Learn more about the technical issues that confront our customers.

Foam in Paint Booth Systems

Aside from being unsightly, foam in wet paint booth systems can cause a variety of problems:

  • Booth balance can be upset potentially interfering with the painting operation itself
  • Foam in the sludge pit, skimmer, or in the sludge consolidation equipment can reduce or even prevent the ability of the equipment to remove sludge
  • Foam in the booth itself could lead to the foam exiting the stacks
  • Foam that gets outside of the booth system could present a safety hazard

Sources of Foam

Foam is usually the result of a combination of mechanical and chemical factors:

  • Booth systems are highly aerated to begin with – sometimes this can be magnified if the booth pump is cavitating – check pump screens for blockage and low levels in the sump
  • Water-based paints tend to have higher foaming tendencies than solvent-based paints
  • Excessive concentrations of chemical products
  • High total dissolved and suspended solids
  • Solvent or paint spills, system contamination
  • Water-based detackification program is out of control
  • High pH or alkalinity

Controlling Foam

Of course, addressing the above sources or reasons is the first line of defense for foam control.  In some cases, that may still be enough however, and a defoamer or antifoaming product may be required.  These products destabilize the foam bubbles so their existence is short lived.  Galaxy Chemical Corporation has a variety of defoamer products to control most paint booth foaming situations.

Defoamer is typically fed at the source of the foam on an as-needed basis. This can range from intermittent, small doses to continuous low level feed using electronic diaphragm pumps.

Consult with Galaxy Chemical Corporation for all of your paint booth chemical and technical needs.

Foam Tech Bulletin

Retention Time in Recirculating Paint Spray Booth Systems

This discussion was put together as a result of a Paint Spray Booth customer adding additional water flow to their system as they added another booth module (this also meant additional paint loading to the system).  This increase in recirculation rate would impact the retention time (RT) by reducing it and the customer wanted to know the potential impact of doing this in their system.  RT is simply calculated by dividing the system volume (V) by its recirculation rate – or RT = V/RR, where RT is minutes, V is gallons and RR is gallons per minute.

This discussion is especially pertinent to systems where it is desired to float the paint solids into a central pit or tank, skimming the floating solids, and then sending the concentrated stream to a flotation/dewatering device – such as a Palin, Hydropac or similar device.

Without question, shorter retention times (RT) in the spray booth system will increase the risk of the paint solids dispersing in the system.  Shorter RTs will provide less time for the paint particles to separate from the water in the pit.  Potentially, the dispersed paint particles would not be picked up by the skimmer to be removed as sludge by the flotation unit.

What is an ideal retention timeFor a floating system, this value can range somewhere between 5 and 10 minutes – but, the closer it is to the high end of this range, the better.  The closer it is to the bottom end of the range or below that, the more likely it is to experience some of the problems listed below.

The potential outcome of shorter RT is:

  1. Increased potential for foaming with higher suspended solids levels in booth water and higher water velocities throughout the booth system
  2. Increased potential for paint solids to recirculate through the system and drop out in lower flow areas
  3. Decreased solids removal in the flotation unit – less sludge being pulled out and reduced sludge removal efficiency
  4. Increased potential for microbiological growth (in particular, anaerobes) where solids may settle out
  5. Increased potential for microbiological-related odors
  6. Increased challenge placed on the detackifier as more solids recirculate around the system

Another question that may be asked is – to what degree might these happen?  That one is a lot more difficult to answer as we know of no easy way to predict these effects.  The booth manufacturer may be able to provide some input on what their system was designed for in terms of RT and what the system can handle.

Another potential area of concern is – the higher recirculation rate in the booths will throw off the booth balance without a commensurate increase in booth air flow.  Spray booths are designed with a specific L/G (Liquid/Gas) ratio in mind – simply said, a certain amount of water must meet up with a certain amount of air to optimize the scrubbing efficiency of the booth.  More water with the same amount of air will most likely decrease the scrubbing efficiency of the booth and increase the potential for live paint overspray to get past the scrubbing chamber, or have overspray back up in the booth.

Our advice to the paint booth customer is to make sure that the booth design can indeed handle more water flow and the proper adjustments can be made to have the booths operate within spec.  If they have variable speed booth air recirculation fans, this may not be a problem.

We know booth balance is critical to having a quality paint job on the vehicle – so the air flow side of this must also be seriously considered.

