Despite the best efforts to contain it, untreated waste from the 88,000 cesspools in Hawai‘i escapes the confines of the system, polluting coastlines and endangering marine life and coral ecosystems. When treated properly, much of the wastewater is released to the ocean rather than reused in the drier regions of the islands. This challenge opens the door to an opportunity. A small band of scientists, politicians, and citizens are heralding the benefits of new technologies that could eliminate the poop in creative and unique ways while adding value to the islands.
According to Stuart Coleman, the grand vision is to have a circular economy approach that recycles all the waste products for irrigation and landscaping. Coleman is the executive director of Wastewater Alternatives and Innovations (WAI), which aims to protect water quality, reduce sewage pollution, and restore healthy watersheds by providing innovative, affordable, and eco-friendly solutions to waste and wastewater management for all people. He is also a member of the Hawaiʻi Department of Health Cesspool Conversion Working Group which wants to implement technologies that could convert solid and liquid waste into byproducts to add value to their communities.
Up in smoke
Reducing waste and excess nutrients, like nitrogen, from entering the environment may be as simple as setting it on fire. The Cinderella Incineration Toilet is a single-family home approach to Hawai‘i’s waste problem, requiring no water or hook-up to a septic or sewage system, but simply an air vent to the outside.
The toilet design is simple. Powered by electricity or propane gas, the incineration process heats solid and liquid waste, burning it to ash at approximately 540 degrees Celsius. The resulting pathogen-free, odorless ash can easily be deposited in the trash or used as fertilizer. Exhaust gas, which contains sulfur, nitrogen, and other possibly polluting gases can be filtered to minimize the sulfur and nitrogen oxides being released into the environment.
Hawai‘i’s first Cinderella toilet was installed at the University of Hawai‘i at Mānoa’s Hawaiʻi Institute of Marine Biology (HIMB) in 2020. While HIMB’s buildings are connected to the municipal water and sewer system, HIMB aims to reduce the burden on these stressed utilities by offsetting demand with the incineration toilet. The current model can process four uses per hour, and the ash container is emptied once a week. HIMB estimates that a five-gallon propane tank can accommodate up to 150 uses.
“This kind of project is important for Hawai‘i because our freshwater resources are continually going to become more scarce, our utilities are going to become more expensive, and our sewage systems are going to have more stressors put on them as population densities increase,” said Judy Lemus, the interim director of HIMB at the time the toilet was installed. “We really need to protect our resources in Hawai‘i and so a solution like the incinerator toilet is a great alternative.”
Filtering to freedom
Beyond the toilet, single-family homes can install Individual Wastewater Systems (IWS) to recycle blackwater (waste from toilets and kitchens) and greywater (waste from bath and laundry) to reduce the waste burden. Bioreactor Gardens make up one component of a new IWS system. Wastewater is directed to a septic tank before it is passed through the bioreactor garden, which is a modified wetland to continue the filtration process. These wetlands contain sand, wood chips, and native plants to filter out nutrients and reduce the volume of treated wastewater. The waste stream then passes into a leach field for continued biological treatment and disposal. This approach does not require electricity or annual maintenance.
“You can’t talk about climate without talking about water,” said Lauren Roth Venu, founding principal of Roth Ecological Design International LLC (REDI), a woman-owned, small business that provides comprehensive water planning and design strategies across Hawai‘i. “Part of climate adaptation is looking at wastewater as a resource, and using technology to transform it from a liability into a valuable water product.”
REDI has designed onsite water and wastewater infrastructure for several projects at the University of Hawaiʻi (UH) and other locations across the islands. For the UH West Oʻahu Administration and Allied Health Sciences Building, REDI developed a plan to direct water from bathroom handwashing sinks and the building’s cooling system for greywater treatment. The resulting treated, non-potable water is used to irrigate the surrounding vegetation. At UH West Hawaiʻi (Palamanui) campus, constructed wetlands perform secondary treatment for blackwater after moving through primary treatment in septic tanks. The water is designed to be recycled for irrigation of the surrounding landscape.
“I think we need to make a bigger lift to meet current and future water infrastructure needs,” said Venu. “We need to mimic the renewable energy industry by managing our water onsite and providing financial incentives to build water-resiliency and water-security.”
The benefits from technology installed in rural and suburban areas can also be used in urban areas. According to Venu, REDI is supporting new urban developments to establish onsite reuse of water from cooling systems and toilets to reduce the overall water burden.
Sustainable for a community
Technologies are also available that scale to the community level to accommodate 20 to 200 homes. These technologies provide a cost-effective way to manage the cesspool crisis by recycling solid and liquid waste for additional use.
“My vision is to implement a system where we use technology to recycle 100 percent of solid and liquid waste to recharge our aquifers and treat water for irrigation and restorative agriculture,” said Coleman. “The circular approach would recycle waste, turn the sludge into biochar and provide a sink for carbon, while also reducing the release of greenhouse gases back into the environment.”
Modular water systems collect and recycle liquid waste from multiple households. The large storage containers can be positioned above or below ground, and the recycled contents can be used for landscape irrigation for the community. This approach saves communities the huge, up-front cost of installing expensive wastewater treatment systems, especially in regions with difficult terrain. Instead, the community can pay monthly fees for the waste processing service and obtain valuable recycled water for irrigation.
Another approach picks up the remaining sludge in the container and applies heat to convert it into biochar. According to Coleman, this leverages the knowledge of Indigenous communities of the Amazon who buried and burned waste to keep minerals in place and increase the fertility and stability of the soil.
The biochar can hold onto nutrients, like nitrogen, phosphorus, and potassium, longer than synthetic fertilizers. It also maintains the stability of the soils to reduce erosion. While not appropriate for many agriculture crops, like leafy greens, biochar can be used for other crops such as fruit trees. The biochar can also be used as a biofilter to collect nutrients and heavy minerals in storm water to reduce pollution of water runoff.
“We could be a leader [on these issues] in our country and the world,” said Coleman. “This is not just a dream, but it is tangibly close to reality. We have to stop wasting our waste.”
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