Physico-chemical characterization of water obtained by condensation of moisture from an atmospheric water generator in Tunisia

doi:10.21203/rs.3.rs-3869627/v1

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Physico-chemical characterization of water obtained by condensation of moisture from an atmospheric water generator in Tunisia

https://doi.org/10.21203/rs.3.rs-3869627/v1

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The availability of water resources is an uphill struggle for many countries in the world since it guarantees environmental, agronomic, food, economic competitiveness, and public health. Water scarcity is becoming a headache worldwide, and this solution has become a must. The technique of condensation of moisture through the water vapor contained in the atmosphere is developed to generate water. Therefore, the purpose of our work is an additional source of water through the process of condensation of moisture to supply drinkable water intended for consumption. In this context, a condensation prototype Kumulus has been adapted. In those studies, tests conducted in different regions of Tunisia to determine the physicochemical quality of the produced water. To improve the quality of the water obtained, a treatment process has been implemented. Dew quality is assessed according to the standards of potable water quality. Ion concentration meets the requirements of the World Health Organization, European Directives, and Tunisian Drinking Water Guidelines. Costs and economic aspects are also considered. The results of water chemistry can therefore be viewed as a "footprint" of regional and local air composition.

This project aims to produce water in areas where access to water is difficult. This technique provides an alternative to other sources of drinking water.

Condensation

Atmospheric water generator

Dew water

Purification

Standards.

Water is a lifeline for humans, animals, and plants. Currently, water scarcity and its fluctuation over time particularly affects ecosystems since water is scarce in arid and semi-arid areas. Drought, which it may be persistent, is a major risk over time, that affects the whole environment directly (Lekouch, 2010). Today, predicted by experts in terms of forecast, global warming is increasing and that a third of the population is under water stress (Ebale et al.,2020). The scarcity of drinking water is one of the main problems in our fast-growing world. 80–90% of the freshwater used by humans worldwide comes from agriculture (Morison et al., 2007). On average, between 1998 and 2002, 67% of water resources were devoted to irrigation (FAO, 1998; 2002). Around 780 million people worldwide lack access to a reliable source of drinking water, according to the World Health Organization. Today, most freshwater resources are polluted by human activities, this creates more health problems every day (Anandu and Meena, 2017). The second half of the 20th century saw a rapid increase in population, water consumption has increased enormously. Development and urbanization, also, have an impact on water resources through increased individual consumption of drinking water because of people’s changing lifestyle. Demand for water consumption has aggravated the economic issues. The drinking water sector, the second largest user of water, uses almost 19% of the resources (National Water Sector Report, 2020).

Tunisia is in North Africa, on the border of the Mediterranean, it is characterized by a temperate climate in the north, with mild and rainy winters and hot summers, and a desert climate in the south. Tunisia is classified as one of the countries lacking in water resources in the Mediterranean basin (Benabdallah, 2003). It has little water potential (National Water Sector Report, 2020). Renewable resources are affected by harsh climates. They face increasing human pressure and many socio-economic challenges. Today, according to international standards, Tunisia is already in a situation of water scarcity, with a water consumption close to 420 m³/inhabitant/year. Without sustainable management, it can become a handicap to economic development (National Water Sector Report, 2020).

Over the past 20 years, various alternative water sources have been tried (Lekouch, 2010). The last century has seen the emergence of scarce natural resources, particularly the crisis of water stocks. In fact, there won't be enough drinking water to go around for everyone. Therefore, it is necessary to find unconventional ways to produce water because of overuse and climate change, freshwater resources are, however, rapidly becoming scarcer, making it difficult to provide potable water on a sustainable basis, which requires rethinking our solutions and investments (Rahman et al., 2022). Clearly, this crisis needs to be addressed urgently since climate change has changed profoundly the precipitation patterns (Jarimi et al., 2020).

In order to combat the world's severe water shortage, new alternative technologies are urgently needed (Lekouch, 2010). Clean fresh water can be produced from alternative water sources (such as wastewater, seawater, brackish water, atmospheric water, and so on) through cost-efficient methods to address the global water crisis (Zhengtong Li, 2021).

