Keywords

3.1 Introduction

Water scarcity and wastewater management are considered significant challenges that affect the ecosystem and the urban environment worldwide. Many countries and regions worldwide continuously face growing pressure on their limited freshwater resources, particularly in arid countries such as Egypt [1]. Egypt is classified among the driest areas and the most water-stressed regions in the world, with an average annual temperature of 25 °C and even higher in summer months, and with limited annual precipitation below 250 mm, resulting in an extremely freshwater scarcity [2, 3]. Moreover, the Grand Ethiopian Renaissance Dam (GERD) in Ethiopia threatens Egyptian water security, and negatively impacts on Egypt’s freshwater since Egypt depends on the Nile River to secure 95% of its total water needs [4,5,6,7,8]. Thus, in Egypt, wastewater reuse is encouraged when it is safe and economically feasible to increase the water demand [9]. Several methods exist to treat wastewater based on different factors, mainly cost and efficiency, while nature-based solutions [10, 11], such as constructed wetlands (CWs), are the most growing technology.

Developing countries fail to use nature-based solutions to solve wastewater crises [1, 12]. About 95% of wastewater is discharged without treatment into lakes, seas, or other reservoirs, posing a threat to water sources and other serious environmental problems. CWs could offer an affordable and accessible solution for lower-income countries. CWs are defined as engineered eco-systems initiated and operated to treat different types of wastewater by manipulating the simultaneous physical, chemical, and biological processes [13, 14]. CWs have been rapidly developed to cover several types of wastewaters, such as municipal and industrial, due to their cost-effectiveness and eco-friendly character [1, 9, 14,15,16,17,18,20]. As a result of the growing attention to CW technology, the hydraulic design, construction, and operation have been extended to introduce various new configurations that facilitate the process as a whole and improve the performance for pollution removal [20,21,22,24, 25]. Locally, this technology has been applied in Egypt for almost 30 years.

From exploring the scientific literature, the significant number of publications related to CWs as individual experimental research or reviews on the Web of Science might be a good indicator of the increased transparency of this field’s knowledge. A Web of Science database research (a tool from Clarivate Analytics, August 15, 2020) using the keyword “constructed wetlands, constructed wetlands in Egypt” resulted in 13,426 and 31 studies, respectively. This indicates that although there is a flourishing publication record available on CWs worldwide, it is limited in Egypt. Figure 3.1 depicts the number of papers per year from 2010 to 2020, showing that the topic has experienced a gradual growth in the number of studies. In addition, many books have been published recently, for instance, CWs hydraulic design [15], CWs as a suitable technology for sustainable water management [26], and CWs for industrial wastewater treatment [16].

Fig. 3.1
A graph of the number of publications versus years has the studies of the constructed wetlands. From 2010 to 2020, the number of publications on Worldwide is 900, 1100, 1110, 1190, 1100, 1200, 1220, 1300, 1450, 1600, 1580, and 820. The number of publications on Egypt is 3, 0, 3, 2, 3, 4, 3, 2, 2, 4, and 5.

Number of studies in the last 10 years on constructed wetlands

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Several review papers discussed CWs’ performance in removing a wide range of pollutants from different wastewater types. These reviews have undoubtedly discussed the dynamics of pollutants, emerging organic pollutants such as antibiotics and pharmaceutical contaminants, and mechanisms of pollutant transformations. As a result of the increased attention to water scarcity in arid and hot regions such as Egypt, authorities have focused on wastewater reuse to protect the limited freshwater resources. Although CWs present a promising technology in Egypt, individual experiments and review papers are rarely reported.

Within this context, this chapter summarizes the current knowledge on CWs applications in Egypt along with the current status of water scarcity, taking into consideration different system configurations, operational parameters, and removal efficiencies. For this, an update on the application of CWs in Egypt is provided through a literature review of the last 10 years. Publications on CWs treating different types of wastewater in Egypt as pilot-scale and full-scale were also reviewed.

3.2 Water and Wastewater in Egypt

Egypt has a dry climate, with 95% of its area being a desert. There is a narrow strip of fertile lands alongside the major stream of the Nile and a comparatively small delta in the north [27]. It became the basis of one of the most distinctive old civilizations’ societal and economic life, where the primary human activity was agriculture [28]. The total precipitation is around 25.7 mm/year; in summer, there is an evapotranspiration rate of about 0.7 mm/day. The relative humidity varies from 45–75%, and the mean daily temperature ranges from 13–38 °C. There are also limited amounts of rain and flash floods. The Nile River is Egypt’s principal and almost sole freshwater supply. The country depends on Lake Nasser’s accessible water to meet Egypt’s annual water quota requirements, which amounts to 55.5 billion m3/year [29].

