**2. Materials and methods**

The area description, materials and methods, water sample collection and laboratory testing procedures, and method of data analysis are discussed in detail in this chapter.

#### **2.1 Description of the study area**

This study was conducted in Addis Ababa city, particularly in the Little Akaki River basin. The Little Akaki River basin is located in the western part of Addis Ababa and the river flows starting from northwest upstream of the city about 40 km before it reaches the downstream of the Aba Samuel reservoir which is indicated in **Figure 1**.

Little Akaki River is highly contaminated with industry effluents and other different anthropogenic activities. According to the Addis Ababa city administration industry development commission report, more than 667 different sized industries are found in Addis Ababa city and the distributions of manufacturing industries are relatively higher in the Little Akaki River catchment area than in other parts of the city. Most of the streams/tributaries flow from the Northwestern side of the catchment area meets Little Akaki River at Gullele area where different industries are found. Gullele Soap and Marble factories, Awash Winery, National Alcohol and liquor factory are found in Little Akaki River catchment around, Lideta and Mekanisa areas [8]. He also explained that tributaries that come from the Northwestern direction also receive wastes from abattoirs. These different industries release their effluents into the river stream thereby adversely influencing the irrigation water quality.

#### **2.2 Water samples collection and sample preparation**

Three water samples were collected from three purposively selected sampling locations from the upstream, middle, and downstream of Little Akaki River on March 2021. All three water samples are collected on a similar day of local time (at morning 4:00 am). The sampling points are selected by considering the different variation factors along the river stream and collecting representative water samples. The collected

**Figure 1.** *Water sampling location map in little Akaki River.*

river water samples were tested for the analysis of major heavy metals (Pb, Cd, Cr, and Cu), selected ions (Chloride, Na, Ca, and Mg), and other physic-chemical quality parameters of the irrigation water. Samples were collected with 500 mL plastic bottles from the representative flowing river water of medium velocity or free from any turbulence by dipping the bottles in the deeper mid-stream of the river flow to fill it to overflowing. The current weather conditions during sample collection were cleared the sky and sunny condition and the air temperature was ranges between 20 and 28°C.

#### **2.3 Water sample laboratory testing procedures**

Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) was used to analyze the concentration level of heavy metals (Pb, Cd, Cr, Cu) and selected ions (chloride, Na, Ca, and Mg). Temperature (T), EC, pH, and TDS were tested onsite using handheld multiparameter testing equipment. After sample collection, the water samples were acidified with 10 ml of concentrated nitric acid and preserved in the refrigerator. The acidified water samples were digested to dissolve the organic matter and then the digested wastewater samples were analyzed for concentration levels of heavy metals (Pb, Cd, Cr, and Cu) and selected ions (chloride, Na, Ca, and Mg) by ICP-OES with ES ISO 11885:2007 testing standard procedures. In ICP-OES the samples are exposed to a high energy source such as inductively coupled plasma (ICP) at a temperature of 5000 to 10,000 K [13] and the elements emit light of a spectrum being characteristics of each element. The emitted light is collected by a photomultiplier and the intensity of emitted light is directly proportional to the concentration of elements within a sample.

*Concentration Levels of Heavy Metals and Selected Ions in the Irrigation Water: The Case… DOI: http://dx.doi.org/10.5772/intechopen.103677*

Chemical oxygen demand (COD) was tested with American Public Health Association (APHA) 5220-B open reflux testing methods. Chemical oxygen demand (COD) is defined as the amount of a specified oxidant that reacts with the samples under controlled conditions [14]. Organic and inorganic components of samples were subject to oxidation [15]. The dichromate ion (Cr2O7 �2 ) is the specified oxidant in 5220-B testing methods. Wastewater samples were refluxed in a strongly acid solution for a minimum of two hours with a known excess of potassium dichromate (K2Cr2O7). After digestion, the remaining un-reduced K2Cr2O7 is titrated with ferrous ammonium sulfate (FAS) to determine the amount of K2Cr2O7 consumed and the oxidized matter is calculated in terms of oxygen equivalence. The very important apparatus that has been used in COD testing was 150 ml Erlenmeyer flasks with ground-glass 24/ 40 neck and jacket Liebig or equivalent condenser with 24/40 ground glass joint and a hot plate having sufficient power to produce at least 1.4 W/cm<sup>2</sup> of heating surface or equivalence.

COD was can be calculated by Eq. (1)

$$\text{COD as mg O}\_2/\text{L} = \frac{(\text{A} - \text{B}) \ast \text{M} \ast \\$000}{\text{mL sample}} \tag{1}$$

Where:

A = mL FAS used for blank (volume of blank titrant).

B = mL FAS used for sample (volume of sample titrant).

M = molarity of FAS (Molarity of titrant).

8000 = mill equivalent weight of oxygen \* 1000 mL/L.

The alkalinity of the wastewater samples was tested with APHA 2320-B titration methods. The alkalinity of water is explained by its acid-neutralizing capacity [16]. Bicarbonate, carbonate and hydroxide ions are the primary contributors to the alkalinity of water, other constituents such as borate, phosphates, or silicates may also contribute to alkalinity [17]. The alkalinity of the wastewater samples was determined from the volume of standard acid required to titrate a portion to a designated pH value. It was titrated at room temperature with a properly calibrated pH meter or electrically operated titration. The most important apparatus used for the alkalinity test were pH meter and electrode, magnetic stirrer, stir bar, Beaker, titration vessel, Burette, standard sulfuric acid titrant, Pipets volumetric, flasks volumetric.

Procedures: standardized sulfuric acid titrant solutions were prepared as required. The clean burette was filled with the standard acid titrant. Samples temperature is equilibrated with the room's temperature and transferred volumetrically enough samples to 100/150 mL beaker to provide the titrant good volumetric precision. The stir bar is placed in the beaker and the beaker is placed on the magnetic stirrer and inserts the pH electrode into the beaker. The sample pH is measured and the initial burette reading was recorded when sample pH is measured above 8.3. And standard acid titrant is added until the pH endpoint of 4.5 is reached. The endpoint pH value of 4.5 is used for routine measurement of alkalinity in most environmental water and wastewater samples. Then the final burette reading is recorded.

Calculation and reporting of alkalinity were done by Eq. (2).

$$\text{Alkalinity as } (\text{T}\_{\text{Alk}}) \text{mg/LCaCO}\_3 = \frac{\text{B} \ast \text{N} \ast \text{50000}}{\text{mL sample (S)}} \tag{2}$$

Where:

B = mL of sulfuric acid titrant used to reach end point pH.

N = normality of the standardized acid titrant.

S = mL of sample volume.

Finally, total alkalinity is reported as "total alkalinity to endpoint pH mg/L as CaCO3".