Improper booth balance and out of spec air/water flows can impact:

  1. Paint quality of the job
  2. Transfer efficiency of the painting operation
  3. Live paint deposition in scrubber, booth back sections and stacks
  4. Paint emissions out the stack

Are there any chemical response actions that can be taken if the paint booth system is going to experience shorter RTs and higher overspray?  Read on:

  1. Higher paint loading/overspray in the booth water is addressed by proportionately increasing the detack level and likely higher polymer feed rates to the sludge conditioning equipment.
  2. The shorter retention time, however, does increase the challenge placed on the particles to float to the surface and be skimmed at the far end of the pit.  In essence, we’re asking Mother Nature to speed up the rate at which the particles come to the surface.
  3. Some assistance can be provided by satellite feeding additional emulsion polymer (which typically goes to the flotation unit) to the return end of the pit.  The emulsion polymer can assist with speeding up solids flotation because it initiates the bridging of the particles and entraps more air with the particles – so they float faster.
    Of course, this can’t be done perfectly as RT continues to decrease – as the rise rate of the more buoyant particles still have to overcome the velocity of the water passing through the sludge pit.
  4. Assuming we have more solids going to the flotation unit, it is likely that the emulsion polymer feed up there may need to be increased as well.  Like detackifiers, emulsion polymers react proportionately with the paint solids.
  5. Additional foaming potential can be handled by more antifoam – to a point.  The best solution to control foam is through mechanical means – lower flows, less splashing, etc.  Of course, shorter RTs take this in the opposite direction.  We would prefer not to feed any antifoam to paint spray booth systems – but in some cases it’s required.  Antifoams become less effective as you increase their feed rates and they can begin to have a negative impact on the detackification program where the charge neutralization and flotation you’re looking for begins to decrease.
    Antifoams reduce the surface tension of the water and break apart bubbles.  This is good when it comes to controlling a foam layer in the system.  It is bad when they’re fed to the point where the small bubbles (in the recirculating water) that enhance flotation are broken and the paint solids no longer float as readily.
  6. Chemicals can only handle these types of changes to a point – and that is something unique to each system out there.  When system mechanics are optimized (correct RTs and correct L/Gs) and we marry that with an optimized chemical program, the overall system results will fall into place.

What can be done to measure the impact of changes to RT and/or higher paint solids loading?

We believe it is important to benchmark certain performance parameters of the systems and to track those parameters as the changes are made.  These would include:

  1. Booth recirculating water turbidity and/or suspended solids levels
  2. Booth water conductivity
  3. Average sludge % solids – this will help in tracking Item 4 below
  4. Paint sludge collection efficiency – this would be done by matching up theoretical daily/ weekly paint overspray solids with the actual amount collected in the bags.  Weighing the bags helps if it can be done.
  5. In parallel, track paint usage and overspray for the above calculation
  6. Develop a foam rating scale – i.e. come up with some measurement on the pit walls (i.e., some plants look at the rungs on a ladder that goes into the pit) and track it
  7. Measure sludge depths in pit – not always easy to do – could try “Sludge Judge” used in waste treatment clarifiers/thickeners
  8. Track other system parameters that may be important to you

Consult with Galaxy Chemical for all of your paint spray booth chemical and technical needs.

Retention Time in Paint Spray Booths Bulletin

Paint Booth Sludge Systems – Float, Sink, or Disperse?

All recirculating paint booth systems require some means of removing the detackified / coagulated paint overspray.  If the paint solids are allowed to build up without removal, the system will begin to suffer from a myriad of problems, including:

  • Sludge build-up on booth equipment – resulting in booth balance issues, loss of water flow in critical areas in the system, high maintenance costs, etc.
  • Odors emanating from bacteria hiding in the sludge
  • High suspended solids in the booth water – could lead to excessive foaming
  • High costs to remove accumulated sludge – sludge may be wet/hazardous

A well designed paint booth system will have some type of paint solids/sludge removal system tied to it.  This design feature will minimize the potential issues described above and will allow the system to run for prolonged periods of time while keeping overall operational costs to a minimum.

This technical bulletin will take a brief look at three conventional approaches that can be taken to deal with the paint solids in a recirculating paint booth system – Float, Sink, or Disperse.

What does each approach accomplish?

Float – This approach is utilized where the cleanest booth water is desired and the sludge is going to be removed on a continuous basis with the appropriate sludge handling equipment.  Flotation units followed by a dewatering step are normally used here.

Sink – Utilized where semi-clean is acceptable and no continuous or semi-continuous sludge removal equipment is in place.

Disperse – Utilized where semi-clean to dirty booth water is acceptable and the paint solids are going to be removed on a continuous or semi-continuous basis with the appropriate sludge handling equipment.  Centrifuges are normally used in this approach.

Some additional details on how each approach is implemented along with advantages, disadvantages, and conditions required are summarized next.


How – Feed detack/coagulant to “kill” the paint, feed flotation/dewatering polymer to flotation unit and potentially an optional feed point to the booth return water stream.


