DAF Spare Parts to Keep On Hand

Murphy’s Law says, “Anything that can go wrong, will go wrong.”

There’s a lot to be said for being prepared. FRC has performed quite extensive testing on all parts used on our DAF systems, and we believe them to be of the highest quality, but inevitably something is going to fail. It might not happen this month, this year, or even next year, but eventually something will go awry. It’s at that time you’ll want to make sure you’ve got your DAF spare parts on hand.

Every FRC DAF system uses the same components, albeit slightly different in size. Here’s the core list of DAF spare parts you should always have on hand. If you don’t have these yet, contact us. We’ve got your file and will quote the right parts to you.

DAF Aeration Assembly

  • Poly Flow Tubing
  • 90 Elbow FNPT x FNPT Fittings
  • NPT Straight Fittings
  • Close Nipple Fittings

Skimmer Assembly

  • Sprockets
  • Pillowblock Bore Bearing
  • Drive Motor
  • Conveyor Chain (assembled)
  • Conveyor Chain (links)
  • Hinge Pins

Auger Assembly

  • Drive Motor
  • Gland Packing

Pneumatic Panel

  • Solenoid Valves
  • Pressure Switch
  • Air Flow Meter
  • Filter Regulator
  • Poly Flow Tubing
  • Misc. Straight, 90 Elbow & Tee NTP x P/L Fittings

If you think your stock of spares is looking pretty slim, use this DAF spare parts request form and we’ll get you what you need.

DAF System Design | Plate Pack vs. Open Tank

FRC has two main DAF system designs: the PCL Plate Pack DAF System and the PWL Open Tank DAF System. How is it that we decide to use one DAF system design over the other for a given wastewater application? That’s a good question.

DAF systems are designed on two key calculations – solids loading rate and hydraulic loading rate. Solids loading rate determines how much free surface area a DAF system should provide to separate solids. Hydraulic loading rate determines how much effective area is required to maintain laminar flow.

Generally speaking, a plate pack DAF unit is suited for high hydraulic and low solids loading rates. Open style DAF tanks are better suited for high solids loading rates.

But before we go and place plate pack DAFs and open tank DAFs into specific applications or industries, let’s understand one concept: anywhere you can use a plate pack DAF unit, you can also use an open tank DAF unit, but the opposite does not hold true. Similar to the rule that says, “a square is a rectangle, but a rectangle is not a square.” The trade off for always going with an open style tank is the amount floor space they occupy, and their overall cost, especially as flow rates rise above a few hundred gallons per minute.

First, let’s discuss solids and hydraulic loading rates, and explore them with some simple examples.

1. Solids Loading Rate

When discussing solids loading rate, what we’re really asking is how many pounds of solids can we separate in one square foot of free area? 2 lbs/sqft is a low solids loading rate, while 15 lbs/sqft is pretty high.

Let’s say we’ve calculated that an incoming stream of wastewater carries 1000 pounds of solids per hour. If we use a solids loading rate of 5 lbs/sqft/hr, that means our DAF system needs to provide 200 sqft of free area. If we use a solids loading rate of 10 lbs/sqft, then our DAF only requires 100 sqft of free surface area.

When to use a specific solids loading rate is largely a function of process experience. Most DAF system designers know that poultry wastewater contains solids that separate very quickly and easily, so they can use higher solids loading rates. Bio-mass separation, on the other hand, occurs much more slowly and the DAF designer should use a lower solids loading rate.

2. Hydraulic Loading Rate

Hydraulic loading rate answers the question – over one hour, how many gallons of wastewater flow over one square foot of effective separation area? In other words, its the amount of water that can be applied per unit of area with time, and not cause turbulence or re-entrainment of solids into the moving water. Where 0.5 gpm/sqft/hr is a low hydraulic loading rate, 2 gpm/sqft/hr is quite high. Let’s consider an example.

An open style DAF tank has 48 sqft of effective surface area. If you feed 65 gpm into the DAF unit and consider a recycle flow of 22 gpm, our calculation would be:
(65 gpm + 22 gpm)/48 sqft = 1.81 gpm/sqft

If the same volume of water is fed into a plate pack DAF unit with 65 sqft of effective area, our hydraulic loading rate would be:

(65 gpm + 22 gpm) / 65 sqft = 1.34 gpm/sqft

The difference in hydraulic loading rates seems small, and it is, but when we consider the size of the DAF unit, we begin to see why plate pack configurations often make sense. The open tank DAF measures roughly 13’L x 8’W x 8’H, while the plate pack unit is only 7’L x 4’W x 8’H. That’s a quarter the size of the open tank unit.

Plate Pack vs. Open Tank DAF Size Comparions

By understanding the solids loading rate and hydraulic loading rate we’ve got almost everything we need to appropriately design and size a DAF system. There’s just one final question.

3. How much floor space do we have for wastewater process equipment?

A seemingly obvious factor to consider in DAF system design is how much floor space is available for the equipment. If we have essentially limitless space, then the footprint of the DAF unit has little bearing on system design.
But when we’re dealing with limited floor space, having the ability to build tall DAF tanks (plate pack style), rather than wide & long DAF tanks (open style), can make all the difference. Let’s consider one more practice problem:

A pork processor produces 250,000 gpd of wastewater, loaded with 3,500 lbs/day of solids. Size an open tank DAF and a plate pack DAF to remove 100% of the solids.

If we make a solids loading rate assumption of 7.5 lbs/sqft based on the application – pork processing, the amount of separation area required is calculated as:

(3,500 lbs / ? area ) = 7.5 lbs/sqft => 467 sqft.

Knowing we need 467 sqft feet of separation area, an open tank DAF unit would need to be approximately 47’L x 10’W x 8’H. A plate pack configuration could provide the same surface area in a unit that’s only 13’ L x 8’ W x 10’ H. Again, the plate pack DAF configuration is about a quarter the size of the open tank unit.


In the end, you want a DAF system to perform its function, while incurring the lowest capital and operational costs possible. That’s FRC’s design approach. Sometimes that’s achieved with an open tank DAF and others with a plate pack DAF. If you’re considering a dissolved air flotation system in your wastewater treatment process, contact us and we’ll find the best solution for you.


5 Reasons Why Operators Love FRC Systems DAF Design

What is it about FRC Systems DAF design that makes wastewater operators jobs so much better? Here are 5 simple reasons we hear most often from the guys keeping plants in compliance.

1. They’re Simple to Operate

Have you ever bought something that you thought would be really good to have, only to figure out later that the thing is way more headache than help? A crazy-cheap used car, perhaps? Say your daughter is turning 16 years old and is begging for a car, so you pay $1200 cash for a lipstick red Volkswagon Jetta. Ten weeks later the thing is in the shop needing a new transmission. Know the feeling? A little bit of anger, mixed with frustration and regret?

We know the feeling too. That’s why when we designed our DAF systems, we made every effort to avoid all possibility of those frustrations. Processes that can be automated are automated and components that can fail are installed with redundancy. Turning the system on is as simple as the push of a button and keeping it running smoothly only requires simple check-ups.

Imagine how simple and reliable a DAF system should be. That’s what you get with an FRC.

2. They’re Resilient to Process Changes

If there’s one thing we know about wastewater, it’s that anything is fair game. Kind of like a 2-year old; leave them alone and there’s any number of things they could get in to – new haircuts, crayon hieroglyphs on the walls, or impromptu bath-time with the dog’s water bowl. The key is to roll with the punches.

The same goes with wastewater process design. Systems have got to be able to handle sudden increases in flow or odd events that happen every so often. FRC brings applications experience into every process to design systems that can take a beating and still perform as required.

3. They Generate Extra-Dry Sludge

Sludge dewatering can be a tricky process. And unless you’ve procured the top-of-the-line dewatering equipment (and even then), you’re likely to experience maintenance down-time, which can literally shut down the rest of your wastewater operation and the entire industrial complex. So, there’s all the more reason to first, get a reliable sludge dewatering process in place and second, minimize wet-sludge volume to whatever extent possible.

The methods FRC’s DAF systems employ to generate extra-dry sludge are explained in the Ultimate DAF System Buyer’s Guide, but to boil it down to its essence, dryer sludge means less of a mess in the dewatering process. It also means smaller dewatering equipment, shorter run-times, and less sludge backing up in the event of down-time for dewatering system maintenance.

4. They Use Standard Parts that are Easy to Access

A less tangible, though equally well thought-out, component of FRC DAF systems is the detailed information we provide regarding every nut and bolt used to build the equipment. When you’re performing regular maintenance and see that some hose could use replacing, you know exactly what it is and where to find the materials. If you like to keep spares on-hand, a list of recommended parts with pricing comes with the package.

Great thought has been given to the placement of mechanical components on FRC’s wastewater process equipment. Valves are at waist-level, gauges and instrumentation are at eye-level. Gauges on the ground don’t make anybody’s job any easier. It’s the simple things that make a difference.

5. Troubleshooting is No Trouble at All

The thing that makes DAF system operators so good at what they do is their ability to identify and rectify a problem before it becomes a disaster. It’s an innate ability that they craft and sharpen with each day on the job.

To help operators excel in their responsibilities, FRC provides a troubleshooting guide that covers the gamut of mechanical and process issues that may arise during system operation. That way if sludge begins to look watery, they know to check the chemical dosing rates, adjust the DAF water level, and adjust skimmer speed and flight clearance with the sludge ramp. Where to start, what to look for, and how to make adjustments are all covered. Should the same issue arise again, they’ve already armed themselves with the right weapons to neutralize the threat before it becomes a bigger problem.


So there you have it. Operators can’t say enough about how happy they are they can rely on an FRC DAF system to do its job, day in and day out. Some have even said they love ’em.

Wouldn’t a system that works so beautifully make you swoon too?

The Ultimate DAF System Buyer’s Guide: Part 1

At a certain point in the project development process you will have qualified a few dissolved air flotation (DAF) system manufacturers from a field of many. Now you have to decide which one will best suit your needs. How do you choose?

Whether you’re an engineer specifying equipment on a client’s behalf, a plant owner working to solve your own wastewater treatment challenge, or someone who is just looking to deepen their understanding of wastewater process equipment, this guide will help you gain clear insight into an expert DAF system manufacturer’s design choices.

Dive into mechanical and process design elements within this series of posts and gain valuable insight as to how you should evaluate DAF systems. With this knowledge you’ll be able to determine design superiority and most importantly, be prepared to make the right purchase decision. You only buy a DAF system once, get it right the first time.

1. DAF Recycle Pump

The recycle pump is the heart and soul of a DAF System – it’s only smart to start here. On it rides the greatest capital and maintenance expenses associated with a dissolved air flotation system. So, what do you look for in a DAF pump?

First off, what kind of pump is it? If the DAF manufacturer is calling it a specialty “whitewater pump,” they’re likely referring to a multistage impeller pump.

Multistage Impeller Pumps

These pumps draw atmospheric air (or receive an inlet feed of compressed air) into the pump chamber where impellers whip the air around with water to form micron-sized bubbles that dissolve into solution. While these specialty pumps do generate quality whitewater, there is cause for concern in a wastewater environment.multistage impeller pump

Multistage impeller pumps have low solids tolerance and will fail when oily, stringy, or gritty materials enter the pump chamber. On DAF systems carry over solids in the effluent can end up in the pump, and that’s cause for concern.

When used in DAF applications, these pumps operate at discharge pressures from 90-120 psi. Again, any solids in the recirculation piping can cause pressure drops and trip pressure alarms resulting in system shut-down.

Finally, multistage DAF pumps use components that are specially machined for that specific pump design. Should any part of the pump require repair, the end-user is limited to the DAF manufacturer as their sole-source for replacement pump parts. This is particularly troublesome for manufacturers that use pumps made overseas, as lead times can extend to several weeks.

There are other applications where multistage impeller pumps perform very well, particularly with higher pressure services like boiler feed water, condensate, pipelines, reverse osmosis, and descaling applications. But in wastewater environments and as an integral component of a DAF system whose sole purpose is to remove solids and oily materials, the multistage pump is just a little out of its element.

If the DAF system manufacturer employs a whitewater pump, but it’s not a multistage impeller pump, they’re likely using a regenerative turbine pump.

Regenerative Turbine Pumps

These are a type of centrifugal pump that use a rotating impeller to increase velocity, however the impeller looks quite different from what you would see in a centrifugal pump. Instead of vanes, the turbine impeller has radially oriented buckets or blades, which make it look like a turbine rotor.Nikuni regenerative turbine pump

As water enters the pump chamber, it moves in a circular path through the turbine buckets. In a DAF application compressed air is fed into the pump and dissolved into solution as the turbine spins and blends the air/water mixture.

Unique to the regenerative turbine pump is its ability to generate high pressures in a compact machine. Clearances in a turbine pump are much tighter than in a traditional centrifugal pump so the pumped liquid must be very clean. The tighter clearances also make this pump type noiser than a standard centrifugal pump.

Similar to multistage impeller pumps, regenerative turbine pumps operate at discharge pressures between 90-120 psi in a DAF application. High operating pressure and very tight internal clearances require liquids to be entirely devoid of solids or oily materials.

The most popular regenerative turbine pump used by DAF system designers is built by Japanese manufacturer, Nikuni Co. Ltd. Any parts that are required for repair have to be acquired through Nikuni’s representative network, which is limited to two companies for all of North America. A spare pump should be kept on-site at all times because lead time on a replacement pump often extends as long as 10-12 weeks.

DAF manufacturers relatively new to the wastewater market have adopted the multistage impeller and regenerative turbine pumps because they are marketed as “whitewater pumps” and under perfect operating conditions, they work very well. There is, however, another DAF pump option that is better suited for the wastewater environment – the ANSI end-suction centrifugal pump.

ANSI Pumps

ANSI pumps are the only dimensionally standard pump type in the pump industry. All components are interchangeable – motor, coupling, impeller, volute, bedplate, etc. End-users who buy DAF systems that employ ANSI pumps don’t have to go to go the DAF manufacturer to source spare or replacement parts because they are readily available from any reputable pump vendor.ANSI pump

ANSI pumps are designed specifically to function in food processing, oil refinery, general manufacturing, pulp and paper, and chemical applications. They can pump liquids with or without solids and can be fitted with various alloys for operation in corrosive environments. When used in DAF applications, ANSI pumps operate at discharge pressures between 70-90 psi.

So how do ANSI pumps generate whitewater?

The trick is, they don’t. The ANSI pump is used to transfer water and that’s it. Whitewater is generated in a static “air dissolving tube” downstream of the pump as water comes in contact with small volumes of compressed air.

By placing the responsibility for generating whitewater on a static tube made of stainless steel, the ANSI pump can focus on what it does best – move water.

DAF pump selection says a lot about the design approach of the manufacturer. Be sure to ask why they use the pump they do. Ask for the reasons why they don’t use the other options. Remember, the DAF pump is the heart and soul of the entire system – it’s worth discussing.


 2. Controls & Automation

Think here for a second about something completely unrelated to DAF systems. Grab your smartphone. Notice how smooth and easy it is to operate? The interface flows logically and simply through the tasks that you want to perform. That’s how a DAF system should operate. FRC DAF Controls App

Many manufacturers build systems with arduous operational procedures in the name of cost reduction, when in fact the headaches caused by such poor design end up costing infinitely more in time, labor, and frustration.

Some DAF systems we’ve gone out and serviced have ridiculous start-up routines that go something like this:

  1. Open all recirculation valves
  2. Energize whitewater pump
  3. Energize air compressor and feed pump x lpm of air at y psi
  4. Begin closing off whitewater discharge valve until discharge pressure gauge reads x-value
  5. Begin closing off whitewater suction valve until pressure switch registers y-value
  6. Open air bleed-off valve until air saturation tank reads z-value
  7. Keep tweaking all valves until whitewater looks good on visual inspection
  8. Run system for 10 minutes to saturate tank with whitewater
  9. Open wastewater influent valve and begin treatment

A well designed and automated DAF system should operate something like this:

  1. Push START button
  2. Watch controls do all the work while you eat a muffin

It’s somewhat comical how difficult certain DAF designs are to use. These systems don’t have to be that way. When you’re considering a buying a DAF system, take into account what it will actually be like running the thing. Ask for a write up of the operating procedure.


Continue to Part 2 of the Ultimate DAF System Buyer’s Guide

The Ultimate DAF System Buyer’s Guide: Part 2

If you haven’t read it yet, make sure you to read Part 1 of the Ultimate DAF System Buyer’s Guide

3. Materials of Construction

When you buy a DAF system, you want something that is going to hold up in a harsh environment. You’re going to use the thing for the foreseeable future and the last thing you want is something you have to replace because it didn’t hold up.

There are several options for materials of construction with regards to the tank structure, each with their own advantages and disadvantages. Let’s look at what’s on the market:

Steel-reinforced concrete basins are typically used in large municipal wastewater treatment plants. Concrete DAF basins are sturdy and leak proof, but can be very expensive because of the required civil work involved, i.e. excavation, steel reinforcement, concrete forming, coating, etc. Since they can only be built in the location where they’re going to operate, concrete DAF basins are not often selected for use in industrial facilities.

Some manufacturers prefer polypropylene because of its lower material cost, good strength and stiffness, and generally broad chemical resistance.
Significant problems arise when polypropylene is exposed to extreme temperatures or UV radiation. If placed outdoors, UV light from the sun causes tertiary carbon bond breakdown and results in discoloration and cracks.

Polypropylene will not hold its shape at temperatures above 260°F and it will crack at temperatures below 32°F. Refurbishing polypropylene tanks for reuse is rarely pursued as the material degrades over time. DAF manufacturers that use polypropylene generally warranty the tank structures for 10 years.

Epoxy-Coated Carbon Steel
Coated carbon steel offers the strength of steel and the general corrosion-resistance of an epoxy coating. Structures of this sort are particularly useful in applications with high Total Dissolved Solids (TDS). But for applications in the food industry, this material isn’t recommended because free fatty acids in floating sludge will eat through the epoxy coatings and rust the steel, compromising the tank’s structural integrity. Epoxy-coated carbon steel is commonly thought of as less expensive than stainless steel, however when constructed to provide the same structural strength and corrosion resistance as stainless, the cost-savings of coated carbon steel is negligible.

Stainless Steel
Stainless steel is used in DAF tank construction for a variety of reasons. Stainless steel resists rust formation because of a passive film of chromium oxide on its surface that blocks oxygen diffusion and corrosion. Stainless steel retains its strength between temperatures of -320°F to 1500°F, so it holds up in indoor and outdoor applications. Welders can easily make modifications to the material without needing to re-apply paint or other coatings. Even after decades of use, stainless steel tanks can be retrofitted and work for decades longer because the steel structure remains sound.

Stainless steel, however, does come at a higher price than some other materials and it is not particularly well-suited for applications with significant concentrations of chlorides, which could potentially cause pitting or corrosion.

Stainless steel DAF tanks retain a high resale value and many manufacturers are willing to buy them back, even after prolonged use.


4. Sludge Thickening Mechanisms

The purpose of a DAF system in the wastewater treatment process is to remove solid and oily contaminants. The trick to increased efficiency and cost-reduction is to get the DAF generating fluffy, thick sludge – not a watery slurry. Sludge thickness is a function of hydraulic, mechanical, and chemical processes – when they come together, engineered in a thoughtful manner, the results speak for themselves.

Co-Current vs. Counter-Current Skimming

The internal hydraulic flow patterns in a DAF system vary from manufacturer to manufacturer and by DAF configurations. DAF systems that employ plate packs often direct wastewater in a down-flow or cross-flow pattern so the following discussion has less relevance to this type of DAF unit. Open style DAF tanks, however, generally employ a flow-through or end-to-end hydraulic process so this conversation is very important.

When considering an open tank DAF system, take a good look at which direction the skimmer assembly rotates. Does it rotate in the same direction (co-current) as the hydraulic flow of the wastewater through the system? Or does it rotate against (counter-current) that flow? Here’s why it matters.

Say you’re looking at the side of an open style DAF tank that’s 40 feet long and 8 feet wide. Wastewater is fed into the DAF unit on the left side and exits out the right. As a layer of sludge begins to form at the water’s surface, the skimmer flights are going to start pushing that sludge in one of two directions. The co-current skimmer is going to push the sludge from left to right, the same direction as the wastewater flow. The counter-current skimmer folds the sludge back over the flow from right to left. Still with me?Co-Current vs. Counter-Current DAF Skimmer

Now, consider where the sludge first begins to reach the surface of the water – is it near the inlet, middle, or outlet side of the tank? Most DAF systems hit the inlet stream of wastewater with whitewater immediately upon entry into the vessel, so sludge forms near the inlet side of the DAF tank. If sludge forms near the inlet side of the DAF tank, what good reason is there to co-currently push that sludge across the entire 40 foot length of the unit? It  makes much more sense to use a counter-current skimmer to push the sludge a shorter distance.

Proponents of the co-current configuration would argue that while sludge is being pushed across the long length of a DAF system, it’s being thickened. However, field data and reviews from operators would argue the opposite. Skimming co-currently more frequently results in watery sludge, extra build-up of material near the sludge ramp, sludge splashing into the effluent chamber, and faster wear and tear on the skimmer motor and flights.

With open-style DAF systems, the counter-current skimmer consistently wins the performance battle, especially when an extra measure is taken to lock sludge in place when it reaches the surface of the water – more on that to follow.

Sludge Dewatering Grid

Another key mechanical feature of DAF systems that are engineered to generate the driest sludge possible is a static grid that sits at the surface of the water, commonly referred to as a Dewatering Grid.

A dewatering grid is a rectangular framework of angled steel plates that help lock sludge in place as it reaches the surface of the water. As sludge accumulates in the dewatering grid, it is held in place until it reaches the point where the skimmer blades slice it off the top and start pushing it toward the sludge ramp. By allowing for a little retention time in the grid, float materials self-dewater before they’re skimmed away. This results in higher dry solids content, or less-watery sludge.

Without the grid the skimmer blades start pushing sludge along before it has had any time to dewater in place. Often times what happens is that the float begins to accumulate right near the sludge ramp and can be forced back down into the water, completely undoing any dewatering that may have occurred before removal. The diagrams below illustrate this point.

