Net Energy Gain Research Articles

Heat transfer and performance analysis of SAH having new transverse finned absorber of lateral gaps and central holes

An experimental work is presented on the performance of solar air heater (SAH) has new designed absorber of finned transverse plate of lateral gaps and central holes. Moreover, a complete heat transfer analysis of the radiation and convection and SAH thermal performance are presented and discussed. The performance of this transverse SAH (TR_SAH) is compared with identical conventional flat plate SAH (FP_SAH) for single (SP) and double-pass (DP) airflow and air mass flow rates (AMFR) of 0.025, 0.05, and 0.075 kg/s. The experimental study is performed under hot climate conditions of Upper Egypt. The findings show that for all studied cases, TR_SAH has higher energy gain, output air temperature, thermal efficiency, and Nusselt number on the absorber plate, thermal-hydraulic performance parameter, and pressure drop compared to FP_SAH. The energy loss and radiation and convection Nusselt number on the TR_SAH glass plate is lower than that of FP_SAH. The maximum TR_SAH energy efficiency of value of about 89% is achieved in the case of DP airflow and high AMFR of 0.075 kg/s, with an enhancement of 24.2% compared to FP_SAH. The higher TR_SAH efficiency at these conditions reflects the optimal TR_SAH absorber design especially at high AMFR and using DP airflow. Despite TR_SAH air pumping power is greater than FP_SAH but it has a negligible effect on net energy gain.

ENERGY EFFICIENCY OF THE MINERAL FERTILIZER APPLICATION IN CEREAL PRODUCTION

Cereal grains have represented the principal component of the human diet for thousands of years. Modern cereal production cannot be imagined without the use of mineral fertilizers, particularly in terms of better utilization of biological potential of the yield of growing plants. The aim of this study was to evaluate the energetic efficiency of wheat and barley production, with special reference to the share of the use of mineral fertilizers in total energy consumption. Input data and yield of wheat and barley fields were collected in the experimental trials in Serbia. Results showed that total energy inputs of wheat and barley fields were 22178.04 and 15921.16 MJ·ha-1, respectively. Total energy outputs for wheat and barley fields were 80037.83 and 104496.08 MJ·ha-1, respectively. The results obtained indicate that mineral fertilizers claim a share of the total energy consumption in cereal production ranging from 49.19% in barley to 52.01% in wheat. Specific energy input, energy output–input ratio (energy use efficiency), energy productivity and net energy gain were 5.13 MJ·kg-1, 3.61,0.19 kg·MJ-1 and57859.79MJ·ha-1in wheat system and 2.75 MJ·kg-1, 6.56, 0.36 kg·MJ-1 and 88574.92 MJ·ha-1 in barley system, respectively. According to the results, it seems that barley production is more efficient from different aspects of energy consumption compared to wheat in the studied region. In general, production in barley fields was more sustainable than wheat production because, in view of ecological indices such as amount of energy use and renewable energy consumption, it was more environment-friendly production.

Gramian-Aware Control Approach for Atmospheric Gust Harvesting

Micro-aerial vehicles (MAVs) lack the endurance times demanded by typical mission applications, and previous work to minimize flight path disturbances has also quantified their high atmospheric sensitivities. This study introduces an approach to modulate the sensitivity through real-time parameter variation that translates into a net energy gain of the vehicle. By applying a control-theoretic disturbance sensitivity framework and observability gramian via a “gust capture metric,” the formulation modulates vehicle gust response to sensed favorable (or unfavorable) vertical gusts. The approach is implemented in a nonlinear simulation and an experimental test environment for a representative 21 g MAV. These results include the development of a system-identified MAV flight dynamics model and the development of an experimental facility to provide automated, repeatable indoor flight tests over a gust field. Nonlinear model simulation indicates that the control law provides altitude gain over an idealized gust field, consistent with theoretical analysis. The experimental flight facility was equipped with a gust field generation capability, and its velocity and turbulence intensity distribution was quantified. The experimental flight tests evaluating altitude gain under vehicle controller modification show agreement with theoretical and simulation results and indicate the importance of turbulence distribution in atmospheric gust harvesting experiments.

