Sobre los resultados.

Globally, fresh water scarcity is a developing problem and natural water resources are becoming inadequate to fulfil demand. This problem is present all over the world e.g. southern Europe, the Middle East, Australia, the southern states of the USA and North Africa.

According to Kivaisi (2001), rainfall is the main water source around the world which produces around 40,000 to 45,000 km3 every year supporting the rapidly increasing population, which is expected to increase by 85 million yearly as reported by Stikker (1998), leading to decline in water supply and subsequently to water conflicts. According to Alcamo, Döll, Kaspar, and Siebert (1997) and Alcamo, Henrichs, and Rösch (2000), 1.8 billion people will experience absolute water scarcity, and two thirds of the world will be living under water-stressed conditions by 2025, while almost half the world will live under conditions of high water stress by 2030 (Scheierling et al., 2011).

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Moreover, about 80 countries around the world are expected to be suffering from serious shortage in water supply every year (Gleick, 1993). According to Stikker (1998), the number of countries facing water scarcity during the last four decades, most of which are developing countries, is expected to increase to 34 by the year 2025 (Table 1.1).

Table 1.1: Countries experiencing water scarcity in 1955, 1990 and 2025 (projected), based on availability of less than 1000 m3 of renewable water per person per year (adapted from Stikker (1998))

Countries in water scarcity category

In 1955 In 1990 By 2025 under all UN population growth projections By 2025 only if they follow UN medium or high projections

Malta Qatar Libya Cyprus

Djibouti Saudi Arabia Oman Zimbabwe

Barbados United Arab Emirates

Morocco Tanzania

Singapore Israel Egypt Peru

Bahrain Tunisia Comoros

Kuwait Cape Verde South Africa

Jordan Kenya Syria

Burundi Iran

Algeria Ethiopia

Rwanda Haiti

Malawi Somalia

In addition to human population growth, industrial and agricultural activities expansion, global warming and climate changes are other reasons contributing to the water scarcity problems in many regions worldwide. However, the present situation of water scarcity in the world is mainly due to the forces of increasing population and economic development (Huang & Xia, 2001).

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This is especially evident for the world’s fastest growing cities which typically are located in low-income developing countries and characterised by poor water infrastructure and unsatisfactory wastewater treatment (Varis & Somlyódy, 1997).

As the population increases, the need for food and water will continually grow.

As a result, the actual consumption of water will quickly approach the limits of the resources available and, subsequently, agricultural land will become rare (FAO, 2003). This will be the main factor limiting development and consequently will be a major economic, social, and political challenge in such regions.

Furthermore, climate change has the potential to impose additional water resources pressures in some regions. The rise in temperature associated with climate change leads to a general reduction in the proportion of precipitation falling as snow, and a consequent reduction in many areas in the duration of snow cover.

This has implications for the timing of streamflow in such regions, with a shift from spring snow melt to winter runoff (Arnell, 1999). As a result, significant reductions in precipitation, or major alterations in the timing of wet and dry seasons may occur in some regions of the world. The second assessment report of the Intergovernmental Panel on Climate Change (IPCC) cautioned that global warming would lead to increases in both floods and droughts (Houghton, 1996).

However, many environment, economy and society aspects are dependent upon water resources and changes in the hydrological resource which may severely affect

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environmental quality, economic development and social well-being (Alcamo et al., 1997). Climate change, however, is just one of the pressures facing water resources and their management over the next few years and decades (Stewart, 2012).

Generally, there are both supply-side and demand-side pressures. The supply-side pressures include climate change (reducing or increasing the amount of water available), and also include environmental degradation, for example the accumulation of organic and inorganic pollutants resulting from different sources, such as domestic, agricultural and industrial, in the surface water, ground waters and plants, leading to degradation in water quality which negatively impacts the receiving ecosystem (Ijeoma &Achi, 2011).

On the other hand, the demand-side pressures include population growth, leading to increased demands for domestic, industrial and agricultural (particularly irrigation) water resulting in sharply increased in wastewater characteristics such as biochemical oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), total suspended solids (TSS), turbidity, and increase in discharge of various types of pollutant such as: nitrogen compounds (i.e. ammonia nitrogen and nitrates), petroleum hydrocarbons, heavy metals like cadmium, chromium, nickel, lead, copper and zinc, and microbes (faecal coliform, E-Coli and salmonella).

These pollutants will cause deterioration in water quality in the receiving water course making these sources are unsuitable for drinking, irrigation and aquatic life. However, climate change may affect the demand side of the balance as well as the supply side (Arnell, 1999).

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Due to this water scarcity problem around the world, it is essential to think about non- conventional water resources for satisfying the increased rates of demand for fresh water. Some countries around the world have made significant steps toward desalination of seawater for meeting the urban demands for their people.

However, desalination methods require large amounts of energy, which is costly both in environmental pollution and in money terms, making this technology limited for domestic purposes (Karagiannis & Soldatos, 2008). Use of different natural water resources, like river, rain, and drainage water or drainage water blended with fresh water, are other alternative options for irrigation purposes in many countries (Pedrero, Kalavrouziotis, Alarcón, Koukoulakis, & Asano, 2010).

Moreover, wastewater is concluded as an available alternative option to overcome the shortage in water supply resulting from previous discussed reasons, particularly population growth (Bichai, Polo-Lopez, & Ibanez, 2012; Noori, Mehdi, & Norozi, 2013, 2014; Almuktar & Scholz, 2015).

However, due to the varying nature of wastewater (in terms of mineral load, organic and biological constituents) the reuse of such water should be monitored regularly to assess potential risks which may affect the whole environment (FAO, 2003).

Inadequate provision of sanitation and wastewater disposal facilities leads to environmental and public health problems, with around 1.8 million people dying every year from several related diseases (Nellemann, Baker, Bos, Osborn, & Savelli, 2010).

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Adequate reuse of wastewater is a necessity to protect public health, the environment and water resources. Direct disposal of untreated wastewater to land and water bodies has a negative impact on human health (Khurana & Pritpal, 2012).

Because of this, wastewater treatment and recycling methods will be vital to provide sufficient fresh water in the coming decades, since our water resources are limited (FAO, 2003) Wastewater reclamation, recycling, and reuse has evolved due to the increasing of pressure on water resources.

The feasibility of producing the specific quality of the reclaimed water to fulfil multiple water use objectives is now of real importance (Asano & Levine, 1996). Understanding the principles of urban wastewater reuse as an alternative and reliable source of water supply and analysis of the cost of wastewater reclamation are essential (Asano, 1994; Mujeriego & Asano, 1999).