THE FATE AND EFFECT OF WASTEWATER DISCHARGE INTO THE SURFACE WATERS OF THE EL ALTO REGION OF BOLIVIA

The El Alto region of Bolivia near La Paz is one of the fastest growing municipalities in the world. Demands for safe drinking water, sewage treatment and cleaner industrial and agricultural methods are not being met and are adversely affecting surface water sources. Poor water quality leads to waterborne illnesses that are debilitating or fatal, especially in young children, the elderly and immune-compromised individuals. The Rio Katari and its tributaries (Rio Seco and Rio Pallina) flow through this region and into Lake Titicaca. The Rio Katari flows through farms and undeveloped land. The Rio Seco and Rio Pallina flow through the heavily populated regions of El Alto (population approximately 1 million) and Viacha (population approximately 20,000), where they are impacted by large quantities of untreated wastewater delivered to the river by open sewers. A wastewater treatment plant (WWTP) is located in El Alto; however the effectiveness of the treatment plant is unknown and it is thought to provide treatment for far less than 50% of the wastewater of the region.

Water samples were collected and flows were measured at various points along the Rio Katari, Rio Pallina and Rio Seco during the wet and dry seasons to determine the water quality in each river. Samples were analyzed for pH, temperature, conductivity, cations, anions, phosphorus and total coliforms. During the dry season analysis was also done for total Kjeldahl Nitrogen (TKN) and chemical oxygen demand (COD). These results were used to determine water quality and waste loadings along each of the rivers, as well as the fate of the sewage-derived constituents.

Surface water TKN concentrations were found to be high, while nitrate concentrations were low, indicating an oxygen-poor environment with limited nitrification. Measurements taken during the dry season indicate that down-river the TKN decreases from its highest concentration of 241.2 mg/L in the Rio Seco to 49 mg/L in the Rio Katari; this decrease is likely due to dilution from WWTP effluent as well as dilution by the Rio Katari and Rio Pallina. Total coliform concentrations decrease by a factor of 10⁶ CFU/L between the Rio Seco and the Rio Katari. The large decrease in total coliform indicates natural attenuation plays a larger role than dilution.