Mass harvesting of marine microalgae using different techniques

Perspectives on cultivation and harvesting technologies of microalgae, towards environmental sustainability and life cycle analysis

The development of algae is seen as a potential and ecologically sound approach to address the increasing demands in multiple sectors. However, successful implementation of processes is highly dependent on effective growing and harvesting methods. The present study provides a complete examination of contemporary techniques employed in the production and harvesting of algae, with a particular emphasis on their sustainability. The review begins by examining several culture strategies, encompassing open ponds, closed photobioreactors, and raceway ponds. The analysis of each method is conducted in a systematic manner, with a particular focus on highlighting their advantages, limitations, and potential for expansion. This approach ensures that the conversation is in line with the objectives of sustainability. Moreover, this study explores essential elements of algae harvesting, including the processes of cell separation, dewatering, and biomass extraction. Traditional methods such as centrifugation, filtration, and sedimentation are examined in conjunction with novel, environmentally concerned strategies including flocculation, electro-coagulation, and membrane filtration. It evaluates the impacts on the environment that are caused by the cultivation process, including the usage of water and land, the use of energy, the production of carbon dioxide, and the runoff of nutrients. Furthermore, this study presents a thorough examination of the current body of research pertaining to Life Cycle Analysis (LCA) studies, presenting a perspective that emphasizes sustainability in the context of algae harvesting systems. In conclusion, the analysis ends up with an examination ahead at potential areas for future study in the cultivation and harvesting of algae. This review is an essential guide for scientists, policymakers, and industry experts associated with the advancement and implementation of algae-based technologies.

A review on biodiesel production from microalgae: Influencing parameters and recent advanced technologies

Microalgae are the important part of carbon cycle in the nature, and they could utilize the carbon resource in water and soil efficiently. The abilities of microalgae to mitigate CO₂ emission and produce oil with a high productivity have been proven. Hence, this third-generation biodiesel should be popularized. This review firstly introduce the basic characteristics and application fields of microalgae. Then, the influencing parameters and recent advanced technologies for the microalgae biodiesel production have been discussed. In influencing parameters for biodiesel production section, the factors of microalgae cultivation, lipid accumulation, microalgae harvesting, and lipid extraction have been summarized. In recent advanced technologies for biodiesel production section, the microalgae cultivation systems, lipid induction technologies, microalgae harvesting technologies, and lipid extraction technologies have been reviewed. This review aims to provide useful information to help future development of efficient and commercially viable technology for microalgae-based biodiesel production.

A review on mycelial pellets as biological carriers: Wastewater treatment and recovery for resource and energy

Mycelial pellets, a new environment friendly biological carrier, have received wide attention from researchers due to porosity, stability and unique biocompatibility. In this article, the theoretical basis and mechanism of mycelial pellets as a biological carrier were analyzed from the properties of mycelial pellets and the interaction between mycelial pellets and other microorganisms. This article aims to collate and present the current application and development trend of mycelial pellets as biological carriers in wastewater treatment, resource and energy recovery, especially the symbiotic particle system formed by mycelial pellets and microalgae is an important way to break through the technical bottleneck of biodiesel recovery from wastewater. This review also analyzes the research hotspots and trends of mycelial pellets as carriers in recent years, discusses the challenges faced by this technology, and puts forward corresponding solutions.

Assessing the Environmental and Economic Sustainability of Functional Food Ingredient Production Process

Development and application of novel technologies in food processing is vital for ensuring the availability of adequate, safe, and convenient food with the desired quality and functional properties. Environmental and economic sustainability of technologies is essential prior to their application in the food processing sector. The objective of this research is to determine the environmental and economic feasibility of ultrasound-assisted extraction (UAE) for recovering functional food ingredients from seaweed. Experimental data is used to conduct a life cycle assessment (LCA) to investigate the environmental performance with a functional unit (FU) of obtaining 1 g of extracted polyphenols, measured as gallic acid equivalents (mg GAE)/g seaweed. A life cycle impact assessment is performed with ReCiPe 2016 at midpoint. The cost of manufacturing (COM) of phenolic-rich extracts (as functional ingredient, bioactive, or nutraceutical) is estimated using time-driven activity-based costing (TDABC). The environmental profile findings show that across all categories, the UAE has considerably lower impacts than the conventional method, with electricity as the most important impact contributor, followed by solvent production. An economic assessment estimates the COM over a one-year period at a large scale using the UAE to be EUR 1,200,304, EUR 2,368,440, and EUR 4,623,290 for extraction vessel capacities of 0.05, 0.1, and 0.15 m3, respectively. Raw materials (including the type of raw material) and operational labour costs are the primary contributors to the COM. The findings thus present evidence to support the adoption of an environmentally and economically viable technology for functional ingredient production.

