when to filter backwash in water treatment plant

In water treatment plants, backwashing can be an automated process that is run by local programmable logic controllers (PLCs

). The backwash cycle is triggered after a set time interval, when the filter effluent turbidity is greater than a treatment guideline or when the differential pressure (head loss) across the filter exceeds a set value.

Full Answer

How much backwash is in a water treatment plant?

The backwash water volume is usually 2–3% of the treatment plant flow. Spent filter backwash water will typically contain 10–20% of the total solids production, and may contain both organic solids and microorganisms as a result of biological growth from the filters.

What is filter backwash in water treatment?

Background Water filter backwash (WFB) is generated when potable water treatment plants treat their well water to reduce suspended and dissolved solids. Sand filter systems pump well water into the top of a tank that is pressurized or gravity fed down through a porous (usually sand-rock) media.

What is the filter backwash recycling rule?

Filter Backwash Recycling Rule Documents. The Filter Backwash Recycling Rule (FBRR) addresses a statutory requirement of the 1996 Safe Drinking Water Act (SDWA) Amendments to promulgate a regulation which "governs" the recycling of filter backwash water within the treatment process of public water systems PWSs.

How do you treat backwash water?

Used backwash water contains high concentrations of particulate material. Typical treatment processes include coagulation, flocculation and sedimentation. High molecular weight synthetic organic polymers are sometimes added to facilitate the formation of settleable floc.

How do you know when to backwash your filter?

0:596:02How Often Should You BACKWASH A POOL FILTER? | Swim UniversityYouTubeStart of suggested clipEnd of suggested clipNormal if your pressure gauge is 10 psi or pounds per square inch over your normal operating.MoreNormal if your pressure gauge is 10 psi or pounds per square inch over your normal operating. Pressure it's time to backwash. A high pressure reading means that your filter has accumulated.

How often should I backwash my water filter?

As a general rule, you should be backwashing your pool about once a week or in conjugation with your scheduled maintenance. Another industry standard is to backwash when your filter's pressure gauge reads 8-10 PSI (pounds per square inch) over the starting level or “clean” pressure.

When should a backwashing operation be performed on a sand filter?

A good rule of thumb is to backwash once the pressure displayed on your pressure gauge is 8-10 psi over the starting level. Backwashing after heavy rains, treating for algae, or when trying to clear cloudy water will keep your filter working efficiently.

What is filter backwash?

What is Filter Backwash. Backwashing is a process that is used in water and wastewater treatment to pump water backward through filter media, which includes anything placed in a filter that changes the quality of water flowing through it.

How long should a backwash last?

2-3 minutesSet the sand filter multi port valve handle to the BACKWASH position and ensure the handle locks in place. Turn on the pump and allow the sand filter to backwash for 2-3 minutes or until the water in the sight glass (typically located on the top of the filter) is visibly clear.

How do you set the backwash on a water filter?

3:1411:397500-M Backwash Filter Installation Video Includes Programming and ...YouTubeStart of suggested clipEnd of suggested clipSo you can use these to scroll back and forth and when you get to one if you want to change you'llMoreSo you can use these to scroll back and forth and when you get to one if you want to change you'll go ahead and push this button. And you'll see it's blinking.

What's the difference between rinse and backwash?

Rinse runs water in the same direction that normal filtering does. Backwash runs it through the sand in the opposite direction. Rinse is to clear any dirt out of the clean side of the sand before you start sending it back to the pool.

What backwash means?

a backward flow or movementDefinition of backwash 1 : a backward flow or movement (as of water or air) produced especially by a propelling force also : the fluid that is moving backward. 2 : consequence, aftermath.

Is backwash the same as waste?

Drain/Waste: Opting the drain or waste setting will remove pool water without forcing it through the filter. Backwash: This clears out any debris, dirt and other contaminants that may have accumulated on the filter. Closed: if you choose this setting, then the flow of water to the pool and filter will be stopped.

Why backwashing of filter is needed?

Backwashing a drinking water system filter means reversing and increasing the water's flow to flush out accumulated debris and particles. Backwashing is not only vital to the life of a filter, it is fundamental to the quality of water coming out of the filter.

