The main advantages of marine outfalls for the discharge of wastewater are:
* the natural dilution and dispersion of organic matter, pathogens and other pollutants
* the ability to keep the sewage field submerged because of the depth at which the sewage is being released
* the greater die-off rate of pathogens due to the greater distance they will have to travel to shore.
They also tend to be less expensive than advanced wastewater treatment plants, using the natural assimilative capacity of the sea instead of energy-intensive treatment processes in a plant. For example, preliminary treatment of wastewater is sufficient with an effective outfall and diffuser. The costs of preliminary treatment are about one tenth that of secondary treatment. Preliminary treatment also requires much less land than advanced wastewater treatment.