Zero-liquid discharge is an emerging wastewater management strategy that maximizes water recovery for reuse and produces a solid waste, thereby lowering the environmental impact of wastewater disposal. Evaporation ponds harvest solar energy as heat for zero-liquid discharge, but require large land areas due to low evaporation rates. Here, we demonstrate a passive and non-contact approach to enhance evaporation by more than 100% using a photo-thermal device that converts sunlight into mid-infrared radiation where water is strongly absorbing. As a result, heat is localized at the water’s surface through radiative coupling, resulting in better utilization of solar energy with a conversion efficiency of 43%. The non-contact nature of the device makes it uniquely suited to treat a wide range of wastewater without contamination, and the use of commercial materials enables a potentially low-cost and highly scalable technology for sustainable wastewater management, with the added benefit of salt recovery.
Subscribe to Journal
Get full journal access for 1 year
only $8.25 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
The data that support the findings of this study are available in the Supplementary Information. Additional data are available from the corresponding author on request.
The Global Risks Report 2018 (World Economic Forum, 2018).
Grant, S. B. et al. Taking the “waste” out of “wastewater” for human water security and ecosystem sustainability. Science 337, 681–686 (2012).
Vörösmarty, C. J. et al. Global threats to human water security and river biodiversity. Nature 467, 555–561 (2010).
Pinto, F. S. & Marques, R. C. Desalination projects economic feasibility: a standardization of cost determinants. Renew. Sustain. Energy Rev. 78, 904–915 (2017).
Gude, V. G. Desalination and sustainability—an appraisal and current perspective. Water Res. 89, 87–106 (2016).
Tong, T. & Elimelech, M. The global rise of zero liquid discharge for wastewater management: drivers, technologies, and future directions. Environ. Sci. Technol. 50, 6846–6855 (2016).
Morillo, J. et al. Comparative study of brine management technologies for desalination plants. Desalination 336, 32–49 (2014).
Giwa, A., Dufour, V., Al Marzooqi, F., Al Kaabi, M. & Hasan, S. W. Brine management methods: recent innovations and current status. Desalination 407, 1–23 (2017).
Juby, G. et al. Evaluation and Selection of Available Processes for a Zero-Liquid Discharge System DWPR No. 149 (US Department of the Interior Bureau of Reclamation, 2008).
Mickley, M. Treatment of Concentrate DWPR Report No. 155 (US Department of the Interior Bureau of Reclamation, 2008).
Ahmed, M., Shayya, W. H., Hoey, D. & Al-Handaly, J. Brine disposal from inland desalination plants. Water Int. 27, 194–201 (2002).
Hoque, S., Alexander, T. & Gurian, P. L. Innovative technologies increase evaporation pond efficiency. IDA J. Desal. Water Reuse 2, 72–78 (2010).
Ghasemi, H. et al. Solar steam generation by heat localization. Nat. Commun. 5, 4449 (2014).
Tao, P. et al. Solar-driven interfacial evaporation. Nat. Energy 3, 1031–1041 (2018).
Shi, Y. et al. Solar evaporator with controlled salt precipitation for zero liquid discharge desalination. Environ. Sci. Technol. 52, 11822–11830 (2018).
Ni, G. et al. A salt-rejecting floating solar still for low-cost desalination. Energy Environ. Sci. 11, 1510–1519 (2018).
Xu, N. et al. Mushrooms as efficient solar steam-generation devices. Adv. Mater. 29, 1606762 (2017).
Finnerty, C., Zhang, L., Sedlak, D. L., Nelson, K. L. & Mi, B. Synthetic graphene oxide leaf for solar desalination with zero liquid discharge. Environ. Sci. Technol. 51, 11701–11709 (2017).
Ni, G. et al. Steam generation under one sun enabled by a floating structure with thermal concentration. Nat. Energy 1, 16126 (2016).
Bae, K. et al. Flexible thin-film black gold membranes with ultrabroadband plasmonic nanofocusing for efficient solar vapour generation. Nat. Commun. 6, 10103 (2015).
Cooper, T. A. et al. Contactless steam generation and superheating under one sun illumination. Nat. Commun. 9, 5086 (2018).
Menon, A. K., Haechler, I., Kaur, S., Lubner, S. & Prasher, R. S. Enhanced solar evaporation using a photo-thermal umbrella: towards zero liquid discharge wastewater management. Preprint at https://arxiv.org/abs/1905.10394 (2019).
Segelstein, D. J. The Complex Refractive Index of Water (Univ. Missouri-Kansas City, 1981).
Principles of Design and Operations of Wastewater Treatment Pond Systems for Plant Operators, Engineers, and Managers (US Environmental Protection Agency, 2011).
Cao, F., McEnaney, K., Chen, G. & Ren, Z. A review of cermet-based spectrally selective solar absorbers. Energy Environ. Sci. 7, 1615–1627 (2014).
Shi, L., Wang, Y., Zhang, L. & Wang, P. Rational design of a bi-layered reduced graphene oxide film on polystyrene foam for solar-driven interfacial water evaporation. J. Mater. Chem. A 5, 16212–16219 (2017).