What is backwash cycle and its purpose?

Backwashing is the term we use for cleaning the filter. All filters eventually become loaded and must either be changed, replaced, or cleaned. Our filters clean themselves. Normally we set our filters up to clean themselves every 3-4 days.

What is backwashing in water treatment and explain when and how it is done?

In terms of water treatment, including water purification and sewage treatment, backwashing refers to pumping water backwards through the filters media, sometimes including intermittent use of compressed air during the process. Backwashing is a form of preventive maintenance so that the filter media can be reused.

What is backwashing water?

Backwashing is a process that is used in water and wastewater treatment to pump water backward through filter media, which includes anything placed in a filter that changes the quality of water flowing through it. This process sometimes involves the intermittent use of compressed air and is a form of preventative maintenance so filter media can be ...

What is semi continuous backwashing?

Backwash water is discharged into the main distribution inlet header for reprocessing. Air from the blower is used in a semicontinuous pulsed-bed filter. When the suspended solids in the effluent cease to filter to an acceptable level of the head, pressure begins to increase, and backwashing begins.#N#Continuous backwashing is an up-flow, moving bed filter that is constructed with various media depths for different applications and configurations. Raw water enters near the bottom of the tank, and suspended solids are filtered out as the raw water flows up through the media bed. As the filtrate reaches the top of the filter, it passes over the effluent weir and is discharged. A portion of the filtrate is diverted through the sand washer and used for cleaning and transferring the waste solids.#N#Hoffman & Lamson is the industry’s global leading specialist of engineered products ensuring reliable, quality, and cost-effective solutions for water and wastewater applications.

What is slow sand filter?

Slow sand filters. All three types of sand filters are used extensively in the water industry throughout the world. Rapid and upflow sand filter methods require the use of flocculant chemicals to work effectively while slow sand filters can produce very high-quality water without the need for chemical aids.

How does backwashing work?

To backwash the membranes, the air is introduced at the bottom of the membrane, and water and air move upward, causing vibration and friction to the membrane. The backwash water is removed. Backwashing is normally done while the process continues and is usually automated.

What is air assist in backwashing?

Air assist is preferred in backwashing as it provides a more vigorous washing action. Air and water are applied for several minutes as the bed is agitated. The wash water that has risen from the backwashing process is removed. Then, a second lower pressure backwash, without air assist, makes sure bubbles are removed from the filtering media.

Where does the feed water go in a sand filter?

The feed water is directed into the filter at the base of the active sand bed. It then flows upward through the downward moving sand bed where the solids are intercepted, and the clean filtrate exits the filter through the overflow weir. The continuous flow of reject washing water is discharged through a separate outlet.

How many blowers per filter?

HOFFMAN & LAMSON multistage centrifugal blowers provide the air for backwashing in this process. The typical arrangement is one blower per filter. The amount of air required depends on the depth of the water and surface area as well as the depth of the filter media.

What happens if you backwash a filter?

Attrition of more friable filter media may result from a vigorous backwash, particularly if air scour is used.

How much water is recycled in a water treatment plant?

In a survey of the 335 water treatment plants in the US that recycle spent filter backwash water, the average generation of spent waters was found to be 2.5% [73]. Most of the plants (88%) use surface water as their source, with 83% of these recycling to the head of the plant and only 2% to just before the filters. Further treatment is provided by 65% of the plants before reuse of the backwash water, the type of treatment varying from site to site. Options include sedimentation with or without added coagulants, dissolved air flotation with and without polymer, oxidation, conventional filtration and membrane filtration. Pilot studies of various methods to establish appropriate strategies showed that 0.5 mg L −1 of a cationic polyacrylamide of very high MW and medium CD removed 99.6% of the turbidity after filtration, and a similar dose of an anionic polyacrylamide removed 99.4% [ 73, 74 ]. The polymers were selected as the best options after jar tests on two cationic, three anionic and three non-ionic polymers. Similar performance was obtained with 15–20 mg L −1 of ferric chloride, but treatment effectiveness was lost soon after a steady state was achieved. Ferric chloride and a CPAM in combination, however, gave stable long-term treatment with the same turbidity result as for CPAM alone. Ferric chloride was superior for DOC removal. Generally, treatment was much better when polymer was added in both sedimentation and dissolved air flotation, which gave equivalent performances. In other work on dissolved air flotation, treatment of a high degree in a very cost effective manner was achieved, a treated water turbidity of 1 NTU being easily obtainable when the original backwash water turbidity was in excess of 50 NTU [78]. Chemical requirements were low, with no primary coagulants being added and only a single low dose (0.1–0.5 mg L −1) of polymer being required to bind the floc particles and form agglomerates that were suitable for flotation. The optimum polymer type was site specific.

