Potential of harvesting water from fog and dew water over semi-arid and arid regions in Syria

Freshwater makes up approximately 2.5% of our planet's total water. About 1.74% of it consists of snow and glaciers, 0.79% lakes, 0.03% rivers and 0.76% groundwater (Bhushan 2019). The shortage of freshwater is one of the greatest challenges of sustainable development, water and food security in any country. The problem of fresh water is clearly visible in Syria because it is located in arid and semi-arid regions, about 75% of its surface is considered arid despite the positive trend towards increasing some annual rainfall rates and characteristics, such as intensity, frequency and continuity, over certain periods. Syria has been suffering from a general decrease in precipitation rates for half a century, given the current climate changes (Eissa 2013; Mawed & Alshihabi 2014). Changes in drought patterns in Syria were evident in terms of increased drought intensity during the rainy season. Changes in drought characteristics were evident in terms of the increased intensity of rainy season drought caused by the increase in spring and winter droughts. The frequency of extreme droughts increased while the frequency of extreme droughts in the spring decreased (Skaf et al. 2017). Population and industry growth are projected to increase water demand from 1,900 million cubic meters in 2010 to 3,150 million cubic meters in 2050. While the average share of fresh water per inhabitant has decreased from 12,185 cubic meters in 1992 to 809 cubic meters in 2012. It will decrease to 440 cubic meters in 2050. Furthermore, climate change will have a serious impact on water resources, resulting in a reduction in surface and ground water by 1,300 million cubic meters, and an increase in the evaporation of water bodies of 190 million cubic meters by 2050. Consequently, the water crisis will worsen if it is not corrected in the near future in the light of population growth and the evolution of irrigation projects in order to guarantee the requirements of food security and industrial development. This could constitute a major threat not only to water security, but also to the national security of an entire country. In addition, traditional freshwater sources have been vulnerable over the past decade to major impacts arising from political and military conflicts in Syria. Among the examples, which deserve to be noted, the low level of the Euphrates comes from Turkey and its direct negative effects on the economy and development of all the eastern region of the country. In addition are the grave threats that struck the source ‘Feijah’ feeding the capital Damascus (Mourad & Berndtsson 2011; Mahmoud & Alsayegh 2017; Selby et al. 2017).

In this paper, we study fog and dew harvesting as unconventional freshwater sources, using passive fog collectors. In addition, we tested some adjustments in order to make it more suitable for the climatic conditions in Syria. Fog and dew harvesting may provide an alternative source or supplement in areas where access to freshwater sources is difficult, especially in the east of Syria. This approach is becoming more importance due to recent studies, which pointed to the possibility of ongoing conflict and the growing drought that afflicts Syria (Abualhamayel & Gandhidasan 2010). This will bring about significant changes in the amount and type of current water sources. Changes in the hydrologic cycle of ecosystems are also expected in response to climate change. Moreover, these transformations include the reduction of annual rainfall in the Mediterranean region. Climate forecast predicts an increase in atmospheric moisture levels for the Mediterranean region by 27% during the summer months by 2080 (Kaseke et al. 2017; Kaseke & Wang 2018). These changes will increase the need for non-conventional sources of fresh water, especially water in the atmosphere.

The atmosphere contains an estimated 13,000 trillion liters of freshwater. Atmospheric humidity is naturally and periodically regenerated in a renewable and durable water resource. Additionally, the atmospheric water collection process, a simple and inexpensive technology, does not produce harmful effects or by-products that are harmful to the environment. However, the majority of atmospheric water collection studies have not been subjected to an independent critical study of the performance, functions and realistic limits placed on atmospheric water collection systems. This has resulted in significant differences in claims and claims regarding the performance and capabilities of water harvesting operations to meet commercial needs. While the project to harvest water from fog and dew is seen as a case study as part of an innovative and comprehensive approach to addressing the complex challenges of water scarcity and sustainable development. Much of this type of research is cross-cutting in fields such as applied engineering, materials science, meteorology, climate science and environmental science. Moreover, this type of water meets World Health Organization (WHO) standards, according to numerous studies. Fog and dew act as air washers, so the chemical state of this water depends on air quality and heterogeneous interactions between the gas, liquid and solid in the surrounding area, which may be used in air pollution studies (Bagheri 2018; Kaseke & Wang 2018).

