Hybrid Control of a Bioreactor with Quantized Measurements: Extended Version

We consider the problem of global stabilization of an unstable bioreactor model (e.g. for anaerobic digestion), when the measurements are discrete and in finite number ("quantized"), with control of the dilution rate. The model is a differential system with two variables, and the output is the biomass growth. The measurements define regions in the state space, and they can be perfect or uncertain (i.e. without or with overlaps). We show that, under appropriate assumptions, a quantized control may lead to global stabilization: trajectories have to follow some transitions between the regions, until the final region where they converge toward the reference equilibrium. On the boundary between regions, the solutions are defined as a Filippov differential inclusion. If the assumptions are not fulfilled, sliding modes may appear, and the transition graphs are not deterministic

A current-driven six-channel potentiostat for rapid performance characterization of microbial electrolysis cells

Knowledge of the performance of microbial electrolysis cells under a wide range of operating conditions is crucial to achieve high production efficiencies. Characterizing this performance in an experiment, however, is challenging due to either the long measurement times of steady-state procedures or the transient errors of dynamic procedures. Moreover, wide parallelization of the measurements is not feasible due to the high measurement equipment cost per channel. Hence, to speedup this characterization and to facilitate low-cost, yet widely parallel measurements, this paper presents a novel rapid polarization curve measurement procedure with a dynamic measurement resolution that runs on a custom six-channel potentiostat with a current-driven topology. As case study, the procedure is used to rapidly assess the impact of altering pH values on a microbial electrolysis cell that produces H-2. A $\times 2$ - $\times 12$ speedup could be obtained in comparison with the state-of-the-art, depending on the characterization resolution (16-128 levels). On top of this speedup, measurements can be parallelized up to $6\times$ on the presented, affordable-42-per-channel-potentiostat

Aeration and operation of an immobilized cell oxidative bioreactor

The primary purpose of this work is to help define the optimum window of operations for an immobilized cell oxidative bioreactor. The analytical technique employed requires no outside verification (such as G.C. analysis) and is independent of liquid flow rate. Method of aeration has been determined to be an important parameter for optimizing bioreactor efficiency, and optimization of the quantity of hydrogen peroxide added to provide oxygen during bio-oxidation has been investigated. Ammonium hydroxide as a fixed nitrogen source can be used to restore the vitality of the bioreactor under certain conditions. The effects of several different methods of providing oxygen on bio-oxidation were analyzed. These methods included aeration at the center of the reservoir (18 from the pump inlet leading to the biosupport), aeration near the pump inlet (3 away), and providing oxygen by means of injection of hydrogen peroxide into the reservoir. Generally, aeration nearer to the cylinder led to faster initial rates of biodegradation of the phenol. With hydrogen peroxide, an injection of 0.5 ml of 30% H2O2 (3.8 ppm H2O2) best facilitated the bio-oxidation of 0.5 g phenol, whereas higher amounts caused inhibition. The use of ammonium hydroxide to speed up slow reaction rates has been demonstrated, with the minimum effective injection determined to be approximately 10 ml concentrated NH4OH (21 ppm). Quantitation using the dissolved oxygen reaction patterns has been briefly discussed. The effect of both dilution and of changing liquid flow rate on baseline dissolved oxygen levels has been analyzed. Also, a guide has been prepared for the recognition of some abnormal dissolved oxygen level patterns for troubleshooting and assessing systemic causes and solutions and general bioreactor operation observations and suggestions have been provided

Exploring Protein Interactions with 23Na Triple-quantum MRS and 1H Chemical Exchange Saturation Transfer MRI

Nuclear magnetic resonance (NMR) allows the non-invasive investigation of proteins using 23Na triple-quantum (TQ) and 1H chemical exchange saturation transfer (CEST) signals. Interactions of sodium ions with macromolecules yield an intracellular sensitive TQ signal. A TQ signal increase has been shown to correlate with the loss of cell viability. However, a deeper understanding of the TQ signal on a cellular level is necessary to determine its capability to serve as a potential biomarker for cell viability. CEST indirectly detects low concentrated organic compounds by their magnetization transfer with water. Protein-based CEST signals have been demonstrated in vitro to be closely connected to the protein folding state and have great potential as a non-invasive diagnostic tool for diseases, like cancer and neurodegenerative diseases. Nonetheless, the detectability of denaturation processes in living cells by CEST NMR remains to be verified experimentally. In the first part of this thesis, a dependence of the TQ signal on the pH and protein folding state was demonstrated using protein solutions. An increase in the availability of negatively charged groups in proteins caused an increase in the TQ signal during pH variation (224.5 +- 25.1%) or protein unfolding (40.7 +- 2.3%). Second, the cellular response to a Na/K-ATPase inhibition was monitored using improved TQ signal detection. The TQ signal increased by 38.9 +- 4.1% and 83.4 +- 8.9% during perfusion with 1 mM ouabain and 0 mM K+ medium, respectively, which agreed with an influx of sodium ions during the Na/K-ATPase inhibition. Finally, the cellular heat shock response was investigated using protein-based CEST signals. Heat shock application resulted in a substantial signal decrease by 8.0 +- 0.4% followed by a continuous signal recovery, which agreed with chaperone-induced refolding of misfolded proteins. The proposed NMR techniques combined with the bioreactor system are promising research tools to non-invasively investigate cellular processes by NMR

