Comparison of mechanical shaking, ultrasonication and Homogenization as techniques used in removing attached Bacteria and their effects on the associated protozoa

Abstract

During studying of Protozoa in the slow sand filter beds in Ashford Common Water Treatment Work (London, U.K.), it was found necessary to study the interstitial and attached bacterial populations involved with sand particles, due to their vital participating role together with the protozoan populations, in decomposing the organic pollutants from Thames River. Three methods were applied in the present study as they were the most commonly used physical techniques in extracting bacteria. It was found that ultrasonication was very effective in this respect within the first 6 minutes only after which its destructive effect became highly pronounced leading to a conspicuous declination of the bacterial densities. On the other hand, mechanical shaking appears to be a safer and more convenient technique taking in consideration the destructive effect of homogenization and ultrasonication on the sand grains and bacterial populations. At the same time, it was proved that these techniques were destructive to the protozoan cells by varying degrees and therefore, it was recommended not to use the same sand samples used previously for bacterial extraction to study the protozoan populations.