• Energy Research

Recent scientific and technological advancements in bioelectrochemical system (BES) research have opened up several avenues for realizing the concept of bio-based economy. Current research within this area has been directed toward exploring their applicability to generate a wastewater biorefinery. Valorization of resources in the form of energy, nutrients, metals, and chemicals has been actively exhibited using this technology. This chapter highlights the fundamentals and technological aspects of bioelectrochemical resource recovery from wastes and wastewaters with detailed emphasis on the latest trends of bioelectrorecovery systems (BERSs). Several wastes and wastewater feedstocks are enlisted and classified based on their prospects for resource and energy recovery. Two representative case studies, existing challenges, and a brief overview of the relative advantages and disadvantages of BERSs over alternative resource recovery options are also included. Further, an outlook is given for realizing resource recovery using BESs as a sustainable technology in the domain of energy and resource management.

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.

Bioenergy production is the most sought-after topics at the crunch of energy demand, climate change and waste generation. In view of this, lignocellulosic biomass (LCB) rich in complex organic content has the potential to produce bioenergy in several forms following the pretreatment. Hydrothermal pretreatment that employs high temperatures and pressures is gaining momentum for organics recovery from LCB which can attain value-addition. Diverse bioprocesses such as dark fermentation, anaerobic digestion etc. can be utilized following the pretreatment of LCB which can result in biohydrogen and biomethane production. Besides, integration approaches for LCB utilization that enhance process efficiency and additional products such as biohythane production as well as application of solid residue obtained after LCB pretreatment were discussed. Importance of hydrothermal pretreatment as one of the suitable strategies for LCB utilization is emphasized suggesting its future potential in large scale energy recovery.

The feasibility of power generation by non-destructive usage of rhizodeposits of Pennisetum setaceum plant formed mainly due to photosynthesis-carbon sequestration mechanism was studied in rhizosphere based microbial fuel-cell (R-MFC). Four fuel-cell assemblies (non-catalyzed graphite-plates; membrane-less operation; air-cathode) were evaluated for their electrogenic activity by varying anode distances from root in rhizosphere [A1 - 0; A2 - 8; A3 - 12 and A4 - 16 cm] at 2 cm depth from soil-layer and analyzed their electrogenic potential. The fuel-cell assembly near to the root zone showed maximum electrogenic-activity (R1, 1007 mV/4.52 mA) followed by R2 (780 mV/4.11 mA), R3 (720 mV/3.4 mA) and R4 (220 mV/1.2 mA). The observed maximum electrogenesis with R1 and minimum with R4 electrode-assemblies enumerated the critical role of root-exudates as substrates. All fuel-cell assemblies showed 10% higher electrogenic activity during day-time operation which can be directly attributed to plant's photosynthetic activity. The study enumerated the potential of plant to harness power in a sustainable way by optimum placement of fuel-cell setup in their rhizosphere.

Abstract Pollutants present in produced water (PW) are recalcitrant in nature and difficult to treat with simple processes. Energetically sustainable and novel approach was developed by integrating electrochemical cell (EC, Primary process) and microbial fuel cell (MFC, secondary process) to treat PW. Five different current densities (26, 36, 48, 59 and 71 mA/cm2) were applied in independent EC experiments (4 h). The effluents from each EC operation was further treated by MFC (10 h), to harness bioelectricity. Operational variations were maintained only in EC phase and kept MFC phase similar. This integration revealed that the extent of bioelectricity generation depends on the electrochemical oxidation of EC process. Overall, maximum power generation of 2.74 mW was registered with EC-effluent from 48 mA/cm2. The integration also showed highest TPH removal efficiency of 89% (EC, 305 mg/L; MFC, 317 mg/L) and COD removal efficiency of 89.6% (EC, 2160 mg/L; MFC, 1960 mg/L) at 71 mA/cm2. Other pollutants of PW, such as sulfates and TDS also removed efficiently (sulfates, 42.6%; TDS, 34.3%). Cyclic voltammetric (CV) and derivative analysis of the anodic biofilm were correlated well with MFC performance during different EC-effluents as substrate, indicating NADH involvement in bioanodic electron transfer. The balance between energy utilization in EC and bioelectricity generation by MFC was depicted that the integration of EC and MFC results in net positive energy. Maximum net power generation of 565 mWh (350 mL of anode volume) was resulted by integration. This integration depicts its potential to generate 1615 Whm−3 from the treatment of 1KL PW.

The performance of aerated and ferricyanide catholytes on the bioelectricity production was evaluated in dual chambered microbial fuel cell (MFC) (mediatroless anode; graphite electrodes) employing selectively enriched H(2) producing mixed consortia as anodic inoculum. Two MFCs with aerated catholyte (MFC(AC)) and ferricyanide catholyte (MFC(FC)) were operated separately to elucidate the difference in power generation potential and carbon removal efficiency under similar operating conditions [ambient pressure; room temperature (28+/-2 degrees C); acidophilic microenvironment (pH 6)]. The experimental data demonstrated the feasibility of in situ bioelectricity generation along with wastewater treatment. Effective power generation and substrate removal efficiency was documented in the fuel cell operated with ferricyanide catholyte (586 mV; 2.37 mA; 0.559 kg COD/m(3) day) than aerated catholyte (572 mV; 1.68 mA; 0.464 kg COD/m(3) day). Maximum power yield (0.635 W/kg COD(R) and 0.440 W/kg COD(R)) and current density (222.59 mA/m(2) and 190.28 mA/m(2)) was observed at 100 Omega resistor with ferricyanide and aerated catholytes, respectively. The study documented both wastewater treatment and electricity production through direct conversion of H(2) in a single system.

Bioelectrochemical systems (BESs) are unique systems capable of converting chemical energy into electrical energy (and vice-versa) while employing microbes as catalysts. Such organic wastes including low-strength wastewaters and lignocellulosic biomass were converted into electricity with microbial fuel cells (MFCs). Likewise, electrical energy was used to produce hydrogen in microbial electrolysis cells (MECs) or other products including caustic and peroxide. BES were also designed to recover nutrients, metals or removal of recalcitrant compounds. Moreover, photosynthetic micro-organisms as well as higher plants were implemented to use solar energy for electricity generation. The diversity on microbial and enzymatic catalysts offered by nature allows a plurality of potential applications. As compared to conventional fuel cells, BESs operate under relatively mild conditions and do not use expensive precious metals as catalysts. The recently discovered microbial electrosynthesis (MES) of high-value chemicals has greatly expanded the horizon for BES. Newer concepts in application as well as development of alternative materials for electrodes, separators, catalysts along with innovative designs have made BES very promising technology. This article discusses the recent developments that have been made in BESs so far, with the emphasis on their various applications beyond electricity generation and resulting performances as well as existing limitations.