Gunda Mohanakrishna

Technological advances in CO2 conversion electro-biorefinery: A step toward commercialization.

The global atmospheric warming due to increased emissions of carbon dioxide (CO2) has attracted great attention in the last two decades. Although different CO2 capture and storage platforms have been proposed, the utilization of captured CO2 from industrial plants is progressively prevalent strategy due to concerns about the safety of terrestrial and aquatic CO2 storage. Two utilization forms were proposed, direct utilization of CO2 and conversion of CO2 to chemicals and energy products. The latter strategy includes the bioelectrochemical techniques in which electricity can be used as an energy source for the microbial catalytic production of fuels and other organic products from CO2. This approach is a potential technique in which CO2 emissions are not only reduced, but it also produce more value-added products. This review article highlights the different methodologies for the bioelectrochemical utilization of CO2, with distinctive focus on the potential opportunities for the commercialization of these techniques.

Bioelectrochemical Systems (BES) for Microbial Electroremediation: An Advanced Wastewater Treatment Technology

Bioelectrochemical systems (BES) have been employed for various applications in recent years including energy production, wastewater treatment, electrosynthesis and desalination. The present chapter emphasizes the advantages and potential applications of BES for the remediation of recalcitrant pollutants present in various types of wastewaters. Bioelectricity generated from the treatment of these wastewaters is an additional energy output from the process along with the possible environmental solution. Since, the treatment mechanism of BES is combination of both microbial and electrochemical reactions, the process can be termed as microbial electroremediation. The current chapter depicts the principles of bioelectrochemical remediation, possible mechanisms at anode and cathode. Further, a comprehensive overview on different types of wastewater as well as nutrients, pollutants and toxic substances, utilized as electron donors or acceptors for their treatment, is discussed in detail under different categories. Microbial electroremediation is still an emerging field of science aimed at harnessing energy from wastewater treatment and it has a potential to boon the waste remediation with net positive energy gain.

Trends & Sustainability Criteria for Biofuels.pdf

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Scaling Up of MFCs: Challenges and Case Studies

Rapid commercialization and expansion of biological and biotechnological platforms can contribute significantly towards realizing the concept of global bio-based economy. Bioelectrochemical systems (BESs) is one such emerging bio-based technology developed over the last few decades with multi-faceted utility. They assist in active valorization of resources in the form of bioelectricity (microbial fuel cell, MFC), biohydrogen (microbial electrolysis cell, MEC), value-added bioproducts (microbial electrosynthesis, MES) with concomitant waste management (bioelectro-treatment, BET) (Lovley 2006; Rosenbaum and Franks 2014; Venkata Mohan et al. 2014a, b). Of these, MFCs are heavily studied BES units and scalability is an important indicator in realizing their potential for practical application and global utility (Logan 2010). Scientific investigations and scale-up studies suggested that MFC operation at high reactor volumes (>5 L) are complex and are often challenged by several limitations. In this chapter, the problems associated with critical governing factors have been enlisted into operational, electrochemical and economic limitations. A brief overview of representative pilot-scale case studies like Bioelectro MET, Value from Urine, EcoBots and Peepower is presented in subsequent sections. Furthermore, possible technical and technological solutions, and future perspective to overcome the mentioned limitations are also included.

