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Modeling the biodegradability and physicochemical properties of polycyclic aromatic hydrocarbonsDimitriou-Christidis, Petros 30 October 2006 (has links)
The biodegradability and physicochemical properties of unsubstituted and
methylated polycyclic aromatic hydrocarbons (PAHs) were investigated. The focus was
on the development of models expressing the influence of molecular structure and
properties on observed behavior.
Linear free energy relationships (LFERs) were developed for the estimation of
aqueous solubilities, octanol/water partition coefficients, and vapor pressures as
functions of chromatographic retention time. LFERs were tested in the estimation of
physicochemical properties for twenty methylated naphthalenes containing up to four
methyl substituents. It was determined that LFERs can accurately estimate
physicochemical properties for methylated naphthalenes.
Twenty unsubstituted and methylated PAHs containing up to four aromatic rings
were biodegraded individually by Sphingomonas paucimobilis strain EPA505, and
Monod-type kinetic coefficients were estimated for each PAH using the integral method.
Estimated extant kinetic parameters included the maximal specific biodegradation rate,
the affinity coefficient, and the inhibition coefficient. The generic Andrews model
adequately simulated kinetic data. The ability of PAHs to serve as sole energy and
carbon sources was also evaluated.
Quantitative structure-biodegradability relationships (QSBRs) were developed
based on the estimates of the kinetic and growth parameters. A genetic algorithm was
used for QSBR development. Statistical analysis and validation demonstrated the predictive value of the QSBRs. Spatial and topological molecular descriptors were
essential in explaining biodegradability. Mechanistic interpretation of the kinetic data
and the QSBRs provided evidence that simple or facilitated diffusion through the cell
membranes is the rate-determining step in PAH biodegradation by strain EPA505.
A kinetic experiment was conducted to investigate biodegradation of PAH
mixtures by strain EPA505. The investigation focused on 2-methylphenanthrene,
fluoranthene, and pyrene, and their mixtures. Integrated material balance equations
describing different interaction types were fitted to the depletion data and evaluated on a
statistical and probabilistic basis. Mixture degradation was most adequately described by
a pure competitive interaction model with mutual substrate exclusivity, a fully predictive
model utilizing parameters estimated in the sole-PAH experiments only.
The models developed in this research provide insight into how molecular
structure and properties influence physicochemical properties and biodegradability of
PAHs. The models have considerable predictive value and could reduce the need for
laboratory testing.
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Role of Cell Membrane Permeability Barrier in Biodegradation Rates of Organic CompoundsShrestha, Ankurman January 2017 (has links)
No description available.
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Modelling Aerobic 4-chlorophenol And 2,4-dichlorophenol Biodegradation-effect Of Biogenic Substrate ConcentrationSahinkaya, Erkan 01 December 2006 (has links) (PDF)
Aerobic biodegradation kinetics of 4-Chlorophenol (4-CP) and 2,4-Dichlorophenol (2,4-DCP) by acclimated mixed cultures were examined separately and in mixture using batch and sequencing batch reactors (SBRs). Biodegradation abilities of acclimated mixed cultures were also compared with those of isolated pure species. Complete degradation of chlorophenols and high COD removal efficiencies were observed throughout the SBRs operation. During the degradation of 4-CP, 5-chloro-2-hydroxymuconic semialdehyde, (the -meta cleavage product of 4-CP), accumulated but was subsequently removed completely. Chlorophenol degradation rates increased with increasing chlorophenols concentration in the feed of the SBRs. Gradually decreasing feed peptone concentration did not adversely affect chlorophenol degradation profiles in SBRs. Only competent biomass was thought to be responsible for chlorophenol degradation due to required unique metabolic pathways. It was assumed that the fraction of competent biomass (specialist biomass) is equal to COD basis fraction of chlorophenols in the feed of the reactors as competent biomass grows on chlorophenols only. Models developed using this assumption agreed well with experimental data.
The performance of a two stage rotating biological contactor (RBC) was also evaluated for the treatment of synthetic wastewater containing peptone, 4-CP and 2,4-DCP at 5 rpm. High chlorophenols (> / 98%) and COD (> / 94%) removals were achieved throughout the reactor operation up to 1000 mg/L 4-CP and 500 mg/L 2,4-DCP in the feed. Results showed that RBC is more resistant than suspended growth reactors to high chlorophenols load.
The change of dominant species during the operation of SBRs and RBC was also followed using API 20NE identification kits.
