Ultrafiltration (UF) is sometimes a nebulous subject for residential dealers. They know it is used internationally to protect people from viruses and bacteria, but since many residential dealers operate on municipal water supplies and in areas where non-municipal water is in compliance with US EPA minimum drinking water quality standards they haven’t realized opportunities to use this innovative technology.
Simply defined, UF is a fluid separation technology that is capable of separating solids greater than 0.1 micron in diameter from water. With average pore sizes in the range of 0.005 to 0.1 micron, ultrafiltration is capable of operating at low pressures (5–100psi) and can effectively remove solids, virus, bacteria, certain oils, colloids and insoluble metals from water.
Ultrafiltration systems are available from a variety of vendors in a variety of configurations, but the most commonly available (and easiest style for POE residential use) is the hollow-fiber element configured in a dead-end, inside-out or outside-in configuration. Hollow-fiber elements incorporate multiple UF fibers, fabricated together in bundles, to allow for operation without a continuous drain, significantly reducing the amount of water used to produce high-quality product water. Inside-out or outside-in flow configuration facilitates easier cleaning of the fibers through the backflush process, depending on the specific characteristics of the individual element.
In the new economy, many US cities have lost significant amounts of their tax base and budgets are falling short of expectations. There is less public money available to maintain, repair and replace our ailing water delivery infrastructure. With less funding available and an aging workforce at the municipal level, it is just a matter of time before we see more incidents of bacterial contamination at the city level. In addition, there may be an increase in other contaminants entering the distribution, system after the municipal treatment plant, such as sediment, rus, and organics.
In residential applications, Ultrafiltration technology can be effectively incorporated within a multi-layered approach for total household water quality management. Today’s residential consumer is concerned about their water quality, especially as the baby boomers age and we see an increase in the number of immune-compromised individuals.
Before specifying a UF system, the smart dealer will gather the following information:
What water quality challenges need to be addressed?
Water quality challenges vary between rural and municipal supplies. On rural supplies, test the raw water for the following at a minimum:
Hardness – While UF really has no net effect on water hardness, it is important to understand the total hardness you’re dealing with, since it will always affect the downstream water quality, especially on issues such as scaling and soap interactions. Extremely hard water can sometimes interact with other ions to contribute to fouling of the UF element.
Iron – Both ferric (red water) and ferrous (clear water) iron levels need to be tested. Ferric iron will be removed by the UF membrane. Uou need to understand how much you’re dealing with to ensure a suitable back-flush/forward-flush interval is scheduled. Ferrous iron is completely unaffected by the ultrafiltration process and will usually have no net effect on membrane service life;however, ferrous iron will manifest in the home once it has a chance to oxidize. Low levels of iron can cause staining, therefore, it would be wise to address this issue at the same time.
pH – Most UF systems will function in a broad pH range, usually anywhere between 3.0 and 10.0; however, pH will have significant effects on other treatment technologies and on appliances in the home. If pH is outside the 7.0 – 8.5pH range, plan for appropriate remediation technologies and techniques.
TDS – Total dissolved solids have virtually no effect on the ultrafiltration element itself, but can have an effect on the aesthetics (taste) as well as potential for corrosion at extremely high or low levels.
Turbidity – Turbidity is simply a measure of the opacity of water, the ability or inability of water to pass light. Turbidity levels can be tested using manual colorimetric tests with color charts, or with colorimeters. Confirm turbidity limitations with individual equipment manufacturers/suppliers.
SDI –Silt Density Index refers to the fouling capacity of water against reverse osmosis and other fine filtration membranes like nanofiltration and ultrafiltration. Measure the rate of flow while flowing water through a 0.45-micron absolute filter at a net driving pressure of 30psi over a period of 15 minutes.
An easy, field-expedient method of measuring SDI requires the following equipment:
- 500ml beaker
- Pressure regulator (30psi)
- -0.45 micron membrane filter pad with holder
- -Tubing and shutoff valve
Many manufacturers and distributors sell prefabricated SDI kits that contain everything
required to measure SDI effectively.
SDI value is easily calculated using the following simple equation:
|SDI||=||( 1 – t1 / t2 ) * 100
Total Time (minutes)
T1= Time in seconds required to collect the first 500 ml sample.
T2 = Time in seconds required to collect a 500 ml sample after fifteen minutes.