To conserve water resources, wastewater treatment has gained a momentum in developing countries, one can generate water from different sources by employing different strategies. Any technical solution is effective if it provides enough water for human consumption including the most vulnerable (Mahunon et al., 2015).

It is, therefore, not surprising that since the conventional method of collecting water from fog began 50 years ago, the collection of atmospheric water has attracted significant attention from researchers worldwide (Jarimi et al., 2020). Obtaining water from humid air through condensation can be a viable solution to the water shortage problem where liquid phase water is unavailable (Lee et al., 2012).

Dew water collection can be used as a water source in many places, in addition to rain and fog water collection, in many different geographical settings (Beysens et al., 2007). There is a global shortage of clean water, and atmospheric water vapor offers a promising alternative (Haechler et al., 2021).

In certain climates and regions, dew water collection can be regarded as an unconventional source of water that can improve water supply (Khalil et al., 2015). In many places there is an abundance of potentially extractible freshwater in addition to weather conditions that favor dew formation. The Earth’s atmosphere contains about 12.9 trillion tons of fresh water, distributed worldwide and rapidly renewed which can be used as an alternative source (Gökcek et al., 2016). A deeper comprehension of the physics, thermodynamics, and radiative cooling processes of condensation substrates over the previous 20 years has led to advancements in dew collection technology (Tomaszkiewicz et al., 2015). Atmospheric water extraction is developing to produce clean water in arid areas, inland areas, and for remote communities (Renyuan Li et al., 2018).

In order to meet our everyday demands for water, the world has discovered innovative methods of harvesting it (Siddiqui, 2022). Water production chillers are used in case the water supply is not accessible. It will be a workable solution to the water problem if that water is extracted from the atmosphere (Siddiqui, 2022). The advantages of condensing steam are alternatives inspired by real and obvious natural phenomena. Therefore, it is an environmentally friendly solution. There are differences in water quality in different regions, especially in terms of physical and chemical parameters. It is unknown why the chemical composition of dew water fluctuates so greatly during time and distance (Inbar et al., 2020). As a result, condensation of humidity is currently the subject of a lot of scientific research in terms of quantity and quality to minimize the water crisis and have access to drinking water (Poredoš et al., 2022).

Based primarily on chemical analyses, many dew researchers claims that this kind of water complies with World Health Organization (WHO) standards (Kaseke and Wang, 2018). Compared to previous studies on atmospheric waters, the characterization of dew water quality has been described by several researchers which chemical analyses were conducted in a few regions of the world; Chile, the USA, Japan, Morocco, and Jordan (Jiries, 2001). Compared with other geographical locations where water has been extracted, studies have shown that dew water is quite corrosive in Chile with a high ionic concentration, very acidic in Japan with a high concentration of sulphates and nitrates, mildly alkaline and weakly mineralized in Jordan. According to research comparing these regions to others where water has been removed contrarily, the dew in Corsica is more alkaline (Muselli et al., 2002; 2006). According to a study done in Morocco, Mirleft region, water is highly mineralized, with an average electrical conductivity of 727.85 S/cm for dew (Lekouch, 2010).

Deposition of aerosols on the dew collection device that can be absorbed by water identifies chemical composition of dew water. Atmospheric water generator is thought to be a promising additional or alternative source of drinking water, the quality of which depends on atmospheric and meteorological parameters (Inbar et al., 2020). In this study we present a chemical profile (metals, ions, pH, turbidity) of atmospheric water collected by an atmospheric water generator tested and developed in Tunisia. In this context, no study regarding the characterization of water produced by moisture in Tunisia, has been conducted. This document reflects the importance of collecting wet air water, as this technology has the potential to achieve self-sufficiency without relying on a freshwater source. The proposed concept aims to reduce water scarcity and preserve the environment. In terms of quality, an analysis of physico-chemical and process efficiency was carried out. The goal was to determine whether the water produced by the machine tested in Tunisia can meet WHO, UE, and Tunisian guidelines for drinking water standards.

