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Bacterial Wiring for Energy Conversion and Remediation

Periodic Report Summary - BACWIRE (Bacterial wiring for energy conversion and remediation)

Project context and objectives:

The aim of the project is to develop a new paradigm for the simultaneous cogeneration of energy and bioremediation using electro-active bacteria. A new nanostructured transducer that efficiently connects to these bacteria will be developed, aiming to the production of devices with superior performance across a range of applications including microbial fuel cells, whole cell biosensors and bioreactors. Elucidation of mechanisms by which bacteria transport electrons to solid electrodes is crucial. In this way, well-defined surfaces of single crystals and multilayered gold deposits on quartz elements will be used to resolve the interfacial electrochemistry of both, bacteria and isolated bacterial surface redox molecules. The spatial distribution of cytochromes in the cell surface will be determined by Atomic force microscopy (AFM) and those involved in the electric connection to electrodes will be studied in detail. Nanoparticle-containing molecular bridges will be designed and constructed to connect electro-active bacteria to the electrode. Afterwards, tethered bacterial biofilms will be used in the development of technological application including reactors for the simultaneous cleaning of wastewater and the generation of clean energy.

The main emphasis of the project is the development of molecular linkers that enhances the connectivity of both between bacteria and the electrode and between bacteria within the biofilm to achieve faster rates of electron transfer that result in an improved power output of the microbial fuel cell. For this purpose, the project involves a range of objectives that span from the study of the redox properties of the bacterial biofilm at the most fundamental level, including well defined electrode surfaces and technics characteristic of a surface science approach (SEIRAS, SERS, AFM), to the more engineering problem of designing an optimum fuel cell with the maximum power output.

Project results:

In the first half of the project a broad knowledge has been gained about the optimum working conditions for the biofilm. These include pH, temperature and organic matter concentration. Different electrode surfaces have been tested as substrate for the growing biofilm, including graphite, ITO and well-defined surfaces of gold and platinum single crystals. Functionalisation of gold electrode surfaces with nanoparticles and different molecular linkers has been tested. These linkers have been designed and synthesised specifically for the project with the aim of enhancing the connectivity between the electrode surface and the redox active molecules in the external part of the membrane of the bacteria. The interaction of the biofilm with the electrode surface has been tested with spectroscopic techniques.

Gold nanoparticles, to be used as charge carriers within the three-dimensional (3D) bacterial network, have been synthesised and characterised. Thiol protected nanoclusters were functionalised and used to interrogate mechanisms for charge transport. The full electrochemical characterisation of these materials required a better analysis of the voltammetric pulse techniques that are currently available. This has been carried out and the results have been accepted for publication.

Several microbial fuel cell prototypes have been built and tested. Different cathode reactions have been tested. Under the optimum conditions, peak values of the current as high as 10 A / m2 and power outputs as high as 80 W / m3 have been achieved, while new geometries are being tested that allow foreseeing power outputs close to 1 kW / m3 as easy achievable. The ultimate goal of the project has been located at 5 kW / m3.

Numerical simulations of both simplified and production bacterial fuel cells have been carried out using computational techniques to map the fluid dynamics, mass transfer and potential distribution in the cells being developed. Preliminary simulations have been compared to experimental results and these methods are now well integrated with the development of the fuel cell engineering.

Potential impact:

The main output of the project will be the construction of a microbial fuel cell prototype based on the novel methods developed to enhance the connectivity between bacteria and electrodes. With a careful selection of the cell design, cathodic reaction, electrode materials and the use of the linkers synthesised in the framework of this project, a power output of 5 kW / m3 has been selected as a rather achievable goal. Such a prototype is expected to exert a beneficial impact in the field of waste water remediation technology.

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