Wastewater sampling was conducted a monthly basis, from January 2018 to December 2018, at the slaughterhouse discharge point. Samples were stored in accordance with the general guide for the storage and handling of samples [7] .

Table 1 below represents the physicochemical parameters studied in our research, the analysis methods used, and their sources.

The wastewater samples from the slaughterhouse show a relatively neutral pH, with optimum values between 7.2 and 7.94. When the pH is below 5 or above 8.5 the growth of micro-organisms is directly affected. As a result, the pH is an important factor in interpreting corrosion in the piping of purification facilities. The temperature ranges between 16.8˚C and 29˚C, with an average of 22.9˚C.

It reflects the overall degree of mineralization, informing us about the salinity level. This is a numerical expression of the water’s capacity to conduct an electrical current, measured in millisiemens per centimeter. These findings imply that the waters from the studied slaughterhouse significantly contribute to high levels of conductivity in the water during both wet periods and dry seasons. The values range from 2670 µs/cm to 2710 µs/cm, with an average of 2690 µs/cm. Significantly, the recorded EC (Electrical Conductivity) concentrations have values exceeding the World Health Organization (WHO) standard, which is 500 μS/cm.

Chloride levels are crucial indicators of water quality, reflecting potential contamination and salinity. The consequences of chloride levels in water are significant. High chloride concentrations can have a negative impact on human health and have ecological consequences, affecting those dependent on water resources. They also pose a potential threat to aquatic ecosystems by disrupting the salinity balance, which can harm aquatic organisms, their habitats, and the overall health of ecosystems (Madhav, et al., 2020) [13] . The average levels recorded the slaughterhouse wastewater are 350.5 mg/L, with extreme values (from 298 mg/L as the minimum value to 403 mg/L as the maximum value). These concentrations are higher than those of the Kenitra slaughterhouse (Belghyti et al., 2009) [14] , and exceed the World Health Organization (WHO) discharges standard of 250 mg/L. The wastewater is moderately saline with a predominance of sodium chloride, given that there are salt deposits upstream of the discharges. Additionally, the high chloride concentration results from the fact that drinking water is too concentrated in chloride (Table 2).

Nitrates, like other nitrogen forms, rapidly evolve in the natural environment according to the nitrogen cycle [15] . The presence of nitrogen in wastewater can be either organic or mineral. Organic nitrogen is characterized as a constituent of proteins, polypeptides, amino acids, and urea. Mineral nitrogen, which includes ammonium ( NH 4 + ), nitrites ( NO 2 − ), and nitrates ( NO 3 − ), make up the majority of total nitrogen. The nitrate values recorded in the wastewater discharges vary considerably over the study period. Thus, the nitrate level in the effluents of the municipal slaughterhouse range between 0.88 mg/L and 1.55 mg/L, with an average concentration of 1.21 mg/L, and they are slightly lower than those recorded in the effluents of the Kenitra slaughterhouse. Comparing the average nitrate concentrations in the analyzed wastewater with the quality standard for irrigation water shows that these concentrations are below 50 mg/L, which suggests that these effluents are acceptable for irrigating crops [16] . Whereas the ammonium ion ( NH 4 + ) concentration values range between 8.55 mg/L and 14.25 mg/L, with an average of around 11.5 mg/L (Table 2). These remain slightly lower than those recorded in the wastewater of the Eljadida slaughterhouse and those recorded in the wastewater from the Kenitra slaughterhouse [17] . The AMMONIUM form is not toxic. However, in water with a pH higher than 7.5 a fraction can be transformed into AMMONIA (ammonia gas suspended in water), which is toxic for fish and organisms living in water, even at low concentrations, (The rise in temperature and pH amplifies the phenomenon).

