A review on flocculation as an efficient method to harvest energy microalgae: Mechanisms, performances, influencing factors and perspectives
TL;DR: It is argued that the production of microalgae biofuels under potential policy intervention should be carried out in a healthy and sustainable way.
Abstract: The energy demands and costs of harvesting microalgal biomass make it unrealistic and unsustainable for economically feasible microalgal biofuel production Therefore, meticulous exploration of the harvesting processes is essential to identify appropriate harvesting techniques for potentially commercialized microalgal biodiesel production Flocculation may be a superior method when considering harvesting efficiency, economic cost, energy consumption and technical feasibility This review sheds some light on the recent progresses of physical/chemical flocculation and bioflocculation applied in the microalgal biomass harvesting processes Physical flocculation techniques are energy-intensive and require special equipment, creating the cost barrier for microalgal biomass harvesting Magnetic particle flocculation is much more efficient and is also recyclable In contrast, chemical flocculation that involves the application of organic and inorganic flocculants, is now in the limelight The microalgae species applied, the dosages of flocculants as well as flocculation recovery efficiencies are compared and presented in detail in this review In addition, bioflocculation as a harvesting techniques is critically described, in particular the mechanisms of autoflocculation, a promising bioflocculation by co-cultivation of microalgae with microorganisms, are explored This review also disclosed the effects of flocculant application on downstream processes, especially when chemical flocculants are applied This review intends to provide guidance for the long-term adoption of these economically beneficial mature flocculation recovery technologies in the biofuel industry Despite of considerable progress, key challenges such as further reduction of costs and the minimization of downstream product pollution risks in conventional and advanced harvesting techniques, must be addressed This article also suggests the directions for future research in microalgae harvesting and argues that the production of microalgae biofuels under potential policy intervention should be carried out in a healthy and sustainable way
Citations
More filters
TL;DR: In this paper, the authors present the advances in the progress of various flocculation harvesting methods with special emphasis on innovative bio-flocculation, the underlying mechanism of microalgae and floculation, and compared the processes in terms of sustainability, technology readiness, and applications in larger scales.
Abstract: Microalgae have been widely explored because of the diverse number of their worthwhile applications and potential as a source biomass for the production of biofuels and value-added materials. However, downstream techniques have yet to be fully developed to overcome techno-economic barriers. Flocculation is a superior method for harvesting microalgae from growth medium because of its harvesting efficiency, economic feasibility. Various kind of bio-flocculation harvesting methods are consider as attractive low cost and environmentally friendly options and able to harvest >90% biomass. Lipid recovery from microalgal cells is a major barrier for the biofuel industry because of process complexity and algae cell structure. Thus, the pretreatment method is necessary to disrupt the cell walls of microalgae and enhance lipid extraction. Many techniques, including dry methods of extraction, are already being implemented but found out that they are not efficient and cost-effective. Various new wet harvesting strategies have been claimed to extract major lipids in cost-efficient (30% less than conventional) way as wet technologies can eliminate the cost of cell drying and associated instruments. It is necessary to develop new methods which are energy and cost-effective, and environmentally friendlier for the commercialization of biofuels. Therefore, this review presents the advances in the progress of various flocculation harvesting methods with special emphasis on innovative bio-flocculation, the underlying mechanism of microalgae and flocculation. In this study also summarize the recent progress on microalgal oil extraction processes, and comparison was made between the processes in terms of sustainability, technology readiness, and applications in larger scales.
125 citations
TL;DR: In this paper, the effects of fungal-algal cultivation on downstream processing for biofuel production, followed by the practical bioenergy conversion performances are analyzed, and the current challenges and future perspectives about harvesting on a large scale, removal of multiple pollutants and exploration of integrated biorefinery are pointed out systematically.
Abstract: As the third generation biofuel feedstock to confront with energy crisis, microalgae have great potential for the exploration of renewable energy fields, whereas the high cost related to biomass production and harvesting is the main bottleneck to hinder the applications on a large scale. To mitigate the environmental impacts in a sustainable mode, co-culturing filamentous fungi with targeted microalgae is a superior method to efficiently accumulate and harvest the total biomass. This paper serves as a base to review current advances in pelletization of microalgae with fungi for the co-cultivation process. The pellet formation is initially introduced, and then electrostatic interactions, hydrophobic interactions and specific components on cell walls as the main harvesting mechanisms are explored and generalized together with the inclusion of critical affecting parameters for efficiency promotion. Apart from the discussion about biomass harvesting, the latest studies of this co-cultivated technology on wastewater treatment in diverse types associated with corresponding removal mechanisms are analyzed as well. Subsequently, this article emphasizes the effects of fungal-algal cultivation on downstream processing for biofuel production, followed by the practical bioenergy conversion performances. Based on the policies support, the implications of this novel co-cultivation technology have shown the potential in further development. Meanwhile, the current challenges and future perspectives about harvesting on a large scale, removal of multiple pollutants and exploration of integrated biorefinery are pointed out systematically.
