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Microalgae are considered to be the feedstock for third‐generation biofuels but there are still no commercial applications of microalgae biomass. This is due to the costly harvesting process, resulting from their specific characteristics such as small cell sizes, negatively charged surfaces, and stable dispersion in culture broths. Chitosan derived from crustacean shells, as a highly efficient and non‐toxic flocculant for the harvesting of microalgae, can simultaneously achieve value‐added recycling of shell wastes and efficient flocculation of microalgal biomass. Shell‐derived chitosan is a biopolymer with a high economic value, which might promote shell waste resource utilization. Its application for microalgae harvesting also has no effect on the downstream process for biodiesel production. More than 90% of microalgal biomass can be harvested under certain conditions using chitosan as the flocculant, demonstrating a strong potential for practical application in future. The application of chitosan to flocculate microalgae still has some limitations, and efforts should be made regarding the enhancement of cost‐effectiveness, improvement of harvesting processes, scalability of practical application, and implementation of supporting policies. The contribution of this study lies in the combination of chitosan production from crustacean shell wastes and its application in microalgae harvesting, which can realize the value‐added recycling of shell wastes and efficient flocculation of microalgal biomass. © 2021 Society of Industrial Chemistry and John Wiley & Sons Ltd [ABSTRACT FROM AUTHOR]

In response to the energy crisis, global warming and climate changes, microalgae have received increasingly global attention as a renewable, alternative and sustainable source for the production of biodiesel. Much original research regarding microalgal biodiesel production has been reported. However, microalgal biodiesel faces plenty of challenges that current cultivation and biodiesel conversion is economically unfeasible for industrial applications on a large scale. This perspective paper first briefly discusses the latest advances in liquid transportation biodiesel production from microalgal biomass, including microalgal growth, biomass harvesting and drying, lipid extraction and biodiesel conversion. Subsequently, strategies for the future development of microalgal biodiesel have been proposed and discussed, in an attempt to reduce the cost gap. From the microalgal biodiesel production chain perspective, genetic and metabolic engineering, isolation of suitable species, high-efficiency bioreactor development, efficient culturing system development, optimal harvest process design, high-efficiency lipid extraction and transesterification method development will have critical roles to play. It is worthy of note that the increase of the outcome credits can also realize the reduction of the economic gap, and the main measures include appropriate glycerol recovery and reutilization, integration with wastewater treatment and CO 2 mitigation together with microalgal biorefinery for the production of multiple co-products with high values. Finally, concluding remarks are put forward. [ABSTRACT FROM AUTHOR]

Microalgal growth requires a substantial amount of chemical fertilizers. An alternative to the utilization of fertilizer is to apply biogas slurry produced through anaerobic digestion to cultivate microalgae for the production of biofuels. Plenty of studies have suggested that anaerobic digestate containing high nutrient contents is a potentially feasible nutrient source to culture microalgae. However, current literature indicates a lack of review available regarding microalgal cultivation with biogas slurry for the production of biofuels. To help fill this gap, this review highlights the integration of digestate nutrient management with microalgal production. It first unveils the current status of microalgal production, providing basic background to the topic. Subsequently, microalgal cultivation technologies using biogas slurry are discussed in detail. A scale-up scheme for simultaneous biogas upgrade and digestate application through microalgal cultivation is then proposed. Afterwards, several uncertainties that might affect this practice are explored. Finally, concluding remarks are put forward. [ABSTRACT FROM AUTHOR]

The syngas derived from a pyrolysis and gasification process was used as a reducing agent to produce iron ore pellets. The reduction temperature was kept between 1123 K and 1323 K, and the time was set 30 min. Results showed that the reducibility increased from 88.1% at 1123 K to 99.95% at 1323 K. The reduction rate increased with increasing reduction temperature. Further, the reaction rate in the early stage was higher than that in the later stage. The X-ray diffraction (XRD) and metallographic microscope analyses of the oxidized pellets and direct reduced iron (DRI) products showed that, the reduction process followed the reaction scheme: Fe 2 O 3 → FeO → Fe. A kinetics analysis indicated that, the reduction rate was controlled by an interfacial chemical reaction with syngas and that the activation energy was 104.76 kJ/mol. The effect of syngas as the reducing gas on the reduction of iron ore pellets was similar to that of natural gas. The use of biomass during DRI production can eliminate CO 2 emissions, energy crisis, and climate change. [ABSTRACT FROM AUTHOR]

In response to the energy crisis, global warming and climate change, microalgae have received a lot of attention as a promising feedstock for the production of biofuels. However, microalgal biofuels are still unaffordable due to low productivity and their substantial requirements in capital investment and operation costs. Much original research regarding the various microalgal cultivation strategies has been reported, in an attempt to promote microalgal biofuel production. However, current literature indicates the fragmented nature of information available regarding the strategies for the improvement of microalgal production for biofuel conversion. From a systematic perspective, this review highlights the main microalgal cultivation strategies for the achievement of improved biomass and biofuel productivity. It first discloses the current state of microalgal production as a biofuel feedstock, giving general introduction to the topic. Subsequently, it summarizes the current microalgae cultivation technology. Microalgal cultivation strategies are then discussed systematically, including integration with wastewater treatment and CO2 mitigation, batch vs. semi-continuous vs. continuous culture, two-stage continuous cultivation, co-culture, stress culture, and microalgal cultivation with harvest water recycling. Finally, concluding remarks are put forward. [ABSTRACT FROM AUTHOR]

