Sai Kishore Butti

A Circular Bioeconomy with Biobased Products from CO2 Sequestration.

The unprecedented climate change influenced by elevated concentrations of CO2 has compelled the research world to focus on CO2 sequestration. Although existing natural and anthropogenic CO2 sinks have proven valuable, their ability to further assimilate CO2 is now questioned. Thus, we highlight here the importance of biological sequestration methods as alternate and viable routes for mitigating climate change while simultaneously synthesizing value-added products that could sustainably fuel the circular bioeconomy. Four conceptual models for CO2 biosequestration and the synthesis of biobased products, as well as an integrated CO2 biorefinery model, are proposed. Optimizing and implementing this biorefinery model might overcome the limitations of existing sequestration methods and could help realign the carbon balance.

Waste Biorefinery: A New Paradigm for a Sustainable Bioelectro Economy.

A waste biorefinery is a means to valorize waste as a renewable feedstock to recover biobased materials and energy through sustainable biotechnology. This approach holistically integrates remediation and resource recovery. Here we discuss the various technologies employable to construct a waste biorefinery platform and its place in a biobased economy.

Spatiometabolic stratification of anoxic biofilm in prototype bioelectrogenic system

A prototype bio-catalyzed electrogenic system integrated with a biological treatment process (SBR-BET) was evaluated to study specific function of anoxic condition on the electrogenic activity. A multiphasic approach was employed, where the influence of DO on bio-electrogenic activity was optimized initially, later optimal anode to cathode inter-electrode distance was enumerated. Amongst the four electrode distances evaluated, 2cm showed higher power output. Bioelectrokinetics analysis was used to validate the system performance with the experimental variation studied. The redox behavior showed an increase in cathodic catalytic activity with an increase in the inter-electrode distance. Spatiometabolic distribution depicted the microbial stratification on the anode. Electrochemically active bacteria present on the anode surface (inner and outer layers of biofilms) showed relatively uniform diversity compared with the suspension culture.

Phasic availability of terminal electron acceptor on oxygen reduction reaction in microbial fuel cell

Oxygen-reduction reactions (ORR) plays a pivotal role in determining microbial fuel cells (MFC) performance. In this study, an attempt to determine the influence of the phasic availability of terminal electron acceptor (TEA) on ORR was made. Two MFCs operated with dissolved oxygen (MFC-DC) and air (MFC-SC) as TEA were constructed and analyzed in continuous mode under open and closed circuit conditions. The bio-electrochemical analysis showed a marked influence of dissolved oxygen resulting in a maximum power density with MFC-DC (769mW/m2) compared to MFC-SC (684mW/m2). The availability of O2 in dissolved phase has lowered the activation losses during the MFC operation as a result of effective ORR. The cyclic voltammetry analysis revealed the TEA dependent biocatalyst activity of NADH and cytochrome complex which enabled electron transfer kinetics and improved substrate utilization. Finally, the study evidenced the critical role of TEA phasic availability to regulate the bio-electrogenic and substrate degradation potential in MFC.

Autotrophic biorefinery: dawn of the gaseous carbon feedstock

CO2 is a resource yet to be effectively utilized in the autotrophic biotechnology, not only to mitigate and moderate the anthropogenic influence on our climate, but also to steer CO2 sequestration for sustainable development and carbon neutral status. The atmospheric CO2 concentration has seen an exponential increase with the turn of the new millennia causing numerous environmental issues and also in a way feedstock crisis. To progressively regulate the growing CO2 concentrations and to incorporate the integration strategies to our existing CO2 capturing tools, all the influencing factors need to be collectively considered. The review article puts forth the change in perception of CO2 from which was once considered a harmful pollutant having deleterious effects to a renewable carbon source bearing the potential to replace the fossils as the carbon source through an autotrophic biorefinery. Here, we review the current methods employed for CO2 storage and capture, the need to develop sustainable methods and the ways of improving the sequestration efficiencies by various novice technologies. The review also provides an autotrophic biorefinery model with the potential to operate and produces a multitude of biobased products analogous to the petroleum refinery to establish a circular bioeconomy. Furthermore, fundamental and applied research niches that merit further research are delineated.

