Why Dissolved Air Flotation Works

The problem of suspended solids in wastewater whether a by product of food processing such as proteins and oils, or mechanical processes where metals such as arsenic and other metals are suspended in water, and the resolution of that problem arise from the same science- and it isn’t always well explained in the best of reference materials.

Here it is: the smaller the particles, the greater the surface area, and therefore- the greater the amount of electro-chemical charge inherent to the particles is present.

Dissolved air by itself isn’t much to crow about. It rises to the top of any water it’s injected into, and escapes.

The basis of the problem, as I said and the cure, dissolved air flotation, both center on this basic physical fact.

Let’s say you have a cube that is 1 foot on each side. That’s 6 sq ft. of surface area, right? Now cut the cube in half. How much surface do you have? You retain the former area and add two more square feet. That’s 8.

Cut each piece in half again and you have 10.67, each piece contributing 1/3 x its original surface area. You grow the surface area by a substantial fraction each time you divide the original. We have a long way to go here because this can go on and on right down to the molecular level, in theory.

You turn a few sq. ft. of surface area into potentially millions when the division gets to the microscopic or molecular level.

If those billions of individual pieces have an electric charge, let’s say a positive charge, you’ve got problems because the particles now have enough charge and small enough mass that they all repel each other- Voila! suspended and unwanted particles in water. They may settle- in days, weeks, months, years… virtually never. You just may want to return the water a little cleaner than you just made it processing food or textiles, so what now?

Dissolved air, as mentioned, won’t help you alone- but you can give it its own charge too. Trace chemicals, usually based on aluminum, usually in parts per million, can be introduced to your water. Seems like more of a mess, doesn’t it?

The chemicals create their own charge and the particles now have something to which they can bond or attach electrically speaking. If you’ve got positive charges on each waste particle, you introduce negative charges on the newly introduced aluminum. A particle of aluminum may attract many waste particles and form a clump. Now we’ve got suspended clumps.

One more introduction of something in very tiny particles with a lot of surface area- and an opposite charge. Air. Not just air bubbles, but microscopic ones with an attitude (a charge) Now we’ve got action. The water is white with these very microscopic bubbles. They have little mass and buoyancy, so they’re not in a dead run for the surface. They collect plenty of your particle/aluminum clusters on their way to the top with millions of units of opposite charged surfaces. All the clusters- original waste solids, clumped in microscopic size bits around flocculant aluminum or other introduced medium, and billions of tiny air bubbles that collect around these larger particles (the air bubbles are extremely small). All rises to the top in a nice sludge the consistency of cooked oatmeal. Skim it off and you have clear water that is clean enough to send back to town without the taxi fare of pollution credits.

This operation is known as dissolved air flotation and it’s relatively cheap compared to systems that use membranes to squeeze water through under high pressure. The equipment that does this is called a DAF so that the acronym becomes a noun. A DAF uses varied techniques and DAF pumps to achieve the right balance of chemicals, charges and volume to clean the water for each application. Formulas are generally used and adjusted while the waste water flow is analyzed and the balance of flocculant and air are tweaked. The biggest expense of the operation tends to be the DAF pumps, followed by chemicals to use as flocculant. The cost of chemicals is ongoing, but when a DAF pump must be replaced, it can far outweigh what was spent on chemicals. The Keystec Air-Whip DAF pump reduces this replacement cost to a fraction because it’s both cheaper to manufacture and buy and lasts far longer than the 6 or 12 month life expectancy of most competitors.

Rent A DAF Now

DAF (dissolved air flotation) wastewater treatment units in varied sizes and designs are now available for rent. In addition to providing effective solid separation for wastewater treatment, these DAF rental units have a modular, space-saving design, stainless steel construction, and low maintenance needs. Since the rental units are in sizes up to several thousand GPM, you can run full capacity tests before choosing to buy a permanent DAF solution. You can visit or call any time for information on DAF Rental equipment.

Dissolved Air Flotation Equipment Rental

PTEC Serve is ready to meet all your DAF purchase and rental needs. Contact them to day for the right wastewater treatment options for your needs.