2.1 Description and operation of the water generating device.

The work is based on using renewable resources already available in nature and converting this energy into water. This device is based on cooling condensation which operates on the principle of atmospheric water production technology. The “Kumulus” machine (Fig. 1) is designed to produce potable water from air.

2.2 Water produced by the atmospheric water generator: Collection and analysis.

Materials

Throughout this work, Water production tests have been conducted using a prototype developed by the company “Kumulus”. To determine to what extent the dew water is potable, a series of physico-chemical analyses was carried out. A comprehensive set of analyses of dew water samples taken from the generator upstream and downstream during the period from November 2021 through November 2022 in three geographical sites in Tunisia; Soliman, Gabes and Tunis City Center. The samples were analyzed and compared to Tunisian and European Union legislation as well as World Health Organization (WHO) recommendations.

Electrical conductivity, pH and temperature of each sample have been measured immediately on the spot. Then, the collected water has been subjected to quality analysis. Chemical parameters are analyzed in a water quality laboratory.

Methodology

Kumulus prototype has been tested in different Tunisian regions to study the quality fluctuations of produced water.

An atmospheric water generator is a device that uses ambient air to generate water. The water vapor contained in the air is condensed and removed by cooling the air. The technology is based on the functional principle of a refrigerator and air conditioner. The refrigeration circuit allows cold liquid to be exchanged with the ambient air entering the machine to condense the vapor contained in the air. The produced water pass through circuit (Fig. 2) consisting of a collector, then a purification and sterilization process by the filters are performed to reduce various type of contamination. A UV system eliminates contamination. The particulate filter purifies water by removing physical impurities. A series of samples based mainly on sampling upstream (before treatment) and downstream (after treatment) were conducted to study the spatial impact on the quality of the upstream water and to evaluate the efficiency of the treatment system before water distribution.

Study Area Selection and Presentation

On the border of the Mediterranean, in North Africa, is the country of Tunisia. With a total area of 162,155 km², it is characterized by a temperate climate in the north, with mild rainy winters and hot summers, and a desert type of climate in the south which are responsible for a significant spatial and temporal variation in water resources. Average annual rainfall ranges from 100 mm in the far south to over 1500 mm in the far north of the country (Benabdallah, 2003). This country belongs to the group of nations in the Mediterranean Basin that have the fewest water resources (Fadia Gafsi, 2016).

Region 1: Soliman

The choice of the Soliman (Fig. 3) study area is based on its location at the seaside with high humidity and specific atmospheric parameters (Table 1).

Table 1

Parameters of atmospheric conditions of condensation during tests in Soliman
Days	1	2	3	4	5	6
Temperature: °C	14	13	13	15	15	15
Relative humidity: %	57	70	80	75	80	80
PM _2.5 ug/m³ (IQ air platform)	9.1	11.6	9.1	9.1	10.1	9.1

Region 2: Tunis the city center

The choice of study area Tunis the city center (Fig. 4), is based on pollution characteristics (Table 2): Intense traffic jam, a smoking zone which is close to a construction site.

Table 2

Parameters of atmospheric conditions of condensation during tests in Tunis Center
Days	1	2	3	4	5	6
Temperature: °C	15	13	15	13	12	12
Relative humidity: %	65	70	65	60	55	56
PM _2.5 ug/m³ (IQ air platform)	18.1	22.3	16.6	25.2	18.6	25.7

Region 3: Gabes

The choice of the Gabes (Fig. 5) study area is based on its proximity to the Chemical Group industry, which has massive air pollution. The characteristics of the atmospheric location are mentioned in Table 3.