  • Cleanest booth water of the three approaches
  • Less deposition, and foaming
  • Continuous sludge removal keeps system cleaner for longer periods of time
  • Antifoam usage is minimized
  • Lowest potential for biological growth in sludge


  • Initial capital outlay for flotation unit and related equipment
  • Some manpower required to operate and maintain equipment
  • Need flotation/dewatering polymer and feed equipment

Conditions/Equipment Required:

  • 5 to 7 minutes (desired) of retention time* in the system
  • Dissolved/entrained air in recirculation water (normally occurs naturally) and in stream feeding the flotation unit (typically injected)
  • Sump/pit design that facilitates flow to a skimmer unit
  • Flotation unit


How – Feed detack/coagulant to “kill” the paint, and nothing else to condition the sludge


  • Semi-clean water
  • Generally no feeding of flocculation/dewatering polymers
  • No sludge removal equipment or operators required
  • No secondary chemical feed equipment


  • Highest deposition potential in booth system
  • Foam potential increases – potential need for (more) antifoam
  • Increased biological activity and resultant odors
  • Higher ongoing system maintenance costs
  • Higher sludge clean-out/disposal costs

Conditions Required:

  • Longer system retention times (10+ minutes)
  • Generally due to the above, the sump/pit will require a very large footprint in the plant
  • Large quiet zones in the sump/pit


How – Feed detack/coagulant to “kill” the paint, feed dewatering polymer to sludge removal equipment (i.e. centrifuge).


  • Smaller sludge removal equipment – smaller footprint
  • Less operator involvement
  • Periodic maintenance of equipment


  • Dirty water
  • Deposition potential is higher
  • Foam potential is higher
  • Higher potential for biological activity

Conditions Required:

  • Short retention time (< 4 minutes) to keep solids moving
  • No quiet zones in sump
  • Better to have individual/smaller sumps versus one large central sump
  • Sludge dewatering device such as a centrifuge

*Retention Time – the amount of time it takes for the recirculating pumps to turn over the system volume once – i.e. Retention Time = System Volume (Gal) divided by Recirculation Rate (GPM)

Float Sink or Disperse

Waterborne vs Solventborne Paints

With ever-increasing pressure to reduce volatile organic compounds (VOC), and for quite a few years now, paint shops across North America have been converting to waterborne paints.  This transition is not industry-specific, but the most visible industry impacted by tighter VOC regulations is the automotive industry.  Paint companies have worked diligently to meet this challenge and continue to develop improvements to waterborne paints for all the paint layers – including primers, basecoats and clearcoats.

This technical bulletin will 1) take a brief look at the differences between waterborne and solventborne paints, and 2) how waterborne paints are dealt with in water recirculating paint booth systems.

Waterborne vs Solventborne Paints

Waterborne Paint Solventborne Paint
Low VOC – less solvent High VOC – more solvent
Emulsifies in water Paint is rejected by water
Can cause foam Lower foaming tendency
Solids content has been increasing Solids content can range from low to high
Need to coagulate paint particles in booth system Need to “detackify” paint particles in booth system
Treated particles are more difficult to separate & dewater in the booth system Treated particles generally easier to separate & dewater in the booth system
Higher BOD/COD content Lower BOD/COD content

Dealing with Waterborne Paints in Recirculating Paint Booth Systems

Waterborne Paint Particles Need to be Conditioned First

Since waterborne paints readily emulsify in water, the challenge begins with conditioning the paint particles so they can be removed from the booth water.  This begins with the paint detackifier, which in this case means it needs to behave more like a coagulant – i.e. it needs to neutralize the electrical charge of the fine paint particles, allowing the paint particles to come closer together and form large clumps. Once in this state, the particles can be more readily accepted by the paint sludge conditioning process, for example, flotation and dewatering.  pH control is also an important aspect of conditioning the waterborne paint particles.  The correct pH level is normally determined by testing as it also plays a key role in the charge neutralization of the paint particle.

Dealing with Foam 

Due to their inherent chemistry, many waterborne paints will enhance foaming tendencies in water recirculating paint booth systems.  This is best addressed by 1) having the booth treatment chemistry in balance, 2) using a defoamer to control the foam to acceptable levels, and 3) minimizing mechanical effects that can magnify foaming tendencies.  Excessive foam can lead to booth operational issues as well as problems with the sludge processing system.

Removing Waterborne Paint from the System

Once waterborne paints are coagulated, they can be removed from the system using a variety of sludge processing devices such as a skimmer/flotation unit or centrifuge.  Typically these devices will pull a side stream (and on occasion, the full flow stream) from the main tank, pit or booth – and will then send the booth water containing the paint solids to the device. These devices are designed to use flotation or gravity to help separate the paint solids from the booth water.  The resulting sludge that comes out of the device is now higher in solids and is readily removed for further dewatering.

A sludge conditioning polymer is typically fed to the stream ahead of the flotation unit or centrifuge.  These polymers are high molecular weight, long chain polymers that wrap themselves around the paint particles to pull them together.  So, the paint particles that are brought together in this step are now transitioned into a sludge that is acceptable for further handling.  The booth water is also much cleaner and can be recycled back into the system – which conserves a lot of water.  Sometimes sludge conditioning polymers will need to be fed to optional locations as well – such as the return water coming back into the pit/sump.

Further Conditioning of the Paint Sludge – Dewatering

In many cases, the sludge coming out of a flotation unit or centrifuge will still contain a significant amount of water – which may be higher in moisture content than is deemed acceptable for final handling/disposal.  The next step in the process that can facilitate further moisture removal, if required, is called dewatering.  Paint sludge can be further dewatered by giving it additional time and the proper conditions to facilitate this.

