Harness the Power of Nanobubble Technology
Updated: Feb 16
Does your municipal or industrial wastewater facility have issues with fats/oils/grease (FOG), floating solids, surfactants, or sustaining BOD? In wastewater treatment, process upsets, poor treatment efficiency, and reduced treatment capacity are often caused by toxic and inhibitory substances like surfactants. These issues have become more prevalent in recent years due to increasing surfactant concentrations in wastewater. This situation has put immense strain on the performance and operations of wastewater resource recovery facilities (WRRFs). In December, our team hosted an online webinar with Moleaer to share information on the nanobubble technology, applications, and incredible results from these tiny bubbles.
Andrea White of Moleaer was the featured speaker. Andrea is the Global Director for Water Process Engineering at Moleaer. Andrea has been with Moleaer for four years; previously working for CDM Smith as a consultant doing wastewater treatment process design - specializing in biological treatment systems, secondary treatment systems and aeration systems. Andrea commented, "I am very excited after four years of development of the nanobubble technology, I am glad I can share the remarkable findings with nanobubble treatment."
Moleaer's nanobubble technology is relatively new to the wastewater industry, yet they have participated in over 2,000 projects and installations in a variety of industries. The nanobubble technology can be applied in industries, such as:
Oil & gas
What is the one item that all these industries have in common? Water. Andrea stated, "If it touches water, we can use nanobubbles to improve water quality or instances with growing food to increase yields. Today we will focus on wastewater."
Overview of the Water Cycle
In constructed wastewater treatment environments, the water enters the plant from stormwater and collections systems from industrial or residential customers. Andrea stated, "The main takeaway is that nanobubbles can be used to reduce the cost to treat wastewater in dollars per gallon. We are looking at lowering O&M and capital costs by increasing treatment capacity through wastewater treatment intensification and overall providing better water quality more efficiently. We are lowering costs associated with chemical consumption and power consumption."
Nanobubble pretreatment generally requires screened, raw wastewater. The preferred injection points are from headworks to the primary equalization tank, or the channels in between the structures. Moleaer requires open access where the nanobubble generator can pull wastewater from a basin or channel. This ensures the water is recirculated through the nanobubble generator and returned back to the process (upstream from biological process.) It is important that the nanobubble treated water is returned back to the process upstream; before the RAS is added back to process.
The Moleaer nanobubble technology is simple in concept. The nanobubble generator or "core technology" requires liquid (water) to be pumped through core technology and the technology requires a gas source. The gas flow is low compared to a classic aeration system. The nanobubble generator generally requires gas pressures in the 30 – 40 PSIG range, and gas flows in order of SCFH instead of SCFM."
Is there a specific type of gas that is required for the nanobubble generator? There are no specific gas requirements and plant air can be used. Moleaer uses the nanobubble generator to pump water through the "core technology" and add the gas supply. Once the gas is added, then the hydraulic conditions within the nanobubble generator produce small nanobubbles (on the range of 100 nanometers in diameter), which is injected into flowing liquid.
What are Nanobubbles
These tiny bubbles were initially discovered within crashing waves in the ocean and have been evaluated in scientific community for over 20 years. In this time, technology has been developed which can measure and study the effectiveness of nanobubbles.
Andrea White stated, "We can now produce the equipment to replicate the effects of the crashing waves by controlling hydraulic conditions to produce high concentrations of nanobubbles. That is where the value is. The nanobubbles are at this scale and size of viruses or bacteria and the bubbles behave differently, as chemistry or chemicals with special properties."
According to Moleaer's website:
Nanobubbles behave differently from larger bubbles because they’re nanoscopic. All of their beneficial attributes — stability, surface charge, neutral buoyancy, oxidation, etc. — are the result of their size. These unique features enable nanobubbles to participate in physical, biological, and chemical reactions while also providing the most efficient gas transfer.
