Microbial Electrochemical Technologies

Sonia M. Tiquia-Arashiro, Deepak Pant, Sonia M. Tiquia-Arashiro, Deepak Pant

• Publisher: CRC Press
• Year: 2020
• eBook ISBN: 9780429944994
• Edition: 1
• Topic: Economics
• Subtopic: Development Economics
• Index: Economics

This book encompasses the most updated and recent account of research and implementation of Microbial Electrochemical Technologies (METs) from pioneers and experienced researchers in the field who have been working on the interface between electrochemistry and microbiology/biotechnology for many years. It provides a holistic view of the METs, detailing the functional mechanisms, operational configurations, influencing factors governing the reaction process and integration strategies. The book not only provides historical perspectives of the technology and its evolution over the years but also the most recent examples of up-scaling and near future commercialization, making it a must-read for researchers, students, industry practitioners and science enthusiasts.

Key Features:

• Introduces novel technologies that can impact the future infrastructure at the water-energy nexus.
• Outlines methodologies development and application of microbial electrochemical technologies and details out the illustrations of microbial and electrochemical concepts.
• Reviews applications across a wide variety of scales, from power generation in the laboratory to approaches.
• Discusses techniques such as molecular biology and mathematical modeling; the future development of this promising technology; and the role of the system components for the implementation of bioelectrochemical technologies for practical utility.
• Explores key challenges for implementing these systems and compares them to similar renewable energy technologies, including their efficiency, scalability, system lifetimes, and reliability.

PART-III

Applications of Microbial Electrochemical Systems in Wastewater Treatment, Bioenergy, Biosensors and Electrosynthesis

CHAPTER
8

Microbial Electrolysis Cell (MEC): A Versatile Technology for Hydrogen, Value-added Chemicals Production and Wastewater Treatment

Abudukeremu Kadier^1,2*, Piyush Parkhey³, Ademola Adekunle⁴, Pankaj Kumar Rai⁵, Mohd Sahaid Kalil^1,2, S. Venkata Mohan³ and Azah Mohamed⁶

¹ Department of Chemical and Process Engineering, Faculty of Engineering and Built Environment, National University of Malaysia (UKM), 43600 UKM Bangi, Selangor, Malaysia

² Research Centre for Sustainable Process Technology (CESPRO), Faculty of Engineering and Built Environment, National University of Malaysia (UKM), 43600 UKM Bangi, Selangor, Malaysia

³ Bioengineering and Environmental Sciences Laboratory, Environmental Engineering and Fossil Fuel (EEFF) Department, CSIR-Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad 500 007, India

⁴ Bioresource Engineering Department, McGill University, 21111 Lakeshore Rd., Ste-Anne-de-Bellevue, QC H9X 3V9, Canada

⁵ Department of Biotechnology and Bioinformatics Center, Barkatullah University (BU), Bhopal 462 026, India

⁶ Research Centre for Integrated Systems Engineering and Advanced Technologies (INTEGRA), Faculty of Engineering and Built Environment, National University of Malaysia (UKM), Bangi 43600, Selangor, Malaysia

* Corresponding author: [email protected]

1. Introduction

The present scenario of the energy crisis is arising due to the depletion of fossil fuels (FFs) and increasing global energy demand. Scientists around the world are engaged to work on various alternative energy sources. Also, the rapid combustion of FFs generates greenhouse gasses, such as CO₂, that contributes to global climate change (Kadier et al. 2016a). The ever-increasing population produce an immense volume of wastewater creating a nuisance to the environment. Collectively, these two major issues, namely energy crisis and wastewater disposal problem requires immediate attention for world’s sustainable development. Wastewater usually contains a complex mixture of organic substrates that has to be removed before being discharged into the surroundings (Lu and Ren 2016). In general, the removal of these contaminants comprises a group of biological, chemical and physical treatment process. Wastewater treatment plants usually use large pumps and blowers that are energy intensive and raise treatment costs. Thus, the operating costs of treating wastewater are sure to rise despite the very fact that a major quantity of the energy inputs can be recovered as biogas via anaerobic digestion (AD). On the other hand, aerobic treatments make matters worse and produce a large amount of sludge that is needed to be disposed of that only adds more to the operating cost (Yu et al. 2018). Nevertheless, the operating costs of treatment plants could be greatly decreased if wastewater treatment is accompanied by green energy and value-added biochemical production (Angenent et al. 2004). It is worth mentioning that wastewater exploitation requires versatile and robust technologies due to its complex composition.

Among the biochemicals or fuels that may be extracted from wastewaters, H₂ occupies a leading position as a result of its attention-grabbing characteristics as a fuel; it is clean and provides CO₂ and other pollutant emissions-free energy carrier (Rai 2016). On burning, H₂ does not produce greenhouse gas (GHG), ozone depletion chemicals or acid rain. It is a high calorific value fuel, and has the highest energy content per unit weight in comparison to other gaseous fuels (Kadier et al. 2016a; Kadier et al. 2018a). H₂ can be generated biologically by various methods, including dark fermentation (DF), photo fermentation and biophotolysis (Nikolaidis and Poullikkas, 2017; Kadier et al. 2017b). However, in the said processes the complete utilization of substrate is not possible as the metabolic pathway of the microorganisms directs the synthesis of alternative by-products (Rai and Singh 2016). Besides, it had been reported that lower H₂ yield achieved in conventional biological hydrogen production processes is due to the thermodynamic barrier. This thermodynamic barrier may be overcome by application of a small input of electrical energy (Rozendal et al. 2006) in a bioelectrochemical system (BES) called microbial electrolysis cell (MEC). MEC is comparatively a new and sustainable approach for H₂ production from organic waste matter, including wastewater (Kumar et al. 2017). H₂ production from wastewater using MECs is a promising approach toward wastewater treatment and green energy generation as it has the potential to overcome the bottlenecks of conventional hydrogen production technologies (Escapa et al. 2016; Zhen et al. 2017). Recent developments demonstrate that MECs represent a promising technology for coupling wastewater treatment and energy recovery by using the wastewater as a source of free electron (Logan et al. 2008; Rozendal et al. 2008, Kadier et al. 2017a). MECs are BESs in which electrochemical reactions are microbially catalyzed. They utilize domestic and industrial wastewater as a feedstock to generate H₂ through the catalytic action of microorganisms in the presence of electric current and absence of oxygen (O₂) (Kadier et al. 2014; Khan et al. 2017). In MECs, external power is supplied to drive thermodynamically favorable reactions at the cathode (Kadier et al. 2015a; Kadier et al. 2015b). The application of MECs is not limited to only H₂ production utilizing wastewater. Breakthrough researches are also going on the application of MECs in the field of value-added product synthesis, biosensor, resource recovery and waste treatment.

