The city has begun hauling raw sewage sludge from its Sand Island Wastewater Treatment Plant to its Waipahu siteas part of a feasibility study to determine whether the program can be expanded to help ease congestion at the Honolulu facility.
Test runs began Tuesday and are scheduled to continue through Sept. 9 as the city attempts to determine the impact of the hauling on the Sand Island and Honouliuli wastewater treatment plants.
One 5,000-gallon tanker is transporting sludge once a day on weekdays only, except on holidays.
The city ultimately plans to send the sludge to plants in Kailua and Waianae — in addition to Honouliuli — as it deals with delays in the expansion of facilities at Sand Island, which takes in sewage within the urban core from Aina Haina to Halawa. Test runs are not being made to Kailua and Waianae at this time because of mechanical issues at those plants, officials said.
Mayor Peter Carlisle also has ordered that a formal environmental assessment be conducted on the plan to haul sewage to all three waste-water treatment plants.
Hauling is seen as a temporary means of relieving the over-capacity "digester" at Sand Island while the administration and City Council work out plans for the safest, most cost-effective way to expand the facility.
The process involves filling one tanker with primary sludge from the Sand Island plant on the morning before the hauling run, said Markus Owens, spokesman for the city Department of Environmental Services.
Early the next morning, the tanker is driven to the Waipahu Pump Station at Waipahu Depot Street, where the sludge is discharged into the system so that it "mixes/blends/dilutes" with the incoming waste water, Owens said.
From the Waipahu station, the sludge travels seven miles through piping to reach Honouliuli Wastewater Treatment Plant.
Monitoring will be done at both Honouliuli and Sand Island, and the impact will be detailed in the final feasibility study, Owens said.
The city is seeking to expand the Sand Island plant and build a second 100-foot-high, egg-shaped digester, which processes the sludge through a method known as "in-vessel bioconversion" and is capable of producing fertilizer pellets from the sludge.
Design and planning for the digester had begun and the city sought $26 million for it this year, but the Council deleted the funds in the current fiscal budget out of concerns about the plant’s operator, Synagro Hawaii, and safety issues raised about the fertilizer pellets.
The city plans to seek the money again next year.
