Summary
Biofuel has emerged as an alternative source of energy to reduce the emissions of greenhouse gases in the atmosphere and combat global warming. Biofuels are classified into first, second, ...third and fourth generations. Each of the biofuel generations aims to meet the global energy demand while minimizing environmental impacts. Sustainability is defined as meeting the needs of the current generations without jeopardizing the needs of future generations. The aim of sustainability is to ensure continuous growth of the economy while protecting the environment and societal needs. Thus, this paper aims to evaluate the sustainability of these four generations of biofuels. The objectives are to compare the production of biofuel, the net greenhouse gases emissions, and energy efficiency. This study is important in providing information for the policymakers and researchers in the decision‐making for the future development of green energy. Each of the biofuel generations shows different benefits and drawbacks. From this study, we conclude that the first generation biofuel has the highest biofuel production and energy efficiency, but is less effective in meeting the goal of reducing the greenhouse gases emission. The third generation biofuel shows the lowest net greenhouse gases emissions, allowing the reduction of greenhouse gases in the atmosphere. However, the energy required for the processing of the third generation biofuel is higher and, this makes it less environmentally friendly as fossil fuels are used to generate electricity. The third and fourth generation feedstocks are the potential sustainable source for the future production of biofuel. However, more studies need to be done to find an alternative low cost for biofuel production while increasing energy efficiency.
• First generation biofuel has the highest biofuel yield and energy efficiency. However, the production of the biofuel opposed many sustainable development goals.
• Third and fourth generation biofuels show potential as a sustainable future green energy.
• Methods of lipid extraction of microalgae biofuel and environmental consequences of the fourth generation biofuel should be further explored.
Hydrogen is a renewable gas, efficient to produce energy that makes it a suitable alternative and effective solution for a carbon-free environment. Unlike other fossil fuels, combustion of hydrogen ...does not produce toxic compounds, such as greenhouse gases, carbon monoxide, hydrocarbons, etc., resulting in less environmental pollution. Agro-industrial residues contain several lignocelluloses that favor the growth of microorganisms to produce valuable products such as hydrogen. Of the diverse techniques in hydrogen production, bioconversion proves to be an efficient method in permuting agro-industrial residues into hydrogen. This review provides detailed information on the bioconversion processes and factors involved in hydrogen production from agro-industrial residues including different fermentation processes such as dark fermentation and photo-fermentation, and fuel cell systems such as microbial electrolysis cell and microbial fuel cell. Different pretreatment techniques to enhance the availability of lignocellulose for hydrogen production have been elaborated in this review. Various factors including pH, temperature and nutrient composition of feed, affecting the production efficiency and purity of the products during fermentation have been discussed.
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•Agro-industrial residues are suitable feedstock for hydrogen production.•Difficulties and future perspectives of biohydrogen conversion are discussed.•Coupling of dark fermentation with MEC increases net energy gain.•Integration of MEC and MFC shows potential over conventional techniques.
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•Effective conditions and upscaling of LBF for lipid extraction were investigated.•74.44 % lipid was recovered with ethanol and (NH4)2SO4 at 20 min flotation time.•Fatty acid methyl ...ester of C5:0, C12:0 and C20:0 were detected using GC-FID.•500 mL LBF system recovered higher lipid yield by 1.68 % compared to 50 mL.
Exponential increase of greenhouse gases has raise a global concern. More than a quarter of the greenhouse gases (e.g. carbon dioxide) are released from the transportation sector driven by the burning of vehicle fuel. Biofuel was introduced to limit the emission of greenhouse gases due to its potential to cut the emissions by up to 86 %. Microalgae have shown to be a suitable biomass for the production of biofuel because they are rich in biomolecules such as lipid. This study focuses on the extraction of natural lipid from Chlorella sorokiniana CY-1 for biodiesel production using liquid biphasic flotation (LBF) system. LBF system is a novel environmentally friendly method used for biomolecules extraction from microalgae. It is an integration of aqueous two-phase system with mass transfer mode of solvent sublation that eases the transfer of biomolecules from the bottom phase to the top phase. The study unveils the potential of the LBF system to recover up to 74.44 % lipid using 100 % (v/v) ethanol and ammonium sulphate in 20 min time. GC-FID confirmed the successful extraction of lipid from the microalgae. Three peaks of fatty acid methyl ester, mainly from the middle chains (C5:0) (C12:0) and (C20:0) were observed, expending new opportunity for microalgae biodiesel technology.
