AbstractsEarth & Environmental Science

The accumulation of sediments in combined sewer systems may give rise to significant quality problems, which sometimes are overlooked. Solids deposited in the network may lead to more frequent overflows into natural waters, where are often discharged without treatment during the beginning of storms events. When organic solids, released from in-sewer deposits, reach natural receiving waters, may produce serious impacts. Waters environments are degraded due mainly to the high oxygen biochemical demand, the ammonia contribution and other pollutants. This study focuses on the release of highly-organic sediments having being accumulated inside a combined sewer network. After prolonged dry-periods, typical in Mediterranean region, sediments are re-suspended and conveyed when storm runoff appears. The aim of the research is to develop a methodology able to predict their potential erosion and subsequent mobilization through the network. To achieve that goal, it is needed to improve the knowledge on the processes occurring during long dry-periods, and analyse the variables involved that might affect the erodibility of the deposits. To achieve reliable results in water quality modelling, it is essential the availability of consistent and detailed field data. Highly-organic non-homogeneous sediment samples collected from a combined sewer system were used for the laboratory assessment of the characteristics and the behaviour regarding erosion. Varying strength of the bed with depth allow for a more appropriate representation of the movement of solids in sewerage by introducing in the model a more realistic behaviour. The results obtained have shown that the prediction of organic sediment mobilization and transport is complex but possible to accomplish. However, more effort is needed to ensure the transferability of the results for a more general application of the predictive model obtained. This research has mainly contributed in a more detailed knowledge of the organic sediment bed structure regarding strength to erosion. The acquired knowledge can be applied for improvements in the prediction of pollutant loads that can reach watercourses, pursuing the receiving waters protection as a final goal.; Los depósitos de sedimentos en sistemas unitarios de alcantarillado pueden dar lugar a importantes problemas de calidad de aguas, muchas veces ignorados. La acumulación de sedimentos en estos sistemas puede generar el aumento en la frecuencia de vertidos a medios naturales receptores durante una tormenta. La presencia de sólidos de origen orgánico en los vertidos de aguas sin tratar puede producir impactos perjudiciales en las aguas receptoras. Los medioambientes acuáticos son afectados principalmente por las altas demandas de oxígeno y las contribuciones de nitrógeno originados en los sedimentos orgánicos. Este estudio se centra en los procesos de re-suspensión de sedimentos altamente orgánicos que se han acumulado en las redes de alcantarillado unitario. Luego de largos períodos secos típicos en la región Mediterránea, los…