Inlet Glucose Research Articles

Sensor fault detection in a biohydrogen production process based on an interval observer and adaptive thresholds

In this paper, an interval observer-based fault detection strategy is proposed to deal with faults in the hydrogen flow rate sensor of a biohydrogen production process. A control Hinf-based robust interval observer is designed to (i) estimate the glucose and biomass concentrations from measurements of the hydrogen flow rate produced, (ii) attenuate the effect of the unknown inlet glucose concentration, and (iii) detect faults in the hydrogen flow rate sensor through adaptive thresholds. The gain is designed by solving a semi-definite optimization problem subject to LMIs. The feasibility of the proposed strategy is demonstrated by simulations.

Experimental validation of an interval observer-based sensor fault detection strategy applied to a biohydrogen production dark fermenter

In this paper, the problem of designing an interval observer applied to a biohydrogen production dark fermenter is addressed, in order to: (i) estimate the glucose and biomass concentrations, and the hydrogen flow rate produced, (ii) reduce the influence of the unknown inlet glucose concentration and the model uncertainties, and (iii) detect the presence of faults in the hydrogen flow rate sensor. Based on literature reports, we propose an interval observer structure, constituted by a Luenberger observer and an interval predictor, for a class of linear systems. The interval observer offers three estimations: the upper and lower estimations provided by the interval predictor, and one estimation given by the Luenberger observer. The upper and lower estimations provide bounds at any instant of time for the state vector of the perturbed/uncertain biohydrogen production bioreactor model from an appropriate initial condition. The design conditions presented in this work are based on control H∞ in combination with pole placement and polytopic parametric uncertainties. The observer design is proposed as a semi-definite optimization problem subject to Linear Matrix Inequalities, which do not depend on the cooperativity property. Based on the proposed observer structure, we also present two fault detection schemes for the same class of uncertain systems to detect the occurrence of sensor faults: one makes use of the logic comparison between the set threshold and the residual produced by the Luenberger observer; the other considers adaptive thresholds for the output signal by using the upper and lower estimates of the interval predictor. Finally, the proposed approaches are validated with experimental data from a biohydrogen production dark fermenter.

Three-dimensional modeling of photo fermentative biohydrogen generation in a microbioreactor

Photo fermentation is an emerging approach of biohydrogen production as it is energy saving and environmentally friendly. Understanding mechanisms of controlling the bacteria growth and biohydrogen production is critical for effective improvements in energy harvest and waste treatment in photo fermentative bioreactors. In this study a comprehensive three-dimensional numerical platform of photo fermentation was developed, based on lattice Boltzmann method coupled with cellular automata. The model accounts for photosynthetic bacteria growth, illumination energy conversion by photosynthetic bacteria, and light transfer under biofilm growth. The results showed a threshold of illumination intensity. Below this threshold, the bioreactor performance increased as the illumination intensity increased. Above the threshold, the performance declined if the illumination intensity rose. The normalized average biohydrogen production at the illumination intensity of 6000lx, increased about 66.31%, 13.82% and 13.12%, respectively, compared to ones at 4000lx, 5000lx and 7000lx. An increase in inlet glucose concentration could increase biohydrogen concentration and extraction but dwindled biohydrogen yield. It was found that a lower inlet velocity had higher biohydrogen production rate and concentration but lower biohydrogen extraction and yield. The results demonstrate that the present LBM-CA platform can be a tool to study and enhance the photo fermentative production of biohydrogen.

Washout and non-washout solutions of a system describing microbial fermentation process under the influence of growth inhibitions and maximal concentration of yeast cells

An unstructured model for the growth of yeast cell on glucose due to growth inhibitions by substrate, products, and cell density is discussed. The proposed model describes the dynamical behavior of fermentation system that shows multiple steady states for a certain regime of operating parameters such as inlet glucose and dilution rate. Two types of steady state solutions are found, namely washout and non-washout solutions. Furthermore, different numerical impositions to the two parameters put in evidence three results regarding non-washout solution: a unique locally stable non-washout solution, a unique locally stable non-washout solution towards which other nearby solutions exhibit damped oscillations, and multiple non-washout solutions where one is locally stable while the other is unstable. It is also found an optimal inlet glucose which produces the highest cell and ethanol concentration.

