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This work implements a multi-objective scoring methodology based on fuzzy set theory to evaluate and compare the sustainability metrics of microalgal biorefining concepts. Fuzzy membership functions are developed for three key metrics: minimum fuel selling price, global warming potential, and net energy ratio. Membership functions yield satisfaction scores (λ) between 0 and 1 for each objective; achieving λ=1 indicates a sustainability metric has fully met its target, while λ=0 is unacceptable for the standards of that metric. The individual λ are combined into an overall satisfaction score, λo, also ranging from 0 to 1, which is used here to simplify the comparison of sustainability metrics. In addition to baseline biorefining conditions, uncertainties across the algal biofuel production system are assessed through a Monte Carlo analysis of λo. A case study is developed to compare Combined Algal Processing (a biochemical conversion pathway) against hydrothermal liquefaction (a thermochemical conversion pathway). Baseline results show that lipids are always heavily favored for fuel production, but no practical cultivation operations would be able to achieve such lipid-heavy biomass. The Monte Carlo analysis reveals that current algal fuel conversion technologies cannot simultaneously satisfy all key sustainability objectives. If biomass productivity is doubled and the feedstock is high in lipids, hydrothermal liquefaction can achieve a mean λo=0.53±0.12, still well below a desirable λo of 1. Combined Algal Processing struggles to achieve high satisfaction scores even in optimistic scenarios and requires a high-lipid feedstock to achieve a mean λo=0.10±0.03. Hydrothermal liquefaction can be integrated downstream of Combined Algal Processing to increase fuel yield and optimistically can achieve a mean λo=0.48±0.07. A combination of system improvements, including biomass productivity, feed composition, fuel yield, and implementation of co-product pathways must work together to satisfy all the relevant sustainability metrics for algal biofuels. The scoring methodology developed here can be readily applied to other microalgal biorefinery concepts and, more broadly, to sustainable fuel development and production.

Over the past years, there were dramatic improvements in identifying and assessing various feedstocks for the production of biodiesel fuels. To promote a particular feedstock as a renewable source of energy, it is important to analyze their energy, economic, and engine performance characteristics. The current work attempts to evaluate the net energy and economic indices for both fossil diesel and coconut-blended diesel (B20) considering the diesel consumption by the Indian railways. Further, we present the experimental results of a multi-cylinder diesel engine operated with neat coconut biodiesel (B100) and fossil diesel at various load and speed conditions. The engine experiments reveal that the coconut biodiesel exhibits leaner combustion and shorter ignition delay than fossil diesel. Lower amount of carbon monoxide, hydrocarbon, and smoke emission is observed in the case of coconut biodiesel, with higher levels of nitric oxide (14%) and fuel consumption than diesel. The coefficient of variation in indicated mean effective pressure is within the range of better driveability zone for both the fuels at all test conditions. Overall the engine performance, emission and combustion results with neat coconut biodiesel are favorable with a penalty in NO emission at high load conditions. The techno-economical study highlights higher production cost per liter of B20 than the cost of fossil diesel. However, the net energy ratio (NER) for B20 is 1.021, favoring higher output than diesel and thus lowers the dependency on crude oil. [ABSTRACT FROM AUTHOR]

The depletion of fossil fuel sources and increase in energy demands have increased the need for a sustainable alternative energy source. The ability to produce hydrogen from microalgae is generating a lot of attention in both academia and industry. Due to complex production procedures, the commercial production of microalgal biohydrogen is not yet practical. Developing the most optimum microalgal hydrogen production process is also very laborious and expensive as proven from the experimental measurement. Therefore, this research project intended to analyse the random time series dataset collected during microalgal hydrogen productions while using various low thermally pre-treated palm kernel expeller (PKE) waste via machine learning (ML) approach. The analysis of collected dataset allowed the derivation of an enhanced kinetic model based on the Gompertz model amidst the dark fermentative hydrogen production that integrated thermal pre-treatment duration as a function within the model. The optimum microalgal hydrogen production attained with the enhanced kinetic model was 387.1 mL/g microalgae after 6 days with 1 h thermally pre-treated PKE waste at 90 °C. The enhanced model also had better accuracy (R 2 = 0.9556) and net energy ratio (NER) value (0.71) than previous studies. Finally, the NER could be further improved to 0.91 when the microalgal culture was reused, heralding the potential application of ML in optimizing the microalgal hydrogen production process. [Display omitted] • Thermal pre-treated palm kernel expeller as a substrate for dark fermentation. • Machine learning-based kinetic model in predicting microalgal hydrogen production. • Integrated Gompertz model with thermal pre-treated function for optimization study. • Energy feasibility to produce green hydrogen from thermal pre-treated substrate. [ABSTRACT FROM AUTHOR]

