Production and comparison of high surface area bamboo derived active carbons.

High surface area activated carbons have been produced from the natural biomaterial bamboo, using phosphoric acid as the activating agent. The effects of phosphoric acid impregnation ratio, activation temperature, heating rate on the carbon surface area, porosity and mass yield are presented. Three of these bamboo derived active carbons, surface areas 1337, 1628 and 2123m(2)/g were assessed for their ability to adsorb Acid Red 18 dye from aqueous solution; these results were compared with three conventional adsorbents: activated carbon F400, bone char and peat. Isotherm data were analysed using Langmuir, Freundlich, Redlich-Peterson and Langmuir-Freundlich isotherms. Different isotherms provided the best fit correlations to the adsorption experimental data but the Langmuir-Freundlich equation provided the best overall correlation of data. The adsorption capacities of two of the selected bamboo derived carbons were much greater than the capacities of the other three adsorbents.

Application of biochemical oxygen demand (BOD) biosensor for optimization of biological carbon and nitrogen removal from synthetic wastewater in a sequencing batch reactor system.

A bench scale reactor using a sequencing batch reactor process was used to evaluate the applicability of biosensors for the process optimization of biological carbon and nitrogen removal. A commercial biochemical oxygen demand (BOD) biosensor with a novel microbial membrane was used to determine the duration of each phase by measuring samples in real time in an SBR cycle with filling/anoxic-anaerobic/aerobic/sludge wasting/settling/withdrawal periods. Possible strategies to increase the efficiency for the biological removal of carbon and nitrogen from synthetic wastewater have been developed. The results show that application of a BOD biosensor enables estimation of organic carbon, in real time, allowing the optimization or reduction the SBR cycle time. Some typical consumption patterns for organic carbon in the non-aeration phase of a typical SBR operation were identified. The rate of decrease of BOD measured using a sensor BOD, was the highest in the initial glucose breakdown period and during denitrification. It then slowed down until a 'quiescent period' was observed, which may be considered as the commencement of the aeration period. Monitoring the BOD curve with a BOD biosensor allowed the reduction of the SBR cycle time, which leads to an increase in the removal efficiency. By reducing the cycle time from 8 to 4 h cycle, the removal efficiencies of nitrate, glucose, and phosphorus in a given time interval, were increased to nearly double, while the removal of nitrogen ammonium was increased by one-third.

Inter-relationship between adsorption and pH in peat biofilters in the context of a cation-exchange mechanism.

A mathematical model of biofiltration McNevin and Barford (1998) has been augmented to include speciation, acid/base equilibria and pH dependence of adsorptive equilibria. It accurately predicts qualitative aspects of dynamic transients observed in an experimental perfusion column and supported a mechanism of adsorption by cation exchange with acidic functional groups on the surface of peat. It mirrored the buffering capacity of peat when solutions of high and low pH flow over the peat surface. This is a direct result of cation exchange where adsorption of cations increases with pH. This buffering capacity makes peat an attractive medium for engineered biological systems which must often operate within narrow pH bands to optimise biological activity.

Biofiltration as an odour abatement strategy.

The chemical, physical and biological processes occurring in biofiltration are reviewed. A survey of operating biofilter performances is also presented and includes some novel comparative methods. It is concluded that biofiltration is a simple and cost-effective technology for odour removal and that an understanding of the many interactions occuring within the biofilter is essential for the optimal performance of the biofilter.

Photocatalytic thin film cascade reactor for treatment of organic compounds in wastewater.

The photocatalytic oxidation of benzoic acid was investigated in a pilot scale-cascade photoreactor. The photoreactor consists of an array of UV lamps (40 W, 365 nm) illuminating a cascade of three inclined 316 stainless steel plates, on which titanium dioxide (TiO2) was immobilized by electrophoretic deposition. The percentage removal of total organic carbon (TOC) of liquid samples was determined. The photocatalytic process was affected by several operating parameters. Increasing the solution temperature was found to reduce the dissolved oxygen (DO) level and to decrease the rate of the degradation process. The Langmuir-Hinshelwood equation was found to be accurate for modeling the degradation of benzoic acid with initial concentrations of 50 ppm, 75 ppm and 100 ppm. The rate of removal of TOC was positively affected by UV light intensity, but appeared to be independent of solution flowrate in the range examined. Control experiments confirmed that the effects of adsorption of the solute onto the TiO2 catalysts and photolytic degradation were negligible.

