New Biocidal Cleanroom Filtration System Boosts HEPA/ULPA Efficiency
By Susan English
Chicago, IL–A new, electrically enhanced filtration (EEF) system for killing E.coli and other bacteria has been developed by PDA Inc. (Midlothian, VA), a manufacturer of ultra high performance cleanroom filtration systems. The patented Bio Plus EEF system removes 95-99.5 percent of sub-micron (0.02-0.5 µm) and bacterial contaminants, depending on the grade of primary filter, at a higher flow velocity (300 to 350 fpm) and lower pressure drop than conventional prefiltration methods. The results are up to two orders of magnitude lower overall penetration or higher efficiency for the same cost as conventional HEPA/ULPA technology, the company says.
The EEF maintains the filter medium within an ionizing field, producing extremely high biocidal effects on bacteria. It also combines extremely high filtration efficiency with low flow resistance and is not subject to spark discharge toward the filter. Unlike conventional filters, which can become a breeding ground for bacteria, almost all microorganisms are trapped on the EEF filter media, where they are continuously subjected to bacteria-killing bombardment. Therefore, final filters never need changing. If ULPAs are used, overall fractional penetrations as low as 10-9 can be obtained, the company claims. The new technology is expected to have application in clean manufacturing zones in the biotech and medical fields, for residential, commercial, and hospital HVAC applications, and printing and spray-painting. In its “Technology 2005 Roundup,” NASA Tech Briefs (January, 1996) predicted a “quick impact in the cleanroom, HVAC and military markets” for the new technology. The EEF received the Small Business Innovation Research (SBIR) Technology of the Year award in the “Environment, Energy & Resource Management” category at the Technology 2005 show last October.
In Class 100 or better cleanrooms, the Bio Plus can operate as a high efficiency, low-pressure drop primary filter with final HEPAs. For Class 10,000 and higher, it may be used without final HEPAs. Standard filtration systems serve flow rates ranging from 600-16,000 scfm, and higher custom design units are available. For flexible (non-recirculating flow) rooms, the company offers central blower units (CBUs) for total flow rates above approximately 4,500 scfm, feeding air to the final HEPA filter ceiling units without blowers via air distribution ducts. One 2- ¥ 2.5-ft primary filter is used for approximately every four 4- ¥ 2-ft HEPA final filters. In many cases, CBUs can be used without final HEPA filters for Class 10,000 and above. The Bio Plus CBU comes with the EEF primary filter unit, blower, distribution ducts, and hose connection kit.
Ceiling-mounted blower/filter units (CMUs) include the EEF primary filter with prefilter, the final HEPA/ULPA filter and the low-noise blower/fan unit. Since the primary EEF filter in the Bio Plus CMU operates at the same velocity as the final HEPA filter, the fractional penetration of the CMU can be as low as 10-8 (99.999999 percent efficiency). For recirculating air flow units, Bio Plus filtration systems are available with or without blowers for use in hard-walled or flexible rooms. They can be designed for remote, floor or ceiling mounting. n