Over the last few decades, the pollution load to the Nile system (e.g., the Nile River, canals, and drains) has grown due to population increase, many new industrial projects, and new projects for agricultural irrigation, and other activities along the Nile River. As a result, the quality of Nile water has declined significantly in the last few years [30, 31]. The Nile system’s dilution capacity is likely to decrease as the policy of expanding irrigated farming progress and industrial capacity development increases the amount of pollutants discharged into the Nile [32]. The primary sources of most hazardous contaminants to the Nile and main canals are effluents from agricultural drains (including heavy metals, pesticides, fertilizers, and microbes) and the treated or incompletely treated municipal and industrial wastewaters. The most contaminated region in the Nile is between Cairo and the Mediterranean Sea within the two branches of the Nile, Rosetta and Damietta [31,32,35].

The industrial sector is the second essential source of water consumption and a contributor to pollution. The Egyptian factories use about 7.8 billion m3/year of water, 4050 million m3/year of which are discharged back to the Nile system. Hence, industrial wastewater is the second source of Nile water pollution due to hazardous organic and inorganic chemical loads in this wastewater. Industrial activities are clustered around large cities like Cairo, Giza, and Alexandria, which use 40% of total water [36]; however, small-scale private agro-industrial factories in Upper Egypt have recently begun contributing to Nile system pollution as well. Roughly 129 plants discharge their wastewater into the Nile River system. Untreated discharge of large amounts of this wastewater impacts river water used for both irrigation and drinking and has a harmful impact on aquatic life [28, 29, 37]. Food processing industries are responsible for more than 50% of the biological oxygen demand (BOD), while more than 60% of heavy metal discharges come from chemical factories. Wastewater from electroplating plants in the Helwan region (south Cairo) has a high content of Fe, Zn, Cr, Cu, and Mn [38]. Several studies have also reported the occurrence and concentration of Lead (0.001–330 μg/L) and cadmium (0.001–80 μg/L) in the Nile water [37,38,39,40,41,44]. Despite all official efforts to avoid these dangerous pollutants, 34 plants still do not comply with the Egyptian regulations for water disposal into the Nile systems [45].

The municipal wastewater effluent is considered as the third main source of Nile system pollution. The increasing population in Egypt along the Nile River leads to more wastewater generation, and policymakers are expected to expand the number of wastewater treatment plants (WWTPs). There are nearly 239 WWTPs in Egypt with an annual flow of 4.5 billion m3, of which 1.3 billion m3/year are discharged to the Nile water system. Toxic chemicals such as organic micro-pollutants and heavy metals are released in this wastewater because of domestic mixing with commercial and industrial activities [29]. These elevated values are higher than the standard limit and, in some areas of the Nile, higher than the permissible limits for healthy water streams. The two Nile branches, Damietta and Rosetta, downstream Delta Barrage, represent the worst River Nile quality. Some antibiotics such as sulfamethoxazole, azithromycin, and ciprofloxacin have been detected in the effluent of municipal WWTP in Beni-Suef city. Additionally, the detection of azithromycin in these municipal WWTP was higher than that detected in municipal WWTP in central Greece, China, and Thailand [46].

3.3 Constructed Wetlands (CWs)

CWs are defined as low-cost wastewater treatment techniques based on natural processes, which simulate the natural wetlands (e.g., swamps, marshes, and boglands) in a controlled environment [47]. CWs can be an effective treatment system, which can be very useful in developing countries [48], as they can remove most pollutants (e.g., pathogens, nutrients, organic and inorganic pollutants).

3.3.1 Constructed Wetland Types

As known, there are four typical types of CWs, i.e., Free water surface (FWS), Horizontal subsurface flow (HSF), Vertical flow (VF), and Hybrid Systems. In Egypt, all those types have been investigated and applied for different types of wastewaters, as shown in Table 3.1. About 60% of the experimental studies indicated that HSF is used either in full-scale or pilot-scale. HSF system in Egypt showed a high potential ability for pollutants removal compared to other systems. Approximately 25% of the reviewed literature revealed that FWS is also applied, while only one study was found on VF and another for a hybrid system.