Energy, exergy, and economic analysis of tubular solar air heater with porous material: An experimental study

• Solar air heater having new designed tubular absorber is examined experimentally. • Assessment of the new tubular air heater with porous medium is presented. • Using porous material with tubular heater enhances its energy efficiency by 8.9% • Using porous media with tubular heater enhances its exergy efficiency by 8.2% • Tubular air heater is more effective compared to flat one based 4E analyses. The performance of solar air heater of having a new design tubular absorber of adjacent parallel tubes called tubular is investigated experimentally via energy, exergy, energy payback time, exergoeconomic, and enviroeconomic approaches. Moreover, the impact of utilizing porous material on the tubular heat performance is analyzed and compared to flat plate air heater at air mass flow rates; 0.075, 0.05, and 0.025 kg/s for single and double passes. Results indicate that the tubular heater has higher net energy gain, output air temperature, energy and exergy efficiencies, and smaller energy loss compared to the flat heater. Using porous material and double pass increases the output air temperature of tubular air heater by 3.4 °C and flat one by 17.7 °C at 0.025 kg/s. Moreover, utilizing porous material with the tubular heater at 0.075 kg/s enhances the energy efficiency by 3.5% and 8.9% and exergy efficiency by 8.2% and 0.9% for single and double pass, respectively. Air pumping power of the tubular heater is greater than flat but its value is very small to influence the tubular net useful energy. Finally, the tubular air heater is more effective compared to flat based on energy payback time, energy cost, exergoeconomic, and enviroeconomic parameters.

Optimization of electrokinetic pretreatment for enhanced methane production and toxicity reduction from petroleum refinery sludge

This study examined the effect of electrokinetic pretreatment on petroleum sludge (PS) released from the wastewater treatment plants of petrochemical industries for enhanced biodegradation and contaminant removal. The application of electric field on PS through direct current is optimized with the combined variation of applied voltage (40–80 V), exposure duration (20–120 min) and distance between graphite electrodes (8–16 cm) using central composite design-response surface methodology (CCD-RSM). The optimization study revealed significant interaction among the response variables to obtain an optimum condition (60 V, 83.5 min, 11.6 spacing) for maximization of solubilization in terms of soluble chemical oxygen demand (230% increment against untreated) and volatile fatty acids (172% increment against untreated) concentrations for accelerated hydrolysis of complex PS. BMP batch assays were performed at different inoculum and sludge ratios (0.3, 0.4, 0.5 and 0.7) based on volatile solids content after pretreatment at the optimized condition which resulted in accumulated methane ranging from 5.16 to 6.61 L/gVSadded (untreated - 3.9 L/gVSadded). The mixing ratio of 0.4 showed the maximum methane enhancement of 69.2% compared to untreated. The maximum removal of organic content (62.8%), oil and grease (71.74%), and total petroleum hydrocarbon (52.9%) were also observed for the mixing ratio of 0.4. The FTIR study showed the efficacy in hydrocarbon dissociation and decomposition after pretreatment of PS. The net energy gain (3508 kJ) and phytotoxicity reduction of batch digestate after the anaerobic digestion suggest the economic feasibility and decontamination efficiency of the electrokinetic pretreatment technique respectively. Further research could be performed to evaluate the viability of this pretreatment for enhanced methane recovery at field-scale levels to relate to these lab-scale postulations.

Exact solution of Hartemann–Luhmann equation of motion for a charged particle interacting with an intense electromagnetic wave/pulse

We report an exact solution of the Hartemann-Luhmann equation of motion for a charged particle interacting with an intense electromagnetic wave/pulse. It is found that the radiation reaction force has a significant affect on the charged particle dynamics and the particle shows, on average, a net energy gain over a period of time. Further, using a MATHEMATICA based single particle code, the net energy gained by the particle is compared with that obtained using Landau-Lifshitz and Ford-O'connell equation of motion, for different polarizations of the electromagnetic wave. It is found that the average energy gain is independent of both the chosen model equation and polarization of the electromagnetic wave. Our results thus show, that the simpler and hence analytically tractable Hartemann-Luhmann equation of motion ( as compared to Landau-Lifshitz and Ford-O'connell equation of motion) is adequate for calculations of practical use (for e.g. energy calculation).

