Showing papers on "Microbial biodegradation published in 1989"

Metabolism of Polycyclic Aromatic Hydrocarbons in the Aquatic Environment

Abstract: Bioavailability of Polycyclic Aromatic Hydrocarbons in the Aquatic Environment. Microbial Degradation of Polycyclic Aromatic Hydrocarbons (PAH) in the Aquatic Environment. Biotransformation and Disposition of Aromatic Hydrocarbons (PAH) in Aquatic Invertebrates. Biotransformation and Disposition of Polycyclic Aromatic Hydrocarbons (PAH) in Fish. Enzymes involved in Metabolism of PAH by Fishes and Other Aquatic Animals: Oxidative Enzymes (or Phase I Enzymes). Enzymes involved in Metabolism of PAH by Fishes and Other Aquatic Animals: Hydrolysis and Conjugation Enzymes (or Phase II Enzymes). Metabolic Activation of Polycyclic Aromatic Hydrocarbons in Subcellular Fractions and Cell Cultures from Aquatic and Terrestrial Species. Factors Influencing Experimental Carcinogenesis in Laboratory Fish Models. PAH, Metabolites, and Neoplasia in Feral Fish Population. Hydrocarbons in Marine Mollusks: Biological Effects and Ecological Consequences. Index.

Microbial degradation of nitrogen, oxygen and sulfur heterocyclic compounds under anaerobic conditions: Studies with aquifer samples

Abstract: The potential for anaerobic biodegradation of 12 heterocyclic model compounds was studied. Nine of the model compounds were biotransformed in aquifer slurries under sulfate-reducing or methanogenic conditions. The nitrogen and oxygen heterocyclic compounds were more susceptible to anaerobic biodegradation than those compounds containing a sulfur heteroatom. Carboxy-substituted compounds were anaerobically metabolized more readily than unsubstituted or methylated analogues. In methanogenic incubations, 47 to 84% of the expected amount of carbon in pyridine, 4-picoline, nicotinic acid and 2-thiophene carboxylic acid was recovered as methane. In contrast, only small amounts of methane were detected in aquifer slurries amended with compounds containing an oxygen heteroatom, even though a decrease in the parent substrate concentration occurred. Pyridine, 2-picoline and 4-picoline were biotransformed within three months under sulfate-reducing conditions. However, longer incubation times were required for the degradation of these substrates in methanogenic aquifer slurries. A literature survey reveals the widespread contamination of ground waters with heterocyclic compounds from waste management practice and fossil-fuel-related industries.

Microbial degradation of benzene and toluene in groundwater.

Abstract: Certain organic pollutants reaching the groundwater are subject to biotransformations. Currently, remedial measures promoting microbial degradation of pollutants are becoming very attractive because of their cost-effectiveness in removal of the contaminants. Current technology for reclaiming groundwater polluted with petroleum hydrocarbons involves (i) pumping the water into an aerated stripping tower, (ii) removal by sorbents, or (iii) biodegradation in situ or pumped into a bioreactor. Among the bioreactors, fixed film and suspended growth reactors are the most popular systems. Gasoline contamination of groundwaters is becoming an alarming and widespread problem. A major concern with petroleum contamination is the benzene, toluene and xylene (BTX) content reaching the groundwater because of their solubility and high toxicity. The state of California Department of Health Services now recommends that remedial action be taken when the concentration of benzene and toluene exceeds 0.7 and 100 {mu}g L{sup {minus}1}, respectively. The purpose of this study was to assess biodegradation of benzene and toluene in groundwater upon amendment with nutrients and an enriched hydrocarbon oxidizing culture.

Microbial degradation kinetics of toxic organic chemicals over a wide range of concentrations in natural aquatic systems

Abstract: The degradation kinetics for several toxic organic compounds (p-cresol, phenol, p- chlorophenol, acetone and methanol) exposed to natural aquatic microbial assemblages were examined over a wide range of concentrations. Compounds were added in radiolabeled form and incubated at 25°C for periods ranging from several hours to one day. The results revealed that degradation kinetics were multiphasic for each of the compounds during at least one sampling period, i.e., the kinetic parameters Kt and Vmax increased with increasing substrate concentration. The observed multiphasicity suggests the presence within the natural microbial assemblages of multiple uptake/degradative systems, each with distinguishable kinetic parameters and each dominating degradation at a different substrate concentration range. If the kinetic diversity is ignored and rates of degradation are calculated based on the assumption that kinetics follow simple hyperbolic (Michaelis-Menten) relationships, then errors as large as 40,000-fold can result. Thus, our results suggest that models for predicting the persistence of such compounds in natural waters should consider changes in kinetic constants with substrate concentration.

