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전명석,( R. W. Lovitt ),( W. R. Bowen ) 한국화학공학회 2007 화학공학의이론과응용 Vol.10 No.2
Long-range interactions are important to understand the physicochemical phenomena of electric field in either micro-biochip or MEMS devices confined to the charged solid wall and to analyze the behavior of complex fluids dispersed by either colloids or nanoparticles. Atomic force microscopy (AFM) results were obtained for electrostatic interaction force profiles between a silicon nitride tip and a silica surface by the traditional method as well as between a spherical silica particle and a silica surface employing a colloid probe technique. Distances ranging several tens of nanometers were successfully measured under a contact mode in 1.0 mM KCl electrolyte solution at different pH values. Experimental results obtained by the colloid probe were compared with the calculations from Derjaguin approximation as well as rigorous numerical method. As the separation distance between the silica surface and silica particle is decreased, the approximation under constant potential gives greater interaction than our measured values, with its difference becoming large. AFM results in PDMS-based microfluidic channel are also presented.
Myrto-Panagiota Zacharof,Robert W. Lovitt 한국생물공학회 2013 Biotechnology and Bioprocess Engineering Vol.18 No.1
Lactococcus lactis species have been and still are extensively investigated due to their significant commercial importance. Current scientific research focuses on strains utilized in food industry, due to their multiple uses in food and beverages fabrication. Biomass of Lactococcus lactis is of great interest as well as the end products of its metabolism such as lactic acid and nisin. However their production is constantly challenged due to end product inhibition occurring during intensive propagation of the coccus in reactor systems. To successfully predict the behavior of the culture, the approach of combining mathematics with biology, ergo the development of an unstructured mathematical model, was taken. Although Luedeking and Piret is the model that has been extensively used to demonstrate growth in end-product inhibition cultures, its applicability is limited due to its dependance on the specific growth and product coefficients, particularly related to the culturing conditions used. To overcome these hurdles, a combination of the non competitive single product end inhibition Taylor and Hinselwood models was used, with the significance of this model laying in the fact that it offers a feasible alternative to the commonly used model of Luedeking and Piret for describing fermentation kinetics governed by end-product inhibitions. The fitting with the experimental values, in batch mode, was tested in terms of the coefficient of determination (R²), having values 0.97 ~ 0.99 and suggesting a very good fitting with the experimental data. The model was further developed to achieve theoretical predictions of volumetric cell productivity in continuous and fed-batch mode of substrate feed in different culturring systems.
Jang, Nulee,Yasin, Muhammad,Park, Shinyoung,Lovitt, Robert W.,Chang, In Seop Elsevier Applied Science 2017 Bioresource technology Vol.239 No.-
<P><B>Abstract</B></P> <P>A mathematical model of microbial kinetics was introduced to predict the overall volumetric gas–liquid mass transfer coefficient (<I>k</I> <SUB>L</SUB> <I>a</I>) of carbon monoxide (CO) in a batch cultivation system. The cell concentration (<I>X</I>), acetate concentration (<I>C<SUB>ace</SUB> </I>), headspace gas (<I>N<SUB>co</SUB> </I> and <SUB> N <SUB> co 2 </SUB> </SUB> ), dissolved CO concentration in the fermentation medium (<I>C<SUB>co</SUB> </I>), and mass transfer rate (<I>R</I>) were simulated using a variety of <I>k</I> <SUB>L</SUB> <I>a</I> values. The simulated results showed excellent agreement with the experimental data for a <I>k</I> <SUB>L</SUB> <I>a</I> of 13/hr. The <I>C<SUB>co</SUB> </I> values decreased with increase in cultivation times, whereas the maximum mass transfer rate was achieved at the mid-log phase due to vigorous microbial CO consumption rate higher than <I>R</I>. The model suggested in this study may be applied to a variety of microbial systems involving gaseous substrates.</P> <P><B>Highlights</B></P> <P> <UL> <LI> First report of <I>k</I> <SUB>L</SUB> <I>a</I> for a batch cultivation system using kinetic simulation. </LI> <LI> Combined microbial kinetics and gas–liquid mass transfer. </LI> <LI> The dissolved CO concentration and mass transfer in a batch system were simulated. </LI> <LI> No dissolved CO assumption leads to a large error in simulating gas cultivation. </LI> </UL> </P>
Chun, Youngpil,Choi, Donggeon,Kim, Daehee,Lovitt, Robert W.,Chang, In Seop Balaban Publishers 2016 Desalination and Water Treatment Vol. No.
<P>Micro-organisms were isolated from intake seawater and reverse osmosis (RO) membrane biofilms collected from a full-scale membrane-based desalination process. The results from a culture-dependent approach using 12 media were combined with the microbial community structure on fouled RO membranes as analyzed by a 16S rRNA clone library construction in our previous study. This was followed by selection of 11 target bacteria for further analysis, which were suspected to be responsible for biofilm formation on membrane surfaces. The adhesion of potential biofoulants differing in surface hydrophobicity and charge was examined. Cell wall hydrophobicity was measured as the contact angle of a lawn of bacteria, and by adhesion to hexadecane. The cell surface charge was investigated by measuring electrophoretic mobility. The data obtained from these methodologies were compared. According to the cell surface charge measurements, Pseudomonas aeruginosa, Acinetobacter venetianus, Cellvibrio mixtus subsp. Mixtus, Bacillus sp. Eur1 9.5, and Escherichia coli K12 could mediate initial adhesion to negatively charged RO membranes through electrostatic attraction. Limnobacter sp. KNF002, A. venetianus, and Simiduia agarivorans showed higher affinity to hexadecane than other bacterial strains tested, and Bacillus sp. Eur1 9.5, C. mixtus subsp. Mixtus, and P. aeruginosa were determined to have greater hydrophobic interactions with hydrophobic RO membranes.</P>
Choi, J.,Choi, W.,Kim, H.,Alaud-din, A.,Cho, K.,Kim, J.,Lim, H.,Lovitt, R.,Chang, I. Royal Society of Chemistry 2014 Analytical methods Vol.6 No.4
Biofouling is a crucial issue, and it causes seawater reverse osmosis membrane to deteriorate the performance of desalination. In this study, excitation emission matrix (EEM) fluorescence spectroscopy and parallel factor analysis (PARAFAC) were used to monitor the strength of biofouling on the fouled membrane which was obtained from real plant. Based on EEM and PARAFAC results of raw seawater, feed water, permeate, brine and fouled membrane, three components were identified as the major peaks: (1) microbial product-like materials at Ex/Em = 280/370 nm, (2) humic-like substances at Ex/Em = 330/420 nm, and (3) aromatic proteins at Ex/Em = 240/320 nm. Using the fluorescence intensity changes, the effects of replacing fouled RO membranes were found to be most significant at one of the components (Ex/Em = 270-300/350-380 nm) which could be considered the substances desorbed from fouled RO membrane. Compared to the data for salt rejection, this component monitoring of the brine EEM image is shown to be more sensitive than conductivity monitoring for predicting the biofouling strength during the desalination process.