Incorporating air or oxygen into irrigation water using nanobubbles can improve crop yields and reduce susceptibility to disease pathogens.
What started out as a way of making wastewater treatment systems more efficient with oxygen enrichment has expanded to how nanobubble aeration technology can improve production of agricultural crops. Moleaer Inc. in Torrance, Calif., filed a patent on nanobubble aeration technology in 2016 with the intention of using it as a way to deliver gas in a number of different applications.
“This nanobubble technology usually relates to some type of oxygen enrichment application to support either biological or oxidation processes,” said Warren Russell, co-founder and chief commercial officer at Moleaer. “We spent most of 2017 focused on wastewater applications, which require oxygen transferred into water to support different treatment processes. In doing so, we inherently understood there were other applications that benefit from oxygen, including hydroponics and aquaculture.”
Moleaer worked with UCLA researcher Michael Stenstrom to determine the efficiency of the nanobubble technology.
“A nanobubble as the name implies is essentially a very small bubble in the nano scale range,” said Russell. “A unique property of a nanobubble is that below a certain size, in this case below 1,000 nanometers, it starts to behave differently, losing its buoyancy and behaving closer to a colloidal particle.
“In the case of Moleaer’s nanobubble generators, they introduce nanobubbles that average around 100 nanometers in size in very high concentrations. In some instances, the generators have been able to produce concentrations up to 500 million bubbles per milliliter of water. This has been validated with a laser particle counting instrument called the NanoSight. Another unique property of the nanobubbles is they have a negatively charged surface. This prevents the bubbles from coalescing and inhibits smaller bubbles from becoming bigger bubbles.”
One of the most important findings about the nanobubbles’ properties is that during the production of nanobubbles a reserve of oxygen bubbles is introduced into the water.
“Instead of there just being dissolved oxygen in the water, nanobubbles introduce a second form of oxygen that creates a battery-like reserve of oxygen that continues to transfer oxygen into the dissolved phase,” Russell said. “We are very interested in how these nanobubbles enhance applications like hydroponics.”
Maintaining consistent oxygen levels
Russell said one of the initial introductions to hydroponics was started with an issue that Hort Americas was having in production trials of leafy greens in its demonstration greenhouse in Dallas, Texas.
“During hot summer months the water in the greenhouse environment becomes very warm and there can be issues with low dissolved oxygen in the irrigation water,” he said. “In other projects that we have been working on, we have observed that our systems and the methods by which we introduce the nanobubbles are able to overcome some of the limiting factors of oxygenating warmer water. We attribute this to the significantly larger surface areas of the nanobubbles and their ability to transfer oxygen more efficiently. We were interested at the onset of the Hort Americas trials to demonstrate not only that we could create a more oxygen-rich environment, but could also maintain it at that level more consistently. We were looking to see if those elevated dissolved oxygen levels could improve crop yields and prevent root diseases like Pythium.”
Moleaer, which is also working with a large commercial hydroponic grower, has shown that its nanobubble generator produces a consistent, cost-effective oxygen level throughout the production system.
“The grower we are working with has six 100,000-gallon deep water tanks,” Russell said. “Before installing our system, the grower was aerating the tanks with oxygen and diffusers. This resulted in a very inconsistent level of dissolved oxygen throughout the tanks. There was a big fluctuation in dissolved oxygen levels ranging from 2-5 parts per million in different zones. When one of our nanobubble generators was installed in a marginal area, the oxygen level was converted to a consistent 9-11 ppm wherever the water was tested with the same utilization rate. This demonstrates how well the nanobubble generator can mix and deliver oxygen throughout a system.”
Russell said the limitation for hydroponics and agriculture in general is that deep water culture tanks and water storage tanks are not very conducive to efficient aeration with conventional aeration technology.