Ready For Hurricane Season? Call Dan Keys

Ready for hurricane season? Of course, we’re not but it’s coming with its wind and waves. What will this do to the oil floating on top of the gulf? It will emulsify much of it, mixing it and dispersing it into such small particles that its electrochemical forces of like charges will suspend each particle in a force field of its own charge, repelling nearby particles with like charges away. The oil, though not chemically bonded to the water stays mixed, creating a sludge of tiny particles that can only be dealt with on a microscopic level. Some of this microscopic environment includes microbes that will readily eat the oil but then there are the little problems of waste and depleted oxygen. Now you have suspended oils, suspended proteins and depleted oxygen. A perfect environment for… nothing. No fish, no wildlife, just a growing dead zone in the gulf. If the problem spreads to wetlands, then you’ll have dead zones forming there as well.

Dissolved air flotation can be applied to these areas and the oil and microbe waste can be collected around the air bubbles and skimmed off. Now what’s needed are long lasting, high rate, high volume capable pumps that can handle the millions of gallons long term.

Enter the Air whip pump by Keystec.DAF pumps that defy common design and outlast most DAF pumps on an exponential scale.

More information at the Keystec website for: DAF pumps.

Dissolved Air Flotation Strategy for Oil Spill – Water Oxygen Replenishment Cleanup

Dissolved Air Flotation offers a double problem solving strategy in cleanup and removal of oil from the BP gulf oil spill. While centrifuges such as those designed by Kevin Costner, separate suspended oil, a more difficult “byproduct” emerges in the process. “Stick” water, the kind usually derived from fish processing. The resulting emulsified oil/water solution is typically separated using DAF – Dissolved Air Flotation equipment onsite at food processing plants.

Complicating the cleanup of oil contaminated water in the gulf the process that nature itself has already begun. Microbes are consuming the oil in a feeding frenzy and multiplying to match the supply. This new population, in turn, creates proteins in their waste and simultaneously depletes available oxygen in the water. Fish are reportedly leaving en-masse for water with enough oxygen to sustain life. Fish which normally avoid each other or hunt each other from sharks to marlin are swimming in virtual refugee convoys.

Dissolved Air Flotation can deal with the emulsified oil in the new dead zones, the proteins and replenish oxygen all at once. The Keystec Air Whip pump, installed in custom Dissolved Air Flotation equipment is the core of a long lasting super air-injecting and waste collecting system that is equipped to speed shallow water marsh recovery.

Dissolved Air Flotation | Experience

The right DAF – Dissolved Air Flotation – for your application.

P-TEC offers equipment and system designs to meet the exact nature of each of our clients’ needs.  Whether your flow is 5 GPM or 3000 GPM, we have a custom solution for your need. Custom Built dissolved air flotation to fit your exact application based on extensive expert experience in DAF design and innovation.  From grease removal in a restaurant to water recovery in a paper mill, we can offer the solutions that will solve your problems.  We have experience in:

Can Your DAF Pump Aerate A Shirt? This One Can… | Dissolved Air Flotation At Low Cost

On one of the early Keystec DAF Pump tests, a client was simply too cheap to install screens in his wastewater system.

During a pilot test one of the workers accidentally dropped his shirt into the whitewater. Later the shirt was retrieved from the processed water- the Keystec Airwhip® pump unharmed.

Multi-stage pumps used to make whitewater cost exponentially more. The in-use pumps at this pilot test were getting clogged within weeks. The company was producing microwave bacon. The plant had five DAFs. The Keystec trial pump that started out as a test, and then placed into service five years ago is still running strong today.

Can Your DAF pump perform like this? Are you saving hundreds of thousands on your DAF processes?

We’re talking price ranges from $2,500 to $10,000 depending on size and application. Pumps that last far beyond competitors at economic cost.

If you want serious data driven, proven information about highly efficient, fractionally priced DAF pumps, check out the Keystec Airwhip® DAF pump series at Keystec. Innovative DAF design pump specialists.

Overall dissolved air flotation related service provided by PTEC.

Dissolved Air Flotation for Solids? How to cope with the problem of white-water systems and pump blockage.

A true DAF generates dissolved air.  The process involves dissolving atmospheric air to the greatest saturation possible under pressure and then releasing the dissolved air in the form of microscopic bubbles with the shock developed in a back-pressure valve or valves.

