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Solar distillation meets the real world: a review of solar stills purifying real wastewater and seawater

Abstract

Solar energy-driven evaporation-based freshwater production is one of the sustainable ways to purify contaminated/salty water. Recent advances in solar absorbers’ assemblies, design modifications, and integrations with heating sources improved the rate of freshwater productivity. However, the type of feed water affects the evaporation rate in a solar desalination system (SDS). Many studies used tap water with added contaminants to test the performance of a SDS and studied the water quality improvement. As a typical result, pH, total dissolved solids (TDS), and electrical conductivity (µS/cm) are reduced after solar evaporation. The performance of SDSs for real wastewaters are also important to understand, e.g., the reduction of high organic pollutants after solar evaporation. In this aspect, the main objective of the present work is to review solar distillation of real wastewaters and seawater by using SDSs. Further, the mechanism of a solar distiller with heat transfer principles, parameters affecting evaporation process, real wastewaters and seawaters purified in a solar distillation system, improvement of various parameters before and after solar evaporation, pathways of handling wastewaters, challenges, and future perspectives are discussed. Conclusively, SDSs are found to remove pollutants effectively after solar evaporation. The evaporation rate is relatively slower due to high concentration of pollutants that reduce vapor pressure. The COD removal of various real wastewaters, including sludge, kitchen, textile, palm oil, petroleum, water plant, and municipal wastewaters, was 98.13%, 97.85%, 96.84%, 96.71%, 87.99%, 86.99%, and 85.67%, respectively. The reduction rate of salt concentration in real seawater after evaporation in the solar distiller was 99.99%.

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Not applicable to this article.

Abbreviations

AEO:

Alcohol polyoxethylene

BOD:

Biological oxygen demand (mg/L)

BG:

Brilliant green

B-MXM:

Bilayer MXene-monoliths

COD:

Chemical oxygen demand (mg/L)

CFU:

Colony-forming unit

CMF:

Carbonized magnolia fruit

CNT:

Carbon nanotube

CVD:

Chemical vapor deposition

DB:

Direct black

DDT:

Dichloro-dipheyl-trichloroethene

DSSS:

Double slope solar still

DNA:

Deoxyribonucleic acid

EP:

Enteromorpha prolifera

EPX:

Epoxiconazole

FSS:

Floatable solar still

GM:

Green moss

GRACE:

Gravity recovery and climate experiment

HCS:

Hierarchical copper silicon

HCP:

Hexachlorocyclohexane

HSS:

Hemispherical solar still

ICP-OES:

Inductively coupled plasma-optical electron microscope

IIT:

Indian Institute of Technology

LSSP:

Localized surface salt precipitation

MB:

Methylene blue

MIT:

Massachusetts Institute of Technology

MLSS:

Mixed liquid suspended solids

MLVSS:

Mixed liquid volatile suspended solids

MO:

Methyl orange

NASA:

National Aeronautics Space Administration

MPN:

Most probable number

NF:

Nanofluid

NP:

Nanoparticle

NTU:

Nephelometric turbidity

PR:

Particulate removal

PPM:

Parts per million

Ppy:

Polypyrrole

PS:

Polystyrene

PVA:

Polyvinyl alcohol

PYC:

Pyraclostrobin

RB:

Reactive blue

rGO:

Reduced graphene oxide

RhB:

Rhodamine B

RO:

Reactive orange

SDS:

Solar distillation system

SFD:

Sun flower disc

SSSS:

Single slope solar still

SSG:

Solar steam generation

SSP:

Shallow solar pond

TDS:

Total dissolved solids (mg/L)

TOC:

Total organic carbon (mg/L)

TSS:

Total suspended solids (mg/L)

VG:

Vat green

WHO:

World Health Organization

USA:

United States of America

US-EPA:

United States-Environmental Protection Agency

UV–Vis-NIR:

Ultraviolet–visible-near infrared

A:

Area of the collector (m2)

M:

Mass of the water (kg)

hfg :

Latent heat of vaporization (2260 kJ/kg or 40.8 kJ/mol)

I:

Intensity of solar irradiation (W/m2)

Tamb :

Ambient-air temperature (°C)

Tw :

Temperature of water (°C)

Tg :

Temperature of glass (°C)

Pw :

Partial pressure of water (N/m2)

Pg :

Partial pressure of glass (N/m2)

Tsky :

Sky temperature (°C)

qc :

Convective heat transfer rate

qe :

Evaporative heat transfer rate

qr :

Radiative heat transfer rate

hc :

Convective heat transfer coefficient (W/m2 K)

he :

Evaporative heat transfer coefficient (W/m2 K)

hr :

Radiative heat transfer coefficient (W/m2 K)

εg :

Emissivity of the glass

σ:

Stefan-Boltzmann constant (5.670374 × 108 W/m2 K4)

Δt:

Temperature difference (°C

References

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Acknowledgements

The list of figures used from “Elsevier,” “RSC Publications,” ‘”CS Publications,” and “Wiley Publications” for reproduction is greatly appreciated.

