Sand Island Wastewater Treatment Plant

About the Project

The City and County of Honolulu’s Sand Island Wastewater Treatment Plant (WWTP) Secondary Treatment Phase 1 project represents a major investment in Hawaii’s critical water infrastructure and environmental stewardship. This large‑scale upgrade modernizes the existing Sand Island WWTP to provide secondary wastewater treatment compliant with a 2010 U.S. Environmental Protection Agency Consent Decree.

Located on a 24‑acre site between Honolulu’s downtown business district and the airport, the project involves both new construction and significant rehabilitation of existing facilities. The upgraded plant treats wastewater using advanced membrane bioreactor (MBR) technology, significantly improving effluent quality before discharge through the existing ultraviolet disinfection system and ocean outfall.

Key elements of the project include construction of a new Intermediate Pump Station and Blower Building, MBR service and processing facilities, sludge thickening and processing systems, enhanced odor control and new effluent flow routing, including tunnels and channels. The project combines new facilities with extensive renovations to the active treatment plant.

Delivered using a design‑bid‑build approach, the project required complex sequencing and close coordination to maintain continuous plant operations throughout construction. The work includes extensive cast‑in‑place concrete, below‑grade construction, dewatering and the installation of mechanical, electrical, instrumentation and process systems critical to wastewater treatment performance.

The Sand Island Wastewater Treatment Plant Secondary Treatment Phase 1 project is the culmination of five years of intricate construction within an active treatment plant, completed three months ahead of schedule. Beyond delivering a major infrastructure upgrade, Hensel Phelps is proud to be a long-term partner in supporting Hawaii’s environmental goals, protecting public health and helping modernize critical wastewater systems for future generations.

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