The goal of this review is to assess renewable power sources as alternatives to the batteries traditionally used for remote environmental monitoring. In this review, we first discuss remote sensors and then we: 1) review the power requirements and traditionally used power sources for remote sensors, 2) describe the working principles of the renewable power sources used for powering remote sensors, 3) evaluate the challenges and potentials of the renewable power sources, and 4) review the power management systems developed for remote power generation and discuss how to use them to generate reliable power. In the description of each of the renewable power sources, we include the current status and future directions of the research. We believe that hybrid systems using more than a single renewable power source can provide more reliable renewable power. We conclude that renewable power sources have been demonstrated to be able to generate sufficient power for remote sensors. Because of the environmental risks and cost of operation associated with batteries, renewable energy sources will need to be used to power remote sensors in the near future. (C) 2013 Elsevier B.V. All rights reserved.

The goal of this study was to develop a power management system (PMS) that could power a submersible ultrasonic receiver (SUR) continuously to keep accurate time and listen to ultrasonic signals when there was enough energy for a complete scan. We developed a PMS and modified the hardware and firmware of the SUR to allow it to be controlled by our PMS. Thus, the SUR became optimized for the SMFC and was controlled by the PMS. The SUR switched to idle mode without stopping the RTC when there was not enough energy for a complete scan. The PMS used a 350-F capacitor to store microbial energy. The SMFC was deployed in the Palouse River, Pullman, WA. The integrated PMS was tested and operated the SUR continuously for six weeks. Our integrated PMS and sensor could make SMFCs a more viable renewable power source for continuous environmental monitoring. We found that the SUR could only be powered continuously if its operation was controlled by the PMS. We believe that future applications of more complex sensors could benefit from our novel approach of controlling the sensor using the PMS for uninterrupted operation even when the data are collected intermittently.

The conversion of biomass to ethanol is an attractive source of alternative green fuels. Current studies look at the thermochemical conversion of biomass to ethanol, but little focus is placed on the biochemical conversion pathway available for this transformation. We present two case studies depicting the potential of a biochemical production of ethanol for fuel purposes. The industrial scale plant design of corn stover conversion is addressed with the purpose of deriving a simple yet complete model for use in economic optimization of large scale supply chains. A lab scale kinetics study for the conversion of waste sweet potato to ethanol is also presented. These two case studies show the potential for research in the area of biochemical conversion of biomass to green fuels.

We have investigated the relative performance of the two enzymes, -amylase and amyloglucosidase, and two microbial strains, Zymomonas mobilisAX101 and 8b, for saccharification and fermentation of sweet potato. Modified Michaelis-Menten and Monod-type mathematical models were developed and verified with experimental results for saccharification using amyloglucosidase and fermentation using Z.mobilis 8b, respectively. The results showed that 91.5% of the starch and sucrose were converted to glucose and fructose using amyloglucosidase at pH 3.5 and 55C. The Z.mobilis 8b was able to convert more than 90% of the total sugars into ethanol within 18h with 87.2% of the theoretical yield and 49.07g/L final concentration of ethanol. A mass balance and cost analysis show that commercial production of ethanol from sweet potato is limited by the feedstock cost.Practical ApplicationsThis study shows that sweet potatoes that are unmarketable, small in size, bruised, cut or damaged otherwise from the harvesting process, supplied by a local farmer in the Central Texas area, can be used to produce bioethanol. Normally, farmers do not collect the damaged sweet potatoes because there is no demand for those in the market. This is supported by the fact that 20% of the total sweet potatoes cultivated are left in the ground due to damage while harvesting with plows. If collected and used for ethanol production, local farms can earn additional revenue.

This study focuses on improving the productivity of a fed-batch ethanol fermentation process by developing and implementing in real time, an optimum feeding policy. A constraint-based stoichiometric model is developed using the systems biology approach, which can quantitatively predict the cellular behavior of the E coli strain, KO11. However, the predictions from this model are accurate under low concentrations of substrate. In order to extend the usage of the model to higher substrate concentrations, we modified this model by introducing changes in glucose utilization rate to restrict the metabolic capacity of the cell. Using the proposed model, the fed-batch optimization problem becomes a constrained optimization problem, and a modified Iterative Dynamic Programming (IDP) algorithm was developed with an adaptive-stage updating methodology, which was applied to solve the global optimization problem. Experiments were carried out based on the optimal feed profile generated using the modified stoichiometric model and the Iterative Dynamic Programming algorithm. Approximately 90% of the theoretical ethanol yield was obtained; the fermentation consumed a total of 521.5 g of glucose and produced 237.5 g of ethanol.

