Recently, the "Energy-Air-Water" interdisciplinary innovation team ITEWA, led by Prof. Wang Ruzhu from School of Mechanical Engineering at Shanghai Jiao Tong University, published a research paper titled "Integrating Rooftop Agriculture and Atmospheric Water Harvesting for Water-Food Production Based on Hygroscopic Manganese Complex" in Advanced Functional Materials. Shan He, a joint Ph.D. student from Shanghai Jiao Tong University and the National University of Singapore, is the first author of the paper, with Professor Wang Ruzhu and Professor Swee Ching Tan from the National University of Singapore as the corresponding authors.

Amidst climate change and population growth, the imbalance in the supply and demand of water and food resources is becoming increasingly severe, particularly in urban areas. Traditional methods that rely on supply chains for food delivery and pipelines for water conveyance not only generate high carbon emissions and energy consumption but also increase the security risks of essential supplies due to their lengthy supply chains. The integration of existing building facilities like rooftop agriculture and heat pump air conditioning with new technologies such as radiative cooling, atmospheric water harvesting, and colored photovoltaics holds broad prospects and will promote urban safety and sustainable development.

To advance the practical implementation of integrated atmospheric water harvesting and rooftop agriculture, Prof. Wang's team collaborated with Prof. Swee Ching Tan to optimize the material dynamics, deployment climatic characteristics, and plant growth traits, leading to the creation of a fully automated atmospheric water source irrigation rooftop farm. Without external water input, this system achieved a water yield of 879.9 g/m² and a food production rate of 1.28 kg/m² over 14 days, offering a new pathway for distributed harvests of food and water in cities and sustainable urban development.

Focusing on large-scale, low-cost preparation and fast kinetics under moderate to high humidity conditions, the research team developed an adsorption material composed of a manganese (II)-ethanolamine complex hygroscopic coordination compound and a porous polyvinyl alcohol aldehyde foam matrix. The final composite material achieved an adsorption capacity of 0.45-2.54 g g-1 at 50-90% relative humidity and a significant increase in water adsorption capacity suitable for regions with large diurnal temperature variations or constantly moderate-to-high humidity. The kinetics of the material adsorption reached 0.0235 g/g/min, with adsorption equilibrium achievable within 240 minutes, suitable for multiple adsorption-desorption cycles. The team also explored the device-level scaled-up material in various conditions including standalone photothermal desorption, spatial heating desorption, and combined waste heat-solar energy interface desorption, providing design assurances for stable performance in complex outdoor climates.

The study showcases the outdoor fully automated atmospheric water source irrigation rooftop farm. Powered by solar panels and batteries, the system uses an Arduino Nano microcontroller and motors to switch between unattended water release and capture modes, with an automated control system finely tuning the adsorption-desorption duration. Over a 14-day unattended outdoor experiment, it successfully achieved a water yield of 879.9 grams per square meter and a food yield of 1.28 kilograms per square meter, demonstrating the feasibility of this technology integration. The research aims to bridge the gap between laboratory material development and device construction, reporting optimized lab performance as well as large-scale synthesis and real-world testing. On the device level, it considers the entire system's heat and mass transfer impacts, evaluating the temperature changes affecting water collection. However, due to constraints, the verification area for the adsorption materials and rooftop farm remains under one square meter, and the scalability and cost-effectiveness of the materials and devices still require further validation.

Combining atmospheric water harvesting technology with rooftop agriculture provides unprecedented opportunities for sustainable urban development. Beyond the apparent benefits of water and food production, this technology can also integrate with unique features of existing buildings. Utilizing waste heat from building HVAC systems as the energy for desorption recycles wasted resources, avoids negative impacts on plant growth, maximizes thermal energy utilization, and regulates indoor temperature and humidity. Additionally, rooftop farms reduce buildings' thermal load and energy consumption by providing shade and transpiration, mitigating the impact of urban heat islands on local climate and environment. Ultimately, this localized method of sustainable water and food acquisition eliminates the need for long-distance transportation, further revolutionizing our understanding of water and food production in urban sustainability, and taking a crucial step towards sustainable urban development at the nexus of energy, water, and food, addressing global food security and supply challenges.

Prof. Wang Ruzhu's "Energy-Water-Air" innovation team (ITEWA) has long been dedicated to addressing the cutting-edge basic scientific issues and key technologies at the intersection of energy, water, and air, aiming to achieve holistic solutions across materials, devices, and systems, and to drive breakthroughs in related fields. Over the past five years, the team has published over 40 interdisciplinary papers in high-level journals such as Science, Nature Water, Joule, EES, Advanced Materials, and explored the potential and power of integrating technologies such as rooftop agriculture, heat pump air conditioning, radiative cooling, atmospheric water harvesting, and colored photovoltaics in a perspective article (doi.org/10.1016/j.energy.2023.129009).

Paper Link: https://onlinelibrary.wiley.com/doi/10.1002/adfm.202402839