How many wastewater treatment plants are there in Hawaii?

Klarifi tracks 3 publicly owned wastewater treatment plants in Hawaii with a combined average flow of 4 million gallons per day, serving about 46,001 residents. 1 of them treat more than 1 MGD and 0 more than 10 MGD.

What is the largest wastewater treatment plant in Hawaii?

Hawaii County Hilo WWTP in Hilo is the largest plant in Hawaii by average flow, treating about 3.53 MGD.

What treatment technologies are common in Hawaii?

0 of Hawaii's plants use lagoon systems and 1 have biogas or anaerobic digestion infrastructure, based on Klarifi's aerial imagery review.

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Wastewater Treatment Plants in Hawaii

Name: Wastewater treatment plants in Hawaii
Creator: Klarifi
License: https://klarifi.io/terms-of-service

3 facilities · 4 MGD combined flow

Klarifi tracks 3 publicly owned wastewater treatment plants in Hawaii with a combined average flow of 4 MGD, serving about 46,001 residents. 1 plants treat more than 1 MGD and 0 more than 10 MGD; 0 use lagoon systems and 1 have digesters or biogas infrastructure. The largest is Hawaii County Hilo WWTP in Hilo at 3.53 MGD.

Every plant below links to a profile with average and design flow, treatment technology, the NPDES permit and its expiry, a three-year compliance snapshot and the capital projects planned in its city.

3 plant locations in Hawaii; dot size follows average flow.

NPDES permits and renewals in Hawaii

Every plant discharges under an NPDES permit that is renewed every five years, usually with tighter limits. The renewal year is the year a plant budgets for upgrades.

All NPDES permits in Hawaii →Find plants near you on the map →

Largest wastewater treatment plants in Hawaii

The 3 largest publicly owned wastewater treatment plants in Hawaii by average flow, with NPDES permit, expiry, treatment technology and three-year violation count. Source: EPA ICIS-NPDES via Klarifi.
Facility	City	Avg flow (MGD)	Design (MGD)	NPDES permit	Expires	Technology	Violations (3y)
Hawaii County Hilo WWTP	Hilo	3.53	5	HI0021377	Apr 2030	Clarifiers, Biogas silos	52
Wailua Wastewater Treatment Plant	Kapaa	0.34	1.5	HI0020257	Oct 2024	Clarifiers	4
County Of Hawaii Papaikou-Paukaa WWTP	Hilo	0.05	0.35	HI0021113	Apr 2031	—	40

Hawaii capital improvement plans →

All 3 plants in Hawaii

Facility	City	Flow (MGD)
Hawaii County Hilo WWTP	Hilo	3.53
Wailua Wastewater Treatment Plant	Kapaa	0.34
County Of Hawaii Papaikou-Paukaa WWTP	Hilo	0.05

Wastewater treatment in Hawaii: questions

Sources and methodology

Flow, permit and violation figures come from the EPA's ICIS-NPDES discharge monitoring records. Population served comes from the Clean Watersheds Needs Survey 2022. Treatment structures are identified by Klarifi's review of aerial imagery, and capital improvement projects are extracted from published municipal budget documents. Violations are counted over the last three years of monitoring reports.

Data refreshed September 11, 2026.

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