3.1. Results
3.1.1. Physico-chemical analyzes
Table 2
Limits of the physicochemical parameters of industrial liquid effluent discharges from the SCS
Parameters
|
Limit
|
Physicochemical analysis results
|
Minimum value
|
Maximum value
|
Mean ± SD
|
pH
|
8,5–6,5 [9]
|
7.4
|
13.2
|
10.53\(_{ - }^{+}\)2.67
|
Temperature ° C
|
30 [9]
|
22.9
|
24.8
|
23.61\(_{ - }^{+}\)0.86
|
Turbidity (NTU)
|
|
2
|
520
|
201.86\(_{ - }^{+}\)201.83
|
Electrical cond (µS / cm)
|
|
320
|
19980
|
9490.00\(_{ - }^{+}\)9054.89
|
TDS (mg L-1)
|
0.2 [6]
|
130
|
13430
|
5362.86\(_{ - }^{+}\)4597.07
|
COD (mg L-1)
|
120 [9]
|
125.32
|
959
|
414.85\(_{ - }^{+}\)259.216
|
BOD5 (mg L-1)
|
35 [9]
|
23
|
99
|
48.43\(_{ - }^{+}\)26.19
|
COD / BOD5
|
-
|
3.79
|
19.67
|
9.42\(_{ - }^{+}\)5.22
|
BOD5 / COD
|
-
|
0.0508
|
0.26
|
0.14\(_{ - }^{+}\)0.07
|
Calcium (mg L-1)
|
-
|
2.4
|
26.4
|
7.09\(_{ - }^{+}\)7.98
|
Magnesium (mg L-1)
|
-
|
3.4
|
10.21
|
4.93\(_{ - }^{+}\)2.23
|
Potassium (mg L-1)
|
-
|
13.31
|
26.53
|
22.02\(_{ - }^{+}\)4.75
|
Sodium (mg L-1)
|
-
|
3.8
|
452.06
|
167.46\(_{ - }^{+}\)180.94
|
Bicarbonates (mg L-1)
|
-
|
2135
|
75640
|
24948.13\(_{ - }^{+}\)31917.52
|
Carbonate (mg L-1)
|
-
|
6
|
13134
|
2250.00\(_{ - }^{+}\)4511.40
|
Nitric nitrogen (mg L-1)
|
-
|
1.12
|
4814.32
|
1137.04\(_{ - }^{+}\)1849.77
|
Nitrate (mg L-1)
|
50 [6]
|
4.96
|
21327.44
|
5037.09\(_{ - }^{+}\)8194.50
|
Ammoniacal nitrogen (mg L-1)
|
-
|
1.12
|
4.48
|
2.56\(_{ - }^{+}\)1.15
|
Ammonium (mg L-1)
|
-
|
3.7
|
14.78
|
8.45\(_{ - }^{+}\)3.81
|
Nitrite (mg L-1)
|
3 [6]
|
3,67
|
15782,3
|
3727.44\(_{ - }^{+}\)6063.93
|
Chlorine (mg L-1)
|
5 [6]
|
39.05
|
223.65
|
112.08\(_{ - }^{+}\)62.79
|
Sulphate mg L-1 (mg L-1)
|
1000 \(\sim\)1200 [6]
|
1049.6
|
9725.2
|
5046.51\(_{ - }^{+}\)3368.62
|
Sulfur (mg L-1)
|
-
|
346.37
|
3209.32
|
1665.35\(_{ - }^{+}\)1111.65
|
Soluble Phosphorus (mg L-1)
|
10 [9]
|
5.64
|
1700.05
|
1113.11\(_{ - }^{+}\)692.77
|
Aluminum (mg L-1)
|
3 [9]
|
0
|
0.03
|
0.01\(_{ - }^{+}\)0.01
|
Cadmium (mg L-1)
|
0.003[6]
|
0.03
|
0.19
|
0.10\(_{ - }^{+}\)0.05
|
Copper (mg L-1)
|
0,5 [9]
|
0
|
0.04
|
0.01\(_{ - }^{+}\)0.01
|
Chromium (mg L-1)
|
0.7 [6]
|
35.76
|
1381.08
|
717.47\(_{ - }^{+}\)412.30
|
Iron (mg L-1)
|
3 [9]
|
0.28
|
17.82
|
7.13\(_{ - }^{+}\)5.86
|
Lead (mg L-1)
|
0.01[6]
|
0.21
|
2.49
|
0.68\(_{ - }^{+}\)0.75
|
Zinc (mg L-1)
|
3 [9]
|
0.51
|
1.98
|
1.72\(_{ - }^{+}\)1.97
|
Dissolved oxygen (mg L-1)
|
-
|
0.32
|
1.92
|
1.10\(_{ - }^{+}\)0.48
|
3.1.2. Temperature
Water temperature is an important factor as it governs the types of aquatic organisms that inhabit it. Its role being, among other things, to dissolve the gases in water, and to separate the dissolved salts, its measurement is necessary. The temperature of the industrial SCS effluents analyzed indicates a variation from one sample to another (Fig. 3). The highest value was recorded for sample P1 (24.8 ° C) and the minimum value for sample P4 (22.8 ° C), with an average value for all samples analyzed equal to 23.61 ° vs. These values are lower than the limit set by the Algerian standard (Table 2).
