V. González-Álvarez

Software sensors for highly uncertain WWTPs: a new approach based on interval observers

This paper presents the practical implementation of a new robust interval observer on a 1 m3 continuous fixed bed anaerobic reactor used for the treatment of industrial wine distillery wastewater. This interval observer is able to generate guaranteed intervals for the unmeasured variables (i.e. acidogenic and methanogenic bacteria, alkalinity and chemical oxygen demand) from few on-line measurements (i.e. input liquid flow rate, CO2 gaseous flow rate, volatile fatty acids and total inorganic carbon). The main advantage of this approach is its independance with respect to disturbances and uncertainty in the initial conditions, in the kinetics and, last but not least, in the process inputs.

Robust Nonlinear Observers for Bioprocesses: Application to Wastewater Treatment

In this chapter, some state estimation schemes used in bioprocesses engineering are firstly reviewed with particular emphasis on the so-called nonlinear observers. Second, two simple robust nonlinear observers are proposed and applied in a number of bioprocesses. The first estimation scheme is a generalized asymptotic observer which has demonstrated to be robust in the face of a complete lack of knowledge of the process nonlinearities whereas the second one has shown to be robust in the face of both, the system nonlinearities and the input uncertainty and yields guaranteed intervals for the non-measured variables from the available measurements. The design of both observer schemes are detailed for a general dynamical system which may be applied in a number of bioprocesses. The interval observer is further developed for fault detection and diagnosis purposes. In addition, detailed stability analysis are developed for both observers. Finally, these observers are tested in an actual experimental pilot plant used for the anaerobic digestion of wine vinasses. Key results are presented and discussed.

A Robust Asymptotic Observer for Chemical and Biochemical Reactors

Abstract A simple state observer is proposed for a class of lumped nonlinear time-varying systems useful in chemical and biochemical engineering. It is shown that this asymptotic nonlinear observer is stable in the presence of time-varying elements and robust in the face of initial conditions uncertainty and a total lack of knowledge on the nonlinearities of the system. Experimental results are presented using a model of an anaerobic digestion process for the treatment of industrial wastewater from a wine distillery and tested using real data obtained from a 1 m continuous fixed bed pilot bioreactor.

Anaerobic treatment of tequila vinasses under seasonal operating conditions: Start-up, normal operation and restart-up after a long stop and starvation period

This study examines the performance of an anaerobic fixed-film bioreactor under seasonal operating conditions prevailing in medium and small size Tequila factories: start-up, normal operation and particularly, during the restart-up after a long stop and starvation period. The proposed start-up procedure attained a stable biofilm in a rather short period (28 days) despite unbalanced COD/N/P ratio and the use of non-acclimated inoculum. The bioreactor was restarted-up after being shut down for 6 months during which the inoculum starved. Even when biofilm detachment and bioreactor clogging were detected at the very beginning of restart-up, results show that the bioreactor performed better as higher COD removal and methane yield were attained. CE-SSCP and Q-PCR analyses, conducted on the biofilm prokaryotic communities for each operating condition, confirmed that the high COD removal results after the bioreactor clogging and the severe starvation period were mainly due to the stable archaeal and resilient bacterial populations.

Regulation of the organic pollution level in anaerobic digesters by using off-line COD measurements.

A sampled delayed scheme is proposed to regulate the organic pollution level in anaerobic digestion processes by using off-line COD measurements. The proposed scheme is obtained by combining an error feedback control with a steady state estimator to track constant references and attenuate process load disturbances. The controller performance is tested experimentally for the treatment of tequila vinasses over a period of 68days under different set-point values and several uncertain scenarios which include badly known kinetic parameters and load disturbances. Experimental results show that the COD concentration can be effectively regulated under the influence of set-point changes and high load disturbances by using only a daily off-line COD measurement, which makes the industrial application of the proposed control scheme feasible.

