Ten Years of Operation of Rio De Janeiro'S Ipanema Submarine Outfall

Abstract

Monitoring and surveys of the Ipanema Submarine Outfall of the city of Rio de Janeiro have been practiced during the 10 years of the outfall operation. The outfall is a 2.4m diameter prestressed concrete pipeline, 4.3 km long, extending 3.3 km seaward to a depth of 27m. It discharges presently 6 m3/s average raw sewage flow, through a 450m long diffuser. A planned survey program was established in order to verify pipe conditions through periodical deep sea inspection, monitored by radio and video recording; this paper discusses the preventive and corrective maintenance of the outfall, especially the failures that occurred in 5 accidents. It discusses also the water quality monitoring program established one year before the outfall began its operation in 1975. A program had been prepared which established beneficial water uses, water quality standards required for protection of the uses,and a monitoring system which provides the input data for verifying compliance with the standards. Pre-discharge studies were conducted for one year prior to operation, to provide background data on the various parameters, and over 70 000 analyses were made during the 10 years of the outfall operation. This paper evaluates the results of grease, coliforms, and hydrobiological indicators, as the most representative parameters of water quality in the sea. It shows that a marked improvement has occurred in the water quality. It also shows that the beaches receive a great amount of pollution through the canals of Visconde de Albuquerque Avenue and Jardim de Alá (Rodrigo de Freitas Lagoon), due to sewage overflows from the sewer network and the storm-water networks. The importance of giving special attention to the sewer network in systems involving submarine outfalls is stressed.