Ecological Exergy Research Articles

Exergy analysis and optimization of bio-hydrogen and bio-methane cogeneration from corn stover based on genetic algorithm

In order to explore the influence of the technological parameters on the exergy efficiency of combined bio-hydrogen and bio-methane production process of corn stalk, an exergy equilibrium model was established based on exergy analysis. The method of genetic algorithm was applied to optimize the exergy efficiency of co-production process. The results showed that the exergy efficiency based on thermodynamics exergy at the optimal substrate concentration, initial pH value, and coupling time node was 23.43 %, 24.25 %, and 36.97 %, respectively. Exergy efficiency based on ecological exergy is 21.19 %, 21.92 %, and 31.46 %, respectively. The exergy efficiency based on thermodynamic exergy and ecological exergy behaves the same variation trend. When the optimal process parameters were substrate concentration 60 g/L, initial pH = 7, and coupling time node 12 h, the exergy efficiency was achieved up to 40.46 %, increased by 72.68 % compared to that without optimization.

Integrated response in taxonomic diversity and eco-exergy of macrobenthic faunal community to artificial reef construction in Daya Bay, China

The degradation of marine habitats (especially coral reefs) and the loss of marine fauna can be mitigated by the construction of artificial reefs (ARs). Macrobenthic fauna are considered excellent indicators of how disturbance or succession affects ecosystems, but the integrated effects of AR construction on taxonomic and thermodynamic indicators of macrobenthic faunal communities have seldom been studied. In the current study, we investigated changes in the taxonomic diversity and ecological exergy (eco-exergy) of the macrobenthic faunal community for 2 years following AR construction in Daya Bay, China. The results indicated that macrobenthic faunal diversity, species richness, and evenness increased but abundance, biomass, eco-exergy, and specific eco-exergy decreased following AR construction; after declining, however, abundance, biomass, and eco-exergy appeared to be increasing at the end of the 2-year sampling period. In terms of biomass and eco-exergy, mollusks were the dominant group at each sampling period and were mainly responsible for the changes in biomass and eco-exergy. Eco-exergy was positively correlated with macrobenthic abundance and was negatively related with evenness. Effects of AR construction on the nearby non-reef habitat were similar to those on the AR habitat. These results indicate that long-term assessment of multiple ecological indicators at diverse study areas is needed to determine the effects of AR construction on marine biological resources.

Short-term effects of artificial reef construction on the taxonomic diversity and eco-exergy of the macrobenthic faunal community in the Pearl River Estuary, China

Artificial reefs (ARs) are widely used to restore coastal habitats and associated biological resources. Although research on the effects of ARs on benthos has been increasing, our understanding of the responses of taxonomic and thermodynamic macrobenthic indicators to AR construction is limited. In the current study, differences in the taxonomic diversity and ecological exergy (eco-exergy) of the macrobenthic faunal community before and after AR construction were explored in AR habitat and nearby non-reef control habitat in the Pearl River Estuary, China. The results indicated that macrobenthic faunal diversity, species richness, abundance, biomass, and eco-exergy tended to increase after AR construction regardless of habitat; the increases, however, were not statistically significant in the AR habitat and were only occasionally significant in the non-reef control habitat. After AR construction, macrobenthic faunal evenness and specific eco-exergy changed irregularly. AR construction did not change the composition of the dominant species of macrobenthic fauna in the study area but did change their dominance values. Eco-exergy was positively related with macrobenthic biomass and abundance, confirming that the eco-exergy of the macrobenthic fauna assemblage was mainly derived from biomass information. The results of this short-term study indicate that AR construction could increase macrobenthic faunal taxonomic diversity and thermodynamic health in both AR and nearby non-reef habitats. However, a long-term assessment of ecological indicators is still needed to determine the effects of AR construction on marine biological resources.

Eco-exergy based self-organization of the macrobenthic faunal assemblage during mangrove succession in Zhanjiang, China

Eco-exergy (ecological exergy) has been used to evaluate the health and self-organization of aquatic and wetland ecosystems following perturbation or natural succession. Although macrobenthic fauna are important components of mangrove ecosystems, their self-organization during mangrove succession is unclear. In this study, eco-exergy was used to quantify the self-organization processes of macrobenthic faunal assemblages in a mangrove chronosequence that included a primary (unvegetated shoal), early (Avicennia marina), middle (Aegiceras corniculatum), and late (Bruguiera gymnorrhiza + Rhizophora stylosa) community in Zhanjiang, China. Eco-exergy and biomass of the macrobenthic faunal community tended to decrease in the wet season during mangrove succession. The specific eco-exergy of the macrobenthic faunal community, in contrast, remained relatively constant in both wet and dry seasons during mangrove succession, although mollusk eco-exergy tended to decrease and arthropod eco-exergy tended to increase. Statistical analyses indicated that the self-organization of the macrobenthic faunal community during mangrove succession was mainly associated with the development of a suite of vegetation characteristics and sediment physicochemical properties, e.g., plant crown breadth, plant density, sediment ammonium nitrogen and sediment total nitrogen. Unlike the diversification trends of species richness and functional groups, this study confirmed the decreased self-organization trend of macrobenthic fauna assemblage mainly derived from biomass and genetic information. These results highlight the importance of conserving the macrobenthic faunal community in mangrove forests, especially in the late successional stages.

