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

A new approach on the management of landfill leachate reverse osmosis concentrate: Solar distillation coupled with struvite recovery and biological treatment

The management of reverse osmosis (RO) concentrate remains a challenging task for operators of Landfill Leachates Treatment Plants. In this article we suggest an integrated treatment scheme for RO concentrate that combines solar distillation, struvite precipitation to reduce ammonia content of the distillate and biological treatment of the supernatant either with mixed cultures of bacteria or with microalgae. Experiments in a pilot-scale solar still, equipped with underfloor heating system, showed that the production rate of the distillate ranged up to 3.17 L/d m2. The distillate was characterized by elevated average concentrations of ammonium nitrogen; 2028 mg/L and 1358 mg/L in the two experiments conducted, respectively. A decreasing trend on concentrations of NH4+-N was noticed during these experiments, while the opposite was observed for COD. Struvite recovery experiments showed that the optimum Mg:NH4:PO3 ratio was that of 2:1:5.8. Under these conditions, the NH4+-N removal reached 88%. Further treatment of the process supernatant into a 4-L hybrid sequencing batch reactor with biocarriers and activated sludge achieved NH4+-N removal higher than 98% in Phases C and D, where 450 and 600 mL of supernatant were added, respectively. Similar removal was also observed in a 2-L bioreactor with microalgae Chlorella sorokiniana when 150 mL of struvite supernatant were added (Phase B) while further increase of the amount of added supernatant to 200 mL resulted to a sharp stop of NH4+-N consumption (Phase C). Calculations for a landfill serving 20,000 inhabitants and a daily RO concentrate production of 6 m3/d showed that the required area for the construction of the solar still was 1893 m2 and the volumes of the hybrid and the microalgae reactor were 54 m3 and 60 m3, respectively. The recovered solid material of struvite process, after characterization for heavy metals and organic micropollutants, could be reused to the fertilizers industry.

Distillate yield improvement techniques for solar still coupled with evacuated tube collector: a review

Many effective solutions to the problem of freshwater scarcity have been offered by the research community across the globe. Evacuated tube collector (ETC)-aided solar thermal desalination devices have succeeded magnificently in providing drinking water to the general public, especially in solar-rich isolated locations. Furthermore, heat transfer fluid ETC solar water desalination units are a much smarter, novel, and cost-effective solution that does not needed additional power and is well-suited to remote locations with a greater rate of self-sustainability. The efficiency of ETC-assisted solar distillation equipment as well as the essential analytical parameters related to the device and heat transfer fluid are thoroughly examined in this study. Literatures published in the last three decades are keenly reviewed and reported. The key finding reveals that solar still integrated with ETC can produce 3.5 to 4 l of freshwater per m2 area with depth varying from 0.01 to 0.03 m. It is discovered that the ETC-assisted solar still has a mean energy efficiency that is around 33% greater than the traditional solar still. When it comes to exergy efficiency, the ETC solar still outperforms conventional stills by 4%. Novel methods adopted for boosting the effectiveness of a solar still combined with ETC are reported for further research.

Carbonized balsa wood-based photothermal evaporator for treating inorganic chemical wastewater

Solar desalination provides a sustainable and eco-friendly solution for purifying wastewater, addressing environmental challenges associated with wastewater treatment. This study focuses on the purification of inorganic contaminants from laboratory chemical wastewater (ICWW) using a spherical solar still (SSS). To enhance the evaporation rate and overcome the impact of heavy metals on absorption efficiency, a carbonized balsa wood (CBW) solar evaporator was employed. Balsa wood pieces, carbonized at 250 °C for 15 min, were arranged in a SSS configuration. The CBW-integrated SSS demonstrated a remarkable freshwater productivity of 2.33 L/m2 for ICWW, surpassing the conventional SSS, which produced only 1.5 L/m2. The presence of heavy metal ions (Na+, Ca+, K+, and Mg2+) in ICWW significantly affected the evaporation rate, and the CBW solar evaporator exhibited an impressive removal efficiency of approximately 99%. Water quality parameters, including pH and chemical oxygen demand (COD), were investigated before and after treatment. The CBW-integrated SSS achieved an outstanding COD removal efficiency of about 99.77%, reducing the COD level from 229.51 to 0.521 mg/L. These results underscore the efficacy of the proposed solar desalination system in purifying ICWW, offering a promising approach to address environmental concerns associated with wastewater treatment.

A detailed review on various aspects of inverted solar still desalination systems proposed for clean water production

Rapid degradation of quality and quantity of the available limited fresh water reserves has forced nations around the globe to search for alternate fresh water sources. This has led to the development of various desalination technologies to generate potable water from abundantly available sea and brackish water. Desalination sector has undergone various upgradations to meet the rising fresh water demand in a sustainable way. One such upgradation is the utilization of solar energy as an energy source. High cost and associated environmental impacts with large-scale desalination systems have shifted the focus of researchers towards research and development of various small-scale efficient solar stills for cheap potable water production in rural, remote, arid, and coastal locations. In this review article, various configurations of a non-conventional solar still, namely inverted solar still, have been reviewed extensively by highlighting its classifications, design aspects, working principle, features, and economics. Moreover, the role of inverted solar still's evaporating and condensing surface characteristics and thermal properties on its distillate productivity has also been discussed. Inverted absorber multi-basin solar still and inverted multi-effect diffusion solar still configurations are highly productive. Economics of inverted solar still is better than other conventional solar still configurations and conventional reverse osmosis plant of few m3/day capacity. This review article will facilitate researchers to select appropriate inverted solar still configuration for further performance improvement and commercialization. The scope for future research works on inverted solar still has also been listed.