Modern DAFs operate the white-water system at about 95 to 120 PSI when operated in a recycle mode to achieve the greatest practical degree of air saturation.  There are numerous ways to create the necessary interface between air and water to do this, but the most popular lately is to inject metered air into the inlet of a multi-stage pump.  A saturation tank follows the pump.  Older designs saturated the full inlet flow at about 35 PSI with a larger saturation tank and a back-pressure valve.

All “white-water” systems can be trouble due to the solids that are entrained in waste water.  They can also be very expensive with tight clearances, unable to tolerate solids passing through the pump.

Dan Keys of Keystec developed a new, solids tolerant white-water DAF pump which can work with unscreened waste streams and is low cost and very easy to repair if it’s needed.  As a DAF design engineer, it had long been one of Dan’s goals to solve this old problem.  The development is now complete and the pump is enjoying great success in every place where it has been applied.  Its ability to handle solids has made it possible to return to full flow inlet aeration and split flow inlet aeration, thus increasing the DAF throughput capacity by freeing the throughput capacity used by recycle flow.

To summarize, proper white-water is achieved by aggressive air saturation which involves maximum air to water interface under pressure and some residence time in the pressurized state to complete the saturation, followed by a high-shock back-pressure valve or valves to force the sudden release of the saturated air.

This represents a revolutionary advance in applications of Dissolved Air Flotation technology.

There are also “entrained air” systems on flotation devices.  Be aware that while this approach can work many cases, the bubbles produces by spinning discs and blowing air through porous filters have different surface charges and are often too large for good flotation.  The ideal environment is produced by 30 to 50 micron bubbles combined with good chemistry that attracts the bubbles to the flocs formed by the chemistry. If the bubbles are able to coalesce while entraped in the floc, the rise rate can increase and allow more aggressive separation.  So, chemical choices are also key to good performance.

Partners in Dissolved Air Flotation Applications

Dissolved Air Flotation – Applications and Limitations in Wastewater Treatment

Dissolved Air Flotation is widely used in Wastewater Treatment as well as in less traditional applications such as:

•   drinking water clarification and color removal
•   Algae removal
•   By-product recovery  (i.e. metals, etc.)
•   Dissimilar solids separation

Within Wastewater Treatment, DAF application can be divided into
•   Primary Treatment
•   Secondary Treatment
•   Tertiary Treatment

In all cases, DAF (dissolved air flotation) is used to separate fine solids (any constituents that are not dissolved) by flotation, assisted by the attachment of microscopic bubbles.  Often, solids that would normally settle are forced to the surface for removal through the attachment of those fine bubbles.

DAF is used in a wide range of situations where the suspended material  can be as little as 20 mg/l (as in algae or color removal) to tens of thousands of mg/l as in rendering or some petro-chemical oil/water separation situations.  Each case must be evaluated for size, flow, and chemical requirements.

To further complicate the issue, the general term, DAF, no longer covers all the approaches to separating solids with microscopic bubbles.  Other similar technologies that are frequently referred to as DAF are:

•   CAF (cavitation air flotation)
-Bubbles produced by a spinning disk without pressure
•   BAF (bubble air flotation)
-Bubbles produced by blowing air through a micro-filter into the water
•   SAF (saponification air flotation)
-Bubbles produced with the aid of a surfactant for more aggressive attachment
•   EAF (entrained air flotation)
-Bubbles produced with relatively low pressure and high shear, entrained in the water

Dissolved Air Flotation

DAF Pumps

DAF Design

Dissolved Air Flotation DAF Solutions For The Dairy Industry, BOD & TSS Removal In Milk Wastewater

Here is a summary of an actual recent pilot test study.  The pilot test demonstrated the effectiveness of DAF treatment of fluid milk wastewater.

PROCESS DESCRIPTION:

Fluid milk, cottage cheese, fruit juices, and other dairy products.

OBJECTIVES

The objective of this study was two-fold:

1. To determine the effectiveness of chemical treatment and Dissolved Air Flotation (DAF) for the removal of BOD, suspended solids, and oil and grease from the plant´s wastewater.

