Use of Carex hirta in electro-biotechnological systems on green roofs

Production of bioelectricity from substrates with growing plants and developing microorganisms is the newest technology of alternative energetics that has great perspectives. The efforts of scientists around the world are aimed at improving biotechnology: the development of effective electrode systems for the collection of plant-microbial bioelectricity, the search for new plants, suitable for technology, testing of new substrates for the development of plants. In this paper, we presented tests of new model electro-biosystems (EBS) consisting of graphite-zinc-steelical systems of electrodes with stainless steel elements placed in plastic containers with soil substrate and planted sedges Carex hirta. The experiment was conducted during the year on the roofs of a university building in the climatic conditions of the Western Ukrainian region to assess the functioning of the electro-biosystems in outdoor conditions. We analyzed the different types of electrode placement in containers: with the horizontal alocation of the electrodes under the root system, with the vertical placement cathodes and anodes in a container and with the increased contact area of the cathodes with the substrate and reinforced connecting of cathodes with each other. During the experiment, we monitored the bioelectric potential of the samples which were in an open circle and under load of an external resistor. To analyze short-term voltage and current, polarization measurements were performed by changing the external resistance from 10 Omega to 5 k Omega, and the current strength, current density and power density were calculated. The conducted experiments showed C. hirta can be successfully cultivated on green roofs in open soil in the climatic conditions of the Western Ukrainian region. The studied electro-biosystems operate round-the-year as the plants are frost-resistant. Metereological conditions, especially the temperature and precipitation intensity, affect the electro-performance of the electro-biosystems on the roofs. The maximum average weekly current of 21.36 mA was recorded in May at optimum temperatures and a favourable humidity level, with an average temperature of 11.4 degrees C and rainfall of 5.39 mm/day. The electrical performance of electro-biosystems decreases during the winter and dry periods without an organized irrigation system. During the winter period, electrode systems are damaged by adverse factors. The configuration of the electrode system EBS3 is less susceptible to breakdowns due to the destructive action of water during freezing in the winter and more effective in collecting bioelectricity. The research represented in the paper is one more step towards improving bioelectricity technology on green roofs.