Nanobubbles have created a new frontier of science and engineering that is changing how entire industries utilize and treat their water. Moleaer’s technology and fundamental understanding of nanobubbles is continuously evolving with recent advancements in nanobubble production methods and ongoing discoveries around how to measure, manipulate, and apply nanobubble properties to solve customer problems.
"As the bubbles get smaller in size, the shape will get to nanoscale. At this size, bubbles exhibit different behaviors such as Brownian Motion. Brownian Motion is a random motion. Rather than the bubbles rising to the surface and bursting like bigger bubbles, the bubbles will move randomly. The nanobubbles have high internal pressure and the pressure, along with negative surface charge, makes the nanobubbles electrochemically active. The bubbles begin to participate in reactions and degrade contaminants that larger bubbles won’t be able to interact with."
High internal pressure
Hard ‘shell-like’ surface
High gas transfer efficiency
Stable & long lasting
Reduces surface tension
What are Surfactants?
Many people don’t realize just how broadly surfactants are found in wastewater. Surfactants are compounds which are used in all of our detergents - from laundry to dishwasher, degreasers, our personal care products like shampoos and our body wash, and our cleaning and disinfection products.
There are four types of surfactants:
Cationic - positive charge, includes quaternary ammonium compounds which are used in disinfecting surfaces in meat, poultry, dairy facilities as well as universities and hospitals for maintaining public safety
Anionic - negatively charged
Nonionic - neutral charge
Zwitterionic - both negatively and positively charged
Amphiphilic vs. Amphipathic
"There is a class of compounds in wastewater that fall under the category of amphiphilic/amphipathic molecules. Specifically in wastewater, we look at FOG and surfactants and how nanobubbles can remove those compounds. These molecules are labeled as such (amphiphilic or amphipathic) because they have a hydrophilic head-group and hydrophobic tail-group."
"When you hear about colloidal materials or the other challenges that are caused from materials that pass through various types of treatment processes, they are hard to treat and cause various problems within an activated sludge process. Those molecules tend to be these amphiphilic amphipathic molecules. The nanobubbles, which have a hydrophobic surface, will get this hydrophobic attraction between the nanobubbles and these molecules. The molecules will line up around the surface of the nanobubbles and when they surround the nanobubble, it collapses. The nanobubble releases its high internal pressure in the form of heat and is sufficient to create the hydroxyl radical. Those two mechanisms lead to what is known as thermal oxidative degradation."
The nanobubble is able to oxidize and degrade contaminants that are within a localized close proximity of the bubble, such as the FOG and surfactants. Wastewater operators know that FOG and surfactants contribute to COD and/or BOD. Some of these compounds are readily biodegradable and they will show up in your BOD. Those compounds that are not readily biodegradable will show up in your COD.
"You are already measuring COD and BOD at the facility. It’s just not necessarily being measured out to the water quality parameters of surfactants for example. These constituents are one of the main inhibitors of the activated sludge process and that’s because of their ability to coat surfaces. At the water surface for example, inside of a gravity pipe or basin, they will tend to accumulate. Their hydrophobic head is in the water and their hydrophilic tail ends up getting a chain of water molecules. The chain of water molecule that is built around the hydrophilic head will get trapped and trained in that water, so it’s very difficult to remove them."
"As they accumulate like this, you can imagine at the surface of the water they impede the transfer of oxygen into that water body. Natural surface transfer that should be happening across process units is not happening. This is why you see things like scum developing on primary clarifiers, septicity, odor - which will ultimately lead to corrosion and other challenges. Getting these materials out of the water enables the dissolved oxygen to transfer from the surface of the water to prevent some of these harmful conditions. Surfactants also coat solids and emulsify wastewater. When you start to get concentrations that are high enough in these materials, you’re emulsifying the wastewater. You can have poor solid separation across solid separating units such as dissolved air floatation, primary and secondary clarifiers."
