Matteo Grattieri

Parameters characterization and optimization of activated carbon (AC) cathodes for microbial fuel cell application.

Activated carbon (AC) is employed as a cost-effective catalyst for cathodic oxygen reduction in microbial fuel cells (MFC). The fabrication protocols of AC-based cathodes are conducted at different applied pressures (175-3500 psi) and treatment temperatures (25-343°C). The effects of those parameters along with changes in the surface morphology and chemistry on the cathode performances are comprehensively examined. The cathodes are tested in a three-electrode setup and explored in single chamber membraneless MFCs (SCMFCs). The results show that the best performance of the AC-based cathode is achieved when a pressure of 1400 psi is applied followed by heat treatment of 150-200°C for 1h. The influence of the applied pressure and the temperature of the heat treatment on the electrodes and SCMFCs is demonstrated as the result of the variation in the transfer resistance, the surface morphology and surface chemistry of the AC-based cathodes tested.

PTFE effect on the electrocatalysis of the oxygen reduction reaction in membraneless microbial fuel cells.

Influence of PTFE in the external Gas Diffusion Layer (GDL) of open-air cathodes applied to membraneless microbial fuel cells (MFCs) is investigated in this work. Electrochemical measurements on cathodes with different PTFE contents (200%, 100%, 80% and 60%) were carried out to characterize cathodic oxygen reduction reaction, to study the reaction kinetics. It is demonstrated that ORR is not under diffusion-limiting conditions in the tested systems. Based on cyclic voltammetry, an increase of the cathodic electrochemical active area took place with the decrease of PTFE content. This was not directly related to MFC productivity, but to the cathode wettability and the biocathode development. Low electrodic interface resistances (from 1 to 1.5 Ω at the start, to near 0.1 Ω at day 61) indicated a negligible ohmic drop. A decrease of the Tafel slopes from 120 to 80 mV during productive periods of MFCs followed the biological activity in the whole MFC system. A high PTFE content in the cathode showed a detrimental effect on the MFC productivity, acting as an inhibitor of ORR electrocatalysis in the triple contact zone.

Self-Powered Biosensors

Self-powered electrochemical biosensors utilize biofuel cells as a simultaneous power source and biosensor, which simplifies the biosensor system, because it no longer requires a potentiostat, power for the potentiostat, and/or power for the signaling device. This review article is focused on detailing the advances in the field of self-powered biosensors and discussing their advantages and limitations compared to other types of electrochemical biosensors. The review will discuss self-powered biosensors formed from enzymatic biofuel cells, organelle-based biofuel cells, and microbial fuel cells. It also discusses the different mechanisms of sensing, including utilizing the analyte being the substrate/fuel for the biocatalyst, the analyte binding the biocatalyst to the electrode surface, the analyte being an inhibitor of the biocatalyst, the analyte resulting in the blocking of the bioelectrocatalytic response, the analyte reactivating the biocatalyst, Boolean logic gates, and combining affinity-based biorecognition elements with bioelectrocatalytic power generation. The final section of this review details areas of future investigation that are needed in the field, as well as problems that still need to be addressed by the field.

Sustainable Hypersaline Microbial Fuel Cells: Inexpensive Recyclable Polymer Supports for Carbon Nanotube Conductive Paint Anodes

Microbial fuel cells are an emerging technology for wastewater treatment, but to be commercially viable and sustainable, the electrode materials must be inexpensive, recyclable, and reliable. In this study, recyclable polymeric supports were explored for the development of anode electrodes to be applied in single-chamber microbial fuel cells operated in field under hypersaline conditions. The support was covered with a carbon nanotube (CNT) based conductive paint, and biofilms were able to colonize the electrodes. The single-chamber microbial fuel cells with Pt-free cathodes delivered a reproducible power output after 15u2005days of operation to achieve 12±1u2005mWu2009m-2 at a current density of 69±7u2005mAu2009m-2 . The decrease of the performance in long-term experiments was mostly related to inorganic precipitates on the cathode electrode and did not affect the performance of the anode, as shown by experiments in which the cathode was replaced and the fuel cell performance was regenerated. The results of these studies show the feasibility of polymeric supports coated with CNT-based paint for microbial fuel cell applications.