90 citations
TL;DR: In this paper, the authors discuss the recent progress of chemical flocculants including organic and inorganic, bio-flocculant and nanomaterials-based processes for biomass recovery.
Abstract: Microalgae have been considered as a potential feedstock for biodiesel production, since its cultivation uses less land than other traditional oil crops and has a higher growth rate. A great challenge is a choice of an effective approach for microalgae biomass recovery and lipid extraction, since the scheduling of these practices are critical and require an economical and environment friendly route. Flocculation has evolved as an efficient and economic approach for harvesting microalgae biomass. This review discussed the recent progress of chemical flocculants including organic and inorganic, bio-flocculants and nanomaterials-based processes for biomass recovery. In addition, the present review describes modifications made in conventional methods for lipid extraction. Several pre-treatment methods such as mechanical, chemical integrated with various solvents and nanoparticles are vastly investigated for lipid extraction. Use of green solvents namely, ionic liquids, supercritical fluids and switchable solvents are also reviewed, with the focus on cleaner biofuel synthesis. Furthermore, the article discusses policies implemented for the advancement in biofuel production, major challenges and considers future directions in microalgae harvesting and lipid recovery processes. This is the first study that extensively compares the recent approaches for biomass and lipid recovery. The present work intended to serve a long-term adaptation of the innovative techniques for copious economic benefit. Thus, this review emphasizes on advanced techniques that influence the microalgae biomass separation and cellular disruption for proficient lipid removal from microalgae, which deliberates towards the development of sustainable microalgae biofuel and heighten the bio-economy strategy.
90 citations
TL;DR: In this paper, the authors summarized the current development of nutrients removal and mutualistic interaction using microalgae-bacteria consortia, and provided the ongoing challenges and future developmental directions for better converting nitrogen and phosphorus wastewater into bioenergy.
75 citations
TL;DR: An approach in searching for biopolymer flocculants sources, flocculation mechanisms, test methods, and factors affecting this process are presented, which may be an indication to look for safer alternatives compared to synthetic polymers.
Abstract: Polymer flocculants are used to promote solid–liquid separation processes in potable water and wastewater treatment. Recently, bio-based flocculants have received a lot of attention due to their superior advantages over conventional synthetic polymers or inorganic agents. Among natural polymers, polysaccharides show many benefits such as biodegradability, non-toxicity, ability to undergo different chemical modifications, and wide accessibility from renewable sources. The following article provides an overview of bio-based flocculants and their potential application in water treatment, which may be an indication to look for safer alternatives compared to synthetic polymers. Based on the recent literature, a new approach in searching for biopolymer flocculants sources, flocculation mechanisms, test methods, and factors affecting this process are presented. Particular attention is paid to flocculants based on starch, cellulose, chitosan, and their derivatives because they are low-cost and ecological materials, accepted in industrial practice. New trends in water treatment technology, including biosynthetic polymers, nanobioflocculants, and stimulant-responsive flocculants are also considered.
74 citations
Cites background from "A review on flocculation as an effi..."
...The flocculation process and its effectiveness are influenced by many factors, such as the chemical structure and properties (including charge) of both the removed substance and flocculant (in the case of polymers important is also average molecular weight and its distribution), their concentration, environment pH, ionic strength, temperature, rate of mixing, and mechanism of the process [5,57,64]....
[...]
References
More filters
TL;DR: In this article, the authors reviewed the technologies underpinning microalgae-to-bio-fuels systems, focusing on the biomass production, harvesting, conversion technologies, and the extraction of useful co-products.