To test the ability fog and dew collection under semi-arid and arid climate conditions, two sites were selected according to the climatic classification of land according to Syrian Directorate General of Meteorology (SDGM) Figure 1(b) (7 September 2020. http://www.mod.gov.sy/index.php?node = 556&cat = 7937&). St₁ (East of Homs-Hama highway, N 35°′02′42 E 36°′45′40, 476 masl) determined as a point in the semi-arid medium. St₂ (N 34°′36′59 E 36°′52′51, 420 masl) determined as a point in a very arid environment Figure 1(a). This study took an entire year between September 2019 and September 2020.

Two models of the device were established. The first model (A) has a fog-collecting area of 1.00 square meters and was set up such that its base is 2 meters above the ground and its top is 3 meters above the ground. The polypropylene mesh support itself and is made from 3 cm metal pipe, as the spacers, as are the spacers. The support legs are made out of 3 cm metal pipes. A trough, which is 15 cm wide and whose bottom slants downward across the base of the mesh, routes any water collected to one side of the collector for 40-liter plastic container (Figure 2). The second model (B) is a cylindrical fog collector, which has two bases for fixing on the top and bottom sides. Mesh is placed on a sheet of metal (stainless steel) slightly concave. From the bottom, there is a metal tube fixed to a pipe ending in its rotation with a plastic container of 40 liters.

In both models, seven mesh types were employed in the first step. (1) Polypropylene single mesh with shading coefficient (SC) 35%. (2) Double polypropylene mesh with SC 35% for each layer. (3) Polypropylene single mesh with SC 50%. (4) Double polypropylene mesh with SC 50% per layer. (5) Polyethylene (PE) single net with SC 60%. (6) Double polyethylene (PE) meshes with SC 60%. (7) Metal mesh with (SC) 40%. In the second stage, each of the previous meshes were coated with a mixture of hydrophobic silica particles and methylphenyl silicon.

In order to improve the efficiency of the water collection process, we increased the resistance of the network to the corrosive climatic factors, and obtained high mechanical stability, the meshes were sprayed with a special coating for this purpose. The coating was prepared by dissolving a mixture of solid SiO₄ (silicon oxide) with methylphenyl silicone (C₇H₈OSi)_n in a solvent of mixture containing 40% tetrahydrofuran, 60% isopropyl alcohol, at following proportions 1: 5: 12 for silicon oxide, silicon methylphenyl, and solvent, respectively (Bhushan 2019).

Atmospheric water collection using this method is dependent on the dominant environmental, climatic and synoptic factors. Rainfall, air temperature, wind direction and velocity, relative humidity, absolute humidity, ground surface temperature, dew point temperature, and air water content (Olivier 2014), (Tables 1–4).

It should be noted that most of the field studies and previous climate modeling studies tended to consider all non-rainfall water inputs, especially the fog and dew, as one category. Although both are derived from different climatic phenomena, due to technical limitations that impede the identification of non- rainfall sources that exist in the atmosphere (Kaseke et al. 2017).

Table 1 shows the top wind speeds average of 8 m/s, It is a ‘gentle breeze’ according to the Beaufort wind scale. A minimum wind speed average of 2 m/s, is classified as ‘light air’. Wind speeds between 2 and 5 m/s, as mentioned previously, are favorable for fog water collection. These results also suggested that the study area may be suitable for the generation of electrical or mechanical energy on a small scale, with several small turbines connected together to generate enough electric power.

Tables 2 and 3 show the temperature behavior throughout the year, with a highest temperature averages from July to September. Relative humidity behaves differently to temperature, decreasing from July to September and increasing from December to March. The minimum average humidity is 50% and the maximum average is 69%, which is appropriate for dew water collection. No significant relationship between temperature and relative humidity was found as the maximum amount of water vapor that air can contain depends on the temperature, although the amount of water is not guaranteed to be the same for each temperature point. Here it was observed that relative humidity does not follow the temperature pattern or vice versa, since each is independent of the other.

The results of the field experiments (Table 4) showed differences between the theoretical data and projections (Tables 1–3) and the quantities of water actually collected. These differences varied between significant and slight differences due to wind direction and mesh collection mechanism. This mechanism was based on collision of water droplets, 10–40 μm, suspended in the air, with the mesh filaments. Therefore, the winds carrying these droplets, in terms of speed and direction towards the mesh, play a significant role in the collection process. When the wind was not perpendicular to the mesh surface, the amount of water decreased as the collision surface decreased, and the amount decreased with the change of the wind direction from perpendicular to the mesh surface level. A solution to the problem of wind direction was the cylindrical design of the model (B). Ideal wind speed value for the combination process was 2–5 m/s. Wind speeds often exceeded this value during wet events ‘troughs’, which have favorable climatic conditions for water collection.

