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Attached microalgal growth of Chlorella vulgaris on palm decanter cake (PDC) under irradiation with various visible monochromatic and polychromatic spectra to produce biodiesel was studied in this work. The results demonstrated that the white spectrum cultivation exhibited the highest microalgal density of 1.13 g/g along with 1.213 g/L day of microalgal productivity. Correspondingly, the biodiesel obtained was comprised mainly of C16 and C18 fatty acids, possessing a high cetane number and oxidation stability from the high saturated fatty acid content (70.38%), which was appealing in terms of most biodiesel production requirements. Nevertheless, the highest lipid content (14.341%) and lipid productivity (93.428 mg/L per day) were discovered with green spectrum cultivation. Blue and white spectra led to similar protein contents (34%) as well as carbohydrate contents (61%), corroborating PDC as a feasible carbon and nutrient source for growing microalgae. Lastly, the energy feasibilities of growing the attached microalgae under visible spectra were investigated, with the highest net energy ratio (NER) of 0.302 found for the yellow spectrum. This value outweighed that in many other works which have used suspended growth systems to produce microalgal fuel feedstock. The microalgal growth attached to PDC is deemed to be a suitable alternative cultivation mode for producing sustainable microalgal feedstock for the biofuel industry. [ABSTRACT FROM AUTHOR]

Abstract With their fast growth rate and ability to accumulate a high percentage of their weight as lipid and carbohydrate, microalgae potentially represent an ideal feedstock for the production of biodiesel and bioethanol. In addition, microalgae offer several environmental benefits, and do not compete with food production for land, fresh water, and nutrients. Therefore, the main goal of this work is to provide a quantitative, systematic and harmonized assessment of current bio-energy potential. The analysis is conducted by considering all the main steps in detail, from cultivation to biodiesel production, and by deriving an overall estimation of energy consumption for biodiesel production. Energy consumption uncertainty is also quantified and discussed. A systematic review of all the main technologies available for all the main processing steps towards the production of biodiesel from microalgae is presented, focusing on the derivation of the Net Energy Ratio (NER) of each combination of technologies, complemented by an uncertainty analysis of the data used and those obtained in the present work. A wide scatter in the data available in the literature has been identified, highlighting the need for an uncertainty analysis. If the average overall energy consumption per unit of biodiesel mass is considered, all the routes adopting a raceway pond have a lower energy consumption, but if the uncertainty on the overall energy consumption is also considered, the minimum value of the range of NER values for some of the routes adopting a photobioreactor is comparable to the NER value obtainable by using raceway ponds. Thus, the present framework proposes a harmonized and comprehensive methodology to compare and contrast technologies for the production of biodiesel from microalgae, and is applied in this paper to identify, with an appreciation of the uncertainty, the most promising combinations of technologies. Highlights • Quantitative, systematic and harmonized assessment of microalgae energy potential. • A step-by-step analysis and overall estimation of energy consumption is given. • A substantial uncertainty on the data in literature has been identified. • The energy consumption uncertainty is quantified and critically discussed. • Derivation of the Net Energy Ratio (NER) for each combination of technologies. [ABSTRACT FROM AUTHOR]

Life cycle assessments of microalgal cultivation systems are often conducted to evaluate the sustainability and feasibility factors of the entire production chain. Unlike widely reported conventional microalgal cultivation systems, the present work adopted a microalgal-bacterial cultivation approach which was upscaled into a pilot-scale continuous photobioreactor for microalgal biomass production into biodiesel from wastewater resources. A multiple cradle-to-cradle system ranging from microalgal biomass-to-lipid-to-biodiesel was evaluated to provide insights into the energy demand of each processes making up the microalgae-to-biodiesel value chain system. Energy feasibility studies revealed positive NER values (4.95–8.38) for producing microalgal biomass but deficit values for microalgal-to-biodiesel (0.14–0.23), stemming from the high energy input requirements in the downstream processes for converting biomass into lipid and biodiesel accounting to 88–90% of the cumulative energy demand. Although the energy balance for microalgae-to-biodiesel is in the deficits, it is comparable with other reported biodiesel production case studies (0.12–0.40). Nevertheless, the approach to using microalgal-bacterial cultivation system has improved the overall energy efficiency especially in the upstream processes compared to conventional microalgal cultivation systems. Energy life cycle assessments with other microalgal based biofuel systems also proposed effective measures in increasing the energy feasibility either by utilizing the residual biomass and less energy demanding downstream extraction processes from microalgal biomass. The microalgal-bacterial cultivation system is anticipated to offer both environmental and economic prospects for upscaling by effectively exploiting the low-cost nutrients from wastewaters via bioconversion into valuable microalgal biomass and biodiesel. [Display omitted] • Algal-to-biodiesel system from new photobioreactor assessed for energy feasibility. • Positive NER values (4.95–8.38) for biomass production at base and best scenarios. • High energy demand from downstream processes lowered overall NER (0.14–0.23). • Lipid extraction solvent process demanded the highest energy requirement at 88–90%. • Residual biomass utilization and pretreatment process reduce overall energy demand. [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]

