Reduction of fecal indicator bacteria in sewage effluent when pumping for crop irrigation.

When sewage effluent was pumped from a lagoon for spray irrigation the pumping process reduced the fecal coliforms (FC) by 66% and the fecal streptococci (FS) by 91%. Bactericidal effects associated with the pumping of effluent were investigated in the laboratory by seeding sterilized effluent with fecal bacteria and repeatedly passing the liquid through a centrifugal impeller type pump at 50 psi pressure. The pumping effect was cumulative, 49 and 90% of FC being killed after two and four passages through the pump, respectively. FC were more susceptible than FS to injury by pressure shock. Very weak chlorination of the effluent increased the destruction of FC but not FS during subsequent pumping. Within the range of experimental conditions used, the percentage of FC killed by pumping was not markedly affected by changes in temperature and pH of the effluent or by differences in the number and age of cells added.