Regeneration of the power performance of cathodes affected by biofouling

© 2016 The Authors. Air cathode microbial fuel cells (MFCs) were used in a cascade-system, to treat neat human urine as the fuel. Their long-term operation caused biodeterioration and biofouling of the cathodes. The cathodes were made from two graphite-painted layers, separated by a current collector. The initial performance of the MFCs was reaching average values of 105.5 ± 32.2 μW and current of 1164.5 ± 120.2 μA. After 3 months of operation the power performance decreased to 9.8 ± 3.5 μW, whilst current decreased to 461.2 ± 137.5 μA. Polarisation studies revealed significant transport losses accompanied by a biofilm formation on the cathodes. The alkaline lysis procedure was established to remove the biomass and chemical compounds adsorbed on the cathode's surface. As a result, the current increased from 378.6 ± 108.3 μA to 503.8 ± 95.6 μA. The additional step of replacing the outer layer of the cathode resulted in a further increase of current to 698.1 ± 130 μA. Similarly, the power performance of the MFCs was recovered to the original level reaching 105.3 ± 16.3 μW, which corresponds to 100% recovery. Monitoring bacterial cell number on the cathode's surface showed that biofilm formed during operation was successfully removed and composed mainly of dead bacterial cells after treatment. To the best of the authors' knowledge, this is the first time that the performance of deteriorating cathodes, has been successfully recovered for MFCs in-situ. Through this easy, fast and inexpensive procedure, designing multilayer cathodes may help enhance the range of operating conditions, if a biofilm forms on their surface

Electricity from wetlands : technology assessment of the tubular Plant Microbial Fuel Cell with an integrated biocathode

