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PubMed2003

Recent developments in broadly applicable structure-biodegradability relationships.

Biodegradation is one of the most important processes influencing concentration of a chemical substance after its release to the environment. It is the main process for removal of many chemicals from the environment and therefore is an important factor in risk assessments. This article reviews available methods and models for predicting biodegradability of organic chemicals from structure. The first section of the article briefly discusses current needs for biodegradability estimation methods related to new and existing chemicals and in the context of multimedia exposure models. Following sections include biodegradation test methods and endpoints used in modeling, with special attention given to the Japanese Ministry of International Trade and Industry test; a primer on modeling, describing the various approaches that have been used in the structure/biodegradability relationship work, and contrasting statistical and mechanistic approaches; and recent developments in structure/biodegradability relationships, divided into group contribution, chemometric, and artificial intelligence approaches.

Artificial Intelligence↗

PubMed2005

Evaluating the biodegradability of sulfamethazine, sulfamethoxazole, sulfathiazole, and trimethoprim at different stages of sewage treatment.

The aerobic biodegradability of four antimicrobials (sulfamethazine, sulfamethoxazole, sulfathiazole, and trimethoprim) was investigated in sewage collected at four treatment stages (primary treatment, activated sludge treatment, aerobic nitrification process, and after disinfection of treated sewage) of a municipal sewage treatment plant. The biodegradability tests were conducted in aerated batch reactors by spiking the sewage with 20 microg/L of each of the test substance. Concentration profiles of the assayed compounds were monitored during a 54-d period using liquid chromatography/electrospray ionization/mass spectrometry. Substantial differences in the degradation curves were observed between trimethoprim and the three sulfonamides. The behavior of the latter was characterized by a general biodegradability in the primary and secondary treatment. The highest degradation rates were obtained in the sewage from the activated sludge treatment, where no adaptation phase was observed. On the other hand, the onset of biodegradation in the sewage from the primary treatment was preceded by a lag phase ranging from 10 to 15 d. In contrast, trimethoprim displayed high resistance to microbial degradation in the sewage from the primary treatment and the activated sludge treatment. However, primary degradation of this compound was completed within only 3 d in the sewage from the nitrification process.

Biodegradation, Environmental↗

PubMed2005

Toxic effect of biosurfactant addition on the biodegradation of phenanthrene.

The effect of the biosurfactant rhamnolipid on phenanthrene biodegradation and cell growth of phenanthrene degraders was investigated. To compare the effect of rhamnolipid addition, two bacterial strains, 3Y and 4-3, which were isolated from a diesel-contaminated site in Korea, were selected. Without the biosurfactant, large amounts of phenanthrene were degraded with both strains at neutral pH, with higher rates of phenanthrene degradation when the cell growth was higher. Upon the addition of 240 mg/L rhamnolipid, the phenanthrene degradation and optical density were reduced, with this inhibitory effect similar for both 3Y and 4-3. To explain this inhibition, the cell growths of both strains were monitored with various concentrations of rhamnolipid, which showed significant toxic effects toward strain 3Y, but was nontoxic toward 4-3. Combining the inhibitory and toxicity results with regard to the biodegradation, different mechanisms can be suggested for each strain. In the biodegradation experiments, the toxicity of rhamnolipid itself mainly was responsible for the inhibitory effect in the case of 3Y, whereas the toxicity of solubilized phenanthrene or the increased toxicity of rhamnolipid in the presence of solubilized phenanthrene could have resulted in the inhibitory effect in the case of 4-3. This study demonstrated that the effectiveness of biosurfactant-enhanced biodegradation can be significantly different depending on the strain, and the toxicity of the biosurfactant should be considered as an important factor.

Biodegradation, Environmental↗

PubMed2005

Biodegradation during contaminant transport in porous media: 7. Impact of multiple-degrader community dynamics.

The biodegradation and transport of phenanthrene in porous media containing multiple populations of phenanthrene degraders is examined with a series of miscible-displacement experiments. A long-term experiment was conducted with a soil containing an indigenous microbial community comprised of 25 identified phenanthrene-degrading isolates. The rate and magnitude of phenanthrene biodegradation oscillated throughout the six-month experiment. This behavior, at least in part, is attributed to multiple-population dynamics associated with the indigenous community of phenanthrene degraders, the composition of which changed during the experiment. This hypothesis is supported by the results of experiments conducted using sterilized porous media that were inoculated with selected isolates obtained from the indigenous soil community. The results of experiments conducted with sterilized soil inoculated with isolate A exhibited an initial extended period of steady phenanthrene effluent concentrations, followed by a uniform decline. The results of experiments conducted using sterilized sand for single-isolate systems with one of three selected isolates and for systems of two-isolate combinations, indicate the existence of apparent synergistic and antagonistic interactions among the isolates. For example, phenanthrene biodegradation was relatively extensive and occurred without a lag phase for isolate A alone. However, biodegradation was constrained when isolate A and B were combined, indicating an antagonistic interaction. Conversely, whereas extensive lag phases were exhibited by both isolates B and C for the single-isolate experiments, there was minimal lag when isolates B and C were combined, indicating a synergistic interaction.

