Suitability of granular carbon as an anode material for sediment microbial fuel cells

Purpose: Sediment-microbial fuel cells (S-MFC) are bio-electrochemical devices that are able to oxidize organic matter directly into harvestable electrical power. The flux of organic matter into the sediment is rather low, therefore other researchers have introduced plants for a continues supply of organic matter to the anode electrode. Until now only interconnected materials have been considered as anode materials in S-MFC. Here granular carbon materials were investigated for their suitability as anode material in sediment microbial fuel cells. Materials and methods: Laboratory microcosms with 8 different electrode materials (granules, felts and cloths) were examined with controlled organic matter addition under brackish conditions. Current density, organic matter removal and microbial community composition were monitored using 16S-rRNA gene PCR followed by Denaturing Gradient Gel Electrophoresis (DGGE). The main parameters investigated were the influence of the amount of electrode material applied to the sediment, the size of the granular material and the electrode configuration. Results and discussion: Felt material had an overall superior performance in terms of current density per amount of applied electrode material i.e. felt and granular anode obtained similar current densities (approx. 50–60 mA/m2) but felt materials required 29% less material to be applied. Yet, when growing plants, granular carbon is more suited because it is considered to restore, upon disturbance, the electrical connectivity within the anode compartment. Small granules (0.25–0.5 mm) gave the highest current density compared to larger granules (1-5 mm) of the same material. Granules with a rough surface had a better performance compared to smooth granules of the same size. The different granular materials lead to a selection of distinct microbial communities for each material, as shown by DGGE. Conclusions: Granular carbon is suited as anode material for sediment microbial fuel cells. This opens the perspective for application of MFC in cultivated areas. In a wider context, the application of granular carbon electrodes can also be an option for in-situ bioremediation of contaminated soils

Influence of Aromatic Structure on the Thermal Behaviour of Lignin

Lignin, a natural biopolymer and abundant by-product, is a particularly promising feedstock for carbon-based materials and a potentially sustainable alternative to phenolic resins, which are typically derived from crude oil. The source and method used to isolate lignin have a large impact on the thermal properties of the polymer, and can affect resultant materials prepared from lignin. Previous investigations into lignin characterisation often utilise a variety of feedstocks and isolation methods, which can make robust comparisons challenging. We present a systematic investigation into the chemical composition of lignins extracted using an identical Organosolv isolation method but from different biomass feedstocks: hemp hurds, eucalyptus chips, flax straw, rice husk and pine. We show how the aromatic structure of lignin can affect the thermal behaviour of the polymer, which correlates to the structure of resulting carbons. Carbons from lignins with a high syringyl unit content display a pronounced foaming behaviour which, on activation, results in a high-surface area material with hierarchical porosity