A simple mathematical formula describing the survival kinetics of E.coli in natural waters

Abstract

The fecal indicator bacteria (Escherichia coli, fecal coliforms and fecal streptococci) are typically used to measure the sanitary quality of water for recreational, industrial, agricultural and water supply purposes. They are natural inhabitants of the gastrointestinal tracts of humans and other warm‐blooded animals. These bacteria in general cause no harm. They are released into the environment with feces, and are then exposed to a variety of environmental conditions that eventually cause their death. In general, it is believed that the fecal indicator cannot grow in natural environments, since they are adapted to live in the gastrointestinal tract. Studies have shown that fecal indicator bacteria survive from a few hours up to several days in surface water, but may survive for days or months in lake‐sediments, where they may be protected from sunlight and predators. In ground water, temperature, competition with bacteria found naturally in the water, predation by protozoa and other small organisms, and entrapment in pore spaces may all contribute to their demise. We assume that pathogens similar to the fecal indicator bacteria die at the same rate as fecal indicator bacteria. Therefore, if we find relatively high numbers of fecal indicator bacteria in an environment, we assume that there is an increased likelihood of pathogens being present as well. This is even true of water, which has undergone treatment for drinking water purposes. The knowledge of enteric bacteria survival kinetic is very important for environmental scientists. For this purpose there are in present use various empirical formulas but the drawback of these formulas is their limited validity. Experience has shown that the results of calculations of this type may lack accuracy. The purpose of this scientific work was to express the survival kinetic of E.coli with a simple formula, which should be applicable, both to the solution of engineering problems and to future research.