Estudio de la digestión anaerobia en dos fases para el tratamiento de las aguas residuales de despulpe del beneficiado húmedo del café

Debido al aumento de los estándares de calidad exigidos internacionalmente, así como por una mayor presión sobre la industria mediante legislaciones ambientales más rigurosas, el sector cafetalero está obligado a buscar, a través de la investigación, un sistema adecuado de tratamiento para las aguas residuales generadas en el beneficiado húmedo del café. En este trabajo se evaluó el funcionamiento de la digestión anaerobia para el tratamiento de las aguas residuales de despulpe. Para ello, se utilizaron dos sistemas anaerobios, uno en una etapa (UASB), y otro con separación de fases (2PUASB). Se investigó el efecto en la digestión anaerobia de tres cargas orgánicas volumétricas (OLR) y de las dos configuraciones de reactor usadas. Los valores de OLR de operación en el sistema UASB variaron en un intervalo de 3.6-4.1 kgCOD m-3 d-1, con una tasa de recirculación del efluente de 1.0. El sistema 2PUASB fue alimentado con OLR similares a las que se emplearon en el sistema en una etapa. El reactor de acidificación fue cargado a 11.0 kgCOD m-3 d-1, mientras que en el reactor metanogénico varió en el intervalo de 2.6-4.67 kgCOD m-3 d-1. El uso de reactores UASB en una etapa y en dos fases, bajo las mismas condiciones de operación ya descritas, propiciaron el logro de una eficiencia de degradación de COD total superior al 75% y al 85% para la COD soluble, respectivamente. Sin embargo, el sistema en dos fases mostró mejores resultados en el tratamiento de este tipo de agua residual, no solo en cuanto a eficiencia de eliminación de la carga orgánica contaminante así como una menor concentración de ácidos grasos volátiles (VFA) en el efluente. Obtenidas las mejores condiciones de trabajo, fue evaluada la separación de fases bajo el efecto de la recirculación. Los grupos de fermentaciones producidos fueron similares a los obtenidos en el experimento sin recirculación, indicando que está última no afectó la composición relativa de los VFA del reactor anaerobio, por lo que no cambió el patrón de degradación del residuo. Una tasa de recirculación de 1.0 del efluente del reactor metanogénico al reactor acidogénico mejoró significativamente el proceso, ya que se incrementó la conversión de los VFA (31%), la eliminación de la fracción total y soluble del residuo tratado (6.5%) y la reducción del consumo de alcalinizante (39%); manteniendo similares producciones de metano. El uso de la digestión anaerobia en dos fases demostró una mejora en la estabilidad del proceso y un incremento de la eficiencia de operación y de la producción de metano, respectivamente.Tesis Doctoral Yans Guardia Puebla Abstract ix ABSTRACT Due to the increase of quality standards internationally demanded, as well as for a greater pressure on the industry by means of more rigorous environmental legislations, the coffee sector is forced to search, through the research, an appropriated treatment system for coffee wet wastewaters generated. In this work the performance of the anaerobic digestion for the coffee wet wastewater treatment was evaluated. For it, two anaerobic systems, one in single-stage (UASB), and another with two-phase (2PUASB) were used. The effect in the anaerobic digestion of three organic loading rates (OLR) and of two reactor configurations used was investigated. OLR operation values in UASB system varied in an interval of 3.6-4.1 kgCOD m-3 d-1, with a recycle rate of the effluent of 1.0. 2PUASB system was fed with OLR similar to those that were used in the reactor in a stage. The acidification reactor was loaded to 11.0 kgCOD m-3 d-1, whereas in the methanogenic reactor varied in the interval of 2.6-4.67 kgCOD m-3 d-1. The use of single-stage and two-phase UASB reactors, under the same operation conditions already before described, a total COD removal efficiency of 75% and 85% for the soluble COD removal efficiency, respectively, was achieved. However, two-phase system showed better results in the treatment of this wastewater type, not only as for removal efficiency of loading organic polluting as well as a smaller volatile fatty acid (VFA) concentration in the effluent. Obtained the best work conditions, the two-phase system under the effect of the recycle was evaluated. Fermentations groups produced were similar to those obtained in the experiment without recycle, indicating that it last one do not affect the relative composition of VFA of the anaerobic reactor, for that reason the degradation pattern of the residue does not change. A recycle rate of 1.0 of the effluent of the methanogenic reactor to the acidogenic reactor improved the process significantly, since it was increased the VFA conversion (31%), the removal of total and soluble fraction of the residue treated (6.5%) and the decrease of the alkalinity consumption (39%); maintaining similar methane productions. The use of the two-phase anaerobic digestion demonstrated to an improvement in the stability of the process and an increase of the operation efficiency and methane production, respectively.