Ye, M. et al. Synthesis of black TiOx nanoparticles by Mg reduction of TiO2 nanocrystals and their application for solar water evaporation. Adv. Energy Mater. 7, 1601811 (2016).
Zhang, L., Tang, B., Wu, J., Li, R. & Wang, P. Hydrophobic light-to-heat conversion membranes with self-healing ability for interfacial solar heating. Adv. Mater. 27, 4889–4894 (2015).
Winston, R. Principles of solar concentrators of a novel design. Solar Energy 16, 89–95 (1974).
Wang, Z. et al. Bio-inspired evaporation through plasmonic film of nanoparticles at the air–water interface. Small 10, 3234–3239 (2014).
Hisatake, K., Tanaka, S. & Aizawa, Y. Evaporation rate of water in a vessel. J. Appl. Phys. 73, 7395–7401 (1993).
Bloch, M. R., Farkas, L. & Spiegler, K. S. Solar evaporation of salt brines. Ind. Eng. Chem. 43, 1544–1553 (1951).
Gunaji, N. N. & Keyes, C. G. Disposal of Brine by Solar Evaporation (US Department of the Interior, 1968).
Marek, R. & Straub, J. Analysis of the evaporation coefficient and the condensation coefficient of water. Int. J. Heat Mass Transf. 44, 39–53 (2001).
Harbeck, G. E. Jr The Effect of Salinity on Evaporation Report No. 272A (US Geological Survey, 1955).
Langbein, W. B. & Harbeck, G. E. Studies of evaporation. Science 119, 328 (1954).
Moore, J. & Runkles, J. R. Evaporation from Brine Solutions Under Controlled Laboratory Conditions Report No. 77 (Texas Water Development Board, 1968).
Turk, L. J. Evaporation of brine: a field study on the Bonneville Salt Flats, Utah. Water Resour. Res. 6, 1209–1215 (1970).
This work was supported by the Laboratory Directed Research and Development Program at Lawrence Berkeley National Laboratory under contract number DE-AC02-05CH11231. The authors thank Z. Huang and S. Mohammed for assistance with thermal and mass transport modelling, and gratefully acknowledge Almeco for providing selective absorber samples. A.K.M. acknowledges funding support from the ITRI-Rosenfeld Fellowship from the Energy Technologies Area at Lawrence Berkeley National Laboratory. I.H. acknowledges funding support from the Zeno Karl Schindler Foundation.
The authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Flow charts showing three different schemes for ZLD using membrane-based and thermal systems; the final step involves the use of either a brine crystallizer or an evaporation pond to extract remaining water and yields a solid waste for disposal.
(a) Absorption coefficient of electromagnetic radiation in water with penetration depth of 30 m in visible wavelengths and 20 μm at mid-IR wavelengths. (b) Blackbody emissive power of the sun (T = 5505 °C) that emits in the visible and near-IR, and a blackbody at 100 °C that emits in mid-IR where water is strongly absorbing.
(a) Reflectance of the selective absorber (TiNOXenergy, Almeco) and black paint emitter measured using an FTIR. (b) Structure of the solar umbrella comprising a selective solar absorber coated on the top surface of an aluminum substrate and a black paint sprayed on to the bottom surface.
The solar umbrella comprises a selective solar absorber and black emitter which is placed on an acrylic tank containing water. The temperature profile and evaporation rate are monitored using thermocouples and a mass balance, respectively. Holes are drilled into the umbrella to serve as vapor escape pathways.
(a) Temperature of the absorber-emitter when exposed to a solar flux showing a fast thermal transient response. (b) Mass change over time due to evaporation under dark conditions, and under one sun illumination with and without the absorber-emitter.
(a) Temperatures of the absorber-emitter, water vapor (measured 2 mm below absorber) and the water surface as a function of low optical concentrations. (b) Mass change over time due to evaporation under different solar fluxes.
Images of the emitter surface and water tank after brine evaporation experiments with a 25 wt% NaCl solution over a five-day period. Salts are deposited on the walls of the tank and there is no evidence of fouling of the emitter surface owing to the non-contact device design.
Schematic showing the heat transfer modes and thermal losses for the solar umbrella and acrylic water tank.
Radiation view factor, F for radiation exchange between the solar umbrella and water surface as a function of distance between the two surfaces, L and the length of the evaporation pond, X. The dashed line represents a view factor of 0.8 required for efficient radiation heat transfer between the surfaces.
Mass transport resistance network for (a) lab-scale prototype and (b) large-scale evaporation pond where the distance between the umbrella and the pond can be very large depending on the dimensions of the pond (1 m is shown here as an example).
About this article
Cite this article
Menon, A.K., Haechler, I., Kaur, S. et al. Enhanced solar evaporation using a photo-thermal umbrella for wastewater management. Nat Sustain 3, 144–151 (2020). https://doi.org/10.1038/s41893-019-0445-5