A techno-economicGIS-based model for waste water treatment and reuse feasibility in the North Western Sahara Aquifer System

Sammanfattning: Water security represents a main challenge in the quest for sustainable development and stability worldwide. Often, such security is closely linked with the demand of water for agricultural irrigation, as it repre-sents the major share of human water withdrawals. The North Western Sahara Aquifer System (NWSAS), is a large aquifer system spreading through three North African countries: Algeria, Tunisia and Libya. It is formed by two superposed groundwater reservoirs, constituting the main sources of fresh water access in the region. To cope with the water demand and alleviate water resources exploitation, Treated Wastewater (TWW) is emerging as a promising solution for the region. This master thesis focused on the development of a GIS-based methodology to asses the techno-economic feasibility of wastewater reclaim, treatment and reuse for crop irrigation in the NWSAS region, considering groundwa-ter quality and depletion, electrical energy requirements and Levelised Cost of Water (LCOW) as main assessment parameters. Such model enables the evaluation, under different scenarios, of the impact that new policies, technologies and measures can have in the overall system. Nine wastewater treatment technologies were analysed, under eight dif-ferent scenarios. The scenarios were constructed based on population water requirements per capita and the behaviour of farmers towards different irrigation water price regimes. The least-cost technologies found, presented a tradeoff between the wastewater treatment capac-ity and the technology chosen, which approximates to the behaviour found in reality. The outcomes of the analysis, evidenced the current medium-to-high stress of the groundwater resource, which is trending to worsen. Moreover, the reuse of treated wastewater in agricultural irrigation, showed to be a viable option for reducing the water stress of the basin. However, to preserve the water resource, measures as better water pricing mechanisms, management strategies to improve water productivity and adoption of more efficient irrigation schemes may be needed. Furthermore, the energy-for-water needs were evaluated. Pumping energy represents by far the major user of electrical energy in the region and the treatment and reuse of waste water, showed to be useful to reduce the dependency on pumped resources, reducing as well the energy-for-water needs. Moreover, the effect of changes in salinity content and depth to groundwater levels, showed substan-tial effects on the energy requirements for desalination and pumping respectively, which can jeopardize the economic sustainability of the agricultural practice in the basin.