Recent advances in the use of different substrates in microbial fuel cells toward wastewater treatment and simultaneous energy recovery

Food waste biorefinery: Sustainable strategy for circular bioeconomy.

The past decade has seen a substantial increase in successful examples of the combination of chemo- and biocatalysis for multistep syntheses. This is driven by obvious advantages such as higher yields, decreased costs, environmental benefits and high selectivity. On the downside, efforts must be undertaken to combine the divergent reaction conditions, reagent tolerance and solvent systems of these ‘different worlds of catalysis’. Owing to progress in enzyme discovery and engineering, as well as in the development of milder and more compatible conditions for operating with various chemocatalysts, many historical limitations can already be overcome. This Review highlights the opportunities available in the chemical space of combined syntheses using prominent examples, but also discusses the current challenges and emerging solutions, keeping in mind the fast progress in transition metal-, organo-, photo-, electro-, hetero- and biocatalysis. Chemical and biological catalysts provide distinct advantages and disadvantages to the synthetic chemist. This Review focuses on efforts to combine chemo- and biocatalysts, outlining the opportunities achievable by this approach and also efforts to overcome any incompatibilities between these different systems.

Opportunities and challenges for combining chemo- and biocatalysis

Resources scarcity and electricity demand have been dramatically increasing. Wastewater is recognized as one of resources for water, energy and plant fertilizing nutrients. Nevertheless, current wastewater treatment technologies have limitations due principally to their energy- and cost-intensive for achieving the conversion target of wastewater recovery. It is desired to develop a new technology to generate alternatives to conventional energy sources in a sustainable manner. An innovative technology based on the use of microbial fuel cells (MFCs) has been proved as a critical pathway for bioconversion processes towards electricity generation, then for addressing energy and environmental problems. Three special features including energy saving, less sludge production and less energy production make MFCs outstanding compared with the existing technologies. Multiform wastewaters could be efficiently degraded through advancing MFCs alone or integrating MFCs with other processing units. However, the low power density and the high operating cost of MFCs have greatly limited their applications on large-scale problems, and then result in some debates and doubts about their development and applications. Therefore, this paper objectively discussed the problems and applications of MFCs in wastewater treatment. Moreover, the integration of MFCs with other treatment processes was presented to verify the practicality and effectiveness of MFCs in contaminants removal. Furthermore, the primary challenges and opportunities for scaling-up and future applications of MFCs in wastewater were analyzed.

Advances in microbial fuel cells for wastewater treatment

Microbial electrochemical technologies have gained much attention in the recent years during which basic research has been carried out to provide proof of concept by utilizing microorganisms for generating bioenergy in an electro redox active environment. However, these bio-electrocatalyzed systems pose significant challenges towards up-scaling and practical applications. Various parameters viz., electrodes, materials, configuration, biocatalyst, reaction kinetics, fabrication and operational costs, resistance for electron transfer etc. will critically govern the performance of microbial catalyzed electrochemical systems. Majorly, the surface area of electrode materials, biofilm coverage on the electrode surface, enrichment of electrochemically active electrode respiring bacteria and reduction reactions at cathode will aid in increasing the reaction kinetics towards the upscaling of microbial electrochemical technologies. Enrichment of electroactive microbial community on anode electrode can be promoted with electrode pretreatment, controlled anode potential or electrical current, external resistance, optimal operation temperature, chemical additions and bioaugmentation . Inhibition of the growth of methanogens also increases the columbic efficiency, an essential parameter that determines the efficacy of bioelectricity generation. Considering the practical implementation of these microbial electrochemical technologies, the current review addresses the challenges and strategies to improve the performance of bio-electrocatalyzed systems with respect to the operational, physico-chemical and biological factors towards scale up. Besides, the feasibility for long term operation, the scope for future research along with the operational and maintenance costs are discussed to provide a broad spectrum on the role of the system components for the implementation of these bio-electrochemical technologies for practical utility.

Mira L.K. Sulonen

Papers

Microbial electrochemical technologies with the perspective of harnessing bioenergy: Maneuvering towards upscaling

Electricity generation from tetrathionate in microbial fuel cells by acidophiles

Quantification of bio-anode capacitance in bioelectrochemical systems using Electrochemical Impedance Spectroscopy

Long-term stability of bioelectricity generation coupled with tetrathionate disproportionation.

Optimisation of the operational parameters for a comprehensive bioelectrochemical treatment of acid mine drainage