The variations in wastewater alkalinity are closely related to those of the degree of mineralization (electrical conductivity, total hardness, pH), which also provides an indication of the degree of oxidation of organic compounds (in the case of wastewater). The concentration of carbonates ( CO 3 2 − ) and bicarbonates ( HCO 3 − ) in water depends on the CO₂ content as the latter is highly soluble in water [16] (207 times more than oxygen), and its solubility depends on temperature and atmospheric pressure. The CaCO₃ content is slightly high in the analyzed samples, which could be attributed to the wastewater discharges that are less loaded with fermentable organic materials likely be oxidized, resulting in high CO₂ production [17] . CaCO₃ is slightly soluble in water; however, the presence of CO₂ gives water a much greater dissolving power by transforming calcium carbonate into calcium bicarbonate, which is more soluble in water according to the following reaction:

CaCO 3 + CO 2 → Ca ( HCO 3 ) 2 → Ca 2 + + 2 HCO 3 −

For comparison, Massé and Masse [18] , reported average values between (83 and 900 mg/L) in CaCO₃, and very high values between 667 and 1056 mg/L for slaughterhouse effluents in Canada, in two separate studies.

To indirectly assess the total organic load present in wastewater, the following main quality parameters are used: the biochemical oxygen demand (BOD5) is defined by the amount of oxygen consumed by micro-organisms to ensure the biological degradation of organic matter. This measure provides an approximation of the biodegradable organic matter load in an urban discharge, and the chemical oxygen demand (COD), which represents the quantity of oxygen consumed, in mg/L, by chemically oxidizable materials present in effluent. Mineral and organic particles present in the receiver are suspended solids.

In this way, the concentration of BOD levels recorded fluctuate between 162 mg/L (minimum value) and 210 mg/L (maximum value), with an average value of 186 mg/L (Table 2). By examining the surface water quality grid, it can be seen that the quality of wastewater from the Souk el Arbaa city slaughterhouse is extremely poor, exceeding 25 mg/L. The high values of BOD could be explained by the abundance of organic matter (stomach debris) and by the concentration of this effluent by the blood from the municipal slaughterhouse discharges.

Throughout the study period, it was observed that COD values show a non-negligible variation. Indeed, the pollutant load of slaughterhouse wastewater, as measured by its COD, remains one of the most important criteria used in designing wastewater treatment to determine the degree of treatment required. Moreover, the recorded values are 230 mg/L as the minimum value and 330 mg/L as the maximum value, with an average of about 280 mg/L, which are slightly higher than the values found in the wastewater of the Kenitra slaughterhouse. The COD values are lower than those of urban waters in Morocco (500 - 1500 mg/L) [18] . These average values are below 500 mg/L, considered as the direct discharge limit value. Furthermore, these wastewaters are classified as very poor according to the surface water quality standards [19] .

Turbidity serves as an indicator of water clarity, reflecting the presence of suspended particles (TSS), which contribute to the water’s composition through their ion exchange effects or absorption on both trace chemical elements and microorganisms. The turbidity levels in this study were lower than what was recorded by [14] (Belghyti et al., 2009), who analyzed water samples from the Sebou River, where slaughterhouse effluents were discharged. High levels of turbidity can hinder photosynthesis by preventing sunlight penetration into the river, which in turn would lead to a decrease in dissolved oxygen production and a reduction in plant survival. According to the results, it is noted that the wastewater from the slaughterhouse carries the same loads as Moroccan urban wastewaters, which TSS concentrations of range between 250 and 700 mg/L [20] . Moreover, these average TSS values in the analyzed wastewater are higher than the value set by Moroccan standards [16] (Table 3). The found values are lower than those recorded in Kenitra and Eljadida. The degradation reactions―aerobic―of organic matter and more broadly, the biological balance of aquatic environments are influenced by the presence of dissolved oxygen. In wastewater treatment systems, its total disappearance is often accompanied by the emergence of H2S in the air, resulting from the reduction of sulfur compounds present in the effluents, and resulting from the acidic attack on the concrete of the pipes [18] . Based on the recorded values of dissolved oxygen in the wastewater, it can be concluded that these waters are classified from medium quality to very poor [21] .