The present chapter provides a brief introduction to MEC, including the working principles, thermodynamics, possible electron transfer mechanisms at the anode and current application of MEC. In addition, a comprehensive overview of different types of conventional technologies for waste-to-energy (WTE) generation and WTE-MEC integrated approaches is presented. Finally, the advantages of MECs over other conventional ones are also discussed in detail. Thus, this chapter is a first comprehensive review of current knowledge in comparing and integrating MEC and other conventional WTE technologies.

2. Microbial Electrolysis Cell (MEC) Technology

2.1 Working Principles

The working principle of the MEC is similar to that of the microbial fuel cell (MFC) as they both rely on oxidation of organic material at the anode and complimentary reduction at the cathode. This oxygen dependence in MFCs implies the non-spontaneity of the process and could be a serious limitation. To overcome this cathodic limitation, Liu et al. (2005) and Rozendal et al. (2006) developed a novel system called MEC where the entire process is assisted with a small voltage. In an MEC, electrochemically active bacteria (EAB) or electrogenic bacteria are the dominant populations at the anode and oxidize organic matters to protons, electrons and CO₂. Finally, H₂ is evolved at the cathode by reducing the produced protons and electrons. This is subsequently reflected in the presence of obligate anaerobes (Logan et al. 2008; Kadier et al. 2018b).

Figure 1: A schematic of a typical two-chamber MEC especially as it relates to oxidation at the anode, reduction at the cathode and electron transfer.

This electrically assisted operation provides robustness to potential applications of this technology. In general, the essential components for the construction and operation of an MEC include a power supply with constant DC source typically between 0.2-0.8V, a microbial enriched anode, a catalyzed cathode (e.g., Pt catalyzed cathode) and a well-designed gas collection system. Different architecture exists (Kadier et al. 2016b; Kadier et al. 2017c) and they are basically optimized for the process/application that the MECs is built on but important parameters considered include anode-cathode distance, flow rates and configuration and presence/absence of a membrane. Recent studies (Call and Logan 2008; Wang and Ren 2013; Kadier et al. 2017c) have confirmed that a single-chamber MEC is cost-effective and lead to an increase in the coulombic efficiency (CE) of the entire process.

2.2 Thermodynamics of MEC

The reactions that lead to H₂ evolution using acetate as an example (Equation 1) in an MEC typically have a positive Gibbs free energy (ΔG), hence will not proceed unless external energy is added (usually a small voltage). This added energy must be greater than the equilibrium voltage that can be calculated as the negative ratio of the Gibbs free energy of reaction and the product of the number of electrons involved and Faraday’s constant as shown in Equation 2 (Logan et al. 2008; Harnisch and Schroder 2010; Kadier et al. 2016a). An alternative method is to use the Nernst equation to determine the difference between the theoretical cathode and anode potential. However, overpotentials at both electrodes could mean that the energy requirement might be greater than required. Thus for H₂ evolution using acetate under standard biological conditions (T = 25 °C, P = 1 bar, pH = 7), the following equation can be derived:

${\text{CH}}_3{\text{COO}}^{-}+4{\text{H}}_2\text{O}\to 4{\text{HCO}}_3^{-}+{\text{H}}^{+}+4{\text{H}}_2\left(\text{Δ}{G}_r^{°}=+104.6\frac{\text{kJ}}{\text{mol}}\right)$

(1)

$E_{eq}=\frac{\text{Δ}{G}_r^{°}}{nF}=-\frac{104.6\times {10}^3}{8\times 96485}=-0.14\text{V}$

(2)

This thermodynamic calculation is important as it eventually affects both the success of the forward reaction as well as the cost. The requirement for H₂ evolution using acetate with the (Liu et al. 2005) minimum required energy supplied or minimum overpotential was estimated at 0.29 kWh/m³ (Log...

Table of contents

• Cover
• Title Page
• Copyright Page
• Preface
• Table of Contents
• PART-I: Fundamentals of Microbial Electrochemistry: Novel Microbial Pathways and Electron Transfer Mechanisms
• PART-II: Optimizing Microbial Electrochemical Systems: Microbial Ecology of Biofilms and Electroactive Microorganisms Strain Improvement
• PART-III: Applications of Microbial Electrochemical Systems in Wastewater Treatment, Bioenergy, Biosensors and Electrosynthesis
• PART-IV: Applications of Microbial Electrochemical Systems in Bioremediation
• PART-V: Materials for Microbial Electrochemical Technologies
• PART-VI: Design of Microbial Electrochemical Systems: Toward Scale-up, Modeling and Optimization
• Index