Biological-Based Produced Water Treatment Using Microalgae: Challenges and Efficiency

Produced water (PW) is the most significant waste stream generated in the oil and gas industries. The generated PW has the potential to be a useful water source rather than waste. While a variety of technologies can be used for the treatment of PW for reuse, biological-based technologies are an effective and sustainable remediation method. Specifically, microalgae, which are a cost-effective and sustainable process that use nutrients to eliminate organic pollutants from PW during the bioremediation process. In these treatment processes, microalgae grow in PW free of charge, eliminate pollutants, and generate clean water that can be recycled and reused. This helps to reduce CO2 levels in the atmosphere while simultaneously producing biofuels, other useful chemicals, and added-value products. As such, this review focuses on PW generation in the oil and gas industry, PW characteristics, and examines the available technologies that can be used for PW remediation, with specific attention to algal-based technologies. In addition, the various aspects of algae growth and cultivation in PW, the effect of growth conditions, water quality parameters, and the corresponding treatment performance are presented. Lastly, this review emphasizes the bioremediation of PW using algae and highlights how to harvest algae that can be processed to generate biofuels for added-value products as a sustainable approach.

Mass cultivation and harvesting of microalgal biomass: Current trends and future perspectives

Microalgae are unicellular photosynthetic organisms capable of producing high-value metabolites like carbohydrates, lipids, proteins, polyunsaturated fatty acids, vitamins, pigments, and other high-value metabolites. Microalgal biomass gained more interest for the production of nutraceuticals, pharmaceuticals, therapeutics, food supplements, feed, biofuel, bio-fertilizers, etc. due to its high lipid and other high-value metabolite content. Microalgal biomass has the potential to convert trapped solar energy to organic materials and potential metabolites of nutraceutical and industrial interest. They have higher efficiency to fix carbon dioxide (CO₂) and subsequently convert it into biomass and compounds of potential interest. However, to make microalgae a potential industrial candidate, cost-effective cultivation systems and harvesting methods for increasing biomass yield and reducing the cost of downstream processing have become extremely urgent and important. In this review, the current development in different microalgal cultivation systems and harvesting methods has been discussed.

Use of ultrasound for aiding lipid extraction and biodiesel production of microalgae harvested by chitosan

In this work, chitosan, a biodegradable flocculant, was investigated to determine its utility in flocculating microalgae, its effect on cell integrity, and its impact on lipid extraction and the conversion to fatty acid methyl ester (FAME). Results showed that chitosan adequately performed flocculation on Chlorella vulgaris microalgae and achieved a high harvesting efficiency of 96.35 ± 1.96% when implemented under the following conditions: chitosan dose = 120 mg/L^-1, pH = 5, mixing speed = 150 rpm for 20 min, followed by 10 min of settling time. Moreover, scanning electron microscope (SEM) combined with transmission electron microscope (TEM) demonstrated that chitosan protected the cells' structure from morphological damage. Finally, the highest lipid extraction yield and biodiesel production was obtained from the chitosan-harvested biomass when the microalgae were pretreated with ultrasound.

Marine Microalgae Contribution to Sustainable Development

The burning of fossil fuels is an unsustainable activity, which is leading to an increase in greenhouse gases (GHGs) emissions and related global warming. Among sustainable energy sources, microalgae represent a promising alternative to fossil fuel and contribute to the achievement of important Sustainable Development Goals (SDGs). In particular, the potential contribution of marine microalgae to sustainable development is large as, among other benefits, they represent a carbon negative energy source and may be applied in many coastal areas around the world. Despite this, significant economic and technological improvements are needed in order to make microalgae biofuels viable on a large scale. This review aims to explore how and to what extent third-generation biofuels (marine microalgae, but also the latest advances in freshwater microalgae) can benefit the realization of these SDGs. From this study we concluded that the production of large-scale marine microalgae biofuels is not yet feasible from the economic perspective at a large scale. However, the cultivation of microalgae in seawater holds great potential for increasing the small to medium viability of this biofuel source. The possibilities for improvement along with the contributions to sustainable development lay the groundwork for continuing to study and apply the potential of sustainable production of microalgae bioenergy.

Single-step dynamic dewatering of microalgae from dilute suspensions using flocculant assisted filtration

Background

Dewatering constitutes a major challenge to the production of microalgae, accounting for 20–30% of the product cost. This presents a setback for the applicability of microalgae in the development of several sustainable products. This study presents an investigation into the dynamic dewatering of microalgae in a combined flocculation-filtration process. The effect of process conditions on the performance of 12 flocculants and their mixtures was assessed.

Results

The mechanism of flocculation via the electrostatic path was dominated by charge neutralization and subsequently followed bridging in a ‘sweep flocculation’ process. Cationic polyacrylamide (CPAM) based flocculants recorded the highest biomass retention with PAM1 and PAM2 attaining 99 and 98% retention with flocculant dosages of 10 and 15 mg/L respectively. Polyvinylamine (PVAM) was also found to improve system stability across the pH range 4–10. Alum was observed to be only effective in charge neutralization, bringing the system close to its isoelectric point (IEP). Chemometric analysis using the multi-criteria decision methods, PROMETHEE and GAIA, was applied to provide a sequential performance ranking based on the net outranking flow (ф) from 207 observations. A graphical exploration of the flocculant performance pattern, grouping the observations into clusters in relation to the decision axis (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pi$$\end{document}π), which indicated the weighted resultant of most favorable performance for all criteria was explored.