Effect of the curing conditions of concrete on the behaviour under freeze-thaw cycles*

The aim of this work is to relate the curing conditions of concrete and the addition of an air-entraining admixture with the damage caused by freeze–thaw cycles. In countries with a continental climate, the curing of concrete in summer is performed under climatic conditions of high temperature and low humidity, and during the winter the concrete suffers conditions of freeze–thaw, often accompanied by the use of de-icing salts. This paper shows the experimental results of the behaviour of concrete specimens cured under climatic summer conditions (high temperature and low humidity) and then subjected to freeze–thaw cycles. Curing of the specimens includes conditions of good and bad practice in relation to wetting and protection of the concrete. It also examines the effectiveness of using an air-entraining admixture in both cases. The experimental programme includes an evaluation of the mechanical properties of the concrete, the study of the cement hydration and the measurement of the volume and pore sizes of the concrete. These tests were performed before and after the application of the freeze–thaw cycles. The results obtained showed that the specimens without air-entraining admixture show a deterioration of mechanical properties after the freeze–thaw test. However, the inclusion of air bubbles benefits the behaviour of concrete against freeze–thaw cycles so even better mechanical properties after the test were observed. This anomalous behaviour is because the cement hydration process continues over the freeze–thaw tests, closing the pore structure. This aspect has been confirmed with the DTA and TG tests performed

Correlation Between Processing Conditions, Microstructure and Mechanical Behavior in Regenerated Silkworm Silk Fibers

Regenerated silkworm fibers spun through a wet-spinning process followed by an immersion postspinning drawing step show a work to fracture comparable with that of natural silkworm silk fibers in a wide range of spinning conditions. The mechanical behavior and microstructure of these high performance fibers have been characterized, and compared with those fibers produced through conventional spinning conditions. The comparison reveals that both sets of fibers share a common semicrystalline microstructure, but significant differences are apparent in the amorphous region. Besides, high performance fibers show a ground state and the possibility of tuning their tensile behavior. These properties are characteristic of spider silk and not of natural silkworm silk, despite both regenerated and natural silkworm silk share a common composition different from that of spider silk.

Fish communities as indicators of biological conditions of rivers: methods for reference conditions

Fish communities are a key element in fluvial ecosystems Their position in the top of the food chain and their sensitivity to a whole range of impacts make them a clear objective for ecosystem conservation and a sound indicator of biological integrity. The UE Water Framework Directive includes fish community composition, abundance and structure as relevant elements for the evaluation os biological condition. Several approaches have been proposed for the evaluation of the condition of fish communities, from the bio-indicator concept to the IBI (Index of biotic integrity) proposals. However, the complexity of fish communities and their ecological responses make this evaluation difficult, and we must avoid both oversimplified and extreme analytical procedures. In this work we present a new proposal to define reference conditions in fish communities, discussing them from an ecological viewpoint. This method is a synthetic approach called SYNTHETIC OPEN METHODOLOGICAL FRAMEWORK (SOMF) that has been applied to the rivers of Navarra. As a result, it is recommended the integration of all the available information from spatial, modelling, historical and expert sources, providing the better approach to fish reference conditions, keeping the highest level of information and meeting the legal requirements of the WFD.

Performance Modeling of Fresnel-Based CPV Systems: Effects of Deformations under Real Operation Conditions

Getting a lower energy cost has always been a challenge for concentrated photovoltaic. The FK concentrator enhances the performance (efficiency, acceptance angle and manufacturing tolerances) of the conventional CPV system based on a Fresnel primary stage and a secondary lens, while keeping its simplicity and potentially low‐cost manufacturing. At the same time F‐XTP (Fresnel lens+reflective prism), at the first glance has better cost potential but significantly higher sensitivity to manufacturing errors. This work presents comparison of these two approaches applied to two main technologies of Fresnel lens production (PMMA and Silicone on Glass) and effect of standard deformations that occur under real operation conditions

Strict and non-strict independent and-parallelism in logic programs: Correctness, efficiency, and compile-time conditions.

This paper presents some fundamental properties of independent and-parallelism and extends its applicability by enlarging the class of goals eligible for parallel execution. A simple model of (independent) and-parallel execution is proposed and issues of correctness and efficiency discussed in the light of this model. Two conditions, "strict" and "non-strict" independence, are defined and then proved sufficient to ensure correctness and efñciency of parallel execution: if goals which meet these conditions are executed in parallel the solutions obtained are the same as those produced by standard sequential execution. Also, in absence of failure, the parallel proof procedure does not genérate any additional work (with respect to standard SLD-resolution) while the actual execution time is reduced. Finally, in case of failure of any of the goals no slow down will occur. For strict independence the results are shown to hold independently of whether the parallel goals execute in the same environment or in sepárate environments. In addition, a formal basis is given for the automatic compile-time generation of independent and-parallelism: compile-time conditions to efficiently check goal independence at run-time are proposed and proved sufficient. Also, rules are given for constructing simpler conditions if information regarding the binding context of the goals to be executed in parallel is available to the compiler.

Influencia de las condiciones de almacenamiento sobre la relajación de aceros de pretensado = Influence of storage conditions on prestressing steel relaxation losses

La pérdida de tensión por relajación en las armaduras activas afecta de forma importante a las estructuras de hormigón pretensado. Por ello se realizan ensayos de relajación de los alambres y cordones de pretensado tras su fabricación. Después, el material es enrollado y almacenado durante periodos que en ocasiones pueden superar el año de duración. Generalmente se desprecia la influencia que estas operaciones posteriores a la fabricación pueden tener sobre el material. Sin embargo, diversos fabricantes y suministradores han constatado experimentalmente que, en ocasiones, el material almacenado durante un periodo prolongado presenta pérdidas de relajación mayores que inmediatamente tras su fabricación. En este trabajo se realizan ensayos de laboratorio para comprobar la influencia que el radio de enrollamiento y el periodo de almacenamiento tienen sobre las pérdidas de relajación. También se propone un modelo analítico que permite predecir de manera razonablemente aproximada el valor del ensayo de relajación sobre un alambre sometido a un enrollamiento prolongado. Este modelo explica la evolución del perfil de tensiones durante el proceso de enrollamiento- almacenamiento-desenrollamiento, así como la influencia de las tensiones residuales.Stress relaxation losses on active reinforcement have significant impact on prestressed concrete structures. This is why relaxation tests are carried out on prestressing steel wires and strands after being manufactured. Then, these materials are coiled and stored for a long-term period, sometimes in excess of one year. The influence of these operations, carried out after manufacturing, is usually neglected. Nevertheless, some manufacturers and contractors have noticed that, sometimes, when relaxation tests are carried out after a long-term storage, the relaxation losses found are higher than those measured immediately after manufacturing. In this work, lab tests are performed to check the influence of the coiling radius and the period of storage on the relaxation test. In addition to this, an analytical model is presented to predict the results of a relaxation

Exploring polysilicon deposition conditions through a laboratory CVD prototype

Cost and energy consumption related to obtaining polysilicon impact significantly on the total photovoltaic module cost and its energy payback time. Process simplifications can be performed, leading to cost reductions. Nowadays, among several approaches currently pursued to produce the so called Solar Grade Silicon, the chemical route, named Siemens process, is the dominant one. At the Instituto de Energía Solar research on this topic is focused on the chemical route, in particular on the polysilicon deposition step by chemical vapor deposition (CVD) from Trichlorosilane through a laboratory prototype. Valuable information about the phenomena involved in the polysilicon deposition process and the operating conditions is obtained from our experiments. A particular feature of our system is the inclusion of a mass spectrometer. The present work comprises spectra characterization of the polysilicon deposition chemical reaction, temperature and inlet gas mixture composition influence on the deposition rate and analysis of polysilicon deposition conditions for the ?pop-corn' phenomenon to appear, based on experimental experience (Actas de la Special Issue: E-MRS 2012 Spring Meeting ? Symposium A

