Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Enhanced solar evaporation using a photo-thermal umbrella for wastewater management


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.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Surface heating using a photo-thermal (solar) umbrella.
Fig. 2: Lab-scale experimental results.
Fig. 3: Outdoor testing of the solar umbrella.
Fig. 4: Thermal model validation and performance prediction for the solar umbrella.
Fig. 5: Simulated performance of evaporation ponds for ZLD.

Data availability

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.


  1. The Global Risks Report 2018 (World Economic Forum, 2018).

  2. Grant, S. B. et al. Taking the “waste” out of “wastewater” for human water security and ecosystem sustainability. Science 337, 681–686 (2012).

    CAS  Article  Google Scholar 

  3. Vörösmarty, C. J. et al. Global threats to human water security and river biodiversity. Nature 467, 555–561 (2010).

    Article  Google Scholar 

  4. Pinto, F. S. & Marques, R. C. Desalination projects economic feasibility: a standardization of cost determinants. Renew. Sustain. Energy Rev. 78, 904–915 (2017).

    Article  Google Scholar 

  5. Gude, V. G. Desalination and sustainability—an appraisal and current perspective. Water Res. 89, 87–106 (2016).

    CAS  Article  Google Scholar 

  6. 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).

    CAS  Article  Google Scholar 

  7. Morillo, J. et al. Comparative study of brine management technologies for desalination plants. Desalination 336, 32–49 (2014).

    CAS  Article  Google Scholar 

  8. 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).

    CAS  Article  Google Scholar 

  9. 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).

  10. Mickley, M. Treatment of Concentrate DWPR Report No. 155 (US Department of the Interior Bureau of Reclamation, 2008).

  11. Ahmed, M., Shayya, W. H., Hoey, D. & Al-Handaly, J. Brine disposal from inland desalination plants. Water Int. 27, 194–201 (2002).

    Article  Google Scholar 

  12. Hoque, S., Alexander, T. & Gurian, P. L. Innovative technologies increase evaporation pond efficiency. IDA J. Desal. Water Reuse 2, 72–78 (2010).

    Article  Google Scholar 

  13. Ghasemi, H. et al. Solar steam generation by heat localization. Nat. Commun. 5, 4449 (2014).

    CAS  Article  Google Scholar 

  14. Tao, P. et al. Solar-driven interfacial evaporation. Nat. Energy 3, 1031–1041 (2018).

    Article  Google Scholar 

  15. Shi, Y. et al. Solar evaporator with controlled salt precipitation for zero liquid discharge desalination. Environ. Sci. Technol. 52, 11822–11830 (2018).

    CAS  Article  Google Scholar 

  16. Ni, G. et al. A salt-rejecting floating solar still for low-cost desalination. Energy Environ. Sci. 11, 1510–1519 (2018).

    CAS  Article  Google Scholar 

  17. Xu, N. et al. Mushrooms as efficient solar steam-generation devices. Adv. Mater. 29, 1606762 (2017).

    Article  Google Scholar 

  18. 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).

    CAS  Article  Google Scholar 

  19. Ni, G. et al. Steam generation under one sun enabled by a floating structure with thermal concentration. Nat. Energy 1, 16126 (2016).

    CAS  Article  Google Scholar 

  20. Bae, K. et al. Flexible thin-film black gold membranes with ultrabroadband plasmonic nanofocusing for efficient solar vapour generation. Nat. Commun. 6, 10103 (2015).

    CAS  Article  Google Scholar 

  21. Cooper, T. A. et al. Contactless steam generation and superheating under one sun illumination. Nat. Commun. 9, 5086 (2018).

    CAS  Article  Google Scholar 

  22. 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 (2019).

  23. Segelstein, D. J. The Complex Refractive Index of Water (Univ. Missouri-Kansas City, 1981).

  24. Principles of Design and Operations of Wastewater Treatment Pond Systems for Plant Operators, Engineers, and Managers (US Environmental Protection Agency, 2011).

  25. Cao, F., McEnaney, K., Chen, G. & Ren, Z. A review of cermet-based spectrally selective solar absorbers. Energy Environ. Sci. 7, 1615–1627 (2014).

    CAS  Article  Google Scholar 

  26. 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).

    CAS  Article  Google Scholar 

  27. 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).

    Article  Google Scholar 

  28. 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).

    CAS  Article  Google Scholar 

  29. Winston, R. Principles of solar concentrators of a novel design. Solar Energy 16, 89–95 (1974).

    Article  Google Scholar 

  30. Wang, Z. et al. Bio-inspired evaporation through plasmonic film of nanoparticles at the air–water interface. Small 10, 3234–3239 (2014).

    CAS  Article  Google Scholar 

  31. Hisatake, K., Tanaka, S. & Aizawa, Y. Evaporation rate of water in a vessel. J. Appl. Phys. 73, 7395–7401 (1993).

    CAS  Article  Google Scholar 

  32. Bloch, M. R., Farkas, L. & Spiegler, K. S. Solar evaporation of salt brines. Ind. Eng. Chem. 43, 1544–1553 (1951).

    CAS  Article  Google Scholar 

  33. Gunaji, N. N. & Keyes, C. G. Disposal of Brine by Solar Evaporation (US Department of the Interior, 1968).

  34. Marek, R. & Straub, J. Analysis of the evaporation coefficient and the condensation coefficient of water. Int. J. Heat Mass Transf. 44, 39–53 (2001).

    CAS  Article  Google Scholar 

  35. Harbeck, G. E. Jr The Effect of Salinity on Evaporation Report No. 272A (US Geological Survey, 1955).

  36. Langbein, W. B. & Harbeck, G. E. Studies of evaporation. Science 119, 328 (1954).

    CAS  Article  Google Scholar 

  37. Moore, J. & Runkles, J. R. Evaporation from Brine Solutions Under Controlled Laboratory Conditions Report No. 77 (Texas Water Development Board, 1968).

  38. Turk, L. J. Evaporation of brine: a field study on the Bonneville Salt Flats, Utah. Water Resour. Res. 6, 1209–1215 (1970).

    Article  Google Scholar 

Download references


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.

Author information

Authors and Affiliations



The idea of non-contact radiative heating was conceptualized by R.S.P. and developed by S.L., S.K. and I.H. A.K.M. and I.H. conducted the experiments, developed the models and analysed the results. A.K.M., I.H., S.K. and R.S.P. wrote the paper. R.S.P. supervised the research.

Corresponding author

Correspondence to Ravi S. Prasher.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Pathways towards zero-liquid discharge.

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.

Extended Data Fig. 2 Radiative heat localization.

(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.

Extended Data Fig. 3 Optical properties of the solar umbrella.

(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.

Extended Data Fig. 4 Lab-scale experimental setup.

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.

Extended Data Fig. 5 Surface heating for enhanced evaporation.

(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.

Extended Data Fig. 6 Performance under optical concentration.

(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.

Extended Data Fig. 7 Brine evaporation experiments.

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.

Extended Data Fig. 8 Energy balance for the system.

Schematic showing the heat transfer modes and thermal losses for the solar umbrella and acrylic water tank.

Extended Data Fig. 9 Effect of view factor.

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.

Extended Data Fig. 10 Comparison between the lab-scale prototype and an evaporation pond.

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).

Supplementary information

Supplementary Information

Supplementary Figs. 1 and 2, Notes 1–7, Table 1 and references.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

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).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing