L. Peixoto

In situ microbial fuel cell-based biosensor for organic carbon.

The biological oxygen demand (BOD) may be the most used test to assess the amount of pollutant organic matter in water; however, it is time and labor consuming, and is done ex-situ. A BOD biosensor based on the microbial fuel cell principle was tested for online and in situ monitoring of biodegradable organic content of domestic wastewater. A stable current density of 282±23mA/m(2) was obtained with domestic wastewater containing a BOD(5) of 317±15mg O(2)/L at 22±2°C, 1.53±0.04mS/cm and pH 6.9±0.1. The current density showed a linear relationship with BOD(5) concentration ranging from 17±0.5mg O(2)/L to 78±7.6mg O(2)/L. The current generation from the BOD biosensor was dependent on the measurement conditions such as temperature, conductivity, and pH. Thus, a correction factor should be applied to measurements done under different environmental conditions from the ones used in the calibration. These results provide useful information for the development of a biosensor for real-time in situ monitoring of wastewater quality.

Towards implementation of a benthic microbial fuel cell in lake Furnas (Azores): Phylogenetic affiliation and electrochemical activity of sediment bacteria

This work was conducted to examine the composition and electrochemical activity of the bacterial community inhabiting lake Furnas sediments (Azores). Fingerprinting analysis of the bacterial 16S rRNA gene fragment was done by denaturing gradient gel electrophoresis. The sequences retrieved from lake Furnas sediments were affiliated to Bacteroidetes/Chlorobi group, Chloroflexi, Alfa-, Delta-, and Gamma-subclasses of Proteobacteria, Cyanobacteria, and Gemmatimonadetes. A cyclic voltammetric study was carried out with an enriched sediment bacterial suspension in a standard two chamber electrochemical cell using a carbon paper anode. Cyclic voltammograms (scan rate of 50 mV/s) showed the occurrence of oxidation-reduction reactions at the carbon anode surface. The benthic microbial fuel cell operated with lake Furnas sediments presented a low power density (1 mW/m(2)) indicating that further work is required to optimise its power generation. These results suggested that sediment bacteria, probably from the Delta- and Gamma-subclasses of Proteobacteria, were electroactive under tested conditions.

Impact of an external electron acceptor on phosphorus mobility between water and sediments

The present work assessed the impact of an external electron acceptor on phosphorus fluxes between water and sediment interface. Microcosm experiments simulating a sediment microbial fuel cell (SMFC) were carried out and phosphorus was extracted by an optimized combination of three methods. Despite the low voltage recorded, ~96 mV (SMFC with carbon paper anode) and ~146 mV (SMFC with stainless steel scourer anode), corresponding to a power density of 1.15 and 0.13 mW/m(2), it was enough to produce an increase in the amounts of metal bound phosphorus (14% vs 11%), Ca-bound phosphorus (26% vs 23%), and refractory phosphorus (33% vs 28%). These results indicate an important role of electroactive bacteria in the phosphorus cycling and open a new perspective for preventing metal bound phosphorus dissolution from sediments.

A flat microbial fuel cell for decentralized wastewater valorization: process performance and optimization potential

A very compact flat microbial fuel cell (MFC), with 64 cm2 each for the anode surface and the cathode surface and 1 cm3 each for the anode and cathode chambers, was tested for wastewater treatment with simultaneous electricity production with the ultimate goal of implementing an autonomous service in decentralized wastewater treatment systems. The MFC was operated with municipal wastewater in sequencing batch reactor mode with re-circulation. Current densities up to 407 W/m3 and a carbon removal of 83% were obtained. Interruption in the operation slightly decreased power density, while the re-circulation ratio did not influence power generation. The anode biofilm presented high conductivity, activity and diversity. The denaturing gradient gel electrophoresis band-pattern of the DNA showed the presence of several ribotypes with different species of Shewanellaceae and Geobacteraceae families.

Investigating bacterial community changes and organic substrate degradation in microbial fuel cells operating on real human urine

The present study investigates the changes in the microbial community and the degradation of organic compounds in microbial fuel cells (MFCs) operated on human urine. An anaerobic community was enriched in “urine-degrading” electroactive microorganisms by stepwise lowering the dilution factor of the anode media from 50 times diluted to undiluted urine. In a duplicated assay a current density of 495 ± 16 mA m−2, a chemical oxygen demand (COD) removal of 75.5 ± 0.7% and a coulombic efficiency (CE) of 26.5 ± 0.7% were obtained during operation on undiluted urine. In a control assay, operated on undiluted urine without the microbial enrichment procedure, a current density of only 81 ± 9 mA m−2 was obtained. The organic compounds commonly found in urine as well as the metabolic products associated with their degradation were analyzed by proton nuclear magnetic resonance (1H-NMR). The main compounds initially identified in the urine were urea, creatinine, glycine, trimethylamine N-oxide and acetate. Most of the organic compounds, except acetate, were depleted within 10 days of operation. The microbial community responsible for urine degradation in the anode of both MFCs was investigated using the Illumina MiSeq platform. Bacteria related with the Firmicutes phyla were enriched in the anodic biofilms compared to the initial anaerobic inoculum, within which Tissierella and Paenibacillus were the dominant genera. Tissierella can metabolize creatinine producing acetate whereas several bacterial species belonging to the Paenibacillus genus demonstrated the ability to function as exoelectrogens. Corynebacterium that comprise urea-hydrolysing bacteria was also amongst the main genera detected in the developed biofilms.

Phosphorus-iron interaction in sediments: can an electrode minimize phosphorus release from sediments?

All restoration strategies to mitigate eutrophication depend on the success of phosphorus (P) removal from the water body. Therefore, the inputs from the watershed and from the enriched sediments, that were the sink of most P that has been discharged in the water body, should be controlled. In sediments, iron (hydr)oxides minerals are potent repositories of P and the release of P into the water column may occur upon dissolution of the iron (hydr)oxides mediated by iron reducing bacteria. Several species of these bacteria are also known as electroactive microorganisms and have been recently identified in lake sediments. This capacity of bacteria to transfer electrons to electrodes, producing electricity from the oxidation of organic matter, might play a role on P release in sediments. In the present work it is discussed the relationship between phosphorus and iron cycling as well as the application of an electrode to work as external electron acceptor in sediments, in order to prevent metal bound P dissolution under anoxic conditions.