The EPA recently announced a new strategy to provide clean, safe drinking water and a novel means by which those of us in the water industry, and citizens in general, can comment on it: an on-line discussion forum.
We at PAX Water Technologies are encouraged that the EPA is seeking out comment and feedback as it formulates its strategy, and we posted this comment to the discussion group today under Topic 2: (Foster development of new drinking water technologies to address health risks posed by a broad array of contaminants).
Focus on the Distribution System
We at PAX Water have noticed that the EPA tends to be somewhat “treatment-centric” in its approach to drinking water technologies. Most of the funding and technical focus for drinking water at the EPA appears to be on treatment technologies targeting very specific regulated contaminants in the treatment plant itself. The potable water distribution system, in contrast, appears to be thought of as a passive system of pipes and tanks – capable only of transporting drinking water from the treatment plant to the customer (and often with some degradation in water quality along the way). This narrow focus misses the potential synergies where new technologies combined with emerging best management practices can have profound impacts which may mitigate the need for many complex and costly treatment systems altogether.
We think the EPA is missing a strategic R&D opportunity. Potable water distribution systems provide municipalities the opportunity to intervene at multiple points and measure and improve water quality all along the way. In-line sensors can continuously monitor water quality and adjust treatment parameters, and distributed disinfectant boosters can “right-size” disinfection to minimize the production of disinfection by-products.
Active mixing is another example. Presently, fewer than 1% of potable water storage tanks in the United States are equipped with active mixers. Yet studies have shown that active mixing in water storage tanks can significantly reduce disinfectant loss, lower DBP production and improve water quality. Similarly, a regular schedule of tank maintenance, clean-out and recoating can preserve the integrity of distribution infrastructure indefinitely. By integrating these practices and technologies into the distribution system, water quality can be increased, and energy and disinfectant chemical use can be lowered.
We encourage the EPA to adopt a strategic approach to distribution system technology. The EPA’s Environmental Technology Verification Program is nice, but it focuses on singular technologies, and not systems of technologies and practices. Similarly, EPA’s SBIR program seems to focus largely on individual technologies and not systems of technologies and how they interact. The Department of Energy has recognized that out-of-the-box technological solutions to critical problems can’t be funded by small-scale programs like SBIR, which is why they created the highly successful ARPA-E program to support innovative energy technologies. Why not an ARPA-W for water?
What do you think? We welcome your comments.
Sincerely,
Peter S. Fiske, Ph.D.
CEO, PAX Water Technologies
We recently spotted this news item: U.S. EPA Categorically Approves Water Main Automatic Flushing Devices For Green Project Reserve Funding. The Green Project Reserve (GPR) program identifies technologies that improve practices to deliver equal or better services using less water.
We understand the rationale... sort of. Automated flushing systems may save water as compared to manual flushing programs.
But is all that flushing really necessary to maintain water quality?
We know that flushing of water storage tanks and lines is widely accepted in our industry as a tool for improving water quality.
But flushing is a sign of underlying problems in the distribution system. Rather than promoting flushing, why not try to improve the performance of your entire distribution system.
Active mixers have been shown to reduce residual loss in storage tanks, and these benefits have been shown to travel out to the rest of the distribution system.
By keeping the contents of storage tanks actively circulated, biofilm growth is inhibited, evaporative losses are reduced, and overall residual demand in the distribution system drops.
One utility recently estimated that the average cost of flushing their 7 tanks came to $66,000 a year. By installing active mixers they will reduce or eliminate the need to flush these tanks, and their investment will pay off in under 4 years.
Now THAT is a green solution that REALLY saves water.
We welcome your comments and questions.
Sincerely,
Peter S. Fiske, Ph.D.
CEO, PAX Water Technologies
It is well known that disinfectant residual levels drop as potable water makes its way through the distribution system. It is also generally believed that the rate of disinfectant loss is a function mainly of time – as water sits in the distribution system, the residual is consumed as it reacts with naturally occurring organic matter.
The Old Town Water District, which serves the municipality of Old Town, Maine (near Bangor) presents data in the latest issue of Opflow titled, Fire and Ice: Tame Temperature Extremes in Water Tanks, that shows that this simple water age/disinfectant loss model may need revision.
