Conversion of microalgae to fossil fuels is facilitated by thermochemical processes such as pyrolysis and gasification. The thermal conversion efficiency is of great importance and is directly related to thermal reaction kinetics. Great efforts have been made to improve thermal conversion efficiency. In fact, there are many factors in the thermochemical conversion stage, and the kinetic parameters are the core for enhancing thermal conversion efficiency and the improvement of reactor design to better utilize microalgae for productivity. There have been several kinetic models for microalgae thermal conversion. This chapter reviews the conventional methods, distributed activation energy models, and model-fitting methods commonly used to study the pyrolysis and gasification kinetics of microalgae in recent years, including their theoretical basis and formula. The advantages and limitations of various methods are analyzed, and reasonable suggestions for their use are discussed.

Microalgae are an encouraging alternative energy source for the future due to their high growth rate, cultivation potential in a wastewater environment, and higher heating value (HHV). However, nowadays, only the properties of pure microalgae species that disregard coagulants used at the harvesting stage are known. Besides, the process of harvesting in itself is still a challenge. This study hypothesized that microalgae biomass from wastewater treatment plants (WWTP) could be a promising feedstock for thermal gasification. An analysis from harvest to gasification challenges is carried out based on the microalgae thermochemical characteristics evaluated through kinetic and heat transfer governed processes. For that, various microalgae properties are assessed by calorific value (low and high heating value), ultimate (C, H, N, S, and O), and proximate (moisture, ash, volatile, and fixed carbon), and thermogravimetric analysis. Then these analysts are used to guide the interpretation of the gasification results in a downdraft gasifier. The biomass microalgae's chemical and thermochemical characteristics were discussed, including the relationship between coagulants for harvest and their effect on the syngas obtained. In the chapter, the advantages and disadvantages pointed out were summarized in the conclusion section, bringing out the technological limitations.

Microalgae (microscopic algae) are mainly photosynthetic microorganisms similar to plants. It is an organism high in antioxidants and has a diverse range of species capable of producing unique compounds. In the last decade, research and the application of microalgae have increased tremendously, with several algal-associated companies. However, due to insufficient information, extensive use of microalgae is yet to materialize, and the immense benefits and advantages of microalgae are yet to be exploited. Microalgae contain valuable compounds such as polysaccharides, lipids, pigments, antioxidants, minerals, and vitamins. They have the potential to be the best food supplement compared to other sources. Past research on microalgae provides the platform for further microalgal studies and the expansion of their applications. The latest genetic engineering techniques allow optimum microalgal potential, including their nutritional compounds to the growth technique. Researchers worldwide have worked extensively on the applications of microalgae in medicine and biotechnology, including algal mass cultivation systems. These include current microalgal applications in medicine (production of bioactive compounds and drugs) and biotechnology (cultivation systems, generation of biofuels, biostimulators, and food additives).The production of biologically active substances has been the focus of many applied algae studies. These microalgal biologically active compounds have been used to treat skin problems (inflammation, wounds, burns, eczema, or lupus) and gynecological diseases. Interestingly, microalgal biostimulators are also one of the main active additives in toothpaste, hair, and skin lotions. In conclusion, various studies and applications of microalgae as an alternative solution are available. The potential biomedical applications of microalgae and their economic contribution and industrial trends are discussed in this book chapter.

Algae are photosynthetic organisms that produce bioactive chemicals such as proteins, lipids, vitamins, beta-carotene, astaxanthin, and pigments in their biomass. Algae are quickly grown and can be found in both freshwater and the marine environment. The diversified gamut of this seaweed displays some fascinating applications in the biotechnological world. The use of algal biomass to produce biofuels, food, feed industries, and bioremediation in wastewater treatment has always been a trend. The pharmaceutical sector is an indispensable arena for human life's survival where algal products offer miscellaneous actions stretching from antibiotics, anticoagulants, antioxidants, to antiinflammatory, antibacterial, antifungal, antiviral, anthelmintic, antiprotozoan, and many more properties. Omega-3-fatty acids, astaxanthin, and beta carotene are bioactive compounds that are responsible for the essence of medicinal quality. With the establishment of integrated culture systems and harvesting processes, algae can be used for cost and energy-effective purposes in the commercial sector. Various culturing conditions for growing algae, including luminescence, temperature, pH, and culture systems, significantly influence productivity and biomass production. Strain selection and harvesting technology involves effective regulation of upstream and downstream processes to achieve economical and high-yield bioproducts. Optimization of unit processes is required to maintain the consistency of the obtained bioproduct. Hence, this book chapter evaluates the integrated algal culture system and harvesting, unraveling its role in the biomedical field.

Microalgae are separated and harvested using natural-based coagulants (NBC). Microalgae are grown to provide bioproducts that may be utilized in the tertiary phase after anaerobic digestion at the wastewater treatment plant (WWTP). Coagulation, flocculation, and sedimentation are the most often used processes for harvesting algal biomass and recovering organic and inorganic components from it. The choice of coagulant is critical because it affects both separation performance and biomass harvesting. On the one hand, inorganic coagulants (such as aluminum-based coagulants) are frequently used and can improve the catalyst process during thermochemical conversion; they are toxic (depending on their subsequent use, such as fertilizers), non-biodegradable, and can increase the biomass ash content, thereby decreasing its heating value. It has therefore been suggested as an alternative to using inorganic coagulants, such as NBC. Other auto-flocculant microalgae like Moringa oleifera seeds and chitosan are examples of the many different kinds of coagulants that have been developed. As a consequence, the chapter discussed the characteristics and uses of natural coagulants, as well as the potential drawbacks of their future use. Additionally, coagulation techniques have been explored, as well as their effects on the characteristics of biomass and their use as fertilizers or energy sources.