Several examples of this include – dewatering bags, gravity filters, vacuum filters, filters presses, and pressure filters, to name a few.  All of these approaches either use gravity or some form or energy to speed up the process of sludge and water separation.  A well-conditioned sludge coming into one of these devices will readily separate from the water creating a sludge dry enough for acceptable handling and disposal/recycling once it leaves the plant.

BOD/COD Issues

Natural organic detritus and organic waste from waste water treatment plants, failing septic systems, and agricultural and urban runoff, acts as a food source for water-borne bacteria. Bacteria decompose these organic materials using dissolved oxygen, thus reducing the DO present for fish.

Biochemical oxygen demand (BOD) is a measure of the amount of oxygen that bacteria will consume while decomposing organic matter under aerobic conditions. 

Chemical oxygen demand (COD) does not differentiate between biologically available and inert organic matter, and it is a measure of the total quantity of oxygen required to oxidize all organic material into carbon dioxide and water. COD values are always greater than BOD values.1

BOD and COD levels can increase in the plant’s waste stream as a result of using waterborne paints.  Depending on the plant’s waste treatment capabilities, the BOD or COD may not be removed to acceptable levels prior to discharge.  There are approaches available to reduce BOD/COD.  Please contact Galaxy Chemical Corporation to learn more about this.

Consult with Galaxy Chemical for all of your paint spray booth chemical and technical needs.

1 Northeast Georgia Regional Development Center, “Watershed Protection Plan Development Guidebook”, Appendix B.

Waterborne vs Solventborne Paints TB04 0114



Paint Spray Booth Chemical Terms

Detackification, Coagulation, Flocculation, Dewatering – What Do These Terms Mean?

All of these terms describe mechanisms by which paint spray booth chemicals might come into play in your paint spray booth/sludge handling system.  Let’s briefly describe each:

Detackification/Detack – Also known as “killing” the paint, is the process of removing the sticky or tacky nature of the paint overspray in the booth recirculating water system.  Paint detackifiers achieve this through charge neutralization (coagulation) and/or encapsulation of the paint particles.  Rapid mixing is required for detackification.

Coagulation – Is the process of neutralizing the surface charge of paint particles to promote attraction of the particles rather than repulsion.  This enhances the ability of the particles to agglomerate and form “pin floc”, slightly visible groups of particles clumping together.  Many coagulants are also paint detackifiers.  Rapid mixing is required for coagulation.

Flocculation – Is the chemical “bridging” process whereby high molecular weight, long chain polymers are used to entangle the pin floc forming larger floc masses.  Flocculants generally work best under slower mixing conditions (to prevent shearing of the bridged floc) and are typically fed in front of equipment where flotation or dewatering of the paint solids are desired.

Dewatering – Is the separation process in which water is removed from the sludge for the purpose of concentrating the solids.  Chemically, this is achieved by promoting a rigid sludge structure of a porosity and pore size to allow drainage of the water.  Mechanically, dewatering is achieved by the use of appropriate equipment such as dewatering bags, gravity filters, vacuum filters, plate and frame filters, centrifuges, and more.

Where are these products fed in a recirculating paint booth system?

Detackifiers are generally fed going back to the booth system to promote maximum paint kill efficiency.

Coagulants can be fed to either the booth header(s) and/or the water going back to the main pit – the latter can sometimes enhance paint particle flotation in the pit.

Flocculants can be fed ahead of where enhanced flotation is required as long as the mixing energy isn’t excessive. They are typically fed into flotation/dewatering equipment.

Dewatering agents are fed directly ahead of the dewatering equipment being utilized. In most cases flocculants and dewatering agents are the same chemical species.


Controlling Biological Odors in Paint Spray Booth Systems

Problem Description

Industrial wet paint spray booth systems can be the source of many odors, be it in the booth itself or in related locations such as the booth sump or sludge room.  Many of the odors are a direct reflection of the materials that make their way into the system – paints, solvents, chemical additives, and more.  Other odors, such as biological odors, could be the signal of a much more serious problem.

These unpleasant odors can lead to worker complaints, lost productivity, and health concerns.  What the odors could also be indicating is that the system is in trouble and that other problems are on the horizon, such as booth operating efficiency, stack emissions control, increased booth maintenance costs, and booth component longevity.

Most biological odors are caused by anaerobic bacterial.  These microorganisms prefer to hide underneath deposits and aerobic biological slime, or deep within sludge masses which have accumulated in the paint spray booth system.  Aside from the obvious unpleasant odor, the bacteria could be working overtime plugging up back sections, spray headers/nozzles, and other booth water components.  This can lead to loss of scrubbing efficiency and untreated paint overspray, resulting in live paint emission and live paint deposits throughout the system.  The anaerobic bacteria which reside underneath the deposits are corrosive, creating the potential for premature both component failure and spiraling maintenance costs.