Farm‐to‐fire analysis of karanja biodiesel

AbstractThis paper analyzes the energy and environmental impact of karanja biodiesel fuel from its production to its utilization (farm to fire), using a life‐cycle assessment method, and comparing it with its fossil diesel counterpart. For this purpose, the net energy ratio, the net energy gain, and the equivalent carbon dioxide (CO2) emission reduction are estimated considering the equivalent energy impacts and CO2 emissions of important input and output quantities. The expressions for estimating equivalent CO2 reduction in production to utilization process are obtained by considering the CO2 absorption capacity of the biodiesel plant. The effects of the eutrophication and acidification potential during the life cycle of the crop are also considered. A sensitivity analysis of the most influential parameters on net energy ratio and CO2 emission reduction is conducted. The analysis shows that the biodiesel yield from seeds and the yield of co‐products are the two critical parameters affecting the net energy ratio. Similarly, the equivalent CO2 emission reduction potential of the karanja biodiesel depends primarily on the brake thermal efficiency and energy equivalent CO2 emission of biodiesel fueled engine combustion. A techno‐economic evaluation of the production of karanja biodiesel for different plant sizes and cost‐recovery periods is also made. The economics of the production of karanja biodiesel, considering different plant sizes and cost recovery periods, suggests that the price of biodiesel decreased for a higher capacity biodiesel plant and a longer cost‐recovery period. Beside these factors, the price of feedstock remains a most significant component of cost estimates. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd

Bio-energetics of black gram (Phaseolus mungo) as influenced by different weed control practices

A field investigation was carried out during kharif season in 2010 at Agronomy Department Farm,Dr.Panjabrao Deshmukh Krishi Vidyapeeth, Akola, to evaluate the energy inputs, energy output, net energy gain and output input ratio of different weed control practices in black gram. It is observed that in herbicidal treatments, pre-emergence application of pendimethalin @ 1.5 kg/ha followed by cultural treatment of two hand weedings at 15 and 30 days after sowing recorded more energy inputs, while weedy check treatment incurred minimum energy input among all the treatments. Whereas, weed free treatment computed maximum energy output and energy balance followed by pre-emergence application of pendimethalin @ 1.5 kg/ha treatment. Similarly weed free and post emergence application (15 DAS) of fenoxyprop-p-ethyl @ 0.125 kg/ha were resulted in higher energy balance per unit input and output-input ratio than weedy check treatment.

Confronting assumptions about prey selection by lunge‐feeding whales using a process‐based model

Abstract The relative energetic benefits of foraging on one type of prey rather than another are not easily measured, particularly for large free‐ranging predators. Nonetheless, assumptions about preferred and alternative prey are frequently made when predicting how a predator may impact its environment, adapt to environmental change or interact with human activities. We developed and implemented a process‐based model to investigate the potential energetic benefit (PEB) of in situ foraging opportunities in rorqual whales. The model integrates and evaluates the energetic importance of measured prey patch characteristics (prey distribution, energy content and predator avoidance) and predator characteristics (morphometrics, foraging tactics and feeding rates). We applied the model to test the assumption that hatchery‐released juvenile salmon are an ‘easy meal’ for humpback whales compared to more common prey: herring and krill. In 11 out of the 13 foraging situations considered, whales were found to be feeding in a manner where net energy gain was greater than the energetic costs of non‐foraging swimming. Humpback whale PEB for hatchery‐released juvenile salmon fell within the range of the PEB for krill and herring but varied by species, from relatively high PEB for chum salmon to relatively low for coho salmon. Our model provides behavioural insight as well, indicating that shallow feeding may be more important for reducing energy expenditure through slower lunge speeds than for increasing prey capture. The model also provides a means of identifying prey patch characteristics, with prey aggregation playing the largest role in determining PEB despite being a poor overall proxy for PEB, supporting the use of the complex model framework. Modelling approaches are especially valuable where they can use reasonable assumptions to substitute for lack of reliable observations, thereby integrating a range of interacting factors into a single framework. Additionally, because process‐based models can be used to make predictions outside the range of previously observed conditions, they will be increasingly useful in a changing climate. A free Plain Language Summary can be found within the Supporting Information of this article.

