Ndiebene Gandiol is a Senegalese municipality situated approximately 20 kilometers from Saint-Louis city, near the Senegal River estuary. It forms part of the Rao district within the Saint-Louis department and region. Its geographical location places Ndiebene at the historical center of the Gandiol area. Following the implementation of the third act of decentralization in 2014, Ndiebene Gandiol has been designated as the administrative center of the Gandiol municipality. Within the Gandiol municipality, several schools have been examined. However, our study will focus primarily on the Gandiol school, which is considered for the implementation of an ecological wastewater treatment system. The location and size of the establishment are illustrated in Figure 1. The specifics of the selected site are recorded in Table 1. This table highlights the sanitary situation and the infrastructure of the “Ndiebene Gandiol 1” school. The institution accommodates 505 students, aged between 7 and 14 years, distributed across 12 classrooms. Despite this significant number of students, the school has only 4 latrines for student use and one reserved for teachers. The latrines are often non-operational. Moreover, the school lacks any functioning water points. Its sanitation system is deemed non-compliant. Lastly, the toilets are in poor condition, frequently blocked, and thus unusable for students and

teachers most of the time. To design an appropriate wastewater treatment system, it is imperative to carry out sampling to determine the quality of the wastewater.

To determine the wastewater quality of the studied site, a characterization methodology was developed. The goal is to assess the main physicochemical and microbiological characteristics of these waters to propose suitable treatment solutions.

Subsequent to site visits and observations, samples of wastewater were taken for comprehensive analysis. The findings from these analyses are outlined in Table 2. Pertaining to Biochemical Oxygen Demand (BOD5), values of 439 mg/l for the first sample and 293 mg/l for the second were recorded, averaging to 366 mg/l. In terms of Chemical Oxygen Demand (COD), the first sample exhibited a

concentration of 1070 mgO/l and the second 1480 mgO/l, averaging to 1275 mgO/l. For Suspended Solids (SS), concentrations of 254 mg/l for the first sample and 162 mg/l for the second were observed, with an average of 208 mg/l. Nitrate levels were 60 mg NO 3 − /l for the first sample and 40 mg NO 3 − /l for the second, leading to an average of 50 mg NO 3 − /l. Regarding Total Kjeldahl Nitrogen (TKN), observed concentrations were 486.2 mg/l for the first sample and 390.3 mg/l for the second, resulting in an average of 438.25 mg/l. Phosphate concentrations were 344 mg PO 4 3 − /l in the first sample and 420 mg PO 4 3 − /l in the second, with an average of 382 mg PO 4 3 − /l. Lastly, for Fecal Coliforms, the first sample registered a high concentration of 1.03E+06 CFU/100ml, while the second showed a more alarming level of 4.00E+07 CFU/100ml. The average for this parameter across both samples was 20,515,000 CFU/100ml. These results derive directly from the analyses performed at [23] and are crucial for an understanding of the wastewater quality of the site.

The wastewater analysis from the site, presented in Table 2, highlights several significant challenges to address. An average BOD5 of 366 mg/l, which is relatively high, indicates a substantial amount of biodegradable organic matter, usually associated with the presence of organic contaminants. This is corroborated by an average COD of 1275 mgO/l, signaling a significant presence of organic materials. Even more concerning is the high concentration of fecal coliforms, with an average of 20,500,000 CFU/100ml, indicative of major bacterial contamination, posing a serious public health risk. Considering that the BOD measured over 5 days (BOD5) represents only a part of the total BOD (or ultimate BOD), the use of the COD/BOD ratio, or more precisely the COD/BOD5 ratio (to stay with the measured parameters), provides a realistic idea of the biodegradability of an effluent according to [31] . The COD/BOD5 ratio is 3.48, falling between 3 and 5, which classifies the effluents in the category of moderately biodegradable according to the results of [31] . These analyses, conducted by the renowned laboratory [23] , attest to the credibility of the results. The breadth of parameters analyzed provides a comprehensive view of the water quality situation. Several of them, especially the high concentration of fecal coliforms, alert us to the severity of the contamination. These data, coupled with the school’s deficient sanitary infrastructure, are all the more concerning. These findings, when placed within the broader context of sanitation in schools and public health issues, underscore the urgent need for targeted sanitation interventions. Indeed, students and teachers are exposed to considerable health risks, which can impact not only their health but also their attendance and academic success. Faced with such a situation, immediate measures are imperative to enhance the water quality at Ndiebene Gandiol school, namely:

- Establishment of an effective wastewater treatment system.