Camelina sativa is a cool-season oil seed crop that has been proven to produce various biofuels. The present study investigated the technical possibilities of using whole camelina biomass as a model feedstock in a biorefinery. This investigation examined the possibilities of using camelina seeds as a source of oil for biodiesel, sugars for ethanol, and meal for oneportfolio products. The camelina harvest residues (straw) can serve as the main source for green sugars. This study found that the energy input for the whole biorefinery process was 25.1 MJ/L ethanol, while the energy output was 54.3 MJ/L ethanol. The net energy ratio of 2.16 MJ/L ethanol was found to be competitive with other energy crops. The process was environmentally friendly, and it reduced greenhouse gas emissions by 40% if the produced biodiesel replaced petroleum diesel. The seed meals and glycerin were found to be a good source of revenue as high valueadded products and can provide an additional revenue of $1/kg of produced oil. [ABSTRACT FROM AUTHOR]

Electricity supply in India is from a centralized grid. Many parts of the country experience grid interruptions. Life cycle energy and environmental analysis has been done for a 27 kWp photovoltaic system which acts as grid backup for 3 h outage in an Indian urban residential scenario. This paper discusses energy requirements and carbon emission for a PV storage system for five different battery technologies in Indian context. This can be used as a metric for comparative analysis for new batteries, with an undeveloped market. The energy requirements for the components are quantified and are compared in terms of energy payback time (EPBT) and Net Energy Ratio (NER). All the calculations are done for Indian context. EPBT is found to be in the range of 2-4.5 years for all the systems, while NER is in the range of 6.6-2.52. NaS has the highest emission factor of 0.67 kgCO/kWh and the least for NiCd (0.091 kgCO/kWh). These factors can be used to select a PV battery option and to target selection of materials and systems based on the reported values. [ABSTRACT FROM AUTHOR]

The Brazilian sugarcane mills already provide significant amounts of renewable products (ethanol and bioelectricity) through self-sufficient bagasse cogeneration. Gaseous outputs of the sector can provide streams rich in biogenic carbon dioxide (CO 2), suitable for the autotrophic cultivation of microalgae and aim, hereinafter, their conversion into biodiesel. This work modeled the integration of an ethanol plant with a cogeneration system, covering the enzymatic hydrolysis of bagasse and the production of microalgae biodiesel. A standard ethanol plant yielding 96 L ethanol/t cane may produce an additional 7.5–30 L microalgae biodiesel/t cane but at the expense of its energy self-sufficiency; the biorefinery must recur to fossil resources unless other biomass (besides bagasse) and coproducts by the plant's neighborhood can be exploited. The process simulation is conducted in nine cases derived from a central composite design with two factors – the fraction of bagasse destined for the hydrolysis system (x 1) and the fraction of ethanol sent to produce anhydrous ethanol (x 2) – and three levels for each factor (0, 50, 100%). Energy ratios between representative outputs and inputs – Net energy ratio (NER) and Fossil energy ratio (FER) –, direct CO 2 emission, and exergy efficiencies were calculated as representative responses to evaluate the plant's technical and environmental efficiencies. Statistical tools (t-Student test, ANOVA, and R2) showed that the constructed models were robust and that the responses varied significantly with x 1 , while x 2 produced mild or negligible effects. The highest achievable NER and FER were 0.83 and 2.09, respectively. The whole system resulted in a FER equal to 1 when bagasse usage is split in half between the hydrolysis and cogeneration systems. This result guarantees that the energy related to the useful products is higher than the requirements of fossil energy inputs, within an acceptable range. The optimum CO 2 emission and exergy efficiency were found when 6–8% of the bagasse is hydrolyzed, which is also a range covering attractive energy ratios. The proposed integration benefits the sector, but resorting to renewable sources to supply energy deficits, developing the technological exploitation over wasted coproducts, and studying heat and mass integration of processes are highly recommended to enhance the global-system performance. [Display omitted] • The highest Fossil Energy Ratio of the biorefinery reached a value of 2.1. • Bagasse usage is the most significant factor in the Central Composite Design. • Exergy efficiency doubled to 60% with the inclusion of more marketable coproducts. • The partial bagasse hydrolysis (6–8% of the total) produced the lowest emissions. • The oil extraction is the crucial step (high energy demand and exergy loss). [ABSTRACT FROM AUTHOR]

