Synagro’s Design-Build-Operate Approach Delivers Schedule Acceleration Needed

The contract awarded to Synagro by the City and County of Honolulu (CCH) is the In-Vessel Bioconversion Facility capacity upgrade. Begun in 2022 and running through 2028, the next steps are underway toward final design and mobilization including demolishing an abandoned effluent screening and pumping structure to make space for the construction of two 2.35 million-gallon (MG) digesters, two 0.54 MG sludge storage tanks and a digester control building connecting to the existing digestion and thermal drying facility. The preliminary design, under a prior CCH/Synagro contract, was initiated in January 2021, and resulted in establishing the scope and costs in April 2022, and this year’s early-January award.

“This project is outstanding because it points to Synagro’s ability to understand and work with our existing customers and provide large-scale projects to meet their needs,” said John Goodwin, senior vice president, Engineering, Synagro. “The City’s Consent Decree requires full secondary treatment by 2035. As the City’s first construction phase, 20 MG per day will be online by 2027. To meet these mandates, our approach was to expand our team to include R.M. Towill Corporation – our engineering partner – and Hensel Phelps – our general contractor. This expanded team, including our local Honolulu operations team, was key to providing design input to this project.”

"The SIWWTP has the largest flows and loads of the nine CCH wastewater treatment plants," said Brian Cataldo, senior project engineer, Synagro. “The plant serves the residential population from Niu Valley to the Aliamanu area including Downtown Honolulu and Waikiki, and one-fifth of the load is due to the tourism industry. Future increases in wastewater solids production and material handling needs at the SIWWTP have led to the need for additional digestion capacity.”

About the Sand Island Wastewater Treatment Plant

In 2007, the CCH partnered with Synagro to develop a system to recycle and reuse the biosolids produced in their main wastewater treatment plant, thus providing a model for a closed-loop environmental system. CCH contracted with Synagro to design, build and operate an in-vessel bioconversion facility located at the Sand Island Wastewater Treatment Plant. The facility consists of an egg-shaped anaerobic digester, centrifuge dewatering and a heat-drying and pelletization facility to produce an Exceptional Quality designated product. The pellets – Granulite® fertilizer – produced provide a natural, organic substitute for synthetic fertilizer to Oʻahu’s agricultural and landscaping communities.

Historically, 93% of the pellets have been marketed to beneficial use annually. The remainder comprises trash pellets rejected from the system and occasional landfilling of product when wet weather prevents beneficial use.
The SIWWTP's Phase 1 Secondary Treatment anaerobic digester annual average day solids design loading rate is a blend of primary and secondary up to 64.5 dry tons per day.

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