Biofuels from Algae

Ashok Pandey, Duu-Jong Lee, Yusuf Chisti, Carlos R. Soccol

• Publisher: Elsevier
• Year: 2013
• Print ISBN: 9780444595584
• eBook ISBN: 9780444595829
• Topic: Technology & Engineering
• Subtopic: Chemical & Biochemical Engineering
• Index: Technology & Engineering

This book provides in-depth information on basic and applied aspects of biofuels production from algae. It begins with an introduction to the topic, and follows with the basic scientific aspects of algal cultivation and its use for biofuels production, such as photo bioreactor engineering for microalgae production, open culture systems for biomass production and the economics of biomass production. It provides state-of-the-art information on synthetic biology approaches for algae suitable for biofuels production, followed by algal biomass harvesting, algal oils as fuels, biohydrogen production from algae, formation/production of co-products, and more. The book also covers topics such as metabolic engineering and molecular biology for algae for fuel production, life cycle assessment and scale-up and commercialization. It is highly useful and helps you to plan new research and design new economically viable processes for the production of clean fuels from algae.- Covers in a comprehensive but concise way most of the algae biomass conversion technologies currently available- Lists all the products produced from algae, i.e. biohydrogen, fuel oils, etc., their properties and potential uses- Includes the economics of the various processes and the necessary steps for scaling them up

Chapter 1

An Open Pond System for Microalgal Cultivation

Jorge Alberto Vieira Costa∗, ^∗Laboratory of Biochemical Engineering, College of Chemistry and Food Engineering, Federal University of Rio Grande, Rio Grande, RS, Brazil

Michele Greque de Morais

Abstract

Microalgal biomasses have a long history of industrial production for application in a variety of fields. The success of commercial large-scale production of microalgae depends on many factors, one which is the development of cost-effective systems. Open pond reactors are the most widely used system in large-scale microalgal cultivation due to their low cost of construction, maintenance, and operation. However, closed photobioreactors have a high photosynthetic efficiency and biomass productivity. This study presents the advantages and disadvantages of open ponds compared with other photobioreactors and examines the factors that affect the cultures and their bioproducts.

Keywords

bioproducts; cultivation; microalga; open pond; photobioreactor.

1.1 Introduction

Microalgal biotechnology has emerged due to the great diversity of products that can be developed from biomass. Microalgal biomass has been industrially applied in areas such as dietary supplements, lipids, biomasses, biopolymers, pigments, biofertilizers, and biofuels. To produce these compounds, microalgae can be grown using carbon dioxide and industrial wastes, which reduces the cost of culture medium nutrients and alleviates the environmental problems caused by these effluents. However, the high cost of production of microalgal biomass (compared to agricultural and forestry biomasses) is one of the major barriers that must be overcome in order for their industrial production to be viable.

Although efforts have been directed at the optimization of the medium and processes, the development of cultivation systems that are cost-effective and highly efficient must be significantly improved for large-scale production to be viable (Wang et al., 2012; Wang and Lan, 2011). Microalgal cultivation on a large scale has been studied for decades (Lee, 2001).

The first unialgal cultivation was carried out with the microalga Chlorella vulgaris by Beijerinck in 1890, who wanted to study the physiology of the plants (Borowitzka, 1999). During World War II, Germany, using open ponds, increased algal cultivation for use as a food supplement. With the onset of industrialization, some study groups at the Carnegie Institute in Washington, D.C., implemented algae cultures for carbon dioxide biofixation. In 1970 Eastern Europe, Israel, and Japan began commercial production of algae in open ponds to produce healthy foods (Ugwu et al., 2008).

Open pond cultivation systems are the most industrially applied because of their low cost of investment and operational capital. This system’s major difficulties are the control of operating conditions, which can cause low biomass productivity, and the control of contaminants, which can be excluded by using highly selective species (Shu and Lee, 2003).

Compared to open ponds, closed photobioreactors may have increased photosynthetic efficiency and higher production of biomass (Wang et al., 2012). However, closed photobioreactors have a high initial cost, and only microalgal strains with specific physiologies may be used (Harun et al., 2010), which is why different types of closed photobioreactors have been developed in recent decades (Wang et al., 2012).

The objective of this study was to present the advantages and disadvantages of open ponds compared to other photobioreactors as well as to examine factors that affect the cultures and the bioproducts obtained.

1.2 Biotechnology and Microalgae

Biotechnology is a major interdisciplinary science, combining biology, chemistry, and engineering and incorporating and integrating knowledge from the areas of microbiology, genetics, chemistry, biochemistry, and biochemical engineering. The key word in this context is biotransformation.

The application of biotechnology to marine organisms and processes is an area of significant industrial importance with ramifications in many areas, including human health, the environment, energy, food, chemicals, materials, and bioindicators. Some areas of interest related to marine biotechnology include the understanding of genetic, nutritional, and environmental factors that control the production of primary and secondary metabolites, based on new or optimized products. Furthermore, there has been an emphasis on the identification of bioactive compounds and their mechanisms of action for application in the medical and chemical industry; there are also bioremediation strategies for application in damaged areas and the development of bioprocesses for sustainable industrial technologies (Zaborsky, 1999).

The cultivation of microalgae as part of biotechnology has received researcher attention. The growth conditions and the bioreactors for cultivation have been thoroughly studied (Borowitzka, 1999). The principle behind cultivation of microalgae for the production of biomass is the use of photosynthesis (Vonshak, 1997), which involves using solar energy and converting it into chemical energy.

Microalgae are photosynthetic prokaryotic or eukaryotic microorganisms that grow rapidly and have the ability to live in different environments due to their unicellular or simple multicellular structure. Examples of prokaryotic microalgae are the cyanobacteria; green algae and diatoms are examples of eukaryotics (Mata et al., 2010).

