Given an ever-increasing worldwide demand for ultrapure water, advances in membrane technology have offered a viable solution. By all accounts, these efforts have resulted in capabilities and performances that were unheard of in the early days of membrane development. As the demand for better water increases, so does the need for better filters. Some of the necessary advancements include: improved filtration efficiency, higher flow rates, higher dirt (particle holding) capacity, reduced waste streams and even lower life-cycle costs.
Nevertheless, there are still certain limitations regarding membranes—whether they are spiral wound or hollow-fiber membranes, or variations allowing a wider pH range that offer greater resistance to a wider spectrum of chemicals and temperatures.
In a system dependent on an intact barrier without a built-in redundancy or second line of defense, any flaw or damage to that barrier can lead to a breach and ultimate failure in that system’s ability to meet its own stated specifications. Depth filtration provides the safety margin that often can be the difference between success and failure.
Additional membrane limitations include the inherently high pressure drop of membranes, their high initial and ongoing maintenance costs and the production of a waste stream.
NanoCeram Filter Media
In 2005, Argonide launched a line of pleated depth cartridges capable of filtering sub-micron particles including viruses with high efficiency, high capacity and at high flowrates. The active component of these filters is an alumina fiber with a diameter of only 2 nanometers, which is about the size of a DNA molecule. In aqueous solution, NanoCeram is highly electropositive and will attract and retain electronegative particles. When fashioned into fibrous depth filters, they can be designed so that they are capable of retaining 99.9999% of virus particles at water flow rates several hundred times greater than virus-rated membranes.
The NanoCeram filter media can be modified to include silver as a bacteriastatic control, further increasing bacteriological retention. Laboratory tests have shown an improvement of approximately 3 to 4 LRV as compared to untreated NanoCeram media.
When compared to the typical ultraporous membrane, NanoCeram begins to show its strength through a unique set of attributes. Each of the following benefits represents a high degree of excellence by itself. With NanoCeram, these benefits are combined into a single filter cartridge.
- Flow Rate: 60 mL/cm2/min (peak flow for the media)
- Low ∆P: <1.5 psi @ 4 gal per minute (2.5- x 10-in. cartridge in a standard housing)
- Efficiency: 99.9% reduction of 0.2µm particulate (A2 Fine Test Dust)
- Turbidity Reduction: <0.01 NTU until reaching terminal pressure drop (35 psi)
- Silt Density Index (SDI): ≤0.5
- Dirt Holding Capacity (DHC): 572 mg/in2 (89 mg/cm2) of A2 Fine Test Dust
- Cyst Retention: >5 LRV
- Bacteria (Klebsiella terrigena): >5 LRV (one layer, multiple layers achieve >7 LRV)
- Virus (MS2): ~ 90% retention (one layer, multiple layers achieve>6 LRV)
- Temperature Range: 39 to 135°F
- Maximum Pressure: 70 psi (4.83 bar)
- Effective pH Range: 5 to 10
Due in part to its ultra-low SDI values and negligible NTU in effluents, NanoCeram technology also provides superior performance when used as a prefilter for other water treatment processes. Using these same attributes, NanoCeram extends its reach as a prefilter in disinfection systems (ultraviolet, ozonation, chlorination) by reducing the organic load challenging the disinfection process. As a result, NanoCeram enables those systems to operate more efficiently and effectively and can contribute to reduced energy and/or chemical consumption.
Viable & Desirable
Membrane technology has not quite reached its zenith, and improvements are on the horizon; however, it is a maturing technology, and advancements are incremental when compared to the paradigm shift in filtration technology presented by NanoCeram.
The NanoCeram electroadhesion technology is both a viable and desirable alternative to membranes as well as an invaluable adjunct to them. Work is ongoing to further optimize this technology for a variety of industries as well as for applications in air filtration.