Abstract: Sustainability is a key principle in natural resource management, and it involves operational efficiency, minimisation of environmental impact and socio-economic considerations; all of which are interdependent. It has become increasingly obvious that continued reliance on fossil fuel energy resources is unsustainable, owing to both depleting world reserves and the green house gas emissions associated with their use. Therefore, there are vigorous research initiatives aimed at developing alternative renewable and potentially carbon neutral solid, liquid and gaseous biofuels as alternative energy resources. However, alternate energy resources akin to first generation biofuels derived from terrestrial crops such as sugarcane, sugar beet, maize and rapeseed place an enormous strain on world food markets, contribute to water shortages and precipitate the destruction of the world's forests. Second generation biofuels derived from lignocellulosic agriculture and forest residues and from non-food crop feedstocks address some of the above problems; however there is concern over competing land use or required land use changes. Therefore, based on current knowledge and technology projections, third generation biofuels specifically derived from microalgae are considered to be a technically viable alternative energy resource that is devoid of the major drawbacks associated with first and second generation biofuels. Microalgae are photosynthetic microorganisms with simple growing requirements (light, sugars, CO 2 , N, P, and K) that can produce lipids, proteins and carbohydrates in large amounts over short periods of time. These products can be processed into both biofuels and valuable co-products. This study reviewed the technologies underpinning microalgae-to-biofuels systems, focusing on the biomass production, harvesting, conversion technologies, and the extraction of useful co-products. It also reviewed the synergistic coupling of microalgae propagation with carbon sequestration and wastewater treatment potential for mitigation of environmental impacts associated with energy conversion and utilisation. It was found that, whereas there are outstanding issues related to photosynthetic efficiencies and biomass output, microalgae-derived biofuels could progressively substitute a significant proportion of the fossil fuels required to meet the growing energy demand.
4,432 citations
TL;DR: This review presents recent advances in microAlgal cultivation, photobioreactor design, and harvesting technologies with a focus on microalgal oil (mainly triglycerides) production and aims to provide useful information to help future development of efficient and commercially viable technology for microalgae-based biodiesel production.
1,662 citations
TL;DR: The main conclusions are that the biochemical composition of the biomass influences the economics, in particular, increased lipid content reduces other valuable compounds in the biomass; the “biofuel only” option is unlikely to be economically viable; and among the hardest problems in assessing the economics are the cost of the CO2 supply and uncertain nature of downstream processing.
Abstract: Following scrutiny of present biofuels, algae are seriously considered as feedstocks for next-generation biofuels production. Their high productivity and the associated high lipid yields make them attractive options. In this review, we analyse a number aspects of large-scale lipid and overall algal biomass production from a biochemical and energetic standpoint. We illustrate that the maximum conversion efficiency of total solar energy into primary photosynthetic organic products falls in the region of 10%. Biomass biochemical composition further conditions this yield: 30 and 50% of the primary product mass is lost on producing cell protein and lipid. Obtained yields are one third to one tenth of the theoretical ones. Wasted energy from captured photons is a major loss term and a major challenge in maximising mass algal production. Using irradiance data and kinetic parameters derived from reported field studies, we produce a simple model of algal biomass production and its variation with latitude and lipid content. An economic analysis of algal biomass production considers a number of scenarios and the effect of changing individual parameters. Our main conclusions are that: (i) the biochemical composition of the biomass influences the economics, in particular, increased lipid content reduces other valuable compounds in the biomass; (ii) the “biofuel only” option is unlikely to be economically viable; and (iii) among the hardest problems in assessing the economics are the cost of the CO2 supply and uncertain nature of downstream processing. We conclude by considering the pressing research and development needs.
1,128 citations
TL;DR: This paper presents an in-depth discussion and consideration of the factors that need to be addressed for optimum performance of this technology.
1,125 citations
TL;DR: In this paper, the authors discuss the technology and production platforms for development and creation of different valuable consumer products from microalgal biomass, including triglycerides which can be converted into biodiesel.
Abstract: Microalgae biotechnology has recently emerged into the lime light owing to numerous consumer products that can be harnessed from microalgae. Product portfolio stretches from straightforward biomass production for food and animal feed to valuable products extracted from microalgal biomass, including triglycerides which can be converted into biodiesel. For most of these applications, the production process is moderately economically viable and the market is developing. Considering the enormous biodiversity of microalgae and recent developments in genetic and metabolic engineering, this group of organisms represents one of the most promising sources for new products and applications. With the development of detailed culture and screening techniques, microalgal biotechnology can meet the high demands of food, energy and pharmaceutical industries. This review article discusses the technology and production platforms for development and creation of different valuable consumer products from microalgal biomass.
852 citations