Calculation of bacterial density.

        The determination of indicator bacteria, total coliform, fecal coliform, and fecal streptococcus or enterococcus is very important for assessing the quality of natural waters, drinking-waters, and wastewaters.

             The procedures for enumeration of these organisms are presented elsewhere (APHA et al., 1995).

          Examinations of indicator bacterial density in water and in wastewater are generally performed by using a series of four-decimal dilutions per sample, with 3 to 10, usually 5, tubes for each dilution. Various special broths are used for the presumptive, confirmation, and complete tests for each of the bacteria TC, FC, and FS, at specified incubation temperatures and periods. MPN method. Caliform density is estimated in terms of the most probable number (MPN). The multiple-tube fermentation procedure is often