First approach on nanofluid-based solar still in high altitude for water desalination and solar water disinfection (SODIS)

Energy-matrices, exergy, economic, environmental, exergoeconomic, enviroeconomic, and heat transfer (6E/HT) analysis of two passive/active solar still water desalination nearly 4000m: Altitude concept

Unsafe drinking water, insufficient sanitation and hygiene behaviour and indoor air pollution are some of the most important environmental risks, which are harmful to health. They cause diarrhoea, pneumonia and sepsis, and are with 65% the leading cause of death in children under 5 years of age. Lack of safe water perpetuates the cycle whereby poor populations become further disadvantaged and poverty entrenched. 
\nPoint-of-use household water treatment and safe storage systems (POU-HWT) represent one of the most promising strategies to block major transmission pathways associated with contracting diarrhoea, especially in low income countries. Home-based solar water disinfection (SODIS) is one of those POU-HWT systems being promoted worldwide. The SODIS-method consists of exposing water-filled, transparent PET bottles to sunlight for at least 6 hours. The evidence base of the health effectiveness of SODIS from population-based scientific evaluations is limited and experiences from large-scale roll outs of SODIS interventions are equally scarce. The community-randomised trial described in this thesis investigates the health effectiveness and the factors that lead to the uptake of the intervention.
\nThe main goal of this thesis was to assess the effectiveness of a Latin American community-level SODIS dissemination programme in reducing child diarrhoea and the determination of factors related to the adoption of SODIS among the population. From 2004 to 2006, a community-randomised controlled trial was thus, conducted in 22 community-clusters situated in Bolivia. SODIS was implemented in the intervention communities by a local NGO over 15 months. The promotion of SODIS consisted of interactive, repeated, and standardised events held on community and household level. In order to comprehensively describe both, application and uptake, and the health effect of SODIS, a health surveillance system with community-based staff measuring compliance with SODIS as well as the occurrence of diarrhoea in children under 5 was established. Since no standards to classify households according to their SODIS-use exist, different indicators for use were measured by evaluators independent from the implementing NGO. Further, surveys assessed household determinants as well as SODIS promotion and -campaign factors, which were associated with the SODIS adoption.
\nDespite the extensive SODIS promotion campaign a possible health impact in this typical rural Bolivian setting was too low to be assessed by this study. The intention-to-treat analysis of the 1-year health monitoring of 725 children <5 (425 households) detected no significant difference in diarrhoea morbidity between the intervention and the control communities. This finding is neither in line with the results of former trials assessing the health impact of SODIS, nor with the results of trials testing a variety of different other POU-HWT technologies. This inconclusive finding might be explained by the moderate compliance or the fact that most of the endemic diarrhoeal disease is not exclusively transmitted through the consumption of contaminated drinking water only, but rather transmitted from person to person by hands, food and other fomites due to poor hygiene practices. Those risk factors could potentially have disguised the health effect of SODIS. Supposedly a more ‘holistic’ approach including community water improvements, sanitation and hygiene may produce better health outcomes than SODIS as a POU-HWT alone.
\nDuring the project and before the cessation of the SODIS promotional activities we measured an overall compliance with the intervention of 32% at any given day during the study. In contrast, around 80% of households reported using SODIS regularly after the first phase and again at the end of the implementation. The SODIS-implementing NGO observed an average SODIS-usage rate of 75%. The remarkable discrepancies of compliance with SODIS registered in our study when assessed by different staff raise questions of how to interpret the compliance rates of other published SODIS-effectiveness studies. The occurrence of bias due to self-reporting and courtesy of villagers resulting potentially in an over-estimation of SODIS-use could be prevented in future SODIS evaluations if assessed by independent agencies.
\nThe continuous monitoring by our community-based staff of adoption, application, rejection and discontinuation of the SODIS intervention allowed the identification of household determinants and SODIS-campaign factors leading to adoption or rejection of the method among different SODIS-user groups. The analysis revealed that households that were more likely to use SODIS were those that participated more frequently in SODIS promotional events, included women, owned latrines, and had severely wasted children living in the home. Those household-level factors are easily assessable indicators that SODIS-programme managers could use to identify early adopters in SODIS promotion campaigns.
\nIn summary, this thesis demonstrates that the SODIS-method promoted in a typical rural Bolivian setting was not effective in reducing diarrhoeal disease in children under 5 years, despite a comprehensive SODIS-dissemination of a local non-governmental organisation. Unless the overall adoption and acceptance of POU-HWT methods, especially across broad levels of the population most in need will be considerably increased, the public health benefit will be modest. This research suggests that additional work is needed to better understand how the well-established laboratory efficacy of this POU-HWT method translates into field effectiveness under various cultural settings and intervention intensities.
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Solar desalination/purification (solar stills, humidification-dehumidification, solar disinfection) in high altitude during COVID19: Insights of gastrointestinal manifestations and systems’ mechanism

Exergy, environ–economic and economic analyses of a tubular solar water heater assisted solar still

Pilot scale continuous-flow solar water disinfection system by heating and ultraviolet radiation inactivating Acanthamoeba cysts and Bacillus spores

