Triplex Oxidation Ditch System Using Draft Tube Channel Technology

Authors:

T.F. Allen

D.H. Fredericks

A.L. Wilcox

The document presents the Triplex Oxidation Ditch System using Draft Tube Channel technology as an innovative solution for upgrading the Fairfield, Iowa wastewater treatment plant to meet stricter effluent standards. This system integrates carbonaceous BOD removal, nitrification, and denitrification within a single oxidation ditch, offering controlled oxygen profiles, energy efficiency, and reduced chemical usage. By retrofitting existing infrastructure with draft tube aerators, the approach provides stable, high-quality effluent at lower life cycle costs compared to traditional treatment systems.

Key Learnings

• The Triplex Oxidation Ditch System combines BOD removal, nitrification, and denitrification within a single treatment unit, improving efficiency and reducing the need for multiple basins.
• Draft tube aerators allow controlled oxygen distribution and complete mixing, independent of oxygen demand, enabling consistent biological treatment even under varying flow conditions.
• Retrofitting existing oxidation ditches with draft tube technology can be mechanically feasible and economically attractive, providing energy savings and lower life cycle costs.
• The system supports recovery of alkalinity and oxygen from denitrification, reducing chemical usage and improving sludge settling characteristics.
• Stormwater flow equalization can be effectively managed using side stream equalization ponds, minimizing shock load impacts on biological treatment.
• Controlled ditch geometry, aerator pumping capacity, and air supply allow optimization of residence time for biological reactions, enhancing treatment stability.
• Effluent quality can exceed NPDES permit requirements while minimizing operational costs, including secondary sludge handling and effluent polishing.
• The Triplex system is particularly suitable for municipal and high-ammonia industrial wastewater, offering flexibility for both new installations and retrofits.