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Efeito da concentração de fósforo na degradação aeróbia do glifosato em reator de leito fixo / Effect of phosphorus concentration on aerobic degradation of glyphosate in fixed bed reactorPaiva, Débora Cristina Aguiar Chaves 21 September 2017 (has links)
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Previous issue date: 2017-09-21 / The present work had as objective to investigate the performance of a fixed bed aerobic
reactor with biomass adhered in the treatment of waters contaminated with glyphosate and
different concentrations of phosphorus. The effect of different phosphorus concentrations on
the adsorption kinetics of glyphosate in a support medium was evaluated by means of the
determination of the exhaust curve in a system composed of an adsorption column filled with
expanded clay. The glyphosate solution used was commercial product based on Glyphosate
Di-ammonium salt 445 g.L-1 (370 g.L-1 equivalent acid) and ultra purified water, with final
glyphosate concentration of 8 mg.L-1. Concentrations of 0.8 mg.L-1 were used in the
adsorbent assays; 8 mg.L-1; and 16 mg.L-1, and the pH values adopted were: 4; 7 and 10.
The results obtained demonstrate the influence of both pH and phosphate ions on the
adsorption of glyphosate in expanded clay, where the adsorption kinetics showed the
influence of both parameters, in general, on higher concentrations of phosphate ions. The
effect of different concentrations of phosphorus on glyphosate biodegradation kinetics was
evaluated by means of temporal profiles of the glyphosate and phosphorus concentration
decay in the same system used in the adsorption tests with aerobic sludge inoculation in the
expanded clay. The glyphosate solution was the same as that used in the 15 mg.L-1
adsorption assays, evaluating the degradation in the presence of concentrations of 2.15 mg.L-
1; 5.37 mg.L-1; 10.75 mg.L-1; 16.12 mg.L-1; 21.5 mg.L-1; 43 mg.L-1 phosphorus. The
results demonstrate the influence of phosphate ions on the degradation kinetics of glyphosate
in expanded clay. It is possible to observe that glyphosate treatment efficiency increased as
phosphorus concentrations increased, indicating that kinetics of degradation was directly
associated to kinetics adsorptive. The data were analyzed by means of multiple regression,
which was able to verify with 95% confidence the effect of the phosphorus (p <0.05) on the
degradation process. / O presente trabalho teve como objetivo investigar o desempenho de um reator aeróbio de
leito fixo com biomassa aderida no tratamento de águas contaminadas com glifosato e
diferentes concentrações de fósforo. Avaliou-se inicialmente o efeito de diferentes
concentrações de fósforo na cinética de adsorção do glifosato em meio suporte por meio da
determinação da curva de exaustão em sistema composto por coluna de adsorção preenchidacom argila expandida. A solução de glifosato utilizada foi composta por produto comercial a
base de sal de Di-amônio de Glifosato 445 g.L-1 (370 g.L-1 equivalente ácido) e água ultra
purificada, com concentração final de glifosato de 8 mg.L-1. Nos ensaios adsortivos foram
utilizadas concentrações de 0,8 mg.L-1; 8 mg.L-1; e 16 mg.L-1, e os valores de pH adotados
foram: 4; 7 e 10. Os resultados obtidos demonstram a influência tanto do pH quanto dos íons
fosfato na adsorção do glifosato em argila expandida, onde a cinética de adsorção demonstrou
a influência de ambos os parâmetros, em geral, em concentrações mais elevadas de íons
fosfato. Posteriormente avaliou-se o efeito de diferentes concentrações de fósforo na cinética
de biodegradação do glifosato por meio da realização de perfis temporais do decaimento da
concentração de glifosato e fósforo no mesmo sistema utilizado nos ensaios de adsorção com
inoculação de lodo aeróbio na argila expandida. A solução de glifosato foi a mesma utilizada
nos ensaios adsortivos na concentração de 15 mg.L-1, avaliando a degradação na presença
das concentrações de 2,15 mg.L-1; 5,37 mg.L-1; 10,75 mg.L-1; 16,12 mg.L-1; 21,5 mg.L-1;
43 mg.L-1 de fósforo. Os resultados demonstram a influência dos íons fosfato na cinética de
degradação do glifosato em argila expandida, sendo possível observar a eficiência de
tratamento do glifosato foi crescente à medida que se aumentou as concentrações de fósforo,
indicando que a cinética de degradação esteve diretamente associada à cinética adsortiva. Os
dados foram analisados por meio de regressão múltipla, a qual foi possível verificar com 95%
de confiança o efeito do fósforo (p<0,05) sobre o processo de degradação.
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