What is raw water pretreatment?

The raw water pretreatment plant is designed principally for solids removal from the incoming Hanover county sewage effluent (grey water), backwash water and wastewater from the oily water collection system. Raw water enters a coagulation/flocculation chamber followed by a clarifier and dual media depth filters. Backwash water from the filters is periodically returned to the clarifier. Clarifier sludge is dosed with polymer before being thickened and then sent to the filter press for dewatering. The cake is sent to landfill and the recovered water returned to the clarifier.

How much higher is a giardia in backwash water?

In a survey of 34 water treatment plants it was found that Cryptosporidium levels were up to 61 times and Giardia levels 16 times higher in the backwash water than in the original raw water [76].

How can we conserve water resources?

In arid areas conservation of water resources can be achieved by recycling spent filter backwash waters, and this is an economic necessity in other locations also. There is a concern that such recycling can compromise product water quality because contaminants can be concentrated to a level beyond the plant's multi-barrier treatment capability, with Cryptosporidium being a particular worry. A major survey of the situation and a pilot plant study of treatment options prior to recycling have been completed recently [ 73, 74 ]. Cryptosporidium has been detected in backwash waters at a range of levels, one result being as high as 9–33 million per 100 litres [75]. In a survey of 34 water treatment plants it was found that Cryptosporidium levels were up to 61 times and Giardia levels 16 times higher in the backwash water than in the original raw water [76]. In the UK it has been recorded that a backwash water contained Cryptosporidium at 1M/100L and supernatant water decanted from a settling tank 100K/100L [77]. The most recent study puts the significantly higher levels of protozoa in backwash water than in raw water at 21 times for Cryptosporidium and 16 times for Giardia [74]. Similar trends have been observed for DOC and other contaminants.

How much of the water is backwashed?

The backwash water volume is usually 2–3% of the treatment plant flow. Spent filter backwash water will typically contain 10–20% of the total solids production, and may contain both organic solids and microorganisms as a result of biological growth from the filters.

When softening and clarification processes are carried out together, the clarifier and softener dry solids should be?

If softening and clarification processes are carried out together the clarifier and softener dry solids should be summated.

Why do we need to review backwash water recycling?

Requires public water systems (PWSs) to review their backwash water recycling practices to ensure that they do not compromise microbial control

What is the purpose of the Surface Water Treatment Rules?

The purpose of the Surface Water Treatment Rules (SWTRs) is to reduce illnesses caused by pathogens in drinking water. The disease-causing pathogens include Legionella , Giardia lamblia, and Cryptosporidium.

What is the purpose of the microbial protection provision?

Provides provisions to ensure that systems maintain microbial protection as they take steps to reduce the formation of disinfection byproducts

What is surface water treatment?

EPA has developed the Surface Water Treatment Rules (SWTRs) to improve your drinking water quality. The regulations provide protection from disease-causing pathogens, such as Giardia lamblia, Legionella, and Cryptosporidium. The regulations also protect against contaminants that can form during drinking water treatment.

Does watershed protection require filtration?

Requires that watershed protection programs address Cryptosporidium for system that are not required to provide filtration

Can water systems be disinfected?

Some water systems are allowed to use disinfection only for surface water sources that meet criteria for water quality and watershed protection. The following is a brief overview of the major components of each rule. This combination of rules is designed to provide protection from microbial pathogens.