Scheffler reflector (10 m2) integrated peppermint oil (PO) extraction distillation system is developed. Optical loss in reflector and thermal loss in solar still, steam line, and condenser are determined. A solar distillation system of peppermint plants is also subjected to thermal energetic and exergetic study. Exergy and optical efficiencies are 27.58% and 52.25%, respectively, with an average irradiance of 970.5 W/m2 and 6 kg of peppermint for 4 h. Thermal efficiency of solar still, steam line, and condenser are 95.90%, 95.68%, and 87.96%, respectively. Efficiency of system and oil yield per unit of energy consumed is 41.98% and 6.24 ml/kWh, respectively, without insulating steam line. System's efficiency is 46.36%, with an improvement of 2.67% in energy gain by insulating the steam line. Thermodynamic analysis of developed solar steam distillation system (SSDS) for PO extraction will help in finding out energy saving potential at various parts of distillation unit and in improving the performance of distillation unit. This research would provide energy conservation opportunities in various parts of PO extraction SSDS. Exergy analysis and detailed investigation of condenser and steam line are also performed. As a result, incorporating solar energy into PO extraction technology improves opportunities for the source of income in rural areas and increases both income and level of food security for farmers.Practical applicationsThis research would provide energy conservation opportunities in various parts of peppermint oil (PO) extraction solar steam distillation system. Exergy analysis and detailed investigation of condenser and steam line are also performed. As a result, incorporating solar energy into PO extraction technology improves opportunities for the source of income in rural areas and increases both income and level of food security for farmers.Novelty StatementMentioned literature includes thermodynamic analysis of oil extraction system available for crops such as rosemary leaves, basil leaves, etc. Thermodynamic analysis of such a system is limited to these crops and applied to other crops like peppermint, eucalyptus, lavender, etc. As these crops possess different chemical properties and have large potential in essential oil market, a comprehensive thermal analysis is needed to identify various thermodynamic parameters to extract peppermint oil (PO) using solar‐assisted steam distillation system. Present work aims to identify energy and power loss due to convection and radiation at different parts of a solar distillation unit. Exergy analysis and detailed investigation of condenser and steam line are also performed. This research would provide energy conservation opportunities in PO extraction solar steam distillation system. Furthermore, the outcomes of present study have been compared with previously published studies.

Water scarcity within the world may be an enormous threat to living beings. Potable water can be produced by renewable energy using solar desalination. In the quest for efficient water desalination methods, researchers have turned to solar stills as a promising solution. One approach to enhancing the productivity of solar stills is the utilization of copper-coated sponge cubes. These cubes, when integrated into the still, provide extended heating periods, leading to higher temperature differences. This, in turn, improves freshwater production by improving the performance of the modified still. In this work, three basin-type solar stills of each 0.5 m2 area have been studied experimentally in the location of Coimbatore, Tamil Nadu. Comparative studies were done between the solar still modified with sponge materials and the modified solar still with sponges coated with copper powder. In these experimental studies, the various performance characteristics related to solar still efficiency have been examined. The sponges were placed inside the water of the basin. The commercially available copper powder was prepared like a paste and coated in the sponges, and it was increased in size to 0.005 m on all sides. The sponges pasted with copper powder reduce the energy losses from the still due to its high thermal conductivity and the evaporation rate also increased by the capillary action of the sponge. High heat transfer to water also occurred due to the addition of copper powder. From the comparative studies, the solar still with sponge materials coated with copper powder gives a higher yield. The proposed solar still with modifications improves efficiency. The solar still without modification gives a yield of 1.3 kg/day, the modified still with sponges gives an output of 1.5 kg/day and the modified still with copper-coated sponges gives an output of 2.35 kg/day. The copper-coated sponge cubes placed still produced an efficiency of 60.07%.

One of the top priorities in the development of solar stills is productivity enhancement. The present study experimentally investigates both passive and active pyramid solar stills. In active mode, the pyramid solar still is integrated with a solar water heater. The tests were carried out with conventional pyramid solar still (CPSS) and active pyramid solar still (APSS) at 1, 2, and 3 cm of water depth, respectively. The experimentation has been carried out in Nagpur (Longitude 21.124042, Latitude 79.002211) from April – May 2022. The finding shows that the pyramid solar still coupled with a solar water heater at a water depth of 1 cm produces the highest productivity of 7.99 L/m2.The hourly thermal efficiency is to be inversely related to the absorber area and the exergy efficiency is inversely related to the absorber area and directly proportional to the still output. Hence exergy and thermal efficiency of CPSS at 1 cm water depth is enhanced by (107.59%) and (49.36%) as compared to APSS, respectively. The cost per liter of fresh water obtained from conventional pyramid solar still and active pyramid solar still are 0.0139$/L and 0.00751$/L respectively. Based on the study, lower basin water depths and secondary heating enhance the solar still’s productivity.