From a sustainability perspective, the potential risks associated with microalgae production for biofuel extraction will be investigated in this paper, including the environmental, economic, social and cultural dimensions. Environmentally, four main concerns are mapped out: first, there are potential water safety risks, such as water resource abuse, water pollution and groundwater recharge deficiency; second, unreasonable construction will lead to land-use overexpansion, land pollution and service expectancy reduction; third, microalgae production may exert a detrimental effect on the local ecosystem, causing algal blooms and biological invasion; finally, microalgae might emit unexpected greenhouse gases [nitrogen oxides (NO x ), methane (CH4)] and ammonia (NH3). From an economic risk standpoint, microalgae production requires an overwhelming investment due to the expensive start-up and operation. Socially, contaminant discharge will threaten the health of local animals and people. Moreover, the safety effects of genetically modified algae may not be immediately apparent or known. In addition, over time, microalgae may become a medium for mosquitoes to spread disease. From a cultural point of view, it requires time for people in developing countries to adapt algal oil to their daily life as an alternative to conventional fossil fuels. Furthermore, personnel changes in the workforce may harm existing cultural structures, and landscape aesthetics may be affected by system construction. Taking the above challenges into consideration, efficient government policies, proactive company behaviours and positive public participation will play an important role in minimising or even eliminating these potential risks. [ABSTRACT FROM AUTHOR]

The development of clean and renewable biofuels has been of wide concern on the topic of energy and environmental issues. As a kind of biomass energy with great application prospects, microalgae have many advantages and are used in the fields of environmental protection and biofuels as well as food or feed production for humans and animals. However, the high cost of microalgae harvesting is the main bottleneck of industrial production on a large scale. Self-flocculation is a cost-efficient and promising method for harvesting microalgal biomass. This article briefly describes the current commonly used technology for microalgae harvesting, focusing on the research progress of self-flocculation. This article explores the relative mechanisms and influencing factors of self-flocculation and discusses a proposal for the integration of algae cultivation and harvesting as well as the co-cultivation of algae and bacteria in an effort to provide a reference for microalgae harvesting with high efficiency and low cost. [ABSTRACT FROM AUTHOR]

Background: Microalgal biomass harvesting using traditional chemicals is costly for the production of biofuels, hindering the scale-up process of the technology. Thus, the search for a cost-effective microalgal harvesting method is extremely important. Using chitosan as a natural flocculant to harvest microalgal biomass seems to be an efficient and convenient solution. Although microalgal biomass flocculation by chitosan has been reported in some previous studies, literature on the harvesting of microalgae C. vulgaris biomass using such polymer is scanty. In addition, there is limited information available on whether the usage of chitosan during the harvesting will affect downstream lipid extraction. Still, whether microalgae can be re-grown with the spent medium after chitosan flocculation is still unknown. Results: In this study, microalgal biomass harvesting using chitosan as a natural flocculant and aluminum sulfate as a traditional flocculant was compared and evaluated. Optimal doses and effects on biomass sedimentation, spent medium recycling and lipid extraction were investigated. The results showed that the optimal doses for chitosan and aluminum sulfate to achieve more than 90% biomass recovery were 0.25 and 2.5 g/L, respectively. The sedimentation time of 10 min was found to be the most appropriate to remove over 90% biomass from culture. The spent medium after chitosan flocculation could be potentially recycled for the re-cultivation of microalgae, which demonstrated robust growth in comparison with those grown in the recycled medium from aluminum sulfate flocculation. The lipid content of microalgae harvested by chitosan reached 32.9, 4.6% higher than that of those harvested by aluminum sulfate, indicating that the application of the natural flocculant would not impact the downstream extraction of microalgal lipids. Conclusion: The results herein presented, demonstrated that chitosan is applicable for microalgal harvesting during the upscaling process. Flocculation method developed by using chitosan as a natural flocculant is a worthy microalgal harvesting method for microalgae-based biofuel production. There is hope that chitosan can be reasonably and technically realistically applied in a full-scale process for the harvesting of microalgal biomass. [ABSTRACT FROM AUTHOR]

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. Image 1 • Filamentous fungi can entrap microalgae to form co-pellets. • Co-cultivation achieves high efficiency in biomass harvesting. • Pollutants in wastewater are efficiently removed by fungal-algal pellets. • Filamentous fungi may cause positive effects on the total biofuel production. • Fungal-algal pellets have enhanced the feasibility on large-scale applications. [ABSTRACT FROM AUTHOR]