Sustainable electricity generation by the plant microbial fuel cell Fossil fuels are currently the main source of electricity production. Combustion of fossil fuels causes air pollution severely affecting human health and nature. This results in an increasing demand for renewable electricity sources. One of the emerging renewable electricity technologies is the plant microbial fuel cell (PMFC) as explained in chapter 1. PMFC generates electricity from the rhizodeposits of living plants. Naturally occurring electrochemically active microorganisms oxidize the rhizodeposits producing electrons at the anode of the PMFC. The electrons flow from the anode, via an external circuit where the electricity is harvested, to the cathode. At the cathode, the electrons reduce oxygen to water. PMFC is based on naturally occurring sustainable and renewable processes without net emissions and competition for arable land or nature. Large scale application of the PMFC is preferred in wetlands because a large waterlogged area is required. Prior to application, the cathode limitations of the PMFC have to be solved. Oxygen reduction at the cathode is slow, limiting the current and power output of the PMFC. An unsustainable chemical cathode is often used in PMFC research to overcome the cathode limitations. The sustainable oxygen reducing cathode has to be catalyzed when integrated in the PMFC. Most chemical catalyst are expensive and prohibit the commercial use in the PMFC. Oxygen reduction can also be biologically catalyzed by cheap and self-replenishing microorganisms. Next to the biocathode, also a suitable design of the PMFC has to be developed before application in wetlands. A tubular design was previously developed which can be invisibly integrated in wetlands. However, this design still used a chemical cathode and energy intensive pumping. The oxygen reducing biocathode should be integrated in the tubular design and oxygen should be passively supplied in the cathode. The objective of this thesis is to apply PMFC in wetlands with a sustainable biocathode. First, the biocathode is integrated in a lab scale PMFC. Afterwards, the PMFC is installed in wetlands using an improved tubular design with an integrated biocathode and passive oxygen supply. Lab scale experiments: integration of the biocathode and electricity localization in the bioanode of the PMFC In chapter 2, the oxygen reducing biocathode is integrated in a flat plate lab scale PMFC replacing the chemical ferricyanide cathode. The PMFC operated as a completely biocatalyzed system for 151 days. The sustainable PMFC with a biocathode was able to generate more power than the PMFC with a chemical cathode. The long term power generation of the lab scale PMFC improved from 155 mW m-2 plant growth area (PGA) to a record of 240 mW m-2 PGA. This record was reached due to the higher redox potential of oxygen reduction compared to ferricyanide reduction. Oxygen reduction was effectively catalyzed by microorganisms lowering the voltage losses at the cathode. As a result, the PMFC with a biocathode operated at a 127 mV higher cathode potential than a similar PMFC with a chemical ferricyanide cathode. The long term current generation of both PMFCs was 0.4 A m-2 PGA. The current generation was likely limited by the substrate availability in the anode of the PMFC. In chapter 3, the biocathode is further investigated. This chapter shows that the oxygen reducing biocathode can also catalyze the reversible reaction, water oxidation. Water is the most abundant electron donor available for electrochemical fuel production like the reduction of protons to hydrogen and the reduction of carbon dioxide to hydrocarbons. However, the water oxidation reaction is currently hampering the development of large scale water oxidation technologies. A bioanode containing electrochemically active microorganisms was able to reach a current density of 0.93 A m-2 at 0.7 V overpotential with a 22 % Coulombic efficiency linked to water oxidation. An optimized system could be used to produce fuels on a large scale. The flat plate PMFC of chapter 2 was also used to localize the electricity generation in the PMFC (chapter 4). In this experiment, the anode was partitioned in 30 separate small anodes at different width and depths. The current generation of each anode was analyzed over time and linked to the plant roots. The results show that after a start-up period of 70 days, significantly higher current was generated at anodes close to the plant roots due to rhizodeposition. Besides rhizodeposition (i.e. electron donors), the plant roots also excrete oxygen which is an electron acceptor lowering the current generation of the PFMC. Also oxygen was measured at the anodes close to the plant roots. This likely resulted in internal currents in the PMFC. Current was likely generated both from living and death roots. The electrons in the PMFC were probably transferred via mediators to locations without roots as mediators were present also at locations without plant roots. These mediators were likely excreted by plants and/or microorganisms in the anode. Electrons were likely not transferred over centimeter distance through conductive microorganism on the plant roots in the PMFC. Installation of the tubular PMFC with an integrated biocathode in wetlands After the successful integration of the biocathode in the PMFC, the focus of the research changed to application in wetlands. Two wetlands with an abundant occurrence in the Netherlands were investigated in this research. The first wetland was a Phragmites australis dominated fen peat soil, a large perennial grass. The peat soil in this research was collected in national park Alde Feanen in the north of the Netherlands. The second investigated wetland was a Spartina anglica dominated salt marsh. Spartina anglica is a perennial grass found in coastlines spread over the world. The salt marsh was collected in the Oosterschelde tidal basin in the southwest of the Netherlands. The first experiment in the wetlands was conducted to investigate the spatial and temporal differences in current and power generation in and between wetlands (chapter 5). PMFCs in the salt marsh were able to generate more than 10 times more power than the same PMFCs in the peat soil (18 vs 1.3 mW m-2 PGA on a long term). The higher power generation is mainly explained by the high ionic conductivity of the salt marsh and the presence of sulfide which is also oxidized next to the rhizodeposits at the anode of the PMFC. The top layer of the salt marsh generated most power due to the presence of the plants and tidal advection. In the peat soil, there was no significant difference in power generation over depth. Even though, in the top layer more living roots were present. Also the dead roots and organics in peat can be oxidized by the PMFC. In chapter 5, also the maximum current and power output of the wetlands was predicted based on rhizodeposition of the investigated plants and microbial processes in these wetlands. The calculations showed that the potential current generation of PMFC in the salt marsh is 0.21-0.48 A m-2 PGA and in peat soil 0.15-0.86 A m-2. In the peat soil, the PMFC is potentially able to generate a power density up to 0.52 W m-2 PGA. The second experiment in the wetland was the installation of a tubular PMFC with an in situ started oxygen reducing biocathode and passive oxygen supply into the cathode (chapter 6). The anode was the outside of the tube and placed directly between the plant roots. The oxygen reducing biocathode was located inside the tube. A silicone gas diffusion tube was placed in the cathode compartment to passively supply the required oxygen. The tubular PMFC with biocathode was successfully installed and started in the peat soil reaching a maximum daily average power generation of 22 mW m-2 PGA. In the salt marsh, the tubular biocathode PMFC only started while supplying pure oxygen in the gas diffusion tube. Air diffusion did not result in the start-up of the biocathode, likely because the oxygen was directly reduced via internal currents and therefore more oxygen was required. Once started with pure oxygen, the tubular PMFC was able to generate 82 mW m-2 PGA which was again higher than the peat soil. Completely biocatalyzed tubular PMFC were installed in both wetlands with natural occurring microorganisms in the anode and cathode. The power generation can be further increased by improving the PMFC design limiting crossover of oxygen and substrate. Future outlook: application of the PMFC in wetlands In chapter 5, the potential power generation of the two investigated wetlands was calculated. In chapter 7, these calculations were extended to a worldwide scale. PMFC applied in all wetlands could generate 0.67 to 1.35 TW and could cover 30 to 60 % of the global electricity consumption. 70 % of all the potential power could be generated in the tropics. Worldwide, 1.1 billion people have insufficient access to electricity from which 88 % lives in the tropics (i.e. Sub-Saharan Africa and South Asia). PMFC could be used to reach universal access of electricity in these locations and decrease the amount of premature deaths due to air pollution. PMFC can be applied with passive or active oxygen supply from the outside air into the silicone tube. The used tubular PMFC with passive oxygen supply can have a maximum length of less than one meter. Active supply of oxygen reduces the net power output of the PMFC, but allowing installation of long tubular PMFC. However, in both cases the material costs should be significantly reduced for economically feasible application at large scale. The costs of the material should be decreased to less than 1 % of the current PMFC costs to have a payback time of 50 years in the Dutch electricity market for only the tubular PMFC. Further cost reduction is required when also the current collectors, electricity transmission, production and installation costs are included. Application of PMFC in remote locations increases the economic feasibility of the PMFC as the PMFC could be applied independent from the grid reducing the transmission costs and avoiding the regular electricity network charges. Application of the PMFC in the total area of Spartina anglica salt marsh in the Oosterschelde, the location were the plants were collected, could produce a total of 11.6 GWh yr-1. The Oosterschelde could produce the electricity consumption of 8,360 persons and as such produce the electricity need of an average village directly located at the tidal basin. The Phragmites australis peat soil in the Alde Feanen national park could produce 2.5 GWh yr-1. The electricity could be directly used for ecotourism purposes, for example for the use of electric boats and a holiday park. </p

