Try to be frugal if you can!

Water sustainability is a target that must be pursued by any means, starting from frugal approaches. Aiming to achieve more with less requires removing nonessential parts, bringing engineering to a different level of complexity. To meet this challenge, we have built a passive multistage and low-cost solar distiller, with a freshwater yield almost twice as much as the existing ones.

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Dec 14, 2018
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The full paper, “Passive solar high-yield seawater desalination by modular and low-cost distillation”, in Nature Sustainability can be found here.

As a swimmer and a scuba diver, I am very fascinated by water, in any form. This also makes me aware that water sustainability is a challenging problem, gradually worsening due to climate change. Water sustainability consists of securing a long-term clean water supply for all living things. Achieving water sustainability requires, primarily, investment in managing freshwater ecosystems and sanitation facilities - on a local level - in several developing countries, as recognized by the United Nations, which indicated access to clean water and sanitation as one of the Sustainable Development Goals. In addition, however, water treatment and desalination technologies will also provide an important contribution in terms of water-energy nexus.

There is an enormous amount of water on Earth, but only 2.5–2.75% is freshwater, with just 0.5–0.75% of available freshwater, or rather that is not frozen in glaciers, ice or snow. The water cycle generates freshwater by evaporation and condensation (precipitation), i.e. by a natural distillation process occurring in the atmosphere of the Earth, which uses solar thermal energy, with low efficiency. This natural process can be mimicked by designing materials and devices for making better solar distillers. Therefore, solar-driven evaporation has recently attracted tremendous research attention owing to its high conversion efficiency of solar energy (see a recent review).

In the summer of 2016, I began to take a keen interest in water sustainability, together with my group, at the multi-Scale ModeLing Laboratory (SMaLL), also thanks to a very inspiring paper. From the very start, the main question that motivated us was, “can we do the same (or even better) with common materials, in order to pave the way to a low-tech technology for impoverished communities?” We made contact with international humanitarian medical non-governmental organizations and started collecting useful feedback. After fruitful discussions, we realized that our approach was the correct way to proceed. Thus, while trying to increase the yield of our distiller, we kept the focus on low-maintenance and low-cost implementations with no moving parts, i.e. experiencing the importance of frugality.

Surprisingly, frugality is unpopular in engineering curricula. We are accustomed to promoting advanced technological solutions, which are taught to the next generation of students. However, achieving more with less is extremely challenging and creates a different level of complexity in the engineering design. Frugal engineering consists of focusing on the minimal robust technology in order to satisfy requirements, by removing nonessential parts. Sometimes, advanced materials and exotic layouts are not essential because they are not scalable, acceptable by end-users or maintainable in the considered application. Like in the Japanese Zen temple garden, the power of the design emerges from its simplicity and harmony (see my favorite one in Kyoto).

(Photo credit: Pietro Asinari, Ryoan-ji Temple, Kyoto, JP)

Therefore, after more than two years of prototypes and many refinements, we have finally built and tested a passive multistage, low-cost solar distiller, where efficient energy management leads to significant enhancement in freshwater yield. Under realistic conditions, we demonstrated a distillate flow rate, which is almost twice the yield of recent passive complete distillation systems. Importantly, we have proven that frugality can be beneficial to improve the long-term sustainability of desalination process.

Pietro Asinari, multi-Scale ModeLing Laboratory (SMaLL, www.polito.it/small), Politecnico di Torino, ITALY

The full paper, “Passive solar high-yield seawater desalination by modular and low-cost distillation”, in Nature Sustainability can be found here.

(Photo credit: Matteo Fasano (left) and Matteo Morciano (right), Varazze, IT)



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Pietro Asinari

Full Professor of Heat and Mass Transfer, Politecnico di Torino

He received his B.S. and M.S. (magna cum laude) in Mechanical Engineering and his Ph.D. in Energetics. He is Full Professor of Heat and Mass Transfer and a member of the PhD Board in Energetics. Since 2002, he has (co-)authored over 90 publications in international journals. He is member of the Board of the European Materials Modeling Council (https://emmc.info/) and of the Advisory Board of OpenKIM (https://openkim.org/). He won the ENI Award. Research fields: Solar Energy, Sustainable Water, Heat and Mass Transfer, Mesoscopic Modelling, Molecular Dynamics.

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