**2. Result and discussion**

Air was injected inside the tank through the air diffuser, and the feed of wastewater to be treated, which was pumped into the tank, activated sludge placed in the experiment tank.

The oxygen transfer rate was recorded through the experiment and the oxygen concentration was measured with an oxygen detector.

Oxygen concentration was measured through the first experiment and recorded with 0.45 PPM at the beginning and 3.2 PPM after 33 minutes as in **Figure 7**.

The temperature of the system raised from 26.7°C at the beginning of the experiment to 27.7°C after 33 minutes as in **Figure 7**.

Oxygen concentration was measured through the second experiment, oxygen concentration was recorded at 3.23 PPM 34 minutes from the beginning and 4.46 PPM after 18 minutes from the beginning of the second experiment as in **Figure 8**.

The temperature of the system raised from 27.8°C at the beginning of the experiment to 28°C after 18 minutes as in **Figure 8**.

Oxygen concentration at the last experiment was recorded as 4.8 PPM after 41 minutes from the beginning of the experiment, concentration of oxygen was recorded at the end of the experiment at 6.01 PPM, Temperature increased from 28 to 28.2°C at this experiment.

*Study of Change Surface Aerator to Submerged Nonporous Aerator in Biological Pond… DOI: http://dx.doi.org/10.5772/intechopen.104860*

**Figure 7.**

*Concentration of oxygen and temperature of liquid with time at 0.5 bar(g) and air flow of 7.5 L.min−1.*

### **Figure 8.**

*Concentration of oxygen and temperature of liquid with time at (0.5–0.65) bar (g) and air flow of 8.7 L.min−1.*

Increasing the temperature can relate to the biological activities of bacteria due to the digesting of wastes in wastewater [20].

The rate of oxygen (air), supplied with an air diffuser in the experiment tank was high compared with the calculated air required by Eq. (2) [6] and as in **Table 1**.

The amount of air supplied was more than that estimated in the third experiment, because the short path of air from the injection point to the surface leads to air bubbles escaping out of the liquid tank, [21], the pressure of injected air increased with the aim to increase the flow rate of air and reach the required concentration of 6.01 PPM.


### **Table 1.**

*Final results and estimated amount of air required.*

### **Figure 9.**

*Concentration of oxygen and temperature of liquid with time at 0.75 bar (g) and air flow of 9.7 L.min−1.*

All three experiments were continuous and pressure increased with the aim to increase the flow rate of air, this was when the oxygen concentration did not increase and stopped increasing and sometimes decreased when the temperature of the liquid increased [22], and this was observed very clearly through the experiments data **(Figures 7, 8** and **9)**.

### **New Aeration System Proposed for Biological Reactor of Waste Water Treatment Complex in DR:**

The biological reactor in wastewater treatment complex in DR will be changed from mechanical aeration to air direct injection by nonporous diffusers, air distributor applied at 1cubic meter capacity can be applied at the biological reactor.

The power duty and oxygen transfer rate (air flow rate) required can be estimated as in Eq. (2) [6]. power duty with 10% over design is 200 hp. at (BOD 250 PPM as a design condition), the amount of air required to realize 6 PPM oxygen concentration is not less than 587 kg.h−1 (454 Nm3 .h−1) at a liquid flow rate of 500 m3 .h−1 as a charge to the biological reactor.

The total number of nonporous diffusers required to cover the required amount of air is 604 with a diffuser capacity of 0.9735 kg.h−1 (12.532 NL.min−1), which was used in the experiments.

*Study of Change Surface Aerator to Submerged Nonporous Aerator in Biological Pond… DOI: http://dx.doi.org/10.5772/intechopen.104860*

**Figure 10.** *Arrangement of air diffusers in biological pool.*

The number of diffusers will be used more than that calculated according to the capacity of the diffuser, in terms of providing the required amount of oxygen required.

The number of diffusers will be 1024, distributed for two sides of the biological reactor of dimensions 16,000 X 32,000 mm, the distance between each diffuser and the other is 1000 mm, and the distance from the wall is 500 mm as in **Figure 10**.

Installing excess numbers of diffusers can provide well mixing and at the same time avoid the dead zones in the biological reactor; dead zones in the biological reactor activate anaerobic bacteria and in consequence reduce the efficiency of waste digesting [22].

The consumption power through the new proposed system of fine bubbles (diffuser nonporous type) will be reduced from 241.4 hp. in surface aeration to 200 hp, and this is due to the reduction in the amount of air required in the aeration process.