- Organization of educational sessions focused on hygiene for students and staff.

- Implementation of modern sanitary infrastructure that meets current standards.

- Strengthened collaboration with local authorities and specialized entities for regular monitoring and maintenance.

- In summary, the data collected highlight the urgency of implementing corrective measures to improve water quality at this institution. It is crucial to take vigorous measures to ensure a healthy study environment conducive to the students’ well-being.

The interpretation of the data collected on the study site reveals crucial aspects to consider for a rigorous analysis [32] . The small number of samples could influence the representativeness of the results. A diversification of samples over a longer period would be ideal to obtain a more comprehensive overview of potential variations in water quality. Not considering the relief might skew the understanding of pollutant dispersion. Integrating this dimension could refine recommendations. The absence of climate variation analysis could affect the relevance of treatment methods, given local seasonal fluctuations. However, the study offers a complete perspective on water quality through the diversity of analyzed indicators. The results, derived from the laboratory [23] , are highly credible. The study suggests recommendations based on both intensive and extensive solutions, allowing for effective wastewater treatment. The emphasis on health indicators, such as fecal coliforms, underscores the health issues associated with untreated wastewater. This study provides guidelines for future interventions. To improve the reliability of future studies, it would be wise to consider a more diverse sampling, to take into account topography, and climate conditions.

The population equivalent (PE) is a standardized unit used to compare the pollutant load emitted by various users in an area (residents, workers, students, etc.) to that of a typical inhabitant. This unit is often used to size sanitation facilities. To determine the population equivalent of our study site, it is crucial to quantify the pollutant load generated by the students and staff, related to on-site activities. However, for a precise evaluation, detailed information on waste generation, water consumption, among others, is required. In the absence of this information, we can still establish an estimate based on certain criteria stated in Table 1. The school has 505 students. We can assume that a student produces a lower pollutant load than an adult (say 50% of an adult’s load). If an adult corresponds to 1 PE, then a student would be valued at 0.5 PE. The fact that all the latrines are out of service, combined with the dilapidated state of the toilets, means that wastewater does not receive proper treatment. While this does not directly influence the PE calculation, it highlights the inadequacy of current infrastructure relative to the defined number of PEs. The absence of a water point suggests limited water consumption or provision from other sources. This situation could reduce the volume of wastewater produced, but it is tricky to assess its influence on the PE without additional data. Assuming one teacher per classroom, i.e., 12 teachers, and estimating that a teacher generates a pollutant load equivalent to an adult, each teacher would be counted for 1 PE. Thus, based on these estimates and the data provided, the study site would represent approximately 265 PEs. It is critical to note that this evaluation remains approximate and that a more detailed analysis would be necessary for refined results. With a population equivalent of 265, the site is positioned as a small to medium-sized entity in terms of wastewater sanitation. Various treatment solutions can be considered for a community of this size, as highlighted by [33] .

When considering an ecological treatment for wastewater, such as phytoremediation, it is essential to have reference values for permissible pollutant loads to ensure optimal system efficiency. These reference values can vary depending on national or local regulations, environmental conditions, and the type of ecological system envisioned. However, here are some general and recommended values for various parameters, widely recognized in the field of sanitation (see Table 3) according to [34] . It is essential to note that these values are general and may vary depending on local regulations, environmental context, and other factors. Moreover, several organizations and publications provide guidelines on this subject, such as the World Health Organization (WHO) [35] , the United States Environmental Protection Agency (EPA) [19] , and European standards [36] . For a specific application, it is recommended to consult local regulations and expert recommendations in the field.