Assessment of sanitary infrastructures and polluting loads in Pojuca river (Brazil)

This study was carried out to quantitatively and qualitatively investigate sources of water pollution in Pojuca river basin, in order to define ameliorative interventions. The basin of Pojuca river is located in Recôncavo Norte region, immediately northwards from Salvador da Bahia, capital city of Bahia State (Brazil). River Pojuca is the main water body of the region and it represents a very important potential source of water to be used for drinking purposes, in order to face the rapidly growing population of Salvador da Bahia Metropolitan Area. According to previous studies, its quality did not meet the minimum standards set for surface water withdrawn for potabilization treatment in 2000. In the present study, the most polluting activities have been identified as urban sewage discharges. Wastewater management coverage rate ranged between 30 and 90% in a high number of municipalities in the basin. Wastewaters were commonly discharged on the soil or into it (by means of septic and rudimental tanks) and also urban sewage systems, where existing, often did not convey wastewaters to treatment plants. Polluting loads were estimated according to a methodology elaborated during the study. The estimation was based on the data collected by the authors through field visits and the ones available in the federal databases (updated to year 2007). It allowed to establish that diffuse loads were major than point loads: point discharges were quite rare, whereas pipelines discharging in water bodies and infrastructures such as septic or rudimental tanks were widespread. Treatment plants and septic tanks presented small removal efficiencies of nutrients. This justified also the high organic and microbiological concentrations registered in the river as well as the high content of nutrients. Water quality could be improved in order to meet standards for drinking purposes by building new wastewater treatment plants or upgrading the existing ones. In particular, in urban areas dynamic systems for wastewater collection and treatment plants should be built, whereas in rural areas scattered households should be provided with septic tanks.