Table 3

Condensation atmospheric conditions parameter in Gabes
Days	1	2	3	4	5	6
Temperature: °C	15	13	15	13	12	12
Relative humidity: %	65	70	65	60	55	56
PM _2.5 ug/m³ (IQ air platform)	25.2	41.2	43.7	18.6	17.6	25.2

Atmospheric factors considered

Although there are numerous models that can calculate dew water, they all need additional measurements (such as long-wave radiometer measurements and condenser surface temperatures) (Muselli et al., 2009) that were not available here.

Dew yield is therefore correlated with the main atmospheric parameters (fine particulate PM2.5, relative humidity, temperature) measured in this study to assess air quality and its impact on water quality (Muselli et al., 2009). Dew and fog, however, act as atmospheric scrubbers, and their chemical composition is dependent on the local environment's air quality and heterogeneous gas-liquid-solid interactions (Kaseke and Wang, 2018).

Dry deposits (gases and aerosols) and traces of soluble gas on the surface forming the dew are factors that influence the composition of the dew. Dew is therefore considered a key mechanism for the deposition of wet contaminants. The chemical composition of dew provides interesting information about the environment and has a significant impact on pollution concentrations in the atmosphere (Hong et al., 2019). Tests of the machine at different geographical sites in Tunisia aimed to study the influence of the geographical area and characterize the quality of the produced water. A series of samples were taken, and physico-chemical parameters have been tested.

Sampling Methodology from the atmospheric water generator

Polyethylene bottles were rinsed with distilled water and then with sample water (From the machine). Sampling was conducted upstream (before treatment) and downstream (after treatment). The samples collected for analysis of physicochemical parameters were kept at low temperature (4°C) until the laboratory where the analyses were performed. The objective was to determine if and how the environment affects the composition of water.

Analysis

Drinking water must be fresh, clear, transparent, and colorless. It must not contain suspended solids. It should not acquire a smell, even after a long time. Chemicals known as contaminants dissolve in water and making it unsafe for human consumption. Since pure water has no flavor, smell, or color, impurities can be easily identified by assessing the water's turbidity, taste, and smell. But the majority are hard to find and need testing to figure out whether the water is contaminated (M.Tyeb et al.,2022). These characteristics must not harm the health of the consumer. Therefore, it is equally essential to make qualitative estimates of several physicochemical parameters such as pH, electrical conductivity, sulfate, chloride, nitrates, potassium, etc…

Numerous water quality parameters need to be analyzed to assess the quality of dew water. These parameters can be measured and evaluated using a variety of techniques and instruments for measuring mentionned in Table 4. (Galal Uddin et al., 2021).

Measure of temperature

It is essential for the solubility of salts and gases, the dissociation of dissolved salts, electrical conductivity, and pH determination (Rodier, 1996). It is one of the most important parameters of water quality. Its definition is the hydrogen ion concentration's negative logarithm (Omer, 2019).

Measure of pH

It is one of the most important parameters of water quality. pH ranges from 0 to 14, with 7 being neutral. A pH below 7 indicates acidity, while a pH above 7 indicates a basic solution. Pure water is neutral, with a pH close to 7.0 to 25°C. Safe pH values are ranged from 6.5 to 8.5 for drinking water (Omer, 2019).

Measure of turbidity

The optical measure of water clarity is called turbidity. One of the most crucial optically active factors in determining the quality of water is this one (V. Pompapathi et al.,2022). It is caused by suspended particles in water, including silt, clay, organic matter, and other particles (Omer, 2019).

Measure of electrical conductivity

Rather of being correlated with dissolved organic matter in water, electrical conductivity is directly proportional to the mineral salts in solution. Therefore, the conductivity increases with the concentration of dissolved particles (Muselli et al.,2022).

Measure of other chemical elements; Anions and cations

The chemical analysis of water identifies the following parameters tested: chemical analysis of major cations (Na⁺, K⁺, Ca²⁺ and Mg²⁺) and major anions (Cl⁻, SO₄ ²⁻ and NO^{3 −}), minor ions (Fe²⁺, Cu²⁺, Cd²⁺, Mn²⁺, Pb²⁺, Zn²⁺, NO²⁻, Br⁻, F⁻), and heavy metals. Methods used for samples analyses are given below (Table 4).