“The way aeration typically works is air or oxygen is generated by power or an oxygen source,” he said. “As the air or oxygen is introduced to the water and the bubbles rise through the column they are dissolving 1-3 percent of oxygen per foot of water, depending on their size. It’s incredibly difficult to achieve a high oxygen transfer efficiency in a deep water culture tank that is only 18 inches deep. That is why growers are seeing such large inconsistencies with conventional aeration systems, even if they are pressurizing the water to increase oxygen saturation. An optimized conventional setup may at best produce up to 50-60 percent oxygen transfer efficiency. When a grower is paying for the oxygen, we consider that an unacceptable loss rate.
“By comparison, our research with Dr. Stenstrom at UCLA validated the oxygen transfer efficiency for the Moleaer nanobubble generators to be about 86 percent per foot of water. That makes a massive difference in the amount of oxygen delivered and is one of the primary reasons why we have an excellent economy of use with oxygen. Most importantly, it makes the use of oxygen more affordable.”
Impact on plant pathogens
Russell said different times of the year will require different levels of oxygen.
“It is going to be a fluctuating variable,” he said. “In summer with warmer temperatures, growers will want to maintain higher oxygen levels because they are more focused on disease prevention,” he said. “During winter when water temperatures are colder and there is less chance of disease, oxygen levels don’t need to be as high. In summer the oxygen level should be between 20-35 ppm. We’ve seen with 90ºF water, if the water is maintained at 29 ppm oxygen that was very effective in terms of yield increase and disease prevention. The results we have gotten are impressive. Also, different plants have different oxygen requirements.
“For some growers, it is going to be a balance between how much they want to spend on oxygen and what value they place on increased yields or improved disease prevention. Some of the growers we are working with are maintaining 15 ppm oxygen and are getting good results. Other growers are focused on doubling that concentration because they are looking to push the bar on what they are doing.”
Hort Americas is experimenting with incorporating air rather than pure oxygen during the cooler months and are seeing favorable results. Russell said that is encouraging from an operational cost perspective.
“Some hydroponic growers want to maintain a water temperature range of 65ºF-75ºF,” he said. “Once the temperature reaches 72ºF growers should definitely be looking at increasing the oxygen level.
“In most cases, disease pathogens are going to prefer an oxygen-deprived environment. An oxygen-rich environment is going to encourage and support beneficial aerobic bacteria to grow and proliferate. As long as these bacteria are healthy and growing they are largely going to starve out the disease pathogens. We are not claiming that nanobubbles are destroying pathogens. Rather they are simply creating an environment that’s not conducive for their growth.”
Ag industry applications
Russell said nanobubble technology has a wide range of applications in the ag industry for different irrigation methods. Nanobubble technology could be used with any crops that are watered with drip irrigation and subirrigation systems including flood-and-drain.
“Types of crops could range from citrus trees, nut trees and various fruit trees,” he said. “A lot of these applications would be to help prevent root diseases, including Fusarium, Phytophthora and Pythium.
“We’re also looking at berries as well. Because methyl bromide is being phased out as a soil fumigant, growers are looking for alternative ways to treat soil pathogens for crops like strawberries.”
Russell said nanobubble technology could be considered as a very effective method of delivering oxidizers to treat or condition soils to prevent disease.
“In hydroponics, ozone remains a common and effective biosecurity tool for many commercial growers,” he said. “But it definitely should not be the primary means of oxygenating irrigation water. Ozone generators are very inefficient at transferring oxygen into water and are definitely costlier to operate, not to mention more capitally expensive for larger systems. By comparison, nanobubble technology can create high levels of oxygen in water and can be a very effective means of preventing disease for a lower capex and operational cost.
“In addition, the high oxygen levels can have an impact on yield. What we have validated and continue to validate through our customers is that highly oxygen-saturated water can help plants develop a healthier root system that aids in or improves nutrient uptake and plant transpiration. Nanobubble generators can achieve much higher levels of oxygen saturation in water and maintain that saturation at very stable levels.”
For more: Moleaer Inc., (323) 389-1896; firstname.lastname@example.org; https://moleaer.com.
David Kuack is a freelance technical writer in Fort Worth, Texas; email@example.com.