Characterization of Ecological Exergy Based on Benthic Macroinvertebrates in Lotic Ecosystems

The evaluation of ecosystem health is a fundamental process for conducting effective ecosystem management. Ecological exergy is used primarily to summarize the complex dynamics of lotic ecosystems. In this study, we characterized the functional aspects of lotic ecosystems based on the exergy and specific exergy from headwaters to downstream regions in the river’s dimensions (i.e., river width and depth) and in parallel with the nutrient gradient. Data were extracted from the Ecologische Karakterisering van Oppervlaktewateren in Overijssel (EKOO) database, consisting of 249 lotic study sites (including springs, upper, middle and lower courses) and 690 species. Exergy values were calculated based on trophic groups (carnivores, detritivores, detriti-herbivores, herbivores and omnivores) of benthic macroinvertebrate communities. A Self-Organizing Map (SOM) was applied to characterize the different benthic macroinvertebrate communities in the lotic ecosystem, and the Random Forest model was used to predict the exergy and specific exergy based on environmental variables. The SOM classified the sampling sites into four clusters representing differences in the longitudinal distribution along the river, as well as along nutrient gradients. Exergy tended to increase with stream size, and specific exergy was lowest at sites with a high nutrient load. The Random Forest model results indicated that river width was the most important predictor of exergy followed by dissolved oxygen, ammonium and river depth. Orthophosphate was the most significant predictor for estimating specific exergy followed by nitrate and total phosphate. Exergy and specific exergy exhibited different responses to various environmental conditions. This result suggests that the combination of exergy and specific exergy, as complementary indicators, can be used reliably to evaluate the health condition of a lotic ecosystem.

有効エネルギー効率を用いた佐波川の河川生態環境評価

An ecosystem assessment method based on exergy efficiency is applied to Saba River. In this method, ecological exergy efficiency, which is calculated by the ratio of organism exergy produced in system to exergy supplied from outside of system (photosynthetically active radiation exergy and organic exergy supplied by flood) is defined as an indicator of health of river ecosystem. Field observations of water quality, river sediment and amount of detritus, attached algae and benthic animal were conducted at 8 points in Saba River. The temporal variations of exergy efficiency at 4 points of Saba River were estimated by these observation results and the prediction model of attached algae and benthic animal. The result shows that the exergy efficiency can clarify the difference of the soundness of river ecosystem between the 4 points of Saba River, where no significant difference was observed in terms of water quality and river sediment.

Ecological exergy as an indicator of land-use impacts on functional guilds in river ecosystems

The cumulative effect of land-use changes is one of the most important factors contributing to the continuous deterioration of river ecosystems. We used ecological exergy to evaluate the impacts of land-use changes on functional guilds of benthic macroinvertebrates. We classified 353 sampling sites into 3 groups based on land-use types: forested, agricultural, and urban rivers. For each sampling site, we calculated ecological exergy based on 5 trophic groups of macroinvertebrates. Differences in exergy, specific exergy, and structural metrics (i.e. species richness and Shannon index) suggested that land-use type was an important determinant of the composition of macroinvertebrate communities. Exergy values of the functional feeding groups and trophic groups were used as input data to train self-organizing maps – unsupervised artificial neural networks. The results showed that functional guilds responded differently to different land-use types: scrapers and carnivores dominated the forested rivers, whilst predators and omnivores, and gatherer-collectors and detritivores dominated agricultural and urban rivers, respectively. These results suggest that ecological exergy can be used as a functional bioassessment indicator to evaluate river condition. A generalized additive model and random forest also highlighted that a combination of both conventional structural indicators (e.g. species richness and Shannon index) and novel functional indicators (e.g. exergy and specific exergy) can be used to assess biotic integrity.

A Study on Relationship between Biomass of Macrophytes and the Health Status of the Lake Ecosystem

Two ecological indicators, exergy (Ex) and structural exergy (Exst), and two ecological indexes, biodiversity and trophic state are calculated using the parameters of water quality and plankton investigated in five different ponds in Shandong province in China. The exergy and structural exergy are applied to evaluate the health state of ecosystems of the five ponds, whereas the biodiversity and trophic state are employed to make eutrophication assessment of the ponds. Via analyzing the relationships among the ecological indicators, the ecological indexes and the biomass of macrophytes, it is revealed that exergy, structural exergy and biodiversity is positive correlated to the biomass of macrophytes and that the trophic state decreases with the biomass of macrophytes. This result demonstrates that the ecosystems with more macrophytes can be regarded to hold better health state.

