Energy Return On Investment Research Articles

PSII-18 Effects of protein level and lysine: net energy ratio in growing-finishing pigs.

PSII-18 Effects of protein level and lysine: net energy ratio in growing-finishing pigs.

Biogas from microalgae: an overview emphasizing pretreatment methods and their energy return on investment (EROI).

Studies have reported enhancements in methane yield from pretreatment methods that benefit the anaerobic digestion (AD) of microalgae. However, energy return on investment (EROI), i.e., methane production enhancement achieved over energy input, may be unfavorable. Aiming to quantify EROI of AD microalgae pretreatment, about 180 experiments applied to 30 microalgae biomasses were compiled through an extensive literature survey, classified into 4 pretreatments (physical, enzymatic, chemical, and hybrid), and analyzed. Most of these pretreatments enhanced methane yield, especially the enzymatic alternative. EROI was evaluated for the most efficient pretreatments. Only in one thermal pretreatment the energy resulting from the increase in methane production exceeded the energy demanded by the biomass pretreatment (EROI 6.8) and other two thermal pretreatments presented EROI 1. The other pretreatments presented EROI < 1, concluding that none of the evaluated methods was energy-efficient. Feasibility of pretreatment requires advancements in low energy-demanding strategies and outstanding biomass densification.

Bioenergy from wastewater resources: Nutrient removal, productivity and settleability of indigenous algal-bacteria polyculture, and effect of biomass composition variability on methane production kinetics and anaerobic digestion energy balance

Algal-bacteria high-rate ponds represent an energy-efficient wastewater treatment approach and a source for affordable and sustainable biomass feedstock for production of renewable energy through anaerobic digestion (AD). However, there is still a need for more data on wastewater treatment efficiency, biomass productivity and settleability from outdoor treatment facilities, as well as on impact of variability in biomass composition and digestibility on methane yield and energy output. Hydraulic retention time (HRT) and wastewater quality fed into 30 m2 raceway ponds had a major effect on algal-bacteria polyculture productivity, settleability, phylogenetic and biochemical compositions, digestibility and methane yield. While Micractinium, Scenedesmus, Chlorella, and pennate diatoms were always among the key species observed, the gross productivity and 2-hour settleability during summer cultivation varied in the first-stage ponds treating primary wastewater from 29 ± 5 to 54 ± 12 gAFDW/m2/d and from 88 ± 8 to 94 ± 4% for HRT of 3 and 2 days, respectively. For these conditions, the effluent had csBOD of 3.4 or 3.3 mg/L and Ntotal (mostly NO3−-N) of 9.2 or 8.2 mg/L, respectively. The second-stage algal ponds (HRT 3 days) showed lower productivity of 16 ± 6 gAFDW/m2/d, settleability of 84 ± 11%, and effluent csBOD 3.7 mg/L and Ntotal 0.8 mg/L. Biomass composition from different ponds was 34–38% protein, 18–28% total lipids and 6–14% FAME. The methane yield varied about 30% with largest value of 0.34 ± 0.01 L/gVS and showed a positive correlation with biomass lipid content (R2 = 0.93). First-order and pseudo-parallel first-order rate kinetic models exhibited a better fit for methane production (most R2 > 0.993) than the modified Gompertz model. The variation in biomass composition led to significant differences in energy output (varied by about 60%), Net Energy Ratios (ranged from 1.6 to 2.2) and Net Energy Efficiency (from 60% to 70%) when projecting the energy balance for a large-scale continuous AD process with an optimal HRT of 20–30 days.

