Gilberto Martins

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.

Structure and activity of lacustrine sediment bacteria involved in nutrient and iron cycles

Knowledge of the bacterial community structure in sediments is essential to better design restoration strategies for eutrophied lakes. In this regard, the aim of this study was to quantify the abundance and activity of bacteria involved in nutrient and iron cycling in sediments from four Azorean lakes with distinct trophic states (Verde, Azul, Furnas and Fogo). Inferred from quantitative PCR, bacteria performing anaerobic ammonia oxidation were the most abundant in the eutrophic lakes Verde, Azul and Furnas (4.5-16.6%), followed by nitrifying bacteria (0.8-13.0%), denitrifying bacteria (DNB) (0.5-6.8%), iron-reducing bacteria (0.2-1.4%) and phosphorus-accumulating organisms (<0.3%). In contrast, DNB dominated sediments from the oligo-mesotrophic lake Fogo (8.8%). Activity assays suggested that bacteria performing ammonia oxidation (aerobic and anaerobic), nitrite oxidation, heterothrophic nitrate reduction, iron reduction and biological phosphorus storage/release were present and active in all Azorean lake sediments. The present work also suggested that the activity of DNB might contribute to the release of phosphorus from sediments.

Water resources management in southern Europe: Clues for a research and innovation based regional hypercluster

European countries are facing increasing pressures on their water resources despite stringent regulations and systematic efforts on environmental protection. In this context, research and innovation play a strategic role reinforcing the efficiency of water policies. The present study provides a multilevel assessment of research and innovation practices in the field of water resource management in southern European countries and regions (more specifically; Cyprus, Albania, Poitou-Charentes in France, Andalusia in Spain and the North of Portugal). The analysis was based on a strategic framework aimed at gaining an insight of the current constraints, as well as of the existing and future technological solutions for a better water resource management. The triple helix model proved to be a useful analytical framework for assessing the efforts of different groups towards a common goal. The analysis proved the existence of a significant evolution in the use of technological tools to assist decision-making processes in integrated river basin management in all regions. Nevertheless, the absence of formal channels for knowledge and data exchange between researchers and water resource managers complicates the formers involvement in the decision-making process regarding water allocation. Both researchers and consultants emphasize the low availability of data, together with the need to advance on water resource economics as relevant constraints in the field. The SWOT analysis showed similar concerns among the participating regions and provided a battery of effective projects that resulted in the preparation of a Joint Action Plan.

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.

Carbon nanotubes accelerate methane production in pure cultures of methanogens and in a syntrophic coculture

Carbon materials have been reported to facilitate direct interspecies electron transfer (DIET) between bacteria and methanogens improving methane production in anaerobic processes. In this work, the effect of increasing concentrations of carbon nanotubes (CNT) on the activity of pure cultures of methanogens and on typical fatty acid-degrading syntrophic methanogenic coculture was evaluated. CNT affected methane production by methanogenic cultures, although acceleration was higher for hydrogenotrophic methanogens than for acetoclastic methanogens or syntrophic coculture. Interestingly, the initial methane production rate (IMPR) by Methanobacterium formicicum cultures increased 17 times with 5 g·L-1 CNT. Butyrate conversion to methane by Syntrophomonas wolfei and Methanospirillum hungatei was enhanced (∼1.5 times) in the presence of CNT (5 g·L-1 ), but indications of DIET were not obtained. Increasing CNT concentrations resulted in more negative redox potentials in the anaerobic microcosms. Remarkably, without a reducing agent but in the presence of CNT, the IMPR was higher than in incubations with reducing agent. No growth was observed without reducing agent and without CNT. This finding is important to re-frame discussions and re-interpret data on the role of conductive materials as mediators of DIET in anaerobic communities. It also opens new challenges to improve methane production in engineered methanogenic processes.

Bacterial Diversity and Geochemical Profiles in Sediments from Eutrophic Azorean Lakes

In the Azores, the advanced trophic state of the lakes requires a fast intervention to achieve the good ecological status prescribed by the Water Framework Directive. Despite the considerable effort made to describe the phytoplankton growing on the water column, the lack of information regarding the microbial processes in sediments is still high. Thus, for the successful implementation of internal management actions, the present work explored the relationships between geochemical profiles and dominant members of the bacterial community in sediments from eutrophic Azorean lakes. Lake Azul geochemical profiles were quite homogeneous for all parameters, while in lake Furnas the total iron profile presented a peak below the aerobic layer. For lake Verde, the concentrations of all studied parameters (20 ± 2% loss-on-ignition; 2.10 ± 0.08 mg g−1 total phosphorus; 1.31 ± 0.50 mg g−1 total nitrogen; 8.06 ± 0.13 mg g−1 total iron) in the uppermost sediment layer were approximately two times higher than the ones in sediments from other lakes, decreasing with sediment depth. The higher amounts of phosphorus and organic matter in lake Verde suggested a higher internal contribution of phosphorus to eutrophication. The dominant members of the sediment bacterial community, investigated by denaturing gradient gel electrophoresis, were mostly affiliated to Proteobacteria phylum (Alpha-, Delta-, and Gamma-subclasses), group Bacteroidetes/Chlorobi and phylum Chloroflexi. The Cyanobacteria phylum was solely detected in sediments from lake Verde and lake Furnas that presented the highest amounts of nitrogen and phosphorus both in the water column and sediments, while the other phyla were detected in sediments from the three studied lakes. In conclusion, management measurers to achieve the good ecological status until 2015 should be distinct for the different lakes taking into account the relative magnitude of the nutrient sources and the bacterial diversity in sediments.

Mineral Cycling and pH Gradient Related with Biological Activity under Transient Anoxic–Oxic Conditions: Effect on P Mobility in Volcanic Lake Sediments

Phosphorus (P) mobility from the sediments to the water column is a complex phenomenon that is generally assumed to be mainly redox sensitive and promoted by anoxic conditions. Thus, artificial aeration of the hypolimnium has been used as a remediation technique in eutrophic water bodies but several times with unexpected disappointing results. To optimize lake restoration strategies, the aim of the present study is to assess the P flux from the sediments under transient anoxic-conditions and to identify the relevant drivers. P sequential extraction, microprofiling (of pH, O2 and H2S), and bacterial community identification were performed on a sediment microcosm approach. The results demonstrated that the overall P release from sediments to the water column during transient phase was higher during the oxic phase, mainly from pH sensitive matrixes. The microprofiles signature suggests that the observed pH gradient during the oxic phase can be a result of H2S oxidation in suboxic layers spatially separated and pared to O2 reduction in top layers, through an electroactive bacterial network. These findings point to an additional driver to be considered when assessing P mobility under transient anoxic-oxic conditions, which would derive from pH gradients, built on the microbial electrical activity in sediments from freshwaters volcanic lakes.

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.

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.