Benzoates↗

PubMedDate not supplied

Enhanced phenanthrene biodegradation in soil by slender oat root exudates and root debris.

To investigate the mechanisms by which slender oat (Avena barbata Pott ex Link) enhances phenanthrene biodegradation, we analyzed the impacts of root exudates and root debris on phenanthrene biodegradation and degrader community dynamics. Accelerated phenanthrene biodegradation rates occurred in soils amended with slender oat root exudates as well as combined root debris + root exudate as compared with unamended controls. Root exudates significantly enhanced phenanthrene biodegradation in rhizosphere soils, either by increasing contaminant bioavailability and/or increasing microbial population size and activity. A modified most probable number (MPN) method was used to determine quantitative shifts in heterotrophic and phenanthrene degrader communities. During the first 4 to 6 d of treatment, heterotrophic populations increased in all amended soils. Both root debris-amended and exudate-amended soil then maintained larger phenanthrene degrader populations than in control soils later in the experiment after much of the phenanthrene had been utilized. Thus, root amendments had a greater impact over time on phenanthrene degraders than heterotrophs resulting in selective maintenance of degrader populations in amended soils compared with controls.

Avena↗

PubMedDate not supplied

Reduced biodegradation of benzonitrile in soil containing wheat-residue-derived ash.

Burning of crop residues is a common agricultural practice that incorporates the resulting particulate matter (ash) of high adsorptivity into soils. To investigate the effect of ash on the biodegradation of pesticides in soils, we measured the sorption, desorption, and biodegradation of benzonitrile in a silt loam in the presence and absence of an ash resulting from burning of wheat (Triticum aestivum L.) residue. Biodegradation experiments were conducted by inoculating sorbent slurries with a pure culture of benzonitrile-degrading bacteria (Nocardia sp.). Both liquid- and sorbed-phase benzonitrile concentrations were quantified over time. The ash was approximately 2000 times more effective per unit mass than the soil in sorbing benzonitrile. Amendment of the soil with 1% ash (by weight) resulted in a 10-fold increase in sorption. Sorption of benzonitrile by the ash significantly decreased the solution-phase concentration in the slurries of ash and ash-amended soil. Desorption of benzonitrile from the ash required approximately 60 min to complete, whereas approximately 20 min were required for desorption from the soil. Benzonitrile in the extracts of various sorbents and soil slurry was completely degraded within 500 min. However, the degradation was substantially reduced in the presence of the ash. At 2000 min, only 20% of benzonitrile in ash slurry and only 44% in ash-amended soil slurry were degraded. An acclimation period of approximately 100 min was observed in extracts and slurries containing the ash. Substantial reduction in the biodegradation of benzonitrile in the presence of wheat ash was apparently due to sorption of benzonitrile by the ash, slow desorption from the ash, and the increased acclimation period. Our results suggest that the presence of crop-residue-derived ash may increase the persistence of pesticides in agricultural soils.

Adsorption↗

PubMed2006

Bioavailability of benzo[a]pyrene during NAPL-enhanced biodegradation in soil and in liquid culture.

The high molecular weight polycyclic aromatic hydrocarbon (HMW PAH) benzo[a]pyrene is generally persistent in the environment and its persistence may be due to bioavailability limitations. However, the presence of degradation-capable microorganisms and a suitable cosubstrate are also necessary. This is especially the case for benzo[a]pyrene because it may only be degraded by fortuitous metabolism. Non-aqueous phase liquid (NAPL)-enhanced benzo[a]pyrene biodegradation and indicators of bioavailability were measured in soil and liquid culture. In soil, 14CO2 from 7-[14C]benzo[a]pyrene mineralisation and overall CO2 production were monitored for 83 d after treatment with different types of NAPLs in biometer flasks. Monitoring was followed by soil extraction and measurement of 14C residues and of the remaining NAPL by gravimetry. In liquid culture, 7-[14C]benzo[a]pyrene mineralisation was monitored after treatment with different NAPLs and followed by a radiocarbon mass balance of 14C residues. Results indicated that although benzo[a]pyrene may have been bioavailable in both media types, benzo[a]pyrene mineralisation only occurred when a suitable NAPL cosubstrate was present to facilitate biodegradation. In soil, rapid increases in the rate and onset of benzo[a]pyrene mineralisation were shown to occur in benzo[a]pyrene-contaminated soils that were treated with mineral oil, which was a relatively non-biodegradable NAPL cosolvent, plus a hexane fraction-NAPL which was biodegradable and contained suitable cosubstrate(s).

