Department of Environmental Services

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Wastewater Treatment & Disposal

Division of Wastewater Treatment & Disposal

Highly trained operators, mechanics, electricians and technicians operated and maintain nine wastewater treatment plants for the City & County of Honolulu on Oahu around the clock, including the SCADA Operations Control Center at Sand Island WWTP. The staff continually investigates new ideas and technologies that will increase efficiency, improve water quality and protect public health.

As wastewater enters the plant, the first step is to remove large objects to protect the plant’s equipment from damage.
Large screens eliminate an amazing array of materials: cans, rocks, sticks, rags, diapers, batteries, lumber, fish heads, money and even jewelry. Gravity settles out the paper waste (toilet paper and towels, cotton balls, dental floss, condoms and feminine products) onto a conveyer belt. A mechanical arm or screen rakes the trash to a hopper. It’s compacted to reduce the water content and trucked to a landfill.

Odor Control
As the wastewater moves along, it produces hydrogen sulfide gas, which emits odor, rusts manhole covers, and in large doses, can cause illness. Air and gases in the plant are monitored and cleansed following the wastewater’s initial screening—and throughout the process—before the air is released through 100-foot towers into the atmosphere. An alarm sounds when H2S levels are too high.
At Honouliuli, giant pumps lift the wastewater to the top of multi-story biotowers. The water trickles down over plastic cubes where bacteria grow. The prolonged exposure to air and oxygen speeds the breakup of solid particles.

Wastewater is pumped into large open-air settling tanks, slowing the movement of the water. As the water stills, gravity pulls organic solids to the bottom (primary sludge). Oil and grease (scum) float to the top.

Revolving arms scrape the solids from the bottom and skim the grease from the top.

Each step of the treatment removes more solid matter from the wastewater. Along the way, microorganisms attack the organic matter from our toilets and garbage disposals and break it down further.

Finally, liquid from the clarifiers is disinfected to destroy bacteria that can cause disease. Some plants use chlorine. At others the liquid runs in a closed channel under ultraviolet cylinders. The procedure removes phosphorus and kills or cripples harmful bacteria to the point where they cannot reproduce. With the conversion of the Sand Island plant to ultraviolet disinfection in 2005, nearly 90 percent of all the wastewater that’s treated by the City & County will use this more advanced disinfection. From Sand Island and Honouliuli WWTPs, the spent water goes to the deep ocean, where nature does the rest. That is, the remaining particles are rapidly disbursed by ocean currents and reduced to their basic elements.
Secondary Treatment

Oahu’s treated wastewater may be discharged into a reservoir or ocean without adverse environmental effects. In fact, the cleansed water is often cleaner than the water where it’s disposed.

Seven of Oahu’s smaller wastewater facilities – Kailua Regional, Waimanalo, Wahiawa, Kahuku, Laie, Waianae and Paalaa Kai wastewater treatment plants – provide a second stage of treatment.

After primary treatment, wastewater still contains small amounts of solid matter. Secondary treatment speeds up what occurs naturally. The primary-treated water enters a series of aeration tanks, the heart of the secondary treatment system. Some secondary treatment plants (Honouliuli, Kailua, Waianae) use biotowers (also called trickling filters) to perform this function.

Microorganisms that break down waste are saturated with “food” (wastewater) and oxygen to break down the pollutants more quickly. Filtered air is pumped into the liquid enabling the microbes to flourish and grow, and they consume most of the pollutants. Chemicals may also be added to improve treatment.

Disinfection kills any remaining harmful bacteria. The processed water is released underground or to a nearby stream or ocean—returning the water and a few left-over impurities back into our ecosystem.

As the wastewater moves along, it produces hydrogen sulfide gas (H2S), which emits odor, rusts manhole covers and, in large doses, may cause illness at higher concentrations. Air and gases in the plant are monitored and cleansed following the wastewater’s initial screening (and throughout the process) before the air is released through 100-foot towers into the atmosphere. An alarm sounds when H2S reaches high levels.

At Honouliuli WWTP, giant pumps lift the wastewater to the top of multi-story biotowers. The water trickles down over plastic cubes where bacteria grow. The prolonged exposure to air and oxygen speeds the break up of solid particles.

Tertiary treatment takes secondary-treated effluent and “polishes” it through fine sand and filters. The process produces a product that has 95 percent of the suspended matter removed.

Sand filtering, UV disinfection and the removal of nutrients (nitrogen and phosphorus) are all part of the tertiary process. Tertiary treatment is required of plants that discharge into freshwater receiving waters.

The Wahiawa WWTP, which discharges to the Wahiawa Reservoir, is a biological, tertiary-level facility, one of the highest levels of wastewater treatment. Laie WRF, recently acquired by the City, is another facility that utilizes tertiary treatment.

Treated Effluent

Most of Oahu’s treated effluent is pumped into the ocean or underground. The Sand Island WWTP discharges 1.7 miles off shore, 230 feet deep. Here the remaining particles are rapidly disbursed by ocean currents. There is virtually no recreational use of the ocean water in that area. In addition, Honouliuli, Waianae and Kailua wastewater treatment plants dispose treated effluent through deep ocean outfalls, which together (with Sand Island) account for about 90 percent of Oahu’s total disposal.

