Thermoeconomic analysis of a combined supercritical CO2 reheating under different configurations of Organic Rankine cycle ORC as a bottoming cycle

Supercritical Brayton cycles have been considered as one of the technologies that present high thermal efficiencies in a wide range of energy conversion systems. Also, these systems can even increase their efficiency by incorporating a suitable bottoming cycle. In this article, a combined supercritical Brayton cycle with an Organic Rankine cycle (ORC) was analyzed. The influence of key system parameters such as the Brayton circuit high-pressure (Phigh), the turbine-1 inlet temperature (TIT), the turbine-1 efficiency ( n t ), and the evaporation pressure ( P e v a p ) on the economic indicators such as the Levelized Cost of Energy (LCOE), the Payback Period (PBP), the Specific Investment Cost (SIC), and net work ( W ˙ n e t ) was studied. Besides, the effect of these parameters on the exergo-economic indicator r k and the relative cost difference r k were studied. Finally, a thermo-economic optimization of the proposed configurations was carried out. The study revealed that the turbine-1 inlet temperature (TIT) was the variable with the most significant effect on the economic and energy indicators of the configurations analyzed. The increase in the turbine temperature up to 850 °C caused a rise of 63.8% for both configurations. Also, the results revealed that the Brayton/SORC configuration presented the best economic performance compared to the Brayton/RORC system. The thermo-economic optimization revealed that temperatures above 800 °C and pressures between 25-30 MPa increase system performance. In addition, the Brayton/SORC configuration has a comparative reduced levelized energy costs and low payback periods, which makes it more attractive.

Growth patterns and breast milk/infant formula energetic efficiency in healthy infants up to 18 months of life: the COGNIS study

Type of feeding during early life influences growth trajectory and metabolic risk at later ages. Modifications in infant formula composition have led to evaluate their effects on growth and energetic efficiency (EE) compared with breast-feeding. Main goal was to analyse type of feeding potential effects during first months of life, plus its EE, on growth patterns in healthy formula fed (standard infant formula (SF) vs. experimental infant formula enriched with bioactive nutrients (EF)) and breastfed (BF) infants participating in the COGNIS RCT (http://www.ClinicalTrials.gov, Identifier: NCT02094547) up to 18 months of age. Infants follow-up to 18 months of age (n 141) fed with a SF (n 48), EF(n 56), or BF (n 37), were assessed for growth parameters using WHO standards. Growth velocity (GV) and catch-up were calculated to identify growth patterns. EE of breast milk/infant formula was also estimated. Infants' growth at 6 months showed higher length and lower head circumference gains in SF and EF infants than BF infants. Both weight-for-length and weight-for-age catch-up growth showed significant differences in formula fed groups compared with the BF. No significant differences in GV or catch-up were found at 6-12 and 12-18 months. Regarding EE, infant formula groups showed significantly lower weight and length gains/g of milk protein, and higher weight and length gains/g of milk lipids, than the BF infants. GV during first 6 months, which may be influenced by feeding, seems to be the main predictor of subsequent growth trajectory. Breast-feeding may have positive effects on growth programming due to its nutrients' EE.

Selection and subsequent physiological characterization of industrial Saccharomyces cerevisiae strains during continuous growth at sub- and- supra optimal temperatures

A phenotypic screening of 12 industrial yeast strains and the well-studied laboratory strain CEN.PK113-7D at cultivation temperatures between 12 °C and 40 °C revealed significant differences in maximum growth rates and temperature tolerance. From those 12, two strains, one performing best at 12 °C and the other at 40 °C, plus the laboratory strain, were selected for further physiological characterization in well-controlled bioreactors. The strains were grown in anaerobic chemostats, at a fixed specific growth rate of 0.03 h-1 and sequential batch cultures at 12 °C, 30 °C, and 39 °C. We observed significant differences in biomass and ethanol yields on glucose, biomass protein and storage carbohydrate contents, and biomass yields on ATP between strains and cultivation temperatures. Increased temperature tolerance coincided with higher energetic efficiency of cell growth, indicating that temperature intolerance is a result of energy wasting processes, such as increased turnover of cellular components (e.g. proteins) due to temperature induced damage.