Benzo(a)pyrene↗

PubMed2006

Biodegradation kinetics of BTE-OX and MTBE by a diesel-grown biomass.

The biodegradation kinetics of BTE-oX and MTBE, mixed all together in the presence of diesel-grown bioaugmented bacterial populations as high as 885 mg/L VSS, was evaluated. The effect of soil in aqueous samples and the effect of Tergitol NP-10 on substrate biodegradation rates were also evaluated. Biodegradation kinetics was evaluated for 54 h, every 6 h. All BTE-oX chemicals followed a first-order two-phase biodegradation kinetic model, whereas MTBE followed a zero-order removal kinetic model in all samples. BTE-oX removal rates were much higher than those of MTBE in all samples. The presence of soil in aqueous samples retarded BTE-oX and MTBE removal rates. The addition of Tergitol NP-10 to aqueous samples containing soil had a positive effect on substrate removal rate in all samples. Substrate percent removals ranged between 64.8-98.9% for benzene, toluene and ethylbenzene. O-xylene and MTBE percent removals ranged between 18.7-40.8% and 7.2-10.3%, respectively.

Benzene↗

PubMedDate not supplied

Zero-valent iron pretreatment for enhancing the biodegradability of Azo dyes.

Azo dyes are a group of chemicals that are largely resistant to aerobic biodegradation and persist in wastewater treatment processes. This study proposed that zero-valent iron can be used to reduce the azo bond, cleaving the dye molecule into products that are more amenable to mineralization by bacteria in biological treatment processes such as activated sludge. Batch anaerobic reduction experiments were performed using two azo dyes, orange G and orange II, to determine reaction kinetics and to identify reduction products. Iron-treated dye solutions were subjected to batch biodegradation tests and respirometric analyses to screen for enhanced biodegradability over parent dyes. Results indicate that treatment of orange G and orange II with scrap iron produces aniline and sulfanilic acid as significant products that are degraded by an acclimated culture within 24 hours. Respirometric data illustrated that iron-treated dye solutions exert a significantly higher biochemical oxygen demand than the solutions containing orange G and orange II, demonstrating that recalcitrant azo dyes can be aerobically biodegraded after iron pretreatment.

Azo Compounds↗

PubMed1998

Controlled drug delivery by biodegradable poly(ester) devices: different preparative approaches.

There has been extensive research on drug delivery by biodegradable polymeric devices since bioresorbable surgical sutures entered the market two decades ago. Among the different classes of biodegradable polymers, the thermoplastic aliphatic poly(esters) such as poly(lactide) (PLA), poly(glycolide) (PGA), and especially the copolymer of lactide and glycolide referred to as poly(lactide-co-glycolide) (PLGA) have generated tremendous interest because of their excellent biocompatibility, biodegradability, and mechanical strength. They are easy to formulate into various devices for carrying a variety of drug classes such as vaccines, peptides, proteins, and micromolecules. Most importantly, they have been approved by the United States Food and Drug Administration (FDA) for drug delivery. This review presents different preparation techniques of various drug-loaded PLGA devices, with special emphasis on preparing microparticles. Certain issues about other related biodegradable polyesters are discussed.

Absorption↗

PubMed2000

[Kinetics for terephthalic acid anaerobic degradation with easily biodegradable organic material co-existence].

The fact of preferential substrate utilization results in a sequence of substrate attack. As typically, the easily biodegradable substrates in TA-containing wastewater are degraded firstly through methane fermentation pathway, and just those intermediate metabolites have been proved to be inhibitors for TA biodegradation. Moreover, TA itself can inhibit the TA biodegradation, too. A kinetic model for the anaerobic digestion of wastewater containing both TA and easily biodegradable pollutants is constructed as q = qmax [formula: see text], The model parameters are estimated with non-linear regression method, the values are as follows: qmax = 1972.0 mgTA/gVSS.d; Ks = 20.2844 gTA/L; Ki,i = 2.041 gCOD/L; Ki,s = 0.0108 gTA/L. The experimental data verification for the model equation is satisfactory. According to the model analysis, a new strategy, a two-step anaerobic system, dealing with this kind of wastewater is suggested.