Ethylic transesterification process for biodiesel production without any chemical or biochemical catalysts at different subcritical thermodynamic conditions was performed using wet animal fat, soybean and palm oils as feedstock. The results indicate that 2 h of reaction at 240 °C with pressures varying from 20 to 45 bar was sufficient to transform almost all lipid fraction of the samples to biodiesel, depending on the reactor dead volume and proportions between reactants. Conversions of 100%, 84% and 98.5% were obtained for animal fat, soybean oil and palm oil, respectively, in the presence of water, with a net energy ration values of 2.6, 2.1 and 2.5 respectively. These results indicate that the process is energetically favorable, and thus represents a cleaner technology with environmental advantages when compared to traditional esterification or transesterification processes. [ABSTRACT FROM AUTHOR]

Microalgae-based biorefineries for the production of renewable biofuels like biodiesel, upgraded bio-oil, biochar, biogas and other high-value chemicals have received great attention in recent decades as potential major sources of energy for the future. Microalgae are a suitable species to produce biodiesel and other high energy density by-products; however, it is questionable whether a net energy gain can be realized or not considering the whole processing chain. In the present study, the energy balances of different algae-based biofuel and bioenergy production technologies are investigated in detail and compared to each other corresponding to a cradle-to-grave overall energetic analysis. The study includes cultivation, harvesting, cell pretreatments (cell disruption, drying, grinding), lipid extraction, transesterification, gasification and hydrothermal liquefaction with bio-oil stabilization and hydroprocessing. The energy consumption and energy gain are estimated for each operational step to determine the net energy ratio (NER, energy output over energy input) for the overall technologies studied. Our detailed investigation enables to detect the most energy consuming unit operation, that is, the bottleneck point(s) of the microalgae-based technologies which should be still improved in the future for the sake of more efficient algae-based biorefineries. The investigation makes also possible to evaluate and compare the different large scale alternatives for biomass transformation. Positive energy balances with a NER value of 1.109 and 1.137 are found in two already existing processes: open raceway ponds and closed photobioreactors, respectively. Our work gives also a detailed algorithm that can be followed at the evaluation of other microalgae-based biorefineries. [ABSTRACT FROM AUTHOR]

Highlights: [•] Wintering cultivation of algae in artificial wastewater was investigated. [•] pH regulation could improve the nutrient removal and biomass productivity. [•] High lipid content and productivity were obtained by regulating pH. [•] Biodiesel yield in the pH-regulated group was 19.44% of dry weight. [•] It is efficient to grow C. zofingiensis in winter by pH regulation using acetic acid. [ABSTRACT FROM AUTHOR]

This study is an experimental determination of the energy return on investment (EROI) for algal biocrude production at a research facility at the University of Texas at Austin (UT). During the period of this assessment, algae were grown at several cultivation scales and processed using centrifugation for harvesting, electromechanical cell lysing, and a microporous hollow fiber membrane contactor for lipid separation. The separated algal lipids represent a biocrude product that could be refined into fuel and the post-extraction biomass could be converted to methane. To determine the EROI, a second-order analysis was conducted, which includes direct and indirect energy flows, but does not include energy expenses associated with capital investments. The EROI for the production process evaluated here was significantly less than 1, however, the majority of the energy consumption resulted from non-optimized growth conditions. While the experimental results do not represent an expected typical case EROI for algal fuels, the approach and end-to-end experimental determination of the different inputs and outputs provides a useful outline of the important parameters to consider in such an analysis. The Experimental Case results are the first known experimental energy balance for an integrated algal biocrude production facility, and as such, are expected to be helpful for setting research and development priorities. In addition to the Experimental Case (based on direct measurements), three analytical cases were considered in this work: (1) a Reduced (Inputs) Case, (2) a Highly Productive Case, and (3) a Literature Model. The Reduced (Inputs) Case and the Highly Productive Case speculate the energy use for a similar system in an improved, commercial-scale production setting. The Literature Model is populated with relevant data that have previously been reported in the literature. For the Experimental Case, Reduced Case, Highly Productive Case, and Literature Model, the estimated second-order EROI was 9.2 × 10, 0.074, 0.22, and 0.35, respectively. These results were dominated by growth inputs (96%, 89%, 87%, and 61% of the total energy requirement, respectively). Furthermore, the EROI was adjusted using quality factors that were calculated according to the price of each input, yielding a quality-adjusted EROI that parallels a partial financial return on investment analysis. For the Experimental Case, the Reduced Case, and the Highly Productive Case, the quality-adjusted EROI was 9.2 × 10, 0.013, and 0.36, respectively. [ABSTRACT FROM AUTHOR]

