Atmospheric Water Harvesting Development and Challenges

The rapid increase in the global population and the reckless behavior of depleting potable drinking water have accumulated into a colossal crisis in previous decades. Some four billion people (i.e., two-thirds of the global population) worldwide face low-to-high water stress. Ensuring access to safe drinking water remains a universal challenge and is now formally recognized as an international development priority by the United Nations framework. In this connection, along with other parallel technologies, Atmospheric Water Harvesting (AWH) is emerging as an effective methods means to overcome the water scarcity in arid regions, especially inland areas lacking liquid water sources. And, Beyond the conventional system engineering that improves the water yield, novel moisture-harvesting materials provide new aspects to promote the AWH technology—benefiting from their high tunability and processability. Innovative material and structural designs at micro/and nanoscale facilitate the water harvesters with desirable features; such as high-water uptake, facile water collection, and long-term recyclability, thus, boosting the rapid development of next-generation atmospheric water generators. In principle, AWH technologies could be classified into three categories; condensation, sorption, and hybrid. This chapter summarizes the water harvesting technologies from perspectives of surface design, material choice, test setups, performance analysis, and significant findings.

In this study, extraction of water from air using double slope condensation surface is investigated. Solar energy as a heat source and Calcium Chloride (CaCl₂) as the desiccant are used. The experimental apparatus involves two parts. The first part, which functions as an absorber has nine channels containing a mixture of Calcium Chloride (CaCl₂) and sand while the second part, which functions as a transparent and condensation surface has a prism shape. At night, the absorber is exposed to atmospheric air where Calcium Chloride (CaCl₂) absorbs moisture from the air. At sunrise, the absorber is covered tightly with the transparent and condensation surface that allows the passage of the sun rays to absorber. Condensate water is collected in sloping channels that are fixed at the bottom inner surface of the transparent surface. The temperature of the transparent surface, air-vapor mixture and absorber surface, solar radiation intensity and amount of collected water are recorded during the experiments per hour for the left and right sides of the apparatus at various operating days. Experimental measurements indicate that the condensed water productivity changes with ambient conditions. It is found that the maximum productivity yield for July 31st was 825 g/day for accumulative solar radiation about 441 kW/m² day. A mathematical model is developed to calculate theoretical solar radiation intensity and amount of collected water. Its results are compared with the experimental data and a reasonable agreement between theoretical results and experimental measurements is achieved.

Due to the rapidly growing population, industry, and agriculture, the potable water shortage is becoming one of the global challenges of our time. Simultaneously, the atmosphere contains 12,900 km³ of moisture available everywhere, regardless of geographical location and climatic conditions. In this context, the technology of Adsorptive Water Harvesting from the atmosphere (AWHA) is considered a promising method for decentralized water supply for domestic and sanitarian purposes in arid regions. The AWHA is based on the reversible sorption of water vapor on a desiccant and heat-powered desorption of the stored water with its subsequent condensation. The sorbent is a key element of AWHA, and its properties strongly affect the system’s performance. New opportunities for AWHA might open up with the development of novel adsorbents with advanced properties. In this chapter, first, the principle and basic technical solutions of AWHA are described and the properties of the sorbent required are outlined. Then the new classes of advanced sorbents suggested for AWHA are reviewed with a special focus on Metal–Organic Frameworks and the composite sorbents based on a hygroscopic salt embedded inside a matrix, the properties of which can be tuned according to the climatic conditions of a specific region, where the process is realized. Finally, the advantages and challenges of these adsorbents are discussed and some prospects on the adsorbents promising for continuously operating and scalable AWHA systems are provided.

Atmospheric water harvesting (AWH) has consistently emerged as a possible source of fresh water, especially in regions where water and energy are scarce. Harvesting water from ambient air has the potential to be largely powered by renewable energy sources. Renewable energy has demonstrated a greater potential to produce water in arid regions using adsorption-based atmospheric water harvesting (ABAWH). Adsorbent is the only component in the ABAWH process that converts ambient air or moisture to water. In this direction, metal–organic frameworks (MOFs) have recently emerged as effective AWH adsorbents. The chapter focuses on the development of MOF-based adsorbents with excellent adsorption performance. Various parameters, such as adsorption kinetics, climatic conditions, and adsorption–desorption rate, have been covered in this chapter. This chapter also looks at the current advancements in AWH technologies and achievements. It is expected that this chapter will provide the reader with challenges that have been identified that retard the potential practical application of MOFs in AWH technology.

Freshwater scarcity is a major problem threatening many countries worldwide, notably those with arid climate conditions that lack access to fresh water. Humidity harvesting represents a reliable source of providing fresh water, especially if it can be extracted affordably and efficiently. Sorption-based atmospheric water harvesting (AWH) has the merit of being powered economically and sustainably by utilizing waste heat or solar energy compared to other AWH techniques. The first part of this chapter comprehensively presents the working principles of the atmospheric water harvesting technology. Afterward, a detailed appraisal of state-of-the-art sorption materials, such as activated carbon fiber, zeolite, silica gel, metal–organic frameworks, calcium chloride with various host materials, and hydrogels, where its adsorption isotherms and kinetics are examined in detail. The challenges and prospects of these sorption materials are also demonstrated. Moreover, numerous designs of solar-powered atmospheric water harvesters, including fixed and movable installations, are summarized and categorized. For the sake of comparison, operation concepts, advantages, disadvantages, and freshwater production capabilities are indicated. In that regard, the viability of those systems is also exhibited under different meteorological conditions. Eventually, the obstacles and limitations that hinder their utilization and future research directions are explored. Accordingly, AWH technology is introduced as a promising solution for freshwater supply, particularly in rural areas and arid deserts where water and energy are scarce.

