Understanding Backwash In Engineering

At first glance, backwash might seem like a boring subject, but in the world of engineering, it is very important.

Backwash is a very important part of many engineering applications, from making sure ion-exchange resin systems work well to keeping swimming pools clean.

As an engineering student or engineer, you need to know everything there is to know about backwash to do well in the field.

In this blog post, I will talk about the different types of backwash, their pros and cons, and how they can be used in different engineering situations.

So fasten your seatbelts and get ready to dive into the interesting world of backwash!

Backwashing in Ion-Exchange Resin Systems

Formal definition:

In an ion-exchange resin system, an upward flow of water through a resin bed cleans and reclassifies the resin particles after exhaustion.

In Ion-Exchange Resin Systems, what is Backwashing?

Backwashing is a process that is used in ion exchange resin systems to loosen the bed and flush out impurities.

It is very important for keeping water clean and getting rid of impurities.

Backwashing is done before brining to open up and loosen the bed.

This helps to flush out impurities and prevents channeling.

The water that goes into the filter has different amounts of suspended solids that get stuck and/or build up in the empty spaces between the resin beads or granular filter media.

As the solids build up, they can make it possible for channels to form in the bed.

Backwashing also helps to get rid of hydraulic compaction and sort resin beds.

How Backwashing Works

During the service run, the resins wear out over time because they bind to dirt and other particles.

When this happens, the resins need to be regenerated to get rid of the ions that have stuck to them.

Backwashing is done before brining to open up and loosen the bed so that it can flush out impurities and avoid channeling.

The backwash cycle starts by sending water backwards up through the resin to move the suspended solids that have built up on top of the resin.

A good backwash can increase the size of the resin bed by 50% and takes about 10 minutes to do.

During backwashing, resin particles work well as filter media because they have ionic charges that help fine particles stick together.

When you backwash, the beads are rubbed together, which helps get rid of any dirt or iron that has built up on their surface.

Types of Ion-Exchange Resin Systems

In cocurrent systems, backwashing is done to loosen the media bed and get rid of impurities before putting a chemical solution called a regenerant into the ion exchange vessel.

In countercurrent systems, however, this step is skipped so that the bed does not get too wet.

Potential Drawbacks of Backwashing

Using too high of a backwash flow rate during the backwash step can cause resin to blow out of the vessel.

This flow rate depends on the temperature, so it needs to be controlled in a certain way.

Also, there must be enough time for backwashing to make sure the bed is clean before chemical regeneration.

When automated backwash systems do not work, workers may be exposed to chemicals or face physical dangers from a stopped process.

Resin buildup is another problem that could happen with backwashing.

Fouled resins could make the ion exchange system need more rinsing, make it more sensitive to changes in temperature and flow rate, or cause the quality of the effluent and the system's operating capacity to drop faster than expected.

Resin loss can also happen when resin beads flow out of an ion exchange column or from one vessel to another because of too much backwashing or a mechanical problem in the underdrain.

Frequency of Backwashing

The pressure drop across the bed tells how often an ion-exchange resin system needs to be backwashed.

Backwashing is only needed when the pressure drop gets worse because of the buildup of solids in suspension or resin particles.

Most of the time, it should be done every 15–20 cycles or when the pressure drop is more than 50% higher than normal.

How often adsorbers are backflushed is based on a maximum pressure drop that can be allowed or a set amount of time.

But backwashing should be done at least once a week.

Factors that Affect the Frequency of Backwashing

The type of resin used, the quality of the water, and the flow rate can all affect how often you need to backwash.

Finer mesh resin systems can filter even smaller particles.

If these particles do not get backwashed out of the systems, pressure drop and channeling can happen, which makes the system work less well.

Ion exchange resin expands in a way that depends on the temperature of the water, the size of the resin beads, and the density of the resin.

Each resin is different in these ways.

Revolutionize Your Ion-Exchange Resin System with This Simple Cleaning Hack

Still hard to understand? Let me change the point of view a bit:

Want to make your ion-exchange resin system more interesting? Do not worry about all that fancy gear and high-tech machinery.

Pour some dirty water in there instead and watch the magic happen.

That is right, it is time to realize that backwash is the best way to clean, and it is been right in front of our eyes the whole time.

Okay, we might be joking a little bit here, but the truth is that backwashing is an important part of keeping resin beds working.

So let us take a closer look at this often-overlooked phenomenon and find out how it can help keep your resin system running smoothly.

Okay, that was just a joke made to look like a TV ad.

Now let's go back to the explanation.

