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Ecology of Wastewater

back to Treatment and Disposal Division

The City & County of Honolulu's (CCH) Department of Environmental Services (ENV) collects between 105-110 million gallons of wastewater each day from toilets, sinks and drains of homes, schools and businesses on Oahu enough to fill Ala Moana Park and Magic Island to a depth of four feet.

Through a system of 2,100 miles of pipeline, assisted by gravity mains and pump stations, wastewater travels to nine wastewater treatment plants (WWTP) spread across Oahu. While there, wastewater is screened to remove debris, organic solids then treated to different levels primary to tertiary depending on the sophistication of the plant.  After the wastewater is processed, the remainder is effluent.

ENV keeps close tabs on effluent through extensive monitoring and discharges it back into the environment to the ocean, a lake or an underground injection well.  A portion of it is also recycled and reused.

In a closed ecosystem, there are no such things as wastes.  Just about everything is eventually recycled.  Nutrients, water and carbon are constantly being recycled in the ecosystem.

The treatment of wastewater borrows upon nature.  The most popular wastewater treatment methods are simply amplifications of what occurs naturally.  Microorganisms that would normally break down the waste products are cultured, harnessed and pampered with "food" and oxygen to break down the wastewater quicker.  In general, obnoxious compounds are broken down and removed and the water (with some impurities) is returned back to the ecosystem.  This type of treatment is called secondary treatment.

CCH has seven secondary WWTPs Kailua, Wahiawa, Kahuku, Laie, Waianae, Waimanalo and Paalaa Kai.  The treated effluent is either injected into the ground, discharged into a lake or released deep into the ocean for recycling.

Primary treatment is another way to handle wastewater.  This process involves removing materials including fats, oils and greases (also referred to as FOG), sand,grit, larger solids and floating materials.  Discharging primary treated wastewater is allowed but only into the deep ocean where dilution, oxygen and distance from land allows the natural treatment process to occur.

CCH has two plants that use primary treatment Sand Island and Honouliuli WWTPs. These two plants treat more than 90% of the CCH's wastewater.

Sludge is the residual semi-solid material left over from the wastewater treatment process.  Due to the physical-chemical processes involved in the treatment, the sludge tends to concentrate heavy metals and poorly biodegradable trace organic compounds as well as potentially pathogenic organisms.  Nonetheless, sludge is rich in nutrients nitrogen and phosphorous while containing valuable organic matter that is useful when soils are depleted or subject to erosion.  The organic matter and nutrients are the two main elements that make the spreading of this kind of waste on land, as a fertilizer or an organic soil improver, suitable.

Sludge is kept in enclosed heated tanks and pressure-cooked in order to break the bond with water.  Bacteria then break it down, reducing volume, odors and microorganisms that can cause disease.  The remains are sent to a landfill or recycled as fertilizer.  Recycling of the solids helps to conserve dwindling landfill space.

CCH contracted Synagro to design, build and operate a municipal biosolids facility near the Sand Island WWTP.  The public/private partnership facility is operational and processing up to 10,000 dry tons of biosolids annually.  Waste that was once landfilled is being turned into a commercial grade Class A organic fertilizer product, marketed by Synagro.  The nutrient-rich pellets are safe for general gardening and landscape use.  Local retailers, landscapers and golf courses as well as large-end commercial growers utilize these products.  Honolulu joins the many cities already utilizing pelletization programs due to landfill and environmental constraints, among them Boston, Tampa, Houston, New York City and Sacramento.

Furthermore, CCH is utilizing recycled water for reuse for irrigation, golf courses and businesses.  To assist CCH in this process, Ultraviolet (UV) disinfection, which uses radiation to penetrate microorganism cell walls to either prevent reproduction or destroy the viability of bacteria and viruses, is being used at WWTPs. 

Kailua and the Wahiawa treatment plants use UV to disinfect secondary treated wastewater before discharging effluent.  At Honouliuli, nearly nine million gallons of secondary effluent is UV disinfected by the Board of Water Supply's Ewa Reclamation Facility as part of reclaiming water for irrigation, golf courses and industrial processes. That water (R-1) is the irrigation grade provided to all of the Ewa golf courses (except Ko Olina).  North South Road, Kapolei Parkway construction areas and Fort Weaver Road use recycled irrigated water to control dust.  Honouliuli WWTP also makes use of R-1 water for processing at the plant.  Furthermore, power plants and refineries in Campbell Industrial Park use RO dimineralized recycled water.

ENV's Regulatory Control Branch reviews business operations to determine if the water they discharge to the sewer poses a threat to the operations and health of the city sewer system.  If an operation is likely to discharge harmful materials like large amounts of fats, oils and grease (FOG) into the city sewer system, they must install a pretreatment system to prevent harm to the city sewer.

Pacific Biodiesel, another public/private partnership, is making renewable energy from a common waste product recycled grease trap and cooking oil.  Through a collective effort with ENV's Regulatory Branch, PB is able to successfully collect and process cooking oil from local restaurants at no charge.  PB processes nearly 200,000 gallons of grease trap waste monthly, recycling it as boiler fuel for businesses at Campbell Industrial Park.  Since 2002, the plant has provided CCH fleets and several private companies with a stable source of biodiesel fuel totaling nearly 40,000 gallons a month.  Though somewhat higher in price than regular diesel, the recycled product helps oxygenate the air, burns cleaner, drives higher-powered vehicles, gets better mileage and saves importing oil from the mainland.

As Oahu heads into the 21st century, the push for "Greening the Government" is one of CCH's highest priorities.  Through the collective efforts of CCH and ENV, Honolulu continues towards a zero waste environment.

Last Reviewed: Tuesday, May 10, 2011