Highly Hydrophobic Wood Surfaces Prepared by Treatment With Atmospheric Pressure Dielectric Barrier Discharges

Atmospheric dielectric barrier discharge (DBD) treatments of wood were done to attain water repellency on wood surfaces. A specially designed frequency controlled parallel-plate DBD reactor was utilized to produce the discharges. Ethylene, methane, chlorotrifluoroethylene and hexafluoropropylene were used as DBD reagents. Contact angle, water absorption, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurements on the modified surfaces were performed. For methane and ethylene, XPS data showed an increased surface atomic concentration of carbon from 72.7% on untreated samples up to 80.7 and 96%, respectively, whereas nearly 50% fluorine concentration was observed with fluorinated reagents. The C1s spectrum of hexafluoropropylene-DBD-treated wood sample showed that the CF3 group was introduced in a relative amount of 19%. AFM images showed distinct features for each of the DBD treatments, such as a deposit of a thin uniform film in the case of ethylene-DBD treatment, whereas the hexafluoropropylene-DBD treatment resulted in the nucleation of plasma-derived entities at the fiber surface and the subsequent growth of a film. Under optimized conditions the water contact angle was in the range of 139°–145°. The combination of depositing a low surface energy polymer on an already rough surface gave the surface-treated wood a highly hydrophobic character.

Stability analysis and passivity properties for a class of chemical reactors: Internal entropy production approach

In this contribution, the stability and passivity properties of a class of chemical reactors are addressed from a thermodynamical point of view. For this purpose, a thermodynamical consistent model is derived from a generic gas reactor model whose rate is based on the reaction progress at the mesoscopic scale. It is shown that the internal entropy production may be used as a candidate Lyapunov function to prove the isolated system stability properties and as a storage function to emphasize the passivity properties when the chemical reactor interacts with the surroundings.

Slow-release effect of N-functionalized kraft lignin tested with Sorghum over two growth periods

Biomass production of fodder sorghum (Sorghum sp.) has been tested in a field trial over two harvesting periods under natural meteorological conditions using ammoxidized kraft lignin (AKL) as a slow-release fertilizer and urea as conventional reference. In the course of the first growth cycle, plants treated with urea gave higher biomass yields because of the better solubility of urea in the initial phase. However, during the second cycle AKL treated plants performed better than urea treated sorghum, indicating that nitrogen from AKL became readily available.

Biogas production in an anaerobic sequencing batch reactor by using tequila vinasses: effect of pH and temperature

In recent years, anaerobic digestion has been recognized as a suitable alternative for tequila vinasses treatment due to its high energy recovery and chemical oxygen demand (COD) removal efficiency. However, key factors such as the lack of suitable monitoring schemes and the presence of load disturbances, which may induce unstable operating conditions in continuous systems, have limited its application at full scale. Therefore, the aim of this work was to evaluate the anaerobic sequencing batch reactor (AnSBR) configuration in order to provide a low cost and easy operation alternative for the treatment of these complex effluents. In particular, the AnSBR was evaluated under different pH-temperature combinations: 7 and 32 °C; 7 and 38 °C; 8 and 32 °C and 8 and 38 °C. Results showed that the AnSBR configuration was able to achieve high COD removal efficiencies (around 85%) for all the tested conditions, while the highest methane yield was obtained at pH 7 and 38 °C (0.29 L/g COD added). Furthermore, high robustness was found in all the AnSBR experiments. Therefore, the full-scale application of the AnSBR technology for the treatment of tequila vinasses is quite encouraging, in particular for small and medium size tequila industries that operate under seasonal conditions.

Selected topics in dynamics and control of chemical and biological processes

Control of Chemical Processes.- Nonisothermal Stirred-Tank Reactor with Irreversible Exothermic Reaction A ? B: 1. Modeling and Local Control.- Temperature Control Via Robust Compensation of Heat Generation: Isoparaffin/Olefin Alkylation.- Control Performance of Thermally Coupled Distillation Sequences with Unidirectional Flows.- Robust Tracking for Oscillatory Chemical Reactors.- Control and Diagnosis of Biological Processes.- Robust Nonlinear Observers for Bioprocesses: Application to Wastewater Treatment.- Robust Nonlinear Control of a Pilot-Scale Anaerobic Digester.- Advances in Diagnosis of Biological Anaerobic Wastewater Treatment Plants.- Dynamics of Controlled Reactors.- Nonisothermal Stirred-Tank Reactor with Irreversible Exothermic Reaction A ? B: 2. Nonlinear Phenomena.- Oscillations in Controlled Processes: Two Experimental Study Cases.