Avaliação dos impactos das descargas dos efluentes da Estação de Tratamento de Águas Residuais do Infulene no Rio Mulaúze

Abstract

The exponential increase in the contamination of surface water bodies has become one of the most widely discussed environmental issues worldwide. This discussion arises from the significant impact of this phenomenon on all living beings, especially humans, who depend on this vital resource for survival. Wastewater treatment, in addition to enabling the reuse of previously discarded water for different activities, helps reduce water scarcity. The Province and City of Maputo generate large amounts of wastewater, which requires daily collection for treatment at the Infulene Wastewater Treatment Plant (WWTP). The Mulaúze River, located in the Infulene neighborhood, passes through the Infulene WWTP, and along its course, there are several farmers engaged in the cultivation of vegetables. The farmers’ constant complaints and dissatisfaction due to the pollution of the river water used for irrigation triggered the motivation for this study. The objective was to evaluate the impact of effluent discharges from the Infulene Wastewater Treatment Plant on the Mulaúze River. Fieldwork was carried out, consisting of the identification of five strategic sampling points. Water samples were collected, and field parameters such as pH, temperature, dissolved oxygen, and electrical conductivity were immediately measured. The samples were then transported to the laboratory for further analyses of nitrates, phosphates, biochemical oxygen demand (BOD), turbidity, total and fecal coliforms. The pH in all sampling points ranged from 7.00 to 7.14. Points 1 (upstream of the WWTP), 3 (between the brewery and the WWTP), and 5 (downstream of the WWTP) showed relatively high levels of dissolved oxygen compared to points 2 (brewery discharge) and 4 (WWTP discharge), which showed a progressive decrease, reaching 0.73 mg/L and 1.28 mg/L, respectively. Biochemical oxygen demand presented higher values for these two points, ranging from 8.9 mg/L to 18.15 mg/L, as expected due to the low dissolved oxygen levels. The water quality of the Mulaúze River shows progressive degradation along its course, especially at the discharge points of the 2M brewery and the Infulene WWTP. This degradation is evidenced by the presence of nitrates, phosphates, fecal coliforms, and E. coli.