This review discusses anaerobic production of methane, hydrogen, ethanol, butanol and electricity from microalgal biomass. The amenability of microalgal biomass to these bioenergy conversion processes is compared with other aquatic and terrestrial biomass sources. The highest energy yields (kJ g1 dry wt. microalgal biomass) reported in the literature have been 14.8 as ethanol, 14.4 as methane, 6.6 as butanol and 1.2 as hydrogen. The highest power density reported from microalgal biomass in microbial fuel cells has been 980 mW m2. Sequential production of different energy carriers increases attainable energy yields, but also increases investment and maintenance costs. Microalgal biomass is a promising feedstock for anaerobic energy conversion processes, especially for methanogenic digestion and ethanol fermenta- tion. The reviewed studies have mainly been based on laboratory scale experiments and thus scale-up of anaerobic utilization of microalgal biomass for production of energy carriers is now timely and required for cost-effectiveness comparisons.
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Background: Nutritional well-being is the prerequisite condition for a sustainable improvement in human wel- fare. Human gut microbiota plays a magnificent role in balancing the condition of metabolic syndrome man- agement. Currently, the gut microbiome mediated immune system is gaining attention for the treatment of several health ailments such as diabetes, gastrointestinal disorders, and malnourishment. Bioactive compounds from marine polysaccharides from seaweeds are found beneficial for enhancing the activity of gut microbes. Scope and approach: There were limited reviews in recent times to discuss the updates on extraction, purification and biological activities of dietary fibers using non-conventional methods. The present review inspects on the proximal and structural composition of seaweed polysaccharides and their methods of extraction and pur- ification aspects. It also focuses on the immune modulating mechanisms of prebiotic-probiotic synergetic in- teraction by stimulating beneficial gut microbial activity and by the production of short-chain fatty acids. The mutual relationship between prebiotics and probiotics that leads to a healthy gut was targeted in the present review.
Key findings and conclusions: Marine seaweeds polysaccharides are the untapped bioresources to be explored for its biotherapeutic properties of dietary fibers. The practical complications on extracting polysaccharides by a single technique could be overcome by adopting the strategy of utilizing combinatorial extraction and pur- ification techniques. Its prebiotic effect aids in the enhancement of gut microbial activity by exhibiting the properties of non-digestibility, fermentability, and pathogen inhibition potential. The impending benefits of dietary fiber from seaweed polysaccharides as prebiotics for formulating functional food ingredients along with probiotic microbes to exhibit immunomodulation applications. Therefore, intended human clinical trials should be carried out to evaluate and discover the probiotic-prebiotic relationship in the human gut, which could step out the research to the next level in the medicinal world.
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Seaplants (a better alternative to the misnomer “Seaweeds”), by all means, are “future plants”; they have been projected as the future viand for ever-increasing human populations, viable and sustainable source for biofuel without disturbing global food scenario, as potential candidates for carbon capture and sequestration that is considered as a practical remedy for global warming, and they have a number of pharmaceutical, industrial and biotechnological applications. However, information on its cultivation methods or life history remain obscure to a majority of marine botanists. While life histories of seaweeds have traditionally been an exotic topic for specialists-language of which is ciphered with scientific jargons incomprehensible to general scientific audience, its agronomy had been a trade secret for coastal communities in East Asian countries, especially Japan, the Philippines and Indonesia. In this up-to-date illustrated review, current scientific understanding on the life-histories of agronomically pertinent seaweeds are presented in a fashion akin to popular science journalism with an overview of major coastal and offshore seaweed mariculture techniques, presented with the aid of clear-tounderstand illustrations. Also discussed in this report are recent advances in the algal natural products; including uses in hydrocolloid and pharmaceutical industries, Integrated Multi Trophic Aquaculture, energy production, environmental impacts of the seafarming and its counter measures, before concluding with an overview of future research avenues.
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While some investigators have attempted to use isozyme electrophoresis to gain information on the genetics of brown algae, most have reported unsatisfactory results. Through exhaustive screening and modification of sample preparation techniques, gel and tray buffers systems, plus staining recipes, we have developed procedures that consistently provide scorable bands for over 20 enzyme systems in several laminarian algae. We have used our procedures to examine geographically diverse populations of Laminaria saccharina and L. longicruris, as well as L. digitata, L. groenlandica, Agarum cribrosum, Alaria esculenta, Chorda tomentosa, and Macrocystis pyrifera. Overall, these kelp species seem to have an extremely low degree of enzyme solymorphism, both within and between populations. While some rare alleles occurred in several enzyme systems, only 3–5 loci were found to be polymorphic. Our results are consistent with the few reported studies that have used molecular genetic techniques to look at the intraspecific variability of laminarian algae. We suggest that at the species level the Laminariales, and perhaps other groups of brown algae, are genetically extremely conservative as compared to other divisions of plants. We further suggest that isozyme electrophoresis provides a quick and useful tool for algal population genetic studies.
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Microalgae have been developed as promising candidates for bioenergy production, coupled with answering challenges related to water pollution and global warming. When combined with wastewater, microalgal biomass production could be freed from a strong dependence on freshwater and chemical nutrients, as well as achieve the additional advantage of wastewater reclamation. However, despite those dual benefits, certain limitations on the growing of algae in wastewater remain to be resolved, including the inevitable presence of bacteria in waste- water, which influences biomass productivity and quality in various ways. Pointing at microalgal-bacterial re- lationships, this study provides an updated review of the application of microalgal-bacterial consortia (MABC) to benefit biomass yield and harvest, and in wastewater remediation, focusing on the main interactions established between the microorganisms integrated within MABC and the factors influencing the behaviours of MABC. The challenges faced by the MABC biotechnology are also discussed, which are primarily rooted in undesirable bacteria that parasitically eat microalgal products and inhibit algal growth through nutrient competition, lysate exudation, or reducing the algal resistance to biotic stress. However, there is a lack of systematic studies on maintaining stable and effective operation of MABCs for wastewater cultivation and high-value bioproduct generation. Knowledge gaps are identified as including systematic information about the responses of MABC to culture conditions and wastewater-borne bacterial communities, and the metabolic mechanisms underpinning the interactions between algae and bacteria in wastewater. Further research focuses and methodologies are proposed in this review, making full use of the advent of omics and computational technology.