Cyanobacteria differentiate into vegetative, akinete, and heterocyst cells. The functions of vegetative, akinete, and heterocyst cells are their ability to carry oxygen in photosynthesis, resistance to climactic conditions, and potential for nitrogen fixation, respectively. Green algae have a defined nucleus, cell wall, chloroplasts containing chlorophyll and other pigments, pirenoide, and a dense region containing starch granules, stigma, and scourge.

Microalgae exist in various ecosystems, both aquatic and terrestrial. More than 50,000 species are known and about 30,000 are studied (Mata et al., 2010). The main advantages of microalgae cultivation as a biomass source are (Vonshak, 1997):

• They are biological systems with high capacity to capture sunlight to produce organic compounds via photosynthesis.

• When subjected to physical and chemical stress, they are induced to produce high concentrations of specific compounds, such as proteins, lipids, carbohydrates, polymers, and pigments.

• They have a simple cellular division cycle without a sexual type stage, enabling them to complete their development cycle in a few hours. This enables more rapid development in production processes compared with other organisms.

• They develop in various environmental conditions of water, temperature, salinity, and light.

1.3 Open Pond Systems

Under phototrophic growth conditions, microalgae absorb solar energy and assimilate carbon dioxide from the air and nutrients from aquatic habitats. However, commercial production must replicate and optimize the ideal conditions of natural growth. The choice of the reactor is one of the main factors that influence the productivity of microalgal biomass.

Open tanks come in different forms, such as raceway, shallow big, or circular (Masojidek and Torzillo, 2008). Circular ponds with a centrally pivoted rotating agitator are the oldest large-scale algal culture systems and are based on similar ponds used in wastewater treatment. The design of these systems limits pond size to about 10,000 m² because relatively even mixing by the rotating arm is no longer possible in larger ponds. Raceway tanks are the most widely used artificial systems of microalgal cultivation. They are typically constructed of a closed loop and have oval-shaped recirculation channels. They are usually between 0.2 and 0.5 m deep, and they are stirred with a paddlewheel to ensure the homogenization of culture in order to stabilize the algal growth and productivity. Raceways may be constructed of concrete, glass fiber, or membrane (Brennan and Owende, 2010).

Compared to closed tanks, the raceway is the cheapest method of large-scale microalgal production (Chisti, 2008). These tanks require only low power and are easy to maintain and clean (Ugwu et al., 2008).

The construction of open tanks is low cost and they are easy to operate; however, it is difficult to control contamination, and only highly selective species are not contaminated by other microalgae and microorganisms. Environmental variations have a direct influence, and the maintenance of cell density is low due to shadowing of the cells (Amaro et al., 2011). Light intensity, temperature, pH, and dissolved oxygen concentration may limit the growth parameters of open tanks (Harun et al., 2010).

Open photobioreactors have lower yields than closed systems due to loss by evaporation, temperature fluctuations, nutrient limitation, light limitation, and inefficient homogenization (Brennan and Owende, 2010). The amount of evaporated water can be periodically or continuously added to the raceway. The amount of evaporated water in raceways depends on the temperature, wind velocity, solar radiation, and pressure of water vapor. Water can also be lost during harvesting; however, recycling of the medium reduces this problem, and nutrients from the culture medium can be reutilized (Handler et al., 2012).

Open ponds are the microalgal cultivation systems that have been studied for the longest time. These reactors are used on an industrial scale by companies such as Sosa Texcoco, Cyanotech, Earthrise Farm, Parry Nutraceuticals, Japan Spirulina, Far East Microalga, Taiwan Chlorella, Microbio Resource, Betatene, and Western Biotechnology (Spoalore et al., 2006). Earthrise Farm began cultivation on a large scale in 1976 with Spirulina. Currently the company produces Spirulina and Spirulina-based products. The cultures are grown in 30 open ponds that are 5,000 square meters in size, each one mixed by a 50-foot paddlewheel (Earthrise, 2012).

Since 1981 Parry nutraceuticals has produced Spirulina in powder form, capsules, pills and tablets, and extracts astaxanthin from Haematococcus pluvialis. The company is located in South India (Oonaiyur), and the crops are grown in open ponds, covering an area of 130 acres (Parry Nutraceuticals, 2012). Cyanotech, located in Kailua Kona, Hawaii, on the Pacific Ocean, develops and markets astaxanthin from Haematococcus in gel capsules and Spirulina in tablet form in an area of 90 acres. Since 1984, Spirulina has been cultivated in open ponds, with the medium supplemented with water from the Pacific Ocean and agitation by paddlewheels (Cyano...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Preface
• Chapter 1. An Open Pond System for Microalgal Cultivation
• Chapter 2. Design of Photobioreactors for Algal Cultivation
• Chapter 3. Metabolic Engineering and Molecular Biotechnology of Microalgae for Fuel Production
• Chapter 4. Respirometric Balance and Carbon Fixation of Industrially Important Algae
• Chapter 5. Algal Biomass Harvesting
• Chapter 6. Heterotrophic Production of Algal Oils
• Chapter 7. Production of Biofuels from Algal Biomass by Fast Pyrolysis
• Chapter 8. Algae Oils as Fuels
• Chapter 9. Production of Biohydrogen from Microalgae
• Chapter 10. Applications of Spent Biomass
• Chapter 11. Hydrothermal Upgradation of Algae into Value-added Hydrocarbons
• Chapter 12. Scale-Up and Commercialization of Algal Cultivation and Biofuel Production
• Chapter 13. Life-Cycle Assessment of Microalgal-Based Biofuels
• Chapter 14. Economics of Microalgae Biomass Production
• Index