Radiação UV-C e ondas de ultrassom no controle do crescimento microbiano em fluidos de corte

Abstract

The metalworking industry makes use of large volumes of cutting fluid, which is essential in most operations. However, the fluid is constantly contaminated by microorganisms, which alter its properties and shorten its useful life. Therefore, the objective of the present work was to evaluate the efficiency of UV-C radiation and ultrasound waves in the control of microbial growth in cutting fluid used in the machining processes inthe metalworking industry. For the application of UV-C radiation, two systems were mounted, one of them without the influence of the radiation (control) and another with two bulbs immersed. Both systems operated under the same conditions (volume, operation time and closed loop fluid recirculation). Two replicates of the experiment were performed, in the first the two systems operated for 36 hours, being turned off at night, and fluid aliquots were collected at times: 0; 1; 3; 6; 12; 24 and 36 hours. In the second repetition, the two systems operated for 60 hours, were also discharged overnight and the aliquot collection times were 0; 1; 6; 12; 24; 36; 48 and 60 hours. Aliquots were collected to perform a standard plaque count to obtain the number of Colony Forming Units (CFU) of bacteria and fungi. For the ultrasonic wave process, samples of 200 mL of the fluid were arranged in Beckeres totaling twelve samples per experiment (performed three replicates). Ultrasound exposure times were 5 and 10 minutes and the power with amplitude of 20, 50 and 80%. Before and after exposure, cut fluid aliquots were collected to perform standard plaque counting to obtain the bacteria CFU and in order to compare the effect of the ultrasonic waves. In relation to the results of the experiments using UV-C radiation, in the first experiment, 67% and 29% decay rates were obtained for bacteria and fungi, respectively. In the second experiment with UV-C radiation the decay rates were 96% of bacteria and 99% for fungi, indicating the need for a longer exposure time of the fluid to UV-C radiation to obtain higher percentages. of ultrasound, percentages of decrease for bacteria and fungi of 99% were reached, with exposure time of 10 minutes and amplitude of 50% of power. It can be concluded that both processes were efficient in the control of microbial growth in the cutting fluid, however, the ultrasound waves were more interesting due to the short application time and power amplitude, which could result in cost savings.