Arid regions are classified on the basis of severe lack of available water which further affects the growth as well as the development of flora, fauna, and human life. The idea of recovering water from atmosphere has remained quite a problem in arid regions. AWH defined as atmospheric water harvesting, is a prominent way to overcome water scarcity. It is considered as an alternative source of fresh water regardless of the physical conditions prevailing in a certain area. Various techniques are used to harvest atmospheric water that comprises adsorption-based technology, fog collector, atmospheric water generator and few other models in other to harvest atmospheric water. In this chapter, our focus will mainly be based on potential behind harvesting atmospheric water in arid regions and we will be going through different case studies to have in-depth knowledge and information regarding it.

Atmospheric water harvesting appears to be a potential way to address water scarcity, particularly in locations where liquid water is scarce. Rainwater harvesting (RWH) is a low-cost, easy approach that requires little special expertise or understanding and has numerous advantages in remote areas. The purpose of this chapter is to examine various types of sustainable atmospheric water harvesting techniques. AWH appears to be a potential methodology for decentralized water production, overcoming the difficulties of long-term conveyance and supply of fresh drinking water in remote areas. Structural designs of innovative materials enable moisture harvesters to have desirable characteristics including high water uptake, durable recyclability, and easy collection of water, accelerating the next generation development of AWH. In this chapter, we first show the sorption mechanism for moisture-harvesting materials, including absorption and adsorption, and then review essential needs and moisture harvester design concepts. The development of an atmospheric water harvester that can generate water irrespective of geographical location, humidity level, low cost, and can be manufactured using local materials is the primary goal of all methods.

Many countries worldwide, particularly those with arid climates, face a serious problem regarding freshwater scarcity. Climate change, accompanied by economic and population growth, are worsening the problem. Remote communities with no access to freshwater are suffering the most from this problem. Clouds, fog near land, and water vapor (humidity) in the surrounding air are the three most common kinds of atmospheric water found in the atmosphere. Humidity in the surrounding air represents a great and reliable source for providing fresh water, especially if it can be extracted in an affordable and efficient manner. Water extraction from the atmosphere, unlike desalination, does not have a significant impact on the hydrological cycle or on vital water sources in the vicinity. The water quality is also adequate for drinking and other residential and agricultural uses because the source of the atmospheric water is usually clean. Depending on the atmospheric water source, the AWH technologies can be categorized into artificial rain, fog water and dew water collection technologies. In arid coastal areas, fog water collection technologies can be feasible and accessible technologies to alleviate the scarcity of freshwater. Moreover, fog water is often collected in a rectangular mesh perpendicular to the wind, which traps fog droplets. In comparison, dew water collection technologies are minimally susceptible to meteorological and geographical limitations compared with fog collection methods. Dew collection technologies are considered condensation-based technologies, which fall into three primary categories: direct condensation harvesting, vapor concentration by adsorbent material, and by-product collection from an integrated system. Furthermore, the vapor concentration and water vapor condensation processes can be classified as passive or active, depending on the energy input to the system. In this chapter, the state-of-the-art of various AWH technologies will be introduced, in addition to techno-economic comparative assessment of these technologies.

With the growing population worldwide, the demand for fresh water is expected to continuously increase over the year, putting an unnecessary pressure on the surface and groundwater. Atmospheric water harvesting which is an air to water system therefore presents a suitable alternative that does not depend on the limited surface water resource and does not require intensive treatment and production of waste by-product. This new technology is now well understood and adopted by various countries around the world and mainly the middle East and Africa for industrial, commercial and residential dispensation needs. The market of atmospheric water generator and related products is booming and research have been carried out to provide both qualitative and quantitative insights with regard to segment, sub-segment and region across the world. An overview about the market drivers and restrains, as well as the share across different sectors will be part of the focus of this chapter.

There is limited awareness about atmospheric water (AW) and its harvesting for drinking purposes in South Africa and Sub-Sahara African countries at large, this trend is mainly characterized by the shortage of articles related to this topic from this region. Most of the referenced papers from search engines are either from Northern Africa or from other continents. The article aims to create awareness within the community of Pretoria North, Gauteng Province in South Africa regarding atmospheric water harvesting (AWH) as an alternative source to the conventional potable water supply. AWH could be crucial, specifically during times of potable water supply challenges in the country; an assessment of awareness has been carried out to postulate on the acceptability of such alternative. A set of questions was formulated by the researcher to address the aim as well as consent form declarations for the participant to voluntarily engage on the survey. The consent form explained the criteria of no race, no identity concept that has no prejudice meaning, the participant could opt to pull out from the survey at any given time. The engagement yielded a positive outcome as 93% of the total questionnaires were answered, of these 27% did not address the randomization validity. The overall results did give a turnaround of 66% valid surveys with question (7) and (9) scoring the highest equal score on “strongly agree”. The outcome of the data collected has proven that most of the people interviewed (60% of the participants) believe that water can be harvested from air, fog and rain for drinking purposes which relates to the fact that they are likely to accept AWH technologies. Similarly, 60% of participants strongly agree that drinking water quality is more important than the cost to acquire such water. The conclusion therefore provides answer to the aim established by the researcher consisting mainly to assess the acceptability of AWH as an alternative source of water. These findings, made available, will require the necessary actions by the relevant authorities to ensure that the community is equipped with the necessary tools to face the challenges similar to those encountered during the drought period a few years ago.