Physico-Chemical Characterization of an Urban Wastewater Effluent and its Impact on the Receiving Environment: Oued Nfifikh (Morocco)

Oued Nfifikh is among the least studied Moroccan rivers. Thus, the primary aim of this study was to shed light on the quality of this undervalued stream. Its downstream part is affected by one of the most crucial environmental issues. It receives the discharges of wastewater evacuated precariously without prior treatment, which might lead to the degradation of the overall ecological status of this fluvial hydrosystem. This research work aimed to study the physicochemical water quality downstream the river Nfifikh through a monthly monitoring of the physicochemical parameters’ indicator of pollution, from August 2018 to July 2019. The results obtained show that the stream is exposed to high pollution which is mainly organic. Consequently, the wastewater represents a major cause of water quality degradation of this receiving environment: ecological and health impacts are therefore to be expected.


INTRODUCTION
The sustainability of sufficient water resources has become one of the major concerns of our century. In fact, it represents an obstacle towards the satisfaction of the growing population's needs in a global context marked by climate change and its hydrological consequences. This problem is not limited to the amount of water resources, it also impacts their quality. For instance, continental aquatic ecosystems are under an increasing stress from a wide array of anthropogenic impacts, which are direct results of the socio-economic growth and climate change. The degradation of the overall ecological status of hydrosystems and the deterioration of their water quality are the main consequences, thereby compromising the various uses of water.
At the national level, numerous studies have reported the various effects of the industrial and urban discharges on the quality of water resources as well as the impact of the pollution on the continental aquatic ecosystems. Amongst those studies, the work of Bzioui  If several streams attracted much interest among the community of scientists as shown previously, no specific study regarding the water quality of Oued Nfifikh had been published according to the available documentation up to date, except the work of Tazi et al. in 2004, which focused on the impact of climate on the estuarian of Oued Nfifikh. This Oued was only briefly mentioned in some environmental impact assessment or water quality reports. For instance, the study published in 2015 by the Hydraulic Basin Agency of Bouregreg and Chaouia (ABHBC) is only giving it as one example amongst many water streams present in the Chaouia watershed-coastal areas, in order to support their point regarding the existence of pollution sources contributing on the degradation of water quality.
Thus, this work is part of a pioneering study of Oued Nfifikh water quality, a stream that has a major socio-economic importance for the inhabitants of its basin (irrigation, livestock watering, potable water, industry …). The current study is focused on its downstream part which is affected by different sources of pollution. It receives liquid effluents, which are discharged in a precarious manner and without prior treatment, from some of the riparian agglomerations of BenYakhlef (Louisia) municipality.

STUDY AREA DESCRIPTION
Due to the maritime influences, the study area is part of the semi-arid bioclimatic belt, where the summers are dry and hot and the winters are mild and humid (Communal monography, 2010; General monography, 2015). Moreover, the area records an average annual rainfall of around 400 mm and a temperature varying between 7°C and 27°C. Peaks can reach up to 40°C during the year, but their frequency remains exceptional (Akil, 1990;General monography, 2015).
Elongated in its general shape, Oued Nfifikh extends over an area of about 607 km 2 . The river takes its source in the region of Ziaida at Benslimane and pours into the Atlantic Ocean at the city of Mohammedia. The stream is not controlled by any upstream dam and the flow characteristics of

MATERIALS AND METHODS
The sampling of surface water was carried out between 9 a.m. and 12 p.m. following the methodology dictated by NF EN ISO 5667-1 [21] using polyethylene bottles, and all the testing equipment used for the in-situ measurements were calibrated in advance according to the manufacturer's instruction. Temperature, pH, electrical conductivity and dissolved oxygen were measured using a portable multi-parameter (pHenomenal MU 6100 H), while turbidity was measured using a handheld infrared turbidity meter (Eutech TN-100). The samples were then stored at 4°C in the dark during transport to the laboratory and analyzed within the same standard cited above.
The analyses of TSS, BOD 5 , COD, nitrogenous compounds and phosphorus compounds were performed according to the methods recommended by the AFNOR standards ( Table 1). All these elements make it possible to evaluate the degree of pollution of Oued Nfi fi kh water and to assess its self-purifi cation capacity.