The Solution

Paint spray booth systems can provide all the ingredients needed for biological growth – moisture, chemical nutrients, oxygen for aerobic bacteria and hiding places or growth sites (solids) for anaerobes, the primary odor causers.

Adequate paint detackification (detack) and solids removal are necessary to minimize the solids build-up which can be the seed for biological growth.  Galaxy offers a broad spectrum of paint detackification and solids agglomeration programs to work in tandem with the sludge processing equipment.

Routine clean-up of booth water locations where solids tend to accumulate is the single most important maintenance chore, aside from chemical treatment, for reducing the ability of anaerobic bacteria to hide out and send their odorous signals.

All odors outside of the booth can be dispersed with adequate ventilation.  However, this doesn’t address the source of the problem (the bacteria), but can provide temporary relief until longer term solutions are in place.

The use of odor maskants can also provide temporary relief, but this only hides the problem leaving the impression the odor has gone away.  In reality, booth performance could be fading every day as the real source of the problem cuts into profits slowly but surely.

Treating the booth recirculating water and booth humidification systems with approved and effective biocides is many times a necessity in paint spray booth systems.

There are two general families of biocides – oxidizing and nonoxidizing.  Some general comparisons of these two biocide groups are shown below:

Oxidizing Biocides (Halogens) Nonoxidizing Biocides
Nonselective organic oxidizer – consumed by organics and oxidizable substances – aka “demand” Not consumed by organics – specific to biological organisms.  Some are consumed by high bulk water solids
Relative low cost per pound (gas/liquid/solid) Moderate to high cost per pound
Use cost variable depending on “demand” Use cost a function of bio-demand
Gaseous chlorine – safety concerns Generally sold as liquids
Liquid chlorine can degrade in container over time esp. in light and with temp. Shelf lives can be 1 year + when stored properly – closed container/cool location
Halogens can be corrosive Generally not corrosive
Halogenated compounds (i.e. chloramines) can release odors Some biocides have an odor
Versatile – effective on many types of organisms Can be specific to certain types of microorganisms

Bio dispersants/wetting agents can be used to supplement a biological control program.  These products allow faster penetration of the biocide into the biomass and can indirectly help with biological control by preventing the biomass from accumulating.

So, biological odors can be kept in check when the proper combination of chemical treatment, equipment maintenance, and biocide application are used together.

Consult with Galaxy Chemical for all of your paint spray booth chemical and technical needs.

Controlling Biological Odors in Paint Booth Systems

Paint Booth Water Chemistry – Why It’s Important

A well run recirculating paint spray booth system requires the combination of two critical components – 1) properly designed and fully functioning booth and sludge handling equipment, and 2) the application of the appropriate paint booth chemical program matched to the equipment.  However, what is often overlooked is the importance of the booth water chemistry that supports the chemical program.  Even the best chemical program can fail if certain key parameters are ignored or not managed well.

This technical bulletin will take a look at some key paint spray booth water chemistry parameters, describing what they are and why they are important.  These include – pH, Alkalinity, Total Dissolved Solids, Conductivity, Turbidity, and Suspended Solids.

pH – is the measure of the acidity or basicity of an aqueous solution.  Paint detackification and sludge conditioning polymers will perform at their optimum level when the pH is maintained within a prescribed range.  This range is normally determined by on-site or lab testing.  pH outside the optimum range can result in loss of paint detackification/coagulation, an increase in suspended solids, loss of sludge dryness, and potentially increased foaming.

pH is measured in a unitless range between 0 and 14 – 0 being very acid, 7 is neutral, and 14 very basic.  Most paint detackification programs run above neutral in the slightly alkaline to alkaline range.

Alkalinity – is the quantitative capacity of an aqueous solution to neutralize an acid.  Total alkalinity is the amount of acid needed to bring the pH of a sample to 4.2.  pH and alkalinity are related and in some cases maintaining a certain alkalinity level is preferred or is measured along with pH.  The same issues that having an out of range pH also apply to alkalinity.

Alkalinity is typically stated as mg/liter equivalent of CaCO3 – mg/L CaCO3.

Total Dissolved Solids (TDS) – is a measure of the content of all inorganic and organic substances contained in a liquid in molecular or ionized form, such as minerals, salts, or metals.  Depending on their form and quantities, dissolved solids can interfere with the charge neutralization that is used in paint detackification, coagulation and flocculation (See Galaxy Technical Bulletin TB 05, “Paint Spray Booth Chemical Terms”, for more information on those processes). The impact of higher total dissolved solids can result in higher suspended solids, paint deposition, wetter sludge and increased potential for foaming.

TDS is typically stated in parts per million (ppm) or milligrams per Liter (mg/L) and does not include suspended solids.

Total dissolved solids can be calculated by multiplying the conductivity by a factor between 0.55 and 0.9 (See Conductivity below).

Conductivity – is the measure of the ability of water to pass an electrical current – and is affected by the presence of inorganic dissolved solids such as chlorides, nitrate, sodium, calcium, magnesium, etc.  Organic compounds like oil, phenol, alcohol do no conduct electrical current very well & therefore have a low conductivity when in water.  Conductivity is affected by temperature – the warmer, the higher the conductivity.