Sustainability Assessment of U.S. Construction Sectors: Ecosystems Perspective

AbstractThe U.S. construction industry accounts for approximately 4% of the gross domestic product. Although quantifying and analyzing the cumulative ecological resource consumption of the construction industry is of great importance, it has not been studied sufficiently. This paper aims to account for the total ecological resource consumption of the construction industry, including its supply chains. This analysis is achieved by using an ecologically based life-cycle assessment model. The impacts on the ecosystem were calculated on the basis of the economic data in terms of cumulative mass, energy, industrial exergy, and ecological exergy. U.S. construction sectors are holistically evaluated by using various sustainability metrics, such as resource intensity, efficiency ratio, and loading ratio. Total ecological exergy values were generally found to be larger for the sectors with higher economic output values. Heavy construction industry sectors, including construction and maintenance of highways, bridge...

Comparative sustainability assessment of warm-mix asphalts: A thermodynamic based hybrid life cycle analysis

Warm-mix asphalt (WMA) has received considerable attention in the past few years as a potential solution for the reduction of energy consumption and emissions during production and construction of asphalt mixtures. However, many concerns and questions are still unanswered regarding its environmental benefits. Although several studies have been conducted to quantify the atmospheric emissions of WMA pavements, the direct and indirect role of ecological resource consumption was generally excluded in these studies. In this study, a thermodynamic based hybrid life cycle assessment model was developed to evaluate the environmental impacts of different types of WMA pavements and compare it to that of a conventional hot mix asphalt (HMA) one. The impacts on the ecosystem were calculated in terms of cumulative mass, energy, industrial exergy, and ecological exergy. Monte Carlo simulation was also conducted to analyze the variability of critical input parameters. The results of this study showed that although the mixing phase is important, it should not be the only phase to evaluate the decreased amount of atmospheric emissions of WMA pavements.

A comprehensive life cycle analysis of cofiring algae in a coal power plant as a solution for achieving sustainable energy

Algae cofiring scenarios in a 360 MW coal power plant were studied utilizing an ecologically based hybrid life cycle assessment methodology. The impacts on the ecological system were calculated in terms of cumulative mass, energy, industrial exergy, and ecological exergy. The environmental performance metrics, including efficiency, loading, and renewability ratios were also quantified to assess the sustainability of cofiring scenarios from a holistic perspective. The analysis results revealed that cumulative mass and ecological exergy consumption were higher for algae cofiring compared to single coal firing due to high material and energy inputs for the algae cultivation. On the contrary, total energy and industrial exergy utilization were reduced with an increasing share of algae cofiring where algae is dried with solar energy. Additionally, natural gas dried algae cofiring scenarios had a lower renewability ratio in comparison with single coal firing. The results of this study are vital for the policy makers to decide on more environmentally friendly algae cofiring options by considering the potential impacts on ecological system.

Comparison between technological and ecological exergy

Exergy function was basically developed in the fields of engineering and is the most useful function to solve problems related to cost-optimization procedures of energy conversion systems and energy policies. However, in the last decades, this function has also been proposed as a tool able to study complex systems, such as ecological systems. The exergy function proposed by Jørgensen, called eco-exergy, is investigated in this paper because of its formulation that differs from the classical one. The two main differences are in the changed reference state, which is more useful for ecological applications, and the contribution of informational exergy that is taken into account. This paper shows how moving from macroscopic to microscopic information storage the exergetic contribution due to information grows and it becomes even three orders of magnitude higher than physical one in the more complex living systems. The capacity of packaging information at the molecular level (DNA) that differs from one organism to another can be taken into account using eco-exergy function.

Nuclear DNA in the determination of weighing factors to estimate exergy from organisms biomass

The application of ecological exergy as a suitable system-oriented development indicator of ecosystems and the estimation proposals from biomass are revised. DNA contents ( C-values) of several groups of organisms are figured, either determined by flow cytometry or taken from literature. The applicability of DNA contents for determination of weighing factors to estimate ecological exergy from the biomass of organisms, as proposed by [Marques, J.C., M.Â. Pardal, S.N. Neilsen, S.E. Jørgensen, 1997. Analysis of the properties of exergy and biodiversity along an estuarine gradient of eutrophication. Ecol. Model. 102: 155–167.], is discussed and putative values for these weighing factors ( β) are presented. This proposal is discussed in theoretical and practical aspects, concerning reliability and eventual application in ecological ‘exergetic’ studies.

An ecological exergy analysis for an irreversible Brayton engine with an external heat source

Brayton cycles have been used extensively in gas turbine power plants and aircraft propulsion systems. In this paper, an exergy analysis, based on an ecological optimization criterion, has been carried out for an irreversible Brayton engine with an external heat source. A cycle pressure ration is solved to yield optimum work done and reduced entropy production. Even though the work output and thermal efficiency are reduced by a certain amount, the ecological exergy analysis results in a better performance than that obtained with the maximum power (or work) output conditions.

Ecological exergy analysis: a new method for ecological energetics research

A new method for ecological energetics research, ecological exergy analysis, is developed based on the exergy analysis in thermodynamics and the characteristics of living systems. This method takes account of both energy quantity and energy quality. Exergy balance equations for both an animal and a plant are constructed, and methods for estimating different types of exergy in living systems are proposed that consider the complex physical-chemical and physiological-ecological processes. Four ecological exergy efficiency indices for evaluating different ecological processes are proposed based on the exergy balance equations.