3.1.3. Hydrogen potential (pH)
The hydrogen potential of water represents its acidity or alkalinity [10]. The pH of the industrial effluents studied reveals a high value for sample P3 (13.2); and a minimum value for the sample P7 (7.4); with an average value for all the samples analyzed equal to 10.53; that exceeds the range required by national and international regulations.
3.1.4. Electrical conductivity (CE)
The electrical conductivity of water is a direct indicator of its salinity. This is an essential factor to follow when considering the reuse of wastewater for irrigation (agricultural field) [11]. A maximum value of the electrical conductivity of the effluents was recorded for the sample P4 (19980 µS / cm), and a minimum value of 320 µS / cm for the samples P7 (Fig. 6), with an average value for all the samples. samples analyzed equal to 9490 µS / cm (Table 2).
3.1.5. Total Dissolved Solids Content (TDS)
Total Dissolved Solids (TDS) is the term used to describe inorganic salts and small amounts of organic matter present in solution in water. The main constituents are generally cations, calcium, magnesium, sodium, potassium, carbonate, hydrogen carbonate, chloride, sulfate and nitrate anions. [6].
The TDS parameter of the effluents analyzed showed a significant Variation from one sample to another (Fig. 7), where the highest value indicated a TDS content of 13430 mg L-1for sample P2, and a content in the lowest TDS equal to 130 mg L-1 for sample P7. The mean TDS value of all samples analyzed was 5362.86 mg L-1.
3.1.6. Nitrate content (\(NO_{3}^{ - }\))
Nitrate concentrations in surface water can change rapidly due to surface runoff, uptake by phytoplankton and denitrification by bacteria, but groundwater concentrations generally show relatively slow changes [6]. The nitrate content of the SCS effluents varies from 4.96 to 21327.44 mg L-1with an average content of 5037.09 mg L-1 (Fig. 7).
3.1.7. Nitrite content (\(NO_{2}^{ - }\))
Nitrite is considered to be an intermediate ion between nitrate and ammoniacal nitrogen, which explains its low concentration in aquatic environments [12].The nitrite contents were between 4.96 and 21327.44 mg L-1, with an average content of 3727.44 mg L-1 (Table 3; Fig. 9).
3.1.8. Sulphate content (\(SO_{4}^{{ - 2}}\) )
Sulphates occur naturally in many minerals and are used commercially, primarily in the chemical industry. They are released to water in industrial wastes and by atmospheric deposition [6].The sulphate content of the industrial effluents analyzed varied from one sample to another (Fig. 10). The highest content is revealed for sample P3 (9725.2 mg L-1) and a minimum value for sample P7 (79.38 mg L-1), with an average value of all the samples analyzed equal to 1049, 6 mg L-1 (Table 2).
3.1.9. Chemical oxygen demand (COD)
The chemical oxygen demand (COD) is an important parameter for determining the organic load in water. In particular, for the operation of wastewater treatment plants, as well as for the characterization of water quality, this parameter is used worldwide and is one of the many directives relating to water quality. [13].
