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Wastewater pilot project offers promising results

Grass-based system filtering more wastewater than researchers expected

A pilot filtration system of nonnative vetiver grass combined with wood chips, gravel and biochar is disposing about 30,000 gallons of wastewater per acre per day from the Kihei Wastewater Reclamation Facility, according to nonprofit Ridge to Reefs and its partner Sunshine Vetiver Solutions. This nature-based system could help with managing and reusing excess treated wastewater leaching into the ground and ocean from cesspools and injection wells in Maui County. RIDGE TO REEFS photos

A team of specialists may have found nature-based, low-cost solutions for managing and reusing excess treated wastewater leaching into the ground and ocean from cesspools and injection wells.

Next to the Kihei Wastewater Reclamation Facility is a 13,000-square-foot test site with a garden of vetiver grass, which, with its “extensive root system,” can soak up, filter and dispose of excess R-1 wastewater from the facility through evapotranspiration.

After 10 months since the planting last summer, the pilot project was disposing about 30,000 gallons of wastewater per acre per day, according to nonprofit Ridge to Reefs and its partner Sunshine Vetiver Solutions in Kihei.

“It was pretty amazing,” said John Astilla, owner of Sunshine Vetiver Solutions. “We didn’t see any runoff coming from the project site and even walking between the rows, it was saturated but not ponding and it wasn’t mucky.”

During the Maui Nui Marine Resource Council’s monthly “Know Your Ocean Speaker Series” on Wednesday night, the project’s team shared their one-year update on the filtration system involving noninvasive vetiver grass in Kihei.

Paul Sturm, founder and executive director of Ridge to Reefs, spoke about the results of a pilot project to dispose of wastewater in Kihei during a meeting on Wednesday with the Maui Nui Marine Resource Council.

“We can use these nature-based solutions to provide high-quality, clean water to farmers and others that are growing crops that help to support us,” said Paul Sturm, founder and executive director of Ridge to Reefs.

At the beginning of the study, the team estimated that this system would take up and dispose of roughly 20,000 gallons of wastewater per acre, but to their surprise, it filtered much more.

Even in high-saturated and rainy situations, the grass still takes up water, Astilla said.

Based on these results, and knowing that the treated wastewater generated at the Kihei Wastewater Plant is at about 2 million gallons, he said that the vetiver-based system has the potential to process 1 million gallons per day per 30 acres.

“We can take that wastewater and irrigate roughly 60 acres with vetiver grass and you know, shut those injection wells off,” Astilla said. “Our nature-based system is low-cost and can be quickly implemented in the interim while longer-term construction of R-1 wastewater reuse infrastructure is underway.

“There’s been a lot of interest in water, especially with drought conditions and we’re all for support anyway to stop those injection wells.”

Currently, there are 88,000 cesspools across the state and over 20 million gallons per day of secondary treated wastewater is being injected into the ground, which impacts groundwater and coastal ecosystems, Sturm said.

In 2017, the Hawaii State Legislature passed Act 125, which mandates that by Jan. 1, 2050, all cesspools in the state, unless granted exemption, must upgrade or convert to a septic or aerobic treatment unit, or connect to a sewer system.

But, replacing a cesspool with an approved septic system is costly for most homeowners, with an average cost of more than $23,000 per cesspool replacement, according to the Maui Nui Marine Resource Council.

“There’s really no clear path forward on a funding mechanism to facilitate the conversion of these cesspools by 2050 as mandated by Act 125,” said Sturm.

Growing vetiver grass combined with native plants in rows or in a raised garden bed, which is excavated and filled with recycled wood chips, gravel and biochar, can trap sediment and is efficient at absorbing and removing phosphorus, nitrogen and other nutrients and pollutants that are coming out of Kihei’s wastewater plant before they reach the ocean.

The first part of the filtration system involves converting ammonia, often found in urine, to nitrate. Then through plant absorption of water and pollutants, the nitrate is converted into nitrogen gas, which goes back into the atmosphere.

There aren’t any smells associated with the system, Sturm and Astilla said.

A University of Hawaii study tested the system from about March to August 2021 and found that it was successful at removing 87 percent of total nitrogen, 80 percent of phosphorus and 95 percent of sediment, as well as meeting national water quality standards, Sturm said.

“So the amount of water lost or the amount of effluent lost to the environment is much less,” Sturm said. “Probably an average two, three-bedroom home probably only uses two to three hundred gallons a day, so we’re able to seriously reduce the amount of pollution that’s actually getting into the groundwater.”

This treatment process happens naturally already in the environment, but this project takes that same concept and mimics it in a more controlled setting.

“We’re just using Mother Nature as a guide,” he said.

Another benefit is that it doesn’t require an external energy source, so “in some ways, this offsets a household’s carbon emissions, which we all know is necessary to reduce the impacts of climate change,” Sturm added.

Vetiver, which has been used in Hawaii for over 30 years, does not have an annual cessation period like other crops or grasses, meaning that it will consume water and nutrients year-round and does not spread. Besides an annual pruning, these systems are low maintenance once made.

Interestingly enough, the team also found out this past year that vetiver grass is not palatable by feral deer and ungulates. With its peak height of about 10 to 12 feet, vetiver may offer an alternative to conventional fencing to keep deer away from native plants, agriculture and ranch lands, Astilla said.

And since it’s locally grown, there is an opportunity to create jobs and support the local economy, he said.

After installing these nature-based systems in several other places worldwide, including for a hotel and restaurant septic tank in Puerto Rico, an elementary school in American Samoa and farms in Virginia and Maryland, Ridge to Reefs found that these projects typically, on average, are about $10,000 less than an aerobic treatment unit, Sturm said.

Still, the organizations hope to conduct more pilot projects in Maui County to continue testing the system and achieve zero discharge, such as in West Maui, by planting vetiver on-site near the injection wells that pollute the coastal waters and degrade the reefs.

“So the idea would be to have some of these systems treat that water and then the effluent from the water be pumped up the hill to the Kaanapali Coffee Farm who really needs the water for growing the coffee,” Sturm said.

There are a range of options to establish a permanent system, such as at the current site above Piilani Highway adjacent to the Kihei Wastewater Reclamation Facility, but expanding in order to filter the 2 million gallons of wastewater coming from the plant, or nailing down smaller-scale sites in strategic locations along current R-1 reuse water lines.

As the demand for R-1 water changes, the amount of water directed to the grass can be adjusted, he said.

“Accessing the land has been challenging for us,” Astilla said.

* Dakota Grossman can be reached at dgrossman@mauinews.com.

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