Significance of the micropores electro-sorption resistance in capacitive deionization systems

Capacitive Deionization (CDI) is an emerging technology representing a potential alternative to the common, energy-intensive desalination methods for low salinity water streams. In CDI an electrical field is applied to separate ionic species from aqueous solutions and electro-adsorb them into a highly porous material. CDI is a complex multi-scale system which requires robust mathematical models to closely describe its performance. Here, a dynamic two-dimensional model is developed coupling the diffusion and advection of the species in the bulk solution with their diffusion and electro-sorption in the porous electrodes. In this model, the adsorption/desorption resistance between the micropores and macropores along with variable non-electrostatic attractive forces in the micropores are also incorporated. The proposed theory is validated against experiments using a circular CDI cell operating under various conditions, where different transport mechanisms are limiting the total ion removal process. Performance of the CDI systems is also evaluated using inclusive figures of merit. The obtained results accentuate the significant effect of the rate-limited transfer of the ionic species from the macropores into the micropores, especially in systems subject to severe ion starvation, where neglecting this electro-sorption resistance leads to up to 50% and 210% overestimation of the energy efficiency and overall desalination performance, respectively. Furthermore, although the commonly used transport theory describing CDI fails to capture the dynamics of the systems at low initial concentration and high adsorption capacity by assuming fast electro-sorption without any resistance, the presented theory closely models the transport mechanisms in such systems. Moreover, we experimentally and numerically demonstrate a trade-off between the energetic and desalination performance in systems with low and high mass Péclet number.

Capacitive biocathodes driving electrotrophy towards enhanced CO2 reduction for microbial electrosynthesis of fatty acids

Electron transfer towards biocathode is a rate limiting step for CO₂ reduction during microbial electrosynthesis (MES). Current study is designed to offer an understanding on electrotrophy using four different electrode materials viz., carbon cloth (CC), stainless-steel mesh (SS), combination of both (CC-SS) and a hybrid material (CC-SS-AC with activated carbon (AC)) as capacitive biocathodes for MES. Non turn-over and turn-over electrochemical investigations revealed electrode properties in terms of electron transfer, capacitance and redox catalytic currents relatively higher with CC-SS-AC and CC-SS. Acetic acid production was higher in CC-SS-AC (4.31 g/l) than CC-SS (4.21 g/l), CC (3.5 g/l) and SS (2.83 g/l) along with noticeable ethanol production with all the biocathodes except SS. Interestingly, long-term operation of all biocathodes witnessed reduction in resistance visualized through Nyquist impedance spectra relatively efficient with CC-SS-AC. Biocompatible property of CC-SS-AC with increased surface area was presumed to be a critical factor for enhancing electrotrophy linked with capacitive nature of biocathode towards enhanced bioelectrochemical CO₂ reduction.

Energetic evolution of cellular Transportomes

BACKGROUND

Transporter proteins mediate the translocation of substances across the membranes of living cells. Many transport processes are energetically expensive and the cells use 20 to 60% of their energy to power the transportomes. We hypothesized that there may be an evolutionary selection pressure for lower energy transporters.

RESULTS

We performed a genome-wide analysis of the compositional reshaping of the transportomes across the kingdoms of bacteria, archaea, and eukarya. We found that the share of ABC transporters is much higher in bacteria and archaea (ca. 27% of the transportome) than in primitive eukaryotes (13%), algae and plants (10%) and in fungi and animals (5-6%). This decrease is compensated by an increased occurrence of secondary transporters and ion channels. The share of ion channels is particularly high in animals (ca. 30% of the transportome) and algae and plants with (ca. 13%), when compared to bacteria and archaea with only 6-7%. Therefore, our results show a move to a preference for the low-energy-demanding transporters (ion channels and carriers) over the more energy-costly transporter classes (ATP-dependent families, and ABCs in particular) as part of the transition from prokaryotes to eukaryotes. The transportome analysis also indicated seven bacterial species, including Neorickettsia risticii and Neorickettsia sennetsu, as likely origins of the mitochondrion in eukaryotes, based on the phylogenetically restricted presence therein of clear homologues of modern mitochondrial solute carriers.

