Removal Characteristics of Coliform Bacteria in Biological Reactors at Domestic Wastewater Treatment System.

Abstract

Total coliforms, fecal coliforms, and pathogenic Escherichia coli O157: H7 were measured in domestic wastewater and biologically treated wastewater from 75 treatment plants serving various types of buildings. The means for the influents of all the plants were 3.7×105 CFU/ml of total coliforms, 1.4×105 CFU/ml of fecal coliforms, and pathogenic E. coli O157 was not detected. The means for the effluents were 4.6×103 CFU/ml of total coliforms, and 1.1×103 CFU/ml of fecal coliforms. Seventy-nine percent of the plants complied with the effluent standards, revealing that efficient treatment can considerably reduce total coliforms even before disinfection. In Johkasous serving multiple dwelling houses, total coliforms in the influents showed relatively small time-serial and seasonal variations, and flow equalization tanks contributed to efficient treatment, resulting in the constant presence of few bacteria in the effluents.A high correlation was obtained between total coliforms and fecal coliforms. A correlation was also found between BOD and total coliforms in the effluents. Total coliforms can be decreased by extending the retention time in a biological reactor, where nitrification can proceed. So operation methods which promote nitrification can reduce total coliforms effectively. The mean removal efficiency of total coliforms was higher using the activated sludge process than the contact aeration process.