58 The Future of Water in African Cities
Wastewater Might Be Valuable There is great potential in urban water systems for water, energy, and nutrient recovery. In particular, wastewater is often grossly undervalued as a potential resource. By employing innovative technologies, water, calorific energy, biogas, and nutrients can be reclaimed from different water and waste streams and reused locally as shown in Figure 2.1 (Bieker et al., 2010; Cornell et al., 2011; Otterpohl et al., 2003). The so-called water machine would also enable the reclamation of water of different qualities that are fit for different purposes. Figure 2.1 Resource Recovery from Wastewater: The “Water Machine” Concept
Source: World Bank, based on Bieker et al., 2010; Cornell et al., 2011; Otterpohl et al., 2003.
A perspective to treatment is emerging that aims to maximize the benefits reaped from every drop of water. Recent advances have generated technologies for simple, low-cost solutions, allowing the “water machine” concept to be applied in developing countries. Wastewater treatment and reuse in agriculture can provide benefits to farmers in conserving freshwater resources, improving soil integrity, and improving economic efficiency. In addition, wastewater has the potential to provide renewable energy and nutrients and will convert current liabilities (energy required for wastewater treatment) into assets (energy from wastewater treatment). Such a perspective raises the possibility of addressing the sanitation challenge in African cities as an opportunity rather than a burden (Howe et al., 2011).