CONCLUSIONS

The results indicate that the transportomes of eukaryotes evolved strongly towards a higher energetic efficiency, as ATP-dependent transporters diminished and secondary transporters and ion channels proliferated. These changes have likely been important in the development of tissues performing energetically costly cellular functions.

Jet aeration as alternative to overcome mass transfer limitation of stirred bioreactors

In industrial biotechnology increasing reactor volumes have the potential to reduce production costs. Whenever the achievable space time yield is determined by the mass transfer performance of the reactor, energy efficiency plays an important role to meet the requirements regarding low investment and operating costs. Based on theoretical calculations, compared to bubble column, airlift reactor, and aerated stirred tank, the jet loop reactor shows the potential for an enhanced energetic efficiency at high mass transfer rates. Interestingly, its technical application in standard biotechnological production processes has not yet been realized. Compared to a stirred tank reactor powered by Rushton turbines, maximum oxygen transfer rates about 200% higher were achieved in a jet loop reactor at identical power input in a fed batch fermentation process. Moreover, a model-based analysis of yield coefficients and growth kinetics showed that E. coli can be cultivated in jet loop reactors without significant differences in biomass growth. Based on an aerobic fermentation process, the assessment of energetic oxygen transfer efficiency [kgO₂ kW^-1 h^-1] for a jet loop reactor yielded an improvement of almost 100%. The jet loop reactor could be operated at mass transfer rates 67% higher compared to a stirred tank. Thus, an increase of 40% in maximum space time yield [kg m^-3 h^-1] could be observed.

Effect of iron deficiency on simultaneous measures of behavior, brain activity, and energy expenditure in the performance of a cognitive task

OBJECTIVES

Iron deficiency (ID) - the highly prevalent nutritional deficiency - has been shown to have deleterious effects on measures of cognitive performance and brain activity. Many of these results are suggestive of the impact of ID on neurotransmitter regulation and myelination. A third critical potential effect of ID on brain function is at the level of brain energy expenditure; however, to date there has not been any method for indirectly estimating the impact of ID on energy expenditure in humans in the context of cognitive work.

METHODS

We report here a study comparing ID and iron sufficient (IS) college students in which simultaneous behavioral, encephelographic (EEG), and metabolic data were collected in a task designed as a cognitive analog to standard physical exertion tasks.

RESULTS

We show that increases in cognitive demands produced decrements in behavioral measures of performance, and increases in EEG and metabolic measures of work. Critically, we found that the magnitudes of those changes were directly related to iron levels.

DISCUSSION

We find support for the idea that brain activity mediates the relationship between cognitive demands and energy expenditure, with ferritin and hemoglobin moderating those relationships in distinct ways. Finally, we show that levels of energy expenditure can be indirectly estimated by measures of EEG spectral power.

An energetics-based honeybee nectar-foraging model used to assess the potential for landscape-level pesticide exposure dilution

Estimating the exposure of honeybees to pesticides on a landscape scale requires models of their spatial foraging behaviour. For this purpose, we developed a mechanistic, energetics-based model for a single day of nectar foraging in complex landscape mosaics. Net energetic efficiency determined resource patch choice. In one version of the model a single optimal patch was selected each hour. In another version, recruitment of foragers was simulated and several patches could be exploited simultaneously. Resource availability changed during the day due to depletion and/or intrinsic properties of the resource (anthesis). The model accounted for the impact of patch distance and size, resource depletion and replenishment, competition with other nectar foragers, and seasonal and diurnal patterns in availability of nectar-providing crops and wild flowers. From the model we derived simple rules for resource patch selection, e.g., for landscapes with mass-flowering crops only, net energetic efficiency would be proportional to the ratio of the energetic content of the nectar divided by distance to the hive. We also determined maximum distances at which resources like oilseed rape and clover were still energetically attractive. We used the model to assess the potential for pesticide exposure dilution in landscapes of different composition and complexity. Dilution means a lower concentration in nectar arriving at the hive compared to the concentration in nectar at a treated field and can result from foraging effort being diverted away from treated fields. Applying the model for all possible hive locations over a large area, distributions of dilution factors were obtained that were characterised by their 90-percentile value. For an area for which detailed spatial data on crops and off-field semi-natural habitats were available, we tested three landscape management scenarios that were expected to lead to exposure dilution: providing alternative resources than the target crop (oilseed rape) in the form of (i) other untreated crop fields, (ii) flower strips of different widths at field edges (off-crop in-field resources), and (iii) resources on off-field (semi-natural) habitats. For both model versions, significant dilution occurred only when alternative resource patches were equal or more attractive than oilseed rape, nearby and numerous and only in case of flower strips and off-field habitats. On an area-base, flower strips were more than one order of magnitude more effective than off-field habitats, the main reason being that flower strips had an optimal location. The two model versions differed in the predicted number of resource patches exploited over the day, but mainly in landscapes with numerous small resource patches. In landscapes consisting of few large resource patches (crop fields) both versions predicted the use of a small number of patches.