Treated effluent from Wahiawa WWTP is discharged into the Wahiawa Reservoir. Paalaa Kai, Kahuku, Laie and Waimanalo release treated efflluent through underground injection wells.

ENV Ocean Team samples and tests water from the outfalls about twice a week to make sure clean water standards are maintained. The cleaned effluent at all treatment facilities consistently meets federal requirements when it leaves the plant. If there is a break to a pipe or sanitary sewer overflow (SSO), the monitoring is increased, even to three times a day, until the problem is rectified.

Dissolved oxygen is forced into a treated effluent. Bubbles attach to the remaining solids and rise to the surface, making the organic matter easier to separate out and compress. The sludge is then heated slowly for hours in an oxygen-free environment, just the opposite of the earlier process. As the wastewater, the remaining bacteria thrive and convert the solids into biologically rich compounds. Liquid is squeezed out of the sludge, resulting in a more concentrated product called biosolids. The more water that is removed, the more concentrated it becomes and the less it costs to process or haul away.

Dissolved oxygen is forced into treated effluent. Bubbles attach to the remaining solids and rise to the surface, making the organic matter easier to separate out and compress. This is only one process that is not used at all plants, dissolved-air flotation thickening.

Sludge is heated slowly for hours in an oxygen-free environment—just the opposite of the earlier process. As the wastewater, the remaining bacteria thrive and convert the solids into biologically rich compounds. This anaerobic process is not used at all plants.

Liquid is squeezed out of the sludge, resulting in a more concentrated product called biosolids. The more water that is removed, the more concentrated it becomes and the less it costs to process or haul away.

Since the beginning of wastewater operations in 1901, the City and County of Honolulu recognized the importance of a solid wastewater infrastructure to ensure public health and safety. As technology and sophistication in the instrumentation and control systems industry evolved over the years, the City capitalized on proven technologies to satisfy the increased wastewater demands and stricter regulatory requirements.

In the mid-1980s with the widespread use of personnel computers in the work place, the City began installation of an island-wide Supervisory Control and Data Acquisition (SCADA) system. This allowed remote monitoring and control of wastewater equipment from a host computer at a central location.

The basic components of the SCADA system integrated remote sites to a centralized monitoring node consist of remote terminal units (RTUs), analog leased lines and personal computers. The RTU is a microprocessor based electronic device that interfaces the physical equipment to the host computer by converting discrete and analog signal parameters into telemetry data, based on programmed control codes. The RTU and host computer uses RS485 communication protocol, which is transmitted over analog leased lines. The personnel computer then translates the raw data and presents the data to the user via the human machine interface (HMI).

Presently, the SCADA central command center is manned continuously (24/7) and monitors 70 wastewater pump stations, two storm drain pump stations, nine wastewater treatment plants and four preliminary treatment facilities.

Since the installation of the SCADA system, it has prevented and/or averted numerous sanitary sewer overflows into the environment. This is accomplished by deploying simple alarm programs in the RTU that check trend cycles of the wastewater pump’s run on-time and off-time. Since each wastewater pump station has a distinct daily flow pattern, we can logically and systematically detect abnormal equipment run patterns. When an abnormality is detected, an alarm is generated that triggers an alert “popup” screen on the monitor, alerting operators and directing their attention to the problem.

The installed SCADA system has become antiquated and obsolete, so CCH recently began upgrading the SCADA system with the latest proven technologies. The new SCADA system will consist of programmable logic controllers (PLC), digital high-speed communication lines and computer servers. The PLC is a microcontroller-based electronic device (mini-computer on single chip) with multiple expandable input and output connections to equipment sensor points. A PLC is programmable to produce “real time” output results to various input conditions. Further, refinements in wastewater controls systems can be achieved with PLCs, which was not feasible with RTUs. The LAN network protocol connecting PLCs to HMI and Historian servers will be over Ethernet. The HMI will be configured in a primary and secondary redundant configuration. In the event the primary HMI fails, the secondary HMI will seamlessly provide information to view clients.

To date, the new SCADA systems are designed and constructed at the Disinfection Facility and Headworks Facility at Sand Island WWTP.

The City & County of Honolulu’s (CCH) Department of Environmental Services (ENV) collects approximately 107 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.

Wastewater Plants

The city’s nine wastewater treatment plants (WWTP) operate around the clock and employ more than 300 workers. Wahiawa WWTP was the first built in 1928 when Oahu’s population was relatively low and life was agrarian. Treatment plants were erected in Kailua and Waianae in the 1960s as a growing economy increased the demands on wastewater capacity. Individual systems were constructed along the coast. Septic tanks and cesspools were widespread.

As Oahu’s population grew, so did national and state awareness of potential risks to the environment and public health. The federal Clean Water Act passed in 1972 and was amended five years later. Sand Island WWTP, Oahu’s largest, opened in 1976 and Honouliuli WWTP followed in 1980. Major upgrades to the system in the 1990s included a new surveillance system (SCADA) that brought centralized monitoring for the entire wastewater pumping and treatment system to the Sand Island Operations Control Center.

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