Reactive Black dye adsorption/desorption onto different adsorbents: effect of salt, surface chemistry, pore size and surface area.

The adsorption of a large reactive dye, Reactive Black 5 dye, onto two bamboo based active carbons using phosphoric acid in a two stage activation process and three conventional adsorbents, carbon F400, bone char and peat, has been studied. The monolayer saturation adsorption capacities for Reactive Black 5 were determined by the Langmuir isotherm analysis and are: 176, 157, 7, 447 and 545 mg dye/g adsorbent for active carbon F400, bone char, peat, bamboo carbon (2123 m(2)/g) and bamboo carbon (1400 m(2)/g), respectively. The equilibrium experiments were analysed using three isotherms, Langmuir, Freundlich and Redlich-Peterson and the based on the lowest SSE values, the Redlich-Peterson was the best fit correlation. The effect of adding salt, in the form of sodium phosphate, on the adsorption capacities has been studied and was found to increase the adsorption capacities of both bamboo carbons to over 900 mg/g.

A screen-printed biosensor using pyruvate oxidase for rapid determination of phosphate in synthetic wastewater.

A screen-printed phosphate biosensor based on immobilized pyruvate oxidase (PyOD, E.C. 1.2.3.3) has been developed for monitoring phosphate concentrations in a sequencing batch reactor (SBR) system. The enzyme was immobilized by a nafion matrix and covered a poly(carbamoyl) sulfonate (PCS) hydrogel on a screen-printed electrode. PyOD consumes phosphate in the presence of pyruvate and oxygen and generates hydrogen peroxide (H2O2), carbon dioxide and acetylphosphate. The electroactive H2O2, monitored at +420 mV vs Ag/AgCl, is generated in proportion to the concentration of phosphate. The sensor has a fast response time (2 s) and a short recovery period (2 min). The time required for one measurement using this phosphate biosensor was 4 min, which was faster than the time required using a commercial phosphate testing kit (10 min). The sensor has a linear range from 7.5 microM to 625 microM phosphate with a detection limit of 3.6 microM. There was good agreement (R2=0.9848) between the commercial phosphate testing kit and the phosphate sensor in measurements of synthetic wastewater in a SBR system. This sensor maintained a high working stability (>85%) after 12 h of operation and involved a simple operation procedure. It therefore serves as a useful tool for rapid and accurate phosphate measurements in the SBR system and probably for process control.

A mathematical model for cell separation technique of centrifugal elutriation.

A mathematical model for the cell separation technique of centrifugal elutriation is developed. The model simulates both steady and non-steady-state operation of the elutriator. The model can be used to predict the required set of flow rates of elutriating liquid necessary to fractionate a cell culture, the required time of sampling before steady state is achieved, and the range of cell size/cell density combinations contained in any fraction. The model predictions were verified experimentally. Variations in cell density and cell size due to the suspending environment have a significant effect on the accuracy (although not the trends) of the model predictions. Quantification of these variations will lead to significantly more accurate model predictions. An enhanced separation method was developed using the model, to yield finer separation of a cell culture than previously possible. The use of the centrifugal elutriator may now be given a firm theoretical basis, with the quality of separation understood in terms of the basic theory of operation.

A general model for aerobic yeast growth: batch growth.

A general model for aerobic yeast growth in batch culture is presented. It is based on the concept that the aerobic metabolism of all yeasts is determined by the relative sizes of the transport rate of sugar into the cell and the transport rate of respiratory intermediates into the mitochondrion. If the rate of sugar uptake rate exceeds the rate of transport of respiratory intermediates into the mitochondrion (as in Saccharomyces cerevisiae, S. uvarum, and S. pombe), the metabolism exhibits the features of ethanol excretion and limited specific oxygen uptake rate. If the rate of transport of respiratory intermediates into the mitochondrion is of the same order as the transport of sugar into the cell (as in Candida utilis), the metabolism is characterized by little or no ethanol excretion and a much higher specific oxygen uptake rate. Batch data from an extensive range of yeast and carbon sources is used to illustrate the use of this model. The ability of this model to fit such an extensive range of experimental data suggests that it can be used as a generalized model for aerobic yeast growth.