The BOD5/COD ratio is often considered to define industrial pollution because it provides very interesting information about the origin of wastewater pollution and the available treatment options. For our research, this ratio presents a high value of approximately 0.664 (Table 4). This generally applies to discharges loaded with organic matter. These wastewaters are quite unstable due to their organic load, meaning they will quickly transform into “digested” forms with odors emitting risk. Indeed, the waters contain mainly organic substances, since it only drains wastewater from the slaughterhouse.

The COD/BOD5 ratio provides an indication of the origin of organic pollution and also allows estimating the biodegradability of an effluent by indicating the characteristics of these wastewaters. If the COD/BOD5 ratio is less than 3, the waters are of a domestic nature [18] . The wastewater from the municipal slaughterhouse presents a COD/BOD5 ratio ranging from 1.419 mg/L to 1.571 mg/L (Table 4), which is consistent with that of urban wastewaters with a domestic predominance. However, since the COD/BOD5 ratio is less than 3, it can be concluded that even though the wastewater from this discharge presents a high organic load, it is easily biodegradable.

The degradation of oxidizable matter by absorbing oxygen does not impact environments, but it can lead to hypoxia or even anoxia of the waters when excessive. The waters are then described as “eutrophied”. It is difficult to directly measure the organic compounds present in water. Therefore, the amount of oxygen required for their degradation is assessed in the laboratory, using either biochemical or strictly chemical methods, in accordance with standardized instructions. According to Table 4, a high BOD5/COD ratio (0.66) is observed for the wastewater of the municipal slaughterhouse, confirming that the wastewater discharged by this outlet contains a high concentration of organic matter. An average TSS/BOD5 ratio of 1.61 confirms the estimation of oxidizable Matter,

which is estimated at about 228.34 mg/L. Furthermore, the ratio between COD and BOD5 is low (1.505), leading to the conclusion that the quantity of organic matter present in the wastewater from this discharge is readily biodegradable, as highlighted by Henze et al. [22] .

The Pearson correlation results for the physic-chemical parameters over d the study period are depicted in the correlation matrix in (Table 5) below. The correlation matrix reveals significant relationships between various water quality parameters. Significantly, temperature exhibits a strong negative correlation with dissolved oxygen (−0.694), suggesting that as temperature increases, dissolved oxygen tends to decrease. This inverse relationship is indicative of potential contamination, affecting the water’s acidity. Moreover, dissolved oxygen (DO) shows a strong positive correlation with Nitrites (0.606), implying that higher Nitrites are associated with increased DO levels, and a strong positive correlation between temperature and electrical conductivity (0.811). However, certain correlations, such as those between Nitrates and NH 4 + (−0.484), indicate complex interactions within the aquatic system.

According to Figure 2 and Figure 3, there is a 1.0 correlation between BOD5 and COD, suggesting a perfect positive correlation. This indicates that, in this specific dataset, BOD5 and COD vary in the same manner.

By the year 2030, the allocation for the city of Souk el Arbaa is 76 L/capita/day. Thus, the volume discharged by the inhabitants is estimated to be 80% of the potable water supply (PWS) allocation.

According to data from Table 6, the wastewater from the collectors of the city of Souk el Arbaa and that of the slaughterhouse produce a pollutant load in BOD5 of approximately 887.74 Kg/day, while that in TSS is about 1431.84 Kg/day

(Table 5). The daily flow amounts to approximately 4772.28 m³/day, with an average hourly rate of 198.86 m³/h, and a peak flow of 332.06 m³/h. The diurnal flow, which corresponds to the 16 consecutive daylight hours during which the station can receive the largest volume of wastewater, is around 298.26 m³/h. The values indicated in Table 6 are similar to those of cities in its category (with a population between 20,000 and 100,000 inhabitants) [23] . This will aid in the future design of a wastewater treatment plant in the city of Souk el Arbaa. Once the degree of organic pollution has been assessed, it can be noted that all the studied parameters (notably BOD5, COD, and TSS) classify the wastewater from the city and the slaughterhouse in the category of medium to high concentrations.