Reverse Osmosis Water Pretreatment
Feedwater pretreatment is very important to maintaining the health of a reverse osmosis or nano-filtration system. Since these systems are so selective, they require feed water that is low in particulate matter. Even moderate concentrations of particulate matter can significantly foul membranes. Implementation of proper pretreatment prior to a reverse osmosis system or nano-filtration goes a long way into preserving membrane life and reducing operational and cleaning costs. Aqua Clear has a wide variety of pretreatment equipment and designs.
Multimedia is one of the most common pretreatment methods used prior to a reverse osmosis system. Multimedia, dual media and mono-media sand filters all belong to a general class of granular media filters. Granular media filters typically contain considerable depths of coarse granular filtration media. Multimedia filters typically contain three layers of granular media which are comprised of garnet, sand and anthracite. Media filtration works by combining three primary transport mechanisms which are diffusion, sedimentation and interception.
Based on the feed water source, the addition of a coagulant may significantly increase the efficiency of media filtration. Aqua Clear has it’s own line of specialty formulated coagulants to help flocculate small colloidal particles for removal in pretreatment filters. To determine if implementation of a coagulant will improve your reverse osmosis feed water, a filtration study can be performed by Aqua Clear’s laboratory services personnel. For more information on coagulation and filtration studies, click on the link below. Aqua Clear has a variety of media filters that effectively utilize these transport mechanisms to produce feed water that fits your needs.
Cartridge and Bag Filters are filters that effectively remove small colloidal particles from water prior to reaching a reverse osmosis system. These filters are generally sorted by particle removal size in microns. Cartridge filters and bag filters are implemented just prior to a reverse osmosis system and should not be relied on as a primary water preatreatment. Cartridge filters and bag filters used as a primary pretreatment method tend to clog very quickly due to their small pore sizes and would need to be replaced often, significantly increasing operational costs. In many instances, these filters act as a last resort in case of failure of upstream pretreatment equipment.
Activated carbon filters are widely used in water pretreatment. Activated carbon filters have a variety of useful properties. Activated carbon media is typically made up of very small carbon based particles that have a high surface area. This high surface area allows for a large contact area for dispersed colloidal material. Additinally, organics such as humic and fulvic acids have a high affinity for carbon based media, making activated carbon filters an excellent means of color removal of water for natural brackish water sources such as rivers, ponds or lakes. Activated carbon filters can also be used to remove free and total chlorine from water prior to reaching a reverse osmosis system. If the primary use for the carbon filter is chlorine removal, chlorine should be monitored downstream as the carbon bed will eventually exhaust its capacity to remove chlorine. Aqua Clear has a line of chemical dechlorinating agents for use in removal of chlorine where implementation of a carbon bed is not practical, feasible or would often need replacement due to high amounts of chlorine in feed waters. See the links below for more information on Aqua Clear’s chlorine removal chemicals and activated carbon filters.
Water softening may be used to remove hardness ions such as calcium and magnesium from a feed water. Softeners are also capable of removing soluble iron and manganese from water, although this is not their primary purpose. Water softening is sometimes used as pretreatment to a reverse osmosis system to prevent hardness based scaling. Antiscalants have largely replaced water softeners prior to a reverse osmosis system, due to the high costs of salts needed for softening and lack of brine disposal issues. For information on Aqua Clear’s antiscalant product line and softener options follow the links below.
Aqua Clear also has a line of chemical injection systems for injecting various types of water treatment chemicals prior to reaching a reverse osmosis system. For more information on products and services offered for chemical injection contact an Aqua Clear water treatment specialist.