Dewatering Grid Diagram

So what’s the big deal with watery sludge? As long as the discharge water meets the requirements we’re good right? Well, that depends on how important saving money is to your operation. More water in sludge means more required storage capacity, bigger dewatering equipment, and more chemical expenses on re-processing filtrate water (the water that separates out of sludge after dewatering) through the DAF system. You have everything to gain by going with a DAF system that’s engineered to produce drier sludge. Ask the DAF vendor how their design helps generate drier, thicker sludge. What mechanisms do they provide to allow operators to adjust sludge thickness?


Keep reading: Part 3 of the Ultimate DAF System Buyer’s Guide



The Ultimate DAF System Buyer’s Guide Part: 3

Make sure you’ve read the Ultimate DAF System Buyer’s Guide Parts 1 & 2 before starting here.

Part 1 of the Ultimate DAF System Buyer’s Guide

Part 2 of the Ultimate DAF System Buyer’s Guide

5. Dissolved Air Distribution Methodology

The method used to distribute whitewater into the incoming wastewater stream makes all the difference in the way sludge forms and floats inside the DAF vessel. Let’s examine two different approaches.

Some DAF manufacturers employ a specialty whitewater pump, vertical saturation pipe and diaphragm valve assembly to generate and inject whitewater into the incoming wastewater. Others use ANSI recycle pumps, an angled air saturation tube, and a whitewater distribution manifold with multiple ball valve and tubing assemblies. A comparison of these two configurations might sound like splitting hairs, but it’s definitely worth some consideration. air bleed off diagram

  1. The vertical saturation pipe configuration is designed to bleed off air that doesn’t dissolve into solution. While most excess air will escape from the top of the tube, the side-mounted whitewater discharge line will draw some portion of it into the tank. As excess air enters the flotation cell, large bubbles form and burp at the water’s surface. These bubbles disturb already floating sludge and immerse solids back into the water.With an angled configuration, excess air escapes out the elevated portion of the tube as whitewater flows out from the lowest point. No undissolved air can enter the flotation tank because the water flows from top to bottom, not the other way around.
  2. DAF systems that use vertical tubes typically only have one dissolved air injection port. When flowing 100 gpm (1.67 gallons per second) of wastewater into the flotation cell, a single dissolved air injection point is unable to effectively and evenly spread whitewater over the entire incoming solution. Some portion of the flow gets a huge shot of whitewater, while other parts go entirely without. It’s up to the hydraulic patterns inside the flotation cell to distribute the bubbles. Often times this works, but it’s unpredictable and uncontrollable. A habitual problem with this design is that solids cannot float to the water’s surface quickly enough to keep up with the incoming flow. By all calculations, a system designed to process 100 gpm of wastewater is unable to achieve that flow rate because solids are not separating quickly enough.air distribution manifold DAF systems with whitewater distribution manifolds do not have this issue. Numerous whitewater injection ports are placed across the width of the flotation cell at different heights to evenly distribute micro-bubbles all throughout the DAF tank in a controllable manner.
  3. The start-up routines for these two configurations also varies by nature of the whitewater injection system. A single air injection port saturates the tank with whitewater from one origin. As tanks are sized longer and wider, it takes more and more time for the bubbles to disperse throughout the whole tank. Some manufacturers’s DAF operation manuals suggest allowing 5-10 minutes for tank saturation before opening the wastewater influent valve and proceeding with treatment. DAF systems with an air distribution manifold are fully saturated within 60 seconds or less. Shorter start-up time means less waiting around and more getting work done.

The lesson is is to get in closer and examine the design differences. The details matter. Ask the manufacturer about their design justifications.

6. Application Specific Design

Think of a hammer, a tool meant to deliver impact to an object. Now, picture one in your mind. What do you see?

If you’ve ever worked in carpentry maybe you visualized a claw hammer.  Metalworking? A ball-peen hammer with a hemispherical head. Maybe you’re a stonemason and thought of a brick hammer with it’s long chisel-shaped blade. Everyone thinks of the hammer they use in their trade. But, no one should know better than the hammer-maker which one is the most appropriate for a specific task.

