Benefits Of Side Stream Filters

A properly designed side stream filter can benefit your system through:

• Reduced corrosion rates
• Increased equipment life
• Better system efficiency
• Reduced maintenance costs
• Increased chemical efficiency
• Decreased chemical biocide use

With heavy solids loading, significant cooling tower improvement might be realized with the use of a side stream filter.

When to Consider Side Stream Filters

The installation of a side stream filter is a capital expense that generally requires return on investment (ROI) consideration for plants to approve. Consider the following as indications that a plant should evaluate prior to the installation of a filter.

• The primary make-up is from an unclarified water source (river, sewage treatment, etc.) that is high in suspended solids and/or iron.
• The system is having a difficult biological problem even though a good biocide program is in effect.
• Heat exchangers are showing fouling even though a good anti-foulant program is being used.
• Excessive corrosion rates can be traced to fouling.
• Loss of heat transfer is attributed to deposition rather than corrosion.
• High levels of solids are building up in the sump.
• Heat exchangers require frequent mechanical cleanings.

Benefits of Using Side Stream Filters

Several benefits can result from the use of a side stream filter. Obviously, not all of those listed below apply to all systems, and good judgment must be applied before making any claims. However, bearing that in mind, the following benefits can be realized.

• Since solids are removed from the system, the corrosion inhibitor will protect clean rather than dirty surfaces, thereby reducing corrosion rates and increasing equipment life.
• When used with good chemical treatment, the filter will keep the system much cleaner and, as a result, the need for mechanical cleaning of exchangers and sumps is reduced, leading to lower maintenance costs.
• A cleaner system means better heat-transfer rates for longer periods of time, leading to lower operational costs.
• In some cases, the removal of suspended solids from the circulating water allows higher cycles, leading to lower membrane exchange and maintenance costs.
• Large biological growths and dead organisms are removed with a side stream filter. This reduces biocide demand and makes non-oxidizing biocides more effective.

Filter Media

Size of the media is important, since it must:

• Prevent suspended solids from passing through the media.
• Hold solids for easy removal during backwashing.
• Be capable of holding a given quantity of solids without clogging.

Medium size is defined by two figures:

• Effective Size: Particle size above which 90 percent of the medium is larger.
• Uniformity Co-efficient: Effective size divided into the particle size above which 90 percent of the medium is larger.

In most cases, because of their high sediment removal ability, sand or anthracite is the filter medium used, and sometimes the two will be used together (i.e., mixed media). The filter beds contain different size layers of the media. Fine sand or anthracite will be on top, with larger and coarser grades underneath. These will be supported on graded gravel or heavy anthracite.

Most filters operate at a filtration rate of 2 to 3 gallons per minute per square foot of filter surface. Backwash rate is enough to expand the filter bed by 50 percent, usually 10 to 20 gallons per minute per square foot.

Filter media will usually be selected to:

• Remove those particles with the greatest tendency to settle.
• Be least expensive for a given water throughput.
• Require a minimal backwash rate.

Filter Design

It is strongly recommended that a particle analysis be done on the representative stream that is to be treated. This can be reviewed while planning your side stream treatment. For most side stream filtration, a centrifugal style filter is optimal. It will remove the major problems your system faces and require very little maintenance or repair. However, each filter product does have its limitations.

Media filters provide depth filtration technology by filtering water through a thick layer of graded granular particles. Suspended solids are trapped and attach to the filtration media. Available in a wide range of media types – sand, crushed glass, active carbon, anthracite, basalt, etc. The filter vessels are available in various tank construction materials, meeting international drinking water standards.

• For removal of low density particles (≥1)
• Filtration degree: down to 1 micron (depending on filter-bed type and raw water quality)