Self sustainable cathodes for microbial fuel cells

Doctoral thesis English OPEN
Gajda, I.

The ultimate goal of this thesis was to investigate and produce an MFC with self-sustainable cathode so it could be implemented in real world applications. Using methods previously employed [polarisation curve experiments, power output measurements, chemical assays for determining COD in wastewater and other elements present in anolyte or catholyte, biomass assessments] and with a focus on the cathode, experiments were conducted to compare and contrast different designs, materials and nutrient input to microbial fuel cells with appropriate experimental control systems.\ud \ud Results from these experiments show that: Firstly, the choice of polymeric PEM membrane showed that the most effective materials in terms of power performance were cation exchange membranes. In terms of cost effectiveness the most promising was CM-I, which was the preferred separator for later experiments.\ud \ud Secondly, a completely biotic MFC with the algal cathode was shown to produce higher power output (7.00 mW/m2) than the abiotic control (1.52 mW/m2). At the scale of the experimental system, the reservoir of algal culture produced sufficient dissolved oxygen to serve the MFCs in light or dark conditions. To demonstrate usable power, 16 algal cathode-designed MFCs were used to power a dc pump as a practical application.\ud \ud It has been presented that the more power the MFC generates, the more algal biomass will be harvested in the connected photoreactor. The biomass grown was demonstrated to be a suitable carbon-energy resource for the same MFC units in a closed loop scenario, whereby the only energy into the system was light.\ud \ud In the open to air cathode configuration various modifications to the carbon electrode materials including Microporous Layer (MPL) and Activated Carbon (AC) showed catholyte synthesis directly on the surface of the electrode and elemental extraction such as Na, K, Mg, from wastewater in a power dependent manner. Cathode flooding has been identified as an important and beneficial factor for the first time in MFCs, and has been demonstrated as a carbon capture system through wet scrubbing of carbon dioxide from the atmosphere. The captures carbon dioxide was mineralised into carbonate and bicarbonate of soda (trona). The novel inverted, tubular MFC configuration integrates design and operational simplicity showing significantly improved performance rendering the MFC system feasible for electricity recovery from waste. The improved power (2.58 mW) from an individual MFC was increased by 5-fold compared to the control unit, and 2-fold to similar sized tubular systems reported in the literature; moreover it was able to continuously power a LED light, charge a mobile phone and run a windmill motor, which was not possible before.
  • References (69)
    69 references, page 1 of 7

    Control Theory ............................................................................................................................63

    Methods specific to the experiment ...................................................................................... 65

    4th Pin connection to poise MFC voltage. Power “boost” ...................................................... 66 Open to air Cathode ....................................................................................................................113

    5.1 INTRODUCTION.................................................................................................................................. 113 5.1.1 Methods specific to the experiment .................................................................................... 114 5.1.2 Results and discussion ......................................................................................................... 115 Direct contact of MPL based electrode and membrane ...........................................................115 MPL based electrode for improved power ...............................................................................118

    5.1.3 Conclusions .......................................................................................................................... 120 WATER FORMATION AT THE CATHODE AND SODIUM RECOVERY ................................................................... 121

    5.2.1 Introduction ......................................................................................................................... 121

    5.2.2 Methods specific to the experiment .................................................................................... 123

    5.2.3 Results and discussion ......................................................................................................... 124

    5.2.4 Polarisation curve experiment ..................................................................................................124 Catholyte accumulation ............................................................................................................125 Relationship between catholyte accumulation and power generation ....................................127 Analysis of the accumulated catholyte .....................................................................................129 Conductivity and pH ............................................................................................................129 EDX and SEM........................................................................................................................130 GC MS and ICP OES ..............................................................................................................130 XRD ......................................................................................................................................131 Significance of catholyte accumulation to environmental cleanup ..........................................133 Sodium recovery through bioproduction..................................................................................133

    Control of catholyte alkalinity.............................................................................................. 134 Carbon capture .........................................................................................................................134 5.2.5 Conclusions .......................................................................................................................... 135

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