Original Authors: Chao Zeng, Amin Mojiri, Jirapat Ananpattarachai, Alireza Farsad, Paul Westerhoff
Introduction:
As water scarcity intensifies globally, atmospheric water harvesting (AWH) presents a sustainable solution for producing clean water directly from air. Our recent study explored sorption-based atmospheric water harvesting (SAWH) technology, focusing on its performance in urban residential and office environments. The study assessed both the water yield and quality over a 12-month period, offering insights into the practical use of SAWH systems for continuous water production.
Key Findings:
We deployed a portable zeolite-based SAWH device in a residential house and an office building in Tempe, Arizona, where the arid climate provided an ideal testing ground. The system achieved a median water yield of 3.6 liters per day, with energy consumption of 0.33 liters per kilowatt-hour (L/kWh). This resulted in a water cost of $0.45 per liter, approximately 30% less than the price of bottled water in the U.S. The highest water yield was recorded during the North American Monsoon season, with up to 5.0 liters per day when relative humidity (RH) was at its peak.
Water Quality Concerns:
The water collected from the well-ventilated office building generally met EPA drinking water standards, but samples from the residential setting contained elevated levels of dissolved organic carbon (DOC)—up to 52.5 mg/L, compared to just 5.8 mg/L from the office. This difference was attributed to activities like cooking, which release volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) into the air.
Specific substances like formaldehyde and acetaldehyde were found at concentrations of 14 mg/L and 0.22 mg/L, respectively, in residential water samples. These substances likely contributed to the lower pH of the residential water, which ranged between 4.1 and 4.9.
Energy Efficiency and Predictive Model:
A predictive model based on the modified Langmuir isotherm was developed to estimate daily water yields. The model, using absolute humidity (AH) as the prediction variable, demonstrated strong predictive accuracy with R² = 0.80. This allowed us to forecast water yields across various conditions, with the theoretical maximum water yield (Ym) estimated at 10.3 liters per day.
Future Challenges and Solutions:
While the SAWH device produced high-quality water in the office building, challenges remain in improving water quality from residential environments. Organic compounds like formate and acetate, which comprised approximately 50% of the DOC, indicate the need for better filtration methods. Standard carbon fiber filters reduced DOC by 19%, but were ineffective at removing aldehydes and volatile fatty acids.
Further research is necessary to refine pre-treatment or post-treatment processes to ensure the safe consumption of water harvested from indoor air, particularly in residential settings.
Conclusion:
Sorption-based atmospheric water harvesting (SAWH) offers a viable solution for continuous water production in urban spaces. With improvements in system design and filtration technologies, SAWH could be a key player in the future of decentralized, sustainable water solutions. In this study, the device successfully demonstrated the potential to supply 3.6 liters/day of water at a low cost, with room for future enhancement in water quality management.
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