*2.2.1.2 Quantitative filtration tests*

Once the best process is chosen, the operating conditions must be optimized. In fact, the best conditions give the maximum of permeate quantity with the least energy (low pressure).

The optimizing of operating conditions is carried out on a semi-industrial "Kerasep" pilot (**Figure 3**). The membranes modules of this system have a nominal surface area of 800 cm2 and 865 mm of length (**Table 1**). In this pilot, all operating parameters are controlled (transmembrane pressure, circulation speed and temperature). Thus, a 50 L of effluent is filtered through membrane module at fixed

#### **Figure 1.**

*Experimental design of tested processes.*

#### **Figure 2.**

*Experimental small scale pilot. (1) effluent thank; (2) volumetric pump with adjustable frequency; (3) control block; (4) inlet pressure gauge; (5) membrane module; (6) outlet pressure gauge; (7) pressure valve adjustment; (8) permeate.*

condition. This operation is repeated many times until reaching the best operating condition. Indeed, this optimization goes through two stages:

• The search for optimal conditions by varying the circulation speed (U) and the transmembrane pressure (TMP). For a given circulation speed (U), the PTM is varied and the permeate flow is measured. The plotting of the permeate flow

*Tertiary Treatment for Safely Treated Wastewater Reuse DOI: http://dx.doi.org/10.5772/intechopen.94872*


**Table 1.**

*Specification of the used membranes.*

curves as a function of circulation speeds and transmembrane pressures makes it possible to choose the best operating conditions.

• Monitoring the evolution of the permeate flow and the volume reduction factor (VRF) as a function of time, makes it possible to identify the nature and state of the membrane clogging.

The VRF is calculated as follows: Vi Vp Vp. −

with Vi: initial volume of the effluent Vp: permeate volume

## *2.2.2 Membranes characteristics and cleaning procedure*

The tubular membranes used are of the mineral type made of monolithic ceramic. They are consisted of an aluminum oxide support and a titanium oxide filtration layer. These characteristics facilitate effective cleaning with acidic or alkali solutions. The specifications of the different membranes used are shown in the **Table 1**.

The membrane and module cleaning protocol is most often provided by the manufacturer. However, this protocol has been modified to making it adapted to the nature of the effluent treated in this work. **Table 2** summarizes the adapted procedure.

### **2.3 Characterization of TWW**

Treated effluents were sampled at the outlet of the Mahres wastewater treatment plant at different times and conserved at −4°C before characterization. Effluent samples were analyzed for pH and electrical conductivity using a pH meter [27] (AFNOR standard method N° NF T 90–008, see AFNOR, 1997) and a conductimeter (AFNOR N° NF EN 27888) respectively. Chemical oxygen demand (COD), suspended solids (SS), biochemical oxygen demand (BOD) and total phosphorus were measured according to standard methods (AFNOR N° NF T 90–018, NF EN 872, NF T 90–103, NF EN 1189). Cations and anions were measured using ion chromatography and trace metals by using Furnace Atomic Absorption

Spectrometry after aqua regia acid digestion (AFNOR N°NF EN ISO 15587-1). Carbonates and bicarbonates were estimated by titration with HCl of an aliquot of the effluent samples (AFNOR N° NF EN ISO 9963-2). Turbidity was determined at 860 nm by using a spectrophotometer DR/4000 U. The apparent color was determined by transmittance between 400 and 700 nm with the same

#### **Figure 3.**

*Experimental semi industrial pilot. (1) effluent thank; (2) volumetric pump with adjustable frequency; (3) flowmeter; (4) exchanger; (5) purge; (6) permeate; (7) membrane module; (8) Retentate.*


#### **Table 2.**

*Membranes cleaning procedure.*

spectrophotometer. The count of the total flora is carried out on Plate Count Agar (PCA) medium by inoculation on the surface and incubation at 37° C for 24 hours.

#### **3. Results**

#### **3.1 Treated wastewater quality**

The WWTP of Mahrès mainly receives and treats domestic wastewater. The quality of this water remains generally stable throughout the year except during

### *Tertiary Treatment for Safely Treated Wastewater Reuse DOI: http://dx.doi.org/10.5772/intechopen.94872*

the summer period which corresponds to an increase in the affluent flow. The results obtained show that the temperature and the pH of the water, leaving the station, increase from January to May (**Table 3**). The treated wastewater always remained alkaline with an average pH of 7.5. The mean electrical conductivity (EC) of the effluents reached 4.27 mS.cm−1, which places the TWW in the class of high salinity according to the FAO legislation. The elevated EC values of the studied effluent are mainly explained by the abundance of free ions such as Na<sup>+</sup> , Cl<sup>−</sup> and SO4 2− which exceed the standards (**Table 3**). Turbidity and SS drop after January. The COD and the BOD are slightly elevated compared to the standards of discharges into nature. Moreover, TWW also contain large amounts of nitrate, phosphate and potassium, which are crucial nutrients for plant growth and soil fertility whatever this water is reused for irrigation. However, excepting Cr concentrations, the heavy metal contents are low. Whereas, the values of the total flora are high (**Table 3**).