Efficient solar desalination for clean water production from different wastewaters

Solar energy is one of the sustainable sources for many fruitful applications. Desalination of wastewater by solar power is a priority research focus and has attracted many researchers and scientists world-wide. However, handling industrial and other wastewater is typically a challenging task for effective treatment and re-use. The presence of contaminants in the effluent is hazardous to the environment and human health. In the present work, an attempt has been made to investigate different wastewaters including (i) garbage wastewater, (ii) waste vegetable water, (iii) landfill leachate, and (iv) pharmaceutical effluent fed into a solar distiller evaporated under natural solar illumination. Herein, different waste waters' pH, chemical oxygen demand (COD), ammoniacal-nitrogen (NH3-N), arsenic (As), Barium (Ba), Cobalt (CO), Chromium (Cr), Iron (Fe), Mercury (Hg), Potassium (K), Manganese (Mn), Magnesium (Mg), Sodium (Na), Nickel (Ni), Phosphate (P), and Zinc (Zn) were investigated by the inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The concentration of NH3-N in the garbage wastewater, vegetables wastewater, landfill leachate, and pharmaceutical effluent were 157 mg/L, 142 mg/L, 161 mg/L, and 164 mg/L, respectively. The evaporated water output of garbage, waste-vegetable water, landfill leachate, and pharmaceutical effluents are 1.7 L/m2.day, 1.8 L/m2.day, 1.9 L/m2.day, and 1.65 L/m2.day, respectively. Finally, the test result reveals that the water quality is greatly improved after consecutive evaporation process by the solar distiller. This is one way to deal with the wastewater through a sustainable process for a better future.

Environmental and embodied analysis of partial shading pyramid solar still

The novelty of this research is shading position in the transparent cover of partially shaded pyramid solar still. The square pyramid transparent cover is used as top cover of partially shaded pyramid solar still. The square pyramid has four sides and each side named as per the direction. Each one of the sides is shaded in the square pyramid transparent cover. The single side or direction shaded is known as 25% of shading in the transparent cover. Similarly, two sides are 50%, and three sides are 75%. Totally, fourteen configurations of experiments are conducted in the partially shaded pyramid solar still for improving the freshwater yield. Fifty per cent of shading in the transparent cover produced higher freshwater yield compared to 25 and 75%. The partial shading increased productivity of freshwater yield by reducing 4 °C of transparent cover temperature compared to conventional pyramid solar still. The north and south direction shaded (50% of shading) produced 4% higher freshwater yield compared to conventional pyramid solar still. The embodied analysis is studied for partially shaded pyramid solar still. The lifecycle conversation efficiency is around 38%, and CO₂ mitigation is 34.1 for 50% shading of partially shaded pyramid solar still.

A study of cover slope effect on productivity of solar still under Tunisian winter and summer conditions

The Tunisian country will suffer from the scarcity of clean and healthy drinking water in the near future. Solar still-based water distillation is one of the simplest cheap technologies that may solve this problem. The present study addresses this problem through experimentally and numerically investigating the feasibility of water desalination with a passive solar still in actual Tunisia Sfax central region climate conditions as well as the glass cover angle effect on the productivity of the solar still. The study was conducted for 2 days so that 1 day is in the summer and another day in the winter for comparison purpose. The flow solution was obtained with the Fluent solver Eulerian multiphase model coupled to a developed C +  + mass transfer code based on the Dunkle model. The considered glass cover angles are 5°, 10°, 20°, 30°, 45°, and 60°. The deviation between the numerical results and test data does not exceed 15% which ensures the validity of the calculation method. Both experimental and numerical results showed that the solar still productivity in summer is by far better than that in winter. The optimal glass cover angle was found to be of 20° in both summer and winter seasons. The maximum daily water yield is of 535.64 ml on January 15, 2021 and 3083.11 ml on June 15, 2021. The results proved that the solar still can be an efficient device for solar desalination in Tunisia central region.

Research on Film Insulation Technology for Artificial, Open Water Delivery Canals Based on Solar Heat Radiation Utilization

A measure of insulation film floating on the water surface was put forward to solve the problems of ice damage to water delivery canals during the winter operation period in cold regions. Firstly, a circulating flume test system was designed in an indoor radiation- and temperature-controlled environment. Secondly, five groups of comparative tests were carried out according to different application scenarios. Lastly, combined with the experimental data, the radiative degree-day method was used to calculate the ice thickness growth under the film. The results show that, in a sufficient radiation condition, a membrane can effectively melt the canal ice and prevent ice formation. In a limited radiation condition, a membrane can delay the ice sealing time and reduce the ice thickness, avoiding ice thrust damage to canal lining. The ice thickness growth formula can predict the development process of water and ice thickness under this technique. The research provides certain theoretical guidance and practical significance for the combination of solar thermal technology and water delivery engineering in cold regions.