Filtration

SLS Technology Pty Ltd designs and supplies a range of media bed water filters, process filters, bio filters, plus membrane and canister housing type filtration equipment.

  • Media Bed Filters include

1. Polishing Filters and Clarifying Filters for TSS reduction

2. Oil recovery Filtration

>>SLS Technology Pty Ltd can design polishing media bed filters for absolute filtration of organic micelles from the feed stream water. Our practical experience covers anthracite, activated carbon and modern fibre textile media bed filtration

3. Process filters for combination chemical treatment and filtration

>>Organic removal, Iron Manganese filters, Fluoride removal media, nutrient       removing haematite media filters

4. Biological process filters for application of biological reactions with simultaneous filtration

>>Media bed filters

>>Activated carbon

Sand Filter

Fabric Media Filter

Each filtration concept has its pros and cons and a great diversity of design options make comparison of water filtering technologies a challenging task, even for an engineer.  In addition, recent technology advances are improving most filter designs and auxiliary treatment equipment making them attractive and applicable to a wider range for applications and requiring review of old age assumptions and textbook opinions.

However, accurate quantitative and qualitative economic and performance based comparisons can be obtained.  Parameters that SLS Technology Pty Ltd can be review to present basic but important comparisons are

  • Procurement costs

  • Particle size separation performance,

  • Maximum feed water suspended solids

  • Machine operating costs

  • Backwash or reject water volumes

Polishing Filter Procurement Costs

A recent study published in a respected journal reported the following information regarding polishing filter applications installed in medium size water treatment projects.  The authors applied an equalising cost adjustment to compensate for different quality auxiliary items such as valves and instruments.

 

The article stated that per unit volume of water to being treated Pre-Coat filters present the lowest equipment cost.  However, due to the lower additional costs associated with delivery, plumbing and automation of the significantly smaller footprint, the textile media water filtering technology presents the lowest installed procurement cost.

Filtration Performance by Particle Size Capture Ability

 

Recently published data displayed in the graph below is based on a swimming pool water filtration. It provides a competent and accurate comparison of performance expectations at optimum design conditions for three common water filter technologies. These water treatment technologies filter particles by significantly different mechanisms and therefore, when compared using identical source water have different cumulative particle size performance curves. 

This graph compares the cumulative separation of suspended solids by particle size.  A Micro Filtration membrane rated at 1 micron absolute produced the best filtrate quality, slightly better than the textile media filter, however the Diatomaceous Earth filter did NOT remove 3 micron particles.  Membrane filters are thus recommended when assurity for the removal of particles greater in size than the membranes’ absolute pore rating is desired.  As indicated in thus study, the absolute rating of the DE was roughly 30 micron. 

The Textile media bed filter was operated at a filtration flux of 70m3/hr and improved filtration via stronger adsorption would be expected at slightly lower filtration flux.

 

 

Filtration Performance by Maximum TSS

Every water polishing filtration technology has a limiting Total Suspended Solids concentration.  Above this concentration, the filter performance drops off to a point where other separation technologies are considered to provide better economic value.

 

The graph below displays the advantage of a Media Bed Filters, which is the capability to process high TSS feed water without significant production capacity penalty or risk of serious irreversible damage.  The graph compares maximum TSS of a cross flow membrane concept against precoat filter and two media bed water filter technologies operating on medium capacity water treatment plants.

 

The data highlights the need to protect a Membrane filter from solids overload.  Hence, a reverse osmosis plant will have media bed filters prior to the membrane filters to protect them from suspended solids overload and irreversible damage.  Likewise, a media bed filter may have a clarifier located before it to prevent solids overloading on the media bed.

 

If the design data indicates turbid high TSS feed water to the filter, even potential for inadvertent process spikes in the TSS, then a competent water treatment design engineer would select a media bed filter.

 

Membrane filters are used in many industries and in many different configurations. Some configurations, for example air swept micro filtration membranes can operate effectively with much higher suspended solids concentrations than cross flow and dead end membranes and this capability makes air swept membranes very useful for bioreactor applications.

Nevertheless, the data shows that textile media bed filtration has a phenomenal application window compared to the other polishing filter technologies.

 

 

Filter Operating Costs

Since media bed and membranes can last several years when sensibly designed and operated, water filter plant operating costs have to be measured over the long term.  Whereas the perlite in a precoat filter may last for one month, sand media may last 2-5 years a Microfiltration membrane will typically last 5 to 10 years whilst a Textile Media Bed will easily out last much more than 10 years of continuous operation.

 

In the long term, replacement of membranes or media bed material represents the largest operating cost associated with a polishing filter application and energy is typically a quite small proportion.  The attraction of media bed and pre coat filters is their significantly lower operating cost compared to the microfiltration membranes.  An experienced and honourable water treatment practitioner would only recommend a micro filtration membrane when the assurance of the absolute particle size removal is paramount for the desired process quality.

 

When the filter design guidelines of any respected international design standard, such as the ANSI NSF system are applied to a media bed filter’s sizing one can expect better than 99% removal of Cryptosporidium. Crypto spores range in size from less than 0.1 micron upto 5 micron and these spores have been successfully filtered from water and wastewater treatment plants for hundreds of years. 

However, this is rarely the case with a swimming pool filter system because the filtration flux in a typical swimming pool sand media or zeolite filter is an order of magnitude or more above the guidelines of the international standards.

Increasing the filtration flux decreases the equipment size and hence lowers the filter equipment cost but if the size reduction is significant it severely compromise the adsorption capability of a media bed filter. When filtrate quality is not highly critical for the water treatment system, as in the recirculated swimming pool or cooling tower, an increased filtration flux can be practical.  However, media bed water filters have been used to safely generate drinking water for more than two millennia and thus despite the many errant claims that can be found on pool company websites they have been proven over and over to successfully filter micron sized particles when sensibly designed and operated.

 

Backwash Water Treatment or Discharge Cost

All water polishing filter technologies generate backwash water.  For a given application, the cost of treatment or discharge is usually a direct correlation with the volume. 

 

Membrane Filtration

 

It’s quite common for SLS Technology Pty Ltd to recommend a membrane filter process step after a media bed water filter if removal of sub-micron contaminants is essential.

In recent year’s significant reliability, purchase cost improvements and an increasing range of materials of fabrication with both micro and ultra filtration membrane technologies has generated a developing market share and importance in the potable water treatment and industrial process liquor filtration segments for membrane filtration applications.  In particular, Ultrafiltration membranes have established a demanding position in the drinking water sector due to the fact that they filter microbial pathogens that are not killed off or separated in any pre-treatment.

The design task for a membrane plant and the process technology required for them is relatively simple for a water treatment company with the experience of SLS Technology Pty Ltd.  Essentially, membranes act like sieves with water passing through the membrane under either a pressure differential or a vacuum suction.  SLS Technology’s design engineered recommendation will consider several parameters such as type of contaminants, footprint, water chemistry and process objective to identify the optimum membrane technology and material for the task.  Design sizing is then essentially a function of the suspended solids and the filtrate flow rate required.

Like all filters, the membrane filtration technology does have its limitations.  Fouling of the pores either by scale formation, precipitate blinding, near size wedging by discrete mineral particles or attachment of biological growth can present severe and permanent restriction on the membrane efficiency.  The competent design engineering team at SLS Technology Pty Ltd understands these risks, and has the knowhow to assess the potential damages and how best to minimise them. 

One powerful method to minimise membrane fouling is by operating a Textile Media Bed Filter prior to the membrane.  The textile is selected with identical absorbing characteristics to the membrane material.  Thus contaminants which will adhere and foul a membrane can be preferentially removed from the membrane feed water.   Customers with sensibly optimal designed pre-treatment processes do report significantly lower operating energy and much longer membrane life.

Membrane filtration is applied when the water treatment process requires a size related security. SLS has experience with the 4 basic types of membrane filter applications.

1. Micro Filtration

2. Ultra Filtration – plate, hollow fibre, dead end tube, cross flow tube filters

3. Bio Filtration 

SLS Technology Pty Ltd offers a diversity of membrane process knowledge that complements our total filtration knowhow enabling the team to guarantee a recommendation based on the best value process for your water treatment goals.

 

  • Canister filters come in a variety of types and are useful for the smaller volume tasks and are most appropriate for critical security filtration barriers.

Cartridge Filters

Sock Filters

Bag Filters

SLS Technology