Although every paint booth system is different, at some point, high conductivity in the booth water can have the same impact as high dissolved solids – since the two are directly related. High conductivity can also increase the potential for corrosion of metal surfaces in the system.

Conductivity is measured in mhos or siemens – i.e. µmhos/cm and µs/cm.

Turbidity – is the cloudiness or haziness of a fluid caused by individual particles/solids suspended in the water.  High levels of turbidity can indicate potential solids that will settle out in the system in undesired locations leading to less paint sludge being removed in the sludge processing equipment.  High turbidity can also trigger higher levels of foam.

Turbidity is typically measured by a device that passes light through a column of the water sample.  Three common units of measure include FTU (Formazin Turbidity Units), JTU (Jackson Turbidity Units), and NTU (Nephelometric Turbidity Units).

Turbidity and Suspended Solids are closely related.

Suspended Solids (aka TSS or Total Suspended Solids) – are small solid particles which remain suspended in an aqueous solution.  High levels of suspended solids can lead to settling in undesired locations leading to less paint sludge being removed by the sludge processing equipment.  High suspended solids can also trigger higher levels of foam.

Suspended solids are measured by passing a prescribed volume of the water through a specific pore size filter, drying, and then weighing the filter.  After subtracting the weight of the filter, the weight of the solids represent the amount of suspended solids – typically measure in milligrams per Liter (Mg/L).

The correlation between suspended solids and turbidity is generally regarded as linear, however site-specific testing should be performed to confirm this.

Consult with Galaxy Chemical for all your paint spray booth chemical and technical needs.

Importance of Paint Booth Water Chemistry Tech Bulletin

Water Wash Paint Booth Balance – The Importance of Water Flow

Needless to say, high quality coating finishes require a high performing paint booth system.  Paint finishers will tell you that one of the key elements to achieving this is having control of “booth balance.”  From the painter’s perspective, booth balance is having the proper air flow in the booth, and if there are multiple booth modules, having proper air flow in each booth module and in between booth modules.

Proper air flow means quite a few things – including the amount (cfm) of air going through the booth module, the direction of airflow, and distribution of air through the booth.  Having all of that in proper balance will ensure that a high quality finish is more likely to occur; along with properly applied paint – whether it’s manually applied or via automatic paint application equipment.

Booth Balance has just as much to do with water flow as it does air flow

In water wash paint booth systems, paint overspray is removed through the interaction of the paint with the booth water – on the flood sheet as well as the booth scrubbing area, which is located in the back section or under section of the booth.  This interaction is critical to properly remove the paint overspray from the air and put it into the water.  If this scrubbing action does not occur, the paint can exit the stacks and leave the plant – not a good thing.  Paint deposits on surrounding areas or on cars in the parking lot will not be received well.

Conversely, paint overspray that does not make its way to the flood sheet and scrubbing area will back up in the booth leading to turbulence in the air flow pattern and redeposit on the object being painted and on booth interior surfaces – again, not a good thing.  Paint quality suffers along with booth interior cleanliness.

So, a properly balanced spray booth requires proper air flow and water flow.  Scrubbing equipment designers refer to something called the “L/G”, or “Liquid/Gas Ratio.”  This ratio of liquid flow to air flow defines how efficient the scrubber can perform.  If the ratio is not within spec, scrubbing efficiency will suffer and either of the two situations described above could occur.

One of the key measuring tools to ensure the booth is in balance is to measure pressure drop across the scrubber.  Another way to think of this is measuring the pressure in and out of the booth and comparing the difference.  A device called a Manometer is almost always installed in well-designed booth modules to obtain this reading.

What other variables influence scrubbing efficiency?

Listed below are the key variables that can impact the scrubbing efficiency of a paint both scrubber:

  • Air flow
  • Water flow
  • Pressure change across the scrubber (air entry and exit pressure in booth module)
  • Paint loading
  • Paint particle size
  • Scrubber design

What are some signs that the water flow is impacting booth balance?

  • Water flow rates are low – not always easily observed, but is best checked by routinely inspecting booth water flow areas for less than desired water movement or lack of coverage in areas such as the water walls (flood sheets) or scrubbing chamber entry points.  Ultrasonic flow meter devices can also be used to get a handle on flow rate in the booth supply piping and headers.  If the piping appears relatively clear, check the recirculating pumps for worn impellers.  Also look for valves that may have been pinched back too much as an adjustment to increase air flow.
  • Water distribution is poor – bare spots on the water walls or gaps in the scrubbing chamber will allow for easier exit points for the air (path of least resistance).  This will disrupt the desired uniform distribution of air across the booth leading to air turbulence patterns and the potential to impact paint finish quality.  Short circuiting of air through water gaps will also bring along paint overspray that will not see chemically treated water – leading to paint deposition in undesired locations including the stacks and surrounding area.  Gaps in the water walls and scrubbing chamber entry points can be caused by any object that is not large           enough to be moved along by the normal water flow velocity.  Common culprits include pieces of booth coating materials, gloves, tape, and chunks of paint that have fallen from the grates or booth structure.  Minimizing the intrusion of debris into the system will help to keep these areas clear and free flowing.
  • Accumulation of debris in certain areas – Areas that would normally be flooded with water but now show signs of paint/debris build-up is a sign that water flow may have fallen off.
  • Paint is accumulating in normally dry areas – If paint overspray is making its way past the scrubber and is building up in the booth under sections, back sections or the stacks – this may be due to inadequate water flow (i.e. the L/G ratio is off) and the paint overspray is not seeing booth water.  Some accumulation over time is inevitable – as no scrubbing system is 100% efficient.  The question is whether the buildup is occurring more quickly than it should.

