synthesis of commodity chemicals and move steadily towards the bio-based economy. The utilization of renewable resources such as seaweeds and waste biomass is often considered as an attractive candidate for biofuels and different bioproducts. However, limitations regarding the robustness of process and selectivity of target products are often considered bottlenecks to their sustainable commercialization. This book discusses such bottlenecks and suggests many feasible applicable techniques to increase the yield of the targeted bioproducts. For achieving the circular economy with the concept of zero-wastes, this book discusses the production of bioethanol from different lignocellulosic wastes and seaweeds and also the production of biodiesel from waste oils and fats using sustainable heterogeneous catalysts. Further, it explains how to reach for a feasible transesterification process that produces high yield of qualified biodiesel to be successfully used as alternative and/or complementary for the conventional petro-diesel without affecting the engine performance. The book also debates how the applications of heterogeneous catalysts valorized from different readily available natural resources would be very beneficial in the production of biodiesel and bioglycerol. It also states the applicability of lipases in production of biodiesel and oleochemicals. The use of ionic liquids (ILs) in the lignocellulosic wastes pretreatment for further use in bioethanol and other biorefineries production has gained considerable attention in this book.
It also clarifies how solid waste management can in general open a new sustainable revolution in different sectors which would indeed lead to the successful achievement of the three pillars of sustainability, social, environment and economic. Special attention is given to valorization as a technical route adopted for the recycling of waste into desirable products having non-toxic economic worth. Moreover, the valorization of different available bio-wastes into different biofuels and value-added products, for example, glycerol, oleochemicals, bioplastics, biopolymers, biofertilizers, animal feed, etc., with the concept of reaching zero-waste is discussed from the perspective of achieving the seventeen goals of sustainability, and overcoming the problems of water scarcity, waste management and climate change.
One of the most important sectors this book covers is the main environmental problems related to landfills including soil, water and air contamination, and it also highlights and discusses some of the sustainable solutions and management for such problems including landfill design and location, leachate management and treatment, gas and emission control. Moreover, the effect of unsuitable locations of landfills on the environment is discussed and evaluated. This book also goes through optimizing the treatment of landfill leachate for minimizing its adverse impacts on the natural ecosystem as it is an urgent concern with the increased municipal solid wastes. It emphasizes on the promising electrocoagulation process for its outstanding ability in decontaminating leachate pollution in an economic, viabile, and green approach. A case study for septage characterization and sustainable fecal sludge management has been also reported in this book.
The multidisciplinary approach discussed in this book extends the different scientific and engineering disciplines to reach all other disciplines including economics, politics and other social sciences. Thus, it is time for engineers, scientists, medical doctors, economists, politicians, military officers and specialists, etc., to join forces in multidisciplinary research and development projects to achieve sustainability for better, stable, peaceful, non-sectarian, prosperous and more clean and sustainable societies.
Nour Sh. El-Gendy
1
An Overview of Electro-Fermentation as a Platform for Future Biorefineries
Tae Hyun Chung and Bipro Ranjan Dhar*
Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, Canada
Abstract
Many countries have set up policies to decrease fossil fuel dependency and petro-based synthesis of commodity chemicals. Fermentative biofuels and bioresource recovery processes are expected to assist considerably in this context of sustainable transition to a bio-based economy. The utilization of renewable resources such as waste biomass is often considered an attractive feature of fermentative bioprocesses. However, limitations regarding the robustness of process and selectivity of target products are often considered bottlenecks to their sustainable commercialization. Particularly, in conventional fermentation processes, microorganisms produce undesired by-products to attain intracellular redox balance, which leads to a low yield of target products. Recently, electro-fermentation has emerged as an innovative approach for changing metabolic pathways of fermentative microorganisms towards target products with higher yields and productivities by changing intracellular redox potential. Lab-scale EF studies have successfully demonstrated superior performance over conventional fermentation to produce a wide variety of biofuels and commodity chemicals. This book chapter provides an overview of fundamental and applied aspects of various value-added products synthesis with the EF process and identifies research gaps for future development.
Keywords: Electro-fermentation, electro-selective fermentation, fermentation, value-added products, biofuel, biorefinery
1.1 Introduction
Microbial electrochemical cell (MXC) is a unique type of bioreactor, which integrates biological processes (e.g., utilizing electroactive bacteria as biocatalyst) with electrochemistry (e.g., introducing electrodes, potentials) to convert the chemical energy in organic matter into bioenergy. To differentiate the various types of MXCs, different names have been assigned based on the products or their provided services. Over the decades, the MXCs were largely focused to generate bio-electricity in microbial fuel cells (MFCs) (Logan, 2008). More recently, MXCs were engineered to produce various biogas, such as bio-hydrogen in microbial electrolysis cell (MEC) (Logan et al., 2008; Wagner et al., 2009) and bio-methane in microbial electrolysis cell assisted anaerobic digester (MEC-AD) (Huang et al., 2020; Zakaria and Dhar, 2019). Nonetheless, the MXCs were also implemented for many other applications, such as water desalination in microbial desalination cell (MDC) (Al-Mamun et al., 2018; Jafary et al., 2020), nutrient recovery (Barua et al., 2019; Qin et al., 2016; Zou et al., 2017), CO2-reduction-to-value-added-products in microbial electrosynthesis (MES) (Lovley and Nevin, 2013; Rabaey and Rozendal, 2010; Zhang and Angelidaki, 2014) and production of chemicals, such as hydrogen peroxide in microbial peroxide producing cells (MPPCs) (Chung et al., 2020b; Rozendal et al., 2009). Due to the extensive studies since the early 2000s, several studies have been dedicated to scaling-up the MXCs (Dhar et al., 2016; Heidrich et al., 2014; Hiegemann et al., 2016; Liang et al., 2018; Sim et al., 2018). However, the main bottleneck of the aforementioned MXC applications was the requirement of high energy input or output, whether the electrons are the main driving force in MECs, MDCs, MES, and MPPCs, or they are the desired product (e.g., in MFCs). Often, challenges in achieving high current density from MXCs was the main argument against further development and scaling-up (Feng et al., 2014; Heidrich et al., 2014; Sim et al., 2018; Zakaria and Dhar, 2019). On the other hand, the MXCs have gained interest for further development when utilized as a biosensor, where they mainly focus on changes in electrical energy (e.g., signal output), not necessarily required to produce high electrical energy output (Chung et al., 2020a; Do et al., 2020; Jiang et al., 2018). Hence, proposing a new application of MXC focusing on using low energy input can also be a novel means.
Fermentation process is one of the bioprocesses that converts complex organics to various types of soluble molecules, such as alcohols and carboxylates, and sometimes, along with some energy-rich biogases (e.g., hydrogen and methane) (Dhar et al., 2015; Elbeshbishy et al., 2017; Ghimire et al.,
