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Friday, September 24, 2021

UC Davis researchers find a source of water in winery wastewater

KATIE LIN / AGGIE
KATIE LIN / AGGIE

University researchers, winery partner discuss safe reuse of vineyard wastewater  

In the face of California’s severe drought, UC Davis researchers have found a viable water source in winery wastewater.

Although vineyards have used winery wastewater previously, most of the data is found in the wine regions of Australia or Spain, and the usage of winery wastewater in California has been unprecedented — until now.

UC Davis researchers compiled data for the two-part study in the California wine regions of Napa and Lodi, hoping to educate California growers on how to reuse wastewater for irrigation in order to avoid harming the soil.

“It’s definitely possible to reuse wastewater,” said Maya Buelow, lead author of the study and UC Davis researcher at the Department of Land, Air and Water Resources. “You need some more tools to do it and these are the things you should probably be thinking about.”

The first part of the study consisted of a survey that included 18 wineries in California. Researchers looked at the chemical and physical properties of wastewater samples before and after treatment in order to characterize different waste streams. They also noted how much wastewater was produced during different seasons. This data was used as a baseline for growers to look back on when deciding whether to reuse wastewater.

“The winery wastewater [that is reused] is just water that’s generated inside of the winery,” Buelow said. “So this isn’t agricultural run-off water [or] water that is used to flush toilets. It’s just water that’s inside of the wineries usually used for cleaning and for chilling.”

The researchers characterized the winery waste stream that would be reused for irrigation as “water used for cleaning,” water that only contained chemicals used for cleaning. Buelow said that this particular kind of wastewater is already fairly clean, making it a viable alternative water source.

“We received monthly samples of the winery wastewater prior to treatment and then after treatment,” said Kerri Steenwerth, co-author and assistant adjunct professor at UC Davis. “We looked at the composition of the water to see what kinds of salts and other constituents, [and] what other kinds of materials were in there that might cause problems for reusing it for irrigation.”

The second part of the survey examined how the chemicals in the wastewater interacted with the minerals in the soil. The researchers focused on the sodium levels, since sodium has the most negative effect on soil.

“Having a high sodium content can cause problems with soil structure and that can affect the ability of the soil to receive water,” Steenwerth said.

To combat the high sodium content that ruins soil, wineries have been switching to potassium-based cleaners.

Researchers focused on three soil types from three different vineyards in Napa. They compared the change that sodium and potassium caused in the different soils, and the results showed that only one soil type could benefit from the potassium-based cleaner.

“The different potassium absorption ratios and the sodium absorption ratios show that the minerality of the soil must be considered when applying winery wastewater,” Steenwerth said.

With this information, vineyards are able to better manage how they reuse wastewater. They can take into account the type of soil they have and whether or not switching cleaners will have any benefits. There are also management practices to combat the negative effects of sodium and potassium on soil.

“When you put gypsum on the soil you’re bumping off the sodium or the potassium and replacing it with calcium,” Buelow said. “That allows the sodium and potassium salt to sort of get washed down.”

Despite the issue of sodium content, wineries are effectively reusing wastewater to combat the drought. By using hot water to sanitize barrels, the Putah Creek Winery, located approximately ten miles from Davis, avoids the problem that is caused by cleaning agents. Their water comes from a well on their 60-acre property in South Davis, and they use a water heater to boil the water used for sanitation.

“We reuse the rinsing water which is the wastewater, hot water that is used to wash barrels, tanks and whatnot. That water flows into a pond that is pumped out and irrigates the vineyard,” said Jessica Chin Foo, managing partner at Putah Creek Winery. “It’s not water that has any agents.”

The findings of the study allow wineries that want to reuse wastewater to make more informed decisions. This resourceful method could prove important in California’s dry terrain.

“The composition of the wastewater after treatment was satisfactory for use in irrigation in most cases,” Steenwerth said. “They were effective at cleaning up the water and they could be reused for irrigation.”

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