The termite mound as atmospheric water harvester

Climate change-related stress on water resources will soon necessitate new technologies to access water, including those that directly harvest it from the air. Common approaches to condense atmospheric vapor at low humidity, which depend on energy-intensive refrigeration, present serious limitations on scalability where they are needed most. Sorbent materials are employed to make the process more efficient and preclude the need for refrigeration, but solutions proposed to date face similar challenges in scalable production. As we are not the first species to face the threat of water scarcity, we look to look to zero-energy solutions that have emerged from eons of natural selection for transformative ideas. Termites of the subfamily Macroterminitae present a stark example: Their brood and fungal crops require tightly controlled temperature and high humidity, yet these species are ubiquitous in regions with extreme daily temperature fluctuations and little to no precipitation or surface water for most of the year. Their survival depends on their ability to construct large, abiotic structures (mounds), towering above their inhabited nests, which passively regulate their climatic needs. We have previously illuminated the mound's passive transport mechanisms, which utilize geometry and material to alternatively dampen and harness external thermal oscillations for thermoregulation and convective internal ventilation, respectively. How they simultaneously manage the precarious water budget is not known. Their water needs are at odds with those of respiration, whose method is non-selective of chemical species. However, simple analysis reveals the necessary features of a sorbent-based, passive atmospheric water generator; use of porous, clay-rich material to enable reversible adsorbance of vapor at significant quantities; passive thermal cycling between uptake and release modes; and cyclic internal flow to transport desorbed moisture to thermally lagging condensation sites. We will present ongoing efforts to characterize and model termite mound performance in this light.