How can Galaxy help?

Galaxy understands how water wall paint booth systems function from a mechanical perspective, and we have the expertise and products on the chemical side.  Galaxy technical experts can assist with system audits and help to identify key areas in the system that need to be addressed – some of which were described above.

It is also important to recognize that even a system which is initially in perfect balance (i.e. air and water flows are in spec), that without a properly implemented chemical detackification program, deposits can begin to form.  As deposits build up in the system, the water flow and air flow rates and patterns will be disrupted ultimately impacting paint finish quality.  Maintenance costs will also increase forcing unwanted down time.

Galaxy has the latest state-of-the art technology in paint detackification programs – including paint detackifiers, coagulants, flocculants, and foam control products.  Coupled with an average of 25+ years of expertise in the industry, our technical specialists can apply our programs to optimize system performance and keep the system running smoothly for as long as possible.

Booth Balance Water Flow Tech Bulletin

Paint Spray Booth Sludge Conditioning Equipment – Some Options

In conjunction with a properly implemented paint detackification program, a water recirculating paint booth system will produce chemically conditioned paint particles that are one step closer to actually becoming paint sludge.  The selection of the proper equipment to make paint sludge is critical in the sense that it needs to be matched to the design of the system.  There is nothing more frustrating than having spent many thousands of dollars on a device to make paint sludge only to find it doesn’t work well with the system you have.

This technical bulletin will provide an overview of some of the most common types of sludge conditioning/processing equipment and what types of system designs for which they are most suited.

Skimmers – Skimmers (sometimes called weir boxes) are used in systems that are designed to float the detackified/ coagulated paint particles.  Skimmers act as collecting devices that will deliver the semi-concentrated paint particles along with some water to a sludge concentrating/ dewatering device.  Skimmers have a dedicated pump that will facilitate the drawing in and delivery of the paint particles and water to that device.

Skimmer design and placement are critical.  Skimmers come in all sizes.  Some are fixed in their position and will require very good control of pit water level so the floating paint particles can actually make their way into the skimmer.  Others are level adjustable units that will move up or down relative to the water level in the pit – either through automatic level sensors and motors or manually where the skimmer can be moved up or down with motors or hand cranking.  In either case, the skimmer needs to see an almost continuous flow of paint particles and water into it to deliver the semi-concentrated paint to the sludge conditioning device.

Placement of the skimmer/weir box is critical in the sense that it has to be in a location where the floating paint particles are moving towards it.  In most central pit systems the skimmer will be placed at the end of the pit nearest the booth recirculating pumps.  The pumps will naturally produce a water current in that direction.  Well-designed pit systems facilitate this movement even further by either having side walls that “V” in towards the skimmer or by installing vertical plates along the sides of the pit that also “V” towards the skimmer.

Flotation Units – Flotation units are typically fed by a skimmer/weir box, receiving the floating paint particles that it has gathered.  The job of the flotation unit is simple – further concentrate the paint particles into becoming a sludge and separating the paint sludge from the booth water.

Well-designed flotation units have several key elements:

  1. Are sized to have enough retention time (volume divided by flow rate) to allow for separation of the floating paint particles from the water.
  2. Have the capability to introduce fine air bubbles into the unit to speed up particle flotation.
  3. Have a chemical flocculent injection point at the inlet – flocculent greatly assists with pulling paint particles together speeding up flotation and producing a sludge that is readily dewatered. It is a good idea to have alternate injection points further upstream in case additional mixing energy is required.
  4. Vertically designed unit to promote good liquid/solids separation with a consolidation zone where the solids concentrate; and a clarification zone where high quality water can return back to the booth system.
  5. A well designed scraper assembly to remove the concentrated paint solids from the unit. The scraper can be driven by air or electric motors.
  6. Utilize a programmable timer so the scraper can remove the floating sludge blanket on a regular basis.

Flotation units are typically not the final step in producing sludge which is ready for disposal.  They are typically followed by a final dewatering step such as dewatering bags, gravity/vacuum filters or potentially a sludge dryer.

Sludge Dewatering Bags – Dewatering bags are an inexpensive way to achieve final sludge dryness following an initial sludge consolidation step, such as a flotation unit.  Sludge dewatering bags are typically made from a durable, porous fabric that allows a properly conditioned sludge to drain its water; while being strong enough to deal with the weight of the sludge it is holding.