Anaerobiosis↗

PubMed2001

Biodegradation of 1,1,1,2-tetrachloroethane under methanogenic conditions.

Chlorinated aliphatic hydrocarbons are widely used as solvents and as intermediates in chemical synthesis, so they can be found in industrial wastewaters and released to the environment where they became a serious health risk due to their toxic properties and high chemical stability. Most of these compounds are xenobiotic and recalcitrant to biodegradation. In this article we report the effect of different co-substrates in the 1,1,1,2-tetrachloroethane (1,1,1,2-TeCA) degradation by anaerobic granular sludge, and its degradative pathway. Our results show that this compound is easy and rapidly biodegradable under methanogenic conditions, even in the absence of external electron donors. 1,1,1,2-TeCA is equimolecularly degraded to 1,1-dichloroethene (1,1-DCE) by reductive dichloroelimination. 1,1-DCE is only completely biodegraded in the presence of lactic acid as co-substrate. Although 1,1,1,2-TeCA can be apparently removed by autoclaved granular sludge, the compound is not transformed but retained inside the granules. The primary biodegradation of 1,1,1,2-TeCE to 1,1-DCE is a biotic process mediated by anaerobic bacteria.

Bacteria, Anaerobic↗

PubMed2001

Biodegradation of bisphenol A in aquatic environments: river die-away.

The biodegradability of bisphenol A (BPA) was assessed in surface waters from seven different rivers across the United States and Europe. Rapid biodegradation of BPA was observed in all rivers following lag phases ranging from 2 to 4 d. Biodegradation half-lives for BPA were typically less than 2 d following the lag phase. Mineralization of BPA was observed in all river waters, with average carbon dioxide yields of approximately 76% of the theoretical maximum (range 59-103%) at the end of the incubation period (< or = 18 d). Short half-lives (0.5 to 3 d) were noted for BPA biodegradation in river waters regardless of geographic location, sampling site (i.e., upstream vs downstream of wastewater outfalls), sediment addition (< or = 0.05%), and initial test chemical concentration (50-5,500 microgram/L). Subsequent studies conducted at environmentally relevant concentrations (0.05 and 0.5 microgram/L) also indicated short half-lives (3-6 d) for BPA and support the extrapolation of the half-lives measured in this study over a wide range of environmental concentrations. The fact that BPA was degraded rapidly in surface waters taken from diverse locations in the United States and Europe as well as in studies recently conducted in Japan suggests that BPA degrading microorganisms are widely distributed in nature. These observations provide clear evidence that BPA is not persistent in the aquatic environment.

Benzhydryl Compounds↗

PubMed2002

Investigation of an onsite wastewater treatment system in sandy soil: sorption and biodegradation of linear alkylbenzene sulfonate.

The objective of this work was to determine the sorptive and biodegradable characteristics of linear alkylbenzene sulfonate (LAS) in a soil below a Florida, USA, septic system drainfield. Three distinct soil samples were collected from the septic system drainfield study site. These soils were used in laboratory sorption and biodegradation studies. Different concentrations of LAS were added, in radiolabeled and unlabeled forms, to a series of test vessels that contained upgradient groundwater and the soils collected from the study site. The sorption test was designed to determine the partitioning of LAS between groundwater and soil in each sample. Results indicated that the sorption distribution coefficient (Kd) decreased from 4.02 to 0.43 L/kg and that the rate of ultimate biodegradation (first-order rate constant, k1) decreased from 2.17 to 0.08/d with increasing distance (0.7-1.2 m vertically below ground surface [BGS] and 0 to 6.1 m horizontally) from the drainfield. The three soils showed 49.8 to 83.4% LAS mineralization (percentage of theoretical CO2) over 45- or 59-d test periods. These results demonstrate that subsurface soils in this system have the potential to sorb and biodegrade LAS.

Adsorption↗

PubMed2003

Biodegradability of terephthalic acid in terylene artificial silk printing and dyeing wastewater.