Conclusion

CPAM based flocculants and their mixtures demonstrated superior performance due to their viscoelastic behaviour under turbulence. The use of PVAM or alum in mixtures with CPAM reduced the required doses of both flocculants, which will provide beneficial financial impact for largescale microalgae dewatering in a flocculant assisted dynamic filtration process. Chemometric analysis based on the physico-chemical properties of the system provides a time saving assessment of performance across several criteria. The study findings provide an important foundation for flocculant assisted dynamic filtration processes.

Towards green extraction methods from microalgae learning from the classics

Microalgae started receiving attention as producers of third generation of biofuel, but they are rich in many bioactive compounds. Indeed, they produce many molecules endowed with benefic effects on human health which are highly requested in the market. Thus, it would be important to fractionate algal biomass into its several high-value compounds: this represents the basis of the microalgal biorefinery approach. Usually, conventional extraction methods have been used to extract a single class of molecules, with many side effects on the environment and on human health. The development of a green downstream platform could help in obtaining different class of molecules with high purity along with low environmental impact. This review is focused on technical advances that have been performed, from classic methods to the newest and green ones. Indeed, it is fundamental to set up new procedures that do not affect the biological activity of the extracted molecules. A comparative analysis has been performed among the conventional methods and the new extraction techniques, i.e., switchable solvents and microwave-assisted and compressed fluid extractions.

Effects of harvesting Spirulina platensis biomass using coagulants and electrocoagulation-flotation on enzymatic hydrolysis

This study aimed to assess the harvesting of Spirulina platensis using coagulants and electrocoagulation-flotation (ECF) and to evaluate its influence on enzymatic hydrolysis. Using nine chemical coagulants, we obtained a biomass harvesting efficiency of up to 99.5%. Using ECF, the harvesting efficiency at the aluminum and carbon electrode was 98%-99% and 33.8%-86.9%, respectively. Hydrolysis efficiency (HE) with amylases varied from 17% to 42%, and the degree of hydrolysis (DH) with proteases varied from 1.26% to 4.07%, compared with an HE of 31% and a DH of 3.57% in the centrifuged biomass. Compared to an HE of 61.75% for the centrifuged biomass, and HE of 99% and 85.46% was obtained for the biomass harvested using the aluminum and carbon electrodes. The HEs with the electrodes were better than those with the alternative methods and centrifugation; hence, with some optimization, the biomass harvested could be used for enzymatic hydrolysis.

Critical processes and variables in microalgae biomass production coupled with bioremediation of nutrients and CO2 from livestock farms: A review

Development of renewable and clean energy as well as bio-based fine chemicals technologies are the keys to overcome the problems such as fossil depletion, global warming, and environment pollution. To date, cultivation of microalgae using wastewater is regarded as a promising approach for simultaneous nutrients bioremediation and biofuels production due to their high photosynthesis efficiency and environmental benefits. However, the efficiency of nutrients removal and biomass production strongly depends on wastewater properties and microalgae species. Moreover, the high production cost is still the largest limitation to the commercialization of microalgae biofuels. In this review paper, the state-of-the-art algae species employed in livestock farm wastes have been summarized. Further, microalgae cultivation systems and impact factors in livestock wastewater to microalgae growth have been thoroughly discussed. In addition, technologies reported for microalgal biomass harvesting and CO₂ mass transfer enhancement in the coupling process were presented and discussed. Finally, this article discusses the potential benefits and challenges of coupling nutrient bioremediation, CO₂ capture, and microalgal production. Possible engineering measures for cost-effective nutrients removal, carbon fixation, microalgal biofuels and bioproducts production are also proposed.

Magnetophoretic Harvesting of Nannochloropsis oculata Using Iron Oxide Immobilized Beads

In this work, the harvesting of Nannochloropsis oculata microalgae through the use of nanosized Fe3O4 immobilized in polyvinyl alcohol (PVA)/sodium alginate (SA) as a flocculant (Fe3O4/PS) is investigated. Using the Fe3O4/PS immobilized beads could reduce the amount of soluble ferrous ions (Fe2+) released from naked Fe3O4 in acid treatment, leading to easy recovery. The characterization was performed under different dosages and pH values of Fe3O4/PS. The results show that the Fe3O4/PS, when applied to the algae culture (500 mg dry cell weight/L), achieves a 96% harvesting efficiency under conditions of a pH of 4 with 200 mT magnetic field intensity. Fe3O4/PS can be directly reused without adjusting the pH value. The recycled Fe3O4/PS shows stability in terms of its surface properties, maintaining more than 80% harvesting efficiency after five recycles. Magnetophoretic harvesting, using immobilized magnetic iron oxide as a particle-based flocculant, is a potential method to reduce challenges related to the cost-effective microalgae-harvesting method.