A general model for aerobic yeast growth: continuous culture.

A general model for the aerobic growth of yeast in continuous culture is presented. The model is capable of simulating the complete range of metabolic responses observed for yeast growth in continuous culture including respiratory repression, saturated respiratory capacity, and respiratory depression.It is postulated that respiratory depression is the result of the adaptation (increase in capacity of the respiratory intermediate transport proteins located at the mitochondrial membrane). Respiratory repression and subsequent saturated respiratory capacity is postulated to be the result of the gradual transfer of biosynthetic intermediates provision from the mitochondrion to the cytoplasm or, possibly, the adaptation (increase) in the capacity of the cell to excrete ethnol. It is difficult to provide a definitive experimental verification of these postulates.Irrespective of the biochemical basis of respiratory repression and depression, the model described is capable of simulating the complete range of metabolic responses obtained for yeast growth in continuous culture. It is the only model reported in the literature capable of achieving this.

Methods and strategies available for the process control and optimization of monoclonal antibody production.

The objective of this paper is to explore the range of methods and strategies available for the process control and optimization of monoclonal antibody production by hybridoma cell culture. Emphasis will be placed on the choice of the level of complexity incorporated into the process control and optimisation procedure. It will be shown that the behaviour of hybridomas in culture is influenced by sophisticated cellular metabolic activities and various interactive environmental factors and that the understanding and modelling of the way hybridomas grow in the bioreactor should enable optimisation of bioreactor operating conditions to achieve maximum monoclonal antibody formation. However, due to the lack of on-line instrumentation of important biological variables and the incomplete knowledge of hybridoma cultivation process, there exist many limitations and challenges to the advent of applications of process control and optimisation in this field. To solve the problem, introduction of industrially practical biological measurements and development of new control concepts are inevitable. At the end of this paper, we shall discuss possible schemes for the control of the physiological state of cells in order that balanced cell growth and maximum monoclonal antibody synthesis may be achieved.

Simulation of an iterative learning control system for fed-batch cell culture processes.

This paper describes an iterative learning control scheme for fed-batch operation where repetitive trajectory tracking tasks are required. The proposed learning strategy is model-independent, and it takes advantage of the repetitive feature of system operations with a certain degree of intelligence and requires only small size of dynamic database for the learning process. The convergence of the learning process is proven. An example of simultaneously tracking two predefined trajectories by iterative learning control with two control inputs is given to illustrate the methodology. Satisfactory performance of the learning system can be observed from the simulation results.

Investigation of the significance of a carbon and redox balance to the measurement of gaseous metabolism of Saccharomyces cerevisiae.

A complete carbon and redox balance for Saccharomyces cerevisiae grown in batch culture with ethanol as the limiting carbon and energy source is reported. A novel method, which allowed the determination of carbon dioxide contained in the culture medium and biomass, is described and revealed amounts considerably in excess of what was expected from equilibrium data. Furthermore, elemental composition of the biomass was used to calculate the amount of oxygen required for biosynthetic reactions. When these corrections are applied to experimentally measured gas metabolism data, apparently anomalous results are shown to be consistent with the overall metabolism of bakers' yeast. These findings have wide implications to the quantitative study of the metabolism and energetics of facultative aerobes.

Effect of feed rate on growth rate and antibody production in the fed-batch culture of murine hybridoma cells.

Batch and fed-batch cultures of a murine hybridomacell line (AFP-27) were performed in a stirred tankreactor to estimate the effect of feed rate on growthrate, macromolecular metabolism and antibodyproduction. Macromolecular composition was foundto change dynamically during batch culture ofhybridoma cells possibly due to active production ofDNA, RNA and protein during the exponential phase.Antibody synthesis is expected to compete with theproduction of cellular proteins from the amino acidpool. Therefore, it is necessary to examine therelationship between cell growth in terms of cellularmacromolecules and antibody production. In this study,we searched for an optimum feeding strategy bychanging the target specific growth rate in fed-batchculture to give higher antibody productivity whileexamining the macromolecular composition. Concentratedglucose (60 mM) and glutamine (20 mM) in DR medium(1:1 mixture of DMEM and RPMI) with additional aminoacids were fed continuously to the culture and thefeed rate was updated after every sampling to ensureexponential feeding (or approximately constantspecific growth rate). Specific antibody productionrate was found to be significantly increased in thefed-batch cultures at the near-zero specific growthrate in which the productions of cellular DNA, RNA,protein and polysaccharide were strictly limited byslow feeding of glucose, glutamine and other nutrients. Possible implications of these results are discussed.