Temperature
In general, the recorded temperature values correspond to a seasonal variation. The lowest value (7.5°C) is recorded during the wet season and the highest (31.2°C) is observed during the dry season (Fig. 2). This variation demonstrates  the relationship between the temperature of water and air. The heat exchange between the two matrices establishes this relationship. This exchange is also strongly favored by the shallow depth of the water at the sampling sites. The average temperature of surface water at (S 1 ) is 19.4°C and at (S 2 and S 3 ) is 20.4°C. As for the waters of the discharge point (DP), the average temperature is 19.9°C.
In order to assess the overall quality of Oued Nfi fi kh waters, the results obtained were compared to the Moroccan standards in the fi eld of water. Thus, on the spatial scale ranging from (S 1 ) to (S 2 and S 3 ) and according to the surface water quality grid, the water from those sites is qualifi ed as good to excellent quality (SEEE, 2007). Regarding the wastewater (DP), the recorded results do not exceed the discharge limit value applicable to direct discharges into surface water (MDCEau, 2014 b).

pH (hydrogen potential)
The pH values obtained for all the sites during the study period vary between 7.5 and 8.3 (Fig. 3). On the basis of these results, the w aters studied are slightly neutral to basic. Overall, the average pH values vary between 7.7 and 7.8 and the average diff erences in hydrogen potential between the dry season and the wet season are generally low. This shows the absence of any seasonal action on the pH, it varies independently of the seasons.
The pH values of the water from the sites S 1 , S 2 and S 3 are in concordance with the Moroccan standards which qualify these waters as of excellent quality (SEEE, 2007). According to the Moroccan standards, the general limit values for discharge into surface water vary between 5.5-9.5, and the average value of this parameter for wastewater from site (DP) is 7.8. Therefore, these waters have no impact on water quality downstream from Oued Nfi fi kh.

Electrical conductivity
The values of the electrical conductivity (EC) varied between 1.46 mS/cm and 4.84 mS/cm. Overall, the average conductivity values vary between 3.01 mS/cm and 4.06 mS/cm for surface water (S 1 , S 2 and S 3 ) and an average value of 2.64 mS/ cm for wastewater from the discharge point (DP).
The results obtained provide the information on the increase in water conductivity in the dry and wet season; this increase is much greater during the rainy period. The high values observed at the sites (S 1 , S 2 and S 3 ) are most likely related to the Triassic outcrops crossed by the water along Oued Nfi fi kh. Gartet et al. (2001) and Nahli et al. (2015) found high conductivity values in Oued Lebéne and Oued Hassar, respectively, which are also related to the Triassic outcrops crossed by the water.
However, similarly to pH, the variations in electrical conductivity are associated with the variations in the dissolved carbon dioxide content, which are linked to the decomposition of organic matter of animal or human origin (Rodier et al., 2009; ADEME, 2013). According to the Francophone network on water and sanitation (Réfea, 2001), the contrasts of the EC make it possible to highlight pollution, and areas of mixing or infi ltration. As a matter of fact, the high values of the conductivity obtained translate continuous external inputs of mineral salts along the water stream.
For instance, the infl uence that the agricultural and livestock activities adopted at the site  As to the other evaluated sites (S 2 and S 3 ), the high conductivity values might be associated to direct discharges of wastewater (grey and black water) and also to domestic waste discharged into the watercourse. By comparing the results obtained with the Moroccan pollution standards and surface water quality grid, the conductivity values of the water from the sites (S 1 , S 2 et S 3 ) are within the range of class 5 of the standard (SEEE, 2007). Thus, they are qualifi ed as of very poor quality.
The average value of conductivity for the discharge point water (DP) does not exceed the value proposed by the standard (MDCEau, 2014 b). However, higher values exceeding the standard can occasionally be recorded during the winter season which is characterized by signifi cant rainfall inputs and by the releases of masses of highly mineralized wastewater from Ben Yakhlef-Louisia's agglomerations.

Turbidity and TSS
The average turbidity values are 45.15 NTU; 163.55 NTU; 99.91 NTU and 39.07 NTU for the sites S 1 , S 2 , S 3 and DP, respectively.
However, variations in the measurements were observed either temporally, represented by the increase in turbidity values during the rainy period (Fig. 5), or spatially along the watercourse. By interpreting the results spatially, the site (S 1 ) represents an average value which according to Rodier et al. (2009) and in the absence of a Moroccan standard, it is within the normal range of turbidity of surface water, while the average values found in sites S 2 and S 3 are very high from the normal range of turbidity given by Rodier et al. (2009).
According to LeChevalier et al. (1981) high measurements or fl uctuations in measurements may indicate a water quality problem. In fact, the highest turbidity values are observed at site (S 2 ). This site is mainly supplied by raw wastewater from the discharge point. In addition, the highaltitude position of the sewage outfall relative to the site (S 2 ), causes the wastewater discharged to arrive in cascade, thus, increasing the turbidity of the water and contributing to the degradation of the environment.
By comparing the turbidity values obtained between all the sites, it was found that itself, the water coming from the discharge point does not have a high turbidity. Its waters are generally gray water from domestic activities and also from the traditional Moroccan Hammam baths installed in the study area (Ben Yakhlef -Louisia). The highest turbidity values of the waters at (S 2 ) were only recorded during the rainy period, when combined gray and black water releases were observed.
However, in Morocco, there are no fi xed limit values for direct effl uent of discharges into the environment or a standard to assess the quality of surface water for turbidity. According to Rodier et al. (2009), above 200 NTU the parameter is no longer relevant. It is then necessary to use the TSS parameter, which in this context is the most faithful parameter to represent and quantify the particulate matter.
The suspended solids content obtained for the water at the studied sites vary between 7 and 414 mg/l (Fig. 6). According to DeVillers et al. The observed increase of TSS is consistent with the results obtained for turbidity (Fig. 5). In fact, the values of suspended solids obtained in the rainy period are high compared to those in the dry period, except for the site (S 2 ) during the December sampling period. The low values of TSS observed during December in the site (S 2 ) would be due to the high foam loadings of the effl uents By comparing the results shown in fi gure 6 to the Moroccan standards, the waters from the site (DP) are per with wastewater discharge standards set at 150 mg/l (MDCEau, 2014 b). Paradoxically and according to the Moroccan standard of surface water quality (SEEE, 2007), the waters from the sites (S 2 and S 3 ) are within the range of class 2 and 3 of the standards, thus qualifying them as medium to good quality, regardless of the very apparent visual degradation of the landscape. As for the waters from the site (S 1 ), the standards allow classifying them as of good quality.