Optimal foraging by a large ungulate in an extreme environment: Wild mountain reindeer select snow-free feeding habitats in winter.

Optimal foraging models predict that individual animals will optimize net energy gain by intensifying forage activity and/or reducing forage energy cost. Then, the free distribution model predicts an animal's distribution in a patchy landscape will match the distribution of the resources. If not modified by other factors, such patterns may be expected to be particularly explicit in variable and extreme, forage‐limited, and patchy environments, notably alpine and Arctic environments during winter. The large ungulate wild mountain reindeer (Rangifer tarandus tarandus) surviving in such environments is used as a model during the forage‐limited winter season. The largest wild reindeer area in Western Europe (Hardangervidda, 8130 km2) is actively managed to sustain 10,000–12,000 wild reindeer. Since 2001, 104 different individuals have been GPS‐tracked at 3‐hr intervals. In winter, mountain reindeer may either choose to seek out and forage in patchy snow‐free habitats, typically on top of wind‐blown ridges, or use energy‐demanding digging through the snow to reach ground forage (cratering). We use late April satellite data from Landsat 5 and 8 (30 × 30 m), airborne laser scanning subsampling (processed to 1 × 1 m grid), and topographic information (1 m resolution) derived from digital aerial photographs (0.25 × 0.25 m resolution) to delineate snow‐free patches, constituting less than 694 km2. By overlaying recorded wild reindeer GPS positions winters 2001–2017 (188,942 positions), we document a strong positive selection for snow‐free patches, which were used about four times more frequently than expected from a “random walk” model. On a daily basis, the preference for snow‐free areas was slightly stronger in the evenings. In the sustainable management of wild mountain reindeer, the area of snow‐free patches is an important predictor of winter forage availability and important winter source areas. It may be derived from remote sensing data.

Increasing plant diversity to mitigate net greenhouse effect of wastewater treatment in floating constructed wetlands

Constructed wetlands (CWs) are an effective wastewater treatment technology but also an important source of greenhouse gases. Converting CW plant biomass to biofuel as an alternative to fossil fuels can reduce carbon dioxide emissions, and plant diversity influences this mitigation effect. However, the impact of plant diversity on net global warming potential combining carbon dioxide and non-carbon dioxide emissions in CWs is less studied, especially in floating CWs where the substrate is absent and both above- and below-ground biomass can be harvested easily for biofuel production. In this paper, four species richness levels were assembled in 90 hydroponic microcosms that simulated floating CWs to explore the effect of plant diversity on global warming potential. The results showed that: (1) increasing species richness increased the aboveground and total biomass but had no effect on belowground biomass, and carbon dioxide emissions were reduced by converting both above- and belowground biomass to biofuel to replace fossil fuels; (2) increasing species richness increased non-carbon dioxide emissions but decreased the overall global warming potential of combined carbon dioxide and non-carbon dioxide emissions; (3) communities containing Oenanthe javanica had lower overall global warming potential; and (4) some species (Oenanthe javanica) had a stronger mitigating effect on global warming potential than species richness. Our observations suggest that it is economically feasible to produce biofuel from hydroponically grown plants in floating CWs, and net energy gain can be achieved. Assembling high species richness and carefully selecting species in floating CWs alongside converting plant biomass to biofuel offers a greener form of wastewater treatment that can contribute to cleaner production strategies.

