Abstract
Green roofs have many benefits, but in countries with semiarid climates the amount of water needed for irrigation is a limiting factor for their maintenance. The use of drought-tolerant plants such as Sedum species, reduces the water requirements in the dry season, but, even so, in semiarid environments these can reach up to 60 L m−2 per day. Continuous substrate/soil water content monitoring would facilitate the efficient use of this critical resource. In this context, the use of plant microbial fuel cells (PMFCs) emerges as a suitable and more sustainable alternative for monitoring water content in green roofs in semiarid climates. In this study, bench and pilot-scale experiments using seven Sedum species showed a positive relationship between current generation and water content in the substrate. PMFC reactors with higher water content (around 27% vs. 17.5% v/v) showed larger power density (114.6 and 82.3 μW m−2 vs. 32.5 μW m−2). Moreover, a correlation coefficient of 0.95 (±0.01) between current density and water content was observed. The results of this research represent the first effort of using PMFCs as low-cost water content biosensors for green roofs.
Highlights
Over the last years, the expansion of urban areas has motivated the development of technologies such as green roofs, which in turn increases the amount of green areas in urban settlements and a series of other positive outcomes
The current generated by plant microbial fuel cells (PMFCs) in the laboratory showed a tight relationship between current density and soil moisture content, which is reflected as an increment in the current as a result of irrigation (Figure 1A)
Water content and current were continuously monitored for two PMFC reactors, representatives of the two higher-power densities produced by the PMFC reactors (i.e., S. rupestre and S. hybridum) [9]
Summary
The expansion of urban areas has motivated the development of technologies such as green roofs, which in turn increases the amount of green areas in urban settlements and a series of other positive outcomes. A previous study, conducted in a semiarid climate during the dry season, demonstrated that an extensive green roof planted with Sedum could require up to 60 mm d−1 of water, which is approximately ten times larger than the evapotranspiration of reference [8]. For this reason, in semi-arid climates an efficient use of water is essential. According to our experience monitoring green roofs [8,9], each of the Sensors 2018, 18, 71; doi:10.3390/s18010071 www.mdpi.com/journal/sensors
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