Production of lipid-containing algal-bacterial polyculture in wastewater and biomethanation of lipid extracted residues: Enhancing methane yield through hydrothermal pretreatment and relieving solvent toxicity through co-digestion

The feasibility of generating a lipid-containing algal-bacterial polyculture biomass in municipal primary wastewater and enhancing biomethanation of lipid-extracted algal residues (LEA) through hydrothermal pretreatment and co-digestion with sewage sludge (SS) was investigated. In high-rate algal ponds, the polyculture of native algal and bacteria species demonstrated a monthly average net and gross biomass productivity of 30 ± 3 and 36 ± 3 gAFDW m−2 day−1 (summer season). The algal community was dominated by Micractinium sp. followed by Scenedesmus sp., Chlorella sp., pennate diatoms and Chlamydomonas sp. The polyculture metabolic activities resulted in average reductions of wastewater volatile suspended solids (VSS), carbonaceous soluble biochemical oxygen demand (csBOD5) and total nitrogen (Ntotal) of 63 ± 18%, 98 ± 1% and 76 ± 21%, respectively. Harvested biomass contained nearly 23% lipid content and an extracted blend of fatty acid methyl esters satisfied the ASTM D6751 standard for biodiesel. Anaerobic digestion of lipid extracted algal residues (LEA) demonstrated long lag-phase in methane production of 17 days and ultimate methane yield of 296 ± 2 mL/gVS (or ~50% of theoretical), likely because to its limited biodegradability and toxicity due to presence of the residual solvent (hexane). Hydrothermal pretreatment increased the ultimate methane yield and production rate by 15–30% but did not mitigate solvent toxicity effects completely leading to less substantial improvement in energy output of 5–20% and diminished Net Energy Ratio (NER < 1). In contrast, co-digestion of LEA with sewage sludge (10% to 90% ratio) was found to minimize solvent toxicity and improve methane yield enhancing the energy output ~4-fold, compared to using LEA as a single substrate, and advancing NER to 4.2.

Scaled-Up Biodiesel Production from Meat Processing Dissolved Air Flotation Sludge: A Simulation Study

For the first time, a steady state computational simulation for the production of biodiesel from meat processing dissolved air flotation sludge via an integrated process of in-situ hydrolysis and esterification technologies has been investigated. Important thermophysical properties of the intrinsic lipids of dissolved air flotation sludge were estimated using chemical constituent fragment methods. The environmental performance and the economic performance of the biodiesel production process were assessed via the estimation of the net energy ratio (NER) and the unit production cost, respectively. Since electrical energy requirements may be satisfied via either non-renewable (case A) or renewable sources (case B), the NER was determined for both scenarios. To enhance the robustness of the study results, uncertainties in the NER and the unit cost of the biodiesel production process due to the variability of the underlying study assumptions were also assessed. Uncertainty analysis indicated that the likely range of the NER for the biodiesel production process for cases A and B are 1.76 to 3.32 and 1.82 to 3.36, respectively, at 95% probability. Uncertainty analysis also showed that the likely range of the unit production cost for biodiesel is $US0.41/kg-biodiesel to $US0.71/kg-biodiesel at 95% probability. The results that were obtained in this study therefore provide evidence of both the environmental sustainability and the economic viability of biodiesel production from dissolved air flotation sludge via the proposed integrated process of in-situ hydrolysis and esterification.

Continuous Hydrothermal Liquefaction of Biomass in a Novel Pilot Plant with Heat Recovery and Hydraulic Oscillation

Hydrothermal liquefaction (HTL) is regarded as a promising technology for the production of biofuels from biomass and wastes. As such, there is a drive towards continuous-flow processing systems to aid process scale-up and eventually commercialization. The current study presents results from a novel pilot-scale HTL reactor with a feed capacity of up to 100 L/h and a process volume of approximately 20 L. The pilot plant employs a heat exchanger for heat recovery and a novel hydraulic oscillation system to increase the turbulence in the tubular reactor. The energy grass Miscanthus and the microalgae Spirulina, both representing advanced dedicated energy crops, as well as sewage sludge as high-potential waste stream were selected to assess the reactor performance. Biomass slurries with up to 16 wt% dry matter content were successfully processed. The heat recovery of the heat exchanger is found to increase with reactor run time, reaching 80% within 5–6 h of operation. The hydraulic oscillation system is shown to improve mixing and enhance heat transfer. Bio-crudes with average yields of 26 wt%, 33 wt% and 25 wt% were produced from Miscanthus, Spirulina and sewage sludge, respectively. The yields also appeared to increase with reactor run time. Bio-crude from HTL of Spirulina was mainly composed of palmitic acid, glycerol, heptadecane and linolelaidic acid, while biocrude from sewage sludge contained mainly palmitic acid, oleic acid and stearic acid. In contrast, biocrude from HTL of Miscanthus consisted of a large number of different phenolics. An energetic comparison between the three feedstocks revealed a thermal efficiency of 47%, 47% and 33% and energy return on investment (EROI) of 2.8, 3.3 and 0.5 for HTL of Miscanthus, Spirulina and sewage sludge, respectively.

