A Comparative Solution Of Wastewater Ocean Disposal Through Submarine Outfall With A Classical Sequencing Batching Reactor Treatment System. Case Study Boraceia Beach-Sao Paulo

Abstract

In the recent years, the investments of Sao Paulo government and of the Japan Bank have allowed a significant improvement in the collection rates and in the treatment of wastewater in the Sao Paulo coast. The Sao Paulo's experience in the ocean disposal systems through submarine outfalls is mainly concentrated in large cities. The work here presented shows that this alternative is also a competitive solution for the smaller communities in the northern coast of Sao Paulo, where are concentrated municipalities with populations of order 50.000 inhabitants or less. The case study is applied for Boraceia beach in the municipality of Bertioga and Sao Sebastiao, with a population, during the summer, of nearly 70,000 inhabitants projected for 2015, and it shows a comparison of sequencing batching reactor inland treatment system with ocean disposal through submarine outfall with preliminary inland treatment solution. Submarine outfall length definition is based in a previous study considering the tide characteristics and bathymetric data in this coastal region and creating a computational grid domain for this region of interest. Representation of the effluent plume dispersion into the simulated region is done by using Visual Plume UM3 software, which results are coupled to the 3D Delft hydrodynamic model. Numerical simulations show dilution coefficient higher than 140 in the near field for open sea 1800 m outfall length with a proper designed diffuser system. A comparative cost analysis for the two alternatives solutions, including construction and maintenance, is also presented, showing a significant advantage when submarine outfall is adopted considering inland preliminary treatment. An additionally environmental advantages of this alternative is that Guaratuba river could be preserved in all of its course, as Class 1, according with the classification of CONAMA resolution 357/2005.