Riverbank protection removal to enhance bar formation for habitat diversity

Over the past centuries natural riverbanks have been transformed into banks with artificial revetments or sheet piles to protect them from erosion, which led to disappearance of important river features for flora and fauna. River restoration projects show that the removal of man-made bank protections may lead to the formation of bars (e.g. Van den Berghe et al., 2012; Schirmer et al., 2014). Habitat diversity in rivers may be enhanced through the formation of river bars with preferably diversity in bar height, size and location. This research aims at gaining knowledge into the effects of removing riverbank protections on bar formation to enhance habitat diversity. Mobile-bed flume experiments were performed in the Fluid Mechanics Laboratory of Delft University of Technology. The experiments were focussed on bar formation related to three variables of a bank protection removal; length, location and flow asymmetry. Geometrical and morphodynamic characteristics were selected for the experiment having a bar mode of one to obtain a system with alternate bars (Crosato and Mosselman, 2009) and showed gravel-bed river similarity based on bankfull river characteristics of Parker (2004). The experimental flume consisted of a 6.2 metre long and 0.2 metre wide straight channel with 0.5 metre wide floodplains on the sides. On both sides of the channel, bank protection could be removed over a limited length with optionally a groyne upstream. After seven hours at the end of each test, photos of the bed topography were taken and the longitudinal bed profile was measured. Bar wavelengths and bar heights in each experimental test were determined from detrended bed profiles. The bar height was divided in two classes: low and high. The areas of low bars, high bars, floodplains and the deep channel were determined from photos of the final bed topographies. Bar types were indicated with terminology from Duró et al. (2015) as forced, free or hybrid. Removal of bank protections resulted in lateral erosion of channel banks over a limited length. The eroded bank line moved in downstream direction, which agrees with the downstream meander migration observed in field and laboratory investigations by many authors (e.g. Odgaard, 1987). Scour holes developed downstream of the widened section, due to turbulent eddies forced by the channel geometry. In the widened reach, flow decelerated which resulted in a lower sediment transport. Consequently, sediment was deposited in the widened reach and caused rising of the mean bed level along with formation of bars. In areas with higher flow velocities an increased sediment transport deepened the channel. When the riverbanks were fixed, relatively low, small, side bars were formed in the channel. In general, the total bar area and bar height increased for an increase in channel widening, due to the removal of bank protection. An increased bank protection removal length up to nine times the channel width or an upstream asymmetrical flow forcing, i.e. groyne, increased the total bar area, whereas a bank protection removal at three different locations with a total length of nine times the channel width did not significantly increased the total bar area. It is recommended to remove riverbank protections over a length of at least nine times the river width on both sides of the river with optionally a groyne upstream as a measure to enhance habitat diversity. It is also valuable to remove the bank protection on one side of the river only. It is advised to construct a groyne upstream of the bank protection removal to increase habitat diversity. This research led to results that can be used in further research. It is advised to conduct larger scale experiments and eventually move to the field.Civil Engineering and GeosciencesHydraulic Engineerin