In their study (which PAX participated in), they installed PAX mixers in two of the three tanks in their distribution system. Initially, their motivation for installing mixers was simply to prevent ice damage during winter. But during the summer months they noticed a substantial decrease in residual loss in their distribution system.
Before installing the first mixer, they would typically lose around 1.2 mg/l of chlorine in their distribution system. But after installing the mixer, chlorine consumption dropped by more than half, which allowed them to reduce the amount of chlorination they did at the plant. After installation of a second mixer, the chlorine loss dropped again.
No other changes were made to the distribution system. The average water age in the distribution system remained the same. The big improvement in residual in the distribution system appears to be the result of the mixers.
How could this happen? We at PAX have worked with many customers who find that some of their storage tanks appear to consume MORE disinfectant than would be predicted based on water age alone.
We suspect that these tanks suffer from poor hydraulics, which prevents fresh, residual-rich inlet water from mixing in the tank. When inlet water does not mix, zones within the tank (principally the sides near the water line) can allow biofilms to grow. These biofilms introduce additional organic carbon to the tank, and tax the remaining disinfectant residual. When the tank is thoroughly mixed, the biofilms are burned back and the overall residual demand in the tank drops.
We believe this will also have a direct impact on DBP levels. As you know, DBPs are the product of the chemical reaction between organic matter and disinfectant. By lowering the consumption of disinfectant in these tanks, you lower DBP production. Water in a well-mixed tank is also cooler than water in an unmixed tank, and lower temperatures slow down the chemical reactions that lead to DBPs.
We welcome your comments and questions.
Sincerely,
Peter S. Fiske, Ph.D.
CEO, PAX Water Technologies
Temperatures are expected to top 100 degrees across much of the Eastern seaboard this week and municipalities large and small will be contending with managing their water quality.
In general, higher temperatures mean higher water use for gardens and recreation. This means higher turn-over in water tanks, which is a good thing. But for areas with large capacity, or low summer demand, high temperature can lead to thermal stratification – which spells trouble for water quality.
Thermal stratification can happen any time of the year, but is often most pronounced during the summer. Water from the treatment plant is typically much colder than the daytime temperature in the summer, and when it enters a storage tank, it typically remains on the bottom of the tank. During daylight hours the sun beats down on the walls of the tank, heating the water inside and causing it to rise. This hot water rides on top of the colder water at the bottom of the tank and can remain in the tank for many days. The graph below shows the water temperature in a 500,000 gallon tank in Redwood City, CA at one foot below the surface (in blue), 3 feet below the surface (in red), 5 feet below the surface (in green) and 8 feet below the surface (in purple). With each day, the temperatures in the upper parts of the tank rise and things don’t cool down at all during the night.
Thermal stratification leads to a host of water quality problems including high water age, loss of residual, and taste and odor complaints.
Active mixing can eliminate thermal stratification in storage tanks. By completely mixing the water and keeping it circulating, operators can be assured that fresh water entering the tank is thoroughly circulated, and temperatures and residual levels will be consistent. Better still, by keeping the tank mixed, air temperatures in the headspace above the water will be lower, reducing the rate of corrosion inside the tank.
We welcome your comments and questions.
Sincerely,
Peter S. Fiske, Ph.D.
CEO, PAX Water Technologies
Are you going to ACE10 next week in Chicago? PAX Water
Technologies will be there.
PAX Water CEO Peter Fiske will give a technical presentation entitled: CFD Modeling and Assessment of Active Mixing in Large Volume Distribution System Storage Facilities at 11:30 a.m. in Tuesday's session: TUE3-Introducing GIS and Alternative Applications into Your Hydraulic Model. We're not quite sure how a CFD talk ended up in a session on hydraulic models... Jeff Cruickshank also has a paper in that session on water age modeling and such models implicitly assume that tanks in a distribution system are perfectly mixed (hint: they are NOT!). We look forward to a lively discussion of this subject.
PAX Water's VP of Marketing, Jason Oppenheimer will present a poster entitled: Mixing Dynamics During De-Stratification in Storage Tanks at the Wednesday morning WED15-Distribution Research Oral/Poster Session. This hybrid poster session/talk will include a 7-minute overview by Jason at 9:52 a.m. (yes, that's right: 9:52 a.m. exactly!). Jason will review our combined modeling and experimental work showing how submersible active mixers can produce better water quality in storage tanks.