Table 4

Test techniques and references.
Parameter	Methods	References
pH	Electrochemistry	ISO 10523 (2008)
Conductivity, Salinity	Electrochemistry	NF EN 27–888 ISO 7888 (1994)
Turbidity	Colorimetry	Turbidimeter WTW Turb 550. This method respects the recommendations of the standard US EPA
Permanganate lndex	Titrimetry (in acid medium)	NF EN ISO 8467(1995)
Carbonate-Bicarbonate	Titrimetry	NF EN ISO 9963–1(1996)
Total hardness	Titrimetry	NF T 90 − 003 (1984)
Dry residue	gravimetry 105°C	NF T 90 − 029 (2002)
Ammonium	Colorimetry	NF T 90-015-2 (2000)
Active chlorine	Colorimetry
Nitrite Colorimétrie	Colorimetry	NF EN 26777 - ISO 6777(1993)
Fluoride, Chloride, Nitrate, Sulfate	Ion chromatography	Iso 10304-1 (2007)
Sulfide	Electrochemistry
Calcium, Magnésium, Sodium, Potassium	Emission Atomique-lCP	Iso 11885 (2007)
Aluminium, Cadmium, Copper, Iron, Lead, Manganese, Nickel, Zinc, Silica, Arsenic, Selenium, Antimony, Boron, Barium	Emission Atomique-lCP	Iso 11885 (2007)
Mercury	Atomic absorption spectrometry	EPA method 7374
Total Cyanides	Electrochemistry	DIN 38405 D13/ISO 6703
Chrome Vl	Spectrometry	Iso T90-043 (1988)
phenol acid	Colorimetry	XP T 90–109 (1976)
Hydrocarbon Division	Analysis by gas chromatography	NF EN ISO 9377-2 (2000)
Detergent	Colorimetry	NF EN 903 (1994)

The water obtained is the result of the condensation of the moisture and its unique chemical characteristics is determined by the dew collector in the atmosphere. Considering dew is essentially purified water, it should not be polluted with heavy metals, until the dew is unable to absorb and dissolve the surrounding air gases and aerosols trapped by the substrate (Beysens, 2006). The composition of the dew therefore depends on the long-range convective atmosphere as well as locally produced gases and aerosols (Muselli et al., 2021).

In this study, experiments were conducted to collect field data by setting up appropriate systems to collect water from atmospheric moisture. To understand the effect of the geographical area on water quality, analytical experiments were conducted.

To determine the quality of dew samples for drinking water, results were compared to World Health Organization (2004) requirements, the Tunisian, and Europeans Guidelines for water human consumption in Table 5. These results show the effect of different climatic conditions and regions on the quality of water in Tunisia. The data presented in this section are derived from laboratory-analyzed sampling campaigns. The characterization of water quality obtained by condensation has been studied to show the quality of the water produced by the generator and its potabilization. The comparison of the composition of the water in 3 different regions in Tunisia (Gabes, Soliman, and Tunis city center) provides interesting information on local environments where environmental characteristics impact dew. The results of the chemical parameters are arranged in Table 5:

Table 5

Analysis Results of samples extracted from atmospheric water generator in the 3 sites.
Parameters	Unit	Tunis		Gabes		Soliman
		Before treatment	After treatment	Before treatment	After treatment	Before treatment	After treatment
pH		7.65 at 16°C	7.30 at 16°C	7.05 at 16.6°C	7.30 at 16.5°C	7.10 at 16.5°C	6.80 at 16.5
Conductivity	µSiem	79.6	71.9	64.2	52.8	93.5	36.5
Salinity	mg/I	71.48	71.7	47.5	57.7	83.8	47.2
Turbidity	NTU	14.73	0.79	19.2	0.88	4.27	0.61
Permanganate index	mgO²/I	< 0.5	< 0.5	0.57	< 0.5	< 0.5	< 0.5
Total hardness	of	2	1	1	2	0.8	1.8
Carbonate	mg/I	0	0	0	0	0	0
Bicarbonate	mg/I	31	28	< 25	< 25	31	< 25
Dry residue	mQ/1	71.5	71.7	47.5	57.7	83.8	47.2
Nitrite	mgNO²/I	< 0.01	< 0.01	< 0.01	< 0.01	< 0.011	< 0.011
Active chlorine	mQCl²/I	< 0.05	< 0.05	< 0.05	< 0.05	< 0.05	< 0.05
Fluoride	mg/I	< 0.1	< 0.1	1.2	< 0.1	< 0.1	0.48
Chloride	mg/I	2.3	0.81	1.2	1	0.7	4.6
Nitrate	mgNO³/I	< 0.5	< 0.5	< 0.5	< 0.5	< 0.5	0.8
Sulfate	mg/I	4.5	2.6	6.2	3.8	1.5	4.8
Sulfide	mqs L· /1	< 0.05	< 0.05	< 0.05	< 0.05	< 0.05	< 0.05
Calcium	mg/I	8.14	5,8	6.92	8.2	3.44	7.4
Magnesium	mg/I	< 0.24	< 0.24	< 0.24	0.36	< 0.24	0.24
Sodium	mg/I	0.84	< 0.60	< 0.60	< 0.60	< 0.68	2.78
Potassium	mg/I	< 0.86	1.04	< 0.86	1.36	< 0.86	1.86
Aluminium	mg/I	0.025	0.01	0.013	0.012	1.49	0.013
Cadmium	mg/I	< 0.001	< 0.001	< 0.001	< 0.001	< 0.001	< 0.001
copper	mg/I	< 0.01	< 0.01	< 0.01	< 0.001	0.039	< 0.01
iron	mg/I	< 0.01	< 0.01	< 0.01	< 0.01	0.055	< 0.01
Lead	mg/I	< 0.01	< 0.01	< 0.01	< 0.01	< 0.01	< 0.01
Manganese	mg/I	0.016	< 0.01	0.037	0.017	< 0.01	< 0.01
Nickel	mg/I	< 0.01	< 0.01	0.01	0.011	< 0.01	< 0.01
Zinc	mg/I	0.032	0.02	0.05	0.027	0.03	0.02
Silica	mg/I	< 0.05	< 0.05	< 0.05	< 0.05	< 0.05	< 0.05
Arsenic	mg/I	< 0.005	< 0.005	< 0.005	< 0.005	< 0.005	< 0.005
Selenium	mg/I	< 0.005	< 0.005	< 0.005	< 0.005	< 0.005	< 0.005
Antimony	mg/I	< 0.005	< 0.005	< 0.005	< 0.005	< 0.005	< 0.005
Boron	mg/I	< 0.05	< 0.05	< 0.05	< 0.05	< 0.05	< 0.05
Barium	mg/I	< 0.05	< 0.05	< 0.05	< 0.05	< 0.05	0.06
Mercury	mg/I	< 0.0002	< 0.0002	< 0.0002	< 0.0002	< 0.0002	< 0.0002
Total cyanides	Mg cN-/1	< 0.03	< 0.03	< 0.03	< 0.03	< 0.03	< 0.03
Chrome VI	mg/I	< 0.012	< 0.012	< 0.012	< 0.012	< 0.012	< 0.012
Phenol index	mg/I	0.51	0.42	0.31	< 0.1	< 0.1	< 0.1
Detergent	Mg SABM/l	0.18	0.14	0.13	0.11	< 0.10	< 0.10

The Figs. 6, 7, 8 show the 3 basic parameters measured during the day when the machine started up before and after treatment. The produced water shows a pH is in the range 7-7.65 (Fig. 6), considered an ideal water according to the standard (Tunisian and WHO guidelines). The pH value of samples and the pH value of drinking water guidelines (range of 6–8) are respected.

