Biochemical Engineering Journal (v.9, #3)
Bej Keywords (II).
Characterisation of activated sludge by automated image analysis by Mauricio da Motta; Marie-Noëlle Pons; Nicolas Roche; Hervé Vivier (165-173).
An automated image analysis procedure has been developed for the simultaneous characterisation of flocs (projected diameter and fractal dimension) and filamentous bacteria (filament length) of fresh activated sludge samples observed by optical microscopy. It has been used to monitor, over a period of 1 year, the activated sludge of a large municipal wastewater treatment plant, located in an area subject to mild continental weather. No relationship could be established between floc characteristics and the sludge volume index (SVI). Filamentous bulking events associated with variations of the SVI were detected from changes of total filament length, of filament number/image and of the proportion of filamentous bacteria with respect to the total activated sludge. The proposed automated method provides quantitative support for the classification of bulking events.
Keywords: Activated sludge; Bulking; Filamentous bacteria; Image analysis; Sludge volume index; Fractal dimension;
A kinetic analysis of the fungal degradation process of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in soil by Byoung-In Sang; Katsutoshi Hori; Yasunori Tanji; Hajime Unno (175-184).
Fungal degradation of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) film in soil was described mathematically in terms of the surface growth rate of fungal hyphae and the degradation ability of fungal depolymerase. The surface growth rate of fungi was derived from the notion of equivalent symmetric tree model and was expressed for the two different growth phases, i.e. exponential phase and deceleration phase. The proposed growth and degradation models represented well the experimental data obtained from fungal PHBV degradation in soil. Fungi degrade PHBV film with the formation of soil aggregate that gives the advantageous condition for fungal growth and PHBV degradation. Fungal degradation rate of PHBV film in soil depends on the population of colonized fungal biomass on PHBV film surface and their degradation ability.
Keywords: Paecilomyces lilacinus F4-5; Biodegradation; Aggregation; Microbial growth; Modeling; Poly(3-hydroxybutyrate-co-3-hydroxyvalerate); Soil;
Structural study of lipase modified with fatty acids by Tatsuo Maruyama; Mitsutoshi Nakajima; Sosaku Ichikawa; Shintaro Furusaki; Minoru Seki (185-191).
Stearic acid modification introduced to lipase a remarkable activation for interesterification reaction. In this study, we analyzed stearic acid-modified lipase using small angle X-ray scattering (SAXS) measurements at various temperatures. We prepared lipases modified with several fatty acids and also other proteins modified with stearic acid. SAXS analysis showed that both the lipase modified with fatty acids and other proteins modified with stearic acid consisted of a lipid lamellar structure in an aqueous buffer and in n-hexane. The long spacing of the modified lipase depended on temperature and the kind of fatty acid.
Keywords: Lipase modified with fatty acids; Interesterification; Lamellar structure; Small angle X-ray scattering;
A sensitive method for detecting AMP by utilizing polyphosphate-dependent ATP regeneration and bioluminescence reactions by S. Tanaka; A. Kuroda; J. Kato; T. Ikeda; N. Takiguchi; H. Ohtake (193-197).
We developed a sensitive method for detecting adenosine monophosphate (AMP) by using polyphosphate (polyP)–AMP phosphotransferase (PPT) and adenylate kinase (ADK) from Acinetobacter johnsonii in conjugation with firefly luciferase. This method allowed us to detect AMP over the concentration range of 0.3–300 pmol per assay. Samples taken from various sources susceptible to bacterial contamination were subjected to AMP assay using the present method because AMP is known to have potential for use as a reliable indicator in hygiene monitoring. The results showed that the present method was able to detect food residues with high sensitivity. The present method was also proved to be useful for the quantification of RNA. After digesting RNA with nuclease S1, the present method could detect RNA at concentrations as low as 600 pg.
Keywords: Adenylate kinase; AMP; ATP; Bioluminescence; Hygiene monitoring; Polyphosphate; Polyphosphate–AMP phosphotransferase; RNA;
Modeling of pH response in continuous anaerobic acidogenesis by an artificial neural network by Jun-ichi Horiuchi; Shuntaro Kikuchi; Masayoshi Kobayashi; Tohru Kanno; Tatsuo Shimizu (199-204).
