JWC At IPPE Atlanta 2018

JWC Environmental will be at IPPE 2018 in Atlanta, GA January 30 – February 1.  Check out booth number C1665 and learn more about:

  • IPEC Internally Fed Drum Screens Want to know how IPEC Internally Fed Drum Screens efficiently recover offal from wasterwater wash water use?
  • FRC DAF System Our expert team can recommend the best DAF system to tackle TSS, BOD and FOG in meat processing wasterwater systems.
  • Monster Industrial Grinders See our live grinder! Powerful Monster Industrial grinders shred down feathers and other solids as well as protect process pumps from clogging.

Want to know how JWC can benefit your processing plant? Stop by to discuss your wastewater treatment needs with JWC experts.

We have been performing successfully in the meat processing industry for over 40 years. Stop by and see what we can do for you!

Buying a DAF System? 7 Topics to Discuss First

There are a lot of companies out there that will sell you anything they think you might need. But it’s your responsibility to make an educated decision when it comes to buying wastewater treatment equipment.

Before getting serious about buying a DAF system, get acquainted with the different manufacturers and ask them why they do things the way they do. Get into the details about their equipment and educate yourself on the differences between manufacturers, and how they will affect how your wastewater treatment system works.

Here’s a quick list of 7 main topics to discuss when evaluating a DAF system:

questions-to-ask-before-buying-a-daf-system

Algae Removal Using Dissolved Air Flotation (DAF)

It happens every year around the US – warm weather during summertime induces algae growth in surface bodies of water. Other times algae comes because of  improper management of discharged wastewater. We’re seeing this very problem at Lake Erie right now.

Algae grow when they have the right conditions, such as adequate nutrients (nitrogen and phosphorus), light levels, pH, and temperature. As the concentration of phosphorus found in a water body increases, algae growth will also increase. Elevated concentrations of algae will then produce dead organic matter and cause anoxic conditions. When lakes are deprived of oxygen, conditions will turn septic, fish and plant life will die and decompose, and noxious odors will follow.

So, what can be done to stop algae outbreaks?

Managing algae blooms can prove to be a daunting challenge without the right technologies for the job. First of all, you’ve got to cut the problem off at the head. Reduce phosphorus concentration in agricultural runoff – it’s the largest contributor to the problem. Then, on the other end where the symptoms are showing do something to remove the growing colonies. There are a few different chemical additives that can be dispersed into a body of water to stop algae from growing, but these don’t actually help remove the floating green mat of solids.

A better approach is to physically remove the algae and reduce the concentration of phosphorus in the water. A simple process of clarification via Dissolved Air Flotation (DAF) and phosphorus precipitation can stop an algae bloom in its tracks.

We’ve used the DAF process many times to help with algae removal in surface bodies of water. Download our free whitepaper below and see how it’s done.

 

 

7 Ways to Reduce Chemical Use in a DAF System

It’s no secret that the greatest operating expense of an industrial wastewater treatment system is in chemical usage. Naturally, finding a way to reduce chemical use would be a good place to start finding savings. The electrical cost of running a PCL-60 DAF system at full capacity (660 gpm) for 24 hours is roughly $30. That figure will fluctuate with up and downtime, but is pretty close to constant. Chemical costs, on the other hand, are directly related to flow rate and wastewater composition (i.e. solids concentration, oil content, pH) and can vary widely from application to application. Where operating a DAF system for one year might cost $11,000 in electricity, chemical costs can easily be five or six times that much.

To paraphrase Einstein, “In every challenge lies an opportunity.” Our challenge here is to reduce chemical use with the opportunity to save thousands on operational expenses. So here we go…

1. Equalize and Mix Flow

A simple way, yet effective way to reduce chemical use is to collect and mix all plant wastewater, rain, and yard runoff into a homogeneous solution. Many plants operate multiple shifts with some generating wastewater with more solids than the others. Rather than treating that heavy load with extra chemicals, blend it in with the lighter loads to dilute the solids concentration. Then you can flow pace your chemical dosing as opposed to dosing based on peaks and valleys in solids loading.