Anodic Electron Transfer Mechanism in Bioelectrochemical Systems

The reality of bacteria in transporting electron beyond their cell wall and ability to electrically interact with electrode has been nearly over a century (Potter 1911). Microbial fuel cells are growing bioelectrochemical systems that use bacteria as a catalyst and generate bioelectricity using organic matter. The bacteria act as powerhouse at the anode of MFC and oxidize organic matter to CO2 by generating electrons and protons (Kondaveeti 2014). These electrons move from anode to cathode and get reduced as water by using oxygen as an electron acceptor. The generated electrons from bacteria can be transferred to anode by direct contact with biofilm or by using mediators, which can be either exogenic or endogenic (Kondaveeti and Min 2015). The natural mediators such as flavins which are secreted by bacteria or other active complexes such as c-type chromosomes present on outer cell membranes can shuttle electrons. Up to date the metal reducing bacterial species such as Geobacter and Shewanella have been widely noticed in MFC technology, due to their external electron transfer mechanism and for synthesis of natural mediators (riboflavins), which can be a rival for other exoelectrogens (Logan 2008). The external insoluble shuttles such as neutral red, and methyl viologen etc. were used in microbial fuel cells for electron transfer from the bacterial cell wall to electrodes. The initial studies in addition of exogenous mediators to MFC were pursued (Cohen 1931; Schroder 2007). In this study low current generation in MFC might be due to lack of electromotive oxidation and reductive force. These were resurfaced in 1980 by Bennetto and coworkers and it was further investigated by many other researchers. In the present chapter, the electron transfer mechanisms such as direct electron transfer, mediated electron transfer and interspecies electron transfer mechanisms with electroactive anode bacteria are discussed.

Reactor Design for Bioelectrochemical Systems

Bioelectrochemical systems (BES) are novel hybrid systems which are designed to generate renewable energy from the low cost substrate in a sustainable way. Microbial fuel cells (MFCs) are the well studied application of BES systems that generate electricity from the wide variety of organic components and wastewaters. MFC mechanism deals with the microbial oxidation of organic molecules for the production of electrons and protons. The MFC design helps to build the electrochemical gradient on anode and cathode which leads for the bioelectricity generation. As whole reactions of MFCs happen at mild environmental and operating conditions and using waste organics as the substrate, it is defined as the sustainable and alternative option for global energy needs and attracted worldwide researchers into this research area. Apart from MFC, BES has other applications such as microbial electrolysis cells (MECs) for biohydrogen production, microbial desalinations cells (MDCs) for water desalination, and microbial electrosynthesis cells (MEC) for value added products formation. All these applications are designed to perform efficiently under mild operational conditions. Specific strains of bacteria or specifically enriched microbial consortia are acting as the biocatalyst for the oxidation and reduction of BES. Detailed function of the biocatalyst has been discussed in the other chapters of this book.

Induced bioelectrochemical metabolism for bioremediation of petroleum refinery wastewater: optimization of applied potential and flow of wastewater

Hybrid based bioelectrochemical system (BES) configured with embedded anode and cathode electrodes in soil was tested for the bioelectrochemical degradation of petroleum refinery wastewater (PRW). Four applied potentials were studied to optimize under batch mode operation, among which 2 V resulted in higher COD degradation (69.2%) and power density (725 mW/m2) during 7 days of operation. Further studies with continuous mode of operation at optimized potential (2 V) showed that hydraulic retention time (HRT) of 19 h achieved the highest COD removal (37%) and highest power density (561 mW/m2). BES function with respect to treatment efficiencies of other pollutants of PRW was also identified with respect to oil and grease (batch mode, 91%; continuous mode, 34%), total dissolved salts (batch mode, 53%; continuous mode, 24%) and sulfates (batch mode, 59%; continuous mode, 42%). Soil microenvironment in association with BES forms complex processes, providing suitable conditions for efficient treatment of PRW.

Bioprocesses for Waste and Wastewater Remediation for Sustainable Energy

Abstract Microbial metabolism of pollutants is the key process involved in energy generation along with remediation. This process led by the different electron acceptors operates under diverse operations. Engineering these for renewable energy products is of prime importance for sustainable development. This chapter describes the bioremediation process in generating the various types of bioenergies that help sustainable development. Anaerobic process of organic matter degradation is the major process that contributes to energy generation. The operating conditions and process control help in the generation of different energy vectors like methane, hydrogen, and electricity. Another approach gaining prominence in wastewater treatment is phytoremediation, led by microalgae. The heterotrophic growth of microalgae aids in the organic contaminants’ removal from wastewater as well as carbon dioxide sequestration from the atmosphere to generate lipids for biodiesel and carbohydrates.