What is Backwashing in Water Treatment?
Updated: Jan 24
All water treatment systems come with a lifespan and will eventually need to be replaced. But did you know you can actually extend how long your water treatment system will last and improve its efficiency?
Preventative maintenance efforts, such as membrane cleaning and backwashing, are effective ways to do this.
The backwash definition basically refers to the process of pumping water backward through the filter's media to remove accumulated particles and debris. During backwashing, dirty water is forced out of the filter bed, flushing out any accumulated impurities. Backwashing helps to maintain the efficiency of the filter and prevents it from becoming clogged with debris. Backwashing can be done manually or automatically using a control system that monitors the pressure drop across the filter.
In this article, we’ll answer the most commonly asked questions about backwashing filters in water treatment. Let’s get started.
Step-by-Step Procedure of Backwashing a Filter
There are several steps involved in the backwashing of media filters. These are-
Taking the filter offline and draining the water to a level above the surface of the filter bed.
Pushing compressed air up through the filter, causes the filter bed to expand and forces the accumulated debris into suspension.
Forcing clean backwash water upwards through the filter bed expansion which will carry the suspense particles into backwash troughs. This is carried out until the turbidity reduces to the desired value.
Terminating the upward flow of water and letting the filter bed settle into its original position.
Directing the dirty backwash water into a sanitary sewer system or treating and recycling it within the plant.
How often should you backwash?
You can assess how clean or cloudy the water coming out of a filter is to decide if the system needs a backwash. A good practice is to schedule a backwash if you get a score of 0.1 nephelometric turbidity units (NTU) on each individual filter’s effluent.
You can also use a negative pressure gauge to check the head loss on the filter. If the negative pressure is high, it indicates a clogged filter that needs to be back-washed. Some other metrics that can be used to check if a backwash is needed are the system’s run time or gallons filtered.
How long should I backwash my water filter?
The easiest way to measure the duration is to simply backwash until the water runs clear.
However, many water systems don’t have access to unlimited amounts of clean water for extended backwashing. It’s important to remember that using water for backwashing is not eating the precious resource. Instead, it’s an essential process to keep filters clean and efficient.
Luckily, there are some techniques you can use to quicken the filter backwash process.
You can add a surfers wash system which is essentially a series of fixed or revolving water jets that come on during the backwashing cycle.
You can also add an air scour system consisting of several small air pipes that blow uncontaminated air to help break up mud balls.
Another technique is to sanitize a regular gravel rake and move it up and down the fluidized filter media to move the backwashing process along.
Lastly, you can try increasing or decreasing the backwash rate. However, remember not to vary it too much to avoid displacing the support gravel.
How can Advanced Watertek Help?
Advanced Watertek provides Water Treatment plants in UAE with both manual and automated PLC-based backwash systems. An automated backwash system automatically conducts a backwash at defined intervals, or if differential pressure is built, ensuring the optimal performance of the system.
Do you have water treatment projects in UAE? Find out more about how Advanced Watertek can help you maintain your water treatment systems.