2. Use Pre-Screening Equipment

This externally fed rotary drum screen reduces TSS from 3500 mg/L to 1200 mg/L.

This externally fed rotary drum screen reduces TSS from 3500 mg/L to 1200 mg/L.

The idea is simple – the more solid contaminants you can remove before using chemicals, the better. Install floor drains with tighter screens, run process wastewater through a rotary drum screen, allow heavy solids to settle in a holding tank.

Simple static and mechanical screening can dramatically reduce the volume of solids sent to wastewater. Then when chemicals are dosed they go after the solids that are harder to separate instead of the ones that should have been removed mechanically.

3. Calibrate Dosing Pumps

Liquid chemical feed pumps come in three main forms: peristaltic, motor driven, and electric metering, each with its own application-specific advantages. Regardless of the type of pump your plant employs, liquid feed pumps have to be calibrated and re-calibrated.

Use a graduated cylinder to measure the volume of water moved through the pump in one minute. Repeat the minute-test on four or five different settings between 10%-90% capacity. If your pump moves 35 ml/min when you set it to 30 ml/min, it’s overdosing by 15%. That could amount to thousands of dollars in no time. Calibrate your pumps.

4. Adjust pH with Correct Chemicals

We’ve already had a good discussion about why using coagulants to adjust pH is wrong, but it’s worth reiterating a couple points. Metal-based coagulants used in wastewater treatment are effective only within neutral pH ranges. When wastewater has a high pH, acidulation is required to bring it to neutral. Aluminum and iron based coagulants are acidic in nature and can achieve this neutralizing effect, but that is not their intended purpose. Instead, using less-expensive pH reagents (i.e. sulfuric acid, hydrochloric acid) to achieve neutralization is the right way to go about it. Not only does it make economic sense, but it’s better for the overall wastewater treatment process. Again, read the aforementioned post.

5. Disperse Chemicals Effectively

Flocculator chemical dispersion

FRC’s flocculators disperse chemicals in mixing zones that increase flow-through velocity

In DAF systems, chemical dosing pumps inject a stream of liquid chemical into a mixing tank or pipe flocculator, what happens to the chemical thereafter depends on the design of the equipment. Chemical reaction tanks use mechanical agitators to blend the chemical with incoming wastewater and do so quite well, barring adequate tank size and mixing velocity. Flocculators rely on shear forces to disperse chemicals as water moves through the serpentine structure. Both systems can work in place of the other, though flocculators are much less-expensive than the alternative.

Chemical reaction tanks can better disperse chemicals by slowing the feed flow rate. Pipe flocculators are designed to maintain a specific flow velocity to disperse and mix chemicals. Whichever method your system employs, make sure you’re following the specified operational procedures.

6. Treat to Permit Requirements

If your permit limit for TSS is <250 mg/L, you’re equally as free to discharge at 200 mg/L as you are at 20 mg/L. Some chemical suppliers may show you a jar of clear water where they’ve reduced TSS to <10 mg/L. The thing is, you don’t need to treat to <10 mg/L, you only need to beat 250 mg/L. We’re not advocating skirting right up to 249 mg/L for TSS, we’re saying reduce chemical use to what you need to comply with your permit. The general axiom is, “use the least amount of chemical necessary to meet the treatment requirements.”

7. Jar Test, Jar Test, Jar Test

The easiest and most immediate way to reduce chemical use is to draw wastewater samples and test dosing rates. Grab 100 ml of wastewater, use a pipette to drop in 1 ml of coagulant, and give it a stir. If you see adequate coagulation, you’re good to go. If DAF effluent quality starts creeping too close to the limit, jar test again and adjust your dosing rate.

If you’re already doing all of these things, well done! If not, then hopefully we’ve helped you identify a couple ways to save a buck on operations.