"Another fact about these compounds is that they are slowly biodegradable. Essentially, they are a carbon source, and they are very hard for the bacteria to get at. Biomass prefers readily biodegradable carbon, so you will end up with a less efficient biological process because your bacteria is working so hard to try and get the carbon from these slowly biodegradable sources. One of the things we have observed with nanobubbles is that as they oxidize, these slowly biodegradable compounds are actually breaking down into a readily biodegradable form - which is then improving the kinetics for these biological processes. In addition to coating solids, surfactants will coat air bubbles (such as those from your fine bubble aeration system) which will impede the transfer of oxygen to that water body."
"This is often captured in the alpha factor and if you have a lot of surfactants in the waste stream you will have a lower alpha factor. This means your facility will have to apply more oxygen. More oxygen means bigger blowers and more diffusers to meet the oxygen demand of the system, because these materials are interfering with the transfer from the bubbles from the aeration system. In addition to coating the biomass and creating other issues related to separating solids and the ability to uptake the carbon, they also impede the transfer of oxygen through the biomass. By removing the surfactants, you can maintain a more aerobic biomass. Surfactants can also be toxic to the plant bacteria. As you may know, these surfactants are widely used in disinfecting chemicals (both industrial and household strength chemicals). They tend to be especially toxic to nitrifiers. Because of the toxicity, this results in lower kinetics and you will see it expressed as poor nitrogen removal efficiency or poor ammonia removal rates."
"Lastly, because surfactants are only partially removed by physical and biological processes, they will pass through the facility slowly biodegrading - unless you have an extended aeration process. It is going to take so long for these materials to break down compared to if they pass into the natural environment. In a natural environment, they will end up breaking down and then they will end up consuming the dissolved oxygen in those receiving waters. If your facility is using a strong oxidant, like chlorine for disinfection, in which case the surfactants will be oxidized by your disinfection system. But the surfactants will cause you to have a higher chemical consumption rate and demand then what would be necessary if you are able to get the compounds out in pretreatment."
Factors that Have Increased Surfactants in Water Treatment
You may ask, "Why are waste streams concentrating over time?" A lot of it has to do with a variety of factors that are going on in our environment and changes in human habits in the past 20 years.
We have switched from using bar soaps to liquid soaps/products.
The pandemic increased the use of disinfection chemicals.
The fear around contaminated food sources, such as lettuce recalls. (Food producers are using disinfection products as a means of protecting themselves from the liability associated with foodborne illness.)
Overall, less water is being used.
Different regulations and building codes have tried to address water conservation in response to drought.
Switching from old appliances (which used a lot of water) to high-efficiency appliances which use less water.
There have also been improvements to our collections systems in reduction of influent infiltration.
Chemical toilet waste from planes, buses, RVs, porta-potties will have chemicals that fall under the category of surfactants.
This is all resulting in the concentrating of contaminants which include FOG and surfactants in the waste streams that are being treated by our facilities.
Surfactants in Wastewater Treatment Process
How do nanobubbles interact with surfactants in the wastewater treatment process? The graphic displayed conceptually shows what it would look with the nanobubble and the surfactant materials lining up around it. You can see the hydrophilic heads pointed outward and their hydrophobic tails pointed towards the hydrophobic surface of the nanobubble. Essentially, there is a hydrophobic force attraction which is bringing these molecules within proximity and causes them to line up around the bubble. When the nanobubble bursts, it is going to break apart these molecules, removing and degrading them.
"By getting these surfactants out of the waste streams, we lower the cost to treat ($/gal), less capital expenditures (CAPEX), and operational expenditures (OPEX). Moleaer nanobubble technology can provide wastewater treatment intensification. What this means is you can use your existing infrastructure to treat more load. Nanobubble technology can also be implemented in a new construction environment. When installed in a new wastewater treatment plant, you would have smaller process units and ancillary equipment to support those units, improved energy efficiency, improved BOD/COD/N removal efficiencies, less chemical usage associated with disinfection systems, as well as potentially lowering ferric and polymer usage. Overall, we are looking to provide best-in-class removal and energy efficiency for wastewater treatment using nanobubble pretreatment," commented Andrea White.
