (TCE) in soils from a large manufacturing facility as a result of in situ oxidation using potassium permanganate (KMn04)Previous microcosm studies established that natural attenuation occurs on-site and that it is enhanced by the addition of ethanol to the system. A potential remediation scheme for the site involves the use of potassium permanganate to reduce levels of TCE in heavily contaminated areas, then to inject ethanol into the system to "neutralize" excess oxidant and enhance microbial degradation. However, it is currently unknown whether the exposure of indigenous microbial populations to potassium permanganate may adversely affect biological reductive dechlorination by these microorganisms. Consequently, additional microcosm studies were conducted to evaluate this remediation scheme and assess the effect of potassium permanganate addition on biological reductive dechlorination of TCE. Samples of subsurface soil and groundwater were collected from a TCE-impacted area of the site. A portion of the soil was pretreated with nutrients and ethanol to stimulate microbial activity, while the remainder of the soil was left unamended. Soil/groundwater microcosms were prepared in sealed vials using the nutrient-amended and unamended soils, and the effects of potassium permanganate addition were evaluated using two permanganate concentrations (0.8 and 2.4 percent) and two contact times (1 and 3 weeks). TCE was then re-added to each microcosm and TCE and dichloroethene (DCE) concentrations were monitored to determine the degree to which microbial dechlorination occurred following chemical oxidation. Evidence of microbial degradation was generally detected within four weeks after TCE addition. Increases in DCE concentrations were consistent with decreases in TCE. The concentration of TCE in the nutrient-amended samples exposed to 2.4% KMnO4 for one week degraded somewhat more slowly than the samples exposed to the 0.8% KMnO4. The rates of degradation did not correlate with the length of KMn04 exposure for the nutrient-amended microcosms. Microbial degradation of TCE in the unamended microcosms was generally similar to that observed in the nutrient-amended microcosms. One treatment condition (unamended, one week exposure, 2.4% KMnO4) was exposed to elevated levels of ethanol and showed little evidence of degradation. It is suspected that the high levels of ethanol were toxic to the microorganisms. The results of the study indicate that exposure of indigenous soil and groundwater microbial populations to KMnO4 at concentrations of 0.8 to 2.4% do not impair the ability of the microbial populations to dechlorinate TCE. Consequently, the combination of chemical oxidation followed by enhanced biological reductive dechlorination appears to be a viable remedial strategy for highly-impacted subsurface areas of the site.

Degradation of Petroleum Oils by a Selected Microbial Association

Abstract: A series of microbial associations capable of the biodegradation of various petroleum oils, emulsols, and crude oil were obtained by selection during periodic or continuous cultivation. Formation of the associations and oil-product degradation occurred most efficiently during aerobic flow cultivation. Under these conditions, oils were degraded by 92% on average. The microbial degradation of a petroleum oil depended on its brand, concentration, emulsification, and aeration.

A Negative Effect of Co-solvent on Atrazine Biodegradation in Experimental River Microcosms

Abstract: A water-miscible solvent, such as acetone, acetonitrile or methanol, is often employed as a co-solvent to dissolve an organic test chemical of low water solubility in an environmental fate study using a laboratory model microcosm. These co-solvents, however, may disrupt the microflora in the water/sediment tested, and affect the biodegradation of the target compound. In the present study, a 0.1% concentration of acetonitrile as a co-solvent greatly suppressed the microbial degradation of herbicide atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] throughout the experimental period (84 days). The rapid growth of specific microbes was considered to deprive atrazine-degrading microbes of their habitat (mainly the surface area of sediment particles) in the microcosm.

Degradation of mineral oils by a selected microbial association

Abstract: A series of microbial associations capable of degrading various petroleum oils, emulsols, and crude oil were obtained by selection during periodic or continuous cultivation. The formation of these associations and oil-product degradation occurred most efficiently during aerobic flow cultivation. Under these conditions, oils were degraded by 92% on average. The microbial degradation of a petroleum oil depended on its brand, concentration, emulsification, and aeration.

Innovative Bioreactors for the Degradation of Polycyclic Aromatic Hydrocarbons

Abstract: The development of biological reactors for the treatment of toxic and recalcitrant organic pollutants is a complex task. Firstly, microbial inoculation, acclimation and selection must be optimized to provide the best microflora possible. Secondly, innovative technologies must be developed to overcome the intrinsic low degradation rates of hardly-degradable pollutants in order to allow short treatment times. Finally, since the pollutants involved are often toxic, it is also important to use well-managed treatment system that limit potential process hazards. Efficient inoculum was provided by using a mixture of indigenous soil microflora, most likely containing contaminant-degrading species, and activated sludge sample to provide microbial diversity as a protection against metabolite accumulation and substrate inhibition effects. Both fed-batch and continuous cultivations were suitable for microbial selection. Since the selection of degrading species depends on the origin of the inoculum and the procedure and system used, inoculation, acclimation and selection should be performed each time the treatment of a new effluent or the performance of a new process is studied. Both Suspended-Carrier and Packed-Bed reactors allowed the fast treatment of diluted contaminated effluent. The packed-bed reactor was preferred since it favored the development of very diverse microflora and was based on the use of a cheaper carrier. Special care should be taken in controlling pollutant adsorption to the carriers. Biphasic reactors were found to be suitable for the treatment of concentrated mixtures of contaminants such as soil extracts. Besides reducing the aqueous toxicity of the contaminants, the use of an organic phase in biphasic reactor advantageously permitted to avoid pollutant volatilization and adsorption. However, their large-scale application remains dependent on several improvements. The potential of algae photosynthesis to produce oxygen in-situ in the reactor, which limits the risk for pollutant volatilization, was clearly demonstrated. Emphasis should be given on optimizing photosynthesis efficiency, which depends on the light intensity and the algal population size, rather that the degradation of the pollutants. Since recording pollutant disappearance does not inform about the mechanism of removal and the pollutants involved are toxic, it is very important to monitor microbial activity during the entire process. The rate of disappearance of the electron acceptor used by the microflora could often be well correlated with the microbial activity and the pollutant biodegradation rate. This could lead to the development of biosensors and monitoring strategies suitable for the biological treatment of toxic and recalcitrant pollutants. Finally, although it was often difficult to avoid abiotic removal mechanisms and to monitor microbial degradation, it was still possible to evaluate and control these phenomena in most of the systems described in this thesis work. This clearly demonstrates a very important advantage of ex-situ remediation processes compared to in-situ processes.

Effective microbial degradation of organochlorines in fluidised bed reactor

Abstract: The aerobic microbial treatment of a groundwater contaminated with several organic compounds was investigated. This microbial process was combined with posttreatment by activated carbon. Mixed cultures were immobilised on polyurethane foam carrier material in a fluidised bed reactor. The main contaminants benzene and chlorobenzene were almost completely eliminated. Elimination rates remained high even at hydraulic retention times of about two hours. A complete elimination of the haloorganic compounds resistant to microbial degradation was achieved by subsequent adsorption on activated carbon. On the basis of the elimination rates and hydraulic retention times, established by these investigations, a technical scale plant combining microbial degradation and polishing adsorption can be designed. Due to the high degree of microbial mineralisation the presented process offers economic advantages over conventional methods. The quantity of residual waste products for disposal is also minimised.