Impacto de la descarga de aguas residuales en la calidad del río Mololoa (Nayarit, México) y propuestas de solución

A relevant problem related to water in the suburbs located in Tepic-Xalisco, Nayarit Mexico is the pollution of the Mololoa River. Due to insufficient and inadequate treatment of the city´s wastewater, the quality of Mololoa River´s water is being constantly afected. In order to evaluate the effect of wastewater drainer some studies on the Mololoa River were developed. The water quality index (WQI) and the efficiency of wastewater treatment plant were obtained by using official data on strategic parameters. The flow was sampled and measured in three different points in reference to the drainer position: Up river (at Pantanal), down river (at La Escondida) and at the drainer position itself. With these data, the Streeter and Phelps’ model for critic oxygen deficit was used to propose the maximum biochemical oxygen demand (BOD5) that has been regulated by the city´s laws. The WQI up and down river at the drainer position was 62.5 and 36.3 respectively. In spite of the efforts of the city´s authorities in the treatment of wastewater, the efficiency of wastewater treatment plant was not enough. Because of this, the tourism, agriculture and fishing are being affected as well, causing in the area a negative impact on the regional economical development. Finally, and considering the real drainer volume, the flow´s characteristics and the use of the water, a water treatment plant is required to depurate a minimum volume of 1300 l/s with a maximum BOD of 17.25 mg/l is necessary to prevent a higher damage to the flow of Mololoa River. With these results, a division of the wastewater treatment plant by areas is suggested, and the implementation of an environmental education, and an integral program to improve the civic culture related to water use. The development of an indicator system to evaluate the decisions made about water is proposed, and the development of a new project for drainage distribution system as well.