Adding adaptable toe stiffness affects energetic efficiency and dynamic behaviors of bipedal walking

In human walking, toes play an important role in supporting the body and controlling the forward motion. These functions are achieved by muscles and tendons around toe joints. To further understand the importance of toe and how toe muscle functions affect the locomotion, we employ a simple bipedal walking model with compliant joints. The ankle joints and toe joints are modeled as torsional springs and the actuation patterns are similar to that of normal human walking. Experimental results show that adding adaptable compliant toe joints could benefit the stability and energy efficiency. By generating plantar flexion moment after heel-off, the toes contribute to stabilize the body and control the forward motion. In addition, multi-joint foot structure could improve the energy efficiency by reducing the energy consumption of ankle joints. A proper toe actuation pattern could result in a proper toe dorsiflexion and reduce the maximal ankle plantar flexion, leading to a smoother and more efficient locomotion.

Integration of the Anammox process to the rejection water and main stream lines of WWTPs

Nowadays the application of Anammox based processes in the wastewater treatment plants has given a step forward. The new goal consists of removing the nitrogen present in the main stream of the WWTPs to improve their energetic efficiencies. This new approach aims to remove not only the nitrogen but also to provide a better use of the energy contained in the organic matter. The organic matter will be removed either by an anaerobic psychrophilic membrane reactor or an aerobic stage operated at low solids retention time followed by an anaerobic digestion of the generated sludge. Then ammonia coming from these units will be removed in an Anammox based process in a single unit system. The second strategy provides the best results in terms of operational costs and would allow reductions of about 28%. Recent research works performed on Anammox based processes and operated at relatively low temperatures and/or low ammonia concentrations were carried out in single-stage systems using biofilms, granules or a mixture of flocculent nitrifying and granular Anammox biomasses. These systems allowed the appropriated retention of Anammox and ammonia oxidizing bacteria but also the proliferation of nitrite oxidizing bacteria which seems to be the main drawback to achieve the required effluent quality for disposal. Therefore, prior to the implementation of the Anammox based processes at full scale to the water line, a reliable strategy to avoid nitrite oxidation should be defined in order to maintain the process stability and to obtain the desired effluent quality. If not, the application of a post-denitrification step should be necessary.

Subsarcolemmal and intermyofibrillar mitochondrial responses to short-term high-fat feeding in rat skeletal muscle

OBJECTIVES

We assessed the alterations in mitochondrial function in skeletal muscle that were elicited by short-term high-fat feeding in sedentary rats.

METHODS

Two groups of rats were pair-fed for 1 wk and received a low-fat or high-fat diet. Body composition, energy balance, and glucose homeostasis were measured. Mitochondrial mass, oxidative capacity, and energetic efficiency as well as parameters of oxidative stress and antioxidant defense were evaluated in subsarcolemmal and intermyofibrillar mitochondria from the skeletal muscle.

RESULTS

Body energy, lipid content, and metabolic efficiency were significantly higher and energy expenditure was significantly decreased among rats that were fed a high-fat diet, as compared with controls. Skeletal muscle mitochondrial energetic efficiency, oxidative capacity for lipid substrates, and antioxidant defense were significantly increased in rats that were fed a high-fat diet as compared with controls.

CONCLUSIONS

Acute isocaloric high-fat feeding is able to induce increased phosphorylation efficiency in skeletal muscle subsarcolemmal and intermyofibrillar mitochondria. This modification implies a reduced oxidation of energy substrates that may contribute to the early onset of obesity.