Nanobubble technology

Features - Technology

A look at this type of oxygenation system, now installed at over 300 greenhouse sites worldwide.

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November 23, 2021

Any new water oxygenation technology must be both effective and economical to be considered as a replacement for existing systems available on the market, most of which use diffusers to blow or mix in ambient air. In 2019, Greenhouse Management first mentioned ‘nanobubble’ technology (bit.ly/nanobubble-hort) developed by a California-based company called Moleaer. Its systems are used across the world in several industries such as wastewater treatment and aquaculture, and are also installed at over 300 greenhouse sites at this point.

Nanobubbles, as you may have guessed, are microscopic. Moleaer explains that they remain suspended in water, delivering consistent and constant super-high dissolved oxygen (DO) levels (see more in sidebar).

Bart Jongenelen, a scientist at Delphy (a Netherlands-based firm that provides independent horticulture testing), has done trials on the Moleaer technology. In summarizing it, he’s explained that “first, nanobubbles deliver oxygen extremely efficiently into water, which allows us to maintain very high saturation levels with minimal loss. This enables us to deliver significantly more oxygen into the root zone and promote healthy root development. Second, the oxidative properties of the oxygen nanobubbles break down algae and suppress pathogens, effectively improving the water quality and maintaining a more hygienic irrigation system.”

To help you get to know this technology, we’ve gathered details of the Delphy study, results of some other studies and contacted two growers.

Trials in Europe and U.S.

Last year at Delphy, hydroponic greenhouse strawberry plants were compared for yield and disease incidence. The control group was exposed to 7-9 mg/l (ppm) DO, while the group in the nanobubble-treated water had 30 ppm (water temperature not measured). Jongenelen and his team concluded that the Moleaer group achieved a yield increase of 14% over the control group, with 74% lower Pythium counts.

Bruce Bugbee, a professor at Utah State University, has found that while Moleaer tech is “excellent at super-elevating DO,” the oxygen can “quickly come out of the water” after irrigation. “We’ve done several studies over the last three years (in deep flow hydroponics and also soilless media) and have had difficulty maintaining super-high DO levels in the root zone.”

Isabel Vandevelde and her colleagues have recently studied Moleaer tech in three types of lettuce grown in peat blocks in a ‘mobile gully’ hydroponics system at the Research Center for Vegetable Production in Belgium. Over five months, they compared plants receiving UVC-disinfected water (250 mJ/cm²) with nanobubble-treated water (achieving generally 18-22 ppm at 71-84°F, measured weekly). They found the average weekly weight of the nanobubble lettuce was 13% higher when UVC was used only to disinfect the water pumped from a silo with drain water to a silo with clean water. In July 2021, when they circulated the water continuously over the UVC in the UVC treatment, there was no difference in weight. She also reports that “in June, we had a natural infection of Phytophthora cryptogea in both lines at the same moment. We saw that the line with nanobubbles [recovered] faster.”

Grower experiences

John McMahon, owner of Schuyler Greens Company hydroponic greenhouse in Schuyler, Virginia, added a Moleaer system in 2018 to his existing UV system for disinfection and Venturi for oxygenation. “At 74°F, the most I could achieve in a Venturi system is 8.4 ppm using ambient air,” he says. “I have easily achieved 26 ppm using a nanobubbler at that temperature, but lowered it to 18 ppm, as there are diminishing returns (more cost than benefit) at the higher level.” McMahon measures DO level regularly throughout his water system, including about an inch away from plant roots.

Since the installation three years ago, he’s seen much improved water sterilization and water quality with no biofilm or algae. There has also been no Pythium, even at higher water temperatures.

Regarding plant performance, McMahon says “root density is much greater and the crops are healthier. In terms of yield, arugula has responded the most, with faster growth and 10 to 15% yield increase, being conservative. It’s been pretty dramatic. With kale, Cristobel lettuce and many other lettuce varieties, I’ve seen a yield increase average of 8%. I achieved ROI somewhere between 12 to 18 months after install.”

Last year in May 2020, Moleaer tech was also installed at One Thousand Palms Associates in Los Angeles, California. It’s a licensed indoor cannabis cultivation firm under white-label contracts for several well-known brands. 

In researching ways to boost DO level, Head of Cultivation Alex Huf says “Moleaer looked promising based on everything we could read online. The sales pitch seemed very grounded in practical scientific realities with no outlandish claims. Finally, we called a trusted cultivator who confirmed that their Moleaer unit was definitely worth it. Previously, we were using very basic strategies to increase the DO level of our nutrient batch tanks (large air stones and waterfall recirculation). This created a lot of maintenance issues and the result was not worth the effort.”

The Moleaer unit was easy to install, says Huf, but did require changes to the layout of the reverse osmosis (RO) system. That is, to maintain the highest DO level for the longest period of time, the surface of the RO water and nutrient solution need to be kept as still as possible. “In our case,” he says, “this meant removing all air stones, air lines, air pumps, waterfall recirculation piping, and re-piping our RO feed spout to fill from the bottom of the tank.”

With the previous air stones and waterfall technique, he had achieved a DO of 8 ppm. The Moleaer tech consistently provides 30+ ppm at 64°F. Keeping the water cold, Huf says, is “another strategy for keeping the most amount of DO in our water for the longest period of time. Colder liquids store a higher base level of dissolved gas at full saturation, but this also has to be balanced against other considerations like RO membrane efficiency (it gets worse as temperature decreases), batch mixing (it takes longer to effectively mix nutrient batches with very cold water) and nutrient uptake (cold feeds can lockout certain nutrients and metabolic pathways).” 

Regarding how this has affected the plants, Huf first explains that the facility is set up in two growth stages, vegetative and flowering. “‘Veg’ is a very static environment with a dialed-in nutrition program, so that’s where we immediately noticed the benefit of having the Moleaer machine,” he says. “Adding super-saturated RO water was the only change we made. It started with the clone station. After switching over to clone nutrient solution that was prepped with super saturated RO water (and immediately feeding after prep), we noticed a complete falloff in incidents of unwanted biological growth in the high-humidity environment. Not only that, but clones rooted with more vigor and looked consistently healthier. The average number of clones that die prior to transplanting also went down sharply.”

After clone transplant, young plants are placed with the bottom of their root ball in the middle of the growing medium container. “Those roots are in an area with the least available oxygen at a point when they are most susceptible to anaerobic bacterial growth,” Huf explains. “Having a nutrient solution that’s supersaturated with oxygen directly addressed this concern. It gives us better rooting during the vegetative stage, more consistent growth across the canopy, a safety buffer for times when a plant is slightly overwatered, and an overall increase in plant vigor.”

Huf adds that all these benefits allow him to push the plants in the flowering stage “to their limits in a way that our previous nutrition programs didn’t touch … The results the Moleaer machine helped create in veg directly translated to an increase in the yield and quality of our product during the flowering phase.” He puts his most conservative ROI estimate at six months and has purchased a second larger Moleaer machine for a new facility.