COD (Chemical Oxygen Demand) and BOD 5 (Biological Oxygen Demand)
For the current study, the values recorded for these two parameters are shown in fi gures 7 and 8: According to the results obtained (Fig. 7), the COD values range from 28.8 mg O 2 /l to 672 mg O 2 /l. In general, the average value of the chemical oxygen demand in the waters of the site (S 1 ) is 69.6 mg O 2 /l. The COD peaks observed in December and January, could be the result of the rain runoff causing the leaching of organic and mineral fertilizers, as well as, the transport of animals' and plants' debris from lands adjoining the sampling site (S 1 ) towards the watercourse.
The comparison of the COD values obtained during this study with the Moroccan surface water quality grid (SEEE, 2007), reveals that the assessed waters from site (S 1 ) are classifi ed as of poor quality.
Afterwards, the average values of the chemical oxygen demand in the waters of the downstream sites (S 2 and S 3 ) are 253.9 mg O 2 /l and 175.2 mg O 2 /l respectively. For these sites, all the COD values obtained during the study period were very high. The results were then compared to the Moroccan quality grid (SEEE, 2007) and revealed the water's quality at the sites (S 2 and S 3 ) to be classifi ed as very poor.
Considering that the two sites are mainly supplied by the water from the discharge point, they are strongly impacted by all forms of contaminants emanating from this wastewater. As a At the discharge point, the BOD showed a minimum value of 70 mg O 2 /l and a maximum value of 440 mg O 2 /l and on average a value of 208 mg O 2 /l. Thereby, the majority of BOD values registered during this study concerning the wastewater were found to be beyond the permissible limit (MDCEau, 2014 b). According to DeVillers et al. (2005), the higher the BOD, the higher the amount of organic matter present in a sample. As a matter of fact, the water coming from the site (DP) is mostly a domestic wastewater that is occasionally mixed with blackwater, and also the water that is highly contaminated by solid and dissolved matter brought by urban runoff discharges. To sum up, the high values of COD and BOD 5 indicate a signifi cant input of organic substances in Oued Nfi fi kh (downstream). Consequently, the discharge of the effl uent coming from DP could constitute a danger for the receiving environment.
While taking into consideration what was deduced previously and according to Rodier et al. (2009), a characterization of the effl uent by the determination of the relationship between the organic pollution parameters was performed. However, the COD/BOD 5 ratio of the wastewater varies from 1.1 to 5.4 and the average value of the COD/BOD 5 ratio is 2.4 (Table 2). Consequently, the wastewater evaluated in the present study can be regarded to have a domestic origin and is biodegradable, which could require a biological treatment before being discharged into the receiving environment, in a way to avoid the accumulation of organic load in a restrained space.