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The optimised reduction of dissolved nutrient loads in aquaculture effluents through bioremediation requires selection of appropriate algal species and strains. The objective of the current study was to identify target species and strains from the macroalgal genus Ulva for bioremediation of land-based aquaculture facilities in Eastern Australia. We surveyed land-based aquaculture facilities and natural coastal environments across three geographic locations in Eastern Australia to determine which species of Ulva occur naturally in this region and conducted growth trials at three temperature treatments on a subset of samples from each location to determine whether local strains had superior performance under local environmental conditions. DNA barcoding using the markers ITS and tufA identified six species of Ulva, with U. ohnoi being the most common blade species and U. sp. 3 the most common filamentous species. Both species occurred at multiple land- based aquaculture facilities in Townsville and Brisbane and multiple strains of each species grew well in culture. Specific growth rates of U. ohnoi and U. sp. 3 were high (over 9% and 15% day21 respectively) across temperature treatments. Within species, strains of U. ohnoi had higher growth in temperatures corresponding to local conditions, suggesting that strains may be locally adapted. However, across all temperature treatments Townsville strains had the highest growth rates (11.2– 20.4% day21) and Sydney strains had the lowest growth rates (2.5–8.3% day21). We also found significant differences in growth between strains of U. ohnoi collected from the same geographic location, highlighting the potential to isolate and cultivate fast growing strains. In contrast, there was no clearly identifiable competitive strain of filamentous Ulva, with multiple species and strains having variable performance. The fast growth rates and broad geographical distribution of U. ohnoi make this an ideal species to target for bioremediation activities at land-based aquaculture facilities in Eastern Australia.
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The interest in algae based biofuels and chemicals has increased over the past few years because of their potential to reduce the dependence on petroleum-based fuels and chemicals. Algae is touted to be the most suitable and sustainable feedstock for producing green energy as the whole process is carbon—neutral in nature and can also be utilized for environment cleaning applications. This review article mainly focuses on how algae can be used as an efficient and economically viable biorefinery feedstock. An effective biorefinery using algae can only be constructed through its integration with other industries. To make sense of the algal biorefinery concept, there is a need to establish a proper connection between the various input and output streams of the products, as well as the services to be provided by the participating industries. Also highlighted in this article, is the entire spectrum of energy and non energy products that can be obtained using algal biomass as the raw material.
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Interest is growing in the production of biohydrogen from algae through dark fermentation, as alternative to fossil fuels. However, one of the limiting steps of biohydrogen production is the conversion of polymeric carbohydrates into monomeric sugars. Thus, physical, chemical and biological pretreat- ments are usually employed in order to facilitate carbohydrates de-polymerization and enhancing biohydrogen production from algae. Considering the overall process, biohydrogen production through dark fermentation leads generally to negative net energy balances of the difference between the energy produced as biohydrogen and the direct ones (heat and electricity) consumed to produce it. Thus, to make the overall process economically feasible, dark fermentation of algae must be integrated in a biorefinery approach, where the outlets are valorized into bioenergy or value added biomolecules.The present study reviews recent findings on pretreatments and biohydrogen production through dark fermentation of algae looking at the perspectives of integrating side streams of dark fermentation from algal biomass, according to a biorefinery approach.
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Background: A wide range of conventional and non-conventional technologies have been employed to extract a wide range of bioactive compounds from the complex matrices of seaweeds. Green extraction technologies are increasingly employed to improve extraction efficiencies.
Scope and approach: The objective of this review was to outline various approaches employed for the extraction of bioactives from seaweeds. This review covers various pretreatment methods generally employed prior to extraction, and their combinations with conventional and green extraction technologies. Novel technologies which can be employed with or without pretreatments to improve existing processes are also discussed.
Key findings: The role of pretreatments is of utmost importance and have significant impacts on the quality and quantity of target compounds. Combinations of different cell disruption technologies and extraction methods can enhance the extractability of compounds with higher purity and contribute towards improved process efficiency.
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Cultivated kelps (brown algae) are a sustainable biomass resource and a potential feedstock for conversion to biofuels and chemicals. Due to seasonal variations, and a short period with optimal biomass composition, preservation and storage of the biomass is required for a year-round operation of a seaweed processing plant. For use of the biomass as a carbon source for fermentation to biofuels, only low-cost preservation methods are feasible. Preservation of Saccharina latissima (sugar kelp) by sulphuric and formic acid has been evaluated as a method to maintain the fermentable carbohydrates laminaran and mannitol. In milled biomass, stored anaerobically for up to 6.5 months at different pH values, laminaran and mannitol were efficiently preserved in samples stored at pH below 3.7, obtained by addition of sulphuric acid. When a combination of sulphuric and formic acid was used, no sugar loss could be detected up to pH 4. The content of free glucose increased during the storage period in the well-preserved samples without loss of sugars. The free glucose levels were highest at the highest storage pH, providing strong evidence for the presence of endogenous β- glucanases that hydrolyse laminaran to glucose. Our work was primarily aimed at preservation of the biomass for application as a carbon source for fermentation. However, the method will be equally suited for other applications of the biomass, such as extraction of valuable compounds for use in functional food, feed or other areas.
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