Backwashing in Pool Maintenance

Backwashing is a way for pool owners to clean their filters and keep the water in their pools clean and clear.

This process involves reversing the flow of water through the filter to get rid of any debris or contaminants that got stuck in the filter medium.

Backwashing should be done until the water in the waste line runs clear.

Frequency of Backwashing

How often you need to backwash depends on things like the type of filter, how often you use the pool, and the weather.

As a general rule, you should backwash the filter when the pressure gauge shows an increase of 8 to 10 psi over the normal operating pressure.

Cloudy water, less water flow, and more chemicals being used are also signs that you need to backwash.

But it is important to note that the frequency of backwashing can change depending on how often the pool is used and the weather.

Some pool owners may need to backwash their pools more often to keep the water quality at its best.

Methods of Backwashing

Depending on the type of pool filter, there are different ways to clean the filter.

For a sand pool filter, backwashing usually means turning off the filter system, locking the backwash hose to the filter's waste port, and turning the valve to the backwash position.

Water flows backward through the filter system and out of the waste port.

Make sure you have enough fresh sand on hand before you start.

Turn off the pump and set the multiport valve to "backwash" to clean a DE (diatomaceous earth) pool filter.

Then, turn on the pump and let it run for one to three minutes.

After that, turn the pump off again and set the multiport valve to "rinse." Turn the pump back on and let it run for 30 seconds.

Finally, turn the pump off one more time and set the multiport valve back to "filter.

Not all filters have a multiport valve, so the backwash process may be different for those filters that do not have one.

For backwashing your filter, it is best to follow the instructions from the manufacturer.

A cartridge filter does not need to be backwashed, but it does need to be cleaned at least once a year by taking apart the internal grid assembly and cleaning it well.

Tips for Backwashing

During the backwash process, it is important to keep the right flow rates to keep the filter system from getting damaged.

After backwashing, you should rinse your filter for at least 30 seconds so that the return jets do not blow sand back into your pool.

Backwashing is an important part of keeping a pool clean, but it can also be a waste of water.

The water that is backwashed out of the pool has chemicals and other contaminants in it that can hurt the environment if they are not thrown away properly.

To waste the least amount of water, it is best to only backwash when necessary and get rid of the water in the right way.

Discharge of Water Softener Backwash

Water softeners are used to get rid of hard minerals in water.

During the backwash process, a brine solution is made, which needs to be disposed of properly.

If you do not do it right, water softener backwash can harm the environment.

Before connecting your water softener's drain to the sewage system, you should check the local rules.

Options for Discharging Water Softener Backwash

There are a few ways to get rid of water softener backwash, such as:

  • Outside your house.
  • In a dry well.
  • In a French drain.
  • In a septic drain field.
  • Through subsurface discharge.

But it is important to know that most states have rules about how backwash can be safely dumped into the sewer system.

This is because most water softeners use salt or ion exchange.

Best Management Practices for Discharging Water Softener Backwash

The Rhode Island Department of Environmental Management has come up with the best ways to get rid of brine from water softeners in areas without sewers.

The document encourages the use of best management practices for the discharge of water softener backwash brine to avoid problems with on-site wastewater treatment systems (OWTS).

Some states have laws that say backwash brine can not be dumped into an OWTS.

Places to Avoid Discharging Water Softener Backwash

When water softener backwash is released into the environment, it is important to avoid environmental hazards and follow local rules and regulations.

Some places where you should not let water softener backwash out are:

  • Surface waters such as lakes and streams.
  • Storm drains that lead directly into surface waters or wetlands.
  • Areas where groundwater is close to the surface or where soil is permeable.
  • Areas near wells or other drinking water sources.

Best Location for a Water Softener Drain Line

The best place for a water softener drain line is about 1.5 inches above a floor drain, a drain standpipe, or a laundry sink rim.

If you want to send your water softener's waste directly into your city's sewer system, you should first find out what the rules are.

Before you choose a way to get rid of your water softener's backwash, make sure you know the rules and regulations in your area about this.


As we wrap up this look at backwash in engineering, it is important to remember that this seemingly simple process has a lot of importance in the field.

Backwashing is important for keeping systems working and making sure they last as long as possible.

It also has the potential to have a big effect on the environment.

As we keep making new technologies and improving old ones, we must remember how important it is to use backwash in a responsible way and what effects it could have on the environment.

So, before you leave this article, take a moment to think about how you can use your engineering skills to help create a future that values both efficiency and caring for the environment.

Links and references

Dowex Ion Exchange Resins Water Conditioning Manual


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