Smart dealers will test at least twice to ensure reliable data. Some innovative vendors now provide microprocessor-controlled SDI testing apparatus that make the process extremely easy. Raw water SDI should always be kept below 3 to protect from fouling.
Chlorine – Chlorine levels should be kept below 2ppm as a general rule. Some elements can tolerate higher levels, but any amount of oxidant in the raw water will cause progressive damage to the element.
TOC Total Oxidizable Carbon. Use standardized testing methods and consult with your supplier on acceptable levels. Total oxidizable carbon is rarely an issue for installations on Groundwater supplied water.
Tannins and lignins – Ultrafiltration systems have a very limited effect on tannins, lignins and related organic compounds. If raw water has any discernable color, a smart dealer will test carefully before assuming that the ultrafilter will remedy this.
On municipal supplies that are US EPA-compliant, most dealers will usually forego the SDI, turbidity, tannin/lignin and TOC tests.
What equipment certification level is required?
While ultrafiltration is generally recognized as an effective bacterial barrier, not all models have been certified by NSF and even fewer have been certified under the US EPA’s ETV program (http://www.epa.gov/etv/). When specifying equipment for a project, be certain of what certification your proposed product carries and make sure it is compliant with local, regional and/orfederal requirements, as well as being suitable for the water quality challenges being addressed.
What flow rate is required?
As with any filtration technology, there will be a drop in product flow and pressure. Carefully evaluate the requirements in the home to ensure the correct number of membrane elements can be installed. Also remember to factor in the complete loss of influent flow during a backflush cycle when sizing the product water storage tank/s.
Will pretreatment equipment be required?
Protect your UF installation. Minimize element fouling by removing solids greater than 30 micron before they reach the ultrafilter and address high hardness levels with an appropriate scale-control technology.
How much space is available for installation?
Some systems are designed to be wall mounted, while others require floor space. Plan for easy system serviceability and element replacements when situating equipment in a room. Be sure to protect equipment from physical and environmental damage.
What drainage is available for periodic flushing?
Many 10-gpm (37.8-L/m) UF elements will flush at anywhere from 1-7 gpm (3.78-26.49 L/m) during back-flushing, depending on the individual design and system configuration. Flush frequency could be as often as every 10 gallons (37.85 liters) or as little as once a week, plan accordingly.
Is an unswitched electrical supply available?
As with any other technologically advanced appliance, an ultrafiltration system requires an unswitched electrical supply to ensure proper system operation. Wise dealers will protect the system further by installing a surge protector or even an uninterruptable power supply (UPS) to protect both from surges, sags and power outages.
If you perform a proper pre-installation analysis, installation will be relatively simple and no more or less difficult than installing any other water treatment device. Remember to install the system in compliance with local prevailing plumbing code, industry best practices and manufacturer’s recommendations. Be especially careful to avoid contaminating the system with installation byproducts such as pipe shavings, flu, glue, solvents and silicone lubricants that could irreversibly damage or foul the UF elements.
Always start ultrafiltration systems slowly, while purging water to a fixture like a bathtub cold faucet that doesn’t incorporate an aerator or strainer. Ultrafiltration elements ship with a disinfectant preservative solution and will require careful rinsing to ensure that output water is not contaminated. Slow startup also protects fibers from water hammer and the physical stress of rapid air evacuation. Many manufacturers recommend rinsing the system for at least 30 minutes before allowing consumption of the water. Once installed and rinsed, program the back-flush/forward-flush controller with intervals specific to the jobsite. Suppliers can be a helpful resource in ensuring that the system is programmed properly.
System maintenance and disinfection
Ultrafiltration systems are no different than water softeners or other filters that require periodic maintenance and disinfection to ensure proper operation and optimum water quality. A UF system should be disinfected at least once a year or sooner, depending on local conditions and manufacturer’s recommendations. Many cleaning and disinfection compounds exist that incorporate disinfectants that are safe for use with ultrafiltration elements, like Clorox® bleach, or even combination disinfection/cleaning products that contain acids, disinfectants, and chelating agents. Dealers should be careful to avoid compounds that contain polyelectrolites, since they will inevitably foul membranes. Hydrogen peroxide and ozone should never be used to disinfect a ultrafiltration membrane.
Ultrafiltration is a valuable technology for any residential dealer to provide their customers with good, clean, safe water.