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Waimanalo Wastewater Treatment Plant Upgrade

Waimanalo Wastewater Treatment Plant Upgrade


Project Highlights:

Project Description:

At a capacity of 0.7 million gallons per day (mgd), Waimanalo Wastewater Treatment Plant did not meet the need presented by large projected future increases in municipal wastewater flows. New urban developments planned by the City and County of Honolulu would translate into flows of 1.1 million mgd. Environet was given the opportunity to prepare a solution, and also remedy a handful of other existing operational inefficiencies.

The bulk of the required upgrades lay in standard replacements or additions of tanks, wells, clarifiers, measuring devices, and other key system components. Environet, however, saw a few opportunities to provide benefits for the client.

Environet's new design instead utilized an anoxic-aerobic treatment process, which minimizes the growth of the filamentous microbes that hinder settleability of biomass solids in the final clarifiers. With the anoxic-aerobic treatment process, there is also potential to remove nutrients from the wastewater for anticipated reclaimed R-1 water reuse.

Some major cost savings were realized due to recommendations made by Environet during the preliminary design process. Instead of converting the secondary treatment tanks into an anoxic basin, Environet proposed converting them into an equalization basin. A new anoxic basin would be built instead of a new equalization basin under the original plan. The alternative solution did not require as many construction modifications, still met the peak wet weather flow of 6.0 mgd, and cut back construction costs by approximately $50,000 to $100,000.

Environet also redesigned the pumping station, utilizing smaller capacity pumps that eliminated both excess pumping and the need for a recycle flow. The recycle flow had been required because the existing pumps were oversized, however, the new design incorporated these larger pumps for use during peak flow conditions. System operation became optimal and monthly power savings came out to an estimated $1,800.

The original schedule allowed 24 months for design. Environet completed it in just 18 months.