Abstract: One necessary criterion for a biofuel to be a sustainable alternative to the petroleum fuels it displaces is a positive net energy balance. This study estimated the net energy ratio (NER), net energy balance (NEB), and net energy yield (NEY) of small-scale on-farm production of canola [Brassica napus (L.)] and soybean [Glycine max (L.)] biodiesel in the upper Midwest. Direct and embodied energy inputs based on well-defined system boundaries and contemporary data were used to estimate the energy requirement of crop production, oil extraction, and biofuel processing. The NER of canola biodiesel was 1.78 compared with 2.05 for soybean biodiesel. Canola biodiesel had a NEB of 0.66 MJ MJ−1 of biofuel compared with 0.81 MJ MJ−1 for soybean biodiesel. The NEY of soybean biodiesel was 10,951 MJ ha−1, less than canola biodiesel which had a NEY of 11,353 MJ ha−1. Use of soybean as a biodiesel feedstock was more energetically efficient than canola primarily due to reduced nitrogen fertilizer requirement. In terms of energetic productivity, canola was a more productive biodiesel feedstock than soybean due to its higher oil content. A best-case scenario based on optimal feedstock yields, reduced fertilizer input, and advanced biofuel processing equipment suggested that potential gains in energetic efficiency was greater for canola than soybean. According to our results, small-scale on-farm biodiesel production using canola and soybean can be an energetically efficient way to produce energy for on-farm use. [Copyright &y& Elsevier]

The present article deals with the study of environmental impacts of using biodiesels derived from jatropha, karanja, and neem tree using an energy life-cycle analysis approach. To evaluate the energy consumption during the life cycle of jatropha, karanja, and neem biodiesel as fuel for compression ignition (CI) engine, a cradle-to-grave analysis is carried out. Net energy ratio is calculated for each biodiesel by the ratio of the energy output of the system in the form of fuel energy delivered to the compression ignition engine and the cumulative energy demand of the system. Net energy ratios for jatropha, karanja, and neem biodiesel life cycles are R1 = 1.2325, R2 = 1.6425, and R3 = 1.6479, respectively. Life-cycle energy ratio of biodiesels shows that all the three fuels are renewable. It is concluded from the study that all biodiesels have higher output than inputs in terms of energy. [ABSTRACT FROM AUTHOR]

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]

• Parabolic trough collector used as intensification tool for enhanced biodiesel production. • CaO catalyst packed column reactor is also used in combination. • Temperature reached around 95 °C in 20 min in day time. • Yield up to 95.84% obtained by recirculating batch reactions. • Net energy ratio and energy efficiency indices were analyzed for various conditions. Waste cooking oil was converted to biodiesel using a parabolic trough collector using solar radiations as a heating source and a parabolic trough collector as an intensifier. Calcium oxide (CaO) derived from seashells was used as a catalyst in order to boost the rate of the reaction. Temperatures of almost 95 °C were reached using this collector although the temperature was limited to below 78.4 °C in order to prevent the vaporization of ethanol. The influence of different parameters on the reaction was analyzed. The maximum yield was found to be 95.84%, obtained under conditions of 180 LPH reactant flow rate, 300 rpm stirring speed, 60 minutes reaction time, 9:1 ethanol to oil ratio and 90 cm catalyst bed height. The composition and properties of the biodiesel were found to be in accordance with literature and ASTM and BIS norms. The energy efficiency of the process was analyzed by net energy ratio (NER). The net energy efficiency index (NEEI) was obtained from the ratio of NER of the solar method to the conventional method. NEEI of the process was found to be 4.16, thereby making the process a highly promising method of biodiesel production. [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]