Potential of Atmospheric Water Harvesting in South Africa

Abstract

The objective of this research project is to assess the viability and accessibility of employing atmospheric water harvesting (AWH) as an alternative drinking water source at a time of drought or upon downtime of conventional drinking water supply systems due to maintenance and natural disasters in South Africa, particularly in a semi-arid high-altitude region. The researcher was further motivated by the droughts that occurred and intensified in 2014 and 2015. The drought was recorded in 2014 in Cape Town in the Western Province, then expanded inland for over two years. Additionally, the lowest amount of rainfall in South Africa was recorded during this time since records began in 1904. This highlighted the need to explore alternative methods of obtaining water for crops, water supplies, and power generation due to the possibility of worsening climate forecasts. The inability to do so would lead to intensified food, energy and water shortages. Furthermore, population growth has been forecasted to reach nine billion by 2050. As such, food production will have to increase by 50%, along with an estimated increase of 15% in freshwater withdrawals. This underscores the urgency of proactive measures to sustainably meet growing demands amid changing climatic conditions.

The study is based on research conducted from a site in a semi-arid region of South Africa (Ga-Rankuwa, global positioning system location 25.5864° S, 27.9876° E, Gauteng Province), which elucidates the use and performance of atmospheric water generators (AWGs) to harvest water from the atmosphere. The success of this direct AWG technology is based on the science of ambient temperature (T) and relative humidity (RH), in which water formation is favoured from temperatures above 15 °C and RH above 30%. The relative humidity decreases as temperature increases, and a balance should be obtained to achieve maximum water harvesting possibilities. Daily and hourly data of dry bulb temperature (T) and RH records have been taken at the case study site from January 2020 until the end of January 2021 to assess variations of these parameters and their impact on water harvesting throughout all seasons in a year. Even though the research happened during the COVID-19 pandemic, this facility continued normal operations as it was categorised as an essential service in terms of the government's COVID-19 operations. The operations had been functional for three months before the commencement of this research. As such, the outcome of this study was aimed at adding value that would result in more growth in the business.

Concurrently, water collected during this time was sampled for drinking water quality assessments at different stages of the AWG's treatment equipment as per the South African National Standard for Drinking water 241(SANS 241). A meteorological study was conducted throughout a Typical Meteorological Year (TMY) for the site study area. The literature review explains TMY as a tool incorporating 8760 hourly climatic conditions, representing long-term ambient observations. A site study TMY consists of collecting climate data from hourly climate simulations each year from 2015 to 2020. The TMY served as a climatic tool that assisted productivity pattern predictions of these AWGs at the time of study. The collected data demonstrated high water productivity, particularly during the spring and summer seasons, due to rain pattern formation during this time. This favours high humidity in the atmosphere. Low productivity occurred between autumn and winter when there was almost no humidity and ambient temperatures were low. At times, there was no production at all for five consecutive days during the winter season. Other observations were made while exploring this technology, such as the electrical control instrumentation of the AWGs with set points indicating when the generator should be switched on and off and how energy consumption played a role in this case. There were two AWGs with a capacity of 5000 L water production per day, and each consumed 105 kW/hr at full capacity, illustrating that the technology is energy-intensive.