Two sewage digesters are operating simultaneously at the Sand Island Wastewater Treatment Plant for the first time ever, an achievement that city officials found worthy enough to celebrate with a lei-untying ceremony Monday.
The dual operation at Synagro Technologies’ bioconversion facility gives the city more sewage capacity and allows for more green disposal of Oahu’s wastewater at Sand Island, the largest sewage treatment plan in the state, city officials said.
The digesters treat the sludge and convert 94 percent of it into fertilizer pellets that can be sold to farmers and others.
A first egg-shaped digester was opened in the early 2000s, and it was joined by a second digester in October 2016.
But the city shuttered the original digester for renovations and refurbishment, so it was only recently that both began operating at the same time.
The new digester cost $33 million, while the refurbishment of the first one cost $13.2 million, officials said.
“Now we have the redundancy and the capacity,” Mayor Kirk Caldwell said. “If we’re going to become more dense in the urban core, we need greater capacity and we need redundancy.”
Before the digesters, the sludge residue went to the landfill. Now about 94 percent is converted into pellets while the remaining amounts are going to HPOWER, the city’s waste-to-energy facility.
City Environmental Services Director Lori Kahikina said that while two digesters will allow for some new housing development, two more are actually needed to meet future growth and achieve total redundancy.
“Within 10 years we should be building another one,” she said.
“We’ve had a lot of development in the urban core in the last six years,” Caldwell said. “None of that could have happened without the commitment to build a second digester. We would have denied very sewer hookup for these projects, including some very affordable using projects.”
Kahikina said that more farmers and the public “need to get over that ick factor” and use the pellets as fertilizer for edible crops.
