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

Greenhouse gas (GHG) emissions from rice paddy soils amended with a plant microbial fuel cell

Microbial metabolism in a mixed culture anode of microbial fuel cell fed with mixed sources of organic carbon largely resembles the metabolism found in anaerobic environments (digesters, sediments) where CH4 is the end product instead of electrical current. It is hypothesized that current generation is a viable competitor to steer or control CH4 emissions from (cultivated) wetlands. It has already been shown that a plant-MFC is capable of efficiently converting organic carbon derived from rhizodeposition into an electrical current. To understand the interaction between methanogenic metabolism and current generation in waterlogged sediments, several microcosm studies have been carried out

Greenhouse gas emissions from rice microcosms amended with a plant microbial fuel cell

Methane (CH4) release from wetlands is an important source of greenhouse gas emissions. Gas exchange occurs mainly through the aerenchyma of plants, and production of greenhouse gases is heavily dependent on rhizosphere biogeochemical conditions (i.e. substrate availability and redox potential). It is hypothesized that by introducing a biocatalyzed anode electrode in the rhizosphere of wetland plants, a competition for carbon and electrons can be invoked between electrical current-generating bacteria and methanogenic Archaea. The anode electrode is part of a bioelectrochemical system (BES) capable of harvesting electrical current from microbial metabolism. In this work, the anode of a BES was introduced in the rhizosphere of rice plants (Oryza sativa), and the impact on methane emissions was monitored. Microbial current generation was able to outcompete methanogenic processes when the bulk matrix contained low concentrations of organic carbon, provided that the electrical circuit with the effective electroactive microorganisms was in place. When interrupting the electrical circuit or supplying an excess of organic carbon, methanogenic metabolism was able to outcompete current generating metabolism. The qPCR results showed hydrogenotrophic methanogens were the most abundant methanogenic group present, while mixotrophic or acetoclastic methanogens were hardly detected in the bulk rhizosphere or on the electrodes. Competition for electron donor and acceptor were likely the main drivers to lower methane emissions. Overall, electrical current generation with BESs is an interesting option to control CH4 emissions from wetlands but needs to be applied in combination with other mitigation strategies to be successful and feasible in practice

Treatment of rainwater runoff in recovery and recycling companies : lab and pilot-scale testing

Wastewater released from the storage and/or processing of recycling and materials recovery can be characterised as rainwater runoff. Recuperation and recycling companies are confronted with wastewater that has a very fluctuating flow rate and composition. The flow rate mainly depends on the amount of rainfall while the composition additionally depends on what is currently stored on site. An analysis of possible physical-chemical treatment (coagulation/flocculation, sand filtration, activated carbon filtration and sedimentation) methods was performed at two different recycling companies in order to find a robust and economical feasible water treatment system that meets the discharge limits at all times. A violation of some measurement values (Cd, Cr, Ni and acenaphthene) after coagulation/flocculation occurred, which could be further reduced by using sand filtration. Good removal is achieved for common parameters as for mono- and poly-aromatic hydrocarbons (MAH and PAH) and polychlorinated biphenyls (PCB). Applying a coupled sand- and activated carbon filtration on runoff resulted in a removal of over 80% of several measurement values (suspended solids, heavy metals). This clearly indicates the applicability of the physical-chemical treatment techniques

Physical-chemical treatment of rainwater runoff in recovery and recycling companies: pilot-scale optimization

Pilot-scale optimisation of different possible physical-chemical water treatment techniques was performed on the wastewater originating from three different recovery and recycling companies in order to select a (combination of) technique(s) for further full-scale implementation. This implementation is necessary to reduce the concentration of both common pollutants (such as COD, nutrients and suspended solids) and potentially toxic metals, polyaromatic hydrocarbons and poly-chlorinated biphenyls frequently below the discharge limits. The pilot-scale tests (at 250 L h(-1) scale) demonstrate that sand anthracite filtration or coagulation/flocculation are interesting as first treatment techniques with removal efficiencies of about 19% to 66% (sand anthracite filtration), respectively 18% to 60% (coagulation/flocculation) for the above mentioned pollutants (metals, polyaromatic hydrocarbons and poly chlorinated biphenyls). If a second treatment step is required, the implementation of an activated carbon filter is recommended (about 46% to 86% additional removal is obtained)