Hot Water Extraction Improves the Characteristics of Willow and Sugar Maple Biomass With Different Amount of Bark

Shrub willows are being developed as a short rotation woody crop (SRWC) that can grow on marginal agricultural land. Willow has a high net energy ratio (energy produced/ fossil fuel energy consumed), low greenhouse gas footprint and high carbohydrate production potential. Willow biomass can be combined with forest biomass, but willow often has a higher proportion of bark that creates challenges because it increases the ash content and decreases the melting point. Hot water extraction is a pretreatment that has been shown to improve the quality of chipped material while producing a marketable stream of byproducts. This study evaluated how the amount of bark (0%, 33%, 66% and 100%) on three willow cultivars and sugar maple impact the output of hot water extraction in terms of mass removal and extract composition, as well as its influence on the heating value, ash and elemental content. The hot water extraction process resulted in ash content up to 50% for sugar maple and willow, but there was variation among the willow varieties. The heating value after hot water extraction was about 5% higher because of the removal of mostly hemicelluloses, which have relatively low heating value. HWE led to significant reductions of calcium, potassium, magnesium and sulfur contents. The hot water extraction provides a fermentable sugar stream and other co-products after multiple separation and treatment steps, and improves the characteristics of willow and sugar maple biomass for combined heat and power. This paper demonstrates how biomass with higher bark content can generate a useable sugar stream while improving the quality of the biomass for combined heat and power by managing its ash content while simultaneously producing other valuable products.

Re-evaluation of energy return on investment (EROI) for China's natural gas imports using an integrative approach

China's gas-import dependency has been growing rapidly, driven by increasing natural gas consumption paired with insufficient domestic reserves. Energy Return on Investment (EROI) has been widely applied to examine the net energy cost for natural gas production in China. EROI analysis for imported gas are, however, limited. The few existing studies on this topic have adopted inconsistent evaluation frameworks and have not considered life-cycle or environment-related energy inputs. This paper builds an integrative evaluation framework for natural gas imports in China and quantifies the EROI values for natural gas from seven major national exporters supplying to China. Results show a downward trend for the EROI of China's gas imports from 2009 to 2015 – more energy inputs were required for the same output – reflecting the increase in gas prices during this period. The average standard EROI of gas imports in 2015 is 10.2, slightly higher than that of domestic gas production at approximately 10. Consideration of life-cycle direct energy inputs and environment-related energy inputs results in a decrease in EROI by 18.2%–48.1%. Establishing an updated standard EROI evaluation framework for gas imports is the central contribution of this study. The updated EROI framework can provide a useful reference for research on gas imports for other countries.

Energy analysis of jojoba plantation systems for the production of biodiesel

ABSTRACTThe aim of this study is to investigate the energy chain of biodiesel production from jojoba seed oil using a life cycle approach. The system boundary starts with jojoba plantation and includes extraction and conversion of seed oil into biodiesel. Energy inputs during fertilizer production and application, jojoba plantation and harvesting, oil extraction, biodiesel production, product transportation and distribution are included. Energy outputs from biodiesel and its co-products (straw, seed cake, and glycerin) are considered in the analysis. Energy efficiency is expressed in terms of the net energy gain (NEG) and the net energy ratio (NER). The results show that the NEG and NER values are calculated at 46724.1 MJ/ha (28.9 MJ/L biodiesel produced) and 2.16, respectively. Nevertheless, if manure is used as fertilizer for jojoba plant cultivation, the primary energy input will fall by 9.52% (to 22.49 MJ/L of biodiesel).

