Degradation Of Chloroform Research Articles

Chloroform degradation in methanogenic methanol enrichment cultures and by Methanosarcina barkeri 227.

The effects of methanol addition and consumption on chloroform degradation rate and product distribution in methanogenic methanol enrichment cultures and in cultures of Methanosarcina barkeri 227 were investigated. Degradation of chloroform with initial concentrations up to 27.3 microM in enrichment cultures and 4.8 microM in pure cultures was stimulated by the addition of methanol. However, methanol consumption was inhibited by as little as 2.5 microM chloroform in enrichment cultures and 0.8 microM chloroform in pure cultures, suggesting that the presence of methanol, not its exact concentration or consumption rate, was the most significant variable affecting chloroform degradation rate. Methanol addition also significantly increased the number of moles of dichloromethane produced per mole of chloroform consumed. In enrichment cultures, the number of moles of dichloromethane produced per mole of chloroform consumed ranged from 0.7 (methanol consumption essentially uninhibited) to 0.35 (methanol consumption significantly inhibited) to less than 0.2 (methanol not added to the culture). In pure cultures, the number of moles of dichloromethane produced per mole of chloroform consumed was 0.47 when methanol was added and 0.24 when no methanol was added. Studies with [14C]chloroform in both enrichment and pure cultures confirmed that methanol metabolism stimulated dichloromethane production compared with CO2 production. The results indicate that while the addition of methanol significantly stimulated chloroform degradation in both methanogenic methanol enrichment cultures and cultures of M. barkeri 227, the prospects for use of methanol as a growth substrate for anaerobic chloroform-degrading systems may be limited unless the increased production of undesirable chloroform degradation products and the inhibition of methanol consumption can be mitigated.

Predicting yields for autotrophic and cometabolic processes

The goal of bioprocess engineering is to state how the optimum design and control strategy for a bioprocess follow from the metabolism of olism of the particular microorganism. A necessary step toward this goal is to show how the parameters used in quantitative descriptions of a process (e.g., yield and maintenance coefficients) are related to those describing the metabolism [e.g., YATP, (P/O)]. The “yield equation” approach to this problem involves dividing metabolism into the separate pathways for catabolism, anabolism, respiration, and product formation and balancing the production and consumption of reducing equivalents and ATP. The general approach demonstrated previously for heterotrophic cell growth and products of fermentation, is illustrated by three new examples: the cell yield for chemoautotrophic iron-oxidizing bacteria, the cometabolic degradation of chloroform by methanotrophic bacteria, and the theoretical yield of succinic acid from glucose.

Trichloroethylene and chloroform degradation by a recombinant pseudomonad expressing soluble methane monooxygenase from Methylosinus trichosporium OB3b.

Soluble methane monooxygenase (sMMO) from Methylosinus trichosporium OB3b can degrade many halogenated aliphatic compounds that are found in contaminated soil and groundwater. This enzyme oxidizes the most frequently detected pollutant, trichloroethylene (TCE), at least 50 times faster than other enzymes. However, slow growth of the strain, strong competition between TCE and methane for sMMO, and repression of the smmo locus by low concentrations of copper ions limit the use of this bacterium. To overcome these obstacles, the 5.5-kb smmo locus of M. trichosporium OB3b was cloned into a wide-host-range vector (to form pSMMO20), and this plasmid was electroporated into five Pseudomonas strains. The best TCE degradation results were obtained with Pseudomonas putida F1/pSMMO20. The plasmid was maintained stably, and all five of the sMMO proteins (alpha, beta, and gamma hydroxylase proteins, reductase, and component B) were observed clearly by both sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western immunoblotting. TCE degradation rates were quantified for P. putida F1/pSMMO20 with a gas chromatograph (Vmax = 5 nmol per min per mg of protein), and the recombinant strain mineralized 55% of the TCE (10 microM) as indicated by measuring chloride ion concentrations with a chloride ion-specific electrode. The maximum TCE degradation rate obtained with the recombinant strain was lower than that of M. trichosporium OB3b but greater than other TCE-degrading recombinants and most well-studied pseudomonads. In addition, this recombinant strain mineralizes chloroform (a specific substrate for sMMO), grows much faster than M. trichosporium OB3b, and degrades TCE without competitive inhibition from the growth substrate.

