Treatment Technologies and Guidelines Set for Water Reuse

*Ahmed Abou-Shady and Heba El-Araby*

### **Abstract**

Water reuse is considered a practice that is currently embraced worldwide owing to the exacerbated water crisis, which is the result of several factors such as the increasing world population, urbanization, industrial sector, global climate change, limited water resources, and agricultural activities. Water reuse is not used intensively only in arid and semi-arid regions, which are characterized by limited water supply but can also be applied in countries that possess sufficient water resources (e.g., Brazil and Canada are implementing policies for water reuse). This chapter discusses the treatment technologies proposed for water reuse and presents some recent guidelines set for water reuse. Treatment technologies typically have three main processes: primary, secondary, and tertiary. There are several set guidelines worldwide for water reuse, however, a universal standard guideline to facilitate the reuse of reclaimed water has not been established. No federal regulations for reusing recycled water have been established in the United States; however, several individual states and territories have established specific regulations to manage reclaimed water for various purposes, including agricultural irrigation, animal watering, and crop production.

**Keywords:** water reuse, water treatment, guidelines, water crisis, process safety

### **1. Introduction**

Globally, a big amount of potable water is being seawater, whereas less than 3% can be considered safe for use. This 3% of potable water exists in groundwater which accounts for 20% (requires energy for extraction and pumping) and glacial ice (79%), accordingly, the available amount of potable water that is suitable for direct use is account for less than 1% [1, 2]. In China, water crisis can be observed in two phases, scarcity and deterioration, in which two-thirds of Chinese cities suffer from water deficiency, river pollution, and lake eutrophication [3]. At present, the global economy withdraws approximately 4000 km3 of water per year from natural resources, among which 45% is the discharged wastewater that cannot be handled in the currently available wastewater treatment facilities (only 11% of the total discharge is being treated through different treatment processes). The wastewater may be comprised agricultural runoff (56%), industrial effluents (28%), and household water in an urban area (14%) [4]. At present, half of the world's natural water bodies are severely contaminated, and by 2030, it will be imperative to reduce the proportion of untreated wastewater by half, according to the SGD agenda 2030 [5].

The scenario of water reuse is considered ancient as human civilizations themselves (e.g., several civilizations, including Egypt, Mesopotamia, and Crete civilizations utilized sewage (domestic wastewater) for agricultural irrigation from the beginning of the Bronze Age (approximately 3200–1100 BC). Afterward, Greek and Roman civilizations adapted water reuse during 1000 BC–330 AD [6].

Almost all continents at present such as Europe, Australia, Africa, Asia, and North America embrace the notion of potable reuse [7]. The amount of water being reused differs from one country to another (e.g., 46% in California, 7% in Japan, 32% in Asia, 75% in Israel, and 44% in Florida). Reclaimed water is being reused for environmental applications in northern Europe (51%). Also, water reuse is account for 44% in southern Europe for agricultural irrigation, 25% in Tunisia, and 25% in Spain for agriculture. In Singapore, approximately 500 Mm3 /year of treated wastewater is being reused to fulfill its water demands and by 2060, this amount is expected to be increased to 55% [5, 8].

Although some countries have sufficient water resources (e.g., Canada and Brazil), the arid regions may suffer in the future owing to the limited water supply. This is particularly true for expanding cities, with the situation being exacerbated by decreasing glaciers and depleting water sources due to climate change [9, 10]. The agricultural sector consumes a huge percentage of the global freshwater (70% of the withdrawal and 90% of the consumption), and the water consumption of this sector can grow in the future, as 56% of the globally irrigated crops experiences extremely high water stress [5, 11]. Approximately 12% of the globally irrigated land (36 million ha) irrigates with some urban wastewater, of which only 15% is reclaimed water [6].

Water crises are more evident in megacities, such as London, where water infrastructure and population growth pose severe challenges. Similar issues and incidents have been reported in Mexico City and Tokyo. In these areas, water reuse is implemented at two scales (large and small). At the large scale, reclaimed water is dedicated to drinking water (DW) (e.g., Texas, Orange County, and California), whereas at the small scale, reclaimed water is used for flushing toilets, cleaning streets, and irrigating urban areas [12]. A recently emerging term, "One Water," should be embraced worldwide; the term is used to promote the ideology that all water has value and should be managed in a sustainable, inclusive, and integrated way. Water reuse may be considered one of the available solution, to ensure sustainable water use and address food insecurity. The "One Water" approach may involve the following provisions: (1) all water types, from raw source water (for DW treatment plants) to water flushed down toilets and drains, should be viewed through the lens of source water protection, and (2) different types of water pollutants must be treated to establish appropriate standards for their intended downstream applications [11].

The main aim of this chapter is to provide an overview of treatment technologies and guidelines set for water reuse as is considered an important factor to overcome the future water crisis.
