News | July 12, 1999

Koch Dendrimers Clean, Maintain Reverse Osmosis Membranes

Koch Dendrimers Clean, Maintain Reverse Osmosis Membranes

Koch Membrane Systems, Inc. (Wilmington, MA), a leading membrane producer, has introduced a new family of dendrimer-based products to pretreat and maintain reverse osmosis (RO) systems. According to the company, the dendrimer-based products prevent rather than control scale growth, and may allow RO systems to operate at higher recovery rates.

RO membranes are used to purify water (and sometimes concentrate constituents) in microelectronic, semiconductor, pharmaceutical, food, and waste processing, as well as in other industries. Companies pretreat and maintain RO membranes to reduce downtime and improve throughput.

Koch's new product line includes KochTreat pretreatments that prevent membrane fouling and scaling and KochKleen cleaners that remove foulants and scalants. KochTreat competes with conventional antiscale ormulations based on phosphates and/or such polymers as polycarboxylic acid, polyacrylamide, and polyacrylic acid. Many antiscalants are formulations contain more than one active ingredient. KochKleen competes with conventional acid, caustic, EDTA, and other cleaners.

While Koch sells conventional membrane treatment chemicals, the use of dendrimers is new. Dendrimers are highly branched polymers. Starting from a central molecule, dendrimers grow branches, which in turn grow branches. The result is a very dense, spherical molecules with a high concentration of active sites.

Reverse osmosis is a high pressure membrane process for separating low-molecular-weight species from a feed stream. Semipermeable membrane allow water to pass while retaining and progressively concentrating salts and macromolecules.

Koch says its dendrimer-based formulations are "priced to market." In the past, dendrimers were considered costly molecules to manufacture because of their complex synthesis. The cost of some dendrimers ran into hundreds of dollars per pound, but Koch says it has found a way to make the materials more affordable. The dendrimers are also used at very low concentrations. Its superconcentrate, for example, uses dendrimers in the 0.5 ppm range.

Dendrimer formulations have several advantages over existing membrane treatments, says Koch:

  • Scale inhibition. Calcium carbonate, calcium sulfate, calcium phosphate, barium sulfate, strontium sulfate, iron, aluminum, copper, and silicates are the chief sources of scale. Conventional antiscalants modify their growth, but only after they form.

Dendrimers inhibit the initial formation of inorganic crystals by reacting with individual ions while they are still in solution. The hyperbranched dendrimer structure produces many active sites that provide a very efficient way to scavenge these ions prior to crystal formation.

  • Stability. With conventional treatments, pump failure, operator error, or high water recovery (removal) rates may lead to rapid concentration of antiscalants. Most treatment formulations start to precipitate out at 10-40 ppm, at which point they foul the membrane. To prevent this, RO operators throttle back operating rates to lower levels than their membranes could theoretically support.

Koch's dendrimers are inherently stable macromolecules, even at concentrations of up to a minimum of 1000 ppm. This allows users to run their systems harder. It also gives users more confidence to treat and maintain their own systems. "For years some customers have relied on a third party for their membrane maintenance," says Randy Truby, Koch Membrane sales and marketing VP for water applications. "Now, we'll be able to have increased confidence in the effectiveness of the chemicals applied to enhance the performance of our membranes."

  • No phosphates. None of Koch's dendrimer-based products contain phosphates, a nutrient that often encourages bacteria growth on membranes.
  • Simplicity of use. Users can combine a dendrimer antiscalant, such as KochTreat ASL720 SC, with other Koch pretreatments used to suppress biological fouling or organic buildup in a single pretreatment tank. Many other pretreatments require separate injection points because they are not compatible with one another.

For more information: Randy Truby, VP, Sales & Marketing, Water Applications, Koch Membrane Systems, Inc., 10054 Old Grove Rd., San Diego, CA 92131. Phone: 619-695-3840 or 800-525-4369. Fax: 619-695-2176.

By Alan S. Brown