Sustainability is an important part of natural resource management since it implies increased production efficiency, reduced environmental effects, and enhanced social welfare. Continuous usage of fossil fuels depletes reserves, generates greenhouse effects, and escalates climate-related problems. Therefore, the primary goal is to generate alternative renewable energy sources capable of satisfying energy demand. First-generation biofuels, derived mostly from food crops and oil seeds, and second-generation biofuels, derived primarily from nonfood crops and feedstock, are inefficient and contribute to the escalation of environmental issues. Recent technological advancements enable the production of third-generation biofuels from microalgae, which can be used as a viable alternative to first- and second-generation biofuels while mitigating the problems associated with first- and second-generation biofuels. Microalgae are photosynthetic organisms that grow in the form of sunlight, carbon dioxide, nutrients (nitrogen, phosphorus, and potassium), and carbohydrates. The principal components derived from microalgae are lipids, carbohydrates, and proteins. These valuable products need less time to produce and are an important source of biofuel. The current chapter focuses on methods for improving microalgae-to-biofuel conversion. It also emphasizes biomass growth technology, harvesting techniques, biomass conversion technologies, and value-added microalgae commodities. Furthermore, it discusses the benefits and environmental prospects of using biofuels as an alternative to renewable energy resources, as well as the challenges and recommendations in commercial biofuel applications.

Green algae as a biofuel feedstock is gaining traction due to rising petroleum prices, rapidly depleting natural oil sources, and, most importantly, the emerging lethal problems related to global warming caused by burning of fossil fuels. Algae are considered the best source of lipids (20%–70%) and have an extraordinary potential for cultivation as a sustainable renewable energy source. Significant research work has been carried out on algal biomass. However, there is little evidence that authors have published detailed information on the engineering of metabolic pathways for high oil production, genetic engineering to control environmental stresses, and low-cost technologies for biofuel production from algae. Therefore, there is a dire need to consolidate and present updated knowledge on all aspects of production, harvesting, and processing of algal biomass as a fuel feedstock. The proposed chapter aims to achieve this goal by explaining and critically evaluating the following topics: (i) Algae as a promising future feedstock for biofuel production, (ii) Types of algal biomass for biofuel production, (iii) Algal cultivation and biomass production, (iv) Biomass harvesting and drying, (v) Lipid extraction and biofuel production, (vi) Techno-economic analysis of algal biofuel production, (vii) Prospects and challenges, and (viii) Conclusions. Extensive literature surveys have been conducted to collect information on algae from cultivation to harvest to biofuel production. Particular emphasis has been given to the conversion of algae oil into biofuel. This chapter will be a ready reference for students, researchers, industrialists, and policymakers and will provide up-to-date knowledge in the subject area.

Microalgae are a promising feedstock for biofuel and biochemical production due to their rapid growth, carbon dioxide (CO2) fixation, less or no competition with food, and high lipid and carbohydrate content. However, the industrialization of microalgae production is hampered by high costs related to the raw materials and the production operation, particularly when only one component (lipids or starch) is used. This chapter explores the technological and economic viability of comprehensive utilization of lipid and carbohydrates directly from wet microalgae of the Chlorella genus. Lee et al. reported a technological study on bioethanol production from residuals of Chlorella sp. KR-1 after lipids were extracted, based on studies discussing either how to use lipids of microalgae as a feedstock for the production of biofuel (mainly biodiesel) or how to utilize carbohydrates of microalgae to produce reducing sugars. Ma et al. discussed not only the technological possibility but also the economic feasibility of comprehensive lipid and carbohydrate usage of wet microalgae.

In recent years, inorganic nanoparticles (NPs) obtained from diatomite biosilica have been explored in nanomedicine. Diatomite is a material of sedimentary origin formed by the remains of diatom skeletons. Diatomite-based NPs (DNPs) can be easily prepared in a size range between 100 and 400nm and possess a porous morphology useful for the efficient loading of chemotherapeutics. The biocompatibility and cellular uptake of DNPs have been demonstrated using different cancer cell lines, including human epidermoid, breast, cervical, and colorectal cancer cells. Several functionalization strategies of the silica surface have been developed to enhance the drug-loading capacity of DNPs and improve the pharmacokinetic and pharmacodynamic profiles of the delivered drug. A hybrid nanostructure constituted by DNPs covered by gold nanoparticles has also been proposed for simultaneous diagnosis by imaging and therapy; this nanosystem constitutes the first example of a multifunctional platform realized from diatomite for delivery and sensing purposes. This chapter summarizes key aspects of DNP functionalization, biocompatibility, and applications in nanomedicine.

Rapid development and the increase in the global population have generated hazardous materials that have led to extensive attention to environmental pollution management. High carbon dioxide (CO2) emissions and the release of polluted water from various industries into the water stream have contributed to major environmental issues globally. Bioremediation using microalgae has been identified as one of the potential approaches to remediating air and water pollution. It is known that bioremediation using microalgae has many advantages, namely (1) atmospheric CO2 reduction, (2) energy-saving, (3) pathogen and pollutant reduction, and (4) nutrient recovery and biomass production. Even though many advantages of microalgal bioremediation have been reported, several limitations, such as type of pollutant, large-scale wastewater treatment system implementation, and microalgae harvesting for further application, need to be considered for the added value of bioremediation. This chapter will discuss the bioremediation of air and water generated by various agriculture, manufacturing, aquaculture, and medical industries using microalgae. The chapter will also discuss the latest insights and future trends in microalgal biorefinery and bioremediation studies.