Bioelectrochemical systems based on the electroactivity of plants and microorganisms in the root environment (review)

Bioelectrochemical systems (BES) based on electroactive processes in the root environment of plants and accompanying microorganisms are a new promising environmentally friendly technology for generating renewable energy. Although the possibility of practical use of bioenergy resources has already been shown in many studies, the nature of electrogenesis and the influence of external parameters on it have not been fully identified. The emergence of a potential difference in living systems is due to a complex of physicochemical processes that maintain an uneven distribution of ions at the cellular, tissue and organism levels (N. Higinbotham, 1970). In the process of plant development along the whole organism, a gradient of electrical potentials arises due to the diffusion of ions, concentration effects and differences in the intensities of biochemical processes (T.A. Tattar et al., 1976). Along with this, microorganisms of the rhizosphere are able to oxidize organic matter secreted by the roots (L. De Schamphelaire et al., 2010), while synthesizing carbon dioxide, protons and electrons. The ions and electrons formed in the course of redox reactions diffuse through the inhabited medium, leading to charge separation (B.E. Logan, 2008); as a result, a gradient of electropotentials is established, associated with differences in the concentrations of charged substances. A complex of processes for converting chemical energy from organic substances into electrical energy forms is the basis of the plant-microbial fuel cell (PMFC). The most common configuration of the PMFC device consists of an anode and cathode chambers, an ion-selective membrane (D.P. Strik et al., 2008); there are also various modifications in the form of a flat plate (M. Helder et al., 2013), a tubular configuration (R.A. Timmers et al., 2013), aimed at increasing the output electrical characteristics. One of the most important components of a BES are electrode systems. Most often carbon materials, which have high electrical conductivity, corrosion resistance, and a large specific surface area, are used. The productivity of BES depends on the composition of the root environment, the presence of potential-forming ions, and on the parameters of the light environment, the efficiency of photosynthesis. A promising option for using PMFC is their combination with significant production processes, in particular, their introduction into agricultural production. The possibility of using BES is shown on a number of cultivated and industrial plants with obtaining the following low-power energy output when growing rice - 140 mW/m2 (N. Ueoka et al., 2016), lettuce - 54 mW/m2 (T.E. Kuleshova et al., 2021), Reed mannagrass - 80 mW/m2 (R.A. Timmers et al., 2012), Common reed - 42 mW/m2 (J. Villasenor et al., 2013), cattail - 93 mW/m2 (Y.L. Oon et al., 2016), Common cordgrass - 679 mW/m2 (K. Wetser et al., 2015), etc., which have found application as food products, fuel, building materials, animal feed, etc. Prospects for the use of BES include power supply for environmental sensors (A. Schievano et al., 2017), light sources (W. Apollon et al., 2020), wireless sensor networks (E. Osorio-De-La-Rosa et al., 2021), the Internet of things (IoT) (Jayaraman P.P. et al., 2016),, phytomonitoring systems in natural conditions, greenhouses, remote areas, partial power supply of plant life support devices in artificial agroecosystems (T.E. Kuleshova et al., 2021), wastewater treatment (L. Kook et al., 2016).