A simple modeling method for microbial dynamic behavior in a chemostat using a neural network was proposed and applied to the pH response in continuous anaerobic acidogenesis. By step shifting the culture pH in the acid reactor from 6.0 to 8.0, the main products were changed from butyric acid to acetic and propionic acids. This phenomenon was reproducible, reversible and was not affected by the dilution rate. A three-layered neural network with a back-propagation algorithm was then used to model the pH step response of the acid reactor. The artificial neural network could successfully model the change in the product distribution in response to a pH shift, leading to the prediction of the transient behavior from one steady state to another steady state in continuous acidogenesis.
Keywords: Modeling; Neural network; pH response; Anaerobic acidogenesis;
Osmotic destruction of Saccharomyces cerevisiae is not related to a high water flow rate across the membrane by Laurent Beney; Iñigo Martı́nez de Marañón; Pierre-André Marechal; Sylvie Moundanga; Patrick Gervais (205-210).
Influence of the kinetics of osmotic pressure variation on yeast viability was related to the rate of water transfer across the yeast membrane. A very high value of membrane hydraulic permeability (L p>6 × 10−11 m s−1 Pa−1) of the yeast Saccharomyces cerevisiae implies the presence of aqueous pores in the yeast membrane and explains the yeast resistance to a very high osmotic flow. The high water flow rate can not explain, by itself, the cell mortality following an osmotic shock. Experiments performed at different osmotic pressure levels show that the yeast death under osmotic shifts was related to the coupled effects of the kinetics of osmotic pressure variation and of the total osmotic pressure level of the medium.
Keywords: Kinetic parameters; Mass transfer; Membranes; Viability; Water activity; Yeast;
Biodegradation of phenol by Pseudomonas putida DSM 548 in a trickling bed reactor by C.S.A Sá; R.A.R Boaventura (211-219).
A trickling bed biofilm reactor packed with PORAVER particles was used to evaluate phenol and total organic carbon (TOC) removal efficiencies by Pseudomonas putida DSM 548. As reported by other authors, it was observed that the average residence time in the reactor is a function of the hydraulic loading rate and the column depth. After the start-up period, the bioreactor was operated at high hydraulic loading rates (16.1 to 32.2 m3 m−2 d−1). Assuming a constant biomass concentration along the reactor, the overall reaction kinetics follows a pseudo first-order model. The obtained biokinetic constants at 25°C were K25°C (phenol) ′=287.6 d−1 and K25°C (TOC) ′=294.8 d−1. It was also observed that metabolites were not consumed along the reactor. The average biofilm thickness was 1.6 mm and the wet and dry biomass densities were 1.04 and 0.17 g cm−3, respectively. Phenol and TOC removal efficiencies, in the temperature range 19–30°C, were expressed as a function of the filter depth and hydraulic loading rate.
Keywords: Phenol; Biodegradation; Kinetics; Trickling bed reactor; Pseudomonas putida;
Automated fed-batch culture of Kluyveromyces fragilis based on a novel method for on-line estimation of cell specific growth rate by Zairossani M. Nor; Melih I. Tamer; Jeno M. Scharer; Murray Moo-Young; Eric J. Jervis (221-231).
A corrected feed-forward control strategy was developed for automated substrate feeding in aerobic fed-batch cultures. The control strategy incorporates a novel method for on-line estimation of specific growth rate as a performance indicator of the fed-batch culture. The estimation is based on the measurement of the maximum substrate uptake rate (MSUR) using on-line dissolved oxygen (DO) concentration data and mass balances. It allows the controller to track changes in the specific growth rate to compensate for process disturbances. The control strategy was applied to fed-batch culture of Kluyveromyces fragilis to maximize the volumetric productivity of lactase. A maximum volumetric lactase productivity of 2.98 U/ml h was achieved. The control was shown to be stable throughout the culture period even at the highest cell density of 69 g/l. This technique is applicable to various aerobic systems, especially for microbial cultures showing high specific oxygen uptake rates, since it only requires on-line measurement of DO concentration without the need for off-gas analysis. In a comparison carried out with three other fed-batch control strategies (DO-stat, exponential feeding and exponential feeding with manual feedback control), the corrected feed-forward control strategy exhibited the best performance by achieving the highest volumetric lactase and biomass productivity.
Keywords: Fermentation; Aerobic processes; Fed-batch culture; Kinetic parameters; Yeast; Lactase;
Cumulative Author Index (233-234).
Cumulative Subject Index (235-246).