(177b) Cleaning of Substrates Using High Pressure Carbon Dioxide Mixtures: Flow Field & Fluid Composition Effects on Biofilm Removal

A biofilm is a layer of microorganisms contained in a polysaccharide matrix, which may form slime on surfaces in contact with water. This biofilm layer accounts for about 80% of all free-floating bacteria. This biofilm reduces heat transfer rate in heat exchangers, affect permeate rate in filtration and in pipelines, biofilm causes decrease in pipe diameter and increases pumping power. Biofilms can also be found in medical implants, which causes infection in humans and animals posing a health hazard. Various methods are used in biofilm removal, which require extensive amount of work. Most of the chemicals used in this removal and sterilization have side effects like degradation of the substrate as in reverse osmosis and other filtration membranes by ozone, which is known to be hazardous. EPA passed out a law to minimize and subsequently eliminate the hazardous chemicals, which are used in industry. Various substitutes were recommended and among them is supercritical carbon dioxide. This research investigated the use of supercritical carbon dioxide mixtures for the removal of biofilms produced by pseudomonas aeruginosa on stainless steel surfaces. Supercritical carbon dioxide and water mixtures of varying compositions were used to remove biofilms from stainless steel at three different temperatures (37 ^oC, 47 ^oC and 57 ^oC) and four different pressures (1200 psi, 1350 psi, 1500 psi and 2000 psi) for each temperature. Six and twelve-hour experimental run times were performed at different conditions. It was observed that the minimum biofilm removal occurred at 37^oC and 1360 psi for 6 hours whilst the maximum film removal took place at 57^oC and about 2079 psi for 12 hours run. The results indicated that increases in fluid temperature and run time led to improved biofilm removal. This work will discuss the effects of the fluid flow field and mixture composition on biofilm removal.