Effect of holding time and temperature on bacterial counts.

Abstract

Water samples of different pollution levels were collected from four different sources, viz., a canal, an open dug well, a deep tube well, and a drinking water tap, stored at refrigerator (4-5 degrees C) and ambient (28-30 degrees C) temperatures, and analysed at 0, 6, 12, 24 and 48 hours in order to find the effect of holding time and temperature on bacterial counts. The samples were analysed for total coliforms and for heterotrophic plate counts (HPC). Results of the study indicate significant reduction in the coliform counts in all the water samples tested at both ambient and refrigerator temperatures. However, the rate of decline was much less in refrigerated samples compared to that in samples stored at ambient temperature. Further, the rate of decline was dependent on the source of water. After 48 hours of storage at ambient temperature, canal water samples showed the sharpest decline of 82% in coliform counts, and water samples from open dug well showed the least decline of 51%. While HPCs of the samples held at refrigerator temperature did not show significant changes with time, those samples held at ambient temperature increased upon storage. Up to 12 hours of storage, there was no significant changes in bacterial counts in any type of water at both the temperatures, which suggests that water samples can be stored at ambient temperatures for 12 hours without significantly affecting the coliform counts.