Autonomous energy harvesting and prevention of cell reversal in MFC stacks

© The Author(s) 2016. This study presents a novel method for avoiding cell reversal whilst optimising energy harvesting from stacked Microbial Fuel Cells (MFCs) by dynamically reconfiguring the electrical connections between them. The sequential changing of in-parallel and in-series electrical connections in an 8-MFC stack resulted in energy being transferred twice as fast into a super-capacitor avoiding cell reversal in MFCs as opposed to a fixed in-series configuration. This approach, allows for a lower internal resistance state within the stack compared to a fixed electrical configuration. This is critical in the initial stages of energy extraction from MFCs connected electrically in-series where the impedance of the capacitor is drawing high levels of current and cell reversals are likely to occur and hinder performance. Automation of electrical connections doubled the extracted power from the stack whilst halving the charging times without any cell reversal occurrence. The electrical reconfiguring of MFCs was performed by a USB-powered switch-box that modulated the stack's connections. This lead to the development of an energy autonomous switch-box circuitry powered solely by the MFC stack with negligible impact on the overall energy harvesting efficiency (i.e. above 90%)

Towards effective small scale microbial fuel cells for energy generation from urine

© 2016 The Authors. Published by Elsevier Ltd. To resolve an increasing global demand in energy, a source of sustainable and environmentally friendly energy is needed. Microbial fuel cells (MFC) hold great potential as a sustainable and green bioenergy conversion technology that uses waste as the feedstock. This work pursues the development of an effective small-scale MFC for energy generation from urine. An innovative air-cathode miniature MFC was developed, and the effect of electrode length was investigated. Two different biomass derived catalysts were also studied. Doubling the electrode length resulted in the power density increasing by one order of magnitude (from 0.053 to 0.580 W m-3). When three devices were electrically connected in parallel, the power output was over 10 times higher compared to individual units. The use of biomass-derived oxygen reduction reaction catalysts at the cathode increased the power density generated by the MFC up to 1.95 W m-3, thus demonstrating the value of sustainable catalysts for cathodic reactions in MFCs

A novel small scale Microbial Fuel Cell design for increased electricity generation and waste water treatment

Microbial Fuel Cells (MFCs) are a sustainable energy technology with minimal carbon footprint, which is promising for wastewater remediation and generation of useful amounts of electricity. This study focuses on the architecture and rapid prototyping materials used for building MFCs and their effect on overall performance. Three MFC variants of the same design were constructed using ABS, PC-ISO and RC25 materials and were compared with an established MFC design. MFCs were assessed in terms of power production and COD reduction both individually and when connected electrically in parallel. In all cases the new design showed a better power output and COD removal. The order of performance in terms of power production and COD reduction for individual MFCs was PC-ISO, RC25 and ABS. However when triplets of the same materials were joined electrically together, then the order was different with RC25 outperforming ABS and PC-ISO, which was dependent on the materials' properties. It is concluded that the best performing individual MFC may not necessarily result in the best performing stack

Artificial control of microbial life: Towards a urine fuelled robot

This study describes the ongoing work with a Microbial Fuel Cell (MFC) stack, which will power the latest version of self-sustainable robots – EcoBot-IV – that uses human urine as the fuel. This paper reports on the dynamic electrical control, power management and hydraulic arrangement of the stack and the effects that these elements have on the rate of energy extraction and consequent shift in metabolism of the microbial 'engine'. We demonstrate that a peripheral system that is manually controlled, can optimise energy extraction from the MFC stack and decrease super-capacitor (1.5F) charging times by 33%. Furthermore, it is shown that connecting MFCs in different cascade configurations can result in varying power outputs and metabolic activity in MFCs, and could dictate the way that urine is supplied to the bacteria

Dynamic electrical reconfiguration for improved capacitor charging in microbial fuel cell stacks

A microbial fuel cell (MFC) is a bioelectrochemical device that uses anaerobic bacteria to convert chemical energy locked in biomass into small amounts of electricity. One viable way of increasing energy extraction is by stacking multiple MFC units and exploiting the available electrical configurations for increasing the current or stepping up the voltage. The present study illustrates how a real-time electrical reconfiguration of MFCs in a stack, halves the time required to charge a capacitor (load) and achieves 35% higher current generation compared to a fixed electrical configuration. This is accomplished by progressively switching in-parallel elements to in-series units in the stack, thus maintaining an optimum potential difference between the stack and the capacitor, which in turn allows for a higher energy transfer. © 2014 Elsevier B.V. All rights reserved

Waste to real energy: The first MFC powered mobile phone

This communication reports for the first time the charging of a commercially available mobile phone, using Microbial Fuel Cells (MFCs) fed with real neat urine. The membrane-less MFCs were made out of ceramic material and employed plain carbon based electrodes. This journal is © 2013 the Owner Societies

Satellite Communications: Research Trends and Open Issues

A panoramic view on the study and design of digital satellite communication links is the focus of this paper. Starting from the characterization of satellite propagation channel in different application environments (from broadcast to fixed terminals, to broadband mobile satellite access), we address physical layer aspects related to satellite communications in the attempt of providing the Reader with an overview of the new trends and open issues in this field

Assessment of electrooxidation as pre- and post-treatments for improving anaerobic digestion and stabilisation of waste activated sludge

8 p.This study evaluates the effects of electro-oxidation as a means for enhancing sludge stabilisation. Boron-doped diamond electrodes were used to treat waste activated sludge and digestate under different operating parameters (current density, conductivity, pH, and time). Electro-oxidation runs affected the solubilisation of organic matter, which seemed to improve anaerobic digestion and dewaterability characteristics. Among the tested parameters, pre-treating sludge via electro-oxidation under alkaline conditions (Treatment T5) resulted in the highest increase in soluble organic material compared to that in the control, with total organic carbon (TOC) and soluble chemical oxygen demand (COD) values of 2753 and 7819 mg L−1, respectively (control TOC and COD values were 385 and 1073 mg L−1). This pretreatment also achieved a high hydrolysis rate (higher concentration in volatile fatty acids) with a concomitant increase in methane yield (approximately 18%). On the other hand, the application of electro-oxidation as a post-treatment for improving digestate dewaterability resulted in noticeable changes in the release of water during drying due to protein and aliphatic matrix modification of the sample.S

Controlling for peak power extraction from microbial fuel cells can increase stack voltage and avoid cell reversal

Microbial fuel cells (MFCs) are bioelectrochemical systems which can degrade organic materials and are increasingly seen as potential contributors to low carbon technologies, particularly in energy recovery from and treatment of wastewaters. The theoretical maximum open circuit voltage from MFCs lies in the region of 1.1 V, but is reduced substantially by overvoltage losses. Practical use of the power requires stacking or other means to increase voltage. Series stacking of MFCs with typically encountered variability in operating conditions and performance raises the risk of cell reversal, which diminishes overall power performance. A novel strategy of MFC subsystem series connectivity along with maximum power point tracking (MPPT) generates increased power from individual MFCs whilst eliminating cell reversal. MFCs fed with lower concentrations of substrate experienced voltage reversal when connected in normal series connection with one common load, but when MFCs and loads together were connected in series, the underperforming cell is effectively bypassed and maximum power is made available. It is concluded that stack voltage may be increased and cell reversal avoided using the hybrid connectivity along with MPPT. This approach may be suitable for stacked MFC operations in the event that large scale arrays/modules are deployed in treating real wastewaters. © 2014 Elsevier B.V. All rights reserved