Photocatalytic Degradation of Chloroform with TiO<sub>2</sub> Coated Glass Fiber Cloth

Photocatalytic Degradation of Chloroform with TiO<sub>2</sub> Coated Glass Fiber Cloth

A sequencing biofilm reactor for the treatment of chlorinated solvents using methanotrophs

ABSTRACT: Laboratory experiments were conducted with a sequencing, packed‐bed bioreactor that was seeded with the methanotroph, Methylosinus trichosporium OB3b. The reactor cycled between a growth mode, in which methane and oxygen were supplied from the gas phase, and a degradation mode, in which water containing chloroform at 100 µg/L was treated in the absence of methane. When the influent was supplemented with formate, chloroform degradation was as great as 90% at an empty bed retention time of approximately 90 minutes. The degradation rate remained stable for several days, but steadily declined thereafter. In the absence of formate, the initial degradation rate was smaller and declined more rapidly than in the presence of formate. Mathematical modeling demonstrated that the pseudo‐first‐order rate constants for chloroform degradation in the reactor were about two orders of magnitude smaller than those measured in suspended growth, batch kinetic studies. The sequencing reactor performed better than a packedbed, continuous‐flow reactor, because a larger, more evenly distributed biomass could be established in the sequencing reactor.

Photolysis of chloroform and other organic molecules in aqueous titanium dioxide suspensions

The photocatalytic degradation of chloroform has been investigated in aqueous suspensions of TiO_2 over the wavelength range of 310-380 nm. A detailed reaction mechanism has been proposed in which the rate-determining step is the reaction of surface-bound *OH with adsorbed CHCl_3. A pH-stat titration technique was developed for the measurement of the rates of degradation of chlorinated hydrocarbons. The quantum efficiency (Ф = 0.56 at ⋋ = 330 nm) of the degradation of CHCl_3, was found to be inversely proportional to the square root of the incident light intensity. This relationship can be explained in terms of a direct competition between a second-order recombination of surface-bound 'OH and the rate-determining reaction of surface-bound 'OH with CHCl_3. The rates of degradation of several electron donors have been correlated with their computed surface speciation. The results of this study show that the adsorption of electron donors and acceptors to the TiO_2 surface plays a more important role in determining the rate of the photocatalytic reactions than the effect of pH-dependent Fermi-level shifts.

The kinetics of the degradation of chloroform and benzene in anaerobic sediment from the River Rhine

In anaerobic methanogenic sediment microcosms14C labelled chloroform was degraded mainly to carbon dioxide. At a concentration of 4 μg.l−1 the mineralization followed first order kinetics with a half life of 12 days at 10°C and 2.6 days at 20°C. At a concentration of 400 μg.l−1 the mineralization rate increased with time and followed logarithmic kinetics with a μmax of 0.02.d−1 at 10°C. The logarithmic kinetics can be explained by growth of the bacteria on the higher concentration of chloroform with a generation time of 35 days. Shaking and oxygenation did not inhibit the mineralization of chloroform, probably because of bacterial consumption of the dissolved oxygen. 14C labelled benzene was mineralized only for a small percentage to14C labelled carbon dioxide while other, not acid extractable, degradation products were formed. Under anaerobic conditions after one day when 5% of the benzene was degraded to carbon dioxide, the mineralization ceased, while the disappearance of benzene proceeded. With air in the headspace of the incubation bottles 25% of the benzene was mineralized to carbon dioxide. The anaerobic degradation of benzene at a concentration of 100 μ.l−1 showed similar kinetics as the degradation at 1 μg.l−1. Hence no adaptation of the microflora in the sediment occurred during the 63 days of the experiment at 100 μg.l−1.

Aerobic microbial degradation of chloroform: Construction of an immobilized enzyme electrode for chloroform assay

Pseudomonas putida has been induced in subsequent culture growth to degrade chloroform as a secondary substrate. Both the growth and the chloroform biodegradation were monitored by the simple but accurate chloride ion selective electrochemical (ISE) method. The enzyme fraction responsible for the degradation was partially purified and then immobilized in conjunction with the chloride electrode. It was used for the assay of chloroform in the 1–50 part per thousand concentration range. The performance of the enzyme electrode was evaluated by comparing the results with those obtained by the dithizone method for the chloride ion produced.

Degradation of chloroform by photoassisted heterogeneous catalysis in dilute aqueous suspensions of titanium dioxide

Mineralisation du chloroforme en produits mineraux par catalyse heterogene photo assistee en utilisant une solution aqueuse de TiO 2 illumine a l'UV

Strahlungschemie von wässrigen Lösungen organischer Halogenderivate I. Radiolyse einer wässrigen Chloroformlösung

In the investigation of the radiolysis of aqueous chloroform solutions, the radiation yield of hydrogen chloride and its dependence on the speed of the energy absorption, the chloroform concentration, and the temperature were determined under various conditions. The effect of dissolved oxygen was studied, and the mechanism of the chloroform degradation and the kinetics of the induction period were treated critically. (tr-auth)