Kuo-g Chen

Immobilization of microorganisms with phosphorylated polyvinyl alcohol (PVA) gel

Abstract A new cell immobilization method based on the usage of phosphorylated polyvinyl alcohol (PVA) was developed. PVA was first crosslinked with boric acid for a short time (10 min-2 h) to form a spherical structure, which was followed by solidification of the gel beads by esterification of PVA with phosphate. The short contact time with boric acid prevented severe damage of the microorganisms. Denitrifying sludge entrapped in phosphorylated PVA gel beads was used in denitrification of wastewater. The effects of pH, temperature, and sludge load of biocatalyst beads on nitrate reduction activity were examined. The operational stability of the immobilized sludge system was studied both in a batch reactor and in a continuous stirred-tank reactor. The reactors were successfully run for 32 days. A steady denitrification efficiency of more than 99% was achieved in the continuous reactor.

Simultaneous carbon-nitrogen removal in wastewater using phosphorylated PVA-immobilized microorganisms

Abstract Acclimated sludge was immobilized by a previously developed phosphorylated polyvinyl alcohol (PVA) gel. The immobilized-cell reactor system was established in a 12-l continuous aeration vessel with a synthetic municipal wastewater as the feed substrate. In addition, a method was developed to estimate the biomass concentration of the suspended sludge and the immobilized-cell beads by detecting the microbial cell protein content. The system was operated at a HRT of 2–10 h in which the COD loading rate ranged from 0.855–4.223 g COD l−1 d−1. More than 90% of COD removed efficiency was obtained at a COD loading rate lower than 2.0 g COD l−1 d−1 accompanied by a total nitrogen removal efficiency at around 45%. The immobilized cell process has yielded highly promising results particularly in terms of maintaining a high biomass concentration to attain high efficiency and reducing production of excess sludge to decrease operation cost. The so-called aerated denitrification occurring inside the gel beads was verified experimentally by measuring the nitrate reduction activity of gel beads. Microscopic observation revealed that three kinds of bacterial species, i.e., BOD oxidizers, nitrifiers, and denitrifiers, developed a habitat segregation from the peripheral surface into the interior part of the gel bead.

Real-time control of an immobilized-cell reactor for wastewater treatment using ORP

The performance of an immobilized-cell reactor for simultaneous carbon nitrogen removal in synthetic wastewater with an intermittent aeration (IA) process under real-time control of oxygen supply was investigated. The oxidation-reduction potential (ORP) was monitored during operation. The ORP-time profile showed distinctive turning points. which directly correlated with the changes in the system chemistry and biological activity. The reactor was conducted by cyclic fixed-time aeration nonaeration operation at the beginning, followed by real-time control technology using ORP setpoint. A moving window along the slope of the ORP curve was employed to search for the nitrate breakpoint of the aeration cycle. Once the breakpoint was found, the reactor was aerated for a fixed period. The treatment process could effectively avoid the anoxic fermentation state under the real-time control. The cycle time was reduced around 30%. The duration of aeration period was found to be optimum at 3 h under the consideration of the removal efficiencies of COD and total nitrogen. The real-time control system not only exhibited a better nitrogen removal efficiency than the fixed-time control operation, but it also showed a stable effluent quality during the change of HRT from 3 to 8 h. Good operation stability was demonstrated even when a very high disturbance of the influent loading occurred.

Effects of the growth of Trichosporon cutaneum in calcium alginate gel beads upon bead structure and oxygen transfer characteristics

Immobilized growing cells of Trichosporon cutaneum were prepared by entrapment into calcium alginate beads. The morphological development and changes in the structure of matrix in the different growing stages of yeast cells were examined using scanning electron microscopy. Once cell population increased drastically in the exponential growth phase, the architecture of gel matrix changed and crater-like pores on the gel surface were observed. The changes of gel construction and dense cell packing in the beads affect the behavior of oxygen transfer. Effects of alginate concentration, cell density and particle size on the oxygen uptake rate of immobilized growing cells were studied. In view of mechanical properties of gels and efficiency of mass transfer, 3% alginate concentrations is a favorable choice. Based on a well-known theoretical model, a calculation method was proposed to estimate the oxygen diffusivity in gels using experimental data. The estimation of oxygen diffusivity was carried out during the incubation of cell beads. It was found that the ratio of oxygen diffusivity in gels to that in water decreased with incubation time, from 32% to a constant level of 20% when the late period of exponential growth phase was reached.