The EC fluctuates significantly, reflecting variations in water mineralization. The dew electrical conductivity ranged between 60 µS/cm and 90 µS/cm, with an average value of 79.1 µS/cm. The electrical conductivity of the samples is in the range of 79 µs/cm, and the drinking water limit is 50 to 500 µs/cm (WHO guidelines) (Fig. 7), so it is up to the standards of the WHO and Tunisian drinking water norms; thus, it is potable. Based on the data in this figure, these three water regions can be considered to have low mineralized water, not exceeding 100 mg/L.

Note that, due to low mineralization in water, pipe materials should be chosen carefully.

Other studies, working on electrical conductivity, (Table 6) show significant fluctuations from one region to another. The water mineralization rate varies in different regions, for instance in Mireleft (Morrocco) it is high compared to other regions Amman, Croatia, Ajaccio, and Bordeaux which have low electrical conductivity. The dew point EC varied between 45 µS/cm and 725µS/cm, highest dew EC values were found during the dry season (Lekouch et al., 2011). Overall, some of the rate of mineralization of dew (generator) depends on natural external factors such as aerosols (sea salts and continental dust) and anthropogenic factors which demonstrates the influence of geographical location on atmospheric water mineralization.

Table 6

Electric conductivity (EC) (µS/cm) and total mineralization in mg/L (≈ 0.77 EC) in Mirleft as compared to other sites (Lekouch et al., 2011).
Site	EC (µS/cm)	Total mineralization
Mireleft	725	560
Amman	129	100
Zaddar (Coratia)	204	160
Ajaccio	114	88
Bordeaux	45	35

Industrial and anthropogenic pollution enriches the air, which influences the composition of water, as proven by the measurement of turbidity. When the water was collected by the machine, it apparently picked up large quantities of dry deposits that had accumulated on the surface captured by the substrate during this period. The key parameter was the high turbidity concentration of the water, which was considerably higher than recommended for all three sites. This is due to local aerosol deposition from the chemical group and road traffic near the test sites. This can be organic matter, which can affect color, odor, and turbidity (Ahsan shah et al., 2013). Suspended solids, such as dust or any undissolved particle greater than 2 µm, are a primary category of physical contaminants. In general, sedimentation or filtration can easily remove suspended particles, as in our case, before using water for domestic purposes. To ensure that the water produced is potable, in accordance with current legislation, the method of physical and chemical treatment is carried out by filters. A purification filter is used to directly intercept impurities in water, remove suspended solids and particles in water, reduce turbidity and purify water (Cheng et al., 2018). The integration of a porosity particle filter strategy has been proposed to reduce any exceedances found. It had a powerful efficiency that decreased the turbidity to almost 0 NTU (Fig. 8). Without pre-treatment or cleaning of the collecting surface, dew collection allowed dust into the system and significantly influenced the chemical composition of dew water (Odeh et al., 2017).

Evaluated water quality parameters (Fig. 9) were sodium, potassium, calcium, magnesium, sulphate, chloride, fluorides, nitrate, and bicarbonate we also found calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), and potassium (K⁺) ions at low amounts ranging from 0.86 mg/L to 8.14 mg/L. From our measured cation concentrations and the literature in figures, we see that in Soliman, concentrations of Na⁺ are higher than those in other sites (closer to the sea) The ions Na+, Mg2+, and Cl are certainly of sea origin, while the presence of Ca2 + is due to coral particles (Muselli et al., 2021). K⁺ and Mg⁺ were totally absent from all sites except for Soliman, with a very low rate. There are no WHO or Tunisian drinking water criteria for these metal ions. It should be mentioned that Mg²⁺ and Ca²⁺ deficit in drinking water can cause a variety of health issues, including tooth loss and cardiac infarction. As a result, dew water should be enriched with these necessary minerals (Offir Inbar, 2020).

