Ocean Outfall System for Dense and Buoyant Effluents

Abstract

The conceptual design of an existing ocean outfall system for disposal of municipal and industrial wastewaters is reported. The wastewaters are fertilizer plant effluent, which contains large amounts of gypsum and fluoride, pulp-mill effluent, and municipal sewage. The effluents are separated into two streams of different characteristics and then discharged through two outfalls. One stream contains the gypsum and is negatively buoyant in seawater. This outfall was designed to minimize pumping power, while achieving sufficient dilution to cause the gypsum to go into solution, thus minimizing deposition of gypsum on the seafloor. The other stream contains the remaining effluents plus the fluoride and is positively buoyant in seawater. This outfall was designed to meet fluoride concentration requirements in the receiving water by maximizing dilution. Unique to this project was the interplay between the outfall design team and the contributing industries, which resulted in onshore design changes to accommodate the separation of effluents and a more effective disposal system.