Optimization of cultivation medium composition for isoamylase production

SummaryThe medium composition for production of isoamylase by Pseudomonas amyloderamosa JD210 was optimized using response surface methodology. The factors chosen for optimization were maltose, soybean protein hydrolysate (SPH), isoleucine, proline, KH2PO4 and MgSO4. Fractional factorial designs (FFD) and the path of steepest ascent were effective in searching for the major factors and optimum medium composition. By a 26–1 FFD, supplementary isoleucine was shown to have a negative effect on enzyme production. The effects of the other five factors were further investigated by a central composite design and the optimum composition was found to be 1.10% maltose, 0.13% SPH, 0.15% proline, 0.38% KH2PO4, and 0.05% MgSO4. When the strain was cultivated in the optimum medium, enzyme production increased 60% compared with ordinary medium. Proline was verified as being a significant factor in promoting enzyme production.

Improvement of gas permeability of denitrifying PVA gel beads

Abstract In order to modify the structure of phosphorylated polyvinyl alcohol (PVA) gel beads for improving their gas permeability, some additives such as soluble starch, partially saponified PVA, and calcium alginate were used. An addition of a small amount of calcium alginate to gel solution during gelation was made. The calcium alginate was later destroyed by treating the beads with phosphate solution, thereby effectively promoting the ability of gas permeation. The modification process with alginate would not cause a significant decrease in the nitrate reduction rate of immobilized beads. The gas permeability of beads increased as high as 62%.

Search method for the optimal medium for the production of lactase by Kluyveromyces fragilis

A rapid and effective method of approach to the optimum neighborhood in medium optimization has been proposed. This method can be used for the production of lactase by Kluyveromyces fragilis. The major components for improving enzyme production were first chosen from the literature sources. The initial test range of each variable for approaching the optimal conditions was selected based on the experimental results of a proposed simplified factorial design. The optimum composition of the nutrient medium was then easily found by using a central composite design (CCD) for shake-flask experiments. The enzyme production was increased by 60% when the strain was cultivated in this medium as compared to the conventional medium composition used in the literature.

11α-Hydroxylation of progesterone in biphasic media using alginate-entrapped Aspergillus ochraceus gel beads coated with polyurea

A novel cell-immobilization technique was developed in this study for increasing substrate partition to the gel matrix by coating a polyurea thin layer on the surface of Ca-alginate beads. The proposed method was simple and could be performed under mild conditions. The bioconversion of progesterone to 11 alpha-hydroxyprogesterone with these polyurea-coating alginate-entrapped Aspergillus ochraceus cells was investigated using different organic solvents in biphasic media. The reaction medium of ethyl acetate could markedly enhance the bioconversion rate with the existence of a hydrophobic layer, most likely resulting from the increasing partition of substrate to gel matrix. Bioconversion with higher substrate concentration was possible using an ethyl acetate-water medium. The conversion rate increased almost linearly with increasing substrate concentration from 10 to 80 g l-1. The rate with 80 g l-1 progesterone increased up to six times greater than the rate with the immobilized cells without coating, and also exhibited a much higher rate than that reported in the literature.

Dissolution-enzyme kinetics of 11β-hydroxylation of cortexolone by Curvularia lunata

The enzyme kinetics of 11β-hydroxylation of cortexolone by whole cells of Curvularia lunata were studied, taking into account the dissolution of the solid substrate. The dissolution behavior of substrate steroid was represented by an empirical expression. A mathematical model was developed to describe the heterogeneous process of steroid hydroxylation, based on the rate of enzyme reaction and the rate of substrate dissolution. The rate of 11β-hydroxylation of solubilized cortexolone coexisting with its solid form was found to be identical to Michaelis-Menten kinetics. The kinetic constants were estimated using experimental data. The good agreement between correlated and experimental values supported the suitability of the established model.

Operational stability of immobilized D-glucose isomerase in a continuous feed stirred tank reactor

Abstract d -Glucose isomerization has been studied using immobilized cells of Streptomyces phaeochromogenes in a continuous feed stirred tank reactor (CSTR) where the external film diffusion resistance was negligible. Experiments conducted with various sizes of enzyme particles indicated that a strong internal diffusion resistance improved the apparent stability of these particles. The performance equations of the CSTR were constructed by associating the material balances for the inside porous support matrix with the bulk liquid phase, and enzyme deactivation was also taken into consideration. An iterative method together with the orthogonal collocation method is proposed for the evaluation of effectiveness factor and the substrate concentration profile within the enzyme particles. The numerical results offer an alternative analytical proof for the observation that under strong internal diffusion control the apparent operational stability of immobilized enzyme is improved .