Side Stream Filtration: Options and Their Advantages/Disadvantages
Side stream filtration is a vital yet often overlooked aspect of an effective cooling water treatment program. This process reduces suspended solids in a system by continuously filtering a portion of the cooling water and returning the cleaner water to the system. The benefits include reduced fouling and biological growth, minimized scale and corrosion, and improved system efficiency.
When choosing a cooling tower filtration system, it’s essential to weigh the available options carefully. Below are some of the most common technologies, along with their advantages and disadvantages. As with any new system, we recommend consulting your water treatment partner and conducting a particle analysis to ensure the proper filter is selected.
Common Filtration Technologies
Media Filters
Media filters are a popular choice for side stream filtration in cooling towers and closed-loop systems. These systems resemble water softeners, with a fiberglass mineral tank, control valve, and filtration media. Depending on the application, various media combinations can achieve filtration down to 10 microns. Multi-media filters, which include 3–5 types of media in one tank, capture a broader range of particles, while single-media options like Filter-AG and Birm are effective for specific needs such as iron and particulate removal.
Media filters use automatic backwashing, triggered by a set timer or pressure difference between inlet and outlet. During backwashing, the media bed is lifted, and trapped solids are flushed out. A rinse cycle then packs the media back into place. While effective, media filters require a high backwash flow rate (up to 5 gpm per square foot of surface area), so it’s best to use a clean water source for backwashing, not the treated water.
Cartridge Filters
Cartridge filtration systems consist of a filter housing and replaceable cartridge filters. Water flows through the cartridge, where particles larger than the micron rating are trapped. Over time, as the filter clogs, the pressure differential between the incoming and outgoing water increases, indicating the need for a replacement.Cartridge filters have a low upfront cost but require ongoing expenses for replacement cartridges and labor. If not replaced when clogged, they cease to function, leaving the system unfiltered.
Turbo Disc Filters
Turbo Disc filters, such as those by Miller Leaman, use stacks of polypropylene discs as filtration media. During normal operation, the discs are compressed together. When the pressure differential exceeds a preset level, compressed air and a small amount of water trigger a backwash cycle. This expands the disc stack and spins it, effectively cleaning the media.
These filters have a compact footprint, use minimal water during backwash (10–12 gallons per cycle), and are easier to maintain than multi-media filters. However, they are limited to filtering particles down to 50 microns.
Centrifugal Separators
Centrifugal separators rely on high-velocity centrifugal force to spin out contaminants. These systems have no screens, moving parts, or filter media, making them a low-maintenance filtration option. However, their filtration capability is limited to particles down to 40 microns.
Centrifugal separators are often paired with cartridge filters to handle smaller particles, reducing the load on the cartridge filters and improving overall efficiency.
Mesh and Weave-Wire Filters
These filters use wire screens inside a housing to trap particulates. Fully automatic and self-cleaning, they operate using water pressure alone, eliminating the need for manual cleaning. As particles collect on the screen, a drop in water pressure triggers a backwash cycle. A Vacuum Screen Cleaner then suctions the dirt from the screen and flushes it out, completing the process in seconds without disrupting the main flow.
Mesh and weave-wire filters are compact, making them suitable for tight spaces, and they require less water for backwashing compared to other systems. However, they may struggle to remove organic solids, necessitating occasional manual cleaning.
Proper Filtration Improves Efficiency and Equipment Longevity
Investing in side stream filtration enhances water quality, improves efficiency, and extends the life of equipment. For help selecting the right filtration technology or to arrange a particle analysis for your cooling water, contact Watertech at 414-425-3339 or
info@watertechusa.com.