Review of the harvesting and extraction program within the National Alliance for Advanced Biofuels and Bioproducts

Extraction methods of algae oils for the production of third generation biofuels - A review

Microalgae are the main source of third-generation biofuels because they have a lipid content of 20-70%, can be abundantly produced and do not compete in the food market besides other benefits. Biofuel production from microalgae is a promising option to contribute for the resolution of the eminent crisis of fossil energy and environmental pollution specially in the transporting sector. The choice of lipid extraction method is of relevance and associated to the algae morphology (i.e., rigid cells). Therefore, it is essential to develop suitable extraction technologies for economically viable and environment-friendly lipid recovery processes with the aim of achieving a commercial production of biofuels from this biomass. This review presents an exhaustive analysis and discussion of different methods and processes of lipid extraction from microalgae for the subsequent conversion to biodiesel. Physical methods based on the use of supercritical fluids, ultrasound and microwaves were reviewed. Chemical methods using solvents with different polarities, aside from mechanical techniques such as mechanical pressure and enzymatic methods, were also analyzed. The advantages, drawbacks, challenges and future prospects of lipid extraction methods from microalgae have been summarized to provide a wide panorama of this relevant topic for the production of economic and sustainable energy worldwide.

Innovation in lignocellulosics dewatering and drying for energy sustainability and enhanced utilization of forestry, agriculture, and marine resources - A review

Efficient utilization of forestry, agriculture, and marine resources in various manufacturing sectors requires optimizing fiber transformation, dewatering, and drying energy consumption. These processes play a crucial role in reducing the carbon footprint and boosting sustainability within the circular bioeconomy framework. Despite efforts made in the paper industry to enhance productivity while conserving resources and energy through lower grammage and higher machine speeds, reducing thermal energy consumption during papermaking remains a significant challenge. A key approach to address this challenge lies in increasing dewatering of the fiber web before entering the dryer section of the paper machine. Similarly, the production of high-value-added products derived from alternative lignocellulosic feedstocks, such as nanocellulose and microalgae, requires advanced dewatering techniques for techno-economic viability. This critical and systematic review aims to comprehensively explore the intricate interactions between water and lignocellulosic surfaces, as well as the leading technologies used to enhance dewatering and drying. Recent developments in technologies to reduce water content during papermaking, and advanced dewatering techniques for nanocellulosic and microalgal feedstocks are addressed. Existing research highlights several fundamental and technical challenges spanning from the nano- to macroscopic scales that must be addressed to make lignocellulosics a suitable feedstock option for industry. By identifying alternative strategies to improve water removal, this review intends to accelerate the widespread adoption of lignocellulosics as feasible manufacturing feedstocks. Moreover, this review aims to provide a fundamental understanding of the interactions, associations, and bonding mechanisms between water and cellulose fibers, nanocellulosic materials, and microalgal feedstocks. The findings of this review shed light on critical research directions necessary for advancing the efficient utilization of lignocellulosic resources and accelerating the transition towards sustainable manufacturing practices.

Enhancing harvest of biodiesel-promising microalgae using Daphnia domesticated by amino acids

Mass production of microalgal biodiesel is hindered by microalgae harvesting efficiency and costs. In this study, Daphnia domesticated by amino acids were used to harvest microalgae via ingesting. The main factors (density of Daphnia, salinity, pH, light-environment, temperature and algal concentration) that were conducive to Daphnia feeding were optimized. Under the optimal condition, Microalgae-feeding Daphnia were domesticated by adding D-glutamic acid and L-cysteine as stimulating factors. After that, the ingestion rate of domesticated Daphnia increased by 24.93%. The presence of Daphnia as a predator can induce microalgae to mass into clusters. Combining Daphnia feeding and the inductive defense flocculation of microalgae, the harvesting rate of mixed algae (Chlorella pyrenoidosa and Scenedesmus obliquus) reached over 95% after 9 h. Overall, this work suggested that Daphnia feeding process is a green and economical approach for microalgae harvesting.

Microalgae harvesting techniques: updates and recent technological interventions

Microalgal biomass has garnered attention as a renewable and sustainable resource for producing biodiesel. The harvesting of microalgal biomass is a significant bottleneck being faced by the industries as it is the crucial cost driver in the downstream processing of biomass. Bioharvesting of microalgal biomass mediated by: microbial, animal, and plant-based polymeric flocculants has gained a higher probability of utility in accumulation due to: its higher dewatering potential, less toxicity, and ecofriendly properties. The present review summarizes the key challenges and the technological advancements associated with various such harvesting techniques. The economic and technical aspects of different microalgal harvesting techniques, particularly the cationic polymeric flocculant-based harvesting of microalgal biomass, are also discussed. Furthermore, interactions of flocculants with microalgal biomass and the effects of these interactions on metabolite and lipid extractions are discussed to offer a promising solution for suitability in selecting the most efficient and economical method of microalgal biomass harvesting for cost-effective biodiesel production.

Repetitive non-destructive extraction of lipids from Chlorella vulgaris grown under stress conditions

The aim of this study was the investigation of non-destructive lipid extraction from Chlorella vulgaris grown under stress conditions of nutrient limitation and salinity. To select a suitable solvent for extraction, the performances of decane, dodecane and hexadecane were tested based on their effect on lipid extraction and cell viability. The results showed that dodecane was the most suitable solvent for the extraction process. The concentration of extracted lipids from stressed cells was 2762.52 ± 11.38 mg L^-1, i.e. a value 1.75 times higher than that obtained from unstressed cells. Long-term extraction was also evaluated with continuous dodecane recirculation during five-stage extraction and a recovery time of 24 h between the extraction steps, which yielded after the fifth extraction stage a total lipid amount as high as 9811.56 mg L^-1. These results showed that non-destructive lipid recovery can be effectively performed by applying stress conditions and in repetitive extractions.