Funding

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2017R1A2B3005415).

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Authors and Affiliations

Authors

Contributions

Thirugnanasambantham Arunkumar: conceptualization, writing—original draft preparation; Ravishankar Sathyamurthy: formal analysis and validation; David Denkenberger: reviewing and editing; Sang Joon Lee: supervision, reviewing and editing.

Corresponding author

Correspondence to Sang Joon Lee.

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The authors declare no competing interests.

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Appendix

Appendix

Appendix 1 Heat transfer in solar desalination system

In general, heat transfer means the flow of heat from one place to another due to temperature differences between them. The utilization of input heat energy and the loss coefficients are determined with an aid of heat transfer calculations. In a solar desalination system, the flow of heat is further classified as internal heat transfer and external heat transfer.

  1. (i)

    Internal heat transfer

Energy is transferred within the system by convection, evaporation, and radiation. Here, the heat transfer occurs due the temperature difference between the any two segments in the system. Convection is driven by the temperature difference between the water and the glass cover (Agrawal et al. 2017).

$$q_{cwg} = \,h_{cwg} \,(T_{w} - T_{g} )$$
(1)

where qc is referred as convective heat transfer, hc is the convective heat transfer co-efficient (W/m2 K), and (Tw − Tg) is the temperature difference between water and the glass surface.

$$h_{cwg} = \,0.884\,\left[ {(T_{w} - T_{g} )\, + \frac{{(P_{w} - P_{g} )(T_{w} + 273)}}{{(268.9 \times 10^{3} - P_{w} )}}} \right]^{{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 3}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$3$}}}}$$
(2)

where Pw and Pg are the partial saturated pressure of water and the glass (N/m2).

Further, the evaporative heat transfer occurs when the flow of vapor from the water liner to internal glass cover (Agrawal et al. 2017).

$$q_{ewg} = h_{ewg} \,(T_{w} - T_{g} )$$
(3)

where qe is the evaporative heat transfer rate and he is the evaporation heat transfer co-efficient (W/m2 K).

$$h_{ewg} \, = \,(16.28\, \times 10^{ - 3} )\,h_{cwg} \,(p_{w} - p_{g} )/(T_{w} - T_{g} )$$
(4)

The radiative heat transfer occurs due to the temperature difference between water liner to the glass cover (Sharma and Mullick 1992).

$$q_{rwg} \, = \,h_{rwg} \,(T_{w} - T_{g} )$$
(5)
$$h_{rwg} \, = \,0.9\,\sigma \,\left( {T_{w}^{2} + T_{g}^{2} } \right)\,\left( {T_{w} + T_{g} } \right)$$
(6)

where qr is the radiative heat transfer rate, hr is the radiative heat transfer co-efficient, and σ is the Stefan-Boltzmann constant (5.67 × 10−8 W/m2 K4).

  1. (ii)

    External heat transfer

The radiative heat transfer between top condensing cover to the sky is given by (Agrawal et al. 2017),

$$h_{rgs} \, = \,\varepsilon_{g} \,\sigma \left[ {\left( {T_{g} + 273} \right)^{4} - (T_{sky} + 273)^{4} } \right]/\left( {T_{g} - T_{sky} } \right)$$
(7)

where ε is the emittance of glass cover.

Tsky can be elaborated from (Agrawal et al. 2017),

$${T}_{sky}=0.0552\times {{T}_{amb}}^{1.5}$$
(8)

where Tamb is the ambient air temperature (K).

The evaporation efficiency of the solar desalination system can be calculated by (Arunkumar et al. 2012),

$$\eta = \frac{{M\, \times \,h_{fg} }}{I\, \times \,A \times \,\Delta t}$$
(9)

where M is the mass of the distillate output, hfg is referred as latent heat of vaporization (2260 kJ/kg or 40.8 kJ/mol) (Kuhle 2011), I is the incident solar irradiation, surface area of the collector is named as A, and time period of experiments in denoted in Δt.

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Arunkumar, T., Sathyamurthy, R., Denkenberger, D. et al. Solar distillation meets the real world: a review of solar stills purifying real wastewater and seawater. Environ Sci Pollut Res 29, 22860–22884 (2022). https://doi.org/10.1007/s11356-022-18720-2

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Keywords

  • Solar energy
  • Wastewater
  • Seawater
  • Desalination
  • Solar still
  • Water quality