What happens if water supplies contain microbial contaminants?

If finished water supplies contain microbial contaminants, illnesses and disease outbreaks may result. The Federal EPA determined that of the 12 waterborne Cryptosporidiosis outbreaks that have occurred at drinking water systems since 1984, three were linked to contaminated drinking water from water utilities where recycle practices were identified as a possible cause. EPA also determined that other disinfection-resistant pathogens may also be removed more efficiently due to implementation of the FBRR. Exposure to other pathogenic protozoa (such as Giardia) or other waterborne bacterial or viral pathogens are likely to be reduced by the FBRR as well.

What is FBRR water?

The FBRR requires filtered surface water suppliers using conventional or direct filtration to, where needed, change the return of recycle flows in their plant's treatment process. The FBRR requires that recycled filter backwash water, sludge thickener supernatant and liquids from dewatering processes be returned to a location so that all processes are employed, including coagulation, flocculation, sedimentation (conventional filtration only) and filtration. Water suppliers may apply to the Department of Environmental Protection for approval to recycle at an alternate location.

How long does it take for PA-DEP to notify you of a record-keeping failure?

The PA-DEP is required to be notified of this record-keeping failure within 48 hours.

How to clean a filter?

Filters are usually cleaned by dosing with an acidic media cleaner. The dosage can be determined by using the analytical test results along with the filter dimensions and media depth. The dose will certainly depend on the overall media condition.

How long does it take for a filter to be inspected?

Since inspection is somewhat time-consuming, try to schedule the evaluation around other large operation and maintenance projects so that you can devote the necessary time to the process. Depending on the number and size of filters, allow at least several days for a complete inspection.

What is a proper filter inspection?

A proper filter inspection should be performed by a qualified firm specializing in such work. You should be able to get a recommendation from your consulting engineer, the AWWA or your state Rural Water Association. Once selected, the inspection firm will need some basic information about your plant’s filters, such as the number of units in service, the dimensions, the media depth, and how many filters can be taken out of service at any one time.

Why do filters need periodic inspection?

Ideally, filters should receive a thorough periodic inspection and evaluation to assess their overall condition and help in planning repairs, upgrades or media replacement. New media of course gets inspected during installation to ensure compliance with design specifications. After that, inspections at regular intervals are recommended to track and document media condition and operational performance.

What does it mean when the media is backwashed?

During backwash, the media should be adequately raised and mixed so as to scrub out impurities. This movement should be uniform and even. Any media surface unevenness after backwash may indicate that the media is being displaced through excessive air release or uneven backwash distribution. Look for any unusual boils during backwash that may indicate a problem.

What is the heartbeat of a water plant?

The filters are the heartbeat of your water plant.

Why should media be raised and mixed during backwash?

During backwash, the media should be adequately raised and mixed so as to scrub out impurities. This movement should be uniform and even. Any media surface unevenness after backwash may indicate that the media is being displaced through excessive air release or uneven backwash distribution.

How many types of water treatment processes produce residuals?

Each treatment process can produce a number of waste streams, all of which have unique handling and disposal requirements. There are six general types of water treatment processes that produce residuals:

What is water treatment?

Water treatment processes are utilized to remove contaminants from water or to alter the contaminant properties in order to produce a potable water. All water treatment processes that remove contaminants produce a waste by-product. That by-product may be liquid, solid, a mixture of the two, or a gaseous vapor.

What are the two types of residuals in coagulation plants?

These coagulation plants produce two major residuals, sedimentation, or clarifier, sludge and spent filter backwash water (SFBW). The second type of treatment plants are those that practice chemical softening for the removal of calcium and magnesium.

What are the types of residuals in water treatment?

The first is produced at those plants that coagulate and oxidize a surface water to remove particles, both organic and inorganic, and dissolved contaminants such as color, organic carbon, iron, manganese, and occasionally trace metals.

Do plants analyze turbidity?

The problem in using these equations is that most plants routinely analyze raw water turbidity , and not suspended solids concentrations. Unfortunately there isn't a one-to-one relationship between the two measurements. Instead, they're related by a "b" factor: