FREQUENTLY ASKED QUESTIONS

Why is it termed a “Fabric Media” water filter?

The technology applies synthetic fibres to provide a filtering media bed.  Microscopic fibre based products have been applied for water filtration for many decades providing numerous advantages for water filtration.  These include a large array of available chemistry to provide ideal performance characteristics for many different industrial filtration tasks. 

 

Unfortunately lengthy fibres prove difficult to engineer into a washable filter media bed product as they naturally knop when agitated.  The best option is to join fibres of the desired chemistry for the filtration task into a textile fabric.  Small wads are then cut from the selected textile fabric and these are used to form the filtering media bed.  Hence the name “Fabric Media Water Filters”. 

What particle size will be removed by a Fabric Media Water Filter?

All media bed filters provide filtration by a combination of separation mechanisms.  The major mechanisms are often explained as adsorption (often termed depth filtration) and size screening mechanisms. The adsorption mechanism is the predominant mechanism as the majority of suspended particles are invariably always much smaller than the aperture size required for laminar flow percolation through an aperture.

Adsorption relates more to the interaction of surfaces and surface tension than to the particle size. Hence rating any media bed filter against a particle size is a misunderstanding of how the media bed separation process occurs. The filtration performance depends on many design and operational parameters, plus attributes of the water and suspended solids.

 

Nevertheless, filtering textiles are available a range of different chemistry, aperture size and shape hence an aperture can be selected appropriate to the filtrate quality desired.  Once advised of a particle size removal objective, the Fabric Media water filter design engineer can apply experience and mathematical based guidance to recommend the appropriate filter tank sizing.

What filtrate quality can be expected?

The filtrate quality is a function of many parameters.  The following are considered the significant performance variables that affect filtrate quality.

  • Suspended solids concentration in the raw feed water.

  • Filtration flux.

  • Properties of the Fabric Media and its’ interaction with the filterable contaminants.

  • Operational practise of the filter.

  • Chemistry of the raw feed water.

  • Pre-treatment of the raw feed water.

 

All standard filtration process control strategies are available options with Fabric Media water filters.

 

If filtrate quality is the critical filter performance parameter, then a filtrate turbidity instrument can be incorporated with the equipment to provide highest filtrate quality security.

 

The option of built in on line turbidity probes, or side stream turbidity instruments can be incorporated with the Fabric Media Water Filter.  The Fabric Media water filter’s product design engineer must be advised of these requirements, even if they are self-procured items.

Does the product warranty cover industrial applications?

 

The product recommendation is subject to a professional design review.  The product warranty and performance guarantee are based on the design review. 

 

Thereafter, the type of application does not affect the product warranty as long as operation of the machine is kept within reasonable guidelines of the operating manual.

Can one FM filter replace ten equivalent sized sand filters?

 

 

 

This picture attempts to display on the 2D page, 3D media beds, sand filter left and fabric media right.  The viewpoint is from above, looking down onto the media bed as is the filtering surface presented to the raw water.   These examples both have a 129 micron minimum aperture width, which is the minimum aperture for a hypothetical sand media consisting of 1mm diameter media particles.  Note, the minimum aperture dimension for the sand filter media is not parallel with the plane of this page; it can be mathematically calculated by an engineer or mathematician or simulated by a 3D CAD model.

 

If comparison of the number of aperture per same 4mm2 cross sectional area is analysed, the fabric media has (14.4x8) 115 apertures, the sand filter media has only 3.  The example above assume a 10 micron fibre textile, if a more robust textile made with 30 micron the number of apertures per 4mm2 decreases to 100.  If smaller or larger particulate size sand media is used, the ratio of aperture openings to cross sectional area remains constant, just the size of the minimum aperture dimension changes in direct proportion to the media bed grain.

 

In most design recommendations a one in ten reduction will be recommended for equivalent filtration performance, however it may be even greater.  Just advice the design engineer what sand filter tank cross sectional area has been recommended and a similar performance Fabric Media water filter will be recommended.

What materials of construction are available?

 

All Fabric Media filter vessels are available in steel alloys, and some smaller models also available in FRP.

Steel vessels are available with or without an internal paint coating or lined with rubber, PE or PTFE.

HDPE tanks and other poly tanks are not cost effective materials for fabrication of low pressure vessel water filters.

What tank life can be expected?

Unlike sand media, Fabric Media is not abrasive, for example the movement of sand media during a backwash will cause abrasion on any steel alloy, including abrasion to a rubber lining, and this will give a relatively short tank life. 

 

As there is no abrasion within a Fabric Media water Tank, the tank life correlates with the corrosion rate of the material of construction with the water contents.

 

Thus, 20 – 50 year life expectation is not unreasonable.

Why does a Fabric Media Water Filter require a Motor?

The backwash applies agitation as the filter’s wash sequence is akin to a laundry washing machine.  However, the agitation is far more vigorous to minimise the off line time required to complete the backwash cycle.

Are chemicals or air required during the backwash?

No, the design intent is for physical agitation forces to dislodge captured contaminants from the Fabric Media.

Can pre-treatment chemicals be applied?

Common pre-treatment chemicals, such as pH adjustment, coagulants and flocculant polymers that provide a gravity clarification or filter aid benefit can be freely applied to the feed stream of a Fabric Media Water Filter.  However, to obtain best design practise, the Fabric Media Water Filter’s design engineer should be advised if such chemicals are to be applied anywhere in a process plant prior to the filtration.

Will flocculant polymers cause irreversible blinding?

No, the mechanical forces applied during the backwash are sufficient to dislodge a flocculant and an antiscalent polymer.

Sand Media filters experience mud ball blinding; will this occur with a Fabric Media water filter?

Mud ball formation in sand filters generally occurs because the desired time between backwash events exceeds the minimum time required for a mud ball formation and the maximum physical forces that can be applied to backwash a sand filter are then insufficient to disintegrate the mud ball.

The physical agitation during the Fabric Media filter’s backwash sequence will definitely disintegrate any potential mud balls, thus high quality long term filtration performance can be confidently assured with the Fabric Media Water Filter for applications that are prone to adverse mud ball formation experienced with sand filters.

Why is a VSD included?

Every application is to some extent unique in either the task or the operational philosophy. 

 

The VSD gives the operator opportunity to optimise the rotation speed.  Increasing the speed provides a shorter backwash time.

 

However, the major determinant on the Fabric Media’s wear life is the degree of agitation during the backwash.  Therefore, each application can apply the VSD speed setting giving the lowest possible operating cost that meets their specific plant filtration performance requirements.

What wear life can be expected for the Fabric Media?

This varies with the type of textile selected as the Fabric Media and the operational philosophy and control set points applied.  However, predictions range between 2,000 and 20,000 normal back wash events.  For many high clarity filter applications only one backwash per day is required, thus a media bed wear life measured in decades is likely, whereas the performance life for a send media bed is generally a few years.

How can the Media be exchanged?

It is extremely unlikely that the media will ever need to be removed from a Fabric Media filter tank.  However, if excess media needs to be removed there are hand hole and manhole access points, through which a wet dry vacuum hose may be inserted.  

 

When a top up of the Fabric Media is desired, this can be inserted through either the hand hole for small filters or the manhole access way for larger volumes. Top ups are usually completed within 20 minutes.

Will a Horizontal filter perform equally to a vertical filter?

If the filter tanks have an identical Fabric Media filter bed depth the vertical filter provides a slightly greater media bed volume for the same cross sectional filtration area.

 

The greater bed volume means a larger surface area for adsorption of microscopic particles and this correlates with the expectation of a slightly longer filtration run for the vertical filter.

 

When the screening mechanism predominates, for example the feed stream contains relatively large suspended solids such as rougher filtration design, there is no discernible performance difference.

 

The advantage of Horizontal Fabric Media filter tanks is they provide a cost saving per unit cross sectional filtration area, which can be significant for larger flow treatment capacities.

What is the maximum backpressure applied for filter design at the outlets?

Design calculations for the standard Fabric Media Water Filter tank assumes the following maximum backpressures;

Note, if either the filtrate receival point or the waste water receival point are located below the filter level, then a vacuum force may occur at the outlets and to ensure pressure vessel design code guidelines the product design engineer must be notified of this prior to any design recommendation.

Are two pumps required?

This will depend on the quality of the raw feed water and the operational practise.  Some projects will benefit from having two water sources available to the filter.  For each project, the product design engineer will provide a recommendation and a P&ID drawing will confirm the requirements.

 

Using a low clarity water to complete the backwash will risk degradation to the Fabric Media, whilst application of higher clarity water will provide a faster wash and back rinse and this becomes significant when the filter plant’s operational practise creates a high solids loading from each filtration run.

 

As a guide only, damage to the Fabric Media can occur if the raw water has potential to contain a TSS above 50mg/L and this includes if a short spike of high concentration is possible.

 

If the backwash can be satisfactorily completed in the raw water, a typical occurrence for a potable water plant, then only one pump is required.

 

If two water sources are required, then water source selecting valves are required.  In this scenario the customer may select a one or two pump installation.

 

If the one feed pump scenario is selected, the water source selecting valves will be placed before the pump.  This scenario is likely if the pumps inlet head pressure is close to identical for both water sources, to avoid potential pump cavitation hammering.  A variable speed drive can also be contemplated to deliver the appropriate flow rates for each step of filters process sequence.

 

If the two feed pump scenario is selected, the water source selecting valves are placed after the pumps and before the filter inlet.  This scenario is the likely recommendation, when the chemistry of the two water sources are significantly different or the pump inlet pressures are different.

What type of pump is best?

The type of pump is not critical; a low pressure high volume centrifugal pump is generally applicable.

How are the pumps sized?

The filter product engineer does not recommend a pump size or type.  Consult a fluid dynamics or pump engineer to provide a recommendation.  Advise the consultant that a standard control package for a Fabric Media Water Filter will shut down the plant when backpressure at the filter inlet reaches 300kPa, less your site safety factor. 

 

The maximum capacity should attain the ideal minimum flow advised by the product design engineer that is required during the forward rinse step of the backwash.  If a second pump is installed to enable high clarity water during the backwash it must meet this capacity.

What volume of wastewater is generated?

This varies significantly depending mostly on the operational practise and the task requirements, varying from as little as 3 tank volumes to as much as 6 tank volumes for demanding tasks.

What concentration are the contaminants in the wastewater?

Again, this varies significantly depending on both the operational practise and the filter performance requirements. A figure in the range 5 to 10 gram per litre is not unusual.

What is a typical product delivery time?

A typical fabrication time is 5 months

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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