Mesophilic biohydrogen production by Clostridium butyricum CWBI1009 in trickling biofilter reactor

This study investigates the mesophilic biohydrogen production from glucose using a strictly anaerobic strain, Clostridium butyricum CWBI1009, immobilized in a trickling bed sequenced batch reactor (TBSBR) packed with a Lantec HD Q-PAC® packing material (132 ft2/ft3 specific surface). The reactor was operated for 62 days. The main parameters measured here were hydrogen composition, hydrogen production rate and soluble metabolic products. pH, temperature, recirculation flow rate and inlet glucose concentration at 10 g/L were the controlled parameters. The maximum specific hydrogen production rate and the hydrogen yield found from this study were 146 mmol H2/L.d and 1.67 mol H2/mol glucose. The maximum hydrogen composition was 83%. Following a thermal treatment, the culture was active without adding fresh inoculum in the subsequent feeding and both the hydrogen yield and the hydrogen production rate were improved. For all sequences, the soluble metabolites were dominated by the presence of butyric and acetic acids compared to other volatile fatty acids. The results from the standard biohydrogen production (BHP) test which was conducted using samples from TBSBR as inoculum confirmed that the culture generated more biogas and hydrogen compared to the pure strain of C. butyricum CWBI1009. The effect of biofilm activity was studied by completely removing (100%) the mixed liquid and by adding fresh medium with glucose. For three subsequent sequences, similar results were recorded as in the previous sequences with 40% removal of spent medium. The TBSBR biofilm density varied from top to bottom in the packing bed and the highest biofilm density was found at the bottom plates. Moreover, no clogging was evidenced in this packing material, which is characterized by a relatively high specific surface area. Following a PCA test, contaminants of the Bacillus genus were isolated and a standard BHP test was conducted, resulting in no hydrogen production.

Study of dynamics of glucose-glucose oxidase-ferricyanide reaction

This work is focused on dynamics of the glucose-glucose oxidase-ferricyanide enzymatic reaction with or without sodium hydroxide in a continuous-flow stirred tank reactor (CSTR) and in a batch reactor. This reaction exhibits pH-variations having autocatalytic character and is reported to provide nonlinear dynamic behavior (bistability, excitability). The dynamical behavior of the reaction was examined within a wide range of inlet parameters. The main inlet parameters were the ratio of concentrations of sodium hydroxide and ferricyanide and the flow rate. In a batch reactor we observed an autocatalytic drop of pH from slightly basic to medium acidic values. In a CSTR our aim was to find bistability in the presence of sodium hydroxide. However, only a basic steady state was found. In order to reach an acidic steady state, we investigated the system in the absence of sodium hydroxide. Under these conditions the transition from the basic to the acidic steady state was observed when inlet glucose concentration was increased.

Performance of a groove-type photobioreactor for hydrogen production by immobilized photosynthetic bacteria

The biofilm technique has been proved to be an effective cell immobilization method for wastewater biodegradation but it has had restricted use in the field of photobiological H 2 production. In the present study, a groove-type photobioreactor was developed and it was shown that a groove structure with large specific surface area was beneficial to cell immobilization and biofilm formation of the photosynthetic bacteria on photobioreactor surface as well as light penetration. A series of experiments was carried out on continuous hydrogen production in the groove-type photobioreactor illuminated by monochromatic LED lights and the performance was investigated. The effects of light wavelength, light intensity, inlet glucose concentration, flow rate and initial substrate pH were studied and the results were compared with those obtained in a flat panel photobioreactor. The experimental results show that the optimum operational conditions for hydrogen production in the groove-type photobioreactor were: inlet glucose concentration 10 g/L, flow rate 60 mL/h, light intensity 6.75 W/m 2, light wavelength 590 nm and initial substrate pH 7.0. The maximum hydrogen production rate, H 2 yield and light conversion efficiency in the groove-type photobioreactor were 3.816 mmol/m 2/h, 0.75 molH 2/molglucose and 3.8%, respectively, which were about 75% higher than those in the flat panel photobioreactor.

