Effect of Water Temperature on Bacterial Killing in Laundry

The increasing cost of energy directed our attention to testing the feasibility of low temperature washing. Hospital laundries use formulated chemicals at high temperature wash waters of 66°C. Wash water effluents and fabric bacterial counts of heavily soiled linen were correlated with alkalinity and temperature measurements to investigate the bacterial killing action of hot and cold wash formulas. Terry towels were found to be contaminated with 10⁷ to 10⁹ organisms per 100 cm² at the beginning of the washing process. The most common gram-negative rods found were Klebsiella, Enterobacter and Serratia species. Staphylococci were the predominant gram-positives. Both cold and hot water washing including the bleach cycle reduced bacterial counts in fabric by 3$log_{10}$. Similarly, wash water cfu/mL declined 3 to 4$log_{10}$. A further 0.5 to 1.0$log_{10}$reduction was effected in the 93.3°C drying cycle. Low temperature wash formulas were comparable to high temperature laundry with respect to bacterial counts and species. Cold water formulas at 31.1°C offer an alternative method to reduce energy consumption and maintain bacteriological and esthetic linen quality.