A DAF system manufacturer should have that same level of expertise and knowledge about which DAF system design is most suited to a specific application. If a designer is using the same DAF system for a dairy acidulation process as they use in a cattle abattoir plant, that’s like a rail worker using a judge’s gavel to pound in a railroad spike – similar tool, wrong application.Railroad worker with gavel

The application specific design largely comes down to materials selection and process engineering. Take for example a DAF system used in a cattle kill plant. Without understanding that these types of facilities generate wastewater laden with sandy, gritty materials, a manufacturer may opt to use their design standard, say a cast iron pump. Unfortunately for the person who buys this DAF system, their gritty wastewater will wear pin holes in the pump casing and eventually cause a pump failure. This results in down-time and replacement of the most expensive component on the system. When something like this happens, not only does it reflect poorly on the manufacturer, but also on the engineer/consultant that presented it to the end client as the right solution. The master craftsman would understand the gritty nature of cattle wastewater and select a pump casing with high Brinell Hardness, like CD4MCu.

On the process side, the DAF designer should understand how to properly calculate and interpret hydraulic surface loading rate, solids loading rate, and air-to-solids ratio based on the application at hand. Solids in poultry kill plant wastewater separate infinitely easier than those from the effluent of an activated sludge system. Using the same values for each of these processes would likely result in an oversized poultry DAF and an undersized bio-mass separator.

You’re the one buying the system, don’t be afraid to question why a specific configuration was selected over another and be sure to ask for an explanation of the calculations behind your system sizing.


Continue to the Conclusion of the Ultimate DAF System Buyer’s Guide

The Ultimate DAF System Buyer’s Guide: Conclusion

At face value DAF systems are pretty much like any other piece of industrial equipment – they’re an investment that you only want to make once. And in the same vane, some designs are simply better than others. With this guide, hopefully you’ve learned which design elements separate one DAF unit from another.

In summary, let’s recap the things you should discuss with a DAF manufacturer before setting a purchase in motion:

  1. What type of DAF pump is used? Why?
  2. What materials are used in DAF tank construction?
  3. What mechanical measures are taken to thicken sludge?
  4. How is dissolved air distributed into the DAF tank?
  5. What is the operating procedure for the system?
  6. What specific design considerations were weighed for your application?

The DAF system manufacturer should be able to address each of these questions with great detail and explain why they design their systems the way they do. If they can’t articulate why they do things one way and not another, then there’s a lack of attention in their engineering approach. Conversely, the manufacturer that can discuss each of these topics is better equipped to become a useful resource and partner in your project as it moves forward.

If you’re satisfied with the reasons behind the manufacturer’s design decisions, then the next step is to take a look at their project history. If they’ve only got a few projects under their belt, their understanding of DAF design may still be largely theoretical or academic. When it comes to large capital expenditures, you don’t want theoretical solutions, you want something that’s guaranteed to work.

So, whether you’re an engineer or an end-user, remember that you only want to select a DAF system once. Make sure you get it right.

If you’d like to discuss a wastewater application where you’re thinking about employing a DAF system, contact us – we’re glad to help.

The Right Way to Perform a DAF System Startup

If you’ve just got your hands on a shiny new DAF system, you’re probably anxious to get the thing running. But before you start muddying it up with wastewater, there are a few important things to run through. Follow this 10-step guide to perform a proper DAF system startup.

1. Review the Operation & Maintenance Manual

You’ve absolutely got to understand how the system functions and the right ways to keep it working for years to come.

2. Set the Operational Valves in Their Correct Position

This includes pump isolation valves, feed valves, chemical valves and aeration system valves.

3. Fill the DAF System with Clean Water

Fill the whole thing with clean water all the way up to the edge of the adjustable outlet weirs. It’s a safety and maintenance issue.

4. Adjust the Outlet Weirs

Bring them all the way up to their highest position. This allows for the greatest volume of water in the tank and is a good baseline for your first run of wastewater.

5. Check your Recycle Pumps

Make sure they’re properly oiled and aligned to eliminate vibration. This will be the heart and soul of the whole operation. Get it set right from the get go.

6. Verify Pump Rotation

The recycle pump is a comes with a 3-phase motor. Bump the motor and make sure it’s rotating in the correct direction.

7. Check Motor Rotation

The DAF system has motors for the auger and skimmer. Skimmer blades should move toward the sludge ramp. Auger should push toward the outlet. Make sure they’re rotating correctly.

8. Test Electrical and Pneumatic Devices

They should actuate when a signal is sent from the panels. Make sure they’re calibrated to close slowly and not slam shut.

9. Perform Whitewater Test

Refer to the O & M manual for the procedure for generating whitewater. When you’ve got it correct, the water coming into the DAF system will look a little like skimmed-milk. After several minutes, the whole tank should be saturated with microbubbles.

10. Check for Obstructions

Confirm that the rotating top skimmer is not obstructed. All hoses and debris should be removed from the tank.