One Final Note…

There are many cases where attempting to save money on operations by eliminating chemistry altogether is absolutely the wrong choice. Many suspended solids will remain suspended without the addition of coagulants or flocculants to bind them into larger, floatable flocs. DAF systems can still remove a significant portion of these solids without added chemistry, however the float sludge is often very watery and the effluent quality is not as good as it could be. This is simply shifting the cost of chemistry in the DAF system to the operations of the sludge management and biological treatment processes.

In other cases the value in using chemistry is realized in the recovered product from the DAF system. For example, a rendering facility might employ a DAF system to recover solids for reprocessing. Without chemistry they recover a certain percentage of the solids which add to their bottom line. With chemistry they recover 5x as many solids and add even more to their bottom line. The extra cost for the chemistry easily pays for itself in the increase in recovered product.

All this being said, it’s important to weigh the options before heading too far down one path. Any questions, shoot us an email to info@frcsystems.com.

 

5 Reasons Why ANSI DAF Pumps Rule

DAF pumps are the key component of all DAF Systems. On it rides some of the largest capital, operations and maintenance expenses involved in wastewater pre-treatment systems. So, why does FRC employ an ANSI pump over a specialty DAF pump?

1. No Air in Pump Chamber

Specialty whitewater pumps come in a regenerative turbine or a multi-stage impeller configuration. These pumps pull atmospheric air (or receive an inlet feed of compressed air) into the pump chamber where impellers mix and shear the air with water to form micron sized bubbles that dissolve to create an air-water mixture. Specialty DAF pumps generate pretty decent whitewater, but anyone that’s ever worked with pumps will tell you that air inside a pump is rarely a good idea – there’s always a risk of cavitation, which causes internal damage and results in more-frequent-than-desired parts replacement.

ANSI pumps on the other hand, don’t pull air into the chamber because they don’t need it. The ANSI pump’s job is to move water, not be responsible for dissolving air into the liquid. No air in the pump, means very little risk for cavitation.

2. Lower Operating Pressure

ANSI pumps as designed for a DAF system are only required to pump water at 70-90 psi. Specialty pumps more typically require 90-110 psi. Lower pressures with the ANSI pump mean lower electrical consumption and savings on operational costs.

3. High Solids Tolerance

By nature of the way they operate, specialty DAF pumps have low solids tolerance.  When you start-up of a DAF system that’s been off over-night, any left over solids that make their way into the pump can cause internal damage and reduce the lifespan of the pump.

This issue is less relevant to ANSI pumps because they have a larger tolerance for solids.

4. Standard Components

ANSI pumps are the only dimensionally standard pump type in the pump industry. Comparable sizes of all manufacturers have identical component dimensions. Manufacturers that employ ANSI pumps in their DAF systems design can source parts from any reputable pump vendor. DAF systems that use a specialty DAF pump, you’re only going to find parts through the DAF manufacturer and you’ll face long lead times, because those parts are likely coming from Asia.

5. Lower Acquisition Cost

Because ANSI pumps are standard across the industry, enormous competition from pump manufacturers has driven costs down. Specialty DAF pumps don’t have that kind of competition so, naturally, their prices are much higher. Hopefully you take care of whatever pump you operate and don’t need to think about replacing it, but if you do eventually have to bite the bullet and get a new one, you’ll be glad it’s just an ANSI pump.

Let’s recap:

Specialty DAF pumps vs Standard ANSI pumps
Specialty DAF PumpsANSI Pumps
Tendency to CavitateHighLow
Operating PressureMedium to High: 90 – 110 psiLow to Medium: 70 – 90 psi
Solids ToleranceLowHigh
Standard PartsNo – sole sourced from manufacturer. Often originating from AsiaYes – available from any pump vendor
Acquisition CostVaries – between $8,000 – $18,000 USD, depending on capacityStandard – usually between $6,000 – $10,000 depending on capacity

So there you have it. ANSI pumps are clearly king when it comes to dissolved air flotation systems.

All hail the king (of pumps)!

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:

Concrete
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.

Polypropylene
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