Dissolved oxygen
Throughout the study period, the evolution of dissolved oxygen (DO) amount in the water of Oued Nfi fi kh exhibits variations going from upstream to downstream (Fig. 9). The levels cover a wide range, with a minimum value of 0.4 mg/l and a maximum value of 14.2 mg/l. Starting by the upstream site (S 1 ), the results show that the oxygen concentrations increase during the wet period due to the decrease in temperature and vice versa. As it happens, Hébert and Légaré (2000) demonstrated that cold water contains more dissolved oxygen than hot water. This  There is a signifi cant drop of the DO content in December at all downstream sites, including the wastewater discharge, which coincides with the increase of the BOD in the same month. In fact, the higher the BOD, the more important the oxygen is depleted in the water. Consequently, the oxygen depletion could be followed by anaerobic conditions, which would result in reduced diversity and distribution of aquatic fauna. Further, the presence of organic matter will promote the accumulation of toxic compounds in water bodies (DeVillers et al., 2005; SIAQUEBA, 2018). The average DO concentration values are respectively 5 mg/l and 6.2 mg/l for the sites (S 2 and S 3 ), thus qualifying these water quality statuses as good (SEEE, 2007).
The lowest values of DO content observed for the wastewater with an average value of 3 mg/l. The forms evaluated in this study are the ammonium ions (Fig. 10) and total phosphorus (Fig.  11). However, measurement of diff erent forms of nutrient variations is strongly needed in order to maintain the water quality of Oued Nfi fi kh. The average concentrations of total phosphorus follow an increasing gradient from upstream to downstream. The same results were found for the wastewaters discharged at the level of Oued Hassar (Fouad et al., 2014;Nahli et al., 2015). The concentrations injected by the discharge from the site (DP) remain constant or even tend to increase. It is perhaps the dilution by rainwater which made it possible to lower these levels (January 2019).
Phosphorus is not toxic to humans or wildlife. However, in order to slow the proliferation of algae in the environment (eutrophication) its content must be controlled (CEAEQ, 2011). By reference to the water resources quality grid, the average total phosphorus content classifies the water from the site upstream (S 1 = 0.16 mg/l) of the Oued Nfifikh in the good quality range (SEEE, 2007). In turn, the average total phosphorus contents in the water of the sites downstream of the watercourse (S 2 = 2.97 mg/l; S 3 = 1.22 mg/l), classify the water as of poor quality (SEEE, 2007). However, no standards are given by the Moroccan law for total phosphorus in domestic wastewater.

CONCLUSIONS
The aim of this work was to assess the physicochemical quality of the Oued Nfifikh and to determine the impacts of urban effluents discharged directly into the watercourse without prior treatment. As limits encountered in this characterization, the absence of Moroccan standards and limit values for some physicochemical parameters, whether for surface water or wastewater discharges, were cited. On the basis of the available water assessment standards, the urban wastewater effluent does not exceed the discharges limits concerning temperature, pH, electrical conductivity, turbidity and TSS. When it comes to the physicochemical parameters of organic pollution, such as, the COD and the BOD 5 , the results obtained are above the standards. Consequently, the discharge of this raw sewage into the downstream part of Oued Nfifikh can have harmful impacts on the ecological status of this ecosystem, as well as on the riparian population.
The variations in surface water flow have a significant impact on water quality. As a matter of fact, when flow rates decrease while discharges remain constant, pollutants become concentrated, and the agriculture and industrial activities (Rodier et al., 2009;Popa et al., 2012;SIAQUEBA, 2018).
Coinciding with the releases of masses of domestic wastewater combined with black water containing urine and faeces, noticeable increases in the NH 4 + concentrations were observed from November, with high peaks in December at downstream sites, including site (DP). Thus, supporting the findings of (Rodier et al., 2009;Popa et al., 2012;SIAQUEBA, 2018). Furthermore, it also demonstrates that the ammonium is the main chemical indicator of direct organic pollution.
The ammonium values recorded in January at the downstream sites are much lower than those found during the months when the releases of masses of grey and black water were observed; this decrease is probably due to dilution by rainwater. The authors Derwich et al. To summarize, the ammonium contents are unsatisfactory in the waters downstream of the Oued Nfikhkh, the overall quality status of these sites is poor to very poor (SEEE, 2007). In contrast, for the upstream site (S 1 ), its overall quality status is excellent (SEEE, 2007). Ammoniacal nitrogen is a toxic by-product for aquatic fauna (SIAQUEBA, 2018). However, no discharge limit value or a Moroccan standard exists in this respect.

Total phosphorus
The concentrations of total phosphorus in the waters analyzed vary between 0.07 mg/l recorded in (S 1 ) and 15 mg/l recorded in (DP) (Fig. 11).
Generally, the presence of this element in natural waters comes from the leaching of certain minerals and the decomposition of organic matter, along with wastewater discharge from anthropogenic Figure 11. Spatio-temporal variation of total phosphorus water quality decreases. Furthermore, during thunderstorms, the flow rates of the stream increase significantly, thus altering the quality. The high-water pressure evacuates the deposits of sludge and dirt accumulated in the pipes. Consequently, the runoff water loaded with the pollutants from leaching land and the road network affects the transparency and the overall quality of the receiving environment. Thus, and according to the surface water quality grid, the water quality of the downstream part of Oued Nfifikh is qualified as poor to very poor, contrary to the upstream part where the average assessed quality is good to excellent.
In the light of these results, it can be recommended that the concerned authorities set up urban wastewater treatment plants and connect these discharges to the station in order to limit or stop the impact of these effluents on the Oued Nfifikh.