With that said, if there’s something you’re not quite sure about, err on the side of safety and send us a note. That’s what we’re here for.

Unintended Effects of Using Coagulants to Adjust pH

If you’re using chemical coagulants to adjust pH, then you’re doing something wrong. You see, if coagulants are meant to be used for adjusting pH, then why do we call them coagulants and not pH reagents? Why add the iron or aluminum salts to the mix? Doesn’t it make much more sense to use an acid (i.e. sulfuric acid) or base solution (sodium hydroxide) to adjust pH? Despite the seemingly obvious nature of the issue, too many wastewater treatment plants unwittingly employ chemical coagulants to adjust pH.

The Purpose of Coagulants is to Coagulate  

It sounds simple, but the concept is lost on wastewater operators and environmental engineers alike – coagulants coagulate solids. Everything else is just a side effect.

While alum and ferric-based coagulants are acidic in nature and produce a drop in pH when added to wastewater, their main purpose is to neutralize electrical charges of fine particles in water and clump them together. The best way to determine coagulant dosing is by performing a jar test. When solids are all tied up in pin flocs and water appears clear, then you know you’ve got you’re coagulant dosing dialed in correctly.

So when does this “using coagulant to adjust pH” problem occur?

It Happens All the Time

Aluminum and ferric-based coagulants operate most effectively within a specified pH range (alum: 5.5-7.5; ferric: 5.0-8.5). Wastewater with higher pH values might require pH neutralization before being sent through wastewater process equipment. The correct approach for this situation would be to use an acid (sulfuric acid, hydrochloric acid) to drop the pH. Far too often what happens is that coagulant is dumped into the wastewater to adjust pH to neutral range. That’s simply not a smart thing to do.

The Unintended Effects

There are plenty of reasons not to use coagulants for pH adjustment. Here are just a few of them.

  • Coagulants are expensive – you can go through totes of coagulant to achieve the pH adjustment attainable with a single drum of sulfuric acid. The right tool for the job makes things much easier.
  • Coagulants generate sludge – they’re metal-based. That means the metals actually add to the volume of solids removed from the wastewater. That means more sludge to store, dewater, and dispose of.
  • Unconsumed coagulants contribute to COD – when there aren’t enough solids for the coagulants to react with, the metal atoms begin reacting with water molecules and dissolve into solution. If you’ve got a secondary treatment process, extra COD could really mess things up.

The key lesson here is that coagulant dosing is directly related to water clarity. If water appears murky after treatment, the operator could probably stand to add a little more coagulant. The general axiom remains, use the least amount of coagulant necessary to achieve the required water clarity. If pH sits a little high on the scale, use acid to bring it within the neutral range and then hit it with the coagulant, you’ll find that the wastewater treatment process becomes much more stable.

For those all-too-familiar with some of the things discussed here, FRC can help build a system to automatically adjust pH with the right chemicals. Contact us and we’ll show you how.

DAF System Operation & Maintenance Schedule

Like any other equipment in your facility, a DAF system absolutely must be maintained if you expect it to perform as designed. Whether you’re in charge of DAF system operation & maintenance or you’re in charge of the guys whose job it is to maintain the DAF system, here’s the list of maintenance procedures that should be performed on a daily, weekly, and monthly basis.


  • Check all control system alarms
  • Monitor effluent quality/turbidity
  • Clean air filter/regulator in pneumatic panel
  • Inspect system for leaks in pipes and pumps
  • Adjust water level to generate thick sludge layer
  • Monitor influent flow rate
  • Check and set recycle pump pressure
  • Eject sediment from drain valves
  • Check and set air flow setting in pneumatic panel
  • Check for clogging in aeration valves
  • Open and reset all bleed-off valves to clear obstructions
  • Monitor skimmer system for smooth operation and correct tension
  • Check and set chemical dosing rates (if chemically equipped)
  • Inspect chemical supply (if equipped)


  • Drain and clean DAF unit
  • Inspect strainers and filters. Replace as necessary
  • Purge plate pack using purge valves
  • Inspect and clear tanks and sumps of sediment


  • Apply anti-seize to frequently-used threaded parts
  • Grease all bearings
  • Check skimmer/auger drive oil
  • Check recycle pump oil/grease (if equipped)
  • Inspect 3rd party components as per their O&M Manuals
  • Check lamps on control panel
  • Switch to alternate pumps/motors

Do these simple tasks and you should be able to keep the system working like a charm. If for some reason something’s not working or needs replacement, give us a call. We stock all DAF System spare parts for immediate shipment.