Honolulu Sewage Plant Pioneers Advanced Primary Treatment, Has Deepest Ocean Outfall

by Wallace S. Miyahira, (M.ASCE), Dir. and Chf. Engr.; Dept. of Public Works, City of Honolulu, Honolulu, Hawaii,
Stanley T. Yamanaka, Jr., (M.ASCE), Chf. Engr.; R.M. Towill Corp., Honolulu, Hawaii,

Serial Information: Civil Engineering—ASCE, 1979, Vol. 49, Issue 6, Pg. 76-77

Document Type: Feature article


Honolulu recently started up a new sewage treatment plant that brings a new twist to decades-old sewage-treatment technology: advanced primary treatment. Key to this primary treatment process is the use of so-called flotation clarifiers. In these clarifiers, tiny bubbles flow up through the clarifier tank, attaching themselves to suspended particles. The bubbles give these particles added buoyancy, floating them to the tank surface, where they are skimmed off. Using this process, 92% to 99% of the floatables and over 99% of the settleable solids are removed. The advanced primary effluent is then discharged through a 13,971-ft long outfall, the diffuser at the end jetting the effluent into the surrounding ocean water at a depth of 240 ft, one of the deepest outfalls in the world. The near-shore part of the outfall is buried in a 15-ft deep trench cut in the ocean floor.

Subject Headings: Clarifiers | Sewage | Wastewater treatment plants | Ocean engineering | Particles | Effluents | Water discharge | Buoyancy | Honolulu | Hawaii | United States

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