Multivariable Tracking Control of a Bioethanol Process under Uncertainties

Bioethanol is one of the most studied alternative fuels nowadays. Due to its production process complexity and the low quality of the mathematical models that describe it, a reliable controller is needed to maximize the fuel production and minimize its environmental impact, even in the presence of uncertainty. Here, a controller for tracking optimal profiles considering model errors and external perturbations is proposed. This work is an improvement of a previously presented technique. To reduce the earlier mentioned uncertainties' effect during the fermentation, some tracking error integrators are added in the control action calculation. This simple modification ensures the tracking error convergence to zero, even in the presence of uncertainties (demonstration available). Different tests are carried out and a performance comparison with the original controller is shown to highlight improvements in the tracking error of up to 98% when integrators are incorporated. Furthermore, a classical PI controller is contrasted with the proposed techniques.Fil: Fernández Puchol, María Cecilia. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Ingeniería Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Pantano, Maria Nadia. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Ingeniería Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Serrano, Mario Emanuel. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Ingeniería Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Scaglia, Gustavo Juan Eduardo. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Ingeniería Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentin

The Effect of Light And Dark Periods on the Growth of Chlorella Sorokiniana: Modeling & Experimentation

Microalgae are abundant unicellular photosynthetic organisms with more than 200,000 species. They are more efficient in harvesting solar energy than land-based plants with green microalgae having more than ten times higher biodiesel productivity than the next best land-based crop. Their ability to grow in harsh environments, non-agricultural lands, and make use of wastewater, and the diversity of the products that can be extracted from them, which include cosmetics, pharmaceuticals, food supplements, biofuels, and many others, gives them the potential to replace fossil fuels and revolutionize the biotech industry. In order to move onto large scale production, first, the growth rate of the cell culture must be increased, which requires screening of promising species, studying their growth kinetics, and selecting their most suitable environment. Second, microalgae use their internal energy reservoirs (lipid bodies) during dark periods; nighttime biomass loss must be prevented. In this study, we analyzed the effect of light intensity on the growth of Chlorella sorokiniana, a promising species for biofuel production. We constructed a growth model that accurately predicts the growth response of the cell culture to varying irradiance conditions and photoperiods. We incorporated the concept of Monod kinetics into our model and quantified the effect of light intensity on biomass accumulation under lightlimiting conditions. We determined that the empirically measured maximum growth rate v parameter has a value of 0.20 h-1 which is limited by the maximum photosynthetic rate. Additionally, we determined the Monod saturation constant to be 238 |imol s-1 m-2. We found that biomass loss rate due to respiration and other metabolic activities peaked during the day (8.7x10-3 h-1), and was constant during nighttime (1.8x10-3 h-1). We determined that 5% of the biomass gained during the 16-hour day period was lost during the following 8-hour dark period, which lead to a 16% lower biomass yield when compared to a continuously illuminated culture after nine days of cultivation at a constant temperature of 30°C in a well-mixed five-liter photobioreactor. Finally, we illustrated that illuminating the dark period with low-consumption red LEDs will prevent biomass loss and enhance cell replication

Super-Twisting-Algorithm-Based Terminal Sliding Mode Control for a Bioreactor System

This study proposes a class of super-twisting-algorithm-based (STA-based) terminal sliding mode control (TSMC) for a bioreactor system with second-order type dynamics. TSMC not only can retain the advantages of conventional sliding mode control (CSMC), including easy implementation, robustness to disturbances, and fast response, but also can make the system states converge to the equivalent point in a finite amount of time after the system states intersect the sliding surface. The chattering phenomena in TSMC will originally exist on the sliding surface after the system states achieve the sliding surface and before the system states reach the equivalent point. However, by using the super twisting algorithm (STA), the chattering phenomena can be obviously reduced. The proposed method is also compared with two other methods: (1) CSMC without STA and (2) TSMC without STA. Finally, the control schemes are applied to the control of a bioreactor system to illustrate the effectiveness and applicability. Simulation results show that it can achieve better performance by using the proposed method

NASA's Microgravity Science Research Program

The ongoing challenge faced by NASA's Microgravity Science Research Program is to work with the scientific and engineering communities to secure the maximum return from our Nation's investments by: assuring that the best possible science emerges from the science community for microgravity investigations; ensuring the maximum scientific return from each investigation in the most timely and cost-effective manner; and enhancing the distribution of data and applications of results acquired through completed investigations to maximize their benefits

NASA's Microgravity Research Program

This fiscal year (FY) 1997 annual report describes key elements of the NASA Microgravity Research Program (MRP) as conducted by the Microgravity Research Division (MRD) within NASA's Office of Life and Microgravity, Sciences and Applications. The program's goals, approach taken to achieve those goals, and program resources are summarized. All snapshots of the program's status at the end of FY 1997 and a review of highlights and progress in grounds and flights based research are provided. Also described are major space missions that flew during FY 1997, plans for utilization of the research potential of the International Space Station, the Advanced Technology Development (ATD) Program, and various educational/outreach activities. The MRP supports investigators from academia, industry, and government research communities needing a space environment to study phenomena directly or indirectly affected by gravity

Protein-Polyelectrolyte Complexes and Micellar Assemblies.

In this review, we highlight the recent progress in our understanding of the structure, properties and applications of protein-polyelectrolyte complexes in both bulk and micellar assemblies. Protein-polyelectrolyte complexes form the basis of the genetic code, enable facile protein purification, and have emerged as enterprising candidates for simulating protocellular environments and as efficient enzymatic bioreactors. Such complexes undergo self-assembly in bulk due to a combined influence of electrostatic interactions and entropy gains from counterion release. Diversifying the self-assembly by incorporation of block polyelectrolytes has further enabled fabrication of protein-polyelectrolyte complex micelles that are multifunctional carriers for therapeutic targeted delivery of proteins such as enzymes and antibodies. We discuss research efforts focused on the structure, properties and applications of protein-polyelectrolyte complexes in both bulk and micellar assemblies, along with the influences of amphoteric nature of proteins accompanying patchy distribution of charges leading to unique phenomena including multiple complexation windows and complexation on the wrong side of the isoelectric point