Stacking of microbial fuel cells with continuous mode operation for higher bioelectrogenic activity

The effect of stacking multiple microbial fuel cells for stable power output was evaluated in continuous mode operation. Three single chambered air cathode CMFCs with Nafion (CMFCN), Terry cotton (CMFCT) as membranes and one without membrane (CMFCML) were operated in continuous mode. Maximum power density (PD) and COD removal efficiency was obtained for CMFCN (0.1 W/m2, 50%) followed by CMFCML (0.062 W/m2, 47%) and CMFCT (0.025 W/m2, 39%) and were stable throughout the operation. To increase the power output further, stacking of CMFCs was carried in series/parallel circuitry, which yielded high power density in parallel (2.0 W/m2; 7.2 W/m3) and high voltage in series (1.1 V). Study also evidenced that stacking resulted in high and stable bioelectricity by minimizing the electron losses in comparison to individual CMFCs operation. Stable and high power output signifies the impact of continuous mode operation that constantlty replenishes the substrate.

Microbial mediated desalination for ground water softening with simultaneous power generation

A novel three-chambered microbial desalination cell (MDC) was designed for evaluating desalination of synthetic ground water with simultaneous energy generation and resource recovery. The specific design enabled efficient interelectrode communication by reducing the distance of separation and also maintained an appropriate surface area to volume ratio. MDC were evaluated in different circuitry modes (open and closed) to assess the desalination efficiency, bioelectricity generation, resource recovery, substrate utilization and bioelectrokinetics. The closed circuit operation has showed efficient desalination efficiency (51.5%) and substrate utilization (70%). Owing to the effective electron transfer kinetics, closed circuit mode of operation showed effective desalination of the synthetic ground water with simultaneous power production (0.35W/m2). Circuitry specific biocatalyst activity was observed with higher peak currents (10.1mA; -5.98mA) in closed circuit mode. MDC can function as sustainable and alternative solution for ground and surface water treatment with power productivity and resource recovery.

Microbial Electrochemical Technology

Abstract Transition from fossil-based to bio-based economy is a global need for the production of renewable forms of energy and products. Microbial electrochemical technologies (METs) are majorly catalyzed by the conventional electrochemical processes through microbial catalysis. This chapter summarizes the origin and history, diversification, and application of MET as a sustainable platform technology in the domain of waste remediation, resource recovery, and bioenergy generation.

Acidogenic Biorefinery: Food Waste Valorization to Biogas and Platform Chemicals

Abstract In recent times, we are witnessing an exigent need to switch towards employing renewable feedstocks owing to the continuous depletion of fossils as a result of various anthropogenic activities. Abundant and low-cost feedstocks like food wastes (FW) are highly sought after these conditions as an alternative feedstock. According to Food and Agriculture Organization (FAO), nearly 1.3 billion tons of FW is being discarded from various sources including food processing plants, kitchens, restaurants, etc., which contain more than 50% of biodegradable organic content that can be transmuted into high-value biobased products. In the near future, unavoidable FW quantities are bound to increase, making it highly essential to establish sustainable treatment strategies by employing bioprocesses like acidogenesis, photosynthesis, bioelectrogenesis, and bioanoxygenesis. This chapter reviews the biotechnological aspects of converting FW into an array of biobased products elucidating the metabolic pathways and subsequently proposing a biorefinery framework to hollistically utilize waste and develop a sustainable green future.

Photosynthetic and Lipogenic Response Under Elevated CO2 and H2 Conditions—High Carbon Uptake and Fatty Acids Unsaturation

Microalgae are some of the most versatile organisms having ability to grow in diverse conditions and utilize both organic and inorganic carbon sources. Microalgal photosynthesis can be employed to transform carbon dioxide (CO2) into essential bioactives and photofuels. In this study microalgae are grown under modified headspace gas compositions resembling the industrial gaseous effluents. Four experimental variations with CO2 + H2 (1:1 V/V), CO2, H2 and Air as the headspace gas were evaluated to determine the photosynthetic efficiency and bioactives production of microalgae. This study reports an enhancement in quantum yield (Fv/Fm: 0.77) and CO2 biosequestration rate (0.39 g.L-1.d-1) under CO2 + H2 headspace gas composition compared to the other experimental variations. The chemoselective functioning of Rubisco under varying gas concentrations was determined, where elevated CO2 conditions negates the oxygenase activity under a high CO2/O2 ratio which enabled higher CO2 sequestration. The enhanced CO2 sequestration and altered redox conditions under the monophasic operation have also led to a higher average degree of unsaturation and carbon chain length of the fatty acids produced. This study provides an approach to augment photosynthetic efficiency and lipogenesis through non-genetic modifications along with the feasibility to cultivate microalgae in integration with industrial flue gases. Exploiting the true potential of microalgae would provide sustenance from climatic changes and environmental pollution while concurrently producing biobased products analogous to the fossil-derived products.