Microbial Energy Conversion

Zhenhong Yuan

• Publisher: De Gruyter
• Year: 2018
• ISBN:
  9783110424867
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Renewable Power Resources
• Index: Technology & Engineering

The book provides an overview on various microorganisms and their industrialization in energy conversion, such as ethanol fermentation, butanol fermentation, biogas fermentation and fossil energy conversion. It also covers microbial oil production, hydrogen production and electricity generation. The content is up to date and suits well for both researchers and industrial audiences.

Ying Guo, Jie Xu, Zhenhong Yuan

1Introduction

Corresponding author: Zhenhong Yuan, E-mail: [email protected]

Ying Guo, Jie Xu, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences; CAS Key Laboratory of Renewable Energy; Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development, Guangzhou 510640, China

Energy has been regarded as the basis of survival and as a source for the development of human kind. Currently, energy utilization is mainly fossil based; however, with the rapid economic development, fossil fuels, as a nonrenewable source of energy, may not be able to meet the growing demand of our society. Therefore, biomass energy as a source of renewable energy will be helpful in alleviating the current pressure on energy supply and will be important to develop a recycling-based economy.

Microbes can substantially degrade almost all naturally occurring substances and synthetic compounds on Earth. In fact, microbes are a rather important part of the entire life cycle of our planet. Microorganisms and their activated enzymes play a key role for energy conversion. They can utilize agricultural waste, forestry waste, and municipal solid waste (MSW), and transform these materials into clean fuels such as ethanol, butanol, biodiesel, biogas, and hydrogen. This is of great strategic and practical significance for the ecological, the economic, and the social environment.

This book attempts to analyze microorganisms, biochemical conversion processes and mechanisms, strain selection, and applications that are involved in the energy conversion process. The theory of microbial energy conversion and its practical application will be systematically introduced, and the readers will gain basic knowledge of microbial energy production.

Section 1:Energy and Microbes

1.1Energy Conversion

A wide range of energy is naturally available and several energy forms have already been developed and utilized; examples can be classified into conventional energy (coal, oil, gas, and water) and new energy (biomass energy, nuclear energy, tidal energy, solar energy, geothermal energy, and wind energy). Table 1.1 illustrates their characteristics [1].

Energy can be classified into 2 categories, the primary energy and secondary energy. Primary energy is a form of energy that exists in nature (such as coal, oil, natural gas, biomass, geothermal, nuclear, and wind), while secondary energy (such as electricity, hydrogen, gasoline, gas, and alcohol) refers to a form of energy that is either directly or indirectly converted from primary energy.

Table 1.1: Energy categories.

Classification way	Type
Availability	Primary energy, secondary energy
Source	Energy from outside the Earth, energy from the Earth’s interior, energy from other celestial bodies
Regeneration	Renewable energy (cycle), nonrenewable energy (consumption)
Utilization method	Fuel energy, nonfuel energy
Storage and transportation	“Receptacle loads,” process energy
Tradition	Conventional energy sources, new energy
Degree of contamination	Clean energy, nonclean energy

Definitions for renewable and nonrenewable energy sources are provided based on whether energy sources can be recycled. Renewable energy, including biomass, hydro, tidal, solar, and wind energy, generally refers to forms of energy that are not dwindling. However, nonrenewable energy suggests a form that will gradually diminish or be completely depleted by exploitation, and the most typical forms of nonrenewable energy are coal, oil, and natural gas.

On the basis of the degree of contamination energy can be divided into clean energy and nonclean energy; the latter is also known as “green energy.” Green energy can be subdivided into two categories: first, it refers to the energy form that can be obtained via utilization of modern technologies, such as biomass, solar, wind, and geothermal; second, it refers to the energy form that can be obtained via utilization of waste such as MSW, agricultural waste, and forestry waste.

A wide variety of energy classifications are currently used, and category approaches for any type of specific energy can be included from different classification perspectives. For example, biomass energy is a renewable energy; however, when it is converted into alcohol, it becomes a secondary energy form.

Primary energy may not meet our demand, and at the same time, primary energy utilization has previously caused severe harm to the ecological environment. In light of this, it is necessary to take specific measures to convert primary energy into secondary energy. Fossil fuels played an indispensable role in the development of human civilization and social progress. However, their nonrenewable nature combined with the sometimes rampant abuse caused significant pressure on the environment. Renewable energy alternatives, such as wind, solar, and biomass, have become an inevitable trend for the future.

Biomass is the only type of renewable energy that can be converted through a variety of ways to meet our needs for all types of energy products, including the three fuel forms (gas, solid, and liquid) in combination with electricity, which can directly replace oil, coal, and other fossil fuels for energy utilization. Furthermore, biomass as carbon resource can provide various types of high value-added chemicals through biorefining processes; therefore, in this case, biomass can be considered as a substitute for mineral resources. Moreover, the development of biomass energy will be a solution to reduce greenhouse gas emissions and environmental pollution, and thus will be helpful for the ecological restoration and rural economic development.

China has a great abundance of biomass resources. According to recent statistics of the China Agricultural University, China has an annual capacity of 740 million tons of agricultural waste, of which 350 million tons can be utilized as feed, paper, and other industrial raw materials, while the remaining 390 million tons of crop straw are approximately equivalent to 200 million tons of standard coal. For example, industrial organic wastewater and livestock farm waste resources can theoretically produce 80 billion cubic meters of methane, which is the equivalent of 57 million tons of standard coal; forest residues waste can replace 300 million tons of standard coal; municipal waste generation can replace 13 million tons of standard coal; and some crops can also be treated as sources of liquid fuels. In the near future, the potential for the total biomass production in China has been estimated at 500 million tons of standard coal equivalent, which will meet more than 20% of China’s energy consumption demand. If rationally processed, this will reduce annual carbon dioxide emissions by nearly 3.5 billion tons, and sulfur dioxide, nitrogen oxides, and dust emissions by nearly 25 million tons [1].