The COD values of the liquid effluents analyzed showed high concentrations ranging from 125.32 to 959 mg L-1 (Fig. 11), with an average value of 414. mg L-1. These results exceed the recommendations of [9].
3.1.10. Biochemical oxygen demand (BOD5)
The importance of the water oxygenation parameter is very clear since the presence of oxygen modulates the aerobic decomposition reaction of organic matter and more generally affects the biological balance of aquatic environments. The organic pollution values expressed in BOD5 show significant variations from one sample to another (Fig. 12). The recorded BOD5 values vary from 33 mg L-1 (minimum value) to 99 mg L-1 (maximum value) with an average value of 48.43 mg L-1 (Table 2).
3.1.11 Organic pollution assessment
Table 3
variation of organic pollution indicators in the MEWOU river.
samples
|
Organic indicators
|
DO (mg L-1)
|
COD (mg L-1)
|
BOD5 (mg L-1)
|
P1
|
1.92
|
959
|
71
|
P2
|
1.28
|
555.3
|
99
|
P3
|
1.28
|
217.5
|
34
|
P4
|
1.28
|
333.5
|
55
|
P5
|
0.96
|
260.85
|
24
|
P6
|
0.64
|
452.52
|
23
|
P7
|
0.32
|
125.32
|
33
|
Biodegradability provides information on the ability of an effluent to be decomposed or oxidized by microorganisms involved in the biological process of water purification. It is expressed by the coefficient K.
-
Si (K < 1.5): This means that the oxidizable materials are largely made up of highly biodegradable materials.
-
Si (1.5 < K < 2.5): This means that oxidizable materials are moderately biodegradable.
-
Si (2.5 < K < 3): This means that oxidizable materials are not very biodegradable.
-
If K > 3: This indicates that oxidizable materials are not biodegradable. A very high K coefficient implies the presence of elements in the water that prevent bacterial growth, such as, detergents, metal salts, hydrocarbons, phenols, etc. [14].
The industrial effluents studied have a K coefficient which varies from 3.79 to 19.67, which corresponds to that of industrial wastewater having a COD / BOD5 ratio greater than [10]. In addition, the average BOD5 / COD ratio of 0.14 reflects the low biodegradability of the substances contained in these effluents.
3.1.11 Metal concentrations
The values of the metals in the sample stream varied as follows: chromium (35.76-1381.08 mg L-1), zinc (0.51–1.98 mg L-1), lead (0.21–2.49 mg L-1), potassium (13.31–26.53 mg L-1), iron (0.28–17.82 mg L-1), copper (0- 0.04 mg L-1), and cadmium (0.03–0.19 mg L-1); the presence of lead is noted here with values greater than the WHO prescription, ie 0.01 mg L-1 in drinking water. The health risks of an elevated lead concentration include, kidney damage, anemia and brain edema [6]. Only the values of copper and Zinc were within the admissible standards; other heavy metals was clearly and unequivocally above allowable standards; which allowed us to establish a definite link between the contamination of the Mewou River with heavy metals and the discharge of industrial effluents from the SCS.
3.2 Discussion
Throughout this study, the pollution assessment of industrial effluents from SCS was carried out by analyzing certain physicochemical parameters which characterize these effluents. To this end, the industrial effluents analyzed were characterized by a hydrogen potential (pH) ranging from 7.4 to 13.2 very alkaline, and located beyond the recommended standard [6], [9]. These variations in pH are strongly influenced by the use of palm oil, chemicals such as nitric acid and caustic soda (NaOH) in the operations of soap production, cleaning and disinfection of equipment and facilities. industrial piping circuits, which can influence the pH of the receiving environment [10].
Even more, the effluent temperature varied from 22.9 to 24.8 ° C. This factor plays a very important role in the solubility of salts and gases (in particular O2) in water as well as the determination of the pH and the speed of chemical reactions. Relatively high temperatures act as additional pollution, thus influencing biological cycles [15] by decreasing dissolved oxygen activities, which can cause serious sewage disposal problems [16].These values depend on the use of hot water where the waste water generated by the pre-rinsing and detergent cleaning operations carried out at temperatures up to 55 and 70 ° C, respectively, is too hot, and the regenerative heat exchange in dairy processing [17].