Integrating continuous-stirred microwave pyrolysis with ex-situ catalytic upgrading for linear low-density polyethylene conversion: Effects of parameter conditions

A continuous-stirred microwave pyrolysis (CSMP) reactor coupled with an ex-situ catalytic bed was developed for the conversion of linear low-density polyethylene (LLDPE) to high-grade fuels. Effects of catalyst-to-reactant ratio and feeding rate on product yield and chemical selectivity were studied. The CSMP of LLDPE produced up to 84.1 wt.% condensate product composed of hydrocarbon fuels. With the assistance of the ex-situ catalytic process with HZSM-5, more refined chemicals dominated by gasoline-range hydrocarbons (C5–C12 hydrocarbons) were observed. When the catalyst-to-reactant ratio was 15 % and the feeding rate was 6 g/min, the condensate oil with a high higher heating value (45.23 MJ/kg) showed the highest selectivity of gasoline-range hydrocarbons (98.0 %). The pyrolysis processes yielded ethylene as the main gas product. With the addition of HZSM-5, propylene and propane were the primary gas components. The plausible pathway for the conversion of LLDPE mainly proceeded through radical mechanism for pyrolysis and carbenium ion mechanism for catalysis was elaborated. The potential net energy gain increased from 34.16 MJ/kg to 48.91 MJ/kg with growing feeding rate from 6 g/min to 30 g/min.

Preparation of bio-oil from Scenedesmus acutus using thermochemical liquefaction in a 1 L reactor

Biomass from microalgae is a potential feedstock for biofuels production. It poses no threat to food security as it does not compete with agricultural crops for arable land. Scenedesmus acutus was used as feedstock to produce bio-oil in a large liquefaction reactor. The influence of reaction temperature (280–360ºC), reaction atmosphere (N2 or CO2) and solvent on bio-oil yield, C-16 fatty acid yield and oil properties were investigated. Oils were characterised using gas chromatography, Fourier transform infrared (FTIR) spectroscopy and ultimate analysis. Higher bio-oil yields were obtained in a CO2 atmosphere (250 g.kg-1 dry microalgae) than in a N2 atmosphere (210 g.kg-1 dry microalgae) whilst higher C16 fatty acid concentrations (600 g.kg-1 bio-oil) were recorded in N2 atmosphere compared to oil prepared in a CO2 atmosphere (500 g.kg-1 bio-oil). The oil yield increased to a maximum at 320°C, after which there were no significant changes. Highest bio-oil yields (425 g.kg-1 dry microalgae) were obtained in ethanol as solvent. FTIR spectroscopy and ultimate analysis showed that proteins present in the feedstock were degraded by breakage of peptide linkages, and nitrogen present in the oils is peptide fragments from protein degradation. The carbon content of all produced oils was high, but the hydrogen content was low, leading to low hydrogen/carbon ratios. Energy consumption and energy efficiency calculations showed that liquefaction in both reaction atmospheres results in a net energy gain, and a CO2 atmosphere is best for high energy efficiency.

Valorization of pineapple peel and poultry manure for clean energy generation

AbstractThe quest for renewable energy generation is fast increasing globally due to environmental degradation by fossil fuels. The energy production from the anaerobic codigestion of pineapple peels (PPs) and poultry manure (PM) was assessed in the present study. Prior to digestion, the PPs were pretreated using a strong acid (sulfuric acid) and a low‐cost mild alkali hydrogen peroxide (H2O2) which was prepared via the adjustment of the pH of H2O2 to 11.5 by adding solution of 5 M NaOH. The physicochemical and structural parameters of the biomass, as well as microbial composition, were evaluated by using standard methodologies, while all structural changes to the biomass after pretreatment were determined using the Fourier transform infrared spectra. The application of alkaline H2O2 pretreatment removed 71.34% of lignin, reduced hemicellulose by 61%, but increased the cellulose content by 39%. The alkaline pretreated pineapple peel (Al‐P PP) was able to produce about 91% more biogas than the acid pretreated pineapple peel (Ac‐P PP) and 36% more than the two untreated biomass samples. The results of the economic assessment of pretreatment also showed that investment into the use of H2O2 for pretreatment is economically feasible with high net thermal and electrical energy gain, while that of acid pretreatment results in loses. Therefore, alkaline pretreatment application to PPs prior to digestion is hereby solicited in the biotechnological conversion of PPs/wastes for biogas and quality digestate which can be used as biofertilizers or soil enhancers especially in those regions where pineapple production is enormous.