Sludge dewatering bags are placed at the exit point of the initial sludge consolidating device, typically below them, so an easy exit and gravity draining can be accomplished.  A well designed sludge processing system will capture the water draining from the filter bag and direct it back to the system.

Dried sludge following sludge dewatering should be dry enough to go to most landfills.

Centrifuge – Centrifuges are best utilized in small water recirculating systems and in paint booth systems where the paint solids are being dispersed (See Galaxy Technical Bulletin TB 03, “Paint Booth Sludge Systems – Float, Sink, or Disperse”) for more information on dispersed systems.

Centrifuges use mechanically induced gravity (spinning) to separate the dispersed paint solids from the booth water.  Concentrated paint solids are drawn to the sidewalls of the centrifuge and are either continuously or semi-continuously scraped from the side walls.  The solids are then captured in a holding bin/container.  If the paint solids are not dry enough, a sludge dewatering bag might be used following the centrifuge.  The cleaner water stays towards the center and is drawn off and returned to the booth system, usually by gravity flow.  When required, the water can be pumped back from a holding tank.

Centrifuges can receive their supply of dispersed paint solids in a variety of ways.  Several possible sources are a side stream off the main booth recirculating header; or pumped separately from a location that is highly active so it sends the most concentrated solids that it can to the centrifuge.

Programmable centrifuges are worth considering as they can 1) reduce the manpower support required and 2) allow for control of the process and cleaning cycle times in semi-continuous units – maximizing sludge dryness and centrifuge efficiency.

At least one flocculent chemical injection point should be installed in front of the centrifuge.  Alternate injection points further upstream are also suggested if additional mixing energy is required.  Some centrifuge manufacturers will install some serpentine piping near the unit to facilitate this.

Gravity/Flat Bed Filters – Gravity/Flat Bed Filters are horizontally oriented sludge concentrating devices that have a roll of traveling filter paper at one end.  A mesh screen located underneath the filter paper provides support and usually travels with the paper.  Some gravity filters have a curved shape which works well for very wet incoming paint solids.  Semi-concentrated paint sludge is delivered to the unit either by gravity or pumping onto the filter paper – and then gravity does its job.  A sludge cake begins to form as it accumulates on top of itself.  Sludge continues to drain and dry while it travels with the filter paper from one end of the unit to the other – while filtered water passes through the paper and is directed back to the booth system.

Gravity/Flat Bed Filters can work well when there is a high water volume accompanied by low to moderate solids loading.

Sludge conditioning polymers (flocculents) are often used in these devices to promote more rapid dewatering of the sludge on the filter media along with a sludge that is more dry.

Vacuum Assist Filters – Vacuum assist filters can come in many sizes and designs, but the common element is that a vacuum is pulled across a surface where the wet fluid or sludge is traveling.  The vacuum helps to pull the fluid through the filter media and through the sludge cake as it builds on the surface.  Clean fluid is collected as it passes through the filter media; while the drying sludge moves from one end of the unit to the other – and then exits on the far end of the unit.

One of the most common designs of a vacuum assist filter is a horizontal orientation – and looks quite a bit like a horizontal gravity filter with most of the same components – traveling mesh screen and filter paper, etc., but it has the additional help of a vacuum to speed up the removal of moisture from the sludge.

Precoated vacuum assist filters can also be used for drawing moisture out of wet paint sludge.  Typically these filters have a rotating drum design that has a filter media, such as diatomaceous earth, that is first drawn to the surface of the filter through a vacuum pulling from the opposite side.  Wet sludge is then pumped into a holding vessel where the precoated filter rotates and draws sludge onto it.  A scraper blade that slowly scrolls inward peels off a small amount of media along with the dried sludge cake that has built on top.  When working well the process looks like a paper towel rolling open.

Although these filters can work well, they require some manpower support to maintain the unit, applying the precoat filter media and switching on the sludge supply.

Filter Presses/Pressure Filters – Using a pump and pressure, these types of filters force the solids-laden water against the surface of a filter media (typically a porous fabric).  One common design is the plate and frame filter press. These filters are a fixed volume and batch operation.  The two major components of the plate and frame filter press are the skeleton and filter pack.

A filter cake builds in between two plates where the porous fabric is positioned on either side. The filtered water passes through the fabric and is returned to the system.  The plates are then pulled apart (either manually or automatically) and the dried sludge falls off and drops to a collection chute or bin placed beneath the unit.

There are other pressure filter designs – but they all have the common design feature of pressure being applied against the surface of a porous media/fabric.

One of the key potential issues using this type of filter is the potential for the sludge to stick to the filter media/fabric if the paint is live/sticky.

Galaxy is familiar with all types of sludge conditioning equipment and can assist with optimizing the output and troubleshooting.  Galaxy also has contacts with many of the equipment companies who design, build and install this equipment.

Paint Sludge Conditioning Equipment TB09 0414