Myung-Keun Chang

Bio: Myung-Keun Chang is an academic researcher from Michigan State University. The author has contributed to research in topics: Sprocket & Substrate (chemistry). The author has an hindex of 3, co-authored 4 publications receiving 287 citations.

Kinetics of competitive inhibition and cometabolism in the biodegradation of benzene, toluene, and p‐xylene by two Pseudomonas isolates.

Abstract: Two Pseudomonas species (designated strains B1 and X1) were isolated from an aerobic pilot-scale fluidized bed reactor treating groundwater containing benzene, toluene, and p-xylene (BTX). Strain B1 grew with benzene and toluene as the sole sources of carbon and energy, and it cometabolized p-xylene in the presence of toluene. Strain X1 grew on toluene and p-xylene, but not benzene. In single substrate experiments, the appearance of biomass lagged the consumption of growth substrates, suggesting that substrate uptake may not be growth-rate limiting for these substrates. Batch tests using paired substrates (BT, TX, or BX) revealed competitive inhibition and cometabolic degradation patterns. Competitive inhibition was modeled by adding a competitive inhibition term to the Monod expression. Cometabolic transformation of nongrowth substrate (p-xylene) by strain B1 was quantified by coupling xylene transformation to consumption of growth substrate (toluene) during growth and to loss of biomass during the decay phase. Coupling was achieved by defining two transformation capacity terms for the cometabolizing culture: one that relates consumption of growth substrate to the consumption of nongrowth substrate, and second that relates consumption of biomass to the consumption of nongrowth substrate. Cometabolism increased decay rates, and the observed yield for strain B1 decreased in the presence of p-xylene.

Rotary bar screen device

Abstract: Provided is a rotary bar screen device. The device includes a driving motor, an up/down pair of driving and driven sprockets, left and right transfer chains, a plurality of screen buckets, a removal unit, and a slide plate. The driving motor is provided over a support frame, and transmits a driving force. The driving and driven sprockets are driven by the driving force. The left and right transfer chains connect the driving and driven sprockets with each other while circulatively moving. The plurality of screen buckets are provided between the left and right transfer chains. The removal unit is provided between the left and right driving sprockets. The slide plate guides the foreign materials dropping from the screen buckets.

Potabilization method and apparatus for producing potable water from desalinated seawater

Abstract: Provided are a method and apparatus for producing potable water by post-processing (post-treating) desalinated water obtained by desalination of seawater through distillation or reverse osmosis. The method includes a carbon dioxide absorption process of excessively supplying carbon dioxide into the desalinated water to absorb the carbon dioxide, a remineralization process of passing the desalinated water into which carbon dioxide is absorbed through a limestone filter in which limestone is filled to form calcium ions and bicarbonate ions, and a carbon dioxide exhaust process of supplying air into the desalinated water passed through the remineralization process to exhaust the carbon dioxide with the air to obtain the potable water. Therefore, a TDS concentration of the desalinated water obtained through a distillation method or a reverse osmosis method can be effectively increased to produce potable water, alkalinity of the potable water can be increased to prevent corrosion of a water distribution system, and the potable water can be produced with a simplified apparatus and low cost.

Combination traveling water screen apparatus

Abstract: Provided is a combination traveling water screening apparatus capable of improving collection and filtering efficiency of floating matters and reducing maintenance costs. The apparatus includes a frame ( 100 ), a motor ( 200 ) installed on the frame and providing a drive force, drive and driven sprockets ( 310 ) installed at both sides of the frame ( 100 ) and driven by the drive force transmitted from the motor ( 200 ), a carrying chain connecting the drive and driven sprockets ( 310 ) and circulated by the drive force, a plurality of screen baskets ( 500 ) circulated by the carrying chain ( 400 ) to filter and convey floating matters, a spray wash ( 700 ) for removing the floating matters in the screen baskets ( 500 ) using an injection pressure of fluid, and a through for collecting the floating matters dropped from the screen baskets, wherein each screen basket includes an upper plate ( 510 ), a lower plate ( 520 ) spaced apart a predetermined distance from the upper plate and bent upward at its front end, side plates ( 530 ) coupled to the upper and lower plates to cover both sides thereof, respectively, a plurality of vertical bars installed between rear sides of the upper and lower plates, and meshes installed behind the vertical bars.