There is still no consensus on the impact of using solar disinfection (SODIS) to reduce the prevalence of waterborne gastrointestinal diseases. The reported reduction in diarrhoea prevalence among SODIS users has been attributed to the consumption of water free of viable pathogens. However, it has also been suggested that ingestion of SODIS-inactivated pathogens may induce protective immunological changes that may also contribute to a reduction in the frequency of diarrhoea. The present study aimed to critically review the epidemiological and immunological gains of using SODIS. We critically reviewed 22 articles published in English, selected from 2118 records systematically retrieved from the databases. All trials (except one) reported a significant reduction in diarrhoea prevalence among children using SODIS, but some of the data from trials report contrary findings. All in vitro and in vivo assays indicate that SODIS-inactivated pathogenic bacteria have the potential to induce immunological alterations that may result in protective immunological effects. Studies with a low risk of bias are still awaited to confirm the ability to use SODIS to reduce the prevalence of diarrhoea. Reducing the prevalence of diarrhoea depends on the success of SODIS delivery strategies in inducing behavioural changes in communities that result in the production of SODIS-compliant outcomes. The results of trials reporting a reduction in the prevalence of diarrhoea due to the use of SODIS seem to support the hypothesis of the contribution of the protective immunological effect against diarrhoea in SODIS users.

Experimental investigation of the effect of angled fins on the energy and exergy efficiencies of solar stills: A comparison between double slope and pyramid solar stills under Tunisia weather conditions

In regions with a restricted availability of drinkable water, solar stills offer a solution for a passive solar desalination method. In this study, three designs for solar stills are examined: the conventional solar still (CSS), the hemispheric solar still (HSS), and the pyramidal solar still (PSS). The experimental investigations were conducted over three consecutive days, thereby varying the total dissolved solids (TDS) concentrations in the basin water at 1000, 2000, and 3000 ppm. A comparative analysis focused on the performance of the various solar stills and the impact of TDS variation. The results revealed that the PSS consistently outperformed the CSS and HSS across all TDS levels. Notably, the PSS exhibited superior daily energy and exergy efficiencies. Furthermore, the daily productivity and energy efficiencies displayed an inverse relationship with the TDS concentration. A cost analysis indicated that the PSS achieved the lowest distilled water price, reaching a value of 0.0151 ＄/L. Specifically, the PSS exhibited a 17.3% and 3.5% higher accumulated daily productivity compared to CSS and HSS, respectively, at TDS = 1000. However, at TDS = 3000, the daily productivity of the PSS decreased by 3.5% and 7.5% compared to TDS = 2000 and 1000, respectively. Similarly, the energy efficiency of the PSS decreased by 5.27% and 8.67% as the TDS increased from 1000 to 3000. Notably, across all solar still types, the lowest cost values were consistently associated with the lowest TDS concentrations, with the PSS yielding the lowest cost overall.

A comparative study of various fatty acids as phase change material to enhance the freshwater productivity of solar still

Effect of Ag, Au, TiO2 metallic/metal oxide nanoparticles in double-slope solar stills via thermodynamic and environmental analysis

Solar water disinfection (SODIS) is a simple, affordable, yet effective method for treating drinking water in under-resourced communities. It has been scientifically proven, internationally recognized, and benefiting many people worldwide. However, the treatment time of the existing protocol is long (6 h or 2 consecutive days when the sky is sunny or partly cloudy, respectively). Previous studies showed that the method could be considerably shortened if the water temperature could be raised to over 50 °C, in order to trigger a powerful synergy between optical and thermal inactivation mechanisms of sunlight. This work has developed a new SODIS container design that can achieve the water temperature range that is conducive to synergistic SODIS inactivation, which has been overlooked by previous work that endeavored to enhance SODIS. Factors that could affect the water-heating performance of a SODIS container were systematically evaluated and subsequently aggregated to create the new design. Extensive field experiments were conducted to assess the disinfection efficacy of the new design under actual, and often unfavorable, weather conditions in a rural community. While still maintaining the simplicity, affordability, and portability of the original SODIS protocol, the new design can disinfect water much more effectively. In head-to-head comparisons with conventional SODIS bottle, the new design could achieve on average 74, 30, and 12 % more reductions of total coliforms than the bottle, in the conditions of at least half a day of strong sunshine, partly cloudy with some sunshine, and completely cloudy, respectively.

The solar energy produced by Scheffler parabola (10 m2) is not fully exploited by the solar distillation system of aromatic and medicinal plants. In this work, the optical losses in the primary and secondary reflectors, and the thermal losses at each part of this system (solar still, steam line, condenser) were determined. A thermal energetic and exergetic analysis were also performed for a solar distillation system of rosemary leaves. For average intensity radiation of 849.1W/m2 and 6 Kg of rosemary leaves during 4 h of distillation, exergy and optical efficiencies of the system achieved up to 26.62% and 50.97%, respectively. The thermal efficiency of the solar still, steam line, and condenser is about 94.80%, 94.30%, and 87.76%, respectively. The essential oil yield per unit of consumed energy and the total efficiency of the solar distillation system, taking into account the heat losses in the solar still, steam line, and condenser, as well as the optical losses in the two reflectors, is 6.18 mL/ kWh and 40.00%, respectively. The efficiency can be as high as 42.42 % if the steam line is insulated. Moreover, the comparison between the solar steam distillation and conventional steam distillation shows that solar distillation is much more efficient since it gives better results and especially it avoids the emission of 12.10 kg of CO2 during extraction.