Thermodynamic and Economic Analysis Between Organic Rankine Cycle and Kalina Cycle for Waste Heat Recovery From Steam-Assisted Gravity Drainage Process in Oilfield

A thermodynamic and economic comparative analysis are presented for waste heat recovery (WHR) from the heavy oil production with steam-assisted gravity drainage (SAGD) process employing organic Rankine cycle (ORC) and Kalina cycle (KC). The liquefied natural gas (LNG) cold energy is employed as the cold source. Thus, a combined cooling heating and power system is proposed. The effect of key parameters on thermodynamic performance is investigated. The results showed that increasing the turbine inlet temperature (TIT), ORC is more appropriate for WHR in SAGD process than KC, but KC provides better energy use and exergy efficiency, while the reverse situation occurs when the evaporation pressure is increased. The compression ratio has little effect on the cold exergy recovery efficiency of the refrigeration cycles. In addition, the total exergy destruction and the total WHR efficiency in the combined SAGD/KC are slightly higher than these in the combined SAGD/ORC. Moreover, for the TIT below 180 °C and the evaporation pressure above 6 MPa, the SAGD/KC can obtain more energy return on investment (EROI) than SAGD/ORC. The results obtained through economic analysis show that the use of the SAGD/ORC is more economical. Through the thermos-economic comparison of the two combined systems, it helps to choose different combined cycles according to the different actual operation, which can facilitate the future engineering applications.

Concentrated Solar Power: Actual Performance and Foreseeable Future in High Penetration Scenarios of Renewable Energies

Analyses proposing a high share of concentrated solar power (CSP) in future 100% renewable energy scenarios rely on the ability of this technology, through storage and/or hybridization, to partially avoid the problems associated with the hourly/daily (short-term) variability of other variable renewable sources such as wind or solar photovoltaic. However, data used in the scientific literature are mainly theoretical values. In this work, the actual performance of CSP plants in operation from publicly available data from four countries (Spain, the USA, India, and United Arab Emirates) has been estimated for three dimensions: capacity factor (CF), seasonal variability, and energy return on energy invested (EROI). In fact, the results obtained show that the actual performance of CSP plants is significantly worse than that projected by constructors and considered by the scientific literature in the theoretical studies: a CF in the range of 0.15–0.3, low standard EROI (1.3:1–2.4:1), intensive use of materials—some scarce, and significant seasonal intermittence. In the light of the obtained results, the potential contribution of current CSP technologies in a future 100% renewable energy system seems very limited.

Synergistic co-digestion of wastewater grown algae-bacteria polyculture biomass and cellulose to optimize carbon-to-nitrogen ratio and application of kinetic models to predict anaerobic digestion energy balance

This study investigated enhancing methane production from algal-bacteria biomass by adjusting the C/N ratio through co-digestion with a nitrogen-poor co-substrate – cellulose. A biomethane potential test was used to determine cumulative biogas and methane production for pure and co-digested substrates. Four kinetic models were evaluated for their accuracy describing experimental data. These models were used to estimate the total energy output and net energy ratio (NER) for a scaled AD system. Increasing the algal C/N ratio from 5.7 to 20–30 (optimal algae:cellulose feedstock ratios of 35%:65% and 20%:80%) improved the ultimate methane yield by >10% and the first ten days production by >100%. The modified Gompertz kinetic model demonstrated highest accuracy, predicting that co-digestion improved methane production by reducing the time-lag by ∼50% and increasing rate by ∼35%. The synergistic effects increase the AD system energy efficiency and NER by 30–45%, suggesting potential for substantial enhancements from co-digestion at scale.