Effect of the application of jasmonic acid and benzoic acid on grafted watermelons yield under greenhouse conditions in the southeast of Spain for mitigation of stress

One of the main problems of watermelon crops in Sou theast Spain is the thermal difference because of c limatic conditions that appear during the first stages of the crop. The objective of this work was to evaluate the effect of inducing the systemic acq uired resistance (SAR) and the induced systemic resistance (ISR) through the application of jasmonic ac id (JA) and benzoic acid (BA), respectively, to counter the abiotic stress. We assessed two treatments of JA and BA, T1 (500 mg·kg-1 + 500 mg·kg -1 ) and T 2 (2000 mg·kg -1 + 2000 mg·kg -1), as well as a control test using an experimental design of randomized blocks with four replications. The results obtained for kg·m -2, fruits/m², kg/plant and fruits/plant did not show statistically significant differences. However, we obtained statistically sig nificant differences in the average fruit weight co mpared with the control test in the two experiments carried out in 2009 and 2010. The results showed that there was no metabolic cost in the plants when applying the assessed treatments of JA and BA.

Simulating improved combinations tillage-rotation under dryland conditions.

The adequate combination of reduced tillage and crop rotation could increase the viability of dry land agriculture in Mediterrenean zones. Crop simulation models can support to examine various tillage-rotation combinations and explore management scenarios. The decision support system for agrotechnology transfer (DSSAT) (Hoogenboom et al., 2010) provides a suite of crop models suitable for this task. The objective of this work was to simulate the effects of two tillage systems, conventional tillage (ConvT) and no tillage (NoT), and three crop rotations, continuous cereal (CC), fallow-cereal (FallowC) and legume-cereal (LegumeC), under dry conditions, on the cereal yield, soil organic carbon (SOC) and nitrogen (SON) in a 15-year experiment, comparing these simulations with field observations.

Sewage sludge gasification. Dolomite performance under different operating conditions

Gasification is a technology that can replace traditional management alternatives used up to date to deal with this waste (landfilling, composting and incineration) and which fulfils the social, environmental and legislative requirements. The main products of sewage sludge gasification are permanent gases (useful to generate energy or to be used as raw material in chemical synthesis processes), liquids (tars) and char. One of the main problems to be solved in gasification is tar production. Tars are organic impurities which can condense at relatively high temperatures making impossible to use the produced gases for most applications. This work deals with the effect of some primary tar removal processes (performed inside the gasifier) on sewage sludge gasification products. For this purpose, analysis of the gas composition, tar production, cold gas efficiency and carbon conversion were carried out. The tests were performed with air in a laboratory scale plant consisting mainly of a bubbling bed gasifier. No catalyzed and catalyzed (10% wt of dolomite in the bed and in the feeding) tests were carried out at different temperatures (750ºC, 800ºC and 850ºC) in order to know the effect of these parameters in the gasification products. As far as tars were concerned, qualitative and quantitative tar composition was determined. In all tests the Equivalence Ratio (ER) was kept at 0.3. Temperature is one of the most influential variables in sewage sludge gasification. Higher temperatures favoured hydrogen and CO production while CO2 content decreased, which might be partially explained by the effect of the cracking, Boudouard and CO2 reforming reactions. At 850ºC, cold gas efficiency and carbon conversion reached 49% and 76%, respectively. The presence of dolomite as catalyst increased the production of H2 reaching contents of 15.5% by volume at 850 °C. Similar behaviour was found for CO whereas CO2 and CnHm (light hydrocarbons) production decreased. In the presence of dolomite, a tar reduction of up to 51% was reached in comparison with no catalyzed tests, as well as improvements on cold gas efficiency and carbon conversion. Several assays were developed in order to test catalyst performance under more rough gasification conditions. For this purpose, the throughput value (TR), defined as kg sludge “as received” fed to the gasifier per hour and per m2 of cross sectional area of the gasifier, was modified. Specifically, the TR values used were 110 (reference value), 215 and 322 kg/h·m2. When TR increased, the H2, CO and CH4 production decreased while the CO2 and the CnHm production increased. Tar production increased drastically with TR during no catalysed tests what is related to the lower residence time of the gas inside the reactor. Nevertheless, even at TR=322 kg/h·m2, tar production decreased by nearly 50% with in-bed use of dolomite in comparison with no catalyzed assays under the same operating conditions. Regarding relative tar composition, there was an increase in benzene and naphthalene content when temperature increased while the content of the rest of compounds decreased. The dolomite seemed to be effective all over the range of molecular weight studied showing tar removal efficiencies between 35-55% in most cases. High values of the TR caused a significant increase in tar production but a slight effect on tar composition.