The effect of tannic compounds on anaerobic wastewater treatment

Abstract: Anaerobic wastewater treatment is an alternative to the conventional aerobic treatment processes for the removal of easily biodegradable organic matter in medium to high strength industrial wastestreams. Anaerobic treatment has several advantages, however one important disadvantage is the high sensitivity of the anaerobic bacteria (ie. methanogenic bacteria) to toxic compounds. The anaerobic technologies were initially developed for the treatment of non-toxic organic wastewaters. As the technology matured, the limits of its application to toxic wastewaters were studied. Past research has been mostly directed towards the toxic effects of compounds introduced by man into the industrial process rather than natural constituents present in agricultural wastewaters. This dissertation investigates the role of natural polar phenolics (ie. tannins and related compounds) on anaerobic digestion. Tannins are important constituents of certain types of agro-industrial wastewaters such as vegetable tannery effluent; olive oil mill effluent; wine vinasse; coffee pulp water; debarking wastewater; and masonite (fiber board) wastewater. A distinct feature of highly hydroxylated phenolics is that they are readily oxidized to darkly colored humic compounds. Such transformations can generate products which differ in toxicity and biodegradability compared to the original tannic compounds. Industrial process waters are often exposed to conditions which promote phenol oxidation, therefore the role of humus forming processes was a major consideration included in this study. The toxicity of tannin compounds to anaerobic bacteria was determined. The concentration of tannins found to cause 50% inhibition to methanogenic bacteria was 350 and 700 mg L -1 of condensed and hydrolyzable tannins, respectively. The condensed tannins were the major inhibitors present in wastewater derived from the debarking of wood at pulping factories. The effects of oxidation treatments on the methanogenic toxicity of phenolic compounds was evaluated. The initial polymerization of monomers led to a higher toxicity due to an increase in tannic qualities. The oligomers formed have stronger hydrogen bonds with proteins than the monomers. They are thus more likely to react with the functional proteins of bacteria. If the polymerization was continued, a decrease in toxicity occurred due to a lower effectiveness of high MW compounds to penetrate bacteria. These results indicated that toxic oligomeric tannins can be detoxified by oxidative polymerization. The application of autoxidation (aeration at a high pH) as a pretreatment prior to anaerobic digestion of tannin containing wastewater was tested. Debarking wastewaters of coniferous trees were successfully detoxified by autoxidation pretreatments. The tannins were converted to poorly degradable humic compounds that were non-toxic. During anaerobic treatment, no inhibition occurred and the fermentable fraction of the wastewater was converted to methane. The high MW humic products were non-toxic for aquatic organisms and thus could be discharged to the surface waters with considerably less environmental impact as compared to the unoxidized tannins. Up to date, methods of combatting toxic organic pollutants have been largely based on microbial degradation or physical-chemical removal. A viable alternative approach to these methods that potentially is applicable for certain aromatic compounds, could be polymerizing these inhibitory compounds to non-toxic humus. The humus forming process is a natural mechanism in the forest environment that detoxifies tannic compounds before such compounds are released into the surface waters. The humus forming reactions were imitated in this study and were an effective method for eliminating the environmental impact of tannins in wastewater. Research should be continued to determine the extent to which humus forming processes can be applied for the treatment of other toxic organic contaminants.

Chemical and microbial diagenesis of humic matter in freshwaters

Abstract: The importance of microbial activity in changing the chemical properties of humic material in brown waters was measured as a function of pH, acid neutralization capacity (ANC), and pKa affinity spectrum from brownwater samples kept in aquaria and sterile flasks. Changes to the humic matter in non-sterile microcosms caused increases in pH and ANC and loss of strong organic acid pKa sites. Microbial activity was shown to be the main contributor to a decrease in acidity of humic material as samples kept under sterile conditions showed less change than non-sterile ones. Microbial processes were shown to be mostly due to sessile organisms on the walls of the aquaria and in sediments. Our data suggest that acid-base properties of brownwaters can be modified based on residence times, as well as by temperature in their basins. Assuming similar starting humic materials, microbial degradation may account for the lower acidity measured in lakes and large rivers, compared to headwaters.

BIOPLUME (biodegradation in aquifers and developing a mathematical model) for contaminant transport affected by oxygen limited biodegradation. Research brief

Abstract: Many of the organic pollutants entering groundwater are potentially biodegradable in the subsurface. The potential has been demonstrated in aquifers contaminated by wood creosoting process wastes and gasoline. The persistence of many of these organic compounds in the subsurface indicated that some factors must be limiting biodegradation. The research described has been aimed at identifying the major processes that limit biodegradation in aquifers and developing a mathematical model (BIOPLUME) for simulating these processes. In order to identify the rate limiting processes for biodegradation, the equations describing microbial growth and decay and transport of oxygen and contaminants were developed and solved in one and two dimensions. The main purpose of the research was to develop the mathematical tools necessary to describe and simulate the process of oxygen limited biodegradation of organics in groundwater. The model was applied at two sites, the United Creosote Company, Inc. site in Conroe, TX and an aviation gasoline spill site in Traverse City, MI. Field work at the Conroe, TX site indicated that oxygen was limiting the microbial degradation of dissolved hydrocarbons present in the shallow aquifer. At the Traverse City, MI site, model predictions for the rates of mass loss closely matched calculated rates from more » the field data. « less