Microalgal Biomass Generation via Electroflotation: A Cost-Effective Dewatering Technology

Microalgae are an excellent source of bioactive compounds for the production of a wide range of vital consumer products in the biofuel, pharmaceutical, food, cosmetics, and agricultural industries, in addition to huge upstream benefits relating to carbon dioxide biosequestration and wastewater treatment. However, energy-efficient, cost-effective, and scalable microalgal technologies for commercial-scale applications are limited, and this has significantly impacted the full-scale implementation of microalgal biosystems for bioproduct development, phycoremediation, and biorefinery applications. Microalgae culture dewatering continues to be a major challenge to large-scale biomass generation, and this is primarily due to the low cell densities of microalgal cultures and the small hydrodynamic size of microalgal cells. With such biophysical characteristics, energy-intensive solid–liquid separation processes such as centrifugation and filtration are generally used for continuous generation of biomass in large-scale settings, making dewatering a major contributor to the microalgae bioprocess economics. This article analyzes the potential of electroflotation as a cost-effective dewatering process that can be integrated into microalgae bioprocesses for continuous biomass production. Electroflotation hinges on the generation of fine bubbles at the surface of an electrode system to entrain microalgal particulates to the surface. A modification of electroflotation, which combines electrocoagulation to catalyze the coalescence of microalgae cells before gaseous entrainment, is also discussed. A technoeconomic appraisal of the prospects of electroflotation compared with other dewatering technologies is presented.

Biomitigation of CO2 from flue gas by Scenedesmus obtusiusculus AT-UAM using a hybrid photobioreactor coupled to a biomass recovery stage by electro-coagulation-flotation

The microalga Scenedesmus obtusiusculus AT-UAM efficiently captured CO₂ from two flue gas streams in a hybrid photobioreactor located in a greenhouse. Uptake rates of CO₂, NO, and SO₂ from a formulated gas stream were 160.7 mg L^-1 day^-1, 0.73 mg L^-1 day^-1, and 1.56 mg L^-1 day^-1, respectively, with removal efficiencies of 100% for all gases. Exhaust gases of a motor generator were also removed with uptake rates of 111.4 mg L^-1 day^-1, 0.42 mg L^-1 day^-1, and 0.98 mg L^-1 day^-1, obtaining removal efficiencies of 77%, 71%, and 53% for CO₂, NO_x, and SO₂, respectively. On average, 61% of the CO₂ from both flue gas streams was assimilated as microalgal biomass. The maximum CO₂ uptake rate of 182 mg L^-1 day^-1 was achieved for formulated flue gas flow rate above 100 mL min^-1. The biomass recovery of 88% was achieved using a 20-L electro-coagulation-flotation chamber coupled to a settler with a low specific power consumption of 0.27 kWh kg^-1. The photobioreactor was operated for almost 7 months without contamination of invasive species or a decrease in the activity. It is a very encouraging result for long-term operation in flue gas treatment.

An Innovative Low-Cost Equipment for Electro-Concentration of Microalgal Biomass

Microalgal harvesting is one of the most challenging processes in the development of algal research and development. Several methods, such as centrifugation, flocculation and filtration, are available at the laboratory scale. However, the requirement for expensive pieces of equipment and the possibility of biomass contamination are recurring gaps that hinder the development of microalgae R&D (research and development) in different parts of the world. Recently, electroflotation has been proved to be a suitable method for the harvesting of different species of microalgae and cyanobacteria. To this day, there are no companies that sell laboratory-scale electroflotation equipment; this is mainly due to the gap in the knowledge of which factors (time, mixing rate, number of electrodes and others) will affect the efficiency of concentration without reducing the biomass quality. This paper aims to build an innovative, low-cost electroflotation system for under 300 USD (United States dollar) with cheap and resistant materials. To achieve our goal, we tested the interaction of three variables (time, mixing rate and amount of electrodes). Results showed that an efficiency closer to 100% could be achieved in under 20 min using > 10 electrodes and 150 rpm (round per minute). We hope this innovative approach can be used by different researchers to improve our knowledge of the concentration and harvesting of algae and cyanobacteria.

Algae as potential feedstock for the production of biofuels and value-added products: Opportunities and challenges

The current review explores the potential application of algal biomass for the production of biofuels and bio-based products. The variety of processes and pathways through which bio-valorization of algal biomass can be performed are described in this review. Various lipid extraction techniques from algal biomass along with transesterification reactions for biodiesel production are briefly discussed. Processes such as the pretreatment and saccharification of algal biomass, fermentation, gasification, pyrolysis, hydrothermal liquefaction, and anaerobic digestion for the production of biohydrogen, bio-oils, biomethane, biochar (BC), and various bio-based products are reviewed in detail. The biorefinery model and its collaborative approach with various processes are highlighted for the production of eco-friendly, sustainable, and cost-effective biofuels and value-added products. The authors also discuss opportunities and challenges related to bio-valorization of algal biomass and use their own perspective regarding the processes involved in production and the feasibility to make algal research a reality for the production of biofuels and bio-based products in a sustainable manner.