Thermophilic biohydrogen production from glucose with trickling biofilter

Thermophilic H2 production from glucose was studied at 55-64 degrees C for 234 days using a continuous trickling biofilter reactor (TBR) packed with a fibrous support matrix. Important parameters investigated included pH, temperature, hydraulic retention time (HRT), and glucose concentration in the feed. The optimal pH and temperature were 5.5 and 60 degrees C, respectively. With decreasing HRT or increasing inlet glucose concentration, volumetric H2 production rate increased but the H2 production yield to glucose decreased gradually. The biogas composition was almost constant at 53 +/- 4% (v/v) of H2 and 47 +/- 4% (v/v) of CO2. No appreciable CH4 was detected when the reactor was under a normal operation. The carbon mass balance showed that, in addition to cell mass, lactate, n-butyrate, CO2, and acetate were major products that comprised more than 85% of the carbon consumed. The maximal volumetric H2 production rate and H2 yield to glucose were 1,050 +/- 63 mmol H2/l.d and 1.11 +/- 0.12 mol H2/mol glucose, respectively. These results indicate that the thermophilic TBR is superior to most suspended or immobilized reactor systems reported thus far. This is the first report on continuous H2 production by a thermophilic TBR system.

Mathematical modelling and optimization of hydrogen continuous production in a fixed bed bioreactor

The purpose of this paper is to investigate, both theoretically and experimentally, hydrogen production from agro-industrial by-products using a continuous bioreactor packed with a mixture of spongy and glass beads and inoculated with Enterobacter aerogenes. Replicated series of experimental runs were performed to study the effects of residence time on hydrogen evolution rate and to characterize the critical conditions for the wash out, as a function of the inlet glucose concentration and of the fluid superficial velocity. A further series of experimental runs was focused on the effects of both residence time and inlet glucose concentration over hydrogen productivity. A kinetic model of the process was developed and showed good agreement with experimental data, thus representing a potential tool to design a large-scale fermenter. In fact, the model was applied to the optimal design of a bioreactor suitable of feeding a phosphoric acid fuel cell of a target power.

Dual substrate limitations in upflow packed‐bed biofilm reactors — a theoretical study

AbstractThe performance of an upflow packed‐bed biofilm reactor has been analyzed under dual substrate limitation conditions. The numerical solution of the proposed equations defining the system has been obtained for a wide range of operating conditions for a case of practical significance involving glucose and oxygen as dual substrates. The results show that the inlet glucose concentration defines the limiting substrate at a position near the inlet of the reactor. For inlet glucose concentrations up to 300 mg/l, glucose acts as the limiting substrate. However, for inlet concentrations of 400 mg/l of glucose or higher, oxygen assumes the role of the limiting substrate at that position. For all other positions in the reactor, glucose acts as the limiting substrate, irrespective of its inlet concentration. Extensive computations were performed in order to define regions where glucose, oxygen or both are limiting. The predicted results have been found to be in agreement with the theoretical criteria, proposed in the literature, of determining the limiting substrate.

Long-Term Adaptive Shifts in Anaerobic Community Structure in Response to a Sustained Cyclic Substrate Perturbation

The response of a glucose-fed anaerobic chemostat community to a long-term (>200 days) periodic substrate perturbation was examined. Identical steady-state communities were established in a ``mother'' and a ``daughter'' reactor at pH 7, 35°C, inlet glucose concentration of 8 g l−1, and dilution rate of 0.1 day−1. After reaching steady state, the daughter reactor was subjected to a periodic organic loading pattern in which the influent glucose concentration was alternately varied from 16 g l−1 to 0 g l−1 (mineral media only) on a 2-day cycle (1 day at 16 g l−1 followed by 1 day without glucose feed). The average organic loading rate for the perturbation cycle was equal to the steady-state glucose loading rate of 0.8 g l−1 day−1. The dilution rate of the daughter reactor was constant at 0.1 day−1 throughout the perturbation period. A rapid accumulation in volatile fatty acids (VFAs) occurred immediately after initiating the perturbation. During the first 45 days, effluent acetate, propionate, and butyrate concentrations increased to ca. 2,500, 800, and 1,200 mg l−1, respectively; effluent chemical oxygen demand (COD) increased from 450 mg l−1 to 5,200 mg l−1. Total gas production decreased from about 600 ml day−1 to an average value of 290 ml day−1; CH4 content of the biogas decreased from 50% to about 30%; and the pH decreased from 7.0 to 6.4. This was followed by a 60-day metastable ``steady'' state during which time the effluent COD and VFA concentrations fluctuated about new median values. A dramatic change in the fermentation products of glucose was observed. At the end of the metastable period, VFA concentrations decreased rapidly. First, a rapid decrease in butyrate concentration occurred. Subsequently, acetate and propionate concentrations decreased to near the original preperturbation steady-state levels. Within ca. 30 days, a new steady state was established. These observations demonstrate that the anaerobic system was able to adapt to the periodic substrate perturbation through a long-term change in community structure. This conclusion was verified by comparison of DNA extracts from the steady-state control ``mother'' reactor with extracts from the perturbed ``daughter'' reactor, changes in substrate degradation rates, and microscopic examination.