Energy optimization in wheat establishment following rice residue management with Happy Seeder technology for reduced carbon footprints in north-western India

Rice residue management (RRM) impacts ecosystems’ sustainability due to change in energy use, C footprints (CFs) and net ecosystem C budget (NECB). The energy input-output and CFs were audited to optimize energy use and C equivalent emissions (CE) in wheat following RRM with Happy Seeder using data collected from 53 farmers during face-to-face interview. Average total energy input (EI) of 23.5 GJ ha−1 produced output energy of 204.8 ± 2.9 GJ ha−1, with energy productivity (EP) of 0.24 kg MJ−1. The net energy gain (NEG) of 181.3 ± 3.0 GJ ha−1 was achieved with energy use efficiency (ER) of 8.81 ± 0.19. Chemical fertilizers were the major hotspots of energy (∼48.4% of EI) and CFs (∼59.2% of CE) in wheat cultivation. Data Envelopment Analysis (DEA) elucidated 23 decision making units (∼43% of total) as energy efficient, whilst 30 as inefficient with average technical efficiency (TE), pure technical efficiency (PTE) and scale efficiency (SE) were 0.94, 0.97 and 0.94, respectively. DEA helped energy saving of 1462.8 MJ ha−1 (∼6.2%), mitigation of 107.8 kg CO2e ha−1 (∼7.6%) with significantly higher NECB of 716.4 kg C ha−1 (∼19.1%) due to change in soil organic C (ΔSOC) pool by 34.8 kg C ha−1 at efficient Happy Seeder sown wheat farms.

Energy budgeting and carbon footprints of three tillage systems in maize-wheat sequence of north-western Indo-Gangetic Plains

Intensive tillage often contributes to yield gains but there is a tradeoff with energy consumption and carbon footprint (CF) challenging agricultural and environmental sustainability. Studies in the past examined the effect of tillage practices on one or two of the metrics viz., crop productivity or energy auditing or CF and a comprehensive evaluation of the three in a single study to identify cleaner and climate-smart production practice is generally lacking. This study quantified the effect of conventional (CT), deep (DT) and no-tillage (NT) with and without straw mulch on energy budgeting, crop productivity, CF and greenhouse gas intensity (GHGI) in maize-wheat sequence in a split plot design field experiment. No-tillage in maize curtailed energy input by 38.4% and 20.1% compared to DT and CT, respectively. Per tonne of maize grain production, NT with mulch (NTM) saved 1044 MJ of energy (41%) and increased grain yield by 35.3% compared with CT without mulch (CTM0). Although grain yield and net energy gain was higher under DT with mulch (DTM) than NTM, yet latter resulted in significantly higher energy productivity and energy use efficiency. Minimum C equivalent emissions and maximum gain in soil organic C in NTM lowered the CF resulting in highest C efficient and sustainable management. Minimal GHGI without yield penalty was achieved by adopting NT with mulching. Energy and C budgeting revealed that NT coupled with mulching is the most energy and C efficient practice followed by DTM; CT without residue retention is the least efficient management practice for intensively cultivated maize-wheat system in north-western Indo-Gangetic Plains.

Hydrothermal carbonization of anaerobic digestate and manure from a dairy farm on energy recovery and the fate of nutrients

Hydrothermal carbonization (HTC) of raw and anaerobically digested (AD) manure with either water or whey was studied, with the goal of recovering energy and nutrients. Specifically, the impacts of HTC reaction temperature (180–240 °C), solid feedstock, and type of liquid on hydrochar quality and aqueous phase properties were tested. Of the hydrochars produced, the calorific value of whey-based hydrochar was the highest, (19.4 and 16.0 MJ/kg for manure and digestate, respectively). Overall, the net energy gain was higher for HTC of manure with whey (7.4–8.3 MJ/kg dry feedstock) and water (4.4–5.1 MJ/kg) compared to the combined AD-HTC process with whey (4.4–5.3 MJ/kg) and water (2.3–2.9 MJ/kg). Digestate-derived hydrochar contained up to 1.8% P, higher than manure-derived hydrochar (≤1.5%). Using whey as a liquid for HTC increased the aqueous-phase N-P-K concentrations up to 3,200, 410, and 7,900 mg/L, respectively, suggesting its potential use as a liquid fertilizer.