You can also find the PAX Water team at our booth #1847 in the exhibit hall. Hear about an upcoming article in OpFlow showing how the Old Town Maine Water Authority used PAX mixers in their storage tanks to overcome water quality and freeze protection issues.
See you in Chicago!
Sincerely,
Peter S. Fiske, Ph.D.
CEO, PAX Water Technologies
It's every municipality's worst nightmare: a wildfire erupts on the boundary of your community, and every available resource must be deployed to fight it.
This was the reality for the residents of South Lake Tahoe on June
24, 2007, when the Angora Fire erupted into existence. The fire destroyed 254 residences and 75 commercial structures and burned 3,100 acres before being brought under control. Property damage from the fire was estimated to be in excess of $150 million dollars, excluding firefighting costs, which approached nearly $11 million dollars.
Ideally, water operators in fire-prone areas would like to keep their storage tanks at maximum capacity throughout the fire season. But keeping water tanks full, especially during summertime months, means an increase in thermal stratification, residual loss, and the potential for water quality degradation.
So water operators face a tense compromise between maximizing storage volume while avoiding water quality problems, especially with those tanks that are farthest from the treatment plant (often the tanks nearest to a fire incident).
With the installation of active mixers, this difficult compromise is no longer necessary. Water operators can keep even low turn-over tanks full all year long without worrying about water quality problems. Active mixing has been proven in multiple communities to improve the residual in water storage tanks by thoroughly circulating the residual to all parts of the tank. [See our case study from Spanaway, Washington.]This prevents biofilms growth, which cause further residual loss.
If you are using deep cycling to manage the water quality in any of
your tanks, you are probably not getting the results you want. And, at least some of the time, your water level is lower than you'd like in the event of an emergency.
Instead of deep cycling and running the risk of encountering an emergency at the worst possible time, consider installing active mixers to keep your water quality AND your water levels as high as you want them to be.
How do you balance water quality with fire storage? We welcome your comments and questions.
Sincerely,
Peter S. Fiske, Ph.D.
CEO, PAX Water Technologies
State and federal water quality regulators, and the operators of drinking water systems, face a common challenge: how to achieve compliance with increasingly strict state and federal water quality regulations.
To reduce the risk of contamination by water-borne pathogens, the Long Term 2 Enhanced Surface Water Treatment Rule calls for better protection through increased treatment efficiency and maintenance of disinfectant residual throughout the system. At the same time, the Stage 2 Disinfectant and Disinfectant Byproducts Rule calls for lower disinfectant by-products throughout the system.
One rule seems to call for increasing the use of disinfectant while the other seems to call for less disinfectant! It turns out that this seemingly paradoxical set of mandates can be achieved by improving the effectiveness of the disinfectant residual itself through active mixing. [See our article, Doing More With Less In The Distribution System: A Mandate of Stage 2 Regulations, from Water Online Magazine.]
Potable water storage tanks can be a major source of disinfectant loss in the distribution system. Biofilms, which like to grow on tank walls and in the nooks and crannies around flanges, corners and appurtenances, react with disinfectant residual and can "use up" a tank's remaining residual. Tanks that are stagnant can form dead zones where disinfectant is entirely used up, allowing biofilms to proliferate. These "high-demand tanks" are like a Roach Motel for disinfectant: healthy levels of disinfectant goes in, but nothing comes out.
Active mixers help in several ways. First, by completely mixing the water inside a tank, the mixer ensures that disinfectant residual reaches every nook and cranny inside a tank, preventing the growth of biofilms. Furthermore, by completely circulating the water, mixing eliminates dead zones where disinfectant can become depleted. As one experienced operator told us: "Water is like a kid: if you give it something to do, it'll stay out of trouble!"
Old Town, Maine, is one municipality that has installed submersible active mixers in a majority of their storage tanks. The results were dramatic: disinfectant residual levels throughout their system improved greatly, and the operator was able to reduce disinfectant concentrations leaving the plant by 30% while experiencing increased levels of residual in their distribution system. (Figure 1).
PAX Water will be hosting a webinar aimed at water quality regulators at the state and federal level on June 9th, 2010. Registration is free, but space is limited.
We will discuss these latest results, and other benefits of using active mixing in your tanks and reservoirs.
We welcome your comments and questions.
Sincerely,
Peter S. Fiske, Ph.D.