Table 3.1 Overview of CWs applied and tested in Egypt
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3.3.2 Plants Used in CWs in Egypt

Local plant species can be used and grow in CWs. The plants in CWs in Egypt are classified into two types; floating plants, and emergent plants (Table 3.2).

Table 3.2 Plant species used in CWs in Egypt
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In Egypt, the water hyacinth (Eichhornia crassipes) plant is an emerged plant and grows in natural waters (Lakes, Nile river, irrigation channels). It is considered an invasive aquatic weed and was found 100 years ago in the Nile Delta for the first time but entered Egypt 200 years ago. Eichhornia crassipes are intensively found in Northern Lakes, creating many problems such as clogging of irrigation canal intakes and flooding, disturbing the operation of hydropower and water supply systems, and resulting in the degradation of the local biodiversity [59]. It is also considered a hyper-accumulator species; however, it has many benefits, and remediation through CWs is one of them. The policies in Egypt concerning Eichhornia crassipes eradicating and controlling the plant from water bodies through mechanical or biological control [57], presented an efficient management scenario for its coverage percentage to enhance the phytoremediation of different pollutants and reduce the water losses instead of fall eradication. Eichhornia crassipes in CWs have a significant role in efficient nutrient absorption and high potential pollutants removal at high rates. Pistia stratiote is a floating aquatic plant, and its leaves spread in a rosette on the water surface that inhibits algae growth. Pistia stratiote is found in Egyptian waters in the spring and fall seasons. It has a high potential ability for contamination removal, as shown by [58]. Lemna spp. (Duckweed) the plant is an aquatic plant amongst the promising aquatic plants having the enormous capacity to treat eutrophicated wastewaters [60]; however, it’s rarely used in Egypt phytoremediation studies. Duckweed is an invasive plant and is found in fresh Egyptian waterbodies. All of floating plants are used in FWS (CWs).

Cyperus papyrus plant is originated in Egypt, which has a historical benefits such as paper made and others. Cyperus papyrus is intensively used in CWs worldwide as a result of its high efficiency for pollutants removal [61]. Also, its root structures provide more microbial fixation sites, sufficient residence time of wastewater, entrapment, and settlement of suspended particles, the surface area for adsorption of contaminants, absorption, assimilation in plant tissues, and oxygen for the oxidation of organic matter and inorganic in the rhizosphere [62]. Canna flaccida is an invasive plant for the Egyptian environment; it hashing high growth rates with big roots, which may be a potential plant species that can be utilized effectively to remediate emerging organic contaminants [48, 63]. Canna flaccida has a colorful blossom, which can add an esthetically pleasing element to treatment sites. Phragmites are a native plant with many different species in Egypt; it usually distributes channels, lakes, and other water bodies. It has a high salinity tolerance so that it can grow on beaches.

Phragmites plant, especially Phragmites australis species, are widely used worldwide in CWs for treated wastewater [64]; in Egypt, many studies have used it, revealing their high ability and tolerance for heavy pollutants removal, as noted in Table 3.2. CWs widely use Typha angustifolia in Egypt, classified as an emergent plant with a high growth rate. Typha angustifolia is an invasive plant that originated from Europe and is distributed widely in many parts of the world [24]. There are many species of typha; Typha angustifolia has12–16 narrow and flat leaves [65]. Typha angustifolia is found in Northern lakes and the Nile River in Egypt. Typha angustifolia is known to have potential phytoremediation ability for various contaminants and has an antimicrobial effect against many pathogenic bacteria [22]. Typha angustifolia has approved its capacity for uptake the pollutants and performed efficiently in CWs. Typha latifolia (Cattails) is a native plant in Egypt found intensively in Lakes and the Nile River. Cattails plant has a wide range of applications, especially for its ability for pollutants removal through CWs.

3.4 Conclusions

Water scarcity and wastewater management are considered significant challenges that affect the ecosystem and the urban environment worldwide, especially in Egypt. With limited freshwater resources, Egypt has a huge amount of wastewater annually, partially treated using different methods, with Constructed wetlands (CWs) technology among them. CWs literature for wastewater treatment in Egypt has been reviewed for a period of the last 10 years. The HSF system was found to be the most widely applied system in either full-scale or pilot-scale, followed by the FWS design. Also, the commonly used plants in this technology were reviewed and showed a wide range of suitable plants growing in the Egyptian environment. This green technology has become increasingly known in Egypt and has a wide implementation potential; however, the number of publications is growing slowly. The currently limited experiences with CWs in Egypt imply the ability of this technology to contribute to addressing the water scarcity issues in Egypt effectively.