During humid climatic conditions, which are usually associated with rain, the process of determining the yield of the collected water, whether it is rainy or not-rainy, becomes not possible. The amount of non-rainwater has been roughly estimated, Table 4, by calculating the average quantities of water collected on days that did not include rainfalls of each month. In order to assess water production for non-rainwater, values were compared with the total values of water collected during the months of December, January, and February (Table 5).

The effect of the wind factor is clearly shown by the difference in the annual mean amount of non- rainfall water collected by flat and cylindrical models using the same mesh. The difference in the amount of non-rainwater collected between the two models is 100% (Table 4). Moreover, the slight difference between the small amounts of collected rainfall water between the two models did not exceed 25% (Table 5), indicating a mechanical collection capacity nearly equivalent. The difference in amounts of non-rainfall water due to meteorological factors were mainly due to wind.

Double mesh made from polypropylene (PP), SC 35% per layer, gave better results than the other types of mesh used. While, polypropylene double mesh with SC 35% per layer, which was coated with silicone and a silica coatings layer, showed 40% better results in collecting non-rainfall water yield than all other types. This was consistent with numerous previous studies which recommended the use of double meshes with SC 35% (Eissa 2013; Davis et al. 2016; Dahman et al. 2017). Double mesh with large SC 50%, 60%, had the lowest water yield. The reason may be the smallness of the mesh openings, at this high ratio of SC, which clog with water droplets, preventing more air carrying moisture and water droplets from passing through it. This is the main purpose of the hydrophobic coating, resulting in higher mobility of the water droplets on the mesh filaments, which makes them move downward due to their weight without staying for long periods in the openings. This can be checked by comparing the collection yield of coated meshes with that of uncoated meshes, as shown in Table 6.

The metallic mesh of SC 40%, which is close to the recommended ratio (35%), mesh yield, for example, was less than the polyethylene (PE) mesh with SC 60%. The same was found for coated metallic mesh. This could be due to a number of potential reasons. Amongst them is the weight of the metal mesh that does not allow horizontal movement of the mesh at low wind speeds compared with the flat model. This means fewer areas of collision between the air transport water droplets and the mesh surface. Moreover, the temperature of the mesh metal decreased in very cold weather, which transformed it into a surface on which the droplets freeze instead of flowing towards the collector stream. Furthermore, the coating on the metal mesh exhibited relatively low stability in difficult climatic conditions in general, in hot conditions in particular, and corroded more rapidly than on other types of mesh.

The quality of the water collected by this method depends on the quality of the surrounding air, the water transported through the air and the surface of the mesh. To check if this water, rainfall and non-rainfall, is safe to drink, chemical analyses were carried out on it. Analyses included pH, electrical conductivity (EC), total dissolved solids (TDS), chemical oxygen demand (COD), total organic carbon (TOC), nitrates (NO₃), nitrites (NO₂), and sulfates (SO₄), in addition to lead, chrome, cadmium and iron. The results were within acceptable limits of the specifications of the Syrian drinking water standards (8 September 2020; Maarouf et al. 2019), and World Health Organization for Safe Drinking Water standards (8 September 2020; Udhayakumar et al. 2016). TDS and EC showed high values, but remained within the permissible limits of the World Health Organization specifications (Table 7).

TDS and EC high values at St₂ could be attributed to dust episodes and southern winds from the desert, which carries dust and micro-particle suspensions, which suspended in the air. The concentrations of Pb, Cr and Cd were below the detection limits, except for Pb at St₁. Probably the reason is the St₁ site located east of Homs, Hama Road, and what strengthens this hypothesis is the high values of total organic carbon (TOC) at the same site compared to other sites.

The semi-arid region had the best results in terms of the amount of non-rainfall water collected, followed by the very arid region. This is in broad agreement with climate data and theoretical projections. In addition, this water obtained met the standards of the Syrian Standards Organization and the drinking water quality standards of the WHO.

A more comprehensive investigation on fog and dew water harvesting is needed for a longer period of time until the results indicate that collecting water from humidity and fog can be another promising additional source of clean freshwater. This is true especially in areas that suffer from difficulties in supplying safe and freshwater, including coastal areas where even mountain villages suffer from the interruption of drinking water for many days.

Therefore, we recommend further research in this area and increase the capacity of collection devices by increasing the area of the meshes. It is necessary to work on increasing the effectiveness of the mesh by improving the mesh material used and carefully examining the climatic conditions adapted to the functioning of each. Research and the development of new and alternative ways of collecting atmospheric water is required because it is a relatively clean, constantly renewable and inexhaustible source.

All relevant data are included in the paper or its Supplementary Information.