Energy transitions and social revolutions

The transition from a traditional agrarian to a fossil fuel based energy regime began before the industrial revolution and is still ongoing. This paper explores the relation of this transition process and social revolutions. Using statistical analysis, we find that at the very beginning of countries' energy transition, a critical phase can be identified, within which social revolutions are most likely to happen. This applies to the grand revolutions across the past five centuries investigated for a core set of industrial and emerging economies, as well as to supplementary samples of Latin American and post-World War II developing countries. No statistically significant relation between the historical time and the pace of transition towards modern fuels is found, which means that the energy transition does not accelerate. Among the sample of developing countries with revolutions after World War II we find an even slower pace of transition to an industrial energy regime. Apparently, transitions in primary energy source and energy abundance are not just a matter of technological change, but strongly interact with the social, institutional and political fabric of societies. Significance statementRevolutions are not randomly scattered in space and time, nor are they confined to a certain historical epoch. They are likelier under certain conditions, the early stages of a transition from an agrarian energy regime to a fossil-fuel-based energy regime. Seemingly, unique historical events like social revolutions followed a pattern linked to the specific mode societies exploit natural resources. Not just human inventiveness and technology matters, but also a gift from nature – fossil energy carriers – is found to be at the roots of the industrial transformation. Their superior energy return on investment (EROI) over traditional biomass, and their sheer quantity, permit a fundamental transformation; these benefits can only be harvested if accompanied by an equally fundamental socio-political transformation. Such insights link the study of politics and history to the study of social metabolism in a systematic way.

Energy Assessment of Pastoral Dairy Goat Husbandry from an Agroecological Economics Perspective. A Case Study in Andalusia (Spain)

This paper presents a methodological proposal of new energy sustainability indicators according to a novel accounting that follows agroecological and ecological economics criteria. Energy output is reformulated to include manure and thus consider the contribution to fertilization made by pastoral livestock farming to agroecosystems. Energy inputs calculations include the grazing resources. These new definitions and calculations allow for new formulations of the energy return on investment (EROI) as measures of the energy efficiency of livestock farming systems (final EROI and food/feed EROI). The environmental benefit of manure is estimated from the avoided energy cost of using this alternative to inorganic fertilizers (AECM). The environmental benefit of grazing is measured through the energy cost of avoiding cultivated animal feed (AECP) and its impact in terms of non-utilized agricultural area (ALCP). The comparative analysis of different livestock breeding systems in three pastoral dairy goat farms in the Sierra de Cádiz in Andalusia, southern Spain, reveals the analytical potential of the new energy sustainability indicators proposed, as well as the potential environmental benefits derived from territorial-based stockbreeding and, more specifically, grazing activities. Those benefits include gains in energy efficiency, a reduction of the dependence on non-renewable energy, and environmental costs avoided in terms of energy in extensive pastoral systems.

A review of EROEI-dynamics energy-transition models

The need for an environmentally sustainable economy is indisputable but our understanding of the energy-economy interactions (dynamics) that will occur during the transition is insufficient. This raises fascinating questions on the future of economic growth, energy technology mix and energy availability. The crucial interactions between energy and economy systems can be usefully described in terms of the Energy Returned on Energy Invested (EROEI) metric (the energy cost of primary energy production). Multiple authors have used this metric to explore the behaviour of the economy over the transition to lower carbon energy sources. The following text is a review of energy-economy models that incorporate the EROEI metric. In particular, the EROEI-dynamics literature is found to describe a common set of dynamics associated with the transition to lower EROEI primary energy resources. These include: the rising resource-cost of primary energy production, the short-term misallocation of resources, the short-term overproduction of energy and the potential decline in economic stability. The literature can be divided into groups of related models. Following the review, a number of key areas for additional work are identified and discussed.

Measurement of sustainable intensification by the integrated analysis of energy and economic flows: Case study of the olive-oil agricultural system of Estepa, Spain

In the late 20th century, new patterns arose in the consumption of energy and materials in agriculture related to sustainable intensification observed in certain rural areas. This article discusses how these changes manifested themselves in the rain-fed agricultural olive-growing region of Estepa, in southern Spain. Considering farm inputs and outputs, it analyses energy and economic balances at different levels of intensification applying a methodology that combines process analysis, Energy Return on Energy Invested (EROI) and Activity-Based Costing (ABC). The results show that the farms following sustainable intensification models increased production from 36.8% to 64.4% and improved revenues per unit of energy invested from 40.0% to 60.0% while maintaining energy consumption. The models of sustainable intensification were related to the extension of integrated farming and have been led by a network of actors.