Improve Treatability & Efficiency of Wastewater Treatment
When Moleaer is designing a wastewater treatment process for a facility, the team looks at the different types of COD or BOD that is in the waste stream. This information helps Moleaer determine which process units are best to use and treat that waste stream.
"We look specifically through doing what is known as COD fractionation or influent wastewater characterization. We want to understand how much of that COD is inert and particulate. Those are the ones that are going to be removed by the separation processes. We have inert and soluble; that’s going to pass through the plant unless you are doing advanced water treatment. Then we have slowly biodegradable which as noted is only partially removed."
"Oftentimes COD is removed with the biomass (coating the biomass) and if you have an anaerobic digestor, you are basically transferring these materials from your liquid stream to your solid stream. Then they are going to create a similar level of chaos within your anaerobic process. Without nanobubbles, we are finding that you have your typical COD fractionation and then when you inject your nanobubbles we are seeing that the slowly biodegradable portion is being degraded to a readily biodegradable."
How We Prove that Nanobubbles Work?
Moleaer offers a mobile lab to facilities and customers where the nanobubble technology is being piloted or the team is gathering information on a new process or assisting with sizing. Andrea White commented, "Having the mobile lab allows the team to dig more into the COD fractionation and the effects of nanobubble pretreatment to get a better understanding of why we are seeing what we are seeing in the field. The mobile lab has everything we need in order for us to collect fresh wastewater samples and conduct the COD fractionation on site. We have discovered going through a third-party lab was not providing the quality data that we need to be able to gain the level of understand that we are looking to gain."
Recent Moleaer Installations & Nanobubble Success Stories
The Copenhagen, Denmark installation was completed in November 2022. This is a 20 MGD treatment plant and they are injecting nanobubbles on the primary clarifier. Pictured here, the plant has a submersible pump that is installed on its side, pulling from the rectangular primary clarifier (after the scum is removed) and injecting back into the same location.
For this application, two NBG6 units are operating in a series. The facility has two other nanobubble generators in a series that returns the nanobubble treated wastewater back to the primary clarifier. The Copenhagen facility has eight primary clarifiers, but Moleaer started off with treating one with nanobubbles to see the effects. "What the team saw within just a few days of operation was incredible. In the pictures below, you can clearly identify the primary clarifier that is receiving the nanobubbles and one that is not. Keep in mind, the clarifiers all looked similar to start with about 5” of scum (FOG) and all the problems associated with that with poor oxygen transfer, odors, septicity, issues with solids going septic," stated Andrea White.
The primary clarifier pictured below with the nanobubbles, you can clearly see the FOG and surfactants are oxidized and removed. Andrea White described, "The interesting thing to me is that with where these clarifiers are being injected. They are being injected at one location, but it really shows the dispersion of nanobubbles throughout the basin to effectively treat the entire surface. It is not just a localized effect, but they are spreading out as you would expect with the Brownian motion from the bubbles."
Another successful Moleaer nanobubble pilot took place at the Goleta Sanitary District with significant, sharable data. The Goleta Sanitation District is located in Goleta, California on the central coast. This facility has a hydraulic treatment capacity or permit capacity of 9.5 MGD and are currently treating 4.2 MGD average annual dry weather flow.
Goleta has a very high-strength wastewater, and it is largely due to the impacts of drought and water conservation in this area. "As a consequence, even though they are not close to their hydraulic loading limit, Goleta is very close to their organic and solid floating limit – so they are operating at capacity," disclosed Andrea White. The treatment plant superintendent for Goleta was aware of the impact of surfactants on the facility since 2016. Goleta did a large study where they identified some sources within their collection system from industrial users (such as the airport and dumping of toilet waste from airplanes). This was causing big problems at Goleta.
After identifying the sources of surfactants, Goleta was able to eliminate those contributors and the issues seemed to get better. In 2020 the pandemic hit. Goleta has large contributions of wastewater from UCSB (University of California Santa Barbara) and hospitals (which started using more of the disinfectants.) Goleta had all their problems return and they were at a loss for how to resolve these issues. The facility was having process upsets, losing their ability to treat and meet compliance with their permits.
In March 2022, the Goleta Operations Superintendent opened TPO magazine, was flipping through it and came across a Moleaer article about how nanobubbles were installed at another facility in Fallbrook, California to remove surfactants. The superintendent contacted Moleaer and got a unit installed and began treating on May 10, 2022.
"With the Moleaer pilot, a self-priming pump was installed after the headworks with NBG6 on plant air. We are pulling water out of a channel at the headworks, sending the flow through the nanobubble generator and returning it back into that channel. Here is information on some surfactant data that we collected at Goleta. We looked at the three primary types of surfactants we see in municipal wastewater and came up with this total concentration. The total concentration of combined surfactants is around 12 mg per liter and this information was taken from Metcalf and Eddie from 2007 (so these numbers might look a lot different today with all of the changes.)"
"From this report, they said it was normal for typical untreated wastewater to have a concentration between 4-10mg. So, the test was more concentrated than the typical range from 2007. This is how many surfactants pass through each one of these processes. You would find surfactants in the Goleta effluent, indicating that obviously not all surfactants are being removed by the biological process. Within the biological process, some of those surfactants are readily biodegradable and could be removed but the majority of the surfactants are binding with the biomass and actually coming out with the sludge," explained Andrea White.
"In these images, we have nanobubble pretreatment and the effects of surfactant removal documented and graphed. We basically did a mass balance across the primary clarifiers to see how many surfactants were being removed both on raw wastewater upstream from NBG and across the clarifier. First, we have our influent (raw wastewater) before the NBG, then the nanobubbles are injected and this is the concentration in the sludge. So, what we found with the three types we tested, we are removing between 40% and 54% of the surfactants. We looked at quaternary ammonium compounds (QAC) and since most the cationic surfactants that you find in wastewater will be quaternary ammonium compounds. When we looked at non-ionic and the anionic, we looked at a lot of different types of surfactants, so these are the totals."
At Goleta, they were able to remove surfactants from the hydraulic equalization basin as well. Prior to nanobubble treatment, it was normal for the facility to see lots of foaming on the basin and there was a distinct odor. The team noted sometimes the foam would be so dense it would cover the entire surface of the basin. "You are not getting much oxygen transfer when you have a large surface area that is being blocked by surfactants and other materials. After nanobubble pretreatment, this is what it looks like now (see picture below.) There is no longer stable foam that accumulates, and their odors have been resolved."
The team also observed significant odor reduction in the primary clarifier because the nanobubbles were from preventing the sludge from going septic. "Because of the nanobubbles, Goleta was able to operate multiple primary clarifiers without risk of septicity. This gave the facility more flexibility with how their sludge handling operation. They are seeing nice compact sludge with clear supernatant above the sludge. There is no evidence of denitrification or fermentation," explained Andrea White.
The Moleaer nanobubble technology also improved TSS removal efficiency in the primary clarifiers. "In our research (chart below), you see here this is before nanobubble treatment (69%). When they started up the nanobubble generators, they immediately saw a 10% improvement. The bubbles were removing some of the compounds that caused the emulsification. That improvement was sustained throughout the entire pilot period."
"When you start removing these materials really far up in the treatment facility, you start to realize the benefits across multiple process units. These statistics are just across the primary clarifier. We can now start to look at what improvements were realized in the downstream process units because of the removal of these contaminants," noted Andrea White.
"Here we have the activated sludge aeration efficiency, specifically with the blower power draw. You can see here – prior to installing the nanobubble generator, the daily energy usage was 122kW. After the nanobubble generator start up, the energy usage dropped to 95kW. Now they have DO (dissolved oxygen) control with flow control valves and turbo-blowers, so they have a very efficient aeration system. That is an important factor to take into consideration because the amount of reclaimed will be directly related to how your system is configured. But, at this facility, they were able to immediately save 22%. That is attributed to the removal of surfactants and the impact of those surfactants on Alpha factor which is oxygen transfer rate."
"Then we start to see another step. Approximately two to three SRTs (solid retention times), you end up replacing the biomass naturally with a new biomass that was grown under nanobubble injection. The biomass that was in the reactors previously was acclimated to all of these toxic surfactants. Once you have removed the surfactants, you see the old biomass get replaced with a more efficient biomass. After the full exchange of biomass post nanobubble generator, you will notice an improved oxygen uptake rate. Post nanobubble generator with the acclimated biomass daily energy usage was 70kW (further reducing energy by an addition 21%.)"
Overall, the installation of the Moleaer nanobubble generator realized a
43% total energy reduction
Wastewater process upsets and swings are very tight now and the plant is not really experiencing process upsets like they were before nanobubble injection.
Activated Sludge: Improved Settleability SVI
According to TPO Magazine - "Sludge Volume Index (SVI) is a valuable measure of sludge settleability characteristics and can be monitored to help prevent process problems." Andrea White commented, "We have recorded real-time sludge volume index (SVI). One of the things the Moleaer team and researchers have noticed is the effect of nanobubbles on sludge settleability. At the nanobubble pilot in Goleta, the plant already had fast settleability because they are strictly a filter activated-sludge facility. After the nanobubble generator was put to the test, they had an even faster settling sludge -achieving 90% settle volume in less than two minutes. Before they were seeing SVIs around 66 within 30 minutes, so very low – border lining on a sludge densification is what they are observing. It’s actually one of the areas we want to start researching next is to understand whether we are forming granular sludge."
Final Effluent: Improvement in Quality
This is the final demonstration with data showing overall improvement in water quality. Andrea White stated, "Before nanobubbles were introduced, you see a divergence between BOD and TSS showing that the process is less efficient. Because your BOD is greater than TSS, what we want to see is that all of your BOD is basically converted to TSS and then it’s removed by your secondary clarifiers. Once the nanobubbles were started, this goes back to converting the slowly biodegradable to readily biodegradable and you see the process improvements. TSS and BOD values are coming into line with one another and after you replace the full biomass with a biomass grown under nanobubbles, they are tracking almost on top of each other. This statistic indicates that implementing nanobubble technology is a much more efficient treatment process because you are converting your BOD to TSS, and the nanobubbles are able to remove that with your secondary clarifiers."
Chlorine Contact Basin: Reduction in Chlorine Demand
Lastly, Andrea addressed the effect of nanobubble technology on the chlorine contact basin. "The data pretty much speaks for itself. Because those slowly biodegradable contaminants can be oxidized, they do consume chlorine. Once we started the nanobubble generator, they saw a 10% decrease in chlorine demand and then after the 2-3 SRTs, they saw it come down by another 34% for a total of 44% decrease in chlorine demand. This is all because they were able to remove those organic contaminants from their final effluent."
Cost/Benefit Analysis of Permanent Installation of Nanobubble Generator
After learning about the nanobubble technology and the numerous benefits to the entire wastewater treatment plant, what does it all mean in terms of dollars? From the data and research taken from the Goleta pilot, Moleaer was able to calculate these savings from installing a nanobubble generator:
Approximate reduction in net energy demand = $32,000/year
Reduction in sodium hypochlorite and sodium bisulfite = $15,000/year
The elimination of bioaugmentation (designer bacteria used during upsets to reseed and maintain compliance permits) = $44,000/year
Removal of one treatment trains from service = $36,000/year
Total Avoided Cost = $127,000/year in OPEX (O&M savings)
Plus, up to $50 million dollars in CAPEX (capital improvement projects) savings associated with plant upgrade to meet impending nutrient regs (for ocean discharge)
To learn more about the Moleaer nanobubble technology, please visit www.moleaer.com.
To watch the complete ICS webinar with Moleaer and nanobubble technology, visit our YouTube channel.
To schedule a Moleaer webinar or presentation for your facility or group of engineers, please contact Kate at email@example.com or call (920) 661-7668.