Bioenergy sources are promising alternatives for sustainable energy production. Nevertheless, significant research and detailed analysis are necessary to identify the circumstances under which such energy sources can contribute to sustainability. This paper reviews the literature of Life Cycle Assessment (LCA) of microalgae-to-energy technologies and focuses in two categories, Greenhouse Gas (GHG) emissions and Net Energy Ratios (NER). The analysis is illustrated with a case study of microalgae biomass combustion to produce heat and compares the influence of different electricity sources with respect to GHG emissions and NER along the supply chain. Selected fossil energy sources were used as reference conditions. The methodology was LCA based on ISO 14044 standard, and most of the data used were extracted from a review of relevant scientific publications. Heat production from microalgae showed higher GHG emissions than those from fossil fuels with United States' electricity grid, but lower than those with the Brazilian one. The NER of heat from microalgae combustion life cycle is still disadvantageous compared to most of fossil options. However, the observation that fossil fuel options performed slightly better than microalgae combustion, in the two categories analyzed, must be understood in the context of a mature fossil energy technology chain. The fossil technology has less potential for improvements, while microalgae technology is beginning and has significant potential for additional innovations. [ABSTRACT FROM AUTHOR]

Abstract: Most renewable energy sources depend to some extent on use of other, non-renewable sources. In this study we explore use of diesel fuel in producing and transporting woody biomass in the state of New Hampshire, USA. We use two methods to estimate the diesel fuel used in woody biomass production: 1) a calculation based on case studies of diesel consumption in different parts of the wood chip supply chain, and 2) to support extrapolating those results to a regional system, an econometric study of the variation of wood-chip prices with respect to diesel fuel prices. The econometric study relies on an assumption of fixed demand, then assesses variables impacting supply, with a focus on how the price of diesel fuel affects price of biomass supplied. The two methods yield similar results. The econometric study, representing overall regional practices, suggests that a $1.00 per liter increase in diesel fuel price is associated with a $5.59 per Mg increase in the price of wood chips. On an energy basis, the diesel fuel used directly in wood chip production and transportation appears to account for less than 2% of the potential energy in the wood chips. Thus, the dependence of woody biomass energy production on diesel fuel does not appear to be extreme. [Copyright &y& Elsevier]

Abstract: Jatropha curcas L. has been considered as a potential feedstock for biodiesel production in several tropical countries. Two Jatropha plantation models currently being considered in Thailand, a perennial plantation for 20 years and annual harvesting, are compared vis-à-vis the energy benefits. The advantage of the perennial plantation is that fruit yield is low in the first 2 years but stabilizes after the second year; thus, the biodiesel production is maximized. On the other hand, the biodiesel yield for annual harvesting is low but substantial energy is gained from the wood which can be used for power production. The overall energy output from the annual system is about twice that of the perennial system whereas the biodiesel production is less than half. The energy values of both the systems are high and the net energy ratios as high as 6–7 indicating a substantial energy benefit. [Copyright &y& Elsevier]

Although several studies have found biodiesel to be a renewable source of energy, there has been a claim that it is not. This article investigates models used to calculate the net energy ratio (NER) of biodiesel production to point out the reasons for the contradictory results, compares their strengths and weaknesses, and proposes a uniform model for interpretation of the final result. Four commonly referenced models were compared for their assumptions and results. The analysis revealed that the most significant factors in altering the results were the proportions of energy allocated between biodiesel and its coproducts. The lack of consistency in defining system boundaries has apparently led to very different results. The definitions of NER used among the models were also found to be different. A unified model is proposed for biodiesel energy analysis to answer the renewability question. Using the unified boundary, a range of probable NERs was calculated using bootstrapping. The mean NER on a mass basis was 2.55 with a standard deviation of 0.38. The economic sustainability ratio (ESR) is defined as the monetary value ratio of biodiesel to biodiesel's share of the energy inputs. The average ESR was found to be 4.43 with a standard deviation of 0.6. [ABSTRACT FROM AUTHOR]

Abstract: Biodiesel from palm oil has been considered for partial substitution of diesel fuel for transportation in Thailand. The Thai government recently has set up a production target of 8.5million liters per day of palm oil-based biodiesel by 2011. The aim of this study is to investigate the energy consumption of palm methyl ester (PME) production in Thailand using a life cycle approach compared to other possible oil crops for biodiesel production including jatropha and coconut. The main contributors to the energy use are cultivation, oil production, transesterification and transportation. Taking into account only fossil fuel or petroleum inputs in the production cycle, the energy analysis provides results in favour of PME in Thailand. The net energy balance (NEB) and net energy ratio (NER) of PME and co-products are 100.84GJ/ha and 3.58, respectively. The NER of PME without co-products is 2.42, which is still higher than one indicating a favourable result. The results are important in selecting an appropriate feedstock for biodiesel production and this study will support policy makers in the energy sector to make informed decisions vis-à-vis promotion of oil palm plantation for biodiesel. This will also support the Thai government in its policy to promote the use of indigenous and renewable sources for transportation fuels. [Copyright &y& Elsevier]