Massachusetts Test Center Looks for Practical Wastewater Reuse Solutions

Hydroponics could provide an efficient way to take advantage of nutrients from decentralized wastewater systems

Massachusetts Test Center Looks for Practical Wastewater Reuse Solutions

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In the summer of 2019, the Massachusetts Alternative Septic System Test Center on Cape Cod started a campaign called Waste No Water. In 2020, the center took the idea a step further by experimenting with recycled water for hydroponics. The intent is to get people thinking about how to care for a resource that may not seem important to Massachusetts residents.

“Around here in the Northeast, we have so much water it’s not something people think a lot about,” says Brian Baumgaertel, director of the center, which is part of the Barnstable County Health Department. “We pump water out of the ground — freshwater — clean it up, send it to a house. A lot of times we spray it on our yard or on our plants, and put it back into the ground. It seems awfully wasteful to waste our wastewater after it’s been treated.”

For a nitrogen removal project, the center staff had built a 36-foot-by-24-foot greenhouse. Inside the greenhouse were sand columns in 55-gallon drums. 

Plants thrive on effluent

“Simple sand columns are really great at treating wastewater,” Baumgaertel says. Most pathogens are removed by the columns, but there is residual nitrogen and phosphorus. Combined with the greenhouse, it was a natural combination for trying some hydroponics, he says. 

“We found that sunflowers love treated wastewater,” he says. Tomatoes, peas, cosmos and marigolds also liked feeding on effluent. “Zinias grow amazingly well.”

Outside the greenhouse are some small gardens fed by water from the center’s “layer cake” treatment system. This is a non-proprietary technology that typically consists of layers of soil and wood chips. The chips act as a carbon source for bacteria that transform nitrate into nitrogen gas. 

For his “cake,” Baumgaertel used a tank bottom that he turned upside down and made into a sand filter. Water from that flowed through a 30-gallon barrel of wood chips for denitrification. The principle is the same for the larger denitrifying systems running at the center, but it’s still amazing to connect a series of odds and ends and see the process work, he says. 

The garden may also eventually become a test system to measure whether its plants will remove more nitrogen from effluent.

“This was all done with spare parts laying around and no money,” Baumgaertel says. 

Testing was done only for fecal coliform to ensure the center’s workers were not at risk, he says. (Coliform was less than 10 cfu per liter, and the threshold for swimming is much higher, he says.)

A vinegar feed?

In typical hydroponics, plant roots are immersed in a solution of water and various nutrients. In the center’s experiment, no chemicals were added to the treated wastewater; plants fed only on effluent. 

“In the beginning I messed around a little bit with the pH,” he says. Initially water from the sand columns was at a pH of 8 or 9, sometimes as high as 10. Baumgaertel experimented with a vinegar feed to correct that, but ultimately it wasn’t necessary because the sand columns rebalanced themselves and began producing effluent at pH 6 to 7. 

“Sand filters are pretty amazing things,” he says. 

There was a very small amount of nitrogen removal in the garden, only 5% to 10% of what came in with the effluent, he says. But his system was on a very small scale, so you wouldn’t expect a major effect, he adds. And there was no consistent sampling; Baumgaertel measured the water with the center’s YSI (a Xylem brand) meter only a few times when he had a spare moment.

“We’d really need to do laboratory analyses to actually do a serious study of the removal rates,” he says. 

Baumgaertel’s hope is to turn the garden and greenhouse into a demonstration project to show people alternative water uses. And the garden and greenhouse systems were built so water moving through them can be sampled for formal studies.

Promoting the idea

How quickly the project matures will depend on the county’s budget, and that is being affected by the COVID-19 pandemic. Baumgaertel says his next step would be to add a subsurface irrigation system.

Although produce from the gardens was not intended for human consumption, that doesn’t mean it won’t happen. 

“If you look at biosolids application, some states allow it for agricultural purposes,” Baumgaertel says. Using recycled water in that way will be a matter of getting the public and regulators comfortable with the idea, he says, but if that comes about, it would open a whole new chapter in water use. 


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