Towards a Microbial Thermoelectric Cell

Abstract

Microbial growth is an exothermic process. Biotechnological industries produce large amounts of heat, usually considered an undesirable by-product. In this work, we report the construction and characterization of the first microbial thermoelectric cell (MTC), in which the metabolic heat produced by a thermally insulated microbial culture is partially converted into electricity through a thermoelectric device optimized for low ΔT values. A temperature of 41°C and net electric voltage of around 250–600 mV was achieved with 1.7 L baker’s yeast culture. This is the first time microbial metabolic energy has been converted into electricity with an ad hoc thermoelectric device. These results might contribute towards developing a novel strategy to harvest excess heat in the biotechnology industry, in processes such as ethanol fermentation, auto thermal aerobic digestion (ATAD) or bioremediation, which could be coupled with MTCs in a single unit to produce electricity as a valuable by-product of the primary biotechnological product. Additionally, we propose that small portable MTCs could be conceived and inoculated with suitable thermophilic of hyperthermophilic starter cultures and used for powering small electric devices.

Thermoelectric Heat Exchange and Growth Regulation in a Continuous Yeast Culture

“…Albeit low, TEHE-based power production proved twice more efficient compared to our previous MTC designed for batch culture. Indeed, a 40-fold increase in electrical power production was obtained in the TEHE compared to MTC, which was 20-fold smaller [8].…”

“…Temperature measurements were performed by thin T-type thermocouples inserted into the different parts of the system and connected to a PC through a data logger. As in previous studies [8], the connections between the thermocouples and the data logger were performed on an ice-water mixture to take into account the unwanted background electric voltage, due to the junction of dissimilar metals in the thermocouple-data logger connection. Temperature and electrical current records were taken every 6 minutes throughout the experiment.…”

“…In a previous work, we described the first Microbial Thermoelectric Cell (MTC), a system designed for batch cultures allowing the partial conversion of microbial metabolic heat into electricity [8]. A range of industrial fermentations are carried out in continuous culture, where stable cellular densities can be maintained during long periods thanks to the supply of fresh medium, which is introduced at a rate that is equal to the volume of product that is removed from the fermenter.…”

Thermoelectric heat exchange and growth regulation in a continuous yeast culture

“…(A) Schematic representation of the continuous culture system. (a) Thermally insulated fermenter; (b,c) peristaltic pumps; (d) Thermoelectric heat exchanger ( TEHE ); (e) ice bath for the compensation of temperature measurements; (f) refrigerated fresh medium tank; (g) wasted medium tank; (h) data logger; and (i) PC with a software (Rodríguez‐Barreiro et al., ) for data recording and automatic control of the peristaltic pumps. All temperature measurements were performed with T‐type thermocouples.…”

“…MTC is based on the Seebeck effect, a thermoelectric property that allows direct conversion of temperature differences to electricity voltage. Taking into account that microbial growth is mainly exothermic, theoretically it is possible to produce an electrical current with the generated metabolic heat by using a thermoelectric cell (Rodríguez‐Barreiro, Abendroth, Vilanova, Moya, & Porcar, ). Nevertheless, a range of industrial fermentations are carried out in continuous culture, where stable cellular densities can be maintained during long periods thanks to the supply of fresh medium, which is introduced at a rate that is equal to the volume of product that is removed from the fermenter.…”