On track for solar grade silicon through a siemens process-type laboratory reactor: operating conditions and energy savings

Polysilicon cost impacts significantly on the photovoltaics (PV) cost and on the energy payback time. Nowadays, the besetting production process is the so called Siemens process, polysilicon deposition by chemical vapor deposition (CVD) from Trichlorosilane. Polysilicon purification level for PV is to a certain extent less demanding that for microelectronics. At the Instituto de Energía Solar (IES) research on this subject is performed through a Siemens process-type laboratory reactor. Through the laboratory CVD prototype at the IES laboratories, valuable information about the phenomena involved in the polysilicon deposition process and the operating conditions is obtained. Polysilicon deposition by CVD is a complex process due to the big number of parameters involved. A study on the influence of temperature and inlet gas mixture composition on the polysilicon deposition growth rate, based on experimental experience, is shown. Moreover, CVD process accounts for the largest contribution to the energy consumption of the polysilicon production. In addition, radiation phenomenon is the major responsible for low energetic efficiency of the whole process. This work presents a model of radiation heat loss, and the theoretical calculations are confirmed experimentally through a prototype reactor at our disposal, yielding a valuable know-how for energy consumption reduction at industrial Siemens reactors.

Bare-tether cathodic contact through thermoionic emission by low work-function materials

A new material, C12A7 : electride, which might present a work function as low as 0.6 eV and moderately high temperature stability, was recently proposed as coating for floating bare tethers. Arising from heating under space operation, current is emitted by thermionic emission along a thus coated cathodic segment. A preliminary study on the space-charge-limited (SCL) double layer in front of the cathodic segment is presented using Langmuir’s SCL electron current between cylindrical electrodes and orbital-motion-limited ion-collection sheath. A detailed calculation of current and bias profiles along the entire tether length is carried out with ohmic effects and the transition from SCL to full Richardson-Dushman emission included. Analysis shows that in the simplest drag mode, under typical orbital and tether conditions, thermionic emission leads to a short cathodic section and may eliminate the need for an active cathodic device and its corresponding gas feed requirements and power subsystem, which results in a truly “propellant-less” tether system for such basic applications as de-orbiting low earth orbit satellites.

Dry cooling with night cool storage to enhance solar power plants performance in extreme conditions areas

Solar thermal power plants are usually installed in locations with high yearly average solar radiation, often deserts. In such conditions, cooling water required for thermodynamic cycles is rarely available. Moreover, when solar radiation is high, ambient temperature is very high as well; this leads to excessive condensation temperature, especially when air-condensers are used, and decreases the plant efficiency. However, temperature variation in deserts is often very high, which drives to relatively low temperatures during the night. This fact can be exploited with the use of a closed cooling system, so that the coolant (water) is chilled during the night and store. Chilled water is then used during peak temperature hours to cool the condenser (dry cooling), thus enhancing power output and efficiency. The present work analyzes the performance improvement achieved by night thermal cool storage, compared to its equivalent air cooled power plant. Dry cooling is proved to be energy-effective for moderately high day–night temperature differences (20 °C), often found in desert locations. The storage volume requirement for different power plant efficiencies has also been studied, resulting on an asymptotic tendency.

Modelling ozone stomatal flux over wheat under Mediterranean conditions

Correct estimation of leaf-level stomatal conductance (gsto) is central for current ozone (O3) risk assessment of wheat yield loss based on the absorbed O3 phytotoxic dose (POD). The gsto model parameterizations developed in Europe must be checked in the different climatic regions where they are going to be applied in order to reduce the uncertainties associated with the POD approach. This work proposes a new gsto model parameterization for estimating POD of Triticum aestivum and Triticum durum under Mediterranean conditions, based on phenological observations over 25 years and gsto field measurements during 5 growing seasons. Results show that POD in the Mediterranean area might be higher than previously estimated. However, caution must be paid when assessing the risk of yield loss for wheat in this area since field validation of O3 impacts is still limited.