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•Microalgae are alternative source of energy, food and essential human needs.•Cultivation and processing of valuable biomolecules from microalgae are expensive.•Wastewater is an ...alternative medium for the cultivation of microalgae.•PVDF and polysulfone membrane recovers the highest amount of biomolecule.•Liquid biphasic flotation system is a promising biomolecule extraction technology.
Microalgae has been utilised in various applications ranging from pharmaceuticals, cosmetics, supplements, liquid fuels as well as food source for human and animals. The upscaling of microalgae production to meet the demand for global consumption has yet to be realized as there are many factors to be considered in the upstream and downstream processing of microalgae biomass. For upstream processing, the high cultivation cost which poses a major setback can be reduced by cultivating the microalgae in wastewater sources, which are widely available and at the same time can lead to bioremediation of these waste sources. The contents of microalgae biomass from wastewater can also be used to produce the desired bioproducts. For downstream processing, the efficiency of traditional processes has long hindered the progression of microalgae to products, hence, the discovery of advanced technologies which can yield higher productivity and good quality products have been studied and upscale to a pilot scale to verify its feasibility. Separation techniques like liquid biphasic system and membrane separation are potential in achieving high yield and separation efficiency to recover valuable products from microalgae and these processes are environmentally friendly and cost-effective. The insights from cultivating microalgae in wastewater sources and the promising technologies to convert them into useful bioproducts will be beneficial to the developments of future upstream and downstream processes.
The increase in global temperature calls for ambitious action to reduce the release of greenhouse gases into the atmosphere. The transportation sector contributes up to 25% of the total emissions ...released, mainly from the burning of vehicle fuel. Therefore, scientists from all around the world are focusing on finding a sustainable alternative to conventional vehicle fuel. Biofuel has attracted much attention, as it shows great potential for the replacement of traditional fossil fuels. However, the main bottlenecks of biofuel are the ongoing controversial conflict between food security with biofuel production. Therefore, this study focuses on a sustainable extraction of lipids from microalgae for the production of biofuel using a liquid biphasic flotation system coupled with sugaring-out method. This is the first study to combine the methods of liquid biphasic flotation system with the sugaring-out technique. It represents a holistic study of optimum and effective conditions needed to extract lipids from the system and to understand the reliability of sugar solution as the agent of cell disruption. At the 15-min flotation time, 150 g/L of fructose solution with a 1:2 mass separating agent-acetonitrile ratio successfully extracted up to 74% of lipid from Chlorella sorokiniana CY-1. Two types of fatty acid methyl esters were recovered from the study, with C5:0 being the main component extracted.
The present research aims to study the long-term impacts of soil extractable carbohydrate content from the conversion of forest to paddy field, using three environmentally friendly methods: ...ultrasound assist (37 Hz/30 min), hot water (80 °C/4 h), and cold water (25 °C/30 min). Soil samples collected at the depth of 0–15 cm from natural forest, rice paddy, and border area were extracted by distilled water at the ratio 1:10 (soil: water). Contents of soil organic carbon (SOC) and extracted carbohydrate (ECH) in the natural forest and rice paddy were similar, and higher than in border area by 50%. Results showed the highest content of ECH was extracted using hot water (304–691 mg.Carbohydrate/kg soil, 4% of SOC), followed by ultrasound (102–305 mg.Carbohydrate/kg soil, 1.7% of SOC), and the lowest amount addressed to cold-water extraction (65–252 mg.Carbohydrate/kg soil, 1.2% of SOC). The ECH/SOC ratios in three soil types were the same and ranged from 0.9% to 4.2%. We conclude the long-term conversion of forest to rice paddy maintain both SOC and ECH, furthermore, hot water extraction at 80 °C/4 h is the optimum method for extraction of carbohydrate using non-chemical solvents.
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•Effects of soil carbohydrate content in long-term rice paddy cultivation.•First study to compare three sustainable methods of soil carbohydrate extraction.•Long-term rice paddy cultivation does not affect carbohydrate content in the soil.•Hot water extraction method of 80 °C/4 h showed the highest soil carbohydrate.