Currently, biomass utilities are applied with a variety of technologies, such as gasification for power, pyrolysis for gaseous and liquid fuel, and synthetic process for chemicals. Biomass gasification is a thermal conversion technology that converts feedstock of low energy density into high energy density fuel, which will then be suitable for storage, transport, and utilization. A gasification approach greatly improves the quality and efficiency of the system.

Fuel ethanol is one of these forms of liquid biomass obtained through chemical and physical hydrolysis of biomass combined with the microbial fermentation of sugars. Ethanol from biomass is one of the closest points of contact with the energy provided by microorganisms. Since the 1970s and in response to the global oil crisis, Brazil and the United States have created specialized agencies to promote the development of fuel ethanol, especially for their most abundant crops (sugarcane for Brazil and corn for the United States). China has also developed its own ethanol industry based on stale rice. In 2010, the global production of fuel ethanol reached 85.8 billion liters [1]. China cannot follow in the footsteps of the United States and Brazil and treat grain as raw material. The technology to develop nongrain fuel based on lignocellulosic feedstock for ethanol and butanol production will be the inevitable choice for the future fuel production of China. At present, China’s biomass fuel ethanol technology is thriving, and the golden age for biomass fuel ethanol will commence in the next few years.

Biodiesel is an environmentally friendly liquid fuel and can replace fossil diesel, thus compensating for the shortage of petroleum resources. In Europe and the United States, the main feedstock for biodiesel is either soybean or rapeseed oil. The high cost of resources determine the biodiesel industries in Europe and America, which can only survive with governmental subsidies. Biodiesel production from plant oil cannot operate in China because of their high price, and the consequential diminishing of the food supply. Therefore, the Chinese biodiesel industry is mainly based on waste oil, and the current distribution of waste oil resources limits the development of the regional biodiesel industry. Biodiesel is also an important part of biomass energy. Jatropha, algae, and other organisms can be converted into biodiesel through either biochemical or chemical processes.

Microbes are of great importance for the biomass energy technology. Biofuels (such as fuel ethanol, butanol fuel, hydrogen, and methane) can be obtained from microbial and the related enzymatic processes. Microorganisms play an important role in the clean utilization of fossil energy such as microbially enhanced oil recovery and coal liquefaction.

1.2Energy Microorganism

Energy microbes are microorganisms that are closely related to energy utilization from natural resources or waste sources, including bacteria, fungi, and algae [2, 3]. This book mainly describes the types of microorganisms that either can or may be used in the energy conversion processes under the current scientific and technologic conditions. These microbes are mainly involved in biomass conversion, and a small part of them have been applied in oil and coal conversion technologies.

1.2.1Energy Microorganism Culture

Microorganisms are the most widely distributed and abundant species on Earth, and it is still difficult to estimate the number of biological communities. In addition, microorganisms can live in extreme environments, such as anaerobic, high temperature, and high salt, which may not be suitable for plants and animals. To adapt to such harsh environmental conditions, microorganisms produce numerous substances with specific activities to withstand environmental pressure. Therefore, microorganisms are a rich source of biologically active substances.

1.2.1.1Microbial Origin

Microorganisms that have been applied for industrial fermentation are divided into three categories based on their sources [4]:

(1)Natural environment

At present, microorganisms that are employed in the industrial process have initially been derived from the natural environment, including from soil, water, animals, plants, and minerals. These are then screened and cultured through a series of steps to meet different needs. It is more likely to find a new species if bacteria samples would be collected from more extensive sources. Many important species are yet to be developed from extreme environments such as high temperature, high pressure, high salt, high pH, low pH, and the ocean.

(2)Screening

If the species that will produce the desired product has been determined, it is good practice to use many different strains of the species. By culturing microorganisms obtained from various microbiological laboratories and deposited units around the world, target strains can be screened for, analyzed, and ultimately improved. Through a strict selection process, strains suitable for energy production can be verified.

(3)Purchased species (typically for patents bacteria, or applied strains from the industry)

Patents for biotechnology have the following criteria in China: The patent should provide the microbe and its corresponding culture conditions for preservation at preservation agency offices. The deposited and patented strain can be purchased from the agency. In addition, strain can be provided through personal exchanges or as kind gift depending on the circumstances.

1.2.1.2Breeding of Microorganisms

Although initial production strains have been derived from nature, the efficiency of natural strains is generally low. The rise of the antibiotic industry in the 1940s promoted the rapid development of microbial genetics and laid a solid theoretical foundation for the microorganism fermentation industry. In recent years, because of the rapid development of systems biology, synthetic biology, and protein engineering, the microbial breeding technology continues to advance. It provides engineered strains to meet production requirements. At present, micr...

Table of contents

• Cover
• Title Page
• Copyright
• Contents
• List of Contributors
• 1 Introduction
• 2 Foundations in Microbiology
• 3 Microbial Biomass Pretreatment and Hydrolysis
• 4 Microbial Ethanol Fermentation
• 5 Microbial Butanol Production
• 6 Microbial Grease Production and Conversion
• 7 Microbial for Methane Production
• 8 Microbial Hydrogen Production
• 9 Microbial Electricity Production
• 10 Microbial Fossil Energy Conversion
• Index