betadex and tenax

The effectiveness of anaerobic bioremediation systems for PAH-contaminated soil may be constrained by low contaminants bioaccessibility due to limited aqueous solubility and lack of suitable electron acceptors. Information on what is the rate-limiting factor in bioremediation process is of vital importance in the decision in what measures can be taken to assist the biodegradation efficacy. In the present study, four different microcosms were set to study the effect of methyl-β-cyclodextrin (MCD) and nitrate addition (N) on PAHs biodegradation under anaerobic conditions in a red paddy soil. Meanwhile, sequential Tenax extraction combined with a first-three-compartment model was employed to evaluate the rate-limiting factors in MCD enhanced anaerobic biodegradation of PAHs. Microcosms with both 1% (w/w) MCD and 20mM N addition produced maximum biodegradation of total PAHs of up to 61.7%. It appears rate-limiting factors vary with microcosms: low activity of degrading microorganisms is the vital rate-limiting factor for control and MCD addition treatments (CK and M treatments); and lack of bioaccessible PAHs is the main rate-limiting factor for nitrate addition treatments (N and MN treatments). These results have practical implications for site risk assessment and cleanup strategies.

Topics: Anaerobiosis; beta-Cyclodextrins; Biodegradation, Environmental; Nitrates; Polycyclic Aromatic Hydrocarbons; Polymers; Soil Pollutants

The potential bioavailability of phenanthrene aged in soil was determined by using a self-dying reporter bacterium, and the results were compared to two physicochemical measures, Tenax TA(®) bead-assisted desorption, and hydroxypropyl-β-cyclodextrin (HPCD) extraction. The reporter bacterium, capable of degrading phenanthrene as a sole carbon and energy source, was genetically reconstructed to die when it degrades phenanthrene. Therefore, population change of the reporter cells can be viewed as the quantification of bioavailable phenanthrene. When Ottawa sand was used as an aging matrix, the amounts of bioavailable phenanthrene (i.e. little gradual decrease) were similar, regardless of aging time, and consistent between the reporter bacterium and the two physicochemical measures. However, decrease in bioavailable phenanthrene with aging was readily evident in sandy loam with organic matter of 11.5%, with all three measures. More importantly, when the reporter bacterium was used, a rapid and significant decrease in the bioavailable fraction from 1.00 to 0.0431 was observed. The extent of decrease in bioavailable fraction was less than 40% in the two physicochemical measures, but was nearly 100% in the reporter bacterium, during the first 3 months of aging. Our results suggest that the phenanthrene fraction available to bacterial degradation, and probably the fraction that really manifests toxicity, may be much smaller than the fractions predicted with the physicochemical measures.

Topics: 2-Hydroxypropyl-beta-cyclodextrin; beta-Cyclodextrins; Biodegradation, Environmental; Biological Availability; Organisms, Genetically Modified; Phenanthrenes; Polymers; Soil; Soil Pollutants; Sphingomonas

The effectiveness of many bioremediation systems for PAH-contaminated soil may be constrained by low contaminant bioaccessibility due to limited aqueous solubility or large sorption capacity. Information on the extent to which PAHs can be readily biodegraded is of vital importance in the decision whether or not to remediate a contaminated soil. In the present study the rate-limiting factors in methyl-β-cyclodextrin (MCD)-enhanced bioremediation of PAH-contaminated soil were evaluated. MCD amendment at 10 % (w/w) combined with inoculation with the PAH-degrading bacterium Paracoccus sp. strain HPD-2 produced maximum removal of total PAHs of up to 35 %. The desorption of PAHs from contaminated soil was determined before and after 32 weeks of bioremediation. 10 % (w/w) MCD amendment (M2) increased the Tenax extraction of total PAHs from 12 to 30 % and promoted degradation by up to 26 % compared to 6 % in the control. However, the percentage of Tenax extraction for total PAHs was much larger than that of degradation. Thus, in the control and M2 treatment it is likely that during the initial phase the bioaccessibility of PAHs is high and biodegradation rates may be limited by microbial processes. On the other hand, when the soil was inoculated with the PAH-degrading bacterium (CKB and MB2), the slowly and very slowly desorbing fractions (F sl and F vl ) became larger and the rate constants of slow and very slow desorption (k sl and k vl ) became extremely small after bioremediation, suggesting that desorption is likely rate limiting during the second, slow phase of biotransformation. These results have practical implications for site risk assessment and cleanup strategies.

Topics: beta-Cyclodextrins; Biodegradation, Environmental; Kinetics; Paracoccus; Polycyclic Compounds; Polymers; Soil Microbiology; Soil Pollutants

Chemical extraction techniques like non-exhaustive extraction with Tenax or hydroxypropyl-β-cyclodextrin (HPCD) have been shown to measure the biodegradable fraction of aromatic contaminants like PAHs in soil. However, there is little research on the chemical prediction of aliphatic hydrocarbon degradation. The aim of this study was to investigate the potential for HPCD and Tenax extractions to predict PAH and petroleum hydrocarbon biodegradation in soil. 11 historically contaminated soils with PAH concentrations between 74 and 680 mg/kg and concentrations of petroleum hydrocarbons from 330 to 4,704 mg/kg were analysed. Both non-exhaustive extraction procedures showed promising results for estimating the available contaminant fraction of both contaminant groups concerning the feasibility, reproducibility and correlation with soil biodegradation applying single point testing. Both methods have the potential to be used to assess the biodegradable hydrophobic organic pollutant fraction in contaminated soils. In a direct comparison of the two extraction procedures, Tenax extraction is assessed to be more time-consuming than HPCD extraction. Furthermore, a sufficient soil/Tenax ratio has to be considered.

Topics: 2-Hydroxypropyl-beta-cyclodextrin; beta-Cyclodextrins; Biodegradation, Environmental; Hydrocarbons; Polymers; Soil Pollutants