Microbial fuel cells in saline and hypersaline environments: Advancements, challenges and future perspectives

This review is aimed to report the possibility to utilize microbial fuel cells for the treatment of saline and hypersaline solutions. An introduction to the issues related with the biological treatment of saline and hypersaline wastewater is reported, discussing the limitation that characterizes classical aerobic and anaerobic digestions. The microbial fuel cell (MFC) technology, and the possibility to be applied in the presence of high salinity, is discussed before reviewing the most recent advancements in the development of MFCs operating in saline and hypersaline conditions, with their different and interesting applications. Specifically, the research performed in the last 5years will be the main focus of this review. Finally, the future perspectives for this technology, together with the most urgent research needs, are presented.

Investigating extracellular electron transfer of Rikenella microfusus: a recurring bacterium in mixed-species biofilms

The optimization of bioelectrochemical systems operating with microorganisms requires a deep understanding of the extracellular electron transfer (EET) processes, however, EET studies have been reported for few bacterial species. Herein, the bioelectrocatalytic properties of Rikenella microfusus, an anaerobic bacterium commonly found in electrode-colonizing biofilms, have been investigated for the first time.

A sustainable adsorbent for phosphate removal: modifying multi-walled carbon nanotubes with chitosan

Phosphorus, a major culprit for eutrophication of aquatic environments, is dissolved in water primarily in the form of phosphate; hence, it is difficult to remove, and different materials are being investigated, aiming at high removal capabilities. Meanwhile, recovery capability must also be considered, since phosphorus present in wastewater may serve as a potential alternative resource for the mineral phosphorus. Carbon nanotubes are promising for the treatment of phosphate pollution; however, studies about their removal potential are limited. Herein, multi-walled carbon nanotubes were modified with chitosan through simply cross-linking to obtain a novel adsorbent for phosphate removal. Our data show that a maximum adsorption as high as 36.1u2009±u20090.3xa0mgxa0Pxa0g−1 was achieved in 30xa0min at pH 3 and 293xa0K. The adsorption capacity of the composite (chitosan/multi-walled carbon nanotubes) could be maintained at 94–98% even after 5 adsorption–desorption cycles. An exothermic process was obtained, according to the Freundlich isotherm model. Based on the reported performance, the composite has a great advantage compared with other novel adsorbents for phosphate removal, indicating that the composite is a highly potential material to treat phosphorus-induced eutrophication of water bodies.

Alginate‐Encapsulated Bacteria for the Treatment of Hypersaline Solutions in Microbial Fuel Cells

A microbial fuel cell (MFC) based on a new wild‐type strain of Salinivibrio sp. allowed the self‐sustained treatment of hypersaline solutions (100u2005gu2009L−1, 1.71u2009m NaCl), reaching a removal of (87±11)u2009% of the initial chemical oxygen demand after five days of operation, being the highest value achieved for hypersaline MFC. The degradation process and the evolution of the open circuit potential of the MFCs were correlated, opening the possibility for online monitoring of the treatment. The use of alginate capsules to trap bacterial cells, increasing cell density and stability, resulted in an eightfold higher power output, together with a more stable system, allowing operation up to five months with no maintenance required. The reported results are of critical importance to efforts to develop a sustainable and cost‐effective system that treats hypersaline waste streams and reduces the quantity of polluting compounds released.

Lag Time Spectrophotometric Assay for Studying Transport Limitation in Immobilized Enzymes

Enzymes are promising catalysts for bioprocessing. For instance, the enzymatic capture of CO2 using carbonic anhydrase (CA) is a carbon capture approach that allows obtaining bicarbonate (HCO3–) with no high-energy input required. However, application in a commercially viable biotechnology requires sufficient enzymatic lifetime. Although enzyme stabilization can be achieved by different immobilization techniques, most of them are not commercially viable because of transport limitations induced by the immobilization method. Therefore, it is necessary to develop assays for evaluating the role of immobilization on transport limitations. Herein, we describe the development of a fast and reproducible assay for screening immobilized CA by means of absorbance measurement using a computer-controlled microplate reader in stop–flow format. The automated assay allowed minimizing the required volume for analysis to 120 μL. We validated the assay by determining lag times and activities for three immobilization techniques (modified Nafion, hydrogels, and enzyme precipitates), of which linear polyethyleneimine hydrogel showed outstanding performance for CA immobilization.