System and method for bio-electrochemical water oxidation

The invention relates to a bio-electrochemical system and method for bio-electrochemical water oxidation. The system according to the invention comprises: - a reactor comprising a bio-electrode compartment with a bio-electrode and a counter electrode compartment with a counter electrode; - a power supply, and a circuit that in use connects the bio-electrode with the counter electrode; and - an ion-selective element separating the bio-electrode compartment and the counter electrode compartment, wherein the bio-electrode compartment comprises micro-organisms capable of non-photosynthetic catalytic bio-electrochemical water oxidation

Alternatieve waterbronnen en decentrale leidingnetten voor een klimaatrobuuste watervoorziening

In het onderzoeksprogramma Water Nexus zoeken we naar alternatievewaterbronnen om tot water-zelfvoorzienende regio’s te komen. Het motto is:‘zout waar het kan, zoet waar het moet’. Maar voor welke waterbron ga je enhoe krijg je het water bij de watergebruikers

Plant microbial fuel cell applied in wetlands : Spatial, temporal and potential electricity generation of Spartina anglica salt marshes and Phragmites australis peat soils

The plant microbial fuel cell (PMFC) has to be applied in wetlands to be able to generate electricity on a large scale. The objective of this PMFC application research is to clarify the differences in electricity generation between a Spartina anglica salt marsh and Phragmites australis peat soil based on experimental data and theoretical calculated potential. PMFC in salt marsh generated more than 10 times more power than the same PMFC in peat soil (18 vs 1.3 mW m-2 plant growth area). The salt marsh reached a record power output for PMFC technology per cubic meter anode: 2.9 W m-3. Most power is generated in the top layer of the salt marsh due to the presence of the plants and the tidal advection. The potential current generation for the salt marsh is 0.21-0.48 A m-2 and for peat soil 0.15-0.86 A m-2. PMFC technology is potentially able to generate a power density up to 0.52 W m-2, which is more than what is generated for biomass combustion or anaerobic digestion using the same plant growth area

Review of methods to assess sustainability of industrial water use

The projected increase of industrial water demands raises the need to assess the environmental sustainability of industrial water use. Assessment methods need to use Sustainable Systems Indicators (SSIs) which relate resource use to the carrying capacity of the local environment. SSIs for water use evaluate whether water use exceeds the natural water renewal (quantity) and whether emissions remain within the assimilation capacity of ecosystems (quality). We systematically reviewed the scientific literature to show which methods are used to assess industrial water use, and of these, which methods incorporate SSIs. In total, 82 assessment methods were identified in 340 papers. The methods were assigned to five categories: Key Performance Indicators, Composite Indices, Environmental Accounting, Material and Energy Flow Analysis, and Life Cycle Analysis. In 26% of the reviewed papers, the assessment methods used SSIs. The number of papers incorporating SSIs is growing at a slower rate than the overall number of papers in the area of sustainability assessments of industrial water use. Considering the expected growth in industrial water use this poses a risk to sustainable water use. The best performing category in terms of incorporating SSIs is Material and Energy Flow Analysis (42% of papers). Papers assessing several industrial sectors in the same study incorporate SSIs more frequently (68%) than research focused on a single industry or process (20%). We discuss examples from the reviewed papers which successfully incorporate SSIs, in order to: (1) identify the elements needed to create SSIs for industrial water use, (2) aid researchers and practitioners in selecting methods which incorporate SSIs, and (3) provide a starting point for future methodological development incorporating SSIs.</p

Stakeholder-based decision support model for selection of alternative water sources - A path towards sustainable industrial future in Vietnam

The combined effect of climate change, rapid industrialisation and traditional water use has created freshwater stress situations in industrial delta regions. Alternative Water Sources (AWSs) offer opportunities to mitigate the freshwater stress issue and, thus, contribute to a sustainable industrial future. This study developed a Decision Support Model (DSM) to assist the decision-makers in selecting the most feasible AWS. In the study location, Tan Thuan Export and Processing Zone (TTZ) of Ho Chi Minh City, rainwater, industrial effluent and brackish water were selected as AWS options and evaluated for technical, environmental, economic, social and institutional criteria. The stakeholder organisations representing government organisations, industrial-zone management organisations and enterprises were selected as decision-makers based on their willingness to explore AWSs. Four DSM scenarios were derived from the varying decision-making power of the selected stakeholder organisations. The results obtained from applying DSM in TTZ showed rainwater as the most feasible AWS for all the scenarios, while the rank of other AWSs fluctuated for different scenarios. To implement the result of DSM in practice, the government should not only focus on formulating clear technological guidelines on AWS quality but also on providing subsidies and creating an environment of social acceptance of AWSs. The DSM allows the decision-makers to determine the most capable AWS in mitigating freshwater stress issues and the changes required to shift towards these AWSs