CEO, PAX Water Technologies
The President's Cancer Panel, a panel of 3 leading cancer specialists who advise the White House each year on the latest developments in cancer risk in the United States, just released their 2008-2009 report - and it contains statements that should make everyone in the water industry sit up and take notice.
For the first time, the panel has identified drinking water disinfection by-products as a significant environmental factor that contributes to cancer risk in the United States.
We in the water industry are well-aware of the issue of disinfection by-products (DBPs), and the EPA and state regulators have established maximum safe levels for drinking water - no news there. But the elevation of this issue in the President's Cancer Panel may be a harbinger of increased public concern over an issue that, until now, has escaped notice.
Are municipal water systems prepared for this increase in public concern? What options are available to deal with DBPs?
We know that DBPs are formed when naturally occurring organic matter reacts with disinfectant. One set of options involve reducing the amount of organic carbon in the source water - but this requires complicated upgrades to treatment plants in the form of enhanced coagulation and sedimentation. Another approach is to switch primary disinfection treatment technique to ultraviolet (UV) treatment or ozone which disinfects without producing DBPs at the plant, also involving major retrofits at a significant cost.
It used to be thought that the switch from chlorine to chloramines would solve the DBP issue for most municipalities. Chloramines are a less powerful disinfectant, but they do not produce tri-halo methanes or halo-acetic acids when they interact with organic carbon in water. Recent evidence has shown that new (unregulated) DBPs are formed when chloramines react with organic carbon - and some of these may pose an even larger health concern than the compounds we monitor today.
The other approach to lower DBP levels would be to lower the amount of disinfectant in the distribution system. But most operators resist this approach because it lowers the level of protection against pathogens. Furthermore, in many distribution systems, disinfectant is "used up" as the water travels through the distribution system - minimum levels of disinfectant must still be present when the water reaches the customer.
But why is so much disinfectant being lost in the distribution system? One reason is poor mixing in storage tanks. When a tank is unmixed, it loses disinfectant residual at the top first. This is because the top water heats up and stratifies (increasing the rate of disinfectant evaporation) and because biofilms readily form on the walls of the tank near the water surface. These biofilms add new organic carbon which reacts with the remaining disinfectant, lowering the residual and increasing the production of DBPs.
In contrast, a well-mixed tank has a much lower disinfectant residual "demand"because the disinfectant residual is circulated to all parts of the tank, keeping biofilms along the walls of the tank at bay. Without the biofilms, the overall residual demand is less. We have many examples of municipalities that have installed the PAX Water Mixer and lowered the amount of on-site dosing by up to 90%. One municipality installed PAX mixers in all their tanks and was able to lower the amount of disinfectant leaving their treatment plant by 30% - while still maintaining great residual levels for the customer.
By lowering the residual demand in tanks, active mixers can allow municipalities to lower their use of disinfectant in general, leading the lower levels of DBPs as a result. For DBP control, active mixing is an economical approach to an otherwise expensive problem.
From page 55 of the President's Cancer Panel 2008-2009 report:
"The Federal standard for disinfection by-products in public water supplies is 80 parts per billion of THM as an annual average.268 THMs are measured because they generally reflect levels of other chemicals in DBP mixtures. If not controlled, DBPs in water systems can range up to several hundred parts per billion. In addition, a recent study 269 suggests that THM levels vary within a water system, with the highest levels found in water that stays in the system the longest after disinfection. In this study, rectal (bromoform THM only) and bladder cancer risks were highest among those who consumed the greatest amount of water at points within the distribution system with the oldest post-disinfection tap water."
--Learn more about how active mixing can reduce DBP production in storage tanks. Join us for a free webinar for water quality regulators on Wednesday, June 9th.--
We welcome your comments and questions.
Sincerely,
Peter S. Fiske, Ph.D.
CEO, PAX Water Technologies
Because mixing in water storage tanks is a new concept, many people don’t realize that there are actually two different types of mixing: active mixing and passive mixing. Most state regulators don’t appreciate the difference either.
Passive mixing systems rely upon the inlet pressure to inject momentum into the tank to stir the water. Passive systems can consist of something as simple as a separated inlet and outlet. More complex (and costly) systems use a series of pipes and nozzles to squirt water in various directions in the tank.