2. To determine coagulant and/or flocculant dosing levels required to treat the wastewater.

EQUIPMENT USED:

Plant effluent was pumped from a manhole to a 300 gallon coagulation / pH buffer tank with a flash-mix agitator. The coagulated / pH adjusted water then gravity-flowed to a 300 gallon flocculation tank with a slow-mix agitator where a flocculant was dosed. The flocculated water then gravity-flowed to a P-TEC Model MD-2442 20 GPM Dissolved Air Flotation (DAF) System. Additional ancillary equipment was also provided; (feed pumps, chemical pumps, tanks, etc.).

TESTING PROCEDURES:

Prior to each test run, the water was jar-tested to determine optimal chemical dosing rates, then the system was started-up and stabilized before sampling took place. Flow rate, chemical dosing, aeration system, etc. were monitored to insure consistent operation.

500-ml samples of the raw wastewater influent and treated effluent were taken every hour to produce daily composite samples. A sludge sample was collected for moisture analysis in order to estimate volume produced.

Sample Analyses

600 PPM aluminum chloride (AlCl3) coagulant and 10 PPM anionic flocculant.

Influent – 3930 mg/l BOD; 1420 mg/l TSS; 514 mg/l O&G

Effluent – 1870 mg/l BOD; 100 mg/l TSS; 16 mg/l O&G

Reductions – 52% BOD; 93% TSS; 97% O&G

Sludge – 15.5 % dry solids; 21.8 % O&G on a dry basis

80 ppm epi-amine coagulant, 12 PPM cationic flocculant, & 6 ppm anionic flocculant.

Influent – 2560 mg/l BOD; 796 mg/l TSS; 616 mg/l O&G

Effluent – 880 mg/l BOD; 22 mg/l TSS; < 5 mg/l O&G

Reductions – 66% BOD; 97% TSS; 99% O&G

Sludge: 39.2 % dry solids; 32.1 % O&G on a dry basis

Dissolved Air Flotation only (no chemicals).

Influent – 1420 mg/l BOD; 608 mg/l TSS; 274 mg/l O&G

Effluent – 1220 mg/l BOD; 232 mg/l TSS; 105 mg/l O&G

Reductions – 14% BOD; 62% TSS; 62% O&G

Sludge – 34.1 % dry solids; 54.2 % O&G on a dry basis

Chemical Cost Comparisons and Estimated Sludge Production

Assumptions: 100,000 Gallons per day water treated.

TSS – 941 mg/l (average of pilot test influent TSS composites)

Treatment with aluminum chloride and polymer:

600 PPM AlCl3 = 60 gal/day X 10.68 lb/gal = 640.8 lb/day X $0.20 /lb = $ 128.16 /day

10 PPM anionic polymer (non-GRAS) =8.34 lb/day X $1.75 = 14.60

142.76 /day

Sludge production:

100,000 gal. X 941 mg/l = 94 gal/day (dry)  15 % dry solids = 627 gals (wet)

Treatment with three organic polymers “3P”:

80 PPM epi-amine = 8 gal/day X 9.5 lb/gal = 76 lb/day X $1.15/lb = $ 87.40 /day

12 PPM cationic polymer (GRAS) =10 lb/day X $2.75 = 27.52

6 PPM anionic polymer (GRAS) = 5 lb/day X $2.50 = 12.50

150 PPM sulfuric acid = 15 gal/day X 15 = 225 lb/day X $0.09/lb = 20.25

147.67 /day

Sludge production:

100,000 gal. X 941 mg/l = 94 gal/day (dry)  35 % dry solids = 269 gals (wet)

NOTES: All chemical prices assume tote or pallet quantities and include estimated freight. “GRAS” – Generally Recognized As Safe (for addition to animal feed).

Note for ALL tests: The pH was maintained at between 6.0 and 7.0 using 150 PPM (by volume) of 66o Be sulfuric acid (H2SO4) during the “3P” and DAF only trials. Little or no acid was required for the aluminum chloride and polymer trial because the 600 PPM dose of aluminum chloride itself lowers the pH to ~6.5. Average influent pH was approximately 9.0, but was observed as low as 4.5 and as high as 11.5.

Dissolved air flotation

Dissolved Air Flotation for Dairy Applications?

Stay tuned for an upcoming article on Dissolved Air Flotation DAF Solutions For The Dairy Industry BOD & TSS Removal in Milk Wastewater

Study shows cost effective use of DAF system to remove solids from dairy wastewater.

Find out now how DAF Technologies can save you big time. Contact Bob Stone at 800-450-0398.