We investigated growth kinetics of microalgae, Chlorella vulgaris, in immobilized arrays of nanoliter-scale microfluidic drops. These static drop arrays enabled simultaneous monitoring of growth of single as well as multiple cells encapsulated in individual droplets. To monitor the growth, individual drop volumes were kept nearly intact for more than a month by controlling the permeation of water in and out of the microfluidic device. The kinetic growth parameters were quantified by counting the increase in the number of cells in each drop over time. In addition to determining the kinetic parameters, the cell-size distribution of the microalgae was correlated with different stages of the growth. The single-cell growth kinetics of C. vulgaris showed significant heterogeneity. The specific growth rate ranged from 0.55 to 1.52 day(-1) for different single cells grown in the same microfluidic device. In comparison, the specific growth rate in bulk-scale experiment was 1.12 day(-1). It was found that the average cell size changes significantly at different stages of the cell growth. The mean cell-size increased from 5.99 ± 1.08 to 7.33 ± 1.3 µm from exponential to stationary growth phase. In particular, when multiple cells are grown in individual drops, we find that in the stationary growth phase, the cell size increases with the age of cell suggesting enhanced accumulation of fatty acids in older cells.

Effect of Location on the Performance of Benthic Microbial Fuel CellsThe lifetime of remote sensors is often limited by battery power. Replacing batteries is costly and time-consuming, and it may be impractical when the sensors are deployed at remote locations. Benthic microbial fuel cells (BMFCs) constitute a promising alternative power source that may replace or supplement batteries. In this study we investigated power generation by BMFCs deployed in coastal...Author(s)Alim DewanTimothy EwingMark E. NielsenClare E. ReimersBart ChadwickKen RichterZbigniew LewandowskiHaluk BeyenalSourceProceedings of the Water Environment FederationSubjectSession 1: Microbial Fuel CellsDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2010ISSN1938-6478SICI1938-6478(20100101)2010:7L.48;1-DOI10.2175/193864710798208520Volume / Issue2010 / 7Content sourceResiduals and Biosolids ConferenceFirst / last page(s)48 - 51Copyright2010Word count182Subject keywordsMicrobial fuel cellremote sensorsrenewable power generation

One of the challenges in using wireless sensors that require high power to monitor the environment is finding a renewable power source that can produce enough power. Sediment microbial fuel cells (SMFCs) are considered an alternative renewable power source for remote monitoring, but current research on SMFCs has demonstrated that they can only produce several to tens of mW of continuous power. This limits the use of SMFCs as an alternative renewable remote power source to mW-level power. Such low power is only enough to operate a low-power sensors. However, there are many remote sensors that require higher power, on the order of watts. Current technology using a SMFC to power a remote sensor requiring watts-level intermittent power is limited because of limitations of power management technology. Our goal was to develop a power management system (PMS) that enables a SMFC to operate a remote sensor consuming 2.5W of power. We designed a custom PMS to store microbial energy in capacitors and use the stored energy in short bursts. Our results demonstrate that SMFCs can be a viable alternative renewable power source for remote sensors requiring high power.

In this study, we compare the efficiencies of harvesting energy from microbial fuel cells (MFC) using two modes of operation: (1) continuous-passing the current through an electrical load-and (2) intermittent-first accumulating the energy in a capacitor and then discharging it through the load. Each of these two modes of operation has advantages and disadvantages: the first mode of operation allows the continuous powering of low-power-consuming devices, and the second mode of operation allows the intermittent powering of high-power-consuming devices. We used a two-compartment MFC: in the anodic compartment, Shewanella oneidensis MR-1 was grown using lactate as an electron donor, whereas in the cathodic compartment we used an electrode made of manganese-based catalyzed carbon bonded to a current-collecting screen made of platinum mesh and oxygen as the electron acceptor. The maximum power generated by harvesting energy intermittently was 152 microW, which is 111% higher than the 72 microW generated by harvesting the energy continuously. We conclude that in the operation of MFCs it is beneficial to harvest the energy intermittently. This not only allows the powering of external devices of high power consumption but also allows generating power with greater energy efficiency than does harvesting the energy continuously.