Optimization of two-stage continuous culture system for production of poly-β-hydroxybutyrate

The optimization of poly-β-hydroxybutyrate (PHB) fermentation process is essential to obtain a high PHB productivity. An optimization of two-stage continuous culture system by complex method for PHB production is presented. PHB production rate of the system obtained in the present study was chosen as the objective function. The PHB production rate of the system was higher than that of the phasewise optimization method which maximizes the growth rate of residual biomass in the first stage and the PHB production rate in the second stage. When the inlet glucose concentration in the first stage increased, PHB content and yield also increased. When the fermentor volume ratio (V2/V1) was 0.5, maximum PHB productivity in the second stage was 2.86 g/L’ h, which is highest compared with the reported value on PHB.

Evaluation of sensors for the control of a continuous ethanol fermentation

A method is presented for the evaluation of sensors used in the control of continuous fermentations. Simulations of open-loop response to input disturbance provided a starting point for the choice of sensor type. This was evaluated quantitatively through a sensitivity ratio. It was shown that in the case of ethanol fermentation, there existed three regions where different sensors could be used for the process control depending on the inlet sugar concentration. Sugar sensors were preferable above an inlet sugar concentration of 50 kg/m3, while ethanol sensors were preferable below 25 kg/m3. In the intermediate region, sugar and ethanol sensors demonstrated equally good performance. A controllability study of a continuous ethanol fermentation was also made. A single-stage continuous stirred-tank fermentor was simulated operating at a dilution rate of 0.1 1/h and inlet glucose concentration of 160 kg/m3. The outlet glucose concentration was controlled with a PI controller. Mean square error of the controller input signal during the first five hours after introducing input disturbance was taken as a measure of the controllability. This was studied in the relation to the two key sensor characteristics, sampling time and accuracy.

Studies on Production of Lipids in Fungi. XXIII

Effects of various cultural factors (dilution rate, nutrient concentrations and C/N ratio) on lipid productivity (PL) and lipid content were examined in a continuous culture of Mortierella rammanniana IFO 8187. Cultural optimization lead to a maximum PL of 1.08 g/L/h at 100 g/L of inlet glucose, 0.15 h-1 dilution rate and C/N ratio of 23.4. PL was 2.9 times that in a batch culture (200 g/L of initial glucose concentration, 34 C/N ratio and 3.5 days of culture). High PL in continuous culture may possibly be related to lower glucose concentration in the culture medium (20 g/L), lower C/N ratio and relatively small decrease in lipid content at a higher dilution rate or growth rate.

Extracellular brain glucose levels reflect local neuronal activity: a microdialysis study in awake, freely moving rats.

The relationship between brain extracellular glucose levels and neuronal activity was evaluated using microdialysis in awake, freely moving rats. The sodium channel blocker tetrodotoxin and the depolarizing agent veratridine were administered through the dialysis probe to provoke local changes in neuronal activity. The extracellular glucose content was significantly increased in the presence of tetrodotoxin and decreased sharply following veratridine application. The systemic injection of a general anaesthetic, chloral hydrate, led to a large and prolonged increase in extracellular glucose levels. The brain extracellular glucose concentration was estimated by comparing dialysate glucose efflux over a range of inlet glucose concentrations. A mean value of 0.47 mM was obtained in five animals. The results are discussed in terms of the coupling between brain glucose supply and metabolism. The changes observed in extracellular glucose levels under various conditions suggest that supply and utilization may be less tightly linked in the awake rat than has previously been postulated.