The quantities of the five anions measured in water (Fig. 10) were significantly lower than the WHO and Tunisian recommendations for specific compounds. Fluoride and chloride levels were two orders of magnitude lower than drinking water regulations, while nitrate levels were minimal at all sites. Except for the Gabes site, HCO^3- is the predominate major anion in all samples. Gabes has higher sulphate concentrations. It is vital to remember that the majority of studies were conducted in cities. Thus, the greater concentration of anthropogenic species in Tunis and Gabes dew water is rather remarkable. Other metals were discovered in trace amounts (a few micrograms per liter) and did not exceed drinking water requirements. The data collected about the characteristics of the water produced during the experiments at the sites tested in Tunisia show a good quality, which can be an alternative source of drinking water void of metallic trace and a very low concentration of nitrates and sulfates. It is, therefore, a slightly alkaline water with low mineralization. All these parameters are within the norms of the WHO and Tunisian guidelines that define potable water.

Compared with other studies mainly based on the analysis of important cations and anion, few studies have reported concentrations of trace metals in dew. However, available data raises serious concerns in this regard. For example, in Ajaccio, water collected from moisture was reported to have elevated levels of aluminum and iron above EU drinking standards and lead levels above World Health Organization norms (Muselli et al., 2006). Other chemical compositions of dew water were investigated in France (Ajaccio): suspended solids, pH, concentration of SO₄^2−, Cl⁻, K⁺, and Ca²⁺ ions. Sometimes, only the Cl⁻ and SO₄²⁻ ions were considered relevant. Despite its low acidity (average pH 6) and large concentration of suspended particles, dew water meets France's drinkable water criteria in terms of the ions listed above (Muselli, 2002). In another study conducted in Tel Aviv, Israel, the chemical composition of water produced by an AWG: metals, inorganic ions, volatile organic volatile compounds (VOCs), and semi-VOCs were analyzed. The main elements found are ammonium, calcium, sulfate, and nitrate (Inbar et al., 2020).

Several studies have analyzed the chemical characteristics of dew water, which indicate that dew chemistry is influenced by terrain profile and weather conditions. In most cases, dew water meets World Health Organization (WHO) drinking water requirements (Inbar et al., 2020).

This paper describes field quality tests on dew collection by an atmospheric water generator. It aims to condense water from moisture, in different places in Tunisia, to characterize its quality.

The chemical parameters measured have been compared with those published in other research papers to discern the geographical position that determines the groups of chemical elements and their probable origins. These results suggest that the production of dew water by an AWG tested in Tunisia can give safe drinking water throughout the year. The concentrations of chemicals varied significantly in water samples.

The produced water quality tests have been carried out, to ensure that the values are recorded within the desirable standards. It is, therefore, potable according to the climatic conditions in Tunisia. The study reflects the importance of atmospheric water collection through moisture condensation technology, which can serve as a viable alternative water source to increase water supply which could help address the world's serious water scarcity, particularly in distant and inland places.

Since no chemical data on dew chemistry in Tunisia have previously been reported, the findings of this study are the first contribution to our knowledge of dew chemistry in the region.

In perspective, this study can be generalized and applied to other regions of Tunisia or other regions around the world, in terms of quality, to assess the geographical impact on water quality.

Conflicts of Interest: The authors declare no conflict of interest.

Data availability and material: All underlying data are available as part of the article and no additional source data are required.

Author Contributions Statement

Ghada Chebbi wrote the main manuscript text and prepared figures. Anis El AOUD and Mohamed Ali Abid participated in the development of the experiments, all authors reviewed the manuscript.

Ethics approval and consent to participate.

All authors have read, understood, and have complied as applicable with the statement on “Ethical responsibilities of authors” as found in the Instructions for authors.

Consent for publication.

We confirm that all authors have read the manuscript and agree to its submission in Environmental Monitoring and Assessment.

Competing interests

The authors declare no competing interests.

Funding

The startup Kumulus finances this work.

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Physico-chemical characterization of water obtained by condensation of moisture from an atmospheric water generator in Tunisia

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Abstract

Figures

1. Introduction

2. Materials and methods

2.1 Description and operation of the water generating device.

2.2 Water produced by the atmospheric water generator: Collection and analysis.

3. Results and Discussion

4. Conclusion

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