Biodegradation kinetics of benzene, toluene, and phenol as single and mixed substrates for Pseudomonas putida F1

Abstract: Although microbial growth on substrate mixtures is commonly encountered in bioremediation, wastewater treatment, and fermentation, mathematical modeling of mixed substrate kinetics has been limited. We report the kinetics of Pseudomonas putida F1 growing on benzene, toluene, phenol, and their mixtures, and compare mathematical models to describe these results. The three aromatics are each able to act as carbon and energy sources for this strain. Biodegradation rates were measured in batch cultivations following a protocol that eliminated mass transfer limitations for the volatile substrates and considered the culture history of the inoculum and the initial substrate to inoculum mass ratio. Toluene and benzene were better growth substrates than phenol, resulting in faster growth and higher yield coefficients. In the concentration ranges tested, toluene and benzene biodegradation kinetics were well described by the Monod model. The Monod model was also used to characterize phenol biodegradation by P. putida F1, although a small degree of substrate inhibition was noted. In mixture experiments, the rate of consumption of one substrate was found to be affected by the presence of the others, although the degree of influence varied widely. The substrates are catabolized by the same enzymatic pathway, but purely competitive enzyme kinetics did not capture the substrate interactions well. Toluene significantly inhibited the biodegradation rate of both of the other substrates, and benzene slowed the consumption of phenol (but not of toluene). Phenol had little effect on the biodegradation of either toluene or benzene. Of the models tested, a sum kinetics with interaction parameters (SKIP) model provided the best description of the paired substrate results. This model, with parameters determined from one- and two-substrate experiments, provided an excellent prediction of the biodegradation kinetics for the three-component mixture.

Degradation of polycyclic aromatic hydrocarbons by pure strains and by defined strain associations: inhibition phenomena and cometabolism

Abstract: Six bacterial strains capable of using, as sole carbon and energy source, at least one of the following polycyclic aromatic hydrocarbons (PAH), naphthalene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene, were isolated. The interactions between these PAH during their biodegradation were studied in experiments involving PAH pairs, one PAH at least being used as a carbon source. All individual strains were found capable of cometabolic degradation of PAH in a range varying among strains. Inhibition phenomena, sometimes drastic, were often observed but synergistic interactions were also detected. Naphthalene was toxic to all strains not isolated on this compound. Strain associations were found efficient in relieving inhibition phenomena, including the toxic effect of naphthalene. Accumulation of water-soluble metabolites was consistently observed during PAH degradation.

Biodegradation of aromatic compounds: current status and opportunities for biomolecular approaches

Abstract: Biodegradation can achieve complete and cost-effective elimination of aromatic pollutants through harnessing diverse microbial metabolic processes. Aromatics biodegradation plays an important role in environmental cleanup and has been extensively studied since the inception of biodegradation. These studies, however, are diverse and scattered; there is an imperative need to consolidate, summarize, and review the current status of aromatics biodegradation. The first part of this review briefly discusses the catabolic mechanisms and describes the current status of aromatics biodegradation. Emphasis is placed on monocyclic, polycyclic, and chlorinated aromatic hydrocarbons because they are the most prevalent aromatic contaminants in the environment. Among monocyclic aromatic hydrocarbons, benzene, toluene, ethylbenzene, and xylene; phenylacetic acid; and structurally related aromatic compounds are highlighted. In addition, biofilms and their applications in biodegradation of aromatic compounds are briefly discussed. In recent years, various biomolecular approaches have been applied to design and understand microorganisms for enhanced biodegradation. In the second part of this review, biomolecular approaches, their applications in aromatics biodegradation, and associated biosafety issues are discussed. Particular attention is given to the applications of metabolic engineering, protein engineering, and “omics” technologies in aromatics biodegradation.

Microbial growth and substrate utilization kinetics

Abstract: Microbial growth on and utilization of environmental contaminants as substrates have been studied by many researchers. Most times, substrate utilization results in removal of chemical contaminant, increase in microbial biomass and subsequent biodegradation of the contaminant. These are all aimed at detoxification of the environmental pollutants. Several microbial growth and biodegradation kinetic models have been developed, proposed and used in bioremediation schemes. Some of these models include Monod’s, Andrews, Bungay’s weighted model, general substrate inhibition models (GSIM) and sum kinetic models. Most research on microbial potentials to degrade chemical pollutants has been performed on a laboratory scale. There is a need to extend such studies to pilot scale as well as to full-scale field applications. Key words: Microbial growth, substrate utilization, biodegradation, kinetics, detoxification, organic contaminants, models, environmental pollutants.

Competitive metabolism of naphthalene, methylnaphthalenes, and fluorene by phenanthrene-degrading pseudomonads

Abstract: Polynuclear aromatic hydrocarbons (PAHs) typically exist as complex mixtures in contaminated soils, yet little is known about the biodegradation of PAHs in mixtures. We have isolated two physiologically diverse bacteria, Pseudomonas stutzeri P-16 and P. saccharophila P-15, from a creosote-contaminated soil by enrichment on phenanthrene as the sole carbon source and studied their ability to metabolize several other two- and three-ring PAHs. Naphthalene, 1-methylnaphthalene, and 2-methylnaphthalene served as growth substrates for both organisms, while fluorene was only cometabolized. We also studied the effects of these compounds on initial rates of phenanthrene uptake in binary mixtures. Lineweaver-Burk analysis of kinetic measurements was used to demonstrate competitive inhibition of phenanthrene uptake by all four compounds, suggesting that multiple PAHs are being transformed by a common enzyme pathway in whole cells. Estimates of the inhibition coefficient, Ki, are reported for each compound. The occurrence of competitive metabolic processes in physiologically diverse organisms suggests that competitive metabolism may be a common phenomenon among PAH-degrading organisms.