**3.1 Natural lagoon**

Natural lagooning is an interesting wastewater treatment process, particularly for small communities, and has been relatively developed since the 1970s [8].

Among the ten stations observed 3 stations (**Table 2**). planned using the natural lagooning process, we are talking about the stations of Djanet, M'Zab, and Illizi (**Figures 2**–**4**), these stations were abused in 2011; 2012 and 2019 respectively. The largest is that of Ghardaïa, which was built during the period 2008–2012

### *Promising Techniques for Wastewater Treatment and Water Quality Assessment*


### **Table 2.**

*Coordinates of natural lagoon stations.*

**Figure 2.** *Ghardaia wastewater treatment plant.*

**Figure 3.** *Illizi wastewater treatment plant.*

**Figure 4.** *Djanet wastewater treatment plant.*

*Reliability and Problems of Wastewater Treatment Processes in the Algerian Sahara DOI: http://dx.doi.org/10.5772/intechopen.96113*

**Figure 5.** *Mechanisms involved in natural lagoon basins [10].*

by the companies AMENHYD SPA as a production company and AQUATECH-AXOR (Canada): a control and monitoring design office; it was commissioned in November 2012 for a maximum capacity of 46,400 m3 /d, corresponding to 331,700 eq/inhab. by 2030. The station spread over 79 ha, has 16 basins divided into 02 floors finalized by 10 drying beds [9].

The purification is ensured through to a long residence time, in several watertight basins arranged in series. The most commonly encountered number of basins is 3. However, using a configuration with 4 or even 6 basins allows more thorough disinfection. The basic mechanism on which natural lagooning is based is photosynthesis. The upper water section of the basins is exposed to light. This allows the existence of algae which produce the oxygen necessary for the development and maintenance of aerobic bacteria (**Figure 5**). These bacteria are responsible for the degradation of organic matter [10].

The carbon dioxide formed by bacteria, as well as the mineral salts contained in wastewater, allow algae to multiply. There is thus a proliferation of two interdependent populations: bacteria and planktonic algae, also called "microphytes". This cycle is self-sustaining as long as the system receives solar energy and organic matter.

At the bottom of the pool, where light does not penetrate, it is anaerobic bacteria which degrade the sediments resulting from the settling of organic matter. A release of carbon dioxide and methane occurs at this level [10].

This type of process was chosen in these regions for various reasons, such as the low energy use or almost non-existent, especially if the difference in level is favorable; good elimination of nutrients phosphorus, nitrogen and pathogenic germs especially in summer when the high temperature. It adapts well to strong variations in hydraulic head which can favor the presence of the water table close to the surface. We also noted in these stations an absence of noise pollution with stable sludge and good integration into the landscape.

On the other hand; these stations encountered several obstacles during the design and operation, such as the large footprint (10 to 15 m2 /pe); investment cost very dependent on the nature of the subsoil. In the Saharan regions, where the terrain is sandy and unstable, this type of process is not recommended; which remains a contradiction with the location of these stations.

For the technical aspect, we noted that the purification performance is lower than intensive processes on organic matter. However, the release of organic matter takes place in the form of algae, which is less harmful than dissolved organic matter for the oxygenation of the environment downstream; and the control of the biological balance and the purification process remains limited. With a variable quality of

**Figure 6.** *Ouargla wastewater treatment plant.*

#### **Figure 7.** *Tamanrasset wastewater treatment plant.*

**Figure 8.** *Sidi khouild wastewater treatment plant.*

**Figure 9.** *Kouinin wastewater treatment plant.*

#### *Reliability and Problems of Wastewater Treatment Processes in the Algerian Sahara DOI: http://dx.doi.org/10.5772/intechopen.96113*


#### **Table 3.**

*Coordinates of aerated lagoon stations.*


#### **Table 4.**

*Characteristics of aerated lagoon stations.*

**Figure 10.**

*Principle of aerated lagooning [12].*

discharge depending on the season, especially in summer when the temperature is very high, which causes very strong evaporation, which influences the concentration of water in the lagoons and the formation of algae due to the long insolation period.

### **3.2 Aerated lagoon**

In the Algerian Sahara, the aerated lagoon system is used frequently; we have identified four stations (**Figures 6**–**9**) among ten (Ouargla, Sidi Khouiled, Kouinin, Tamanrasset), where the largest nominal capacity is that of Kouinin with a flow of 33,251 m3 /d (**Tables 3** and **4**).

In this type of process, oxygenation is provided mechanically by a surface aerator or air blowing (**Figure 10**). This principle differs from activated sludge only by the absence of a sludge recycling system or continuous sludge extraction. The energy consumption of the two sectors is, at equivalent capacity, comparable (1.8 to 2 kW/kg BOD5 eliminated) [11].

The Algerian authorities often orient themselves towards this system since this system is very tolerant to variations in significant hydraulic and organic load as in the case of the regions mentioned above as well as their tolerance to effluents imbalanced in nutrients.

**Figure 11.** *Principle of wastewater gardens system [12].*

According to our investigations, in addition to the average quality of rejection on all parameters and noise pollution, the station managers have some problems such as high energy consumption, and the presence of electromechanical equipment requiring maintenance by a specialized agent; which sometimes takes a considerable amount of time with a non-operating station.

Among the most apparent problems in the region is the inflow of water from the water table and the excess parasitic irrigation in the sewerage network which can influence the performance of the station in two due to the high salinity of the water who can wait 13000 μ/cm, and the rapid change in raw sewage concentration.

#### **3.3 Wastewater gardens system (WWG)**

The Wastewater Gardens unit is an eco-technology that uses ecologically based wastewater treatment principles [11].

Is a waterproofed basin, filled with gravel and plants whose roots are tolerant of water saturated conditions (**Figure 11**). There may be one or more compartments, depending on the size of the system and the area available for construction. The efficiency of a Waste Water Gardens pond is based on the time the wastewater residences within it before they flow into the drain area.

We have identified two stations in our region using this system.

#### *3.3.1 Horizontal flow planted filters*

The Temacine pilot station (**Figure 12**) is located in the city of Temacine next to old Ksar (**Table 5**), it was mainly created with the aim of treating 15 m3 /d of wastewater by the production of 100 people and at a reasonable rate. of 150 l/inhabitant/day. The surface of the WWG basin is 400 m2, and the total volume is 260 m3 . The water level in the basin is 0.5 m, covered by a layer of gravel ranging from 10 to 15 cm (gravel is a physical filter). The WWG basin is also filled with plants that can live in an environment saturated with wastewater (plants collect their nutrients and water through their roots).

This system offers low energy consumption; no need for advanced qualification for maintenance; and good reaction to load variations. On the other hand; this system has not been developed in the region because of their strong footprint, including the surrounding area, this is of the order of 10 m<sup>2</sup> /pe (equivalent to the footprint of a natural lagoon).

*Reliability and Problems of Wastewater Treatment Processes in the Algerian Sahara DOI: http://dx.doi.org/10.5772/intechopen.96113*

**Figure 12.**

*Temacine wastewater treatment plant.*


**Table 5.**

*Coordinates of horizontal flow planted filters stations.*