Effect of oxygen on steady-state product distribution inBacillus polymyxa fermentations

Bacillus polymyxa ferments glucose to 1-2,3 butanediol, acetoin, ethanol, acetic acid, lactic acid, and formic acid. This research investigates product formation as a function of oxygen availability. A predictive model that simulates product distribution at known oxygen transfer rates is developed on the hypothesis that, in an energy-limited environment, B. polymyxa utilizes glucose and oxygen in the most efficient manner. The efficiency of utilization of glucose and oxygen is measured in terms of the ATP yields of each oxidative pathway. The identity of the products constituting the profile at the given oxygen transfer rate is determined by comparing the ATP production and consumption rates. While the ATP generated is calculated from a knowledge of the oxygen transfer rate and ATP yields of the oxidative pathways, the ATP consumption is estimated by the Pirt expression in terms of growth- and nongrowth-associated components. The product formation rates are obtained by solving ATP and NAD balance equations. They equate the production and consumption rates of these intermediates and are derived from the pseudo-steady-state hypothesis. The model is applied to continuous culture systems that are both open and closed with respect to biomass. At a given oxygen transfer rate, dilution rate, and inlet glucose concentration, the model predicts steady-state concentrations of two dominant fermentation end products with the help of four parameters that can be determined from independent experiments. In contrast with earlier approaches, the experimental studies are carried out in continuous culture. Product profiles are obtained at various oxygen transfer rates, fer rates, inlet glucose concentrations, and dilution rates. The effect of pH on the relative distribution of products is also demonstrated. Results indicate that the model is fairly successful in predicting product profiles as a function of oxygen availability.

Glucose oxidation in a dual hollow fiber bioreactor with a silicone tube oxygenator

A dual hollow fiber bioreactor, consisting of an outer silicone membrane for oxygen supply and an inner polyamide membrane for substrate permeation, was used as an immobilized enzyme reactor to carry out enzymatic glucose oxidation. Attaching a silicone tube oxygenator to provide an additional oxygen supply improved the conversion in glucose oxidation when the oxygen supply was rate-limiting. The reactor was operated in both diffusion and ultrafiltration modes. In the latter case, the conversion was much higher, but the stability of the immobilized enzyme was better maintained in the diffusion mode. As the inlet glucose concentration increased from 10mM to 500mM, the conversion decreased from 70 to 20%.

High productivity ethanol fermentations with crossflow membrane separation techniques for continuous cell recycling

Productivity of the fermentation of glucose to ethanol by Saccharomyces cerevisiae has been significantly improved by coupling a crossflow microfiltration module to the fermenter in a single-stage continuous configuration. At a cell concentration of approximately 90 g/l in the reactor, and an inlet glucose concentration of 182 g/l, productivity was 44 g ethanol/l-hr at a dilution rate of 0.64 1/hr. These productivities are significantly higher than those described in literature for continuous fermentation with yeast in CSTRs.

The Role Of Limited Respiration In The Incomplete Oxidation Of Glucose By Saccharomyces Cerevisiae

The respiratory capacity of Saccharomyces cerevisiae growing in continuous culture on glucose and on mixtures of glucose and ethanol was investigated. An oxygen uptake rate of 8 mmo1 g−1 h−1 was found to limit the ability of the organism to degrade a substrate purely oxidatively. On glucose as sole energy and carbon source, this respiration rate was invariably achieved at an identical growth rate and thus at an identical substrate uptake rate when the inlet glucose concentration was varied. The rate of ethanol co-consumption together with glucose was strictly governed by this limiting maximum respiratory capacity and no repression of respiration was observed at dilution rates where ethanol was excreted by the cells. Hence, a limitation in some step in the oxidative branch of catabolism is likely to be responsible for incomplete oxidation of glucose at high growth rates rather than an undefined action of glucose repression.