Sensors and Acoustic Modems Powered by Benthic Microbial Fuel Cells at the MARS Observatory Paul S. Schrader, Cody Doolan, Clare E. Reimers College of Earth, Oceanic & Atmospheric Sciences Hatfield Marine Science Center, Oregon State University Newport, United States creimers@coas.oregonstate.edu Peter R. Girguis Biological Laboratories Harvard University Cambridge, United States Michael Wolf, Dale Green Teledyne Benthos, Inc North Falmouth, United States Abstract— The goals of this project were three-fold: 1) to power underwater instruments with energy harvested from deep sea, organic poor sediments using Benthic Microbial Fuel Cells (BMFCs); 2) to relay instrument data acoustically –and in near- real time- through a cabled seafloor observatory or surface vessel, as appropriate; and 3) to characterize the operational performance of these interactive systems during in situ deployments. Two BMFC- underwater sensing/communications packages were demonstrated near the Monterey Accelerated Research System (MARS) observatory in Monterey Bay, California. MARS is a cabled observatory that resides in deep water (~890 m), about 37 km (23 miles) seaward of the Monterey Bay Aquarium Research Institute (MBARI). The BMFCs were constructed using a cylindrical chamber design with a 0.28 m 2 footprint. Each BMFC was used to power an Aanderaa dissolved O 2 /temperature or conductivity/temperature sensor, as well as a Teledyne Benthos compact acoustic modem which contained an integrated power management platform (PMP) for the complete system. The packages were deployed from a surface vessel and allowed to descend freely to the seafloor, at locations approximately 0. 5 km away from the MARS node, at depths of 863 and 895 m. The PMPs were programmed to record data from both the sensors and the BMFC (whole cell voltage, capacitor voltage, and battery voltage) on an hourly basis, and to monitor overall microbial fuel cell energy production on a daily basis. Post-deployment, BMFC 1 generated a net surplus of energy from days 98 through 166, and remained operational for 210 days. BMFC 2 began generating a surplus of energy on day 54 and remained operational for 158 days. Data recovered from the oceanographic sensors was transmitted acoustically over both the MARS node and to a research vessel, underscoring the utility of this technology. Keywords— Benthic Microbial Fuel Cells (BMFCs), Monterey Accelerated Research System (MARS) observatory, deep water deployment, energy production I. INTRODUCTION The first functional prototypes of benthic microbial fuel cells (BMFCs) were constructed just 12 years ago [1, 2]. BMFCs are bioelectrochemical devices driven by the naturally generated potential difference between anoxic sediment and oxic seawater. Electrons are delivered to the anode by microorganisms either directly from organic material or indirectly from inorganic products of organic matter degradation [3].These electrons reduce dissolved oxygen to form water at the cathode. Microorganisms play several roles in these systems including: maintenance of the redox gradient, production of redox mediators, generation of electron-rich metabolites (e.g. sulfide ions), and in some cases, delivery of electrons to an electrode through direct electron transfer [4-7]. BMFCs are very promising power sources for a variety of marine sensors that have low power requirements [8-10]. Most oceanographic and surveillance instruments on the seafloor have no cable connection with the surface and therefore must store the information collected until the instrument can be recovered while utilizing batteries as their only energy source. The main drawbacks of batteries are limited lifetime and high cost of periodic replacement, particularly in deep water deployments. In the past 10 years, the continuous generation of power densities ranging from 1 to 10 mW/m 2 (with areas representing chamber or simple plate electrode footprint) has been demonstrated in a wide variety of marine environments with peak power densities typically 10 - 30 mW/m 2 [2, 11-13]. Under unique operational conditions, when a chambered BMFC was deployed at a methane cold seep, peak power densities as high as 380 mW/m 2 have been observed [12, 14]. To date, BMFCs have only just begun to be applied to power a range of environmental sensors and thus to prove themselves as a viable means of providing long-term, uninterrupted power for submarine devices [11, 13, 15]. The objective of this study was to demonstrate benthic microbial fuel cell powered underwater sensing/acoustic communications in conjunction with the deep sea scientific research infrastructure at the Monterey Accelerated Research