Recovery of Water
Water is one of the most important substances on earth, such that all plants and animals need water to survive (Simate, 2015). In other words, water supports life (EU Directive, 2000). Furthermore, water is at the centre of economic and social development (Goswami and Bisht, 2017). Though fresh water is considered a renewable resource through a continuous cycle of evaporation, precipitation, and runoff - commonly referred to as the water cycle (Goswami and Bisht, 2017), in the recent past, the demand for water has exceeded the supply of water in many places (UNEP 2012). Indeed, water is now a scarce commodity that is fast becoming an issue of prime concern globally (Masindi et al., 2019). Therefore, it is important to find alternative sources of water in order to meet the demand. Most importantly, developing additional sources of water supply such as the non-conventional ones is vital; and AMD is one such a non-conventional source for water supply.
In fact, studies in many countries including South Africa have reported that there are large volumes of AMD produced (Bologo et al., 2012; Masindi, 2016; Masindi et al., 2018), which, without doubt, can be used as an alternative source of water for various applications. In fact, the removal of heavy metals from AMD using the technologies discussed in the previous sections simultaneously recovers water (Simate and Ndlovu, 2014). However, the processes have several disadvantages which include pH dependence, which means that the removal of the mixture of heavy metals cannot be achieved at a single pH level (Simate and Ndlovu, 2014). Therefore, it is imperative that other technologies which are not pH dependent are pursued. In this regard, there have been significant advances by scientists and engineers to recover water from AMD. Therefore, this chapter will focus on conventional methods (e.g., electrodialysis, nanofiltration, reverse osmosis, etc.) and recently developed alternative technologies (e.g., membrane distillation, etc.).