Second generation bioethanol production from Arundo donax biomass: an optimization method

In last decades environment has suffered strong and negative consequences resulted by a massive consuming fossil energy. As a result of this process, bioenergy has been intensively increased in recent years. Transportation sector has the largest impact in the use of bioenergy and bioethanol is a type of biofuel which can easily used for transports in place of traditional fossil fuels. Bioethanol production from 1st generation biomass such as corn, sugarcane, has been already commercialized but it is usually not sustainable because it could be seriously damage the food supply. For this reason scientific community has turned his interest to second generation bioethanol from specific energy crops or cultivation of biomass feedstock whose required land for cultivation cannot be used for food cultivations. The case arboreal lingo-cellulose Arundo donax is an example of the latter group. The present paper deals with a simulation method to optimize the performances of second generation bioethanol production by using Arundo donax as feedstock. The bioethanol production was analyzed by means of a life cycle assessment (LCA). The total energy consumption was calculated thanks to Monte Carlo method. The simulation of this second-generation biomass technology was optimized by considering the reuse of light components and of the energy recovery for the agriculture and industrial process. Thanks to these optimizations it was obtained an Energy Return On Investment (EROI) = 1,52 revealing that this technology may certainly be convenient from the energetic point of view.

Energy analysis of biodiesel production from jojoba seed oil

Abstract In this work, energy analysis is carried out to account for inputs and outputs of energy and GHG emissions associated with the biodiesel production system. Jojoba oil is obtained by cultivation of the jojoba plant, harvesting of seeds followed by extraction of oil, which is then converted to biodiesel by the process of transesterification. Energy efficiency is expressed in terms of the net energy balance (NEB) and the net energy ratio (NER). The use of the byproducts (husk, cake or meal, waste residues and glycerin) are also included as a part of the system boundary. The results show that the NEB and NER values are calculated at 46724.1 MJ/ha (28.9 MJ/L biodiesel produced) and 2.16, respectively. At the same time, the total amount of GHG emissions are estimated at 2.28 kg-CO2eq/L biodiesel produced (66.0 g CO2eq/MJ biodiesel produced). Nevertheless, if manure is used as fertilizer for jojoba plant cultivation, the primary energy input will fall by 9.52% (to 22.49 MJ/L of biodiesel).

The net energy impact of substituting imported oil with coal-to-liquid in China

Abstract To alleviate the high risks to oil supply caused by high dependency on oil imports, China is actively seeking alternative energy sources to reduce its imported oil (IO). Coal-to-liquid (CTL) is regarded as an option in China. However, few analyses have examined the net energy impact of substituting IO with CTL and determined how effective the substitution would be. Energy return on investment (EROI) analysis, an important index to characterise the viability of a natural resource from an energy standpoint, can provide insights into these issues. This paper first introduces new methods to calculate the EROIs between CTL and IO from a life-cycle perspective. Then, based on the EROI values, a new, simple method is provided to calculate the net energy change resulting from the substitution of IO with CTL. The results show that without considering the environmental inputs, the mean EROI of CTL with/without internal energy inputs is 0.29/1.44, and that of IO is approximately 5.60. When environmental inputs are considered, these values decrease to 0.27/1.09 and 5.07, respectively. In general, IO has a better net energy return than CTL. Moreover, substituting 1 MJ IO with CTL would lead to a net energy loss of 0.3–4.6 MJ. The above results suggest that China should be more cautious in developing the coal liquefaction industry from a net energy perspective.

Estimating the EROI of whole systems for 100% renewable electricity supply capable of dealing with intermittency

Until the last few years it has not been possible to estimate the energy return on energy invested (EROI) for 100% renewable energy supply systems, because simulations indicating the amount of capacity required were not available. This study takes the finding of a recent simulation for 100%renewable Australian electricity supply, along with commonly quoted EROI values for the technologies involved, and derives a conclusion for total energy supply system EROI. The EROI values for individual renewable technologies do not provide a reliable guide to the system value because of the large amount of redundant plant that must be on hand to enable whole systems to meet demand reliably despite intermittency. The general finding is that 100% renewable supply systems probably have values that are too low to sustain energy intensive societies.