Book dossier

Anaerobic biotechnology for bioenergy production

by Samir Kumar Khanal

Technological advances have improved the quality of life throughout the 20th Century. Although we have been quick to enjoy the benefits of our technological prowess, we have been slow to acknowledge its negative consequences. Increasingly, we are forced to confront these negative consequences: climate change, increased global demand for energy, growing energy insecurity, and continuous exploitation of limited natural resources. World energy demand is expected to grow by as much as 50 percent by 2025, mainly due to increasing demand from rapidly growing Asian countries such as China and India. Sustainability must be the foundation for economic growth in the 21st century. We need to re-direct our efforts toward bioenergy production from renewable, low cost and locally available feedstocks such as biowastes and agri-residues. Such efforts will not only alleviate environmental pollution, but also reduce energy insecurity and demand for declining natural resources. The most cost-effective and sustainable approach is to employ a biotechnology option. Anaerobic biotechnology is a sustainable technology that generates renewable bioenergy and biofuels and helps us achieve our environmental and energy objectives. Information on this subject is limited, and this textbook will be a first reference for both undergraduate and graduate students, researchers, instructors, consulting engineers, and others interested in bioenergy. The book is intended to be a useful resource to both engineering and science students in agricultural, biological, chemical and environmental engineering, renewable energy, and bioresource technology. The book does not assume a previous background in anaerobic biotechnology, although most readers should have a good working knowledge of science or engineering. The first six chapters cover the fundamental aspects of anaerobic processes. The remaining six chapters focus on applications with an emphasis on bioenergy production from wastes and agri-residues. Pertinent calculations and design examples are included in each chapter. Chapter 1 presents an overview of anaerobic fermentation, including definitions, biochemical reactions, major considerations in an anaerobic system, benefits, limitations, and calculations of the energy generation from various feedstocks. Chapter 2 covers the common metabolic stages of the anaerobic fermentation of organics and microbiological processes, and aims to provide readers with the necessary basics of microbiology, biochemistry and stoichiometry involved in an anaerobic system. Chapter 3 focuses on the effect of environmental factors such as temperature, pH, nutrients, and toxicity on the growth of key microbial groups involved in bioenergy production. Chapter 4 describes the biokinetics of anaerobic systems and application of mathematical modeling (e.g. anaerobic digestion model 1 (ADM1)) as a tool in design, operation and optimization of anaerobic processes for bioenergy production. Chapter 5 covers bioreactor configurations and growth systems (e.g., attached, granular and suspended) used in anaerobic processes. Appropriate reactor selection and design for bioenergy production are also addressed. The modern molecular techniques in anaerobic fermentation and their application for the generation of methane, hydrogen, ethanol and butanol are presented in Chapter 6. Chapter 7 outlines the selection of a suitable reactor design and operating conditions for bioenergy production from a sulfate-rich feedstock without sulfide inhibition. Strategies for sulfide control by converting aqueous and gaseous sulfides to elemental sulfur are also discussed. The next chapter covers bioenergy production from residues of emerging biofuel industries, including feedstocks, biofuel production processes from these feedstocks, stillage and glycerin generation, and anaerobic digestion of these residues. Also covered are water reclamation/reuse and biosolids disposal issues in biofuel industries. Chapter 9 describes the fundamentals of fermentative hydrogen production, including the hydrogen production pathway, strategies of obtaining enriched cultures, factors affecting hydrogen yield, process engineering, and microbiology. In addition, the concept of a bio-electrochemical-based microbial reactor for hydrogen production is also covered. The focus of Chapter 10 is development of the microbial fuel cell (MFC), with emphasis on principles, stoichiometry, energetics, microbiology, design, and operation. Different pretreatment technologies to enhance hydrolysis of high solids feedstocks are discussed in Chapter 11. The last chapter provides an overview of digester gas production from various feedstocks along with a discussion of the cleaning requirements and energy use options.