A microbial fuel cell (MFC) is capable of powering an electronic device if we store the energy in an external storage device, such as a capacitor, and dispense that energy intermittently in bursts of high-power when needed. Therefore its performance needs to be evaluated using an energy-storing device such as a capacitor which can be charged and discharged rather than other evaluation techniques, such as continuous energy dissipation through a resistor. In this study, we develop a method of testing microbial fuel cell performance based on storing energy in a capacitor. When a capacitor is connected to a MFC it acts like a variable resistor and stores energy from the MFC at a variable rate. In practice the application of this method to testing microbial fuel cells is very challenging and time consuming; therefore we have custom-designed a microbial fuel cell tester (MFCT). The MFCT evaluates the performance of a MFC as a power source. It uses a capacitor as an energy storing device and waits until a desired amount of energy is stored then discharges the capacitor. The entire process is controlled using an analog-to-digital converter (ADC) board controlled by a custom-written computer program. The utility of our method and the MFCT is demonstrated using a laboratory microbial fuel cell (LMFC) and a sediment microbial fuel cell (SMFC). We determine (1) how frequently a MFC can charge a capacitor, (2) which electrode is current-limiting, (3) what capacitor value will allow the maximum harvested energy from a MFC, which is called the “optimum charging capacitor value,” and (4) what capacitor charging potential will harvest the maximum energy from a MFC, which is called the “optimum charging potential.” Using a LMFC we find that (1) the time needed to charge a 3-F capacitor from 0 to 500mV is 108min, (2) the optimum charging capacitor value is 3F, and (3) the optimum charging potential is 300mV. Using a SMFC we find that (1) the time needed to charge a 3-F capacitor from 0 to 500mV is 5min, (2) the optimum charging capacitor value is 3F, and (3) the optimum charging potential is 500mV. Our results demonstrate that the developed method and the MFCT can be used to evaluate and optimize energy harvesting when a MFC is used with a capacitor to power wireless sensors monitoring the environment.

The goal of this study was to quantify the relation between the surface area of the current-limiting electrode of a microbial fuel cell (MFC) and the power density generated by the MFC. Shewanella oneidensis (MR-1) was grown anaerobically in the anodic compartment of an MFC utilizing lactate as the electron donor. Graphite plate electrodes of various sizes were used as anodes. Commercially available air electrodes, composed of manganese-based catalyzed carbon bonded to a current-collecting screen made of platinum mesh, were used as cathodes, and dissolved oxygen was used as the cathodic reactant. The surface area of the cathode was always significantly larger than that of the anode, to ensure that the anode was the current-limiting electrode. The power density generated by the MFC decreased as the surface area of the anode increased, which fits well with the trend we detected comparing various published results. Thus, our findings bring into question the assertion that the overall power density generated by an MFC with large electrodes can be estimated by extrapolating from an electrode with a small surface area. Our results indicate that the maximum power density generated by an MFC is not directly proportional to the surface area of the anode, but is instead proportional to the logarithm of the surface area of the anode.

Sediment microbial fuel cells (SMFCs) are considered to be an alternative renewable power source for remote monitoring. There are two main challenges to using SMFCs as power sources: 1) a SMFC produces a low potential at which most sensor electronics do not operate, and 2) a SMFC cannot provide continuous power, so energy from the SMFC must be stored and then used to repower sensor electronics intermittently. In this study, we developed a SMFC and a power management system (PMS) to power a batteryless, wireless sensor. A SMFC operating with a microbial anode and cathode, located in the Palouse River, Pullman, Washington, U.S.A., was used to demonstrate the utility of the developed system. The designed PMS stored microbial energy and then started powering the wireless sensor when the SMFC potential reached 320 mV. It continued powering until the SMFC potential dropped below 52 mV. The system was repowered when the SMFC potential increased to 320 mV, and this repowering continued as long as microbial reactions continued. We demonstrated that a microbial fuel cell with a microbial anode and cathode can be used as an effective renewable power source for remote monitoring using custom-designed electronics.