Precipitation, chelation, and the availability of metals as nutrients in anaerobic digestion. I. Methodology.

A methodology has been developed for the quantitative assessments of the individual effects of precipitation and chelation of metal ions in an anaerobic digester.

Precipitation, chelation, and the availability of metals as nutrients in anaerobic digestion. II. Applications.

The relative importance of the individual effects of precipitation and chelation of metal ions in anaerobic digestion is assessed. Experimentally determined soluble metal ion levels are compared with predicted levels obtained by using a previously described methodology.(1) It is found that soluble metal complexes may increase the level of soluble metals in the presence of CO(3) (2-) and S(2-) by a factor of up to 10(4). The formation of a soluble complex may increase or decrease the availability of the metal ion in question for microbial uptake. Two case studies are presented, one using a defined medium and one a complex medium. It is possible, in the case of the defined medium, to accurately predict the free metal ion concentration using the methodology previously developed.(1) While the identification of the presence of natural chelating compounds in a complex medium is not routinely possible, the significant discrepancy between the measured level of the soluble metal ion Fe(2+) and the calculated level in the case studies presented indicates that natural chelating compounds may play a vital role in providing available metal ions to the microorganisms of an anaerobic digester.

Simulation of animal cell metabolism.

A simulation of hybridoma growth and antibody production has been developed. It is capable of simulating all major variables of interest (e.g., specific growth rate, cell yield, sugars and amino acids profile, and antibody yield). This simulation is the most complete reported to date including such factors as cell composition, media composition, substrate and product effects, osmolarity etc. The stimulation of a large range of experimental data for hybridomas illustrates that this simulation is a powerful tool in the rational assessment of factors influencing the growth and metabolism of hybridoma cells.

Simulation and dynamic optimisation of animal cell culture.

In animal cell culture, there are some 25 substrates that both have a significant effect on the culture performance and which can be measured with relative ease. A detailed dynamic simulation for such a culture has been produced and an optimisation policy that use this model to identify ideal media conditions has been developed. This paper describes an extension of that work to include the dynamic optimisation of cultures under fed-batch operation. Two different types of feeding policy were considered - in the first, discrete shots of feed were supplied, while in the second, feed was added continuously. Both policies offered significant improvements in the predicted productivity of the culture - up to 30% that of an experimentally "optimised"batch culture.

Amino acid metabolism during batch culture of a murine hybridoma, AFP-27.

This paper presents batch culture data of the murine hybridoma, AFP-27, cultured in conventional basal media and in a nutrient-rich modified version. Expression of antibody was fivefold higher in the enriched formulation, with significant product secretion in the decline phase. Cultures were initiated at conventional inculation densities (1 ∼ 2 × 10(5) viable cells ml(-1)) and high inoculation densities (1.5 ∼ 1.7 × 10(6) viable cells ml(-1)). Amino acid levels have been reported for all cultures, with apparent differences described. Relative levels of intracellular amino acids are also reported, with significant accumulation of proline, glycine and alanine. The results have significance in the design of enriched media which are clearly beneficial for commercial production of antibodies from hybridomas.

Structured modelling of animal cells.

Recent advances in computer technology have promoted the design and use of detailed, computer-based models for biological systems. For many non-biological systems, the complexity of such simulations may be considered inappropriate and unwieldy, but in biological systems, and more specifically in animal cell culture, this level of complexity simply mimics what is only beginning to be understood about metabolic processs. With this in mind, we contend that complex, structured models are vital tools in the investigation of fundamental biological processes. An example of such a simulation, which describes the commercial production of therapeutic proteins by animal cell cultures, is considered.