As the characteristic pollutant, terephthalic acid (TA) was in charge of 40%-78% of the total COD of terylene artificial silk printing and dyeing wastewater (TPW-water). The studies on biodegradability of TA were conducted in a serial of activated sludge reactors with TPW-water. TA appeared to be readily biodegradable with removal efficiency over 96.5% under aerobic conditions, hardly biodegradable with removal efficiency below 10% under anoxic conditions and slowly biodegradable with a turnover between 31.4% and 56.0% under anaerobic conditions. TA also accounted for the majority of BOD in TPW-water. The process combined by anoxic, anaerobic and aerobic activated sludge reactor was suitable for TA degradation and TPW-water treatment, Further, the aerobic process was essentially much more effective than the anaerobic or anoxic one to degrade TA in TPW-water.

Bacteria, Aerobic↗

PubMed2003

Characterization of phenol biodegradation by Comamonas testosteroni ZD4-1 and Pseudomonas aeruginosa ZD4-3.

OBJECTIVE: To investigate the characteristic and biochemical mechanism about the phenol biodegradation by bacterial strains ZD 4-1 and ZD 4-3. METHODS: Bacterial strains ZD 4-1 and ZD 4-3 were isolated by using phenol as the sole source of carbon and energy, and identified by 16S rDNA sequence analysis. The concentrations of phenol and total organic carbon (TOC) were monitored to explore the degradation mechanism. The biodegradation intermediates were scanned at 375 nm by using a uv-vis spectrophotometer. The enzyme assays were performed to detect the activities of dioxygenases. RESULTS: Bacterial strains ZD 4-1 and ZD 4-3 were identified as Comamonas testosteroni and Pseudomonas aeruginosa by 16S rDNA sequence analysis, respectively. The growth of the two strains was observed on a variety of aromatic hydrocarbons. The strains ZD 4-1 and ZD 4-3 metabolized phenol via ortho-pathways and meta-pathways, respectively. In addition, the results of enzyme assays showed that the biodegradation efficiency of phenol by meta-pathways was higher than that by ortho-pathways. Finally, the results of induction experiment indicated that the catechol dioxygenases, both catechol 1,2-dioxygenase (C120) and catechol 2,3-dioxygenase (C230), were all inducible. CONCLUSION: The strains ZD 4-1 and ZD 4-3 metabolize phenol through ortho-pathways and meta-pathway, respectively. Furthermore, the biodegradation efficiency of phenol by meta-pathways is higher than that by ortho-pathways.

Biodegradation, Environmental↗

PubMed2003

[Aerobic biodegradation performance of six volatile organic compounds by activated sludge acclimated with toluene].

The degradation performance of six volatile organic compounds (VOCs), toluene, o-xylene, m-xylene, p-xylene, benzene and chlorobenzene by activated sludge acclimated with toluene were studied. The experimental results showed that the biodegradation rates of o-xylene, m-xylene, p-xylene, benzene and chlorobenzene increased with increasing of their initial liquid concentration; when concentrations of o-xylene, m-xylene, p-xylene, benzene and chlorobenzene were less than 149 mg/L, 129 mg/L, 133 mg/L, 234 mg/L and 146 mg/L respectively, neither of them brought any notable inhibition or poisonous effects on microbes, and their aerobic biodegradation accorded with first-order reaction. When concentrations of toluene were more than 85 mg/L, its biodegradation rate didn't increase with increasing of its initial liquid concentration and the biodegradation of toluene accorded with the Monod equation.

Aerobiosis↗

PubMed2004

Ozone treatment and biodegradation of industrial wastewater containing thioethers.

Wastewater from an Akzo Nobel production site contains refractory sulfur components (cyclic thioethers). These components end up in the effluent of the existing biological wastewater treatment plant. The possibilities of (partial) oxidation and increasing biodegradability by ozone treatment for these types of compounds have been investigated. Ozonation experiments were carried out at laboratory scale, varying pH, temperature and catalysts. Biodegradability was evaluated from BOD measurements and BOD/COD ratios. Ozonation experiments at pH = 10 without catalyst addition or heating were found to give the best results with the simplest means: COD was removed for 80-90% and biodegradability increased from BOD/COD = 0.2-0.3 to > 0.7. These results could not be improved any further by adding catalysts like iron and manganese (hydr)oxides or activated carbon, by heating or by further increasing pH. Aftertreatment at pH = 10 required about 3 kg ozone per m3 for about 80-90% removal of the total COD. This results in high annual operating costs and is therefore less suitable in practice. Biodegradability already increased to 60% at COD removal of 50% and ozone consumption of 1.4 kg/m3 wastewater. On the basis of these findings, it was calculated that ozonation has potential as pretreatment for a side stream containing the major fraction of the cyclic thioethers mixture.

Biodegradation, Environmental↗