Regarding the sulphate content of the discharged industrial effluents which was between 1049.6 and 9725.2 mg L-1, these values are not tolerable because the WHO suggests that the sulphate content limit should not be higher than 1000 1200 mg L-1[6].
The BOD5 values obtained by the analysis of industrial effluents indicated an average value of 48.43 mg L-1. This result is close to that found by [4] which ranged from 34 to 71 mg L-1, whose high BOD5 values could be explained by the abundance of organic matter. Chemical oxygen demand (COD) is the amount of oxygen consumed by materials present in water that can oxidize under defined operating conditions. Indeed, the measurement corresponds to an estimate of the oxidizable matter present in the water either from its origin (organic or mineral) [18].
The COD values ranged from 125.32 to 959 mg L-1, these values were much too high compared to the limits prescribed by the regulations [9]. These high concentrations were due to the high pollutant loads of organic matter released by the water, since the production of soap involves the use of large quantities of palm oil [19].These results are similar to those reported by [4] 122–958 mg L-1. An industrial effluent with such a high COD can pose serious problems with reducing the oxygen concentration in waterways.
Nitrate concentrations in surface water can change rapidly due to surface runoff, uptake by phytoplankton, and denitrification by bacteria, but groundwater concentrations generally show relatively slow changes. Some groundwater can also be contaminated with nitrates due to the leaching of natural vegetation[6]. The nitrate content ranged from 4.96 to 21327.44 mg L-1; this is probably due to the use of nitric acid as a chemical disinfectant for closed pipeline circuits [20], by the nitrification reaction of the organic nitrogen present in industrial effluents at the basin level . In fact, nitrification is a two-step process in which ammoniacal nitrogen is oxidized to nitrites (NO2-) then to nitrates (NO3-) [21].
Conductivity is a measure of the ability of water to conduct an electric current, therefore an indirect measure of the ionic content of water. Indeed, contrasting measurements on an environment make it possible to highlight the existence of pollution, mixing or infiltration zones [22]. The electrical conductivity of the industrial effluents studied was between 320 and 19,980 μs / cm, which can be explained by the mineral composition of the soap and also by the use of NaOH. These values were higher than those cited by [4], for industrial effluents from the SCS, with turbidity values ranging from 355 to 1859 μs / cm.
Turbidity, which is caused by suspended chemical and biological particles, can have implications for both water safety and aesthetics for the drinking water supply. Turbidity in itself does not always represent a direct risk to public health; however, it can indicate the presence of pathogenic microorganisms and be an effective indicator of hazardous events throughout the water supply system, from abstraction to point of use. For example, high turbidity of water sources can harbor microbial pathogens, which can attach to particles and interfere with disinfection; high turbidity in filtered water may indicate poor elimination of pathogens; And an increase in turbidity in distribution systems may indicate flaking of biofilms and oxide scales or the penetration of contaminants through faults such as power outages [23].
The effluents studied have turbidity values ranging from 2 to 520 NTU, due to the presence of colloidal materials from palm oil used for soap production. These results are close to those found by (Gouafo and Yerima, 2013) which were from 37.4 to 105.5 NTU.
The origin of the accumulation of nitrite may be linked to the inhibition of nitration, or to the incomplete denitrification or even decoupling of the activities of the various reducing enzymes in the denitrification[24]. The values obtained which ranged from 3.67 to 15782.3 mg L-1 were 5,000 times higher than the prescribed standards ([6].
The COD / BOD5 ratio according to [25], [26] makes it possible to deduce whether the wastewater directly discharged into the receiving environment has the characteristics of domestic wastewater. this COD / BOD5 ratio is greater than 3 in our case, which means that the oxidizable materials thus released are not biodegradable. It can be deduced that the low biodegradability of these industrial wastewater from SCS may be associated with the presence of certain inhibitor products, such as palm oil heavily used for soap production, or with a high load of organic matter.