Comparative study of continuous-stirred and batch microwave pyrolysis of linear low-density polyethylene in the presence/absence of HZSM-5

A continuous-stirred microwave pyrolysis (CSMP) reactor was designed for linear low-density polyethylene (LLDPE) conversion. Its performance was compared with the batch microwave pyrolysis (BMP) under identical conditions. During the pyrolysis, the continuous-stirred system generated more condensate products with higher selectivity in long carbon chains (C14–C20), whereas the batch system was more selective for gas products with a higher proportion of methane. An ex-situ catalytic bed with HZSM-5 was assembled to upgrade pyrolysis vapors, corresponding to improved gasoline-range hydrocarbons and propylene production. The comparison of catalytic processes showed similar product yields for both configurations, with differences primarily on chemical species selectivity. For instance, the products from the continuous-stirred system had narrower carbon number distribution (C7–C10) and higher selectivity to mono-aromatics (72.3%). The proposed pathways for LLDPE conversion from the two systems showed slight differences in the thermal cracking process but similarities in the catalytic cracking process. During the catalytic processes, the potential net energy gain was 34.16 MJ/kg for CSMP and −38.86 MJ/kg for BMP, compared with the non-catalytic processes, when the figures were 9.85 MJ/kg and −42.86 MJ/kg, respectively.

Effects of temperature and body-mass on the standard metabolic rates of the round stingray, Urobatis halleri (Cooper, 1863)

Using an intermittent respirometer, we measured the thermal sensitivity (metabolic Q10) and scaling relationship (b) of the round stingray, Urobatis halleri, based on their standard metabolic rates (SMR). A total of 33 individuals (mass range = 0.03–0.86 kg) were acclimated for over 14 days at three temperature treatments (15°, 23°, 27 °C) spanning the seasonal water temperature variation in southern California. An average thermal sensitivity (Q10) of 3.1 was estimated for the round stingray across the range of experimental temperatures. Estimations of size dependent Q10 was 3.8 in juveniles while 2.6 in adults. Our model showed a negative relationship between this species mass-specific scaling exponent (b) and temperature (b = 0.99 at 15 °C, b = 0.86 at 23 °C, and b = 0.79 at 27 °C). Results indicate that the round stingray is relatively sensitive to the thermal fluctuations they experience in southern California. While adults with a relatively high metabolic Q10 may optimize their daily net energy gain by exploiting the local thermal heterogeneity, a higher thermal sensitivity in juveniles could have adverse effects on the population fitness under a pervasive increase of ocean's temperature. Given that the scaling exponent can be affected by temperature, modeling studies should consider correcting for this effect when using scaling relationships as an input for more precise bioenergetic models under various thermal scenarios.

Effect of residence time during hydrothermal carbonization of biogas digestate on the combustion characteristics of hydrochar and the biogas production of process water

The biogas digestate from anaerobic digestion of cow manure and energy crops was treated by hydrothermal carbonization (HTC) at 210 °C for 0.5 to 5 h to understand the effect of HTC residence time on the combustion characteristics of hydrochar and the biogas production of process water. The increase in HTC residence time slightly reduced the higher heating values (16.3–16.0 MJ/kg) but improved most slagging and fouling indices of the hydrochar. However, the slagging and fouling during hydrochar combustion were almost impossible to avoid. The specific methane yield of the process water was not significantly influenced by the HTC residence time. Energy assessment demonstrated that HTC for 0.5 h achieved the highest process efficiency and net energy gain when the combustion energy was obtained from hydrochar and CH4 (from process water). Therefore, the HTC condition of 210 °C, 0.5 h is suggested to valorize biogas digestate for energy production.