Advocates of passive mixing systems like to claim that these systems are better because there are “no moving parts”. Unfortunately, that’s not the case. The pumps in your distribution system are the “moving parts” and the additional back-pressure exerted by the nozzles force those pumps to work harder (requiring more power and increasing maintenance costs).
Because passive mixing systems need a minimum amount of momentum to be effective, they lock an operator into required minimum turn-over rates that, in many cases, are more than the tank would otherwise experience. Instead of expanding the operational parameters under which a tank can be safely maintained, passive systems restrict operator options.
Passive systems involving multiple nozzles and piping can be very expensive to install, but the costs don’t end there. During repainting or maintenance, those pipes and nozzles require more time and labor to work around.
But the most important problem with passive systems is that they don't work very well. Passive mixing systems only are “on” when the tank is filling: once the inlet shuts off, the mixing is over – whether or not the tank chemistry (disinfectant residual) is homogeneous. When a tank becomes thermally stratified during hot sunny weather, the brief fill period is likely to be insufficient to homogenize the temperature within the tank. Plus, fill cycles occur typically during the night, when mixing is least needed.
Active mixing systems use a motor to turn an impeller inside a tank and keep contents moving 24 hours a day, 7 days a week. Yes, active mixing systems have “moving parts” but their overall costs tend to be lower, and their maintenance requirements are minimal. Once installed, active mixing systems such as the PAX Water Mixer require no further operator intervention.
Operators can keep their tanks as full as they want and, even with low turn-over, the active mixer ensures that the entire volume of water is homogeneous and consistent in quality.
When it comes to mixing, you don’t want to be passive: get ACTIVE!
Interested in learning more about the operational benefits of active mixing? Attend our free webinar for Operators on May 20th.
We look forward to your comments and questions.
Sincerely,
Peter S. Fiske, Ph.D.
CEO, PAX Water Technologies
Active mixing has been shown to eliminate thermal stratification, prevent the formation of dead zones, reduce disinfectant residual loss and improve overall water quality in potable water storage tanks.
But how much mixing is enough? And how should an engineer or an operator address mixer performance when writing a specification?
This issue came up recently when an engineering firm asked us how to specify mixing performance for a 1.5 MG standpipe with a common inlet/outlet. The tank showed signs of pronounced thermal stratification during much of the year, and water quality was generally low.
Based on our experience, we gave the engineer three pieces of advice:
1. Don't use "pumping rate" as the sole criterion.
Some equipment manufacturers claim various pumping rates for their equipment, with very little data to substantiate it. (One should ALWAYS ask manufacturers for the PROOF of their pumping rates!) It might be tempting to assume that, if a piece of equipment pumps 1250 GPM, that it would turn over a 1.5MG tank in 20 hours. But this assumes the pumping action is thoroughly mixing the tank. If the flow pattern created by such equipment fails to reach some parts of the tank, then this assumption is invalid.
2. Temperature is a reliable way of measuring mixing performance.
If a tank is not uniform in temperature, it is by definition, poorly mixed. (Unfortunately, tanks that are uniform in temperature may still be chemically stratified - with little or no disinfectant residual in some places and high residual in other places.) We often install submersible temperature sensors along with the PAX Water Mixer to demonstrate to a customer that the entire volume of a tank is completely mixed. We recommend a temperature specification to measure mixing effectiveness: "Temperatures in the tank will be maintained to within 1 degree F at all times" is an example of such a temperature-based specification. In addition, we recommend a specification for chemical uniformity, such as "disinfectant residual levels within the top five feet of water and bottom five feet of water will converge to within 0.20 ppm".
3. CFD can clarify the flow field created by the mixer.
We often use advanced Computational Fluid Dynamics (CFD) calculations to model the action of a mixer in a tank. CFD enables engineers to visualize the flow field created by the mixer and to quantitatively assess the overall turn-over achieved inside the tank. We recommend that engineers require CFD validation that a mixing system will create a flow field that will fully mix the tank. Any reputable manufacturer should be able to provide such analysis.
Interested in learning more about specifying mixing systems? Join us tomorrow for a free webinar - Specifying Active Mixing Systems.
Our purpose at PAX Water Technologies is to bring together the latest science, technology and engineering to create energy efficient products that meet